Scanning mirror system

Abstract

The scanning mirror system (1100) includes a MEMS scanning mirror assembly (310), which includes a reflective surface (334) configured to reflect light from two different light sources. One light source (308a) is a source for a primary beam (312) that forms a probe beam after reflection by the reflective surface. Another light source (158,502) is a source for a secondary light beam (400) that forms a mirror position reference beam (402) after reflection by the reflective surface (334). The system (1100) also includes a position detection element (PSD) (160) configured to detect incident light of the mirror position reference beam (402), the PDS (160) being configured to generate a feedback signal (1704) indicating where the mirror position reference beam (402) is incident on the position detection element (160), and to transmit the feedback signal (1704) to a controller (1700). The controller is configured to generate a drive signal in response to a beam direction input signal and a feedback signal. The scanning mirror system also includes a mirror movement mechanism (1708) configured to be controlled by a drive signal (1706) from the controller (1700) to adjust the position of the MEMS mirror reflective surface (334) to control the direction of the probe beam.

Description

[Technical Field]

[0001] This disclosure relates to scanning mirror systems, and more particularly to scanning mirror systems including a compact asymmetric optical feedback assembly for beam steering using a two-dimensional MEMS (Micro Electro Mechanical Systems) based scanning mirror assembly. In particular, the scanning mirror system includes, but is not limited to, a scanning mirror assembly including an optical feedback assembly that can be used for beam steering in optical coherence tomography (OCT) scanner designs and related embodiments. In particular, it relates to, but is not limited to, a compact OCT scanner adapter for surgical microscopes.

[0002] Optical coherence tomography (OCT) is performed using optical instruments that enable the generation of cross-sectional images of living tissue. Using monochromatic light with a constant phase difference, it is possible to achieve axial resolution far below 8 microns, which makes OCT scanning useful when probing living tissue (in vivo) and in other applications. Because OCT scanning cannot penetrate to great depths, it is particularly useful for probing skin tissue and in ophthalmology. To generate images with depth information, the OCT scanner generates several one-dimensional scans known as A scans, performed along the scan line and stacked together, to create a two-dimensional image known as B scans. By acquiring B scans quickly and at sufficient close range, it is also possible to obtain three-dimensional images of the OCT-probed sample tissue.

[0003] To generate a three-dimensional image, an OCT scanner scans a sample using a beam path across two-dimensional spatial positions. Such scanning systems known in the art generally use orthogonal galvanometer mirrors to handle the desired two-dimensional spatial positions of the sample. To avoid Petzval curvature of the resulting interference image plane caused by the spatial separation of the galvanometer mirrors, a relay optical system is required to combine the pupils of each scanning mirror into a common pupil, which can then be focused onto an image plane with a common optical path length for each galvanometer mirror. Alternatively, electromechanical 2D scanning mirror systems using a single pupil for each scanning axis are also known in the art; however, these operate at much lower scanning speeds due to the physical size limitations of the art, making them less desirable than systems capable of faster scanning.

[0004] OCT scanners are available for use in a variety of surgical procedures where depth information is advantageous. For surgical procedures in small areas, or when access to the area of ​​tissue to be surgically treated is limited, for example, when using an OCT scanner during ophthalmic surgery, the form factor of the OCT scanner must be significantly different from that of an OCT scanner where access to the area probed by the OCT scanner during the OCT scan is not limited or is not required.

[0005] Scanning systems typically use two spatially separated orthogonal galvanometer mirrors to handle the desired 2D spatial position of a sample. To produce a flat tomographic image plane, the spatial separation of the galvanometer mirrors requires a relay optical system that couples the pupils of each scanning mirror to a common image pupil. However, known systems result in large formats, and such multi-optical element scanner designs are less desirable for intraoperative systems requiring minimal sterile field volume.

[0006] OCT systems that rely on galvanometer scanning mirrors are known due to their fast response time, enabling closed-loop operation by using integrated optical feedback. Two-axis scanning requires two galvanometer scanning mirrors, one for each scanning axis, which must be spatially separated due to mechanical limitations. In the case of 2D scanning mirrors such as those in MEMS devices, orthogonal incidence angles are typically used to avoid geometric distortion of the resulting scanning pattern.

[0007] The use of OCT scanners during surgical procedures introduces additional design constraints on the form factor of the OCT device. One such limitation is the physical constraint on the size of the combined microscope and OCT adapter. For example, the overall height of the OCT device and any attached microscope used by the surgeon performing the surgical procedure is limited by design to allow the surgeon to view the area being scanned through the microscope while still being able to access the area under the OCT / microscope using surgical tools for the surgical procedure.

[0008] MEMS (Micro-Electromechanical Systems) based optical reflective devices can be used to reduce the physical size limitations of scanning mirror assemblies and to support higher scanning speeds even with much smaller effective apertures. While small effective aperture optical designs have been used in the past for OCT applications, low numerical apertures result in low lateral resolution in the image plane or complex design results due to the use of a focused light beam incident on a small-aperture MEMS mirror.

[0009] For applications such as measurement or intraoperative OCT that benefit from a flat tomographic image plane, spatial separation of galvanometer mirrors requires combining the pupils of each scanning mirror into a common pupil, and then a relay optical system to focus them onto the image plane. This results in a large, multi-optical element scanner design, which is undesirable for intraoperative systems that require the smallest possible sterile field volume. Optical designs based on small numerical aperture reflective scanners result in low numerical aperture designs, and using a focused light beam with a large incident angle in a small aperture MEMS mirror leads to either low lateral resolution or a complex optical design.

[0010] Therefore, the design of OCT scanning systems for surgery, particularly OCT scanning systems for ophthalmic surgery where OCT light must access the inside of the eye through the pupil, is subject to various design constraints. Using an OCT scanner during ophthalmic surgery can impose various design constraints that may be mutually contradictory. It is known in the art to replace the microscope objective lens with an objective lens that is part of the OCT scanner system in order to keep the height of the microscope, or other dimensions of the device between the surgeon and the orientation of the tissue being operated on, as short as possible, depending on the form factor of the microscope. The OCT scanner system objective lens is aligned with the optical channel of the microscope optics, thereby enabling the OCT scanner to use the same focal plane as that used by the microscope. However, known OCT microscope adapter systems currently have a form factor that adds at most about 50 mm to the stack height of the microscope when they are attached. Therefore, it is desirable to improve the optical design of the OCT adapter to better minimize these stack heights (or other dimensions between the surgeon and the surgical area) when the microscope and OCT adapter assemblies are fixed together. Reducing the stack height can improve access to areas probed by OCT scanning for surgical procedures.

[0011] In optical feedback systems known in the art, the mechanical separation of two galvanometer mirrors results in different optical path lengths for each mirror. For telecentric imaging, two optical methods are generally employed when using galvanometer scanning mirrors. First, the rear focal length of the objective or telecentric lens is positioned on one or the other mirror surface, or between the two. However, this results in a flat image plane with respect to the scanning axis corresponding to the mirror positioned at the rear focal length of the lens, and therefore the remaining axis will have a curved image plane. The other optical method used when scanning with galvanometer mirrors is to image the pupils of each galvanometer scanning mirror onto an intermediate image plane, resulting in a common pupil or intermediate image plane for both scanning mirrors, and therefore equal optical path lengths for both axes.

[0012] Summary of the Invention The disclosed technology seeks to mitigate or prevent at least some of the design limitations by using a very low stray light optical design for feedback on MEMS mirrors, based on a common planar optical orientation for the lowest height opticmechanical layouts. For example, by using an emitter such as a laser diode as a light source for the scanning mirror reference beam and positioning the emitter on an emitter surface located above the central OCT optical surface on the reflective surface of the MEMS scanning mirror assembly, the back reflection from the position sensing element (PSD) can be guided along a path that is incident on the scanning mirror reflective surface at a position equal to but opposite to where the emitter light is incident. This can eliminate stray light. Some of the disclosed exemplary embodiments can further reduce back reflection stray light via a non-distorting (ND) filter placed in front of the position sensing element. Some of the disclosed embodiments can further reduce back reflection stray light via the addition of a low specular reflectance absorbing material placed at the position of the PSD back reflection beam. Some of the disclosed embodiments can further reduce stray light via a spatial filter in the emitter optical path, either additionally or instead.

[0013] The summary description outlines features of the disclosed technology that may be preferred features in some embodiments. However, the present invention is defined by the appended claims.

[0014] The disclosed technology relates to OCT scanner designs and related embodiments. Several embodiments of the disclosed technology provide an OCT scanner having an optical configuration that particularly supports a compact housing design. Such designs are beneficial for use in surgical applications, where the OCT scanner is provided as an adapter for a microscope.

[0015] According to a first aspect of the disclosed technology, the scanning mirror system includes a MEMS scanning mirror assembly comprising a reflective surface configured to reflect light from two different light sources, the two different light sources comprising a primary light source comprising a light source for a primary beam that forms a scanning beam after reflection by the reflective surface, a secondary light source comprising a light source for a secondary light beam that forms a mirror position reference beam after reflection by the reflective surface, and a position detection element (PSD) configured to detect incident light of the mirror position reference beam, the PSD being configured to generate a mirror position feedback signal indicating where the mirror position reference beam enters the position detection element; and a mirror movement mechanism configured to be controlled by a drive signal derived from the mirror position feedback signal in order to adjust the position of the MEMS mirror reflective surface and control the direction of the scanning beam.

[0016] In some embodiments, the scanning mirror reflects light from two different light sources in different optical planes.

[0017] In some embodiments, the scanning beam is an OCT scanning or probe beam, and the primary light source can supply OCT scanning light to the MEMS scanning mirror assembly from a remote light source.

[0018] In some embodiments, the scanning mirror system further includes a controller configured to generate drive signals for controlling the position of the reflective surface of a MEMS scanning mirror assembly in response to a beam direction input signal and a mirror position feedback signal derived with respect to the position of the reflective surface, the PSD is configured to transmit the mirror position feedback signal to the controller, and the mirror movement mechanism is configured to be controlled by the drive signals from the controller to adjust the position of the MEMS mirror reflective surface and control the direction of the scanning beam.

[0019] The beam direction input signal can be implemented by suitable applications for configuring a scan, which can also use user input parameters to configure the OCT scan. For example, the user can define the area to be scanned in a series of B scans, or the area to achieve a specific resolution.

[0020] In some embodiments, the system further comprises a housing having a primary beam inlet for the primary beam, which also provides a primary beam exit for the return scanning beam. The scanning mirror assembly and mirror movement mechanism are located within the housing. In some embodiments, the housing may comprise an optical block.

[0021] In some embodiments, the mirror movement mechanism is configured to adjust the tilt position of the MEMS mirror reflective surface in at least two dimensions.

[0022] The mirror position feedback signal may be a digitized signal based on the analog signal generated by the PSD.

[0023] In some embodiments, the mirror position feedback signal is digitized by one of the following devices: a PSD, a controller, or another device configured to perform analog-to-digital signal conversion on an analog signal received from the PSD, and the resulting digitized signal is output to the controller as the mirror position feedback signal.

[0024] In some embodiments, the secondary light source is also configured to receive a drive signal from a controller, and the drive signal is generated by the controller based on information derived from the received feedback signal. For example, the drive signal from the controller may, in some embodiments, control the power output of the secondary light source and / or turn it on and off.

[0025] In some embodiments, the system further includes a controller.

[0026] In some embodiments, the controller is configured to generate respective drive signals for the light source and the mirror movement mechanism to two-dimensionally position the scanning mirror reflective surface using closed-loop control in response to receiving a drive signal from a scanning driver.

[0027] In some embodiments, the secondary light source, the scanning mirror reflective surface, and the PSD are configured such that the secondary light beam is incident on the reflective surface at an optical surface offset from the optical center of the reflective surface, and the optical surface on which the light beam is incident on the reflective surface is different from the optical surface on which the return reference beam reflected from the PSD is incident on the reflective surface.

[0028] In some embodiments, the incident angle of the secondary beam incident on the MEMS mirror reflective surface may be less than 67.5 degrees with respect to the surface plane of the mirror. This can reduce the angular geometric distortion of the scanning beam profile at a ratio of 2:1.

[0029] In some embodiments, the reference beam is detected by the PSD as a plurality of beams, and the plurality of beams may be individually detectable as separate beam spots at the PSD.

[0030] In some embodiments, the beam spot data generated by the PSD when the PSD detects the beam spot position of the incident mirror position reference beam is communicated to the controller by the PSD.

[0031] In some embodiments, the controller is configured to control the horizontal and vertical tilt positions of the reflective surface of the scanning mirror assembly.

[0032] In some embodiments of the scanning mirror system, beam spot data generated by the PSD when the PSD detects the beam spot position of the incident reference beam is communicated by the PSD to a controller, which is configured to control the horizontal and vertical inclination positions of the reflective surface 334 of the scanning mirror assembly.

[0033] In some embodiments, the controller is configured to implement closed-loop control of the position of the scanning mirror reflective surface using mirror position feedback signals.

[0034] In some embodiments, the scanning mirror assembly is part of the OCT scanner system, and the primary beam is the OCT scanning beam.

[0035] In some embodiments, the mirror position reference beam is focused by a PSD imaging lens before it is detected by the PSD.

[0036] In some embodiments, the scanning mirror system further includes a neural density filter positioned between the PSD imaging lens and the PSD.

[0037] In some embodiments, the scanning mirror system further includes a low specular reflectance absorbing material along the optical path followed by a portion of the scanning mirror reference beam that is returned toward the scanning mirror reflective surface.

[0038] In some embodiments, the scanning mirror system further includes a spatial filter in the optical path of the secondary beam traveling from the secondary light source to the reflective mirror surface.

[0039] In some embodiments, the light source for the secondary beam is located vertically above the light trap, and the light trap is configured to capture light from a portion of the mirror position reference returned from the PSD, which is reflected back toward the secondary light source via the MEMS mirror surface (334).

[0040] In some embodiments, the scanning mirror system (1100) includes an optical block.

[0041] In some embodiments, the scanning mirror assembly includes a MEMS scanning mirror assembly within an OCT adapter for a surgical microscope, and the primary light source is an OCT light source that, after reflection, forms an OCT scanning mirror for scanning a tissue area or specimen that can also be viewed through a surgical microscope.

[0042] In some embodiments, the scanning mirror assembly comprises an optical block configured to act as a MEMS scanning mirror assembly within an OCT adapter for a surgical microscope.

[0043] In some embodiments, the scanning mirror assembly includes a high-speed scanning mirror assembly configured to perform more than 400 B scans per second.

[0044] Another second aspect of the scanning mirror system includes a housing having a primary beam inlet and a primary beam outlet, and a MEMS scanning mirror assembly located within the housing, the MEMS scanning mirror assembly including a reflective surface configured to reflect light from two different light sources, namely, one light source which is a source for a primary beam that, after reflection by a reflective surface, forms a scanning beam that passes through the primary beam outlet and is received through the primary beam inlet, and another light source which, after reflection by a reflective surface, is a light source for a secondary light beam that forms a mirror position reference beam, the mirror position reference beam assembly includes a position detection element (PSD) configured to detect incident light of the mirror position reference beam, the PSD configured to generate a feedback signal indicating where the mirror position reference beam is incident on the position detection element, and to transmit the feedback signal to a controller, and a mirror movement mechanism configured to be controlled by a drive signal, the mirror movement mechanism which is received from a controller, the mirror movement mechanism configured to adjust the position of the MEMS mirror reflective surface in response to the drive signal to control the direction of the probe beam.

[0045] Another third aspect of the scanning mirror system includes a MEMS scanning mirror assembly comprising a reflective surface configured to reflect light from two different light sources, namely, one light source which is a source for a primary beam that forms a probe beam after reflection by the reflective surface, and another light source which is a light source for a secondary light beam that forms a mirror position reference beam after reflection by the reflective surface; a position detection element (PSD) configured to detect incident light of the mirror position reference beam, the PSD configured to generate a feedback signal (1704) indicating where the mirror position reference beam is incident on the position detection element, and to transmit the feedback signal to a controller; a controller configured to generate a drive signal in response to a beam direction input signal and a feedback signal; and a mirror movement mechanism configured to be controlled by the drive signal from the controller in order to adjust the position of the MEMS mirror reflective surface and control the direction of the probe beam.

[0046] In some embodiments, the scanning mirror system comprises a micro-electromechanical system (MEMS) two-dimensional scanning mirror assembly having an optical design including a movable MEMS scanning mirror having a reflective surface; a point source for a primary light beam, e.g., an optical fiber connected via an optical fiber connector which can form a primary inlet and act as a primary source for the primary light beam; and a collimating lens assembly configured to receive the light beam and output a collimated light beam toward the reflective surface. In some embodiments, the collimated beam has an output beam diameter from the collimating lens assembly configured to exceed an output beam diameter threshold. In some embodiments, the scanning mirror assembly further includes an objective lens assembly, and the scanning light beam reflected from the reflective surface passes through the objective lens assembly before exiting the scanning mirror assembly via the primary beam outlet. The scanning mirror reflective surface may be configured to reflect the incident collimated primary light beam from the scanning beam exiting the mirror assembly and the objective lens assembly. The scanning beam exits the scanning mirror system via the primary beam outlet. The scanning beam exits as a telecentric beam toward the telecentric image plane with a resolution better than the output beam threshold resolution. In some embodiments, the optical system of the scanning mirror system is configured to achieve a total track length L of the path from a point light source, for example, from the end face of an optical fiber or fiber ferrule, to a telecentric image plane of less than 40 mm.

[0047] In some embodiments, the 2D scanning mirror primary light source is an optical coherence tomography (OCT) light source.

[0048] In some embodiments, the collimating lens realizes a primary beam having an output beam diameter of at least 3 mm, preferably at least 3.1 mm.

[0049] In some embodiments, the threshold for telecentric beam resolution in the telecentric image plane is a resolution better than 6 microns; in other words, the image can be resolved to a degree smaller than 6 microns.

[0050] In some embodiments, the numerical aperture of the optical fiber and the focal length of the collimating lens assembly are set to set the OCT collimating lens output beam diameter threshold to at least 3.1 mm.

[0051] In some embodiments, the combination of the focal lengths of the scanning mirror objective lens and the scanning mirror field lens from which the scanning beam exits the mirror assembly determines the total track length L.

[0052] In some embodiments, the mirror assembly scans by + / - 5 degrees.

[0053] In some embodiments, the optical fiber has an numerical aperture of 0.14.

[0054] In some embodiments, the objective lens comprises an F2.7 biconvex doublet lens, and the field lens includes an F19 positive / negative meniscus doublet field lens.

[0055] In some embodiments, the optical path difference (OPD) of the telecentric scanning beam output by the scanning mirror assembly has a radius of curvature of 100 mm or less.

[0056] In some embodiments, the telecentric beam is more telecentric than an incident angle of 0.03 degrees in the telecentric image plane.

[0057] In some embodiments, the mirror assembly is a scanning mirror within the OCT apparatus, and the optical fiber provides a point source for the OCT light beam.

[0058] In some embodiments, the OCT device is an OCT adapter for a microscope, preferably a surgical microscope.

[0059] In some embodiments, the OCT light returning from the sample along the OCT probe arm has a transverse optical resolution of 6 μm or more, in other words, the resolution is better than 166 line pairs per mm.

[0060] In some embodiments of the MEMS scanning mirror assembly, the reflective surface of the MEMS scanning mirror comprises a large-diameter gold-clad silicon mirror bonded to the underlying mechanical structure.

[0061] In some embodiments, the OCT light returning from the sample along the OCT probe arm has a transverse optical resolution of 6 μm or more, in other words, the resolution is better than 166 line pairs per mm.

[0062] A MEMS 2D scanning mirror assembly comprises a scanning mirror optical system, which comprises at least a movable MEMS scanning mirror having a reflective surface; an optical fiber connected via an optical fiber connector and configured to act as a point source for an OCT beam illuminating the reflective surface; and a collimating lens assembly configured to output OCT light from the point source toward the reflective surface with an output beam diameter of at least 3.1 mm, wherein the reflective surface is configured to reflect the incident collimated OCT light beam to form an OCT scanning beam that exits from the mirror assembly as a telecentric beam toward a telecentric image plane with a resolution of up to 6 microns, and the optical system of the scanning mirror assembly comprises a collimating lens assembly configured to achieve a total track length L from a) the end face of a fiber ferrule providing a point source inserted into the optical fiber connector to b) a telecentric image plane of less than 40 mm. In some embodiments of the scanner system, an objective lens assembly is realized within the probe arm of the scanning mirror assembly to configure the telecentric OCT beam.

[0063] In some embodiments, the feedback system is used in an optical coherence tomography (OCT) scanner system that includes a microelectromechanical system (MEMS) two-dimensional scanning mirror assembly disclosed herein.

[0064] Advantageously, the OCT scanner system may include exemplary embodiments of the MEMS scanning mirror assembly disclosed herein within an OCT adapter for a microscope. The OCT adapter system design has a compact configuration in the sense that it is laterally compact, as the optical design of the MEMS scanning mirror allows the optical channel formed by the microscope optics and the mounted OCT scanner objective lens to require an optimally short housing stack height, the optical path through which the probe light travels within the scanning mirror assembly block is less than 40 mm, and it supports a high scanning speed with a resolution of 6 microns or less in the resulting OCT image.

[0065] This is useful when a surgeon needs to use a microscope or similar device to generate a magnified image of the surgical area using a microscope optics, allowing the surgeon to better view the surgical area while keeping the patient within reach of the surgeon's arm during ophthalmic surgery. In other words, some embodiments of the OCT scanner system designs disclosed herein result in a combined stack height of the microscope and the mounted OCT adapter that is much shorter than previously possible. The design better balances design constraints, allowing the surgeon to view the area being scanned by the OCT scanner through one or more eyepieces of the microscope and keep the scanned area within the focal plane of the microscope optics, while still allowing the surgeon to physically reach the scanned area to perform the surgical procedure.

[0066] Other embodiments of the disclosed technology offer additional advantages. For example, as described elsewhere, in some embodiments, the design of the scanning mirror assembly reflects the beam used to feed back to the scanning mirror position in an optical plane different from the optical plane used by the OCT scanning beam, and the optical path of the reference beam used to determine the scanning mirror position is advantageously configured to reduce the possibility that the return light from the feedback arm will contaminate the mirror position reference beam or its light source, or contaminate the OCT scanning beam.

[0067] The embodiments described above, the appended claims, and / or the examples disclosed above and below herein can be appropriately combined with each other, as will be apparent to those skilled in the art.

[0068] Additional features and advantages are disclosed in the following description, claims, and drawings, and it may be readily apparent that such features disclosed in the context of one aspect or embodiment above can be combined with those disclosed in the description of a person skilled in the art. [Brief explanation of the drawing]

[0069] Herein, some embodiments of the disclosed technology will be described, merely as examples, with reference to the accompanying drawings. [Figure 1] This diagram schematically illustrates the basic method of a spectral region OCT system. [Figure 2A] This figure schematically shows a front perspective view of an OCT scanner adapter for a microscope according to several embodiments of the disclosed technology. [Figure 2B] This figure schematically shows a rear perspective view of an OCT scanner adapter for a microscope, according to several embodiments of the disclosed technology. [Figure 3A] This figure schematically shows the components of an example of an OCT scanner adapter according to several embodiments of the disclosed technology. [Figure 3B] This is another diagram schematically showing the components of an example of an OCT scanner adapter according to several embodiments of the disclosed technology. [Figure 4] Figures 3A and 3B show enlarged views of the OCT scanner adapter. [Figure 5A] This figure schematically illustrates an example of the optical design of a MEMS scanning mirror assembly according to several embodiments of the disclosed technology. [Figure 5B] Figure 5A schematically shows further details of the input arm of the scanning mirror assembly. [Figure 6] Figure 5A schematically shows an example of a collimating lens assembly for the input arm of a scanning mirror assembly. [Figure 7] Figure 5A schematically shows an example of an objective lens assembly for a scanning mirror assembly. [Figure 8] This figure schematically shows an example of a MEMS scanning mirror optical beam splitter configuration having an optical design different from the optical design of the disclosed embodiment of the technology. [Figure 9] This figure schematically illustrates an example of a light source assembly for realizing a reference beam for mirror position feedback in a MEMS-based scanning mirror assembly according to several embodiments of the disclosed technology. [Figure 10] This figure schematically shows an example of a position detection element assembly for detecting the mirror reference beam position in a MEMS-based scanning mirror assembly according to several embodiments of the disclosed technology. [Figure 11A] This figure schematically illustrates an example of discontinuous ray tracing of an optical feedback channel in a MEMS-based scanning mirror assembly according to several embodiments of the disclosed technology. [Figure 11B] This figure schematically shows an example of a Zemax ray trace of a laser diode illumination reference beam reflected from an example of a MEMS scanning mirror and imaged onto an example of a position detection element, according to several embodiments of the disclosed technology. [Figure 11C]This figure schematically illustrates an example of a Zemax ray trace of a laser diode illumination reference beam reflected from a position-sensing element, reflected from a MEMS mirror, and propagating to an optical trap position, according to several embodiments of the disclosed technology. [Figure 12] This figure shows examples of beam spot positions on the reflective surface of a MEMS scanning mirror according to some exemplary embodiments of the disclosed technology. [Figure 13] This figure shows an example of the relative beam spot position between the laser diode illumination reference beam and the return reference beam reflected from the PSD at the optical trap position. [Figure 14] This figure schematically illustrates examples of the location of optical traps in a MEMS scanning mirror assembly according to several embodiments of the disclosed technology. [Figure 15] This figure shows examples of geometric composite angle scanning distortion as a result of non-normal incidence angles to a MEMS-based 2D scanning mirror, according to several embodiments of the disclosed technology. [Figure 16] This figure shows an example of a Zemax spot diagram of a PSD surface according to several embodiments of the disclosed technology. [Figure 17] This figure schematically illustrates a closed-loop optical feedback system according to several embodiments of the disclosed technology.

[0070] Detailed explanation The detailed description below provides examples of embodiments of the disclosed technology, which are described in sufficient detail to enable those skilled in the art to carry out the disclosed technology.

[0071] There are two forms of OCT scanning: time-domain OCT (TD-OCT) and spectral-domain OCT (SD-OCT). SD-OCT uses spectral matching of the spectrum in the OCT interferometer output.

[0072] Figure 1 schematically illustrates the operating principle of an exemplary spectral-domain optical coherence tomography (SD-OCT) interferometer scanner system 100, including some examples of embodiments of the disclosed technology.

[0073] In the exemplary SD-OCT system 100 shown in Figure 1, the SD-OCT system 100 can be used to generate an optical coherence tomography image of an in vivo tissue sample 116, such as a human eye, by probing into the tissue sample 116 using an OCT optical scanning beam.

[0074] System 100 is schematically shown in Figure 1 and it will be clear that it is not drawn to scale. The positions and relative sizes of the various components of the SD-OCT system 100 shown in Figure 1 do not necessarily reflect their actual or relative positions or sizes in exemplary embodiments of the disclosed technology.

[0075] Hereinafter, references to OCT scan images or image data may, as will be apparent to those skilled in the art, refer to, as necessary, one-dimensional A scans, two-dimensional B scans including multiple A scans, or stereoscopic scan images including multiple B scans.

[0076] As shown in Figure 1, the SD-OCT system 100 includes a low-coherence broadband optical scanning light source 102. The scanning light source 102 is appropriately connected to a coupler 104 configured to split the light from the light source 102 into an OCT optical reference beam following an optical path 103a along a reference arm 103 and an OCT optical probe or scanning beam following an optical path 105a along an OCT probe arm 105. The OCT light returned along the reference arm 103 and probe arm 105 has different phase shifts that produce interference when the returned light is recombined at the coupler 104. The combined optical signal is output from the coupler along a detection or output arm 107, and the optical interference pattern is detected using a spectrometer 136. The output optical signal 146 from the spectrometer 136 is then processed by an image processor 148, for example, to apply a Fourier transform to the output optical signal 146, which then generates OCT scanning data that can be displayed on a suitable display 152.

[0077] The resulting interference pattern, which is the different phase shift between the OCT light returned from the reference arm and the OCT light returned from the probe arm, occurs because the OCT light is returned from different depths in the scanned tissue sample 116 or from one or more different structures within the scanned tissue sample 116. In some embodiments, the scanned tissue sample may instead include a different type of object of interest 112 than the in vivo tissue sample located in a region of the human body.

[0078] The phase shift that generates interference is influenced by the different depths returned by structures within the sample scanned by the OCT light. The interference from the phase shift allows the signal output 146 of the spectrometer 136 to generate an image known as tomography, which provides visual indication of the depth and location of one or more such structures within the scanned or probed region.

[0079] In some embodiments of the SD-OCT system 100 shown in Figure 1, the broadband OCT light source 102 has a center wavelength of 860 nm over a bandwidth of 100 nm. In some embodiments, two or more light sources 102 are used to realize broadband low-coherence OCT scanning light over a desired bandwidth.

[0080] The probe OCT beam is returned after being backscattered, reflected, or otherwise returned from any structure at a specific depth within region 116 containing the tissue sample being scanned. In some embodiments, one or more or all of the optical paths 101a, 103a, 105a, 107a are realized using a suitable single-mode optical fiber and may include one or more sections in which the beam following the optical fiber travels through free space.

[0081] In the embodiment of the SD-OCT system 100 schematically shown in Figure 1, the reference beam exits from the coupler 104, travels along the reference arm 103 via the collimator lens 106, is reflected by the translationally moving reference mirror 108, and returns along the reference arm 103 towards the coupler 104. The optical paths 103a along the reference arm 103 and 105a along the probe arm 105 are configured to have equivalent optical path lengths toward the focal plane 154 that illuminates the sample being scanned or other object of interest. Based on the detected interference between the returned reference beam light and the returned OCT probe beam light when recombined at the coupler 104, the depth of any structure in the sample to which the probe beam light has been backscattered, reflected, or otherwise returned can be determined by outputting the detected interference signal 146 to the image processor 148.

[0082] In some embodiments, interference between the return reference beam and the return OCT probe beam light occurring along the output arm 107 is measured using a suitable spectrometer 136, such as the one shown in Figure 1, to determine the depth of the scanned cross-sectional image. Other embodiments of the OCT system 100 may use other techniques to measure the interference and generate an output signal 146.

[0083] In some embodiments of the OCT system 100, one or more or all of the optical paths 101a, 103a, 105a, 107a include one or more sections through which an outward or inward (relative to the coupler 104) OCT beam following the optical fiber travels in free space, comprising a suitable single-mode optical fiber and / or an outward or inward (relative to the coupler 104) OCT beam following the optical fiber travels.

[0084] In some embodiments of the disclosed technology, the optical path lengths of the reference beam and the probe beam are the same, but the dispersion characteristics of the optical fibers through which each beam travels are configured to be different in order to improve the removal of complex conjugate images from the OCT image output and to improve the quality of the OCT scan image and the speed at which the complex conjugate-resolved OCT scan image is acquired.

[0085] In some embodiments, the term OCT scanning is used herein to refer to B-scan and stereoscopic scanning images of a tissue region (also referred herein to as a tissue sample) 116 generated using a spectral-region SD-OCT scanner system 100.

[0086] In the schematic example of spectral region OCT shown in Figure 1, a broadband light source 102 generates an OCT probe beam that illuminates a region of tissue 116 that is scanned by the OCT probe beam over the range of near-infrared wavelengths.

[0087] The spectrometer 136 shown in Figure 1 includes a collimating lens 138 through which the reflected light passes through a grating 140 to generate a spectrally dependent interference pattern. The interference pattern is focused onto a line camera 144 via an objective lens 142, and the image signal representing the interference pattern is sent from the output 146 to a suitable image processing system 148. However, in an alternative embodiment, another suitable type of interference detector in the output arm 107 may be used.

[0088] In the embodiment of the SD-OCT system 100 shown in Figure 1, the spectrometer 136 measures the spectral interference of the returned OCT light beam by measuring the intensity modulation of the returned light as a function of frequency. The rate of change of intensity over different frequencies indicates the location of different reflective layers within the sample.

[0089] The OCT probe beam travels from the coupler 104 along the OCT probe branch 105 of the coupler 104, following the optical path 105a, and then enters the OCT scanner 164. An exemplary OCT scanner 164 shown in Figure 1 includes a collimating lens 110 and a scanning mirror assembly 310 (for example, shown in Figures 3A and 5 below) which includes a scanning mirror 112 having a reflective surface 334 (for example, see Figure 3A or Figure 5) that deflects the OCT scanning beam from the scanner 164 through the objective lens 114 toward a focal plane 154 in the scanning region 116. The scanning mirror assembly 310 includes a mirror positioning system which includes a secondary light source 158 that is reflected toward the sample region 116 being scanned by the scanning mirror 112 of the scanning mirror assembly. The scanning mirror assembly includes a mirror positioning system 156 which includes a light source 158 for detecting the mirror position and a mirror position detector (PSD) 160. The OCT scanner 164 also includes an objective lens 114 that focuses the OCT scanning beam onto a focal plane 154 within the region of the tissue or sample 116 being scanned.

[0090] The scanning mirror 112 may include a micro-electromechanical system (MEMS) scanning mirror that is angularly moved by a mirror moving unit (not shown in Figure 1). The movement of the scanning mirror 112 moves the OCT probe beam across the sample being scanned or other object of interest, and the resulting interference pattern is used to generate an OCT B scanning image from the system output 156.

[0091] The movement of the mirror movement unit is performed under the control of the controller 162. The controller 162 may be located within the scanning mirror assembly, which includes the scanning mirror 112, or it may be located separately from it.

[0092] The mirror position system 156 shown in Figure 1 includes an optical angular displacement mirror position measuring system 156. This system provides feedback on the mirror position to the controller and, in some embodiments, enables closed-loop control of the MEMS-based scanning mirror position in some embodiments.

[0093] When the OCT scanner 164 is in use, the scanning mirror 112 is moved by a mirror movement mechanism under the control of the controller 162 to guide the OCT beam along the scanning path. After reflection by the mirror 112, the OCT probe beam passes through a telecentric objective lens 114 that focuses the OCT probe beam to different positions within the focal plane 154 in the sample tissue 116 being scanned. As schematically shown in Figure 1, the focal plane 154 is shown as being in the conceptual xy plane, and depth information is supplied orthogonally along the z axis.

[0094] The telecentric objective lens 114, through which the probe beam passes to reach the sample 116 and through which the return probe beam light also passes, is shown in Figure 1 with three exemplary emerging telecentric beams that focus at different positions within the focal plane 154 in the xy plane, as shown in Figure 1. Each of the exemplary emerging telecentric beams results from a different position on the scanning mirror assembly 112; in other words, Figure 1 schematically shows only three sequential telecentric beam positions as an example. This is to schematically illustrate how the telecentric OCT scan or probe beam is moved to illuminate different regions as the B scan or stereoscopic scan progresses.

[0095] The scanning area includes a sample of tissue 116. In Figure 1, this includes tissue from an eye 116, which may be an in vivo or in vitro tissue sample. In other uses of the OCT scanner system, where OCT scanning images may be useful for visualizing internal structures at various depths within tissue, other types of human or animal tissue can be scanned in vivo or in vitro.

[0096] For example, as shown in Figure 1, the eye 116 is schematically shown and comprises a pupil 118 surrounded by the iris 120, with the posterior chamber 122 and zonal fibers 124 located behind it, and the lens 126 and cornea 128 anterior to it. Figure 1 also presents the anterior chamber 130 of the eye, as well as the ciliary muscle 132 and ligaments 134, all of which can be shown as internal structures in a tomographic image scanned using an OCT system such as OCT system 100 and presented on a display 152.

[0097] The likelihood of a successful outcome from surgical procedures performed on tissues such as the human eye or the eye of another organism, where access is extremely limited, can be improved by using OCT. In some embodiments, the OCT system 100 may be used to create images based on two-dimensional or three-dimensional scanning of the area of ​​the eye 116 being operated on, which can be presented to the surgeon in real time. This allows for a better understanding of the depth of any procedure being performed as the surgery is being carried out. Providing this depth information of the area to be surgically treated in real time can help the surgeon avoid making incisions that are too deep (which may unnecessarily damage the underlying tissue) or too shallow (which may result in an unsuccessful surgery and / or prolonged healing of the surgical tissue).

[0098] As schematically shown in Figure 1, the interference signal output 146 of the spectrometer 136 of the OCT system 100 is post-processed by the image processor 148. For example, the signal output 136 may be image-processed using a Fourier transform or other suitable signal transform for the OCT scan. This can first generate a distorted OCT scan image, and then undergo additional image processing to correct the distortion of the OCT image before the OCT scan image 150 is output to a suitable display 152. Some embodiments of the OCT scanner system 100 may also use image processing to remove complex conjugate artifacts and improve the depth range of the resulting image.

[0099] The display 152 may be part of the apparatus hosting the SD-OCT system 100 that performs image processing, or it may be a separate apparatus. In some exemplary embodiments of the disclosed technology, a series of OCT scan images 148 are generated using an OCT probe light beam quickly enough to supply a live stream video containing OCT scan images 150 onto the display 152. In some embodiments, the display 152 may be a near-eye display. In some embodiments, the display 152 may be a large display system comprising multiple displays for presenting information to both the surgeon and / or others in the operating room. The display 152 may be integrated into the SD-OCT system 100 or it may be external to it.

[0100] One or more of the components shown in Figure 1 that form the OCT scanning system 100 may be housed separately from the optical system that forms the OCT scanner device 164. By separating the OCT scanner optical system, the OCT scanner 164 can have a more compact form factor. A more compact OCT scanner 164 can be better positioned closer to the sample area being scanned.

[0101] In some embodiments, the OCT scanner system 100 includes an OCT scanner 164 provided as an adapter for a microscope, for example, an OCT scanner adapter 206 for a microscope 200 schematically shown in Figures 2A and 2B. In some embodiments, the microscope 200 includes a surgical microscope suitable for use during surgical procedures. In some embodiments, the housing 202 of the microscope 200 has a lower carriage configured to accept one or more microscope accessories, thereby allowing the OCT scanner adapter 206 to be mounted on the lower carriage of the microscope housing. In this case, the OCT scanner adapter optical system objective lens 114 can also function as a microscope objective lens 210 (see also Figures 3A, 3B, and 4 of the drawings).

[0102] Example of a microscope system with an OCT scanner adapter Figures 2A and 2B show schematic front and back perspective views of an OCT scanner adapter 206 for a microscope, in other words, an OCT scanner microscope accessory 206, according to several embodiments of the disclosed technology. The term OCT scanner adapter, as used herein, refers to an OCT scanner adapter microscope accessory. In some embodiments of the disclosed technology, references to an OCT scanner adapter may also refer to an apparatus including an integrated OCT scanner adapter.

[0103] Figures 2A and 2B show how the OCT scanner adapter 206 in Figures 3A, 3B, and 4 may be mounted on the lower carriage of the microscope 200. For example, the microscope accessory of the OCT scanner adapter 206 can be retrofitted to the microscope 200 by removing any existing microscope accessories from mounting points located on the lower carriage of the microscope and using these microscope mounting points to mount the OCT adapter 206 to the lower carriage of the microscope 200 instead. Once properly secured in place, the form factor of the OCT scanner adapter aligns the objective lens 210 with at least one of the optical channels of the microscope optics, e.g., the rear channel or the channel used by the microscope camera. In some embodiments, the lower carriage of the OCT adapter may also provide mounting points for additional accessories.

[0104] In some embodiments, the OCT scanner adapter 206 has a vertically compact form factor so as not to add excessive height h2 to the height h1 of the microscope to which it is mounted when in use. Reducing the additional vertical height h1 of the OCT scanner adapter 206 improves the ease of access to the scanning area in use of the scanner when generating cross-sectional images of the scanning area 116 while the microscope is being used simultaneously. The OCT scanner adapter 206 is also laterally compact. This means that when mounted on the microscope 200, it does not excessively obstruct surgical access to the area of ​​tissue being scanned, allowing for simultaneous surgical procedures.

[0105] In the following description, height is referred to in the context that the OCT scanner adapter 206 is used to scan the tissue sample 116 from a position above the tissue sample, such as when the OCT scanner adapter 206 is mounted on the lower carriage of the surgical microscope 200.

[0106] Some embodiments of the OCT scanner 206 described herein maintain a similarly compact form factor and may be used in other contexts. Furthermore, in some embodiments, the OCT scanner 206 may be integrated into another device, such as a microscope 200. In some embodiments, the OCT scanner 206 may be distributed as an optional accessory for such devices, so that it may be distributed and sold independently of the microscope which may be attached later for use. Thus, unless the context clearly prohibits it, references to height may apply equally to other dimensional directions of the OCT scanner that are substantially or nearly orthogonal to the plane of any device to which the OCT objective lens and OCT scanner are mounted, and the orientation of the OCT scanner and microscope stack may also differ depending on the patient orientation and one or more of the configuration of the microscope optics and the position of the eyepieces.

[0107] In other words, references to height in the overall context of “height” are based solely on the assumed orientation of the OCT scanner and microscope for a supine patient when surgery is being performed on the patient. While the patient is supine, the surgeon can access the area to be operated on beneath one embodiment of the OCT scanner adapter 206 according to the disclosed technology, and at the same time, can physically access the eyepiece of the microscope 200 to which the OCT scanner 206 is mounted. This geometric configuration can vary in some embodiments depending on the configuration of the microscope optics and / or the orientation of the patient and / or the position of the area to be operated on. Thus, in the following description, references to the height of the microscope and OCT scanner adapter 206 and / or the combined stack height may also refer to other dimensions of the microscope and OCT scanner adapter 206 that act as constraints on the form factor of the OCT scanner, which will be apparent to those skilled in the art.

[0108] Returning to Figures 2A and 2B, the microscope optics housed in the microscope housing 202 form an optical channel that provides a view of the area below the objective lens 210 of the OCT scanner adapter 206. In some embodiments, the objective lens 210 realized by the OCT scanner adapter 206 for microscope 200 includes the objective lens 114 of the OCT scanner system 100 schematically shown in Figure 1. Thus, references to the objective lens 210 in this description may refer to the objective lens 114 of the OCT system 100, including different types of OCT scanners 164, unless the context explicitly limits the reference to the use of an OCT scanner as an adapter or accessory for a microscope.

[0109] In an exemplary embodiment of the OCT scanner adapter 206 shown in Figure 2A, the OCT scanning optical design has a compact form factor, adding a minimum additional height h2 to the height h1 of the microscope optical system housing 202.

[0110] Figures 2A and 2B also show microscope handles 204a,b which help position the microscope 200 above the area to be scanned (and viewed). The OCT scanner adapter 206 includes a housing 208 fixed to the lower carriage of the microscope 200 as shown. However, as described above, in some embodiments the OCT scanner adapter 206 may have different configurations and / or orientations when in use. Such different configurations and / or orientations of the OCT scanner adapter 206 in use can also implement the compact principle of the OCT scanner design disclosed herein.

[0111] Figure 2B shows a different rear view of the OCT scanner adapter 206 shown in Figure 2A. The rear view shows a data and / or power port 212, for example, an RSJ45 Ethernet port or a USB port, and an optical port 214. Port 212 supplies power to the OCT scanner adapter 206 and, in some embodiments, may include a power over Ethernet port.

[0112] In some embodiments, the OCT scanning light is returned from the OCT scanner adapter 206 to the interferometry components of the OCT scanning system 100 via the optical port 214, as shown in Figure 1.

[0113] For example, in the embodiment shown in Figure 1, the OCT light returning from the sample 116 returns via the objective lenses 210 and 114 and is output along the optical fiber 308a via the optical port 214. Thus, the optical fiber 308a, the optical path through the mirror lens assembly, and other optical components of the OCT scanner adapter 306 located along the optical path followed by the OCT scanning beam toward the sample being scanned form part of the probe arm 105 of the FD-OCT system 100.

[0114] The OCT light is emitted to illuminate the scanned sample tissue 116, then reflected, backscattered, or otherwise returned. The returned OCT light then passes through the coupler 104 and returns, where it interferes with the light returned from the reference arm 103. The returned OCT and reference beam then propagate along the output arm 107 to the spectrometer 136, which outputs an OCT and reference beam light interference signal 136 for image processing to generate OCT imaging data 146 presented on the display 152.

[0115] For example, in some embodiments of the disclosed technology, such as those shown in Figures 1, 2A, and 2B, the return OCT light is exported from the OCT scanner adapter 206 to the coupler 104 via the optical port 214, and through there it is passed to the spectrometer 136 of the spectral OCT system 100.

[0116] The OCT scanner housing 208, including the objective lens 210, adds a height h2 to the height h1 of the microscope 200 in the embodiments shown in Figures 2A and 2B. The additional stack height H2 introduced by attaching the OCT scanner adapter 206 to the microscope housing 202 is minimized by using the optical design of the OCT scanner optical components within the OCT scanner adapter 206 according to embodiments of the disclosed technology.

[0117] For example, several embodiments of the optical component design of the OCT scanner adapter 206 may have the optical design schematically shown in Figures 3A, 3B, 4, 5A, and 5B. This optical design raises the OCT beam emerging from the scanning mirror assembly 310 by a minimum amount from the plane of the objective lenses 114, 210 before the OCT appears through the objective lenses 114, 120. This allows the additional stack height h2 of the OCT scanner adapter to be less than 40 mm, and in some embodiments, the additional stack height h2 is 36 mm or less.

[0118] Figures 2A and 2B are not to scale, and the x, y, and z axes shown in the figures are schematic and merely illustrative of general front and rear perspective views. As shown in Figures 2A and 2B, the stack height of the microscope housing body is h1 and is aligned with the Z axis, while the microscope housing base and OCT scanner adapter 206 are mainly aligned with the XY horizontal plane. The stack height h2 of the OCT scanner system mounted below the carriage is also aligned with the Z axis. As a result, the total stack height h3 of the microscope body housing the microscope optics combined with the OCT scanner mounted below the carriage is determined by h1 and h2. Preferably, the combined height h3, h1 + h2 = h3, is short enough to allow the microscope to be positioned to allow manipulation by a user performing surgery on or through the area including the focal plane of the microscope objective lens 210 through which the OCT beam emitted from the microscope passes. The OCT optical design, for example in some embodiments, allows for the minimization of h2 to 36 mm while still maintaining a suitable output beam diameter of 10.6 mm and still having a stack height of 36 mm or less.

[0119] Therefore, by using the optical design for scanning mirror assembly optics according to the embodiments of the disclosed technology, the combined stack height h3 = h1 + h2 can be made much shorter than was possible with previous optical design configurations.

[0120] By reducing the stack height as much as possible, the microscope can be better positioned for surgery. For example, it can be positioned far enough away from the focused tissue sample to allow the user access to the tissue sample under surgery, but close enough to fit a typical human physical form factor. In other words, the OCT adapter height h2 is preferably reduced as much as possible to allow conventional operation of the microscope by a user who is also performing surgery, while the microscope is optically focused on the focal plane on the tissue sample using the microscope objective lens 210 of the OCT scanner adapter 206 from which the OCT probe beam is emitted onto the tissue sample.

[0121] Some embodiments of the OCT scanner adapter 206 microscope accessory shown in Figures 2A and 2B include a scanning mirror assembly 310 (described in more detail below) having a compact optical design that allows the h2 to be minimized to 36 mm or less.

[0122] For example, in some embodiments, as will be described later with reference to Figures 3A, 3B, and 4, the OCT scanner adapter 206 includes an ultra-compact large numerical aperture microelectromechanical system (MEMS) based two-dimensional (2D) scanning mirror assembly 310, which uses a position-sensing detector 160 and a point light source 158 to determine the position of the reflective mirror surface 334 in its optical design.

[0123] Some embodiments of OCT scanner assemblies using the PSD160 can support very high scanning rates, e.g., more than 36,000 A scans per second, where an A scan is a depth scan at a given point in the tissue. Each B scan is formed from multiple adjacent A scans, and the A scans can be used to generate an image with depth information about the scanned area in the form of slices through the sample being scanned, showing the structure at different depths along the slice. In other words, the B scan provides information about the structure in the z-direction or depth direction along a single linear cross section of the tissue sample, e.g., a linear scan along a line definable by xy coordinates as schematically shown in Figure 1. Some embodiments of the OCT assembly enable the generation of very high-resolution images, e.g., 400 B scans per second in real time, across the entire field of view (FoV) being scanned, which may be an area of ​​20 mm × 20 mm or larger. By performing a series of B scans sufficiently quickly and in close proximity across the sample, a three-dimensional stereoscopic scan or composite scan can then be formed from the scanned region and presented on the display 152.

[0124] An embodiment of the scanning mirror assembly, shown as optical block 310 in Figures 3A-3B and 4, and shown in more detail in Figures 5A and 5B, includes various optical components arranged in an optical design configured to reduce the height h2 and lateral footprint of the OCT scanner adapter 206.

[0125] Some embodiments of the optical design of a scanning mirror assembly specify one or both of the minimum and maximum exit beam diameters of one or more optical components. For example, the beam diameter of an OCT beam input via optical fiber 308A preferably exceeds a threshold diameter of 3.1 mm when exiting the collimating lens assembly 516, shown as collimating lens 602 in Figure 6, and the beam diameter from the collimating lens may have an exit pupil diameter of 3.3 mm in some embodiments. Other design constraints may depend on the exit pupil diameter of the OCT beam from the collimating lens. For example, in some embodiments, the collimated OCT beam exits the collimating lens assembly with an exit pupil diameter of at least 3.1 mm, and possibly as large as 3.3 mm, to have a wavefront error of less than (approximately) 1 / 2 wave (rms).

[0126] Another selected output beam diameter is the beam diameter of the OCT beam 312 that outputs from the focusing lens assembly 314 of the OCT scanner adapter 206 and then enters the folding mirror 316. The focusing lens 314 expands the OCT scanning or probe beam diameter to 10.6 mm and sets the resolution for the OCT scanner system based on the OCT system numerical aperture, and ultimately the focal length of the OCT microscope objective lens 210. For the objective lens 210 with a working distance (not focal length) of 175 mm, the lateral resolution is 30 μm, in other words, the resolution is better than 33 line pairs per millimeter. This can be compared to a resolution of 6 microns, 166 line pairs / mm, at the mid-image plane located at the exit of the OCT objective lens assemblies 510, 512.

[0127] In some embodiments, the maximum FoV that a user can set for scanning is a 20mm x 20mm area, using a user interface for an apparatus implementing the image processing system 148 shown in Figure 1, which includes or is connected to a display 152. In some embodiments, the user interface is configured to allow the user to adjust the position of the OCT scan FoV within a 25mm box, even if the entire FoV of the OCT scan image remains a 20mm x 20mm area.

[0128] Embodiments of the disclosed technology used in surgical procedures and other applications requiring real-time image processing may utilize a highly dispersed configuration of the OCT system 100 having an OCT scanning adapter 206.

[0129] As used herein, the term "real-time" refers to a small processing delay of, for example, 60 ms or less, and in some embodiments, delays of approximately 30 ms or less are achievable. This design incorporates a high incident angle at the scanning mirror to reduce composite angle coupling when performing 2D scanning of the sample with both high lateral optical resolution and a telecentric image plane.

[0130] The following description of the optical design of the scanning mirror assembly 310 shown in Figures 3A, 3B, 4, and 5A incorporates a high incident angle at the scanning mirror reflective surface 334 to reduce composite angle coupling when performing a 2D scan of a sample, enabling the OCT scan to be performed in both high lateral optical resolution and telecentric image plane. Each OCT scan includes a number of one-dimensional scans, A scans, which provide depth information at points within the region being scanned (e.g., of a sample). Several A scans are stacked together to create a two-dimensional image, referred to herein as B scans. B scans provide slices through the scanning region, showing depth information along the path of the A scans. Multiple B scans traversing the scanning region can provide a three-dimensional stereoscopic scan of the scanning region.

[0131] The scanning mirror assembly 310 includes a movable reflective surface 334 equipped with a micro-electromechanical system having a suitable large numerical aperture. The term “large numerical aperture” here refers to the effective aperture diameter of the reflective surface 334, preferably larger than about 4 mm in diameter. The term “effective aperture diameter” means the range of angles that can be imaged through the aperture without obstruction from supports, clips, or other forms of retaining elements. A larger effective aperture diameter of the scanning mirror reflective surface 334 results in a slower scanning rate because the probe beam covers a larger diameter. While MEMS mirrors with an effective aperture diameter of about 7 mm are already known in the art, even with optical feedback, these known MEMS mirrors with large effective aperture diameters cannot scan at speeds acceptable for real-time imaging applications such as those required for OCT during optical surgery. In some embodiments, the scanning mirror has an effective aperture diameter of 5 mm. In some embodiments, a 4.2 mm effective aperture diameter scanning mirror assembly is used, enabling scanning to be performed at speeds fast enough for the SD-OCT system shown in Figure 1 to be used for real-time surgical applications.

[0132] In OCT, axial and transverse characteristics are separated. Transverse resolution is determined by the objective lens and focusing medium in front of the sample. The axial characteristics of interferometry are defined by the coherence characteristics of the OCT scanning light source and how the return OCT signal is sampled by the detector after it has been returned from the sample. OCT axial resolution depends on the spectral bandwidth and center wavelength of the OCT scanning light source. Axial imaging depth defines the axial range covered by the B scan. It is also defined by the maximum fringe frequency that can be detected as the maximum frequency of the interference spectrum, which decodes the maximum depth scanned.

[0133] A scan is an amplitude depth scan along a one-dimensional axis, usually referred to as the z-axis, through the sample, while B scans are two-dimensional transverse scans across the sample formed by a series of A scans. In other words, for each sample point, the spectrally dependent interference fringe pattern generated by back reflections from the OCT interferometer's reference mirror and back reflections from the sample is recorded as an A scan. Multiple A scans are performed to generate other scans, such as B scans, which allow for the generation of a complete depth profile of the sample reflectivity at the beam position.

[0134] In some embodiments, the aperture diameter is 4.2 mm or larger.

[0135] In some embodiments, the OCT scanner adapter 206 includes a high-speed OCT MEMS-based mirror scanning assembly 310 that uses a position sensing detector system 160 to implement control loop feedback for controlling the positioning of the OCT beam during scanning. The control loop feedback has a technical advantage in that it enables the OCT scanner to generate more B scans per second of the object of interest being scanned. In other words, the control feedback loop implemented in some embodiments of the disclosed technology enables the suppression of ringing and resonant behaviors caused by step changes in the drive voltage at the ends of the scan line.

[0136] Example of OCT microscope adapter design Figure 3A schematically shows an exemplary embodiment of the MEMS microscope OCT scanner adapter 206 according to the disclosed technology, which is suitable for mounting on the lower carriage of the microscope 200 shown in Figures 2A and 2B, as it consists of optical components that are designed to optimally reduce the lateral and vertical footprint while maintaining optical quality characteristics suitable for OCT applications.

[0137] In Figure 3A, an illustrated exemplary embodiment of the OCT scanner adapter 206 comprises several components housed within or mounted on an adapter housing 208. The adapter housing 208 includes data / power ports 212, such as an Ethernet Power over Ethernet port or a high-speed USB port.

[0138] Furthermore, an optical port 214 is provided for inputting and outputting OCT scanning light to the OCT scanner adapter 206. The optical fiber 308a connected to the optical port 214 supplies OCT light from the coupler 104 shown in the OCT scanning system 100 of Figure 1 to the scanning mirror assembly optical block 310 shown in Figure 3A via the optical fiber connector 308. The return OCT light returns along the coupler 104 shown in Figure 1 via the optical fiber 308a. Thus, the optical fiber 308a is part of the optical path 105a shown in the OCT scanning system 100 of Figure 1, through which OCT probe light illuminates the sample to be scanned, and through which OCT light returned from the sample is output toward the coupler 104 of the OCT scanning system 100 shown in Figure 1. The optical fiber 308a has a suitable numerical aperture, preferably 0.14, to allow OCT light in the near-infrared region to propagate along it in single mode.

[0139] The OCT light from the OCT light source 102 follows optical path 101a along the illumination arm 101 to the coupler 104, and then takes optical path 105a along the probe arm 105 in Figure 1, which is partly formed by the optical fiber 308a. The OCT light following the optical fiber 308a is injected into the scanning mirror assembly optical block 310 via the OCT data connection fiber connector 308, and then follows the OCT arm 518 of the MEMS scanning mirror assembly 310 (see Figure 5A).

[0140] In some embodiments, the optical fiber connector 308 into which the OCT light is input to the MEMS mirror block 310 is a fiber connector relative to an angle-polished connector.

[0141] The optical block housing the MEMS scanning mirror assembly 310 also houses the optical components of an optical angular displacement mirror position measuring system 156 for the scanning mirror assembly, shown in Figure 1 as a mirror position measuring system 156. A controller 162 (see Figure 1, not shown in Figure 3A) is used to adjust the reflective surface 334 of the scanning mirror 112 shown in Figure 1 using the mirror movement mechanism (not shown) of the MEMS scanning mirror assembly 310. The controller 164 may be implemented within the OCT scanner adapter 206 or may be remotely located, in which case the control signal may be transmitted to the mirror movement unit in the MEMS scanning mirror assembly 310 via the data port 212 of the OCT scanner adapter 206.

[0142] In some embodiments, the same mirror reflective surface 334 in the scanning mirror assembly housed within the optical block 310 reflects both the input OCT beam and the mirror positioning reference beam from a different light source (see Figure 5A below for more details). However, as will be apparent to those skilled in the art, in other embodiments, it is possible to use separate mirrors mounted on the same tilt axis, provided that this is done in a manner that does not adversely affect the stack height h2 of the OCT scanner adapter 206.

[0143] The OCT light, which travels along the optical path 105a and is received via the OCT data connection fiber 308, is reflected by an optical surface of the reflective surface 334 that is different from the optical surface on which the light from the light source of the angular displacement mirror measurement system 156 is reflected.

[0144] The reflected OCT beam then follows an optical path through the OCT scanner adapter 206, from which it emerges via the microscope objective lens 210 to probe a tissue sample of interest, such as in vivo ocular tissue schematically shown in Figure 1. Other types of tissue samples of interest may include tissue samples for fields such as ophthalmology and dermatology, dentistry, angiography, and cardiology, as well as other tissue samples for the diagnosis of diseases, including cancer.

[0145] OCT light reflected, backscattered, or otherwise returned from structures within the tissue sample then returns through the scanning mirror assembly of the optical block 310 and follows the return path 105a along the optical fiber 308a. The returned OCT light is then emitted from the OCT scanner adapter 206 via the optical port 214 and supplied to the OCT system 100, where it is combined with and interferes with the light returned from the reference arm 103 at the coupler 104. The resulting interference pattern is detected by a spectrometer 136 in the OCT system 100 in Figure 1, which generates image data, and the image data can then be image-processed to obtain a tomographic image showing scanned structures within the tissue located within the scanning FoV.

[0146] In an exemplary embodiment of the OCT adapter 206 shown in Figure 3A, the OCT probe beam 312 is output from an optical block housing a MEMS OCT scanning mirror assembly 310 and travels toward a beam splitter 318 toward a folding mirror 316 that lifts the OCT beam a minimum amount from its optical plane toward the beam splitter 318. The beam splitter 318 reflects the incident OCT beam toward the objective lens assembly 210 of the OCT scanner adapter 206, which also functions as the objective lens of the microscope optics housed in the microscope 200 when the OCT scanner adapter 206 is mounted on the microscope 200. The OCT probe beam emerges from the objective lens 210 as a telecentric beam focused on a focal plane 154 in the tissue being scanned, in the xy plane schematically shown in Figure 1. The resulting reflected OCT light can be used to generate an OCT A scan that provides depth information in the z direction, orthogonal to the focal plane 154, in other words, as shown in Figure 1. The movement of the reflective mirror surface 334 shifts the position of the telecentric beam across the focal plane 154 within the scanned region 116, enabling the generation of an OCT B scan image.

[0147] In Figure 3A, the OCT scanner adapter 206 is configured so that the objective lens 210 can be used as an objective lens by the microscope optical system and the OCT scanner system 100. A light-shielding gasket 320 is provided around the aperture formed in the OCT scanner adapter 206, through which the OCT objective lens 210 is aligned with and extends the optical channel formed by the microscope optical system of the microscope 200.

[0148] The configuration of the folding mirror 316, beam splitter 318, and objective lens assembly 210 of the OCT scanner adapter 206 is collectively designed so that the OCT beam is lifted only a small amount from the plane it follows through the scanning mirror assembly so that it can exit through the objective lens 210. The amount of lift required is influenced by the inclination angles of the beam splitter and folding mirror, as well as the beam incidence geometry. Thus, the additional height h2 that the OCT scanner adapter 206 adds to the height of the microscope is also minimized by using this optical design. For example, in some embodiments, the OCT scanner adapter housing 302 adds 40 mm or less to the overall height h1 of the microscope housing 202. In some embodiments, the additional height h2 is 36 mm or less. This can be achieved with a lift of 27 mm or about 27 mm by using suitable inclination angles for the beam splitter and folding mirror in some embodiments.

[0149] In some embodiments, as shown in the exemplary embodiment of Figure 3A, the OCT probe beam 312 exits an optical block housing a scanning mirror assembly, travels through free space, and first proceeds to a focusing lens assembly 314, which allows the focal plane of the scanned image to be adjusted. This adjusts the focus of the scan at different depths. The focusing lens assembly 314 is driven by a motor 326, which further includes a movement limiter or stopper 324. In some embodiments, the focusing mechanism provided by the adapter's focusing lens assembly 314 is adjustable to control the OCT focal plane within a range of ±30 mm, thereby allowing a range of depths in the sample to be focused for scanning. The OCT focal plane can be adjusted over a range of + / -30 mm and may be optimized for the best SNR during initial image acquisition. This should not be confused with the technique of shifting the focus at an A scan rate, which is used to extend the depth of focus in the sample. The focusing lens assembly 314 moves more slowly than required for A-scan sampling and does not adjust without user intervention unless the system detects a large movement of the sample.

[0150] In some embodiments, as shown in Figure 3A, the OCT scanner adapter 206 is attached to the microscope 200 using a fixture, for example, a screw, the screw being provided in recesses of mounts 328a and 328b and extending from mounts 328a, 328b into the lower carriage of the microscope 200, to corresponding receptacle openings or holes, preferably screw holes, in the lower carriage of the microscope 200, so as to fixate the OCT scanner adapter 206 to the microscope. In some embodiments where the OCT scanner adapter 206 functions as a microscope accessory, the OCT scanner adapter 206 may also include receptacle openings or holes at positions on its base corresponding to the positions of receptacle openings or holes in the lower carriage of the microscope 200. Different types of microscope accessories that are otherwise attached to the lower carriage of the microscope 200 can be attached to the lower carriage of the OCT adapter instead by having the same or similar receptacle positions within the base of the OCT scanner adapter microscope accessory 206 as the receptacle positions in the lower carriage of the microscope. In other words, in some embodiments, the OCT scanner adapter 206 is configured to be mounted on the lower carriage of a microscope as a microscope optical system accessory. Some embodiments of the OCT scanner adapter microscope accessory 206 allow the OCT scanner adapter accessory 206 to have another microscope accessory mounted on the base of the OCT scanner adapter.

[0151] Figure 3B shows an alternative diagram of the OCT scanner adapter 206 in Figure 3A. However, in Figure 3B, the position of the light source or emitter 158 of the mirror positioning light beam 400, shown in Figure 4, which illuminates the scanning mirror, is more visible, as is the position of the position detection element (PSD) 160 of the optical angular displacement measurement system 156 within the optical block 310.

[0152] Furthermore, Figure 3B schematically shows an exemplary incidence angle θ of the mirror positioning illumination beam 400 shown in Figure 4 on the reflective surface 334 of the MEMS scanning mirror, which forms a mirror positioning reference beam that, after reflection, travels toward the PSD160.

[0153] It should be understood that the incident angles and positions of the beam paths shown in the drawings are for illustrative purposes only and are not to scale.

[0154] The MEMS scanning mirror assembly is designed such that the illumination mirror positioning light beam 400, shown in Figure 4, is reflected by the scanning mirror's reflective surface 334 at different optical surfaces to form a reference beam 402 that passes along the positioning reference arm of the OCT scanning mirror assembly 310 from the optical surface where the incident OCT scanning or probe beam 312 is reflected, as shown in Figures 4 and 5A. The scanning mirror assembly is also configured such that the return positioning light is reflected by the mirror at a different optical surface, which is different from the optical surface where the incident mirror positioning beam is reflected, and which is different from the optical surface where the incident mirror positioning beam is reflected, resulting in minimal interference with any of the light sources of the OCT beam, the incident mirror positioning beam, or the mirror positioning beam.

[0155] Figure 4 of the attached drawings schematically shows an enlarged view of the OCT scanner adapter 206 in Figures 3A and 3B. In Figure 4, the mirror position illumination beam 400 (shown by a dashed line) from the point light source 158 is incident on the reflective surface 334 of the OCT scanning mirror 500 shown in Figure 5A at an incident angle of interest (AOI) indicated by θ. The mirror position reflected beam 402 (shown by a dashed line in Figure 4) is reflected toward the PSD 160, where it is detected. For clarity, the reflected light from the incident beam in the PSD 160 is not shown in Figure 4.

[0156] The OCT scanner optical components shown in Figures 3A to 4 are arranged so that the OCT light appearing from the optical surface of the scanning mirror assembly is lifted slightly from that optical surface by the folding mirror 316 toward the beam splitter 318. The beam splitter 318 allows the OCT probe beam to be transmitted through the microscope optics and returned to the microscope optics, while reflecting the OCT probe beam to the same focal plane 154 as the microscope light. By optimally positioning the beam splitter and folding mirror relative to the objective lens 210, it is possible to reduce the height that the OCT probe beam must be lifted by the folding mirror before it is reflected by the beam splitter 318 and exits through the objective lens 210.

[0157] In some embodiments, the folded mirror elevates the OCT beam by 27 mm from the optical surface of the scanning mirror assembly.

[0158] Example of optical design for scanning mirror assembly Figure 5A of the attached drawings schematically shows an example of an optical design for a two-dimensional (2D) scanning mirror assembly, such as a 2D scanning mirror assembly housed in the optical block 310 shown in Figures 3A, 3B, and 4.

[0159] The optical design of the 2D scanning mirror assembly is suitable for use with other types of OCT scanners, such as the OCT scanner 164 and OCT scanner adapter 206 shown in Figure 1. The scanning mirror assembly 310 shown in Figure 5A has an optical design that can be used for non-OCT applications that use scanning light requiring mirror positioning.

[0160] In other words, the optical design of the 2D scanning mirror assembly in Figure 5A is not limited in all its embodiments to OCT applications or devices such as those shown in Figures 1 to 4 of the accompanying drawings. It can be usefully implemented in any other type of optical scanning device where a compact lateral optical surface is beneficial.

[0161] Some exemplary embodiments of the micro-electromechanical system (MEMS) two-dimensional scanning mirror assembly 310 shown in Figure 5A have an optical design comprising a movable MEMS scanning mirror having a reflective surface 334, a connector 308 to a point source for a scanning light beam, and, for example, an optical fiber 308a connected via the optical fiber connector 308 as shown, where the end of the optical fiber 308a (see Figure 5B) functions as a point source for the light beam.

[0162] The scanning mirror assembly optics also includes a collimating lens assembly 516 for light introduced via connector 308. The collimating lens assembly 516 is configured to output light from a point source with an output beam diameter exceeding a threshold output beam diameter toward a reflective surface suitable for the desired scanning application. After being reflected by the reflective surface 334 of the scanning mirror 112, the scanning light beam passes through the objective lens assemblies 510, 512 and exits the scanning mirror assembly.

[0163] The reflective surface 334 is configured to reflect the incident collimated light beam to form a scanning beam, for example, an OCT probe beam if the point source realizes OCT light, and the OCT light, as a telecentric beam 312, exits the mirror assembly via the objective lens 510 and the field lens 512 (collectively referred to as the objective lens assembly 510, 512) toward the telecentric image plane 154. The optical design of the components within the scanning mirror assembly is configured to ensure that the scanning beam can perform scanning with a resolution better than the resolution threshold.

[0164] The optical system of the scanning mirror assembly is configured to achieve a total track length L of the path from the point source, for example, from the end face of an optical fiber or fiber ferrule (see also Figure 5B), to the telecentric image plane (700) of less than approximately 40 mm, which helps to keep the lateral dimension X of the scanning mirror assembly small enough to allow the OCT scanner housing 308 to be below the desired lateral footprint in its design. For example, as shown in Figure 5, the width X of the scanning mirror assembly is preferably less than 41 mm, and may be 40.6 mm or less in some embodiments, for example. The optical design is also configured to keep the depth Y as small as possible, as shown in Figure 5A, and may be 35 mm or less, for example, and may be as short as 34.5 mm or less in some optical designs.

[0165] Therefore, in some embodiments, the total track length L is kept as short as possible, allowing the optical design layout to minimize the lateral footprint X and depth footprint Y as much as possible, and as a result, the scanner housing with the scanning mirror assembly 310 can have a similarly small footprint.

[0166] By keeping the lateral footprint X as small as possible, lateral access to the area being scanned is improved, which is particularly beneficial when the scanning mirror assembly 310 is a scanning mirror assembly for the OCT scanner adapter 206, which is a surgical microscope accessory, as this can improve access to the area being operated on while the microscope to which the scanning mirror assembly is attached is in use.

[0167] In some embodiments of the scanning mirror assembly, the threshold for the exit beam diameter from the collimating lens 516 is at least 3 mm, preferably at least 3.1 mm. By having an exit beam diameter of at least 3.1 mm, the scanner benefits from better lateral resolution than that enabled by a smaller exit beam diameter.

[0168] In some embodiments of the scanning mirror assembly, the threshold for telecentric beam resolution at the telecentric image plane 700 is better than 6 microns. In other words, the scanned image can resolve features of the scanned sample smaller than 6 microns.

[0169] In some embodiments, the scanning mirror 112 may be moved by, for example, a controller 162. In some embodiments, the scanning mirror assembly may be configured to move about its optical axis and to scan over a range of + / - 5 degrees.

[0170] In some embodiments of the scanning mirror assembly, both the numerical aperture of the optical fiber and the focal length of the collimating lens determine a preferred threshold of at least 3.1 mm for the exit beam diameter of the collimated beam from the collimating lens in order to achieve the resolution designed at the focal plane. The combination of the focal length of the scanning mirror objective lens and the focal length of the scanning mirror field lens from which the probe beam exits the mirror assembly determines the total track length L, which is preferably less than or near 40 mm.

[0171] In some embodiments, for example, when the scanning mirror assembly is used for OCT purposes, the optical fiber has a numerical aperture of 0.14. The optical fiber supplying light to the scanning mirror assembly by acting as a point source may have a different preferred numerical aperture value that enables supplying sufficient light to the scanning mirror assembly for other use cases along the single-mode optical fiber 308a in other embodiments of the scanning mirror assembly.

[0172] In some embodiments of the scanning mirror assembly, the objective lens 510 comprises an F2.7 biconvex doublet lens, and the field lens 512 comprises an F19 positive / negative meniscus doublet field lens.

[0173] In some embodiments of the scanning mirror assembly, the optical path difference (OPD) of the telecentric probe beam output by the scanning mirror assembly has a radius of curvature greater than 100 mm.

[0174] In some embodiments of the scanning mirror assembly, the telecentric beam is more telecentric than an incident angle of 0.03 degrees in the telecentric image plane.

[0175] In some embodiments of the MEMS scanning mirror assembly, the reflective surface 334 of the MEMS scanning mirror includes a large-diameter gold-clad silicon mirror bonded to the underlying mechanical structure.

[0176] Embodiments of the scanning mirror assembly 310 design schematically shown in Figure 5A can be implemented as an optical block within an OCT scanning system, such as the OCT scanning system 100 shown in Figure 1. For example, in some embodiments, the scanning mirror assembly is implemented as an optical block having the X, Y footprint shown in Figure 5A within a compact OCT scanner adapter 206 for a microscope, such as an optical block housing the scanning mirror assembly 310 shown in Figures 3A, 3B, and 4.

[0177] However, as described above, the scanning mirror assembly 310 shown in Figures 5A and 5B has an optical design that can be used in a variety of different usage scenarios in other types of scanner systems. In some embodiments, the mirror assembly shown in Figures 5A and 5B is realized as a scanning mirror assembly for an OCT device, such as those shown in Figures 3A to 3B, to receive light fed in by the optical fiber 308a. In other embodiments, a different point source may be used instead of the optical fiber 308a, which functions as a point source for the OCT light beam, as shown in Figures 3A, 3B, 4, 5A, and 5B.

[0178] In some embodiments, the mirror assembly 310 may be located within an OCT scanner adapter 206 used as an OCT scanning accessory for a microscope 200. In some embodiments, the microscope may be a surgical microscope, and the scanning mirror assembly 310 may be used to generate OCT scans of the tissue sample being operated on at a speed high enough to allow live OCT tomography of the tissue sample area to be generated while the surgical procedure is in progress.

[0179] In some embodiments, the SD-OCT scanning system shown in Figure 1 includes an OCT scanner adapter 206 comprising scanning mirror assemblies 112,310 having an optical design as shown in Figures 5A and 5B and described herein.

[0180] In some embodiments, the scanning mirror assembly 310 is configured such that the OCT light returned from the sample along the OCT probe arm 105 has a lateral optical resolution of 6 μm or more, in other words, a resolution better than 166 line pairs per mm.

[0181] In some embodiments, the scanning mirror assembly 310 comprises a MEMS 2D scanning mirror assembly including at least a movable MEMS scanning mirror having a reflective surface 334, an optical fiber 308a connected via an optical fiber connector 308 and configured to function as a point source for an OCT beam illuminating the reflective surface 334, and a collimating lens assembly 516 configured to output OCT light from the point source toward the reflective surface 334 with an output beam diameter of at least 3.1 mm. The reflective surface 334 is configured to reflect both an incident collimated OCT light beam for forming an OCT probe beam and a mirror positioning reference beam. The OCT probe emits the mirror assembly as a telecentric beam toward the telecentric image plane with a resolution of at most 6 microns. The optical system of the scanning mirror assembly 310 is configured to achieve a total track length L from a) the end face of the fiber ferrule providing the point source inserted into the optical fiber connector, to b) in some embodiments less than 40 mm, preferably less than 36 mm, to the telecentric image plane. In some embodiments, the objective lens assemblies 510, 512 are located within the probe arm of the scanning mirror assembly to focus the telecentric OCT beam through the OCT scanner (microscope) lenses 114, 210.

[0182] The scanning mirror assembly 310 has an optical design that includes a reflective surface 334 of a MEMS mirror configured such that the incident mirror positioning beam is reflected by an optical surface different from the optical surface on which the incident OCT scanning beam is reflected. In this way, the scanning mirror assembly can also be used with a mirror positioning system, such as the angle-tilting mirror positioning system schematically shown in Figure 1 of the drawings.

[0183] As described above, some embodiments of the MEMS-based scanning mirror assemblies shown in Figures 5A and 5B and described herein are implemented in an OCT scanner 206 as shown in Figures 3A, 3B, and 4, as part of an SD-OCT scanning system shown in Figure 1. Accordingly, some embodiments of the disclosed technology include an OCT scanner system 100 comprising an OCT scanner 206 including a microelectromechanical system (MEMS) two-dimensional scanning mirror assembly 310 having a compact optical design according to the disclosed technology.

[0184] In some embodiments of the MEMS scanning mirror assembly 310, the scanning mirror 112 is mounted on a lower mechanical structure or support 500 that provides a mirror movement mechanism that allows the mirror surface 334 to pivot around its optical axis under the control of a controller 162, as shown in Figure 5A.

[0185] In some embodiments, the reflective surface 334 of the MEMS scanning mirror assembly includes a large-diameter gold-clad silicon mirror bonded to the underlying mechanical structure 500.

[0186] The angular displacement measurement system 156 shown in Figure 1 is implemented in the embodiment of the MEMS mirror assembly in Figure 5A by a light source 158, which is a preferred point light source, for example, a laser diode 502. The point light source generates a light beam, referred to herein as the mirror positioning light beam 400 (shown as a dashed line in Figure 5A), which passes through the collimating lens 503 so that the collimated mirror positioning beam 400 is incident on the scanning mirror surface 334 at an incident angle θ.

[0187] The angular displacement measurement system 156 is used to determine the angular position of the MEMS scanning mirror assembly 310 relative to the incident mirror positioning beam 400, thereby determining the mirror position of the incident light beam when performing a scan and adjusting it as the scan progresses. OCT scanning (e.g., B-scanning or stereoscopic scanning) is performed by moving the mirrors using the controller 164 according to arbitrary scanning parameters for a particular scanning configuration (these are, in some embodiments, input by the user and / or can be automatically determined for a particular type of scan).

[0188] The position of the movable MEMS mirror surface 334 can be controlled in some embodiments using a suitable angular position controller (not shown in Figure 5A) that uses closed-loop control based on feedback from a position sensing detector 160 that detects the reflected mirror positioning beam 402.

[0189] In some embodiments, the scanning mirror assembly 310 described above with reference to Figures 3A, 3B, 4, 5A, and 5B includes a position sensing detector 160 configured to transmit feedback mirror position data to a controller 162 configured to control the position of the MEMS scanning mirror surface when scanning is performed. However, in some embodiments of the compact OCT scanning mirror assembly 310 of the drawings, the controller is housed remotely. For example, in some embodiments, it may be housed elsewhere within the OCT scanner adapter 206. Alternatively, in some embodiments, it may be housed together with other system components of the OCT scanner system 100, or it may be hosted on a different platform having a user interface that allows input of scanning parameters. Control signals may be transmitted from the remote controller 162 via a suitable data connection, such as a data port, such as 212, in some embodiments.

[0190] In some embodiments, the mirror positioning light source illuminates the reflective surface of the mirror assembly for the optical mirror position feedback channel at an incident angle θ greater than 62 degrees, preferably 67.5 degrees, from the normal to the plane of the reflective mirror surface 334.

[0191] In some embodiments, the OCT light source illuminates the reflective surface of the mirror assembly of the OCT light channel at an incident angle θ of less than 28 degrees, preferably 22.5 degrees, from the normal to the plane of the reflective mirror surface 334.

[0192] In some embodiments, the minimum usable aperture on the reflective mirror surface is at least 4 mm, which is particularly useful when the mirror assembly is incorporated into an OCT scanner device, such as the compact OCT scanner 206 microscope accessory used for surgical applications.

[0193] In some embodiments of the disclosed technology, the OCT apparatus may use closed-loop feedback to control the scanning mirror position. The use of closed-loop feedback may be useful in embodiments requiring high scanning rates, such as when a live video or other form of OCT scanning image sequence is required. The use of closed-loop feedback allows the mirror to be moved fast enough and accurately to achieve high scanning rates and / or high scanning resolution (in other words, high OCT image B-scan or stereoscopic scanning resolution), thus supporting low-latency, high-speed OCT scanning for time-sensitive applications, such as when OCT scanning is implemented to guide surgical procedures. However, in some embodiments, open-loop control may be provided.

[0194] The disclosed technology attempts to address at least some of the design constraints that exist when designing OCT systems for surgical microscopes. For example, one design constraint is that smaller diameter scanning mirror surfaces are better suited to achieving higher scanning rates. Numerical aperture is related to resolution. The effective aperture diameter, i.e., the mirror diameter, is related to the scanning size in that the underlying mechanical structure of the MEMS is the same, and therefore a smaller diameter mirror, such as 2 mm in diameter, can tilt further before hitting the MEMS base (up to + / - 7 degrees), while a larger diameter mirror, such as 7.5 mm in diameter, can tilt only + / - 1.5 degrees before hitting the base. This means that a larger area can be scanned using a smaller diameter mirror, but this comes at the expense of resolution.

[0195] In some embodiments, the threshold for the exit beam diameter of the OCT light beam is based on the numerical aperture of the optical fiber and the focal length of the collimating lens assembly.

[0196] In some embodiments, the two-dimensional scanning mirror assembly is configured to reflect a mirror positioning light beam (400) incident on a reflective surface (334) in a first optical plane toward a position sensing element (160) configured to generate information about the tilt angle of the scanning mirror reflective surface (334).

[0197] In some embodiments of the optical angular displacement measurement system 156 for the scanning mirror assembly 310 shown in Figure 5, mirror positioning light from a light source 158 is first collimated by a preferred collimating lens assembly 503 to form a collimated illumination light beam 400 that is incident on the reflective mirror surface 334. The collimated illumination light beam 400 (circularly represented by a short dashed line in Figures 3B, 4, and 5A) is then incident on the reflective MEMS mirror surface 334 at AOI = θ and reflected to form a mirror position reference beam 402 (shown by a longer dashed line in Figures 3B, 4, and 5A), which moves along the mirror position reference arm 501 of the scanning mirror assembly, through the PSD lens assembly 504, and in some embodiments, through an optional attenuation filter 506, toward the PSD 160.

[0198] However, the mirror positioning beam 400 may be reflected by the PSD160 toward the reflective surface 334 of the MEMS mirror or otherwise returned (the reflected beam is not shown in Figure 5A). This is undesirable because such reflected light may contaminate the illumination positioning beam and / or the input OCT light beam. Other issues with stray light reflectivity in the mirror position detector system include the detection of an incorrect spot position when stray light is present on the PSD160, and the potential for changes in diode behavior when reflected light is incident on the diode cavity, which can cause intensity fluctuations in the position detector beam that the PSD detects as a change in position.

[0199] To prevent the return reflecting element of the positioning beam from being reflected by the MEMS mirror assembly 310, some embodiments of the disclosed technology include additional components such as optical traps. The optical traps are appropriately configured and positioned to reduce the re-incidentation of any reflected mirror positioning reference beam light into the emitter for the mirror positioning beam and / or contamination of the return probe beam 312 before it reaches the interferometer.

[0200] As described above, some embodiments of the MEMS-based scanning mirror assemblies shown in Figures 5A and 5B have a reflective surface designed so that OCT light input via the OCT optical coupler 308 is reflected from a mirror positioning reference beam 402 and from another region of the MEMS mirror surface 334 to which the OCT scanning or probe beam is reflected from a different optical surface.

[0201] After reflection, the OCT scan or probe beam reflected by the MEMS mirror surface 334 of the scanning mirror assembly 310 passes along the optical path through the OCT objective lens 510 and the OCT field lens assembly 512, which outputs the OCT beam as a telecentric beam into free space toward the folding mirror 316. As shown in the embodiments of Figures 3A and 3B and Figure 4, the beam passes through the focusing lens assembly 314 before being incident on the folding mirror 316, which lifts the beam away from the optical surface of the scanning mirror assembly. In some embodiments, this allows the OCT focal plane to be focused within a range of + / - 30 mm, in other words, a range of different depths can be focused into the scanning area. However, the focusing lens optics may be omitted in some embodiments of the OCT scanner.

[0202] The folding mirror 316 lifts the OCT scanning (or probe) beam from the plane of its optical path through the scanning mirror assembly by reflecting the incident OCT scanning or probe beam toward the beam splitter 318. The beam splitter reflects the OCT scanning or probe beam from the microscope objective lens 210 of the OCT scanner adapter 206 toward the focal plane 154 for scanning the tissue or similar object of interest, which may be an in vivo or in vitro tissue sample. The beam splitter 318 also allows the scanned OCT illuminated area to be viewed through the microscope optics housed within the microscope 200.

[0203] In some embodiments, as shown in Figures 3A and 3B, the OCT probe beam 312 is input to the optical block by traveling along the optical path 105a in the optical fiber 308a and is incident on the scanning mirror optical block 310 via the OCT data connection fiber input 308. The OCT scanning or probe beam 520 then passes toward the scanning mirror reflective surface 334 via the collimating lens 516. The mirror surface 334 reflects the OCT beam from the optical block, including the scanning mirror assembly 310, via the probe arm 508, at which point the OCT beam folds back toward the mirror 316 in free space.

[0204] As shown in the embodiments of the OCT adapter in Figures 3A, 3B, and 4, the OCT scan or probe beam 312 is focused by passing through a focusing lens assembly 314 before reaching the folding mirror 316. The focusing lens assembly is driven by a motor 336 that adjusts the position of the focusing optical system to allow a range of depths of focus to be achieved when performing a scan. In some embodiments, the focal range can vary from + / - 30 mm.

[0205] The returned OCT light is reflected via the MEMS scanning mirror surface 334, along the OCT arm 518 of the scanning mirror assembly 310, toward the coupler of the OCT system 100 shown in Figure 1.

[0206] In the scanning mirror assembly 310, the input OCT light beam enters from the end face 532 of the optical fiber 308a via the optical fiber connector 308, passes through the optical fiber ferrule 530 (see also Figure 5B), and then through the OCT collimating lens 516 towards the scanning mirror assembly. The track length, in other words, the measurable physical distance of the path from the end face 532 to the surface of the scanning mirror, is shown as L1 in Figures 5A and 5B.

[0207] Figure 5A also shows the track length L2 from the scanning mirror surface to the telecentric image plane 700. The total track lengths L=L1 and L2 are preferably less than or equal to the track length design threshold of 40 mm.

[0208] Figure 5B is an enlarged view of Figure 5A, showing more clearly the positions of the optical fiber ferrule 532 and optical fiber end face 530, which cause the optical fiber 308a, acting as a point light source, to incident OCT light onto the mirror scanning system 310. The OCT light travels from the end face 532 of the fiber to the collimating lens 516, and the collimated illumination OCT beam is then incident on the reflective surface 334 of the MEMS scanning mirror, which reflects it toward the OCT probe arm 105 (shown in Figure 1) or 508 shown in Figure 5A.

[0209] For clarification, in the return direction not shown in Figure 5A or Figure 5B, the return OCT light travels in the other direction along the OCT arm 518 (see also the description in Figure 6), through the collimating lens 516, then along the optical fiber 308a via the OCT data connection fiber 308, and then out of the OCT scanner adapter 206 via the optical port 214.

[0210] In some embodiments, the OCT scanner is implemented using off-the-shelf (OTS) MEMS (micro-electromechanical systems), where the MEMS scanning mirror reflective surface 334 is provided by a large-aperture protective gold-coated silicon mirror bonded to a mechanical structure 500 beneath the optical block 310. The OCT scanner 206 formed by such a design provides a simplified and miniaturized optical system with the same optical performance as much larger galvanometer scanning mirror type systems known in the art for use in intraoperative OCT systems.

[0211] In some embodiments, the optical block design of the OCT MEMS mirror assembly 310 includes a 2D scanning mirror assembly and a complementary optical angular displacement measuring system 156 for measuring the position of the MEMS mirror system.

[0212] A mirror positioning system for measuring the angular displacement of a scanning mirror reflective surface 334 comprises a mirror positioning light source 158 and a position sensing detector (PSD) 160. The PSD may also include a PSD lens assembly 504 and a light-reducing filter 506, similar to the PSD 160. An example of a suitable PSD detector is the Hamamatsu S5991 4mm × 4mm active area position sensing detector.

[0213] In some embodiments, the angular optical displacement measurement system 156 is located within the same optical block as the MEMS scanning mirror assembly 310. In some embodiments, the optical angular displacement measurement system 156 is used to achieve closed-loop control of the MEMS scanning mirror position. Closed-loop control can be achieved by measuring the incident angle θ using the PSD 160 and supplying information indicating the mirror position derived therefrom to the controller, thereby enabling the controller to more accurately control the tilt angle of the scanning mirror reflective surface 334 when scanning is performed.

[0214] This closed-loop feedback can enable very high B-scan rates. For example, using closed-loop control of a 4.2 mm diameter effective aperture mirror 112, it is possible to achieve at least 400 B-scans per second as the maximum scan rate with full-angle deflection relative to the maximum field of view (FoV).

[0215] In embodiments without closed-loop control, i.e., open-loop scanning, a low-pass filter can be used to prevent the MEMS scanning mirror moving device from reaching a natural frequency excitation state where it may resonate due to uncontrolled vibrations (which could damage the MEMS scanning mirror moving device). In embodiments where open-loop scanning is performed, the maximum scanning rate may be about 50 B scans per second, which can be compared to the speed achievable with closed-loop control. In some embodiments with closed-loop control, the scanning rates achievable using exemplary embodiments of the MEMS scanning mirror assembly 310 according to the disclosed technology are about 400 Hz or higher.

[0216] In some embodiments, the optical components of the MEMS scanning mirror assembly 310 are configured to collectively achieve a predetermined system numerical aperture for a desired system optical resolution through the microscope objective lens 210. In other words, in some embodiments, the MEMS scanning mirror system components are appropriately configured to allow the diameter of the collimated OCT beam 312 output along the OCT data connection fiber 308 to match a desired minimum system optical resolution after passing through the microscope objective lens 210.

[0217] In some embodiments, all air-to-glass interfaces within the OCT scanner adapter 206 are designed to be convex in order to minimize back reflection from the OCT beam as it propagates through the optical system.

[0218] Figure 6 shows an exemplary embodiment of an OCT collimator lens 516, also referred to herein as an OCT collimator lens assembly, such as the collimator lens 516 shown on the OCT arm 518 of an optical block including the scanning mirror assembly 310 shown in Figure 5 of the drawings. The OCT collimator lens 516 is provided along the OCT arm 518 of the scanning mirror assembly optical block 310. In Figure 6, OCT light supplied to the collimator lens assembly 602 via the optical fiber ferrule end 532 appears as a collimated OCT output beam 604 having a collimated beam diameter of at least 3.1 mm. The collimated OCT beam then travels toward the scanning mirror reflective surface 334 and is reflected from there. The returned OCT light follows a reverse path through the scanning mirror assembly and is focused toward the end of the optical fiber 308a that collects the returned light via the collimated beam, and then the returned OCT light can propagate toward the coupler 104 of an interferometer system such as the OCT system 100 shown in Figure 1.

[0219] A preferred example of the OCT collimator lens 516 that may be used in some embodiments of the disclosed technology is an F3.2 biconvex doublet lens. Such lenses have a thick crown glass portion that reduces the radius of curvature of the lens surface, thereby improving color performance. In some exemplary embodiments, the collimator lens has a focal length of 10 mm with a depth of focus of 100 microns, enabling good mechanical focus stability. In some embodiments, the OCT collimator lens realizes an output beam having a collimated beam (exit pupil diameter) of 3.1 mm in diameter with <1 / 4 wave (root mean square, rms) wavefront error.

[0220] Figure 7 shows an example of an OCT objective lens assembly 510, 512 in which the OCT beam 312 contains light 312a of a certain range of wavelengths, for example, light of a certain range of wavelengths over the near-infrared portion of the optical spectrum.

[0221] The OCT light is reflected from the reflective surface 334 of the scanning mirror assembly, first focused by the OCT objective lens 510, then by the field lens 512, and subsequently emerges as a telecentric beam 312b. Multiple angle-dependent telecentric beams 312b 1,2,3 However, these beams are focused onto the telecentric image plane 700, as shown in Figure 7, and each beam 312b 1,2,3 This indicates the location where the OCT beam 312b appears at a specific scanning angle; in other words, the telecentric exit beams 312b1, 312b2, and 312b3 are sequential beams generated as the B scan progresses.

[0222] The OCT beam 312 deflected from the mirror surface, in other words, passes through the OCT objective lens assembly 510 (including the field lens 512 in some embodiments), and the light 312b forming the OCT beam 312, schematically shown in Figure 7 as OCT exit beams 312b1, 312b2, and 312b3, can be designed to exit perpendicular to the intermediate image plane at all scanning angles and thus be telecentric.

[0223] In some embodiments, all air-to-glass interfaces, such as 514, are convex to eliminate back-reflection artifacts in the OCT image. Therefore, the OCT objective lens assembly shown in Figure 7 receives the angular input OCT scan or probe beam 312a reflected from the MEMS scanning mirror surface 334, and the telecentric OCT scan or probe beam 312b (or rather, beam 312b) 1,2,3The telecentric OCT scan or probe beam 312b is converted to one of the following, which in some embodiments is then output to free space. In some embodiments, the telecentric OCT scan or probe beam 312b is first focused using a focusing lens assembly 314 before being lifted towards the beam splitter 318 by a folding mirror 316, as shown in Figures 3A and 3B. Alternatively, for example, the telecentric OCT scan or probe beam 312b may pass directly through free space to the folding mirror 316, where it is reflected towards the beam splitter 318.

[0224] The focusing lens assembly 314 functions as the optical interface for the telecentric OCT beam 312b to the microscope objective lens 210. The scanning mirror assembly can be used without the focusing lens assembly 314 in some embodiments, but this requires that the sample be positioned on the intermediate image plane 700, which is focused when the telecentric OCT beam 312b emerges from the scanning mirror assembly. Therefore, to use the OCT scanner 206 without the focusing lens assembly, the sample must be positioned on the intermediate image plane 700 in some way. For example, as shown in the exemplary embodiments of the OCT scanner in Figures 3A, 3B, and 4, the lens is required to optically couple to the microscope objective lens 210, or alternatively, the objective lens 210 would require a much shorter focal length. Such short focal lengths are not useful for surgical applications. However, in some embodiments of the disclosed technology, the OCT scanner may omit the focusing lens assembly 314 when used for a different type of application. For example, an OCT scanner 206 used for imaging eyes, especially animal eyes, may not require a focusing lens 314.

[0225] In some exemplary embodiments of the OCT scanner adapter 206 used in surgical microscopes, a focusing lens assembly 314 collimates and magnifies the incoming telecentric OCT beam 312b to a suitable back focal length, so that it has a collimated beam diameter of 10.6 mm at the exit. As the OCT beam 312 exits the focusing assembly, it is collimated and therefore focuses on the focal plane of the microscope objective lens 210, as with the microscope optics.

[0226] Alternatively, the target distance is effectively adjusted by adjusting the position of the focusing lens assembly 314 relative to the intermediate image plane. This allows the focal position of the microscope objective lens 210 to be changed as appropriate for OCT scanning, while the focal position remains fixed for the microscope optical system.

[0227] An advantage of having a focusing lens assembly 314 in some embodiments of the OCT scanner, such as those shown in the exemplary embodiments in Figures 3A, 3B, and 4, is that if the surgeon moves their eyeballs during a surgical procedure, the OCT scanning system can keep the OCT focused on a designated anatomical feature using appropriate automatic focusing techniques known in the art.

[0228] Another advantage of the embodiment of the OCT scanner 206 including the focusing lens assembly 314 is that it can be used in some situations even if the microscope optics are improperly set up by the user of the microscope 200, for example, a surgeon or assistant. For example, if the microscope is parfocal, in other words, if the microscope eyepiece is set to infinity for a user with corrected vision via contact lenses or glasses, the microscope optics will focus on the focal plane of the microscope objective lens. If the microscope eyepiece is not set to accommodate the refractive error of the microscope user's vision, some users may adjust or compensate for the refractive error of their own vision by moving the entire microscope using handles 204a,b, as shown in Figures 2A and 2B, for example. However, this movement of the microscope optics results in the scanned tissue sample or other scanned object of interest (e.g., an eye under surgery) no longer being positioned on the actual focal plane of the microscope objective lens 210 realized by the OCT scanner system 206. In other words, if the microscope is used improperly, the focus of the OCT beam 312 may need to be adjusted accordingly to compensate using a focusing lens assembly such as the focusing lens assembly 314.

[0229] In some embodiments, the OCT objective lens 510 shown in Figure 7 is an F2.7 biconvex doublet lens. The objective lens 510 is coupled with an F19 positive / negative meniscus doublet field lens 512 to direct the scanned collimated OCT beam 312, reflected from the surface 334 of the MEMS scanning mirror, to the intermediate telecentric image plane shown in Figure 7. The OCT return beam passes through the OCT field lens, then through the OCT objective lens, then is reflected again via the reflective surface 334 of the MEMS mirror, and enters the interferometer assembly (see SD-OCT system 100 in Figure 1, not shown in Figure 5A) via the OCT collimated lens 516 (see also Figure 5A) along the OCT output arm 518.

[0230] In some embodiments, as shown in the exemplary embodiments of Figures 5A and 7, all air-to-glass interfaces, such as the surface 514 of the objective lens assembly 510 for the outward OCT beam 312 and the return OCT beam (not shown), and the collimating lens 516, are convex to eliminate back reflection artifacts in the OCT image.

[0231] In some embodiments, the total track length L in the optical block of the scanning mirror assembly is the sum of the length L1 from the end face 532 of the optical fiber 308a in the optical fiber ferrule 530 to the reflective surface 334 of the scanning mirror, and the track length L2 from the surface 334 to the telecentric image plane 700, as shown in Figure 5A. The total track length L = L1 + L2 is preferably less than 40 mm.

[0232] In some embodiments, the optical path difference (OPD) in the scanned sample has an OPD curvature greater than 100 mm.

[0233] In some embodiments, the OCT scan or probe beam is telecentric better than an incident angle of 0.03 degrees.

[0234] In some embodiments, a focusing system 314 is provided to adjust the OCT beam 312 so that the OCT focal plane can be controlled within a range of ±30 mm and aligned with the microscope optical channel focal plane.

[0235] In some embodiments, the MEMS OCT scanner has a lateral XY profile where X is less than 42 mm and Y is less than 35 mm, as schematically shown in Figure 5A, so that the OCT scanner system housing can be laterally fitted into the lateral housing profile of the microscope optical system carrier footprint. This is advantageous as it reduces obstruction in the sterile field for surgical applications. In some embodiments of the optical block that implements the scanning mirror assembly 310, the dimensions of the optical block are a width X of about 40.6 mm or equal to it and a depth Y of about 34.5 mm or equal to it, and a track length L of about 40 mm or less.

[0236] In some embodiments, the scanning mirror assembly further comprises an optical angle displacement measuring system 156 for determining the inclination angle of the reflective surface with respect to incident light, the system comprising at least a point light source, a collimator lens assembly for collimating light from the point light source to form a collimated mirror position measuring light beam incident on the reflective surface, and a position sensing detector, wherein the reflective surface is configured to reflect the incident collimated light beam at a first optical surface to form a reflected position measuring light beam that travels toward the position sensing detector.

[0237] In some embodiments of the scanning mirror assembly 310 described above with reference to Figures 5A and 5B of the drawings, closed-loop control of the position of the reflective surface of the MEMS mirror is achieved by a position-sensing detector configured to supply angular displacement measurement information to a controller configured to control the inclination angle of the reflective mirror surface with respect to the irradiated light beam. In some embodiments, closed-loop control uses a PID feedback loop to adjust the drive voltage to the MEMS based on the position and to attenuate ringing artifacts caused by rapid directional changes.

[0238] Advantageously, in some embodiments, the scanning mirror assembly includes a scanning mirror assembly 310 within the OCT scanning device 206, where the input beam includes an OCT probe beam 312 that is reflected toward the sample or similar object of interest 116 through optical components along the OCT probe beam arm of the scanning mirror assembly. The scanning mirror assembly 310 is configured to output the OCT probe beam 312 toward the focal plane 154 of the sample as a telecentric OCT probe beam, and the optical path length of the OCT probe beam from the light source 102 to the sample focal image plane 154 is configured to be equal to the optical path length of a reference OCT beam from the same OCT light source 102 along the reference arm 103 of an interferometer OCT system 100 connected for 2D scanning of the sample region 116.

[0239] In some embodiments, the MEMS scanning mirror assembly 310 disclosed herein is provided as an optical block 310 within an OCT scanner adapter 206 for a surgical microscope 200 that forms part of a connected OCT system 100. Such an OCT scanner adapter 206 preferably has at least a lateral footprint X within or equal to the footprint of the surgical microscope housing, and preferably also has a length or depth footprint within the footprint of the microscope. The OCT system 100 outputs an interference signal containing OCT scanning data 146 to an image processor 148 of the OCT system 100. The image processor 148 can then process the interference signal 146 and perform signal transformations, such as a Fourier transform, which enables the display of an OCT image showing internal scanning structures within a scanning area on a display 152. This image can be generated in real time to guide a surgeon and / or, in some embodiments, to guide other parties on one or more preferred displays 152.

[0240] In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 206 is configured to be fixed to the lower carriage of the housing of the microscope optics of a surgical microscope, and the OCT scanner adapter 206 adds less than 40 mm, preferably less than 36 mm, to the stack height of the surgical microscope.

[0241] In some embodiments of the OCT scanner adapter 206, the OCT scanner adapter 206 is configured to be fixed to the lower carriage of the microscope optical system housing, and the objective lenses 114, 210 of the OCT scanner adapter 206 are aligned with the optical channels of the microscope optical system when the lateral footprint of the housing 208 of the OCT scanner adapter 206 is located within the lateral footprint of the housing 202 of the surgical microscope 200.

[0242] In this way, a surgical microscope 200, such as the one shown in Figures 2A and 2B, comprising a microscope optical system, a housing 202 for housing the microscope optical system, and an OCT scanner adapter 206, can be provided according to the disclosed technology, the OCT scanner adapter 206 including, for example, a scanning mirror assembly according to the disclosed technology, as shown as an example in Figures 5A and 3B. The OCT scanner adapter 206 may be configured to output image data that will later be input to an image processor of an OCT system, such as the OCT system shown in Figure 1.

[0243] Accordingly, some embodiments of the micro-electromechanical system (MEMS) two-dimensional scanning mirror assembly (310) disclosed above include a scanning mirror assembly having an optical design comprising: a movable MEMS scanning mirror having a reflective surface 334; a point light source 308a for a light beam; a collimating lens assembly 516 configured to receive light from the light source and output a collimated light beam having an output beam diameter exceeding a threshold toward the reflective surface 334; and objective lens assemblies 510, 512 toward which the collimated light beam reflected from the reflective surface exits the scanning mirror assembly. The reflective surface 334 is configured to reflect the incident collimated light beam to form a probe beam 312, which exits the mirror assembly as a telecentric beam (312) toward a telecentric image plane with a resolution better than the threshold of the telecentric beam resolution. The optical system of the scanning mirror assembly is configured to achieve a total track length L from the point source to a telecentric image plane (700) of less than 40 mm, and the scanning mirror assembly can be realized within an optical block having a width of 41 mm or less, preferably 40.6 mm, and a length of 35 mm or less, preferably 34.5 mm, excluding the optical fiber connector 308 and the MEMS support 500 (see X and Y of the block dimensions shown in Figure 5A).

[0244] Examples of beam steering and feedback control In some embodiments, the scanning mirror assembly includes a system for controlling beam steering, which uses a closed-loop feedback mechanism to enable high scanning speeds. In some embodiments, an embodiment of the closed-loop feedback system for the scanning mirror is used in the scanning mirror assembly 310 of the OCT system 100. For example, in some embodiments, this can be used in an OCT scanning mirror assembly provided in an OCT adapter 206 for a microscope, such as the surgical microscope 200 shown in Figures 2A and 2B.

[0245] Some embodiments of the disclosed feedback system include a mirror positioning detection system 156 and a controller 162, which form part of the OCT scanner 164 shown in Figure 1.

[0246] Figures 11A to 11B show the optical configuration for determining the position of the scanning mirror used in the optical feedback system 1100. In the exemplary embodiments shown in Figures 11A to 11C, the scanning mirror reflective surface 334 is configured to reflect a primary light beam, including, for example, OCT probe beam light (e.g., light from the OCT light source 102), on one optical surface, and also to reflect light from another light source, referred to as a secondary light source 158,502, used to determine the tilt angle of the mirror reflective surface 334, on a different optical surface. Separating the light beam onto two different optical surfaces can advantageously help achieve a sufficiently high signal-to-noise ratio in the position detection element 160 to more accurately and quickly determine the tilt angle position of the scanning mirror reflective surface 334 of the scanning mirror assembly 310. This can support real-time image processing at a resolution level suitable for providing OCT images of a sample or tissue when the sample or tissue is being operated on by a surgeon or similar user.

[0247] Achieving such high scanning speeds can be difficult, given the design constraints imposed on OCT adapters for surgical microscopes.

[0248] Figure 8 schematically illustrates an example of a known beam steering configuration using a 2D mirror, such as a MEMS device, having an optical configuration different from that of the disclosed embodiments. In the example shown in Figure 8, a series of one or more optical beam splitting devices are used to ensure the orthogonality of the input and output optical beams and the reflected beam from the MEMS mirror surface. As shown in Figure 8, the input beam is incident on beam splitter #1, which reflects the input beam so that it is incident perpendicular to the steering or scanning mirror surface. The reflected beam passes through beam splitter #1 and is then partially reflected from another beam splitter #2 as a mirror position reference beam that can be detected by a position sensing element, and partially transmitted through beam splitter #2 to form the output beam. In this way, the input beam is not subjected to combined angular distortion, and therefore scanning distortion is limited to the mechanical limitations of the MEMS mirror device itself. Known beam steering configurations of this type have a PSD, but do not use the PSD for closed-loop control, and as a result the MEMS mirror is driven at a relatively slow scanning speed. Another disadvantage of these known systems when used for interferometric imaging applications such as OCT is artifacts in the OCT scan image, as the parallel plane of the optical beam splitter acts as a secondary reference plane. Another drawback is that beam splitting results in unacceptable signal-to-noise degradation.

[0249] Accordingly, some embodiments of the disclosed technology attempt to mitigate or avoid some of the above technical problems by providing a beam steering system that uses a MEMS scanning mirror assembly illuminated by a scanning mirror position reference beam incident at an off-normal incidence angle on an optical surface off-axis of the mirror's reflective surface. The use of a reference illumination beam incident at an off-axis and / or off-normal incidence angle (AOI) helps to reduce or eliminate reflections from any secondary reference surface and thus maintain a much better signal-to-noise ratio than known systems can provide.

[0250] Several embodiments of beam steering assemblies according to the disclosed technology can be used to provide beam steering for scanning mirror assemblies such as the scanning mirror assembly 310 shown in Figure 5A described herein, wherein the optical feedback mechanism comprises a laser diode light source 158 that directs a reference light beam 400 to the MEMS scanning mirror. The reference light beam is incident on the scanning mirror reflective surface 334 at an angle θ. The reflected reference beam 402 then travels onto the PSD 160 via the PSD imaging lens assembly 504 and optionally via a light-reducing filter 506.

[0251] The beam steering assembly disclosed herein maintains a very high signal-to-noise ratio in the PSD160 of the scanning mirror assembly 310 to optimize the performance of an optical feedback scanning control system that controls the position of the reflective surface 334 of the MEMS mirror assembly in a manner that supports high A scanning speeds.

[0252] To maintain a very high signal-to-noise ratio on the PSD160, scattered or stray light is reduced as much as possible within the optical feedback channel.

[0253] Some embodiments of the scanning mirror assembly 310 achieve this by setting the geometric distortion ratio at the reflective surface 334 to approximately 2:1. This allows the optical feedback channel to be physically offset from the central optical axis (see, for example, Figures 13, 14A, and 14B below). This allows any undesirable reflective elements of the mirror positioning beam 402 reflected from the surface of the PSD 160 to be offset equally, but in the opposite direction, from the optical axis, enabling suppression of back reflection via optical traps (see, for example, Figure 14B), as opposed to direct reflection to the laser diode illumination source 158 of the optical feedback channel via the reflective surface 334.

[0254] Figure 9 schematically shows an example of a light source assembly for realizing a reference beam for mirror position feedback for a MEMS-based scanning mirror assembly according to several embodiments of the disclosed technology, for example, a MEMS-based scanning mirror assembly 310 as shown in Figure 5A. In some embodiments, the light source may be used within an OCT scanner 206, such as those shown in Figures 2A, 2B, 3A, 3B, and 4.

[0255] Figure 9 shows in more detail an example of one embodiment of the optical emitter assembly 900 of the scanning mirror assembly 310. As shown in Figure 9, the optical emitter assembly includes a laser diode, such as a point light source, for example, a point light source 158 shown in Figure 5A, and more specifically, a collimating lens 503, also shown in Figure 5A, for the angular displacement measuring optical feedback mechanism 156. The laser 158 is configured to direct an optical beam 400 (see Figure 5A) towards the reflective surface 334 of the MEMS scanning mirror assembly 310.

[0256] A collimating lens 503 (see Figure 5A) is used to reduce the divergence of the light beam 400 emitted from the laser diode. The collimating lens is held in place via a lens spacer 906. In some embodiments, the lens spacer 906 comprises a 250 μm thick polycarbonate film, which is held by a suitable retainer 904, such as an O-ring or, for example, a square-profile acrylonitrile butadiene O-ring. However, in other embodiments, a spring steel retainer ring 904 may be used instead or in addition to hold the lens spacer. In the embodiment of the optical emitter assembly 600 shown in Figure 6, the point light source 158 is a laser diode. In some embodiments, this is appropriately mounted on a support, for example, on a printed circuit board.

[0257] The light source 158 for the reference beam 400 may be aligned and focused via a plurality of fine-pitch screws, for example four (only two pitch screws are visible in Figure 9), as shown as 902a, 902b in Figure 9. These screws 902a-d are screwed into receiving openings 908a,b as shown in Figure 9. The openings 908 are preferably threaded to allow for screw receiving openings. In some embodiments, a 2 mm thick fluoropolymer elastomer provides spring tension to stabilize the optical emitter assembly when the pitch screws 902a,b engage with the corresponding receiving openings 908a,b.

[0258] Figure 10 schematically shows an example of a position detection element (PSD) assembly 1000 for detecting the mirror reference beam position in a MEMS-based scanning mirror assembly according to some embodiments of the disclosed technology, for example, a MEMS-based scanning mirror assembly 310 as shown in Figure 5A. In some embodiments, the PSD assembly 1000 may be used in an OCT scanner 206, such as the scanning mirror assembly shown in Figure 5A, as shown in Figures 2A, 2B, 3A, 3B, and 4.

[0259] Figure 10 shows an exemplary embodiment of a PSD assembly 1000 comprising an imaging or focusing lens assembly, for example, an imaging lens 504, also shown in Figure 5A. In Figure 10, light from a MEMS mirror reflective surface 334 (not shown) first passes through a focusing lens 504 held by a preferred lens retainer 1002, and then, in some embodiments, through an optional light-reducing filter 506 separated from the PSD 160 by a retainer ring 1004.

[0260] The PSD imaging lens 504 (also referred to herein as the PSD focusing lens 504) sets the spot size of the reference beam in the PSD 160 to exceed the minimum threshold required for detection in the PSD. The PSD 160 can include any suitable type of PSD, for example, in some embodiments it can include a silicon photodiode PSD. Figure 10 also shows a screw 1006 for allowing adjustment of the PSD position, but in other embodiments other suitable adjustment mechanisms may be used.

[0261] The PSD imaging lens 504 shown in Figure 10, together with other optical components 506, 1002, 1004, and 1006, constitutes the PDS160, which can be used to capture the position of a MEMS mirror within a range of inclination angles, for example, a MEMS motion of ±5 degrees around its axis of rotation. The PSD lens reflects the incident reference beam 402 onto a photosensitive area of ​​the PDS160 of an appropriate size, e.g., 4 mm × 4 mm. This configuration has been shown to enable closed-loop control of the MEMS scanning mirror with far greater accuracy than systems known in the art.

[0262] In Figure 10, the attenuation (ND) filter 506, positioned adjacent to the PSD retainer ring 1004, is optional in some embodiments. When used in one embodiment, the attenuation filter 506 significantly reduces the magnitude of stray light based on the attenuation value of the attenuation filter 1008 acting on its beam in both directions. This is achieved by a double pass through the attenuation filter 506 required by stray light from back reflection from the PSD 160, reducing the sensitivity of the PSD 160 to spurious stray light from the emitter light source 158.

[0263] Figure 11A schematically shows an exemplary non-sequential ray trace of an optical feedback channel, with RGB colored rays rendered using a grayscale color scheme. The color scheme is an artifact used to distinguish the spatial separation of beams; that is, each color rendered as a gray shade represents a beam from a different mirror angle and does not represent a chromaticity reference because the mirror positioning light source 158, in other words, the laser diode 502, is a single-wavelength emitter.

[0264] Figure 11A schematically shows one embodiment of an optical feedback system 1100 for a MEMS scanning mirror assembly 310, which includes optical emitters such as the optical emitters 158, 502 shown in Figures 1 and 5A of the drawings of the OCT system 100 and scanning mirror assembly described herein. The optical emitters 158, 502 emit a light beam that passes through a collimating lens 503. The collimated illumination laser light beam 400 is directed to a reflective surface 334 of a two-dimensional MEMS scanning mirror assembly having a vertical optical axis 1102 from which the mirror is tilted to perform scanning. The mirror reflective surface is two-dimensional in the sense that it reflects the incident light beam 400 with separate optical surfaces for any optical surface of OCT incident light by tilting both vertically and horizontally. The reflected light beam forms a mirror position reference beam 402.

[0265] A collimated reference beam 400 from the laser diode light source 158,502 forms a reference beam 402 for determining the tilt position of the scanning mirror around its optical axis using the PSD assembly 160. The reference beam 400 is incident on the reflective surface 334 of the MEMS mirror assembly at an angle that reduces geometric distortion in the vertical plane above the optical center 1116 of the reflective mirror surface 334.

[0266] The optical feedback system 1100 shown in Figure 11A demonstrates how a 2:1 geometric distortion ratio along the y-axis scanning length of the MEMS mirror assembly 310 can be used to offset the incident optical path 1104 (dashed line in Figure 11A).

[0267] In embodiments where the optical feedback system 1100 is used within a scanning mirror assembly for OCT scanning, such as a scanning mirror assembly 310 in an OCT adapter 206, the optical center of the mirror along the optical axis 1116 is the location where the OCT scan or probe beam 312 (not shown in Figure 11A) is incident.

[0268] In the embodiment shown in Figure 11A, the reflected PSD reference beam 402 follows an optical path 1104 from the reflective mirror surface 334 to the PSD device 160 via a PSD focusing lens 504 and a light-reducing filter 506. In the PSD detector 160, the reference beam is detected as a spot on its detection surface. In Figure 11A, multiple spot positions represent different mirror positions. This is shown as the beam being deflected to different spots 1108a,b,c. Each spot position represents a different tilt angle around the vertical axis of the reflective surface. The reference beam reflected from the PSD 160 returns as beam 1110 along the optical path 1106 towards the MEMS scanning mirror, where the beam is incident on the optical surface below the optical center 1116 of the reflective surface 334. The reflective surface 334 then reflects the incident beam 1110 to form beam 1114, which travels into the optical trap 1112. The optical trap 1112 is positioned so as not to interfere with the emitter 158 or the emitted reference beam 400. The optical trap 1112 is described in more detail below.

[0269] Figure 11B schematically shows another diagram of the non-sequential ray tracing shown in Figure 11A. In Figure 11B, an example of Zemax ray tracing of a laser diode illumination reference beam 400 reflected from the reflective surface 334 of the MEMS scanning mirror assembly is shown from a side that is clearer how the reference beam 400 is imaged onto the PSD160 according to several embodiments of the disclosed technology.

[0270] In Figure 11B, the laser diode light source 502 is the emitter 158 of an illumination reference beam 400 that is incident on the reflective surface 334 of the MEMS scanning mirror assembly 310 via a collimating lens 503. The reflected reference beam 402 is centered on the optical path 1102 in the optical plane above the central optical surface of the reflective surface 334. The reference beam 402 passes through the focusing lens 504 and the attenuation filter 506 to the PSD 160, where it is reflected as a reflected reference beam 1110 (not shown in Figure 11B, see Figures 11A and 11C) and returns along the optical path 1106 towards the MEMS mirror. Figure 11B illustrates, as an example, how the reference beam forms spots 1108a,b,c on the surface of the PDS 160 as scanning progresses. Figures 11A and 11C show non-sequential ray traces, in other words, ray traces in both the forward and reverse directions.

[0271] In some embodiments, the configuration of the optical components shown in Figures 11A, 11B, and 11C results in equal offsets of the illumination reference beam 400 and the reflection reference beam 402 around the optical center of the MEMS mirror, as shown in Figure 11C. In some embodiments, the laser diode light source illumination beam 400 is offset by approximately 1 millimeter from the optical center 1116 of the reflective surface 334 of the MEMS mirror. As described above, the optical center of the MEMS mirror coincides with the optical axis of the OCT channel (OCT light is not shown). The same numbering scheme used in other drawings is used in Figures 11A, 11B, and 11C.

[0272] Figure 11C shows another schematic diagram of an exemplary Zemax ray trace of the laser diode illumination reference beam 400 reflected from the PSD160 in the embodiments of Figures 11A and 11B.

[0273] In Figure 11C, the ray trace shown in Figure 11B includes the reflected beam 1100 from the PSD 160 to the reflective surface 334 as it propagates back through the attenuation filter 508 and the focusing lens 504, and this reflective surface 334 reflects the reflected reference light beam 1110 as beam 115 to the optical trap 1112. As shown in Figure 11C, the optical trap 1112 is located below the emitter 158, in other words, below the laser diode 502. In the embodiment of Figure 11C, the reflected beam 1110 from the PSD 160 is reflected by the reflective surface 334 in an optical plane that is equal to, but oppositely offset from, the optical axis of the central MEMS mirror, indicated as 1116. In some embodiments, the illumination beam 400 and the return reference beam 1110 are separated by only about 2 millimeters in the vertical (y-axis) direction at the laser diode source and optical trap location, as shown in Figure 12.

[0274] The reference beam 400 has a sufficiently large angle of incidence relative to the reflective mirror surface to allow separation of the emitted reference beam 400 and the reflected reference beam 402 from the beam 1110, which is the return or reflected beam from the PSD. By allowing the reference beam to pass through the focusing PSD lens before it is incident on the detection surface of the PSD 160, the beam 402 is focused toward the MEMS mirror optical axis 1116, and the resulting reflected beam 1110 has an equal but opposite offset relative to the MEMS mirror optical axis 1116. In some embodiments of the feedback system shown in Figures 11A to 11C, if the angle of the reference beam when the reference beam light is incident on the scanning mirror is less than 62 degrees, the beam spread is so large when incident off-axis that the emitted reference beam may not be distinguishable from the return reference beam light and / or, in some embodiments, the OCT beam light.

[0275] In other words, a high AOI of beam 400 relative to the MEMS surface 334 generates increased distortion in the Y direction. When the mirror is tilted by + / - 5 degrees in the horizontal (X) direction, the scan length remains unchanged for all AOI values. However, as the AOI increases from the normal position relative to the MEMS mirror surface 334, the obtained scan length in the Y direction from a + / - 5 degree tilt in the vertical direction begins to shorten so that the Y scan length is approximately half the value of the X scan length by the time an AOI of 67.5 degrees is reached. Therefore, the higher the AOI, the greater the distortion (contraction) in the Y direction, and if the contraction distortion in the Y direction is too great, the input beam 400 may be offset by 1 mm from the optical center 810, and the beam 402 from a + / - 5 degree tilt still passes through the PSD lens, which is the limiting aperture.

[0276] The disclosed embodiment of the technology uses a PSD lens 504 that refracts (focuses) the 402 beam onto the PSD surface 1108. As a result of refraction, the 402 beams strike the PSD surface at a given AOI, and the PSD surface reflects these 402 beams at equal but opposite exit angles AOE. This results in a vertical separation between the mirror positioning reference beam 402 and the reflected beam 1110. If the PSD lens 504 is not provided, the mirror positioning reference beam 402 is incident on the PSD detection surface at a 90-degree angle when the MEMS mirror is not tilted, in other words, when it is tilted at 0 degrees. This results in a direct back reflection from the PSD to the light source, in other words, a back reflection to the laser diode 502.

[0277] The data from the position detection element 160 is transmitted to the mirror position controllers 162 and 1700 of the control system, which will be described later with reference to Figure 17.

[0278] FIG. 12 shows an example of the beam spot position on the reflective surface of a MEMS scanning mirror according to some exemplary embodiments of the disclosed technology. In FIG. 12, the relative positions of both the laser diode irradiation beam 400 on the surface 334 of the MEMS scanning mirror and the subsequent reflected beam 1110 from the PSD 160 are shown in x-y coordinates corresponding to the x-y coordinates shown in FIGS. 11A-11C.

[0279] FIG. 13 shows an example of the relative beam spot positions of the reference beam 400 and the return beam 1114 reflected from the PSD 160 with respect to the position of the optical trap 1112. The relative positions of both the laser diode light source beam exit 1402 (see FIG. 14) and the subsequent reflected beam 1114 from the PSD device traced back to the optical trap position are shown. The scales shown in FIGS. 12 and 13 and FIGS. 15 and 16 are merely examples, as will be understood by those skilled in the art.

[0280] As shown in the embodiment of FIG. 14, the optical trap location is positioned directly below the laser diode source beam exit 1402. The offset of the laser diode light source optical axis with respect to the optical trap 1112 allows the return reference beam 1110 from the PSD 160 to be equally offset within the optical plane with respect to the optical plane where the illumination beam 400 is incident on the reflective surface 334 of the MEMS mirror assembly. This provides a clear separation between the illumination beam 400 and the reflected beam 402. Without such an offset, the reflected beam 1114 could directly collide with the laser diode source beam when exiting the exit 1402, which could cause laser cavity instability among other problems.

[0281] FIG. 15 includes a graph showing an example of the geometric synthetic angle scanning distortion (y-axis) as a result of the non-normal incidence angle (x-axis) for a MEMS-based 2D scanning mirror assembly 310 including an optical feedback system 1100 according to some embodiments of the disclosed technology.

[0282] Several embodiments of a scanning mirror assembly 310 using an optical feedback system comprising the optical components shown in Figures 11A to 11C are shown in Figures 3A, 3B, and 3C. The scanning mirror assembly 310 uses an off-axis or non-normal incidence angle (AOI) so that the emitter beam 400 avoids the secondary reference plane and maintains a better, preferably as high as possible, signal-to-noise ratio.

[0283] In some embodiments, the rotation axis of the two-dimensional (2D) scanning mirror assembly 310 is not separated. This can be contrasted with a coupled conventional galvanometer-based scanning mirror structure. However, as a result, geometric distortion may be introduced due to the resulting composite angle that defines a nonlinear reflection angle. Such a nonlinear reflection angle is obtained from the linear angular deflection from the 2D mirror for any given angle of incidence. In other words, a scanning mirror system using linear mirror tilt results in the generation of a parabolic scanning trace. The magnitude of the distortion with respect to the angle of incidence is shown in Figure 15.

[0284] The geometric distortion shown in Figure 15 is most pronounced at the deflection angle of the emitter beam 400 perpendicular to the AOI when incident on the 2D reflective mirror surface 334. In other words, if the AOI defines the deflection in the X-axis, the y-axis deflection is more affected by the geometric distortion. Thus, a symmetrically square mirror angle tilt results in a series of parabolic curves that are symmetric with respect to the optical axis plane.

[0285] As shown in Figure 15, the resulting geometric scanning distortion due to the combined angle of the incident and reflected beams consists of a parabolic function that can be derived as a function of the AOI and the mirror tilt angle. Figure 15 shows a series of tilt angles in 0.5-degree increments in both the orthogonal x and y directions, over ±5 degrees around AOIs of 22.5 degrees and 67.5 degrees at a focal length of approximately 100 mm. This can be contrasted with the perpendicular, orthogonal, in other words, 90-degree AOI of the input and reflected beams in the mirror shown in the exemplary prior art system in Figure 8.

[0286] The parabolic function in the y direction for a tilt angle of -5 degrees at an incident angle of 67.5 degrees can be represented by y = 0.02x 2 + 2E-15x + 17.6. On the other hand, the parabolic function in the y direction for a tilt angle of +5 degrees can be represented by y = 0.008x 2 + 1E-14x - 17.6. It is symmetric with respect to the origin but has vertices with opposite signs and is common with y = 0.003x 2 + 2E-15x + 17.6 and y = 0.001x 2 + 1E-14x - 17.6 and is common with the 22.5-degree incident angle.

[0287] The parabolic function in the x direction for a tilt angle of -5 degrees at an incident angle of 67.5 degrees can be represented by y = 0.07x 2 + 9.2x + 58.4. On the other hand, the parabolic function in the y direction for a tilt angle of +5 degrees can be represented by y = 0.07x 2 - 9.2x + 58.4. It can be represented by y = 2.3x 2 + 95.4x + 940 and y = 2.3x 2 - 95.4x + 940. As shown, it is symmetric with respect to the origin but has vertices with opposite signs and is not common with the 22.5-degree incident angle.

[0288] Figure 15 schematically shows how the selection of a specific incident angle for the optical feedback channel can reduce the magnitude of the beam movement along the y-axis. In the example schematically shown in Figure 15, the magnitude of the y-axis movement can be reduced by approximately half between the 22.5 AOI (the thicker and darker contour in Figure 15) and the 67.5 AOI (shown by the thinner and lighter contour in Figure 15). The curvature can also be seen in the Zemax ray trace spot diagram on the surface of the PSD, as schematically shown in Figure 16. If the AOI is not sufficient to break the rectangle, in other words, if it is not sufficient to shorten the Y-axis scanning length in Figure 15, it may not be possible to spatially separate the input reference beam 400 and the output beam 1116.

[0289] Figure 16 shows an example of a Zemax spot diagram of the reference beam 402 when incident on the detection surface of the PSD160, according to several embodiments of the disclosed technology.

[0290] As shown in Figure 16, different spot positions 1108a to 1108i of the reference beam light 402 are detected during scanning. The detected spot position data is then appropriately communicated or transmitted by the PSD160 to a remote controller of the MEMS mirror position control system so that closed-loop control can be automatically implemented. The remote controller and control system are configured to implement a closed-loop feedback system, although not shown in Figure 16. Spot 1108a can, for example, in some embodiments, represent a mirror tilt of -5 degrees in the x direction and +5 degrees in the y direction around the optical axis z; spot 1108g can represent a mirror tilt of +5 degrees in the x direction and +5 degrees in the y direction; spot 1108c can represent a mirror tilted at -5 degrees in the x direction and -5 degrees in the y direction; and spot 1108i can, in some embodiments, represent a scanning mirror surface 334 tilted at +5 degrees in the x direction and -5 degrees in the y direction around its z-direction optical axis.

[0291] By configuring the scanning mirror assembly 310 to have a closed-loop feedback system using an optical feedback system having the design shown in Figures 11A, 11B, and 11C, which has a suitable AOI for the collimated illumination reference beam from the laser diode light source 502, a very high signal-to-noise ratio can be maintained on the PSD 160. This allows the scanning mirror assembly 310 to be used in OCT systems for surgical microscopes and similar applications that require a very high signal-to-noise ratio to be maintained on the PSD in order to support high scanning speeds.

[0292] Advantageously, the disclosed embodiments of the technology have an optical mirror positioning design that can reduce any source of scattered or stray light in the optical feedback channel and thus provide an improvement over prior art systems.

[0293] In some embodiments of the disclosed technology, the geometric distortion ratio GDR of the scanning mirror, for example, the GDR shown in Figure 6, is set to approximately 2:1. Such a GDR allows the optical feedback channel to be physically offset from the central optical axis of the scanning mirror, which allows undesirable beam reflections from the surface of the PSD160 to be offset equally, but in the opposite direction, from the optical axis, as schematically shown in Figure 11A, for example. This makes it possible to implement back reflection suppression, for example, via an optical trap, instead of direct reflection from the emitter light source for the optical feedback channel.

[0294] Some embodiments of the micro-electromechanical system (MEMS) two-dimensional scanning mirror feedback system 1100 shown in Figures 11A to 11C include a plurality of optical components, such as an emitter or light source 158 for an illumination reference beam 400, such as a laser diode 502; a position detection element (PSD) 160; an optical trap 1112; and a scanning mirror assembly 310 having a reflective surface 334 configured to reflect the incident light beam 400 from the light source 158 toward the position detection element 160 as a reference beam 402. The light source 158, the reflective surface 334, and the PSD detector 160 are configured such that the illumination light beam 400 is incident on the reflective surface (334) in an optical plane offset from the optical center 1116 of the reflective surface 808 of the MEMS mirror assembly 310. The illumination reference beam 400 incident on the reflective surface 334 of the MEMS mirror assembly 310 is in a different optical plane from the optical plane from which the beam 1110 returned, reflected, backscattered, or otherwise returned from the PSD detector 160 is incident on the reflective surface 334 of the MEMS mirror assembly 310. The optical trap 1112 is configured to capture the returned light 1114 from the PSD 160 that has been reflected from the surface 334 of the scanning mirror assembly.

[0295] In the embodiment of the feedback system 1100, the incident angle AOI of the illumination beam 400 incident on the MEMS mirror reflective surface 334 results in a reduction of the angular geometric distortion of the scanning beam profile by a ratio of 2:1, and allows any illumination light 1110 returning from the illumination beam 400 and PSD 160 to be spatially separated in different planes on the MEMS mirror.

[0296] This allows the reference beam to be detected as multiple beams, which can be detected as separate beam spots 1108a~i in the PSD160. The PSD160 is configured to generate beam spot data for multiple different incident beam positions, and this beam spot data is then communicated to the controller of the scanning mirror tilt position.

[0297] In some embodiments, beam spot data is used by the controller to implement closed-loop control of the scanning mirror position, which allows for higher scanning speeds than when open-loop control is implemented instead.

[0298] In some embodiments, the scanning mirror system is an OCT scanning mirror system.

[0299] In some embodiments, the OCT scanning mirror feedback system 1100 is part of a scanning mirror assembly for OCT, including a light source for the OCT scanning beam that is incident on the optical center 1116 of the reflective surface 334 of the scanning mirror assembly 310.

[0300] In some embodiments of the feedback system 1100, the illumination beam 400 incident on the reflective surface of the MEMS mirror lies in a light plane that is offset by an amount equal to the offset of the light plane in which the reflected reference beam 1110 returning from the PSD detector 160 is incident on the reflective surface 334.

[0301] In some embodiments of the feedback system 1100, the geometric distortion ratio of the reflective surface 334 of the scanning mirror assembly 310 is about 2:1.

[0302] In some embodiments of the feedback system 1100, the reflective surface 334 of the OCT scanning mirror assembly 310 is configured such that an incident OCT scanning beam is incident near or at the optical center of the reflective surface 334, while an illumination reference beam 400 used to provide optical feedback to the tilt position of the scanning mirror is incident on the reflective surface 334 in the optical plane that is vertically offset from its optical center. In some embodiments, the reference light beam 400 is also offset from the vertical optical axis 1102 of the reflective surface where the mirror rotates.

[0303] In some embodiments of the feedback system 1100, a dimming filter 506 is positioned between the PSD 160 and the focusing lens 504 of the PSD lens assembly.

[0304] In some embodiments of the feedback system 1100, a low specular reflection light absorbing material is provided along the optical path 1106 traversed by the light beam 1110 that returns from the PSD 160 and travels toward the reflective surface 334 of the scanning mirror assembly.

[0305] In some embodiments of the feedback system 1100, the system further comprises a spatial filter within the emitter optical path.

[0306] In some embodiments, the emitter light source 158 of the feedback system 1100 is a laser diode emitter 502.

[0307] In some embodiments, the emitter light source 158 is positioned vertically above the optical trap 1112.

[0308] In some embodiments, the feedback system 1100 is included in the optical block of the MEMS scanning mirror assembly 310, such as the one shown in Figures 3A, 3B, and 4, which comprises an OCT adapter 206 for the microscope 200, for example, the optical block of the MEMS scanning mirror assembly 310 as shown in Figures 5A and 5B, or in any of the embodiments disclosed herein.

[0309] In some embodiments, the scanning mirror is a high-speed scanning mirror capable of generating B scans at, for example, 400 Hz.

[0310] Figure 17 schematically shows a MEMS-based scanning mirror optical feedback system such as system 1100, which is schematically shown in Figures 11A to 11C.

[0311] In an embodiment of the scanning mirror position optical feedback system 1100 schematically shown in Figure 17 for a microelectromechanical system (MEMS) two-dimensional (2D) scanning mirror assembly 310, the optical feedback system comprises at least the following components, namely, a MEMS 2D scanning mirror assembly 310 including a reflective surface 334 as described above with reference to Figures 3A, 3B, 4, 5A, and 5B of the drawings. The reflective surface 334 is configured to reflect light from two different light sources to two different optical surfaces. A first light source 308a is a source for a primary beam 312, which is used as a scanning beam when it emerges from the scanning mirror assembly and is steered by the inclination of the mirror surface; this is not shown in Figure 17. Other light sources 158,502 are light sources for a secondary light beam 400, which is used to determine the position of the reflective mirror surface using a position detection element (PSD) 160 shown in Figure 17. The PSD160 provides feedback regarding the mirror position to the controller 162, allowing the controller to more accurately update the mirror position as scanning using the primary light source progresses.

[0312] The feedback system can be used in various different use cases to determine the current position of the mirror surface 334 and to control how the mirror position changes during scanning. Thus, in embodiments in which the scanning mirror assembly 310 is used with an OCT adapter such as the OCT scanner adapter 206 shown in Figures 2A to 4, the primary beam 312 reflected by the scanning mirror reflective surface 334 includes an OCT beam 312 generated by the source 112 and input to the scanning mirror assembly 310 via the optical fiber 308a.

[0313] As shown in Figure 17, the secondary light beam 400 is reflected by the reflective surface 334 to form a mirror position reference beam 402. This reference beam 402 propagates toward the position detection element, PSD 160, either directly or via one or more optical focusing elements, through a suitable PSD focusing system including, for example, the PSD lens 504 and / or attenuation filter 506 shown in Figure 5A.

[0314] The PSD160 shown in Figure 17 is configured to detect incident light from the mirror position reference beam 402. The PSD160 has a suitable photodetector 2D surface for detecting light of various wavelengths, configured to generate an optical feedback signal 1704 indicating where the mirror position reference beam 402 is incident on the photodetector 2D surface. The PSD160 is configured to transmit the optical mirror position feedback signal 1704 to the controller 1700 using a suitable data connection.

[0315] In some embodiments, the mirror position feedback signal is an optical analog signal transmitted to the controller along an optical fiber link. The signal can then be digitized in the controller 1700. Alternatively, as will be apparent to those skilled in the art, the analog optical feedback signal may be appropriately digitized in an intermediate analog-to-digital converter system before reaching the controller 1700, or before exiting the detector.

[0316] In some embodiments where the analog signal is generated by the PSD, this is sent to a controller circuit, for example, a controller printed circuit board (PCB) assembly. This circuit may include an operational amplifier and one or more other signal conditioning components, such as a dedicated low-noise analog-to-digital converter. This allows for a better quality signal to be passed to a microcontroller chip for the mirror movement mechanism used to control the movement of the scanning mirror reflective surface 334. While such controller circuits do not fit inside the optical block, in some embodiments they may be stored within the OCT adapter housing 208 and, for example, in some embodiments, may be provided as a printed circuit board 321, as shown in Figure 3B.

[0317] In some embodiments, a microcontroller chip used to implement a closed-loop feedback mechanism receives a signal from the PSD and transmits it along with a position request signal, which may be determined, for example, by scanning configuration parameters, and based on this, transmits a control signal to the mirror movement mechanism 1708.

[0318] For example, in some embodiments, a user may select a scanning pattern using a user interface for an application that configures OCT scanning using the OCT system 100 shown in Figure 1 together with the OCT scanner adapter 206 shown in Figures 2A to 5A above. The OCT system application may generate a location table for each data point scanned in voltage space and transmit the location table to the scanner 206, for example, to a microcontroller chip via a data port 212. In some embodiments, the user interface may be used to configure A scanning characteristics. In some embodiments, the UI may also allow the user to request, in some embodiments, simply "B scanning," etc., or other higher level inputs for scanning. The OCT system application reads from the voltage table stored in memory and sends a control signal to the microcontroller 321, which instructs Miller to direct the OCT probe beam to each individual point in the voltage table.

[0319] By providing closed-loop feedback as shown in Figure 17, which will be described in more detail below, it is possible to position the scanning mirror reflection surface more accurately and quickly so that the OCT probe beam is correctly centered at each scanning position indicated in the voltage table using the mirror movement mechanism 1708.

[0320] Figure 17 schematically illustrates how, in one embodiment of the disclosed technology, an exemplary mirror movement mechanism 1708 is configured to be controlled by a drive signal 1706 from controllers 162, 1700. The drive signal 1706 is generated by controller 1700 in response to information transmitted by a feedback signal 1704. The mirror movement mechanism 1708 is configured to adjust the position of the MEMS mirror reflective surface 334 in at least one dimension, and preferably two dimensions in some embodiments, in response to receiving the drive signal 1706 from controller 1700. In some embodiments, the mirror movement mechanism is part of a MEMS mirror system.

[0321] In some embodiments of the system shown in Figure 17, the position of the MEMS reflective mirror surface 310 is detected by reflecting a reference beam 400 from a collimating light source, such as a laser diode 502, on the reflective mirror surface 334, into the PSD arm 501 of a scanning mirror assembly, which moves toward the PSD 160. The analog optical signal from the PSD 160 is appropriately digitized and supplied to a digital controller 1700 configured to drive the MEMS mirror movement, generating a closed-loop control configuration. The controller 1700 is also configured to receive a control signal 1710, which includes a position command input from an external scanning drive engine, such as the OCT system 100 shown in Figure 1. In some embodiments, the mirror position drive signal 1706 is determined based on the control signal received from the external scanning drive entity and a feedback signal 1704 from the PSD 160.

[0322] In some embodiments, the mirror movement mechanism 1708 is configured to adjust the position of the MEMS mirror reflective surface 334 in at least two dimensions, in other words, a closed-loop feedback system for controlling the two-dimensional tilt of the MEMS-based scanning mirror assembly 310 is provided in some embodiments.

[0323] Depending on the type of detector array that constitutes the detection array on the detection surface of the PSD160, the output of the PSD160 may be an analog or digital signal. However, in some embodiments, the PSD generates an optical analog feedback signal 1704, which is transmitted in analog form and later digitized by controllers 162 and 1700.

[0324] In some embodiments, a light source 158, for example, a laser diode light source 502, is configured to receive a drive signal, for example, a laser driver signal 1702, from a controller 164,1700. The driver signal 1702 is generated by the controller based on information derived from a received feedback signal 1704 and / or a control signal 1710 from an external scanning driver system. In some embodiments, the driver signal may be configured to turn the laser on / off and to control the laser diode power so as not to saturate the PSD. In some embodiments, the controllers 164,1700 are external components located outside the optical block forming the scanning mirror assembly 310 but within the scanning device, for example, within the OCT adapter 206. Alternatively, in some embodiments, the controller 1700 may be located within a different system, for example, on the same device that hosts other interferometer components of the SD-OCT system 100 shown in Figure 1, and / or as part of the device that hosts the image processing system 148. Data from the PSD160 may be transmitted using a data connection via wireless or wired connection that provides a suitable data transmission rate for supporting these, enabling the controller to generate and send back control signals to move the scanning mirror 112 based on the received information. The received scanning mirror position data and control signals 1710 may be transmitted along the same or different physical links. In some embodiments, for example, the data connection is via optical fiber or other high-speed data wired connection connected to the data communication port 212 shown in Figure 2B. It may also be possible to transfer data to the scanning drive system using one or more other types of high-speed data connections.

[0325] The maximum scanning speed of the mirror is at least in part based on the rate at which the controller receives data from the PSD160. It is possible to achieve a 2D scanning speed of scans including multiple a scans stacked to form b scans exceeding 400 Hz, in other words, in some embodiments, a closed-loop feedback system 1700 can be used to achieve more than 400 B scans per second. Achieving such high scanning speeds is possible in some embodiments due to the high signal-to-noise ratio of the light detected by the PSD160, which is a result of the separation of the optical plane of the exit reference beam 402 when it is reflected by the scanning mirror reflective surface and the optical plane to which the beam, after detection by the PSD160, is reflected by the scanning mirror reflective surface 334.

[0326] In some embodiments of the feedback system 1100, the system includes a controller 1700. The controller 1700 generates drive signals (1702, 1706) for the light source (1702) and the mirror movement mechanism (1708), respectively, in response to a scanning position drive signal 1710 from the scanning driver. This allows the controller to position the scanning mirror reflective surface 334 in two dimensions using closed-loop control in some embodiments of the feedback system 1100.

[0327] In some exemplary embodiments, the scanning mirror system comprises an optical feedback mechanism 1110 for a MEMS scanning mirror assembly 310, wherein the MEMS scanning mirror assembly has a reflective surface configured to reflect light from two different light sources, the two different light sources comprising: a primary light source including a light source for a primary beam that forms a scanning beam after reflection by the reflective surface; and a secondary light source including a light source for a secondary light beam that forms a mirror position reference beam after reflection by the reflective surface; a position detection element (PSD) configured to detect incident light of the mirror position reference beam, and configured to generate a mirror position feedback signal indicating where the mirror position reference beam enters the position detection element; and a mirror movement mechanism configured to be controlled by a drive signal derived from the mirror position feedback signal in order to adjust the position of the MEMS mirror reflective surface and control the direction of the scanning beam.

[0328] The scanning mirror reflects the emitted mirror positioning light with an optical plane different from any returned mirror positioning light, and reflects the light from the scanning light source with another optical plane. In some embodiments, the primary light beam may comprise an OCT scanning or probe beam, and the primary light source may be a source in the scanning mirror assembly, such as the end of an optical fiber, configured to supply OCT scanning light to the MEMS scanning mirror assembly from a remote light source, such as light source 112 shown in Figure 1.

[0329] In some embodiments, the scanning mirror system further includes controllers 162,1700 configured to generate drive signals for controlling the position of the reflective surface 334 of the MEMS scanning mirror assembly 310 in response to a beam direction input signal and a mirror position feedback signal derived with respect to the position of the reflective surface 334. The PSD 160 is configured to transmit a mirror position feedback signal indicating the position of the scanning mirror reference beam on its detection surface to the controllers 162,1700 in response to detection of the scanning mirror reference beam on its detection surface. The controllers 162,1700 use this feedback signal to generate drive signals for controlling the mirror movement mechanism of the scanning mirror. The drive signals from the controllers cause the mirror movement mechanism to adjust the position of the MEMS mirror reflective surface 334 to move the scanning beam according to a set of scanning parameters.

[0330] The beam direction input signal can be implemented by suitable applications for configuring a scan, which can also use user input parameters to configure the OCT scan. For example, the user can define the area to be scanned in a series of B scans, or the area to achieve a specific resolution.

[0331] In some embodiments, the system further includes a housing 208 having a primary beam inlet 214 for the primary beam, which also acts as a primary beam outlet for the return scanning beam. The scanning mirror assembly and mirror moving mechanism are located within the housing 208. Within the housing 208, the scanning mirror assembly and mirror moving mechanism may be housed in an optical block, such as the optical block 310 shown in Figure 3A, in some embodiments.

[0332] In some embodiments, the mirror movement mechanism is configured to adjust the tilt position of the MEMS mirror reflective surface in at least two dimensions.

[0333] The mirror position feedback signal may be a digitized signal based on an analog signal generated by the PSD. The mirror position feedback signal may be digitized by the PSD, a controller, or another device configured to perform analog-to-digital signal conversion on the analog signal received from the PSD, and output the resulting digitized signal to the controller as the mirror position feedback signal.

[0334] In some embodiments, the secondary light source is also configured to receive a drive signal from a controller, which is generated by the controller based on information derived from the received feedback signal. For example, in some embodiments, the drive signal from the controller may control the power output of the secondary light source and / or turn it on and off.

[0335] In some embodiments, the feedback system may also include controllers 162, 1700, although the controllers may be remotely located in some embodiments. In other words, in some embodiments, a scanning mirror system for supplying optical feedback using a mirror position system such as the feedback system 1100 shown in Figures 11A to 11C may comprise a MEMS scanning mirror assembly 310, the MEMS scanning mirror assembly comprising two different light sources, namely one light source 308a which is a light source for a primary beam 312 that forms a scanning beam or probe beam after reflection by a reflective surface, and another light source 158, 502 which is a light source for a secondary light beam 400 that forms a mirror position reference beam 402 after reflection by a reflective surface 334, and a position detection element (PSD) 160 such as a PSD assembly which includes a reflective surface 334 configured to reflect light from and a light-reducing filter and / or a focusing lens that focuses the light onto the detection surface of the PSD 160. The PSD160 assembly is configured to detect incident light from the mirror position reference beam 402, and in response, a feedback signal 1704 is generated indicating where the mirror position reference beam 402 is incident on the position detection element 160, and is transmitted to the controllers 162,1700. The system also includes controllers 164,1700 configured to generate a drive signal 1706 in response to the reception of a beam direction input signal and a feedback signal from the PSD160. The system also includes a mirror moving mechanism, shown as 1708 in Figure 17, which in some embodiments may be part of a MEMS support 500, also shown in Figure 5A. The mirror moving part 1708 is controlled by the drive signal 1706 to adjust the position of the MEMS mirror reflective surface 334 and control the direction of the probe beam. In some embodiments, the controllers 164,1700 are configured to generate respective drive signals for the light source and the mirror moving mechanism to position the scanning mirror reflective surface in two dimensions using a closed-loop control scheme shown in Figure 17, in response to receiving a drive signal from the scanning driver.In some embodiments, the controller is configured to control the horizontal and vertical tilt positions of the reflective surfaces of the scanning mirror assembly. In some embodiments, the controller is configured to implement closed-loop control of the position of the scanning mirror reflective surfaces using mirror position feedback signals.

[0336] In some embodiments, the secondary light source incidence point to the scanning mirror assembly, the scanning mirror reflective surface, and the PSD are configured such that the secondary light beam is incident on the reflective surface either at the optical center of the reflective surface or in an optical plane slightly offset from the optical center of the reflective surface. The optical plane of the reflection of the scanning light, for example, in some embodiments the OCT scanning light, is different from the optical plane on which the mirror position reference light beam 402 is incident outward on the reflective surface 334, and also different from the optical plane on which the return reference beam reflected from the PSD is incident on the reflective surface.

[0337] In some embodiments, the incident angle of the secondary beam incident on the MEMS mirror reflective surface may be less than 67.5 degrees with respect to the mirror's surface plane. This can reduce the angular geometric distortion of the scanning beam profile by a ratio of 2:1.

[0338] In some embodiments, the reference beam may be detected by the PSD as multiple beams, and these multiple beams may be individually detectable as separate beam spots in the PSD. In some embodiments, beam spot data generated by the PSD when it detects the beam spot position of the incident mirror-positioned reference beam is communicated by the PSD to the controller.

[0339] In some embodiments of the scanning mirror system, beam spot data generated by the PSD when the PSD detects the beam spot position of the incident reference beam is communicated by the PSD to a controller, which is configured to control the horizontal and vertical inclination positions of the reflective surface 334 of the scanning mirror assembly.

[0340] In some embodiments, the scanning mirror assembly is part of the OCT scanner system, and the primary beam is the OCT scanning beam.

[0341] In some embodiments, the mirror position reference beam is focused by a PSD imaging lens before it is detected by the PSD.

[0342] In some embodiments, the scanning mirror system further comprises a light-reducing filter positioned between the PSD imaging lens and the PSD.

[0343] In some embodiments, the scanning mirror system further comprises a low specular reflectance absorbing material along the optical path followed by a portion of the scanning mirror reference beam that is returned toward the scanning mirror reflective surface.

[0344] In some embodiments, the scanning mirror system further includes a spatial filter in the optical path of the secondary beam traveling from the secondary light source to the reflective mirror surface.

[0345] In some embodiments, the light source for the secondary beam is located vertically above the light trap, and the light trap is configured to capture light from a portion of the mirror position reference returned from the PSD, which is reflected back toward the secondary light source via the MEMS mirror surface 334.

[0346] In some embodiments, the scanning mirror system 1100 includes an optical block such as the optical block 310 described above, as shown in Figure 3A.

[0347] In some embodiments, the scanning mirror system 1100 includes a MEMS scanning mirror assembly within an OCT adapter for a surgical microscope, where the primary light source is an OCT light source that, after reflection, forms an OCT scanning mirror for scanning a tissue area or specimen that can also be viewed through the surgical microscope.

[0348] In some embodiments, the scanning mirror assembly comprises an optical block configured to act as a MEMS scanning mirror assembly within an OCT adapter for a surgical microscope. The terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. Where used herein, the singular forms “a,” “an,” and “the” are intended to include the plural form unless the context explicitly indicates otherwise. Where used herein, the term “and / or” includes any and all combinations of one or more of the enumerated items relating to the disclosure. The terms “comprises,” “comprising,” “includes,” and / or “including,” where used herein, specify the presence of the described features, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.

[0349] The terms "first," "second," etc., may be used herein to describe various elements, but it will be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, without departing from the scope of this disclosure, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element.

[0350] Relative terms such as "below," "above," "upper," "lower," "horizontal," and "vertical" may be used herein to describe the relationship between one element and another, as shown in the figure. It will be understood that these terms, and the terms described above, encompass different orientations of the device in addition to the orientation shown in the figure. When one component is referred to as being "connected" or "bonded" to another component, it should be understood that it may be directly connected to or bonded to the other component, but there may also be other components in between. In contrast, when one element is said to be "directly connected" or "directly bonded" to another element, there are no intervening elements.

[0351] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as those generally understood by those skilled in the art to which this disclosure belongs. Terms used herein should be construed to have meanings consistent with those in the context of this specification and related art, and it will be further understood that they should not be construed in an idealized or overly formal sense unless expressly defined herein.

[0352] As used herein, the term "and / or" includes all possible combinations of one or more of the items listed herein and may be abbreviated as " / ".

[0353] While several embodiments have been described in the context of the apparatus, it is clear that these embodiments also represent descriptions of the corresponding methods, where blocks or apparatus correspond to steps or features of steps. Similarly, embodiments described in the context of steps also represent descriptions of the corresponding blocks, items, or features of the corresponding apparatus.

[0354] This disclosure is not limited to the embodiments described above and illustrated in the drawings, and it should be understood that those skilled in the art will recognize that many changes and modifications can be made within the scope of this disclosure and the attached claims. The embodiments disclosed in the drawings and specification are illustrative and not restrictive, and the scope of the concept of the invention is set out in the following claims.

Claims

1. A scanning mirror system (1100), wherein the scanning mirror system (1100) is A MEMS scanning mirror assembly (310) comprising a reflective surface (334) configured to reflect light from two different light sources (308a, 158, 502), wherein the two different light sources (308a, 158, 502) are A primary light source (308a) including a light source for a primary beam (312) that forms a scanning beam after reflection by the reflective surface (334), A secondary light source (158, 502) including a light source for a secondary light beam (400) that forms a mirror position reference beam (402) after reflection by the reflective surface (334), and A MEMS scanning mirror assembly (310) includes a position detection element (PSD) (160) configured to detect incident light of the mirror position reference beam (402), and the PSD (160) is configured to generate a mirror position feedback signal (1704) indicating the location where the mirror position reference beam (402) is incident on the position detection element (160), A mirror moving mechanism (1708) is configured to be controlled by a drive signal (1706) derived from the mirror position feedback signal (1704) in order to adjust the position of the MEMS mirror reflective surface (334) and control the direction of the scanning beam, A scanning mirror system (1100) including the above.

2. The system further includes controllers (162, 1700) configured to generate the drive signal (1706) for controlling the position of the reflective surface (334) of the MEMS scanning mirror assembly (310) in response to a beam direction input signal and the mirror position feedback signal (1704) derived with respect to the position of the reflective surface (334), The PSD (160) is configured to transmit the mirror position feedback signal (1704) to the controller (164, 1700). The scanning mirror system (1100) according to claim 1, wherein the mirror moving mechanism (1708) is configured to be controlled by a drive signal (1706) from the controller (164, 1700) in order to adjust the position of the MEMS mirror reflective surface (334) and control the direction of the scanning beam.

3. The aforementioned system (1100) The housing further includes a primary beam inlet for the primary beam, which also acts as a primary beam outlet for the return scanning beam (312), The scanning mirror system (1100) according to claim 1, wherein the scanning mirror assembly (310) and the mirror moving mechanism (1708) are located within the housing.

4. The scanning mirror system (1100) according to claim 1, wherein the mirror moving mechanism (1708) is configured to adjust the inclination position of the MEMS mirror reflective surface (334) in at least two dimensions.

5. The scanning mirror system (1100) according to claim 1 or 2, wherein the mirror position feedback signal (1704) is a digitized signal based on the analog signal generated by the PSD (160).

6. The scanning mirror system (1100) according to any one of claims 1 to 5, wherein the secondary light source (158, 502) is also configured to receive a drive signal (1702) from the controller (1700), the drive signal (1702) being generated by the controller based on information derived from the received feedback signal (1704).

7. The system further includes the controllers (164, 1700), Scanning mirror system (1100) according to any one of claims 1 to 6, wherein the controller is configured to generate drive signals (1702, 1706) for the light source (1702) and the mirror moving mechanism (1708), respectively, in response to a drive signal (1710) from a scanning driver, for positioning the scanning mirror reflective surface (334) in two dimensions using closed-loop control.

8. The scanning mirror system (1100) according to any one of claims 1 to 7, wherein the incident angle of the secondary beam (400) incident on the MEMS mirror reflective surface (334) is less than 67.5 degrees with respect to the normal to the surface plane of the mirror.

9. The reference beam (402) is detected as multiple beams by the PSD (160), The scanning mirror system (1100) according to any one of claims 1 to 8, wherein the plurality of beams can be individually detected as separate beam spots (1108a to 1108i) in the PSD (160).

10. The scanning mirror system (1100) according to claim 4, wherein the controller (162, 1700) is configured to implement closed-loop control of the position of the scanning mirror reflective surface (334) using the mirror position feedback signal (1704).

11. The scanning mirror assembly (310) is part of an OCT scanner system (206), and the primary beam is an OCT scanning beam, according to any one of claims 1 to 10, the scanning mirror system (1100).

12. The scanning mirror system (1100) according to any one of claims 1 to 11, wherein the mirror position reference beam (402) is focused by a PSD imaging lens (504) before being detected by the PSD (160).

13. The scanning mirror system (1100) according to claim 12, further comprising a light-reducing filter (506) located between the PSD imaging lens (504) and the PSD (160).

14. The scanning mirror system (1100) further includes a low specular reflectance light absorbing material along the optical path (1106) followed by a portion of the scanning mirror reference beam (1100) that is returned toward the scanning mirror reflective surface (334).

15. A scanning mirror system (1100), The scanning mirror system (1100) is A housing having a primary beam inlet and a primary beam outlet, A MEMS scanning mirror assembly (310) located within the housing, comprising two different light sources, namely, A light source (308a) is a source for the primary beam (312) that forms a scanning beam that passes through the primary beam exit after reflection by the reflective surface and is received through the primary beam inlet, and A MEMS scanning mirror assembly (310) includes a reflective surface (334) configured to reflect light from another light source (158, 502) which is a light source for a secondary light beam (400) that forms a mirror position reference beam (402) after reflection by the reflective surface (334), A position detection element (PSD) (160) configured to detect incident light of the mirror position reference beam (402), wherein the PSD (160) is configured to generate a feedback signal (1704) indicating the location where the mirror position reference beam (402) is incident on the position detection element (160), and to transmit the feedback signal (1704) to a controller (1700), A mirror moving mechanism (1708) configured to be controlled by a drive signal (1706), wherein the drive signal (1706) includes the mirror moving mechanism (1708) received from the controller (1700), The scanning mirror system (1100) is configured such that the mirror movement mechanism (1708) adjusts the position of the MEMS mirror reflective surface (334) in response to the drive signal (1706) to control the direction of the probe beam.

16. A scanning mirror system (1100), wherein the scanning mirror system (1100) is A MEMS scanning mirror assembly (310) comprising two different light sources, namely, One light source (308a) is a source for the primary beam (312) that forms the probe beam after reflection by the reflective surface, and A MEMS scanning mirror assembly (310) includes a reflective surface (334) configured to reflect light from another light source (158, 502) which is a light source for a secondary light beam (400) that forms a mirror position reference beam (402) after reflection by the reflective surface (334), A position detection element (PSD) (160) configured to detect incident light of the mirror position reference beam (402), wherein the PSD (160) is configured to generate a feedback signal (1704) indicating the location where the mirror position reference beam (402) is incident on the position detection element (160), and to transmit the feedback signal (1704) to a controller (1700), A controller configured to generate a drive signal in response to a beam direction input signal and the feedback signal, A scanning mirror system (1100) including a mirror moving mechanism (1708) configured to be controlled by a drive signal (1706) from the controller (1700) in order to adjust the position of the MEMS mirror reflective surface (334) and control the direction of the probe beam.

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