Optical measurement device, system and method

Abstract

An optical measurement device, system and method. The optical measurement device comprises: a beam splitter comprising a first reflective portion and an adjacent first transmissive portion distinct from the first reflective portion; and a beam combiner disposed spaced apart from the beam splitter, the beam combiner comprising a second reflective portion and an adjacent second transmissive portion distinct from the second reflective portion, wherein the first transmissive portion and the second transmissive portion define a transmission path, and the first reflective portion and the second reflective portion define a reflection path; wherein responsive to directing a beam to the transmission path, the beam focuses on a first focal point on a target object, and wherein responsive to directing the beam to the reflection path, the beam focuses on a second focal point on the target object.

Description

OPTICAL MEASUREMENT DEVICE, SYSTEM AND METHODCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202402214T filed 25 July, 2024, the contents of which are hereby incorporated by reference in their entirety for all purposes.TECHNICAL FIELD

[0002] This application relates generally to the field of ophthalmology, and more particularly, to an optical measurement device and an optical measurement system.BACKGROUND

[0003] Optical coherence tomography (OCT) is an in vivo optical imaging technology that provides micrometer resolution and millimeter penetration depth in human tissues. Conventionally, OCT has been established as a clinical diagnostic tool for various applications such as imaging the eye, coronary arteries, digestive tracts, pulmonary airways and many other organ systems, with ophthalmology being one of the dominant OCT applications.

[0004] Fourier-domain OCT (FD-OCT), which includes spectral domain OCT (SD-OCT) and swept source OCT (SS-OCT) (otherwise known as optical frequency domain imaging (OFDI)), is a frequency-based OCT technology commonly used for ophthalmology. In conventional FD-OCT, the ranging depth of OCT, which is primarily determined by spectral resolution, remains a limitation in both SD-OCT and SS-OCT. In SD-OCT, the ranging depth of most devices are less than 16 mm, which is insufficient for imaging the whole eye (~40 mm in air from cornea to retina). In SS-OCT, the ranging depth which is the maximum optical path delay difference that can be measured, is primarily determined by the sampling rate of thedigitizer. However, a digitizer suitable for a typical ophthalmic biometer for measuring an axial length of > 40 mm (in air), is extremely costly.SUMMARY

[0005] According to an aspect, disclosed herein an optical measurement device. The optical measurement device comprises: a beam splitter comprising a first reflective portion and an adj acent first transmissive portion distinct from the first reflective portion; and a beam combiner disposed spaced apart from the beam splitter, the beam combiner comprising a second reflective portion and an adjacent second transmissive portion distinct from the second reflective portion, wherein the first transmissive portion and the second transmissive portion define a transmission path, and the first reflective portion and the second reflective portion define a reflection path; wherein responsive to directing a beam to the transmission path, the beam focuses on a first focal point on a target object, and wherein responsive to directing the beam to the reflection path, the beam focuses on a second focal point on the target object.

[0006] According to another aspect, disclosed herein an optical measurement system, comprising the device as described above; and a controller in signal communication with a beam director, the controller being configured to control a position of the beam director. In various embodiments, the system is an optical biometer.

[0007] According to yet another aspect, disclosed herein a method of optical measurement. The method comprises: directing a beam to a transmission path to focus the beam on a first focal point on a target object, the transmission path being defined by a first transmissive portion of a beam splitter and a second transmissive portion of a beam combiner; and directing the beam to a reflection path to focus the beam on a second focal point on the target object, the reflection path being defined by a first reflective portion of the beam splitter and a second reflective portion of the beam combiner, wherein the beam splitter is disposed spaced apartfrom the beam combiner, wherein the first reflective portion is adjacent to and distinct from the first transmissive portion, and the second reflective portion is adjacent to and distinct from the second transmissive portionBRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various embodiments of the present disclosure are described below with reference to the following drawings:

[0009] FIG. 1 is a schematic diagram of an optical measurement system according to embodiments of the present disclosure;

[0010] FIG. 2 is an exemplary axial profde of the eye obtained from the optical measurement system of FIG 1 ;

[0011] FIG. 3 is a schematic diagram of an optical measurement device according to embodiments of the present disclosure;

[0012] FIG. 4 is a sectional view of an eye of a subject;

[0013] FIG. 5 is a perspective view of an optical measurement device according to embodiments of the present disclosure;

[0014] FIG. 6 is another perspective view of the optical measurement device of FIG. 5;

[0015] FIG. 7 is a perspective view of an optical measurement device according to embodiments of the present disclosure;

[0016] FIG. 8 is a perspective view of an optical measurement device according to embodiments of the present disclosure;

[0017] FIG. 9 is a perspective view of an optical measurement device according to embodiments of the present disclosure;

[0018] FIGs. 10A and 10B are front view of a beam splitter and a beam combiner according to embodiments of the present disclosure;

[0019] FIGs. 10C and 10D are front view of a beam splitter and a beam combiner according to embodiments of the present disclosure;

[0020] FIG. 11 is a flowchart illustrating a method of optical measurement according to embodiments of the present disclosure;

[0021] FIGs. 12A and 12B are schematic diagrams of an optical measurement system according to an exemplary implementation;

[0022] FIGs. 13 A and 13B are schematic diagrams of an optical measurement system according to another exemplary implementation;

[0023] FIGs. 14A and 14B are schematic diagrams of an optical measurement system according to yet another exemplary implementation;

[0024] FIGs 15A and 15B show an exemplary beam splitter and an exemplary beam combiner;

[0025] FIGs. 16A and 16B show another exemplary beam splitter and another exemplary beam combiner;

[0026] FIGs. 17A and 17B are schematic diagrams of an optical measurement system configured as a biometer according to an exemplary implementation;

[0027] FIG. 18 is a schematic diagram of an exemplary beam splitter and beam combiner according to an exemplary implementation;

[0028] FIG. 19A illustrates a reflection path / mode before combiner angle adjustment;

[0029] FIG. 19B illustrates a reflection path / mode after combiner angle adjustment;

[0030] FIGs 20A and 20B illustrate a Zemax simulation of a sample arm beam of a Tomographic deconvolution phase microscopy (TDPM), with FIG. 20A illustrating a transmission mode / path for posterior segment imaging, and FIG 20B illustrating a reflection mode / path for anterior segment imaging;

[0031] FIG. 21 A shows a sectional view of an OEMI-7 eye model;

[0032] FIG. 21B shows cross-sectional images (top) and corresponding depth profile (bottom) of the anterior segment (left) and posterior segment (right), respectively. CCT: central corneal thickness, ACD: anterior chamber depth, LT: lens thickness, AL: axial length, OPD: optical path-length difference between transmission mode (posterior segment imaging) and reflection mode (anterior segment imaging). LI: optical distance of cornea anterior boundary away from DC, L2: optical distance of retina surface from DC;

[0033] FIG. 22A shows an exemplary cross-sectional image, with R: reflection mode; T: transmission mode;

[0034] FIG. 22B shows the depth profiles of optical signal from anterior segment images for ocular biometry; and

[0035] FIG. 22C shows the depth profiles of optical signal from posterior segment images for ocular biometry.DETAILED DESCRIPTION

[0036] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0037] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0038] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0039] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0040] As used herein, terms “concurrently”, “simultaneously”, “at the same time”, or the like, may refer to events or actions that coincide or overlap within a period of time, regardless of whether the events start at the same time instant, and regardless of whether the events end at the same time instant.

[0041] As used herein, the term “optical axis of an eye” may generally be defined as an axis corresponding to a theoretical line extending from an anterior to a posterior pole of the eye, passing through the centers of curvature of the cornea and lens. The “optical axis of an eye” as used herein may correspond to and / or is co-axial to a ranging depth of the optical measurement system.

[0042] The term “distinct” may be used interchangeably with the terms “non-overlapping”, “specific”, “defined”, “definite”, etc as it may be understood from the context. The term “distinct portions” or “distinct regions” may generally refer to two or more defined portions / regions which are non-overlapping. As an example, a common border between two distinct regions may be demarcated by or defined with an edge or a line / curve.

[0043] The term “reflective portion” may be used interchangeably with the terms “reflective region”, “mirror portion”, “mirror region”, and may generally be defined as a substantially reflective surface or reflective bulk material for reflecting an incident beam, such as an optical beam. It may be appreciated that under certain conditions, the incident beam may be substantially reflected (but not fully reflected) by the reflective surface. For instance, a majority portion of the incident beam may be reflected by the reflective portion with a minority portion of the incident beam absorbed. In an example, the reflection surface may be a mirror surface.

[0044] The term “transmissive portion” may be used interchangeably with the terms “transmissive region”, “transmissive volume”, “transmissive zone”, and may generally bedefined as a substantially transmissive volume, surface or bulk material for transmitting an incident beam, such as an optical beam. It may be appreciated that under certain conditions, the incident beam may be substantially transmitted (but not fully transmitted) through the transmissive surface. For instance, a majority portion of the incident beam may pass through the transmissive portion with a minority portion of the incident beam absorbed or reflected. In avoidance of doubt, as an example, the transmissive portion may include an air volume in which the incident beam passes through.

[0045] Myopia screening, monitoring, and correction is a rapidly growing market. Ophthalmic biometer is the standard-of-care device for prediction, screening and monitoring the myopia progression. In particular, the axial length is the primary parameter used in eye clinic and optometry for this purpose. However, there is a need for low-cost ophthalmic biometers that is suitable for screening large populations in primary care or community settings, such as primary / secondary schools, community, and glass shops.

[0046] In ophthalmic biometry, spectral resolution is one of the primary factors determining the ranging depth for conventional Fourier-domain OCT (FD-OCT), such as spectral domain OCT (SD-OCT) and swept source OCT (SS-OCT). However, improving spectral resolution is often costly and at times infeasible. For SD-OCT, the ranging depth of conventional devices are often limited to around 16 millimetres (mm), which is insufficient for imaging a whole eye of a subject (~40 mm in air from cornea to retina). For SS-OCT, the ranging depth, which is the maximum optical path delay difference that can be measured, is primarily determined by the sampling rate of the digitizer. For example, the digitizer suitable for measuring the ranging depth (axial length) of at least 40 mm (in air) may cost a third of a conventional ophthalmic biometer This is on top of other component costs such as high-speed photodetector, high throughput electronics, and corresponding data processing capacity that are directly related with the sampling rate.

[0047] The present disclosure proposes an optical measurement device and an optical measurement system which addresses the limitations as described above. The optical measurement system may be a FD-OCT system for ophthalmology or more specifically, for ophthalmic biometry. The proposed optical measurement device and optical measurement system depart from the need for high-speed digitizer, high throughput electronics, and data processing solution. In addition, the proposed optical measurement system and device enable SD-OCT based technology to be deployed or implemented for biometer. This is not viable for conventional SD-OCT due to the limited ranging depth.

[0048] Departing from conventional approaches, the proposed optical measurement system for OCT imaging may include a sample arm configured with a dual beam arrangement. The dual beam configuration enables partial imaging of the eye in a sequential manner. The dual beam configuration may sequentially and independently target or image a first segment (such as an anterior segment which includes the cornea) of the eye and a second segment (such as a posterior segment which includes the retina) of the eye. In various embodiments, the dual beam configuration may image the anterior segment and the posterior segment of the eye in a nontime-overlapping manner. In other words, the imaging of the anterior segment and the posterior segment are performed separately and non-concurrently.

[0049] The dual beam configuration bypasses the imaging of the vitreous body of the eye, which is anatomically located between the anterior segment and posterior segment but is typically not useful in ophthalmic biometry. Bypassing the vitreous body, which represents a major segment along the whole eye length, alleviates or at least mitigates the limitation of ranging depth during FD-OCT imaging.

[0050] In various implementations, the two beams may be focused on the cornea and the retina of the eye. In various embodiments, the imaging of the anterior segment and the posterior segment (or retinal images) may be pathlength encoded. The pathlength differences between asample beam through the sample arm and a reference beam through a reference arm may be independently adjusted such that the vitreous body part may be ‘omitted’ from the depth measurements / images.

[0051] Despite the provision of the dual beam arrangement, a ranging depth of approximately 20 millimeters (mm) or more may still be required, which is inclusive of the length of anterior segment and posterior segment, and accounting for subject eye motion(s). This results in the optical measurement system requiring a relatively long ranging depth and costly digitizer (1.8 G Samples / s).

[0052] For instances where the ranging depth of the optical measurement system is too short, the images of the anterior segment and the posterior segment may overlap resulting in an increased difficulty in differentiating the respective segments One reason is due to the significant variation in eye length among subjects, while the path-length difference between the focal points of the anterior segment and the posterior segment is limited (and often fixed) upon completion of device adjustment / alignment.

[0053] The proposed optical measurement system further addresses the limitations of ranging depth of the dual beam configuration. The proposed optical measurement system may comprise a beam splitter which is configured to direct an incident sample beam to and be switched between two beam paths or two beams, with a short or near instantaneous transit time between the two beam paths. As a novel approach towards short transit time, the beam splitter is provided with a reflective edge (mirror edge), which acts as a separator between a reflective portion / region and a transmissive portion / region, for switching between the two paths. Moving the beam across the reflective edge reduces the transit time to the level of microseconds which is more than 2 orders of magnitude smaller than conventional galvo scanners. Further, this enables the measurement error caused by eye motion or motion artifact(s) to be effectivelyreduced or even eliminated. In addition, the proposed optical measurement system is also able to reduce the duration and light exposure to the retina.

[0054] In addition, the proposed optical measurement system may also comprise a beam combiner which is configured to combine the two beams by wavefront, i.e. one beam is focused at a transmissive portion / region of the beam combiner and another beam is collimated at the reflective portion / region of the beam combiner. This allows the two beams to be directed independently and focused at different segments of the eye. Due to the non-interfering or minimal interfering nature of the two beams, minimal optical power loss for both beams may be achieved, such that the signal -to-noise ratio (SNR) may be significantly higher (up to 4 times greater) than conventional devices. This may also aid in reducing the cost of the light source and improving the signal strength.

[0055] FIG. 1 illustrates an optical measurement system 50 or FD-OCT system according to various embodiments of the disclosure. The optical measurement system 50 may be an optical biometer. The optical measurement system 50 comprises a beam source 210; an optical splitter 220; a photodetector; a sample arm 100 and a reference arm 300. The beam source 210 may be a light source such as a laser source providing a laser optical beam. The beam source 210 may provide a source beam 70 or an optical beam to an optical splitter 220. The optical splitter 220 may split or divide the source beam 70 into a reference beam 72 (reference light radiation) and a sample beam 90 (sample light radiation). In various embodiments, the optical splitter 220 may split the source beam 70 into the reference beam 72 and the sample beam 90 with substantially equal intensity.

[0056] In various embodiments, the sample beam 90 (sample light radiation) may be directed or guided by the sample arm 100 towards an eye 80 (or a tissue sample) of a subject along an optical axis 86. In various embodiments, the sample arm 100 may include a beam scanner or beam director, such as a galvometer scanner, and various optical modules, such asfocusing optics. A reflected sample beam 91 (reflected / backscattered light radiation) may be formed / generated through the interaction between the sample beam 90 and the different depth levels of the eye 80 along the optical axis 86 of the eye 80. The reflected sample beam 91 may be directed / guided by the sample arm 100 towards the optical splitter 220 in a direction opposite to the sample beam 90.

[0057] Similarly, the reference beam 72 may be directed / guided through the reference arm 300 and may be reflected by a reference reflector disposed in the reference arm 300 to form a reflected reference beam 73 (reflected reference light radiations) directed towards the optical splitter 220. The reflected reference beam 73 reflected by the reference arm 300 and the reflected sample beam 91 from the sample arm 100 may be recombined through the optical splitter 220 (or a separator beam splitter in the configuration of Mach Zehnder interferometer), to be guided to a photodetector 235. A spectral interference signal 75 corresponding to the reflected reference beam 73 and the reflected sample beam 91 may be received and recorded by the photodetector 235. The photodetector 235 may thereafter provide a photo signal 77 based on the spectral interference signal 75 to a processor 240 for processing, to obtain an axial profile 79 or axial image of the eye 80. F1G.2 illustrates an exemplary axial profile 79 of the eye 80.

[0058] In various embodiments, the axial line profile (A-line) may be retrieved by Fourier transform of the spectral interference signal. A two-dimensional (2D) cross-sectional amplitude frame, An(x,z), may be obtained by transversely scanning the sample light along the fast axis (X) radiation using the beam scanner (SC) while continuously acquiring axial (z) line profiles (A-lines). A three-dimensional (3D) image may be obtained by transversely scanning the sample light using 2-axis (fast axis x and slow axis y) scanners. If the light beam is positioned at a given y position over a sample, the amplitude frame may be given by:An(x,z)=DFT[2 (Rr Rs(z))*S(k)cos(2kAp)] (1)where n is amplitude frame sequence number along the slow axis (Y), k is the free-space wave number, DFT is discrete Fourier transform with respect to 2k, z is the geometrical distance, and Rrand Rsrepresent the reference reflectivity and sample reflectivity at depth z, respectively, S(k) is the source power spectral density, and Ap is the optical path delay difference between the reference and sample beams.

[0059] Ranging depth is the maximum depth in air in an OCT or biometer that may be measured. The ranging depth of OCT may be determined by the following equation:Az=l / 4 *(XA2) / (5k) (2) where is the center wavelength and 5 is the spectral resolution. While the center wavelength may be fixed for a given type of biometer, the spectral resolution is the primary factor that determines the ranging depth.

[0060] FIGs. 3 and 4 illustrate the structure and operation of an optical measurement device 100 or an optical measurement module according to various embodiments of the disclosure. The optical measurement device 100 may be configured as a sample arm of a FD-OCT system. The optical measurement device 100 may be a part of an optical measurement system 50 used for measuring an eye 80 of a subject. The optical measurement device 100 may be a sample arm 100 of the optical measurement system 50. The optical measurement device 100 may be configured to directly or indirectly receive a beam (such as an incident optical beam) from a beam source 210 of the optical measurement system 50. The optical measurement device 100 may define an axial axis 102. The axial axis 102 may be substantially parallel to an optical axis 86 of the eye 80.

[0061] In various embodiments, the optical measurement device 100 may be a modular device configured to work with various optical measurement systems. The optical measurement device 100 may be a replacement device for an existing conventional sample arm of an optical measurement system. The optical measurement device 100 may be interchangeable betweenvarious optical measurement systems. The optical measurement device 100 may be detachable and re-attachable to another optical measurement system.

[0062] According to various embodiments, the optical measurement device 100 may comprise a beam director 110; a beam splitter 120 disposed spaced apart from the beam director 110; a beam combiner 130 disposed spaced apart from the beam splitter 120; and a beam reflector 140. In various embodiments, the beam combiner 130 may be disposed spaced apart from the beam splitter 120 along the axial axis 102. In various embodiments, the beam reflector 140 may be disposed spaced apart from the beam splitter 120 and the beam combiner 130 along a transverse axis 104.

[0063] According to various embodiments, the beam director 110 (or a galvometer scanner) may comprise a reflective surface for directing a sample beam or a beam 90 (such as an incident optical beam) from the beam source 210 towards the beam splitter 120. In various embodiments, the beam director 110 or the reflective surface may be displaceable relative to the beam splitter 120. In various embodiments, displacing the beam director 110 may direct the beam 90 to incident on (or strike) two or more portions / regions of the beam splitter 120. In various embodiments, the optical measurement system 50 may comprise a controller (not shown) in signal communication with the beam director 110. The controller may be configured to control a position of the beam director 110.

[0064] According to various embodiments, the beam splitter 120 may comprise a first reflective portion; and an adjacent first transmissive portion. The first transmissive portion may be distinct from the first reflective portion The beam combiner 130 may comprise a second reflective portion and an adjacent second transmissive portion. The second transmissive portion is distinct from the second reflective portion. In various embodiments, the first transmissive portion and the second transmissive portion define a transmission path 92. The transmission path 92 may be characterized by substantial transmission of the beam 90 through the beamsplitter 120 and the beam combiner 130. The transmission path 92 may be characterized by an axial axis 102 of the optical measurement device 100.

[0065] In various embodiments, the first reflective portion and the second reflective portion define a reflection path 94. The reflection path 94 may be characterized by substantial reflection of the beam 90 by the beam splitter 120 and the beam combiner 130.

[0066] In various embodiments, the beam reflector 140 may comprise one or more reflective surfaces for directing the beam 90 from the beam splitter 120 to the beam combiner 130. As an example, the beam reflector 140 may be an optical prism. As such, the reflection path 94 may be characterized by substantial reflection of the beam 90 by the beam splitter 120, the beam reflector 140 and the beam combiner 130.

[0067] Responsive to displacing the beam director 1 10 relative to the beam splitter 120, the beam director 110 changes the portion or region on the beam splitter 120 in which the beam 90 is incident or directed. This causes the beam splitter 120 to direct the beam 90 towards either the transmission path 92 or the reflection path 94. In various embodiments, the beam 90 may be directed solely towards either the transmission path 92 or the reflection path 94. In other words, the beam 90 may not be directed towards both the transmission path 92 and the reflection path 94 concurrently. As the beam 90 is directed towards the transmission path 92 or the reflection path 94 independently and non-time-overlapping, this enables minimal optical power loss for the beam 90.

[0068] In various embodiments, responsive to directing the beam 90 to the transmission path 92, the beam 90 focuses on a first focal point on a target object, such as an eye 80 of a subject. Similarly, responsive to directing the beam 90 to the reflection path 94, the beam 90 focuses on a second focal point on the eye 80

[0069] In various embodiments, the beam director 110 may be used to direct the beam towards the transmission path 92 or the reflection path 94. Referring to FIG. 4, responsive tothe beam director 110 being displaced to or disposed in a first position, the beam director 110 directs the beam 90 to the transmission path 92 to focus on a first segment 82 of the eye 80 of the subject. The first segment 82 may be a posterior segment which comprises a retina of the eye 80 of the subject. Further, responsive to the beam director 110 being displaced to or disposed in a second position, the beam director 110 directs the beam 90 to the reflection path 94 to focus on a second segment 84 of the eye 80 of the subject. The second segment 84 may be an anterior segment which comprises a cornea of the eye 80 of the subject. In various embodiments, the first position and the second position may be angularly offset relative to one another.

[0070] Accordingly, the sample arm 100 is configured with a dual beam arrangement, i.e. via the transmission path 92 and the reflection path 94. In various embodiments, the beam director 110 may direct the beam 90 to the transmission path 92 and the reflection path 94 nontime-overlapping relative to each other. Displacing or actuating the beam director 110 enables partial imaging of the eye 80 in a sequential manner. This enables the optical measurement system 50 to image the anterior segment 84 and the posterior segment 82 of the eye 80 in a nontime-overlapping manner. The dual beam configuration of the sample arm 100 bypasses the imaging of the vitreous body 83 of the eye 80, which is a major segment anatomically located between the anterior segment 84 and posterior segment 82 along the optical axis 86. As the vitreous body 83 is typically not useful in ophthalmic biometry, bypassing the vitreous body 83 alleviates or at least mitigates the limitation of ranging depth during imaging.

[0071] It may be appreciated that the optical measurement system 50 and the optical measurement device 100 may not be limited to imaging the anterior segment 84 and posterior segment 82 of the eye 80. In various applications, the optical measurement system 50 and the optical measurement device 100 may also be used to image other portions of the eye 80, such as various portions of the vitreous body 83.

[0072] In various embodiments, along the transmission path 92, the beam 90 may be focused at one or both of: the first transmissive portion 122 and the second transmissive portion 132. In various embodiments, along the reflection path 94, the beam 90 may be collimated at one or both of: the first reflective portion 124 and the second reflective portion 134. In various embodiments, the second transmission portion 132 may be substantially smaller in area (or size) in comparison to the second reflective portion 134, to maximize a transmission efficiency (or transmission power) of the transmission path 92 and a reflection power efficiency (reflection power) of the reflection path 94. Specifically, the transmission efficiency of the transmission path 92 at the second transmission portion 132 and the reflection power efficiency of the reflection path 94 at the second reflection portion 134 are both maximized. In other words, a size of the second transmission portion 132 is minimized sufficiently such that the beam 90 passes through the second transmission portion 132 with maximum / optimal transmission power. In addition, a size of the second reflective portion 134 is maximized such that the beam 90 is reflected by the second reflection portion 134 with maximum / optimal reflection power. In various examples, the second transmission portion 132 may typically be tens of micrometres in diameter or width (e g. between 10pm to 50pm), which corresponds to or matches the beam size of a focal spot of the transmission light in the transmission path 92. The second reflective portion 134 may typically be a few millimetres in diameter or width (e g. between 1mm to 5mm), which corresponds to or matches the beam size of the collimated beam in the reflection path 94. For example, a relative size ratio between the second transmission portion 132 and second reflective portion 134 may be 1 : 10, 1 :20, 1 :100, 1 :500, etc. A person skilled in the art will appreciate that the relative size between the second transmission portion 132 and second reflective portion 134 may be determined according to various operating parameters, with the examples provided above being non-limiting.

[0073] FIGs. 5 and 6 illustrate an optical measurement device 100 or a sample arm, according to various embodiments of the disclosure. The optical measurement device 100 may comprise a beam director 110; a beam splitter 120 disposed spaced apart from the beam director 110; a beam combiner 130 disposed spaced apart from the beam splitter 120 along the axial axis 102; and a beam reflector 140 disposed spaced apart from the beam splitter 120 and the beam combiner 130 along a transverse axis 104.

[0074] In various embodiments, the beam director 110 may be configured as a galvometer scanner comprising an angularly displaceable mirror for directing a beam 90 from a beam source 210 towards the beam splitter 120. The mirror may be angularly displaceable 112 relative to a pivot of the mirror.

[0075] According to various embodiments, the beam splitter 120 may comprise a first reflective portion 124, and an adjacent first transmissive portion 122. The first transmissive portion 122 may be distinct from the first reflective portion 124, or in other words, nonoverlapping. The first transmissive portion 122 may comprise a generally transmissive bulk material such that the beam 90 may be substantially transmitted or passed through the first transmissive portion 122. The first reflective portion 124 may comprise a generally reflective surface such that the beam 90 may be substantially reflected by the first reflective portion 124. In various embodiments, a transition between the first transmissive portion 122 and the first reflective portion 124 may be defined by a reflective edge 123, such that the beam 90 transits from being transmitted to being reflected or vice versa, when directed across the reflective edge 123.

[0076] According to various embodiments, the beam combiner 130 may comprise a second reflective portion 134 and an adjacent second transmissive portion 132. The second transmissive portion 132 may be distinct from the second reflective portion 134. In various embodiments, the second transmissive portion 132 may be configured as a slit or an openingacross the beam combiner 130 such that the beam 90 may be substantially transmitted or passed through the second transmissive portion 132. In some embodiments, the beam combiner 130 may be a slitted mirror or a mirror with a slit opening. In other embodiments, the second transmissive portion 132 may be configured as a generally transmissive bulk material such that the beam 90 may substantially transmitted or passed through the transmissive bulk material. In various embodiments, the second transmissive portion 132 of the beam combiner 130 may be an optical conjugate of a pivot of the beam director 110.

[0077] According to various embodiments, the beam reflector 140 may comprise one or more reflective surfaces 142 / 144, such as a pair of reflective mirrors. Each of the reflective surfaces 142 / 144 may disposed spaced apart from the beam splitter 120 and the beam combiner 130, respectively along the transverse axis 104.

[0078] In various embodiments, the first transmissive portion 122 and the second transmissive portion 132 may define a transmission path 92. The transmission path 92 may be characterized by substantial transmission of the beam 90 through the beam splitter 120 and the beam combiner 130.

[0079] In various embodiments, the first reflective portion 124 and the second reflective portion 134 may define a reflection path 94. In various embodiments, the beam reflector 140 may be disposed in the reflection path 94 to redirect the beam 90 from the beam splitter 120 to the beam combiner 130. Hence, the reflection path 94 may be characterized by substantial reflection of the beam 90 by the beam splitter 120, the beam reflector 140 and the beam combiner 130.

[0080] In various embodiments, angularly displacing the beam director 110 may direct the beam 90 to incident on the first transmissive portion 122 or the first reflective portion 124 of the beam splitter 120. Therefore, angularly displacing the beam director 110 may direct the beam 90 towards either the transmission path 92 or the reflection path 94. With the provisionof the reflective edge 123, the beam 90 may transit from the transmission path 92 to the reflection path 94, or vice versa, in a short duration.

[0081] In various embodiments, the beam 90 may be directed solely towards either the transmission path 92 or the reflection path 94. In other words, the beam 90 may not be directed towards both the transmission path 92 and the reflection path 94 concurrently. As the beam 90 is directed towards the transmission path 92 or the reflection path 94 independently and nontime-overlapping, this enables minimal optical power loss for the beam 90. As such, an optical power of the beam 90 may be substantially preserved passing through each of the transmission path 92 and the reflection path 94.

[0082] During imaging, responsive to directing the beam 90 to the transmission path 92, the beam 90 focuses on a first focal point or retina 82 on an eye 80 of a subject. Similarly, responsive to directing the beam 90 to the reflection path 94, the beam 90 focuses on a second focal point or cornea 84 on the eye 80.

[0083] In various embodiments, the transmission path 92 and the reflection path 94 may partially overlap one another. The transmission path 92 and the reflection path 94 may partially overlap before being incident on (or at the moment of striking) the beam splitter 120, or after being incident on the beam combiner 130. For example, the transmission path 92 and the reflection path 94 may partially overlap between the beam director 110 and the beam splitter 120.

[0084] In various embodiments, the respective beams 90 passing through the transmission path 92 and the reflection path 94 may be partially co-axial to each other. The respective beams 90 passing through the transmission path 92 and the reflection path 94 may be partially co-axial before being incident on the beam splitter 120, or after being incident on the beam combiner 130. For example, the transmission path 92 and the reflection path 94 may partially co-axial to each other in the eye 80 of the subject.

[0085] In various embodiments, the transmission path 92 and the reflection path 94 incident on the beam combiner 130 may be non-parallel. In other words, portions of the transmission path 92 and the reflection path 94 that strike the beam combiner 130 may form an angle and hence be non-parallel. In some examples, the transmission path 92 and the reflection path 94 incident on the beam combiner 130 may form a right angle, an acute angle or an obtuse angle.

[0086] FIG. 7 illustrates alternative embodiments of the optical measurement device 100. Similar to previous embodiments, the optical measurement device 100 may comprise a beam director 110; a beam splitter 120 disposed spaced apart from the beam director 110; a beam combiner 130 disposed spaced apart from the beam splitter 120 along the axial axis 102; and a beam reflector 140 disposed spaced apart from the beam splitter 120 and the beam combiner 130 along a transverse axis 104. The beam splitter 120 may comprise a first reflective portion 124; and an adjacent first transmissive portion 122. The first transmissive portion 122 may be distinct from the first reflective portion 124, or in other words, non-overlapping.

[0087] As an alternative to transmissive material, the first transmissive portion 122 may be an air space or air volume such that the beam 90 may be substantially transmitted or passed through the first transmissive portion 122. This beneficially improves the transmissibility of the beam 90 due to a lack of optical material (and hence reflection). Hence, the beam splitter 120 may be configured as a single reflective surface which is positioned away from the transmission path 92 along the transverse axis 104.

[0088] Further, the first reflective portion 124 may also comprise a generally reflective surface such that the beam 90 may be substantially reflected by the first reflective portion 124. In various embodiments, a transition between the first transmissive portion 122 and the first reflective portion 124 may be defined by a reflective edge 123, such that the beam 90 transits from being transmitted to being reflected or vice versa, when directed across the reflective edge123.

[0089] Further referring to FIG. 8, in various embodiments, the beam splitter 120 and the beam combiner 130 may be integrally formed. For example, the beam splitter 120 and the beam combiner 130 may collectively form an inverted “V” structure. Similar to previous embodiments, the integrally formed beam splitter 120 and beam combiner 130 may define a transmission path 92 and a reflection path 94 for the beam 90.

[0090] Further, in various embodiments, in addition to imaging the anterior segment 84 and posterior segment 82 along the optical axis 86, the optical measurement system 50 may also perform imaging of the eye 80 along the transverse axis 104 by displacing the sample arm 100 along the transverse axis 104. Referring again to FIG. 4, due to curvature of the anterior segment 84 and the posterior segment 82 of the eye 80 along the transverse axis 104, a respective focusing module (such as one or more optical elements or lenses) may be provided along each of the transmission path 92 and reflection path 94, to control the respective focal points of the beam 90 along the respective paths 92 / 94.

[0091] Referring again to FIG. 8, in various embodiments, the optical measurement device 100 may further include one or more optical elements 230 disposed along the transmission path 92 and the reflection path 94. This enables control of the focal points in each of the transmission path 92 and the reflection path 94 during imaging along the transverse axis 104. In various embodiments, the optical elements 230 may independently or collective displace along the axial axis 102 to effect a shift in focal point along the axial axis 102. In avoidance of doubt, each of the optical element 230 may comprise a single optical lens element or a group of optical lens elements, for example a group of cemented optical lens elements.

[0092] FIGs. 9 to 10D illustrate an optical measurement device 100 according to various embodiments of the disclosure Similar to previous embodiments, the optical measurement device 100 may comprise a beam director 110; a beam splitter 120 disposed spaced apart from the beam director 110; a beam combiner 130 disposed spaced apart from the beam splitter 120along the axial axis 102; and a beam reflector 140 disposed spaced apart from the beam splitter 120 and the beam combiner 130 along a transverse axis 104. The beam splitter 120 may comprise a first reflective portion 124; and an adjacent first transmissive portion 122. The first transmissive portion 122 may be distinct from the first reflective portion 124, or in other words, non-overlapping.

[0093] In various embodiments, the beam splitter 120 and the beam combiner 130 may define a plurality of transmission paths 92 and a plurality of reflection paths 94. Referring to FIG. 10A, in various embodiments, the beam splitter 120 may comprise a planar surface 127 defining a first direction 126 and a second direction 128 orthogonal to the first direction 126. In various embodiments, the first reflective portion 124 may comprise or correspond to one or more reflective strips 125, wherein each of the reflective strips 125 may define a respective reflective edge. The reflective strips 125 may be spaced apart from one another along the second direction 128. It may be appreciated that the surfaces / bulk material between each pair of reflective strips 125 may be configured as transmission strips 121 which correspond to the first transmissive portion 122. As such, the first transmissive portion 122 may correspond to the complementary surfaces / bulk material of the beam splitter 120 which is distinct from the reflective strips 125. The transmission strips 121 of the first transmissive portion 122 and the reflective strips 125 the first reflective portion 124 may be disposed alternating along the second direction 128.

[0094] Further referring to FIG. 10B, in various embodiments, the beam combiner 130 may comprise a planar surface 137 defining a third direction 136 and a fourth direction 138 orthogonal to the third direction 136. In various embodiments, the second transmissive portion 132 of the beam combiner 130 may comprise or correspond to one or more openings 133. The openings 133 may be through opening or formed from a transmissive bulk material. The openings 133 may be spaced apart from one another along the fourth direction 138. It may be 1appreciated that the surfaces / bulk material between each pair of openings 133 may correspond to the second reflective portion 134. As such, the second reflective portion 134 may correspond to the complementary surfaces / bulk material of the beam combiner 130 which is distinct from the openings 133.

[0095] During an imaging scan (or a fast axis scan), the beam director 110 directs the beam 90 along the second direction (or transverse axis 104) across the field of view, the beam 90 may be directed towards multiple transmission strips 121 and reflection strips 125, and hence towards multiple alternating transmission paths 92 and reflection paths 94 sequentially. This beneficially enables the beam 90 to alternatingly focus on the retina 82 and the cornea 84 of the eye 80, enabling imaging of the anterior segment and posterior segment of the eye 80 to be acquired in each imaging scan. As each of the transmission path 92 and reflection path 94 are non-time-overlapping, and hence independent from each other, overlapping issues due to concurrent imaging are mitigated. In various embodiments, half of the field of view for each anterior / posterior segment of the eye 80 may be captured for each fast axis scan.

[0096] Referring to FIG. 10C, in various embodiments, the first reflective portion 124 of the beam splitter 120 may comprise a plurality of offset reflective strips 125 arranged along the first direction 126 and the second direction 128. In other words, each pair of the reflective strips 125 may be spaced apart in an offset or alternating configuration in both the first direction 126 and the second direction 128. The first transmissive portion 122 of the beam splitter 120 may comprise a plurality of offset transmission strips 121. As such, the transmission strips 121 of the first transmissive portion 122 and the reflective strips 125 of the first reflective portion 124 may be disposed alternating along the first direction 126 as well as the second direction 128.

[0097] Further referring to FIG. 10D, in various embodiments, the second transmissive portion 132 of the beam combiner 130 may comprise a plurality of offset openings 133 arranged along the third direction 136 and the fourth direction 138. In other words, each pair of theopenings 133 may be spaced apart in an offset or alternating configuration in both the third direction 136 and the fourth direction 138.

[0098] With the provision of the offset reflective strips 125, in which the reflective strips125 and transmission strips 121 are in an alternating configuration along both the first direction126 and second direction 128, as well as the corresponding offset openings 133, in which the openings 133 are in an alternating configuration along both the third direction 136 and the fourth direction 138, a full field of view for each anterior / posterior segment of the eye 80 may be captured in two fast axis scans.

[0099] The slow axis (Y) scanner may first position the beam 90 to one side of the beam splitter 120 during the first fast axis scan, in which half field of view is imaged, following with a re-positioning of the beam 90 to the other side of the beam splitter 120, where the strip pattern is opposite (or phase shifted by pi), for the second fast axis scan. During the second fast axis scan, the other half field of view which was not previously imaged in the first fast axis scan may be obtained.

[0100] In alternative embodiments, two or more beam splitters 120 and two or more beam combiners 130 as illustrated in FIGs. 10A and 10B, may be placed adjacent to each other in an offset manner for the re-positioning process as described above.

[0101] According to various embodiments, referring again to FIG. 9, each of the transmission path 92 and reflection path 94 may include optical modules / optical elements which are specific to the respective transmission path 92 and reflection path 94. In some embodiments, the optical measurement device 100 may further include at least one first optical element 250 disposed in the transmission path 92, and at least one second optical element 260 disposed in the reflection path 94. As such, the transmission path 92 may comprise first optical element(s) 250 unique from the second optical element(s) 260 of the reflection path 94. In avoidance of doubt, each of the first / second optical element 250 / 260 may comprise a single optical lenselement or a group of optical lens elements, for example a group of cemented optical lens elements. In various embodiments, the optical measurement device 100 may be configured as a 4f relay system or configuration.

[0102] In various embodiments, the optical measurement device 100 may further comprise a beam shaper 105 for shaping the beam 90 into an elliptical beam. As an example, the beam shaper 105 may be an anamorphic prism pair. The beam shaper 105 may be disposed prior to the beam director 110 to provide the elliptical beam to be directed towards the transmission path 92 or the reflection path 94.

[0103] According to another aspect of the disclosure, FIG. 11 illustrates a method of optical measurement 700. In various embodiments, the method 700 comprises in 710, directing a beam to a transmission path to focus the beam on a first focal point on a target object (such as an eye of a subject), the transmission path being defined by a first transmissive portion of a beam splitter and a second transmissive portion of a beam combiner; and in 720, directing the beam to a reflection path to focus the beam on a second focal point on the target object, the reflection path being defined by a first reflective portion of the beam splitter and a second reflective portion of the beam combiner In various embodiments, the beam splitter is disposed spaced apart from the beam combiner. In various embodiments, the first reflective portion is adjacent to and distinct from the first transmissive portion, and the second reflective portion is adjacent to and distinct from the second transmissive portion.

[0104] In various embodiments, the method 700 further comprises in 730, sequentially directing the beam to the transmission path and the reflection path. In various embodiments, the method 700 further comprises in 740, directing the beam to sequentially alternate between a plurality of transmission paths and a plurality of reflection paths

[0105] Exemplary Implementations

[0106] The present section discloses various implementations of the proposed optical measurement system and optical measurement device. For brevity, the description focuses mainly on the different implementations of the optical measurement device or the sample arm optical configuration.

[0107] Referring to FIGs. 12A and 12B, in a first implementation, a light output or sample beam from the sample arm fiber of an OCT system is collimated by a lens (L1 ), and a collimated beam is reflected by one or more galvanometer (galvo) scanning mirrors 110. The galvo scanning mirrors 110 are located at the back focal plane of the scan lens L2. The scan lens L2 and tube lens L3 collectively form a 4f system which serves as relay optics from the galvo scanning mirrors 110 to the eye, and vice versa. The above-mentioned optical configuration may be implemented for ophthalmic OCT.

[0108] Further, a mirror edge (or reflective edge) is positioned at the front focal plane of the scan lens L2 (which also corresponds to the back focal plane of the tube lens L3). This mirror edge serves as a beam splitter 120. In various instances, when the sample beam is directed by the galvo scanner to a position below the mirror edge, the sample beam passes through the beam splitter 120 and is focused on a retina of an eye 80 through the posterior path (or transmission path). The posterior path may comprise the beam passing through the lens L3, lens L4, a beam combiner, lens L5 and the retina of the eye, as shown in FIG 12A. In various instances, when the sample beam is directed by the galvo scanning mirror 110 onto the mirror portion of the beam splitter, the sample beam is reflected by the mirror portion to the anterior path (or reflection path). The anterior path may comprise the beam passing through lens L6, a beam combiner 130, lens L5, the anterior segment of the eye, and is focused on a cornea of the eye, as shown in FIG. 12B.

[0109] Still referring to FIGs. 12A and 12B, the beam combiner 130 (or slit beam combiner) may comprise a slit and a reflective mirror in areas other than the slit. The slit beam combiner130 may be located at the front focal plane of L4 and the back focal plane of L5. A position of the slit may be adjusted such that when the sample beam passes through the beam splitter 120, the sample beam also passes through the slit of the beam combiner 130. The slit of the beam splitter 120 is aligned along with the mirror edge of the beam combiner 130 such that when the sample beam is scanned along the mirror edge, the sample beam always passes through the slit. [001 10] When the sample beam is scanned onto the mirror portion of the beam splitter 120, the reflected beam may be collimated by L6. The most of or substantial portion of the collimated beam may be reflected by the beam combiner 130 as the diameter of the collimated beam is larger than the slit width of the beam combiner 130. The reflected beam from the beam combiner 130 is then focused by L5 onto the cornea of the eye 80.[001 11] It may be appreciated that the implementation is exemplary in nature, and does not put any limitation to the number of mirror edges, slits, and the different number or combination of optical elements / modules as well as the combination of transmissions / reflections for each anterior and posterior path.

[0112] According to another exemplary implementation, referring to FIGs. 13A and 13B, a collimated sample beam from the beam source is firstly converted to an elliptical beam by a pair of anamorphic prisms or other beam shaping mechanism. The elliptical beam (or sample beam) is then directed by the galvo scanners 110 and focused by Lens 1 (LI). The galvo scanners 110 are located at the back focal point of the LI and a slit beam splitter 120 is positioned at the front focal plane of LI. As shown in FIG. 13A, when the sample beam is directed by the galvo scanner 1 10 at the slit of the beam splitter 120, the sample beam passes through the slit and is focused onto a retina of an eye through Lens 2 (L2). The beam splitter 120 may be configured to be mostly reflective other than the slit, which is transparent When the sample beam is directed by the galvo scanner 110 onto a reflective portion of the beam splitter 120, the sample beam is reflected towards Lens 3 (L3) and is focused onto a cornea ofthe eye through Lens 4 (L4) and a beam combiner 130. The beam combiner 130 comprises a slit mirror oriented along the same direction as the slit of the beam splitter 120. The slit mirror reflects the sample beam partially to be focused at the cornea by L4

[0113] According to another exemplary implementation, referring to FIGs. 14A to 15B, the implementation includes a 4f relay system comprising L2 and L3 after the galvo scanner 110. Further, the galvo scanner 1 10 is positioned at the back focal point of L2. As shown in FIG. 15A, the beam splitter 120 comprising interlaced reflective strips 125 and transmission strips 121. The beam splitter 120 is positioned at the front focal plane of L2 and the back focal plane of L3. The implementation further includes an additional 4f system comprising scan lens L4 and tube lens L5 which are positioned after L3. A beam combiner 130 is positioned at the front focal plane of the L4, as well as the back focal plane of the L5. As shown in FIG. 15B, the beam combiner 130 comprises a linear array of small rectangular openings or holes 133 which are of high transmittance, while all the other areas / portions / regions 134 of the beam combiner 130 are of high reflectance. The locations and the size of the transmission holes 133 are configured based on the positions and width of the transmission strips 121 of the beam splitter 120, such that whenever the sample beam passes through the beam splitter 120, the sample beam will pass through the beam combiner 130.

[0114] Referring to FIG. 14A, in the transmission mode, the galvo mirror 110 scans the sample beam onto the transmission strips 121 such that the focused beam passes through the beam splitter 120 as if it is a transparent window. Referring to FIGs. 14B and 15B, in the reflection mode, the galvo mirror 1 10 scans the sample beam onto reflective strips 125 such that the focused beam is reflected to the transmission path comprising lens 6 (L6). L6 collimates the diverging sample beam, and directs the sample beam (collimated beam spot 99) to the beam combiner 130.

[0115] When the galvo mirror 110 scans the sample beam across the field of view covering multiple transmission strips 121 and reflection strips 125, the imaging mode or imaging path will be switched between the transmission and reflection rapidly. As the sample beam is focused on the retina and cornea in the transmission and reflection mode, respectively, both images of the anterior segment and posterior segment of the eye is acquired during each fast axis scan. Note that in either image, there are only signals from one segment, which precludes the overlapping issue and require significantly shorter ranging depth than conventional solutions. This implementation enables half of the field of view for each anterior / posterior segment of the eye to be captured for each fast axis scan.

[0116] Referring to FIGs. 16A and 16B, in another exemplary implementation of the beam splitter 120 and the beam combiner 130, the strip pattern (reflective strips 125 and transmission strips 121) are opposite laterally (from between the left side and the right side). This configuration aids in imaging the full field of view in two fast axis scans. The slow axis (Y) scanner positions the sample beam to one side of the beam splitter during the first fast axis scan, in which half field of view is imaged. After the first fast axis scan, the sample beam can be quickly re-positioned to the other side of the beam splitter where the strip pattern is opposite (or phase shifted by pi) before the second fast axis scan. During the second fast axis scan, the half field of view that is missed in the first fast axis scan is covered. The corresponding beam combiner 130 also has two sides that are opposite in pattern or phase.

[0117] Referring to FIGs. 17A to 18, in another implementation, the beam splitter 120 and beam combiner 130 may be adjacent to each other with no optical elements or optics in between. The beam splitter 120 and beam combiner 130 may be mounted together mechanically or bonded together integrally, such that there is no relative motion therebetween. The beam splitter 120 has at least one transmission portion 122 and at least one reflection portion 124, or multiple transmission strips as shown in above implementations (FIGs. 15Ato 16B). The beam combiner130 is mostly reflective except for a slit 132 or a number of slits, which allow the beam to be focused by Lens 1 (LI) to pass through with high transmission efficiency. The optics or optical elements are arranged or configured such that the slit 132 is located at the focus point of LI and the eye pupil is an optical conjugate of the scanning pivot of the galvanometer scanner (Galv) 110. This aids in realizing wide-field retinal scanning with minimal or no vignetting effect. In the reflection mode (FIG. 17B), the beam is scanned by galvanometer (Galv) 1 10 such that the beam is incident on a reflective portion / region of the beam splitter 120 after LI. A reflection optics (or beam reflector), for example a right-angle prism with or without assisting optics, redirects the beam reflected by the beam splitter 120 to the beam combiner 1 0, Lens 2 (L2) and the cornea. The optics are configured such that the slit 132 is the conjugate of the scanning pivot of the galvanometer scanners 1 10. By doing so, the optical beams in both transmission path / mode (FIG. 17A) and reflection path / mode (FIG. 17B) arrive at the same position (slit 132) on the beam combiner 130. In another words, the principal ray of the two beams crosses at the slit 132. Therefore, even when the galvanometer scanner rotates or scan angularly, the reflection beam via the reflection path (FIG. 17B) is always incident at the slit 132.[001 18] FIG. 19A illustrates a reflection path / mode before combiner angle adjustment, and FIG. 19B illustrates a reflection path / mode after combiner angle adjustment. As it may be known, axial length measurement requires that the beam focused on the cornea and the beam focused on the retina to be co-axial, e.g. the principal ray of the two beams overlap in the eye. In anatomical terms, the measurement beams have to pass through the apex of the cornea and the center x from the principal ray of the transmission beam, and consequently the beam is reflected by the beam splitter 120. Since the slit 132 is the conjugate of the pivot of the galvanometer scanner 110, the reflected beam may still pass through the point of slit 132 and cross the principal ray of the transmission beam there. However, the angular scanning of the optical beam by the galvanometer scanner 110 causes the reflected beam to deviate from theprincipal ray of the transmission beam again after the beam combiner, which may result in the ray being incident on a point of the cornea surface a distance away from the apex of the cornea. As a result, referring to FIG. 19A, the reflection beam is not co-axial with the transmission beam. Addressing this limitation, referring to FIG. 19B, the angle of the beam combiner 130 may be adjusted with the slit position being the rotational axis such that the reflection beam is co-axial with the transmission beam.

[0119] Simulation

[0120] An optical configuration of a proposed biometer (or optical measurement system) is shown in FIGs. 20A and 20B. The optical path length difference between the transmission path / mode and the reflection path / mode is measured to be ~ 29.07 mm.

[0121] FIGs 21 A and 21 B illustrate Tomographic deconvolution phase microscopy (TDPM) imaging of an eye model with light beam scanning along the transmission / reflection strip of the beam splitter. FIG. 21A shows the OEMI-7 eye model. FIG. 21B shows cross-sectional images (top) and corresponding depth profile (bottom) of the anterior segment (left) and posterior segment (right), respectively. CCT: central corneal thickness, ACD: anterior chamber depth, LT: lens thickness, AL: axial length, OPD: optical path-length difference between transmission mode (posterior segment imaging) and reflection mode (anterior segment imaging). LI : optical distance of cornea anterior boundary away from DC, L2: optical distance of retina surface from DC.

[0122] Referring to FIG. 21A, an eye model (OEMI-7 eye model) was imaged with fast-axis (X-axis) mirror scanning the sample beam along the transmission strips of the beam splitter 120 for corneal imaging (Fig. 20A) and along the reflection strips for retinal imaging (Fig. 20B). With the clear identification of the interface between ocular components, ocular biometric data including but not limited to corneal thickness (CT), anterior chamber depth (ACD), and axial length (AL) may be obtained (Table 1).Table 1. Anatomical dimensions of eye model measured with TDPM biometer prototype* Refractive index = 1.3375 provided by commercial biometer

[0123] FIGs. 22A, 22B and 22C illustrate TDPM imaging of an eye model (OEMI-7) with sample beam scanning across multiple transmission / reflection strips of the beam splitter. The eye model (OEMI-7) was imaged with fast-axis mirror scanning across multiple transmission / reflection strips of the beam splitter. Anterior and posterior segment structures located at different positions were without overlap and thus could be readily differentiated (FIG. 22A). This scanning approach also allows the identification of the interface between ocular elements (FIGs. 22B and 22C).

[0124] Clinical trial

[0125] The proposed optical measurement system was implemented in a clinical trial. Table 2 shows the results from the clinical trial, in which the axial length measurement repeatability was measured to be 8.92 micrometers in 36 eyes aged 20-40, and measured to be 7.36 micrometers in 8 eyes aged 40-50 in vivo, which is equivalent to that of the gold standard (IOL Master 700, Carl Zeiss).Table 2 Measurement repeatability (standard deviation)

[0126] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.

Claims

CLAIMS1. An optical measurement device, comprising: a beam splitter comprising a first reflective portion and an adj acent first transmissive portion distinct from the first reflective portion; and a beam combiner disposed spaced apart from the beam splitter, the beam combiner comprising a second reflective portion and an adjacent second transmissive portion distinct from the second reflective portion, wherein the first transmissive portion and the second transmissive portion define a transmission path, and the first reflective portion and the second reflective portion define a reflection path, wherein responsive to directing a beam to the transmission path, the beam focuses on a first focal point on a target object, and wherein responsive to directing the beam to the reflection path, the beam focuses on a second focal point on the target object.

2. The device as recited in claim 1 , further comprising: a beam director being configured to direct the beam from a beam source, wherein responsive to the beam director being in a first position, the beam director directs the beam to the transmission path to focus on a first segment of an eye of a subject, wherein responsive to the beam director being in a second position, the beam director directs the beam to the reflection path to focus on a second segment of the eye of the subject.

3. The device as recited in claim 2, wherein the first position and the second position are angularly offset relative to one another.

4. The device as recited in claim 3, wherein the second transmissive portion of the beam combiner is an optical conjugate of a pivot of the beam director.

5. The device as recited in any one of claims 2 to 4, wherein the beam director directs the beam to the transmission path and the reflection path non-time-overlapping relative to each other.

6. The device as recited in any of the above claims, wherein the transmission path and the reflection path partially overlap one another.

7. The device as recited in any of the above claims, wherein the respective beams passing through the transmission path and the reflection path are partially co-axial.

8. The device as recited in any of the above claims, further comprising at least one first optical element disposed in the transmission path, and at least one second optical element disposed in the reflection path.

9. The device as recited in any of the above claims, further comprising a beam shaper for shaping the beam into an elliptical beam.

10. The device as recited in any one of the above claims, wherein the transmission path is characterized by an axial axis of the device, the axial axis being substantially parallel to an optical axis of the eye.

11. The device as recited in claim 10, wherein the beam combiner is disposed spaced apart from the beam splitter along the axial axis.

12. The device as recited in any one of the above claims, wherein the transmission path and the reflection path incident on the beam combiner are non-parallel.

13. The device as recited in any one of the above claims, further comprising a beam reflector, wherein the beam reflector is disposed in the reflection path to redirect the beam from the beam splitter to the beam combiner.

14. The device as recited in claim 13, wherein the beam reflector comprises at least one reflective surface.

15. The device as recited in any one of the above claims, wherein the first reflective portion of the beam splitter comprises at least one reflective strip, each of the at least one reflective strip defining a respective reflective edge.

16. The device as recited in claim 15, wherein the beam splitter comprises a first planar surface defining a first direction and a second direction orthogonal to the first direction, and wherein the first reflective portion of the beam splitter comprises a plurality of offset reflective strips arranged along the first direction and the second direction.

17. The device as recited in any one of the above claims, wherein the beam combiner is a slitted mirror.

18. The device as recited in any one of the above claims, wherein the second transmissive portion of the beam combiner corresponds to at least one opening19. The device as recited in claim 18, wherein the beam combiner comprises a second planar surface defining a third direction and a fourth direction orthogonal to the third direction, and wherein the second transmissive portion of the beam combiner comprises a plurality of offset openings arranged along the third direction and the fourth direction.

20. The device as recited in any one of the above claims, wherein the beam splitter and the beam combiner define a plurality of transmission paths and a plurality of reflection paths.21 . The device as recited in any one of the above claims, wherein the beam splitter and the beam combiner are integrally formed.

22. The device as recited in any one of the above claims, wherein along the transmission path, the beam is focused at one or both of: the first transmissive portion and the second transmissive portion.

23. The device as recited in any one of the above claims, wherein the second transmission portion is substantially smaller in area than the second reflective portion, to maximize atransmission efficiency of the transmission path at the second transmission portion and a reflection power efficiency of the reflection path at the second reflection portion.

24. The device as recited in any one of the above claims, wherein along the reflection path, the beam is collimated at one or both of: the first reflective portion and the second reflective portion25. The device as recited in any one of the above claims, wherein an optical power of the beam is substantially preserved passing through each of the transmission path and the reflection path.

26. An optical measurement system, comprising the device as recited in any one of the above claims; and a controller in signal communication with a beam director, the controller being configured to control a position of the beam director.

27. The system as recited in claim 26, further comprising a beam source for providing the beam to the beam director.

28. The system as recited in any one of claims 26 and 27, wherein the system is an optical biometer.

29. A method of optical measurement, comprising: directing a beam to a transmission path to focus the beam on a first focal point on a target object, the transmission path being defined by a first transmissive portion of a beam splitter and a second transmissive portion of a beam combiner; anddirecting the beam to a reflection path to focus the beam on a second focal point on the target object, the reflection path being defined by a first reflective portion of the beam splitter and a second reflective portion of the beam combiner, wherein the beam splitter is disposed spaced apart from the beam combiner, wherein the first reflective portion is adjacent to and distinct from the first transmissive portion, and the second reflective portion is adjacent to and distinct from the second transmissive portion.

30. The method as recited in claim 29, further comprising: sequentially directing the beam to the transmission path and the reflection path.

31. The method as recited in any one of claims 29 and 30, further comprising: directing the beam to sequentially alternate between a plurality of transmission paths and a plurality of reflection paths.

Images