Parallel optical coherence tomography system using integrated photonic devices

Abstract

An integrated photonic chip and associated systems and methods suitable for parallel optical coherence tomography scanning are disclosed, including multiplexed data detection and transmission of a DAC to a single channel, or parallel data detection and transmission of a multi-channel DAC to separate channels.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Application No. 63 / 288,822, filed December 13, 2022, the entire disclosure of which is hereby incorporated by reference herein.

[0002] (Reference material) Not applicable.

[0003] (Statement Regarding Federally Sponsored Research and Development) This invention was made with government support under award EB025209 from the National Institutes of Health. The government has certain rights in this invention.

[0004] (Technical field) The present disclosure generally relates to systems, devices, and methods for performing parallel Optical Coherence Tomography (OCT) imaging of biological tissue. [Background technology]

[0005] Optical coherence tomography (OCT) is an emerging biomedical imaging technology that enables noninvasive imaging of cross-sectional and three-dimensional (3D) images of biological tissues at the micron scale. OCT acts as a type of "optical biopsy," imaging the fine structure of tissues with a resolution approaching that of standard histopathological examination under a microscope, while eliminating the need to remove and process tissue samples.

[0006] OCT is similar to ultrasound imaging, but uses light instead of sound, providing 10 to 100 times greater resolution than ultrasound. To date, OCT has been used in a wide range of human clinical applications, including ophthalmology, cardiology, endoscopy, urology, dermatology, and dentistry. OCT is widely used in ophthalmology clinics as a standard diagnostic tool for diabetic retinopathy, macular degeneration, glaucoma, and other retinal and corneal diseases.

[0007] Improving imaging speed is a major driving force behind the development of optical coherence tomography (OCT). Spatial division multiplexing optical coherence tomography (SDM-OCT) is a recently developed parallel OCT imaging method that aims to achieve several-fold speed improvements. However, the assembly of the numerous fiber optic components traditionally used in such systems can be laborious and prone to error, making mass production difficult. Furthermore, the numerous components of OCT systems are space-consuming and difficult to integrate into compact imaging devices used in various medical diagnostic settings and other applications. Therefore, improvements to SDM-OCT systems are needed.

[0008] Other objects and features of the present disclosure will be in part apparent and in part described hereinafter. [Brief explanation of the drawings]

[0009] Those skilled in the art will understand that the drawings, described below, are for illustrative purposes only and are not intended to limit the scope of the present teachings in any way.

[0010] [Figure 1] Schematic diagram showing the components of a fiber-based parallel OCT imaging system. The components within the red dashed box could potentially be integrated into a photonic chip. [Figure 2] FIG. 1 is a schematic diagram showing a photonic chip-based parallel OCT imaging system. [Figure 3] FIG. 1 is a schematic diagram showing elements of a photonic chip for a parallel OCT imaging system including a single waveguide input from an external light source. [Figure 4] FIG. 1 is a schematic diagram showing elements of a photonic chip including input from an external light source and input / output from an external reference arm. [Figure 5]Schematic diagram showing elements of a photonic chip for a parallel OCT imaging system, including a single waveguide input from an external light source and Fabry-Perot-Bragg gratings (FPBGs) integrated into both the OCT and MZI circuits. [Figure 6] Schematic diagram showing the elements of a photonic chip for a parallel OCT imaging system, including an external light source, an external reference arm, and Fabry-Perot-Bragg gratings (FPBGs) integrated into both the OCT and MZI circuits. [Figure 7] Schematic diagram showing the elements of a photonic chip for a parallel OCT imaging system, including a single waveguide input from an external light source, Fabry-Perot-Bragg gratings integrated into both the OCT and MZI circuits, and an array of balanced photodetectors integrated into the photonic device as active components to detect interference signals from the parallel OCT imaging channels, incorporating bandpass filters and signal mixing / combining circuitry before the OCT signals are acquired by the data acquisition card. [Figure 8] Schematic diagram showing the elements of the photonic chip for the parallel OCT imaging system, including an external light source, an external reference arm, Fabry-Perot-Bragg gratings integrated into both the OCT and MZI circuits, and an array of balanced photodetectors integrated into the photonic device as active components to detect interference signals from the parallel OCT imaging channels, along with bandpass filters and signal mixing / combining circuitry before the OCT signals are acquired by the data acquisition card. [Figure 9] Schematic diagram showing the elements of the photonic chip for the parallel OCT imaging system, including a single waveguide input from an external light source, Fabry-Perot-Bragg gratings integrated into both the OCT circuit and the MZI circuit, and an array of balanced photodetectors integrated into the photonic device as active components to detect interference signals from the parallel OCT imaging channels. [Figure 10]Schematic diagram showing the elements of the photonic chip for the parallel OCT imaging system, including an external light source, an external reference arm, Fabry-Perot-Bragg gratings integrated into both the OCT circuit and the MZI circuit, and an array of balanced photodetectors integrated into the photonic device as active components to detect interference signals from the parallel OCT imaging channels.

[0011] While the drawings illustrate the configurations described herein, it should be understood that the present embodiments are by way of illustration and not limited to the precise configuration. While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative aspects of the present disclosure. It should be understood that the present invention can be modified in various aspects without departing from the spirit and scope of the present disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. DETAILED DESCRIPTION OF THE INVENTION

[0012] In various aspects, devices, systems, and methods are disclosed that achieve significant improvements in optical coherence tomography (OCT) imaging speed and reduce the system footprint by using integrated photonics. Parallel OCT imaging is achieved by simultaneously illuminating multiple locations on a sample and simultaneously detecting interference signals. In various aspects, photonic integrated circuit (PIC) technology is used to design and fabricate passive and active optoelectronic circuits on the same chip.

[0013] The resulting photonic chip offers various enhancements and additional capabilities over existing photonic chip designs. Existing photonic chip designs are described in U.S. Patent Nos. 9,400,169, 10,107,616, and 11,079,214, the contents of each of which are incorporated herein by reference in their entirety. In some embodiments, the photonic chip includes a Mach-Zehnder interferometer (MZI) integrated to perform precise phase calibration of the OCT image signal. In other embodiments, the photonic chip includes Fabry-Perot-Bragg gratings (FPBGs) integrated in both the OCT circuit and the MZI circuit to enable registration of the OCT and MZI signals. In further embodiments, the photonic chip includes at least two Fabry-Perot-Bragg gratings in either the OCT channel or the MZI channel to minimize phase jitter caused by the laser light source. In other further aspects, the photonic chip includes an array of balanced photodetectors integrated into the photonic device as an active component for detecting interference signals from the parallel OCT imaging channels. In yet other additional aspects, the photonic chip includes bandpass filters and signal mixing / combining circuitry configured to condition and combine interference signals from the parallel OCT imaging channels detected by the array of balanced photodetectors for collection by a data acquisition card. In various aspects, OCT systems including the disclosed photonic chips can significantly reduce the footprint and cost of OCT systems while improving their performance.

[0014] Parallel OCT imaging system and method

[0015] In various aspects, the disclosed photonic chips provide parallel imaging beams to improve OCT imaging speed while maintaining resolution and sensitivity. In various aspects, a parallel optical coherence tomography (SDM-OCT) system according to the present disclosure splits an imaging beam on a sample arm to simultaneously illuminate multiple physical locations on a sample. In some embodiments, a single sample arm may be used. Each beam is optically delayed by the SDM-OCT system, and signals from different physical locations are detected at different frequency bands (i.e., imaging depths) as an image is formed. Advantageously, this enables parallel detection of signals from multiple imaging points, thereby dramatically improving OCT imaging speed while maintaining system resolution and sensitivity. In various aspects, the SDM-OCT system may utilize commercially available light sources.

[0016] 1 illustrates a non-limiting, exemplary embodiment of an SDM-OCT system 100 that utilizes a tunable light source (e.g., a swept-source laser). The SDM-OCT system 100 may generally include, but is not limited to, a swept-source laser 102 or other light source, a first optical device 104 such as an optical coupler including a 5 / 95 optical coupler, a second optical device 106 such as a 20 / 80 optical coupler, a reference arm R that defines a first optical path (i.e., reference channel), a sample arm S that defines a second optical path (i.e., sampling channel), and other components as further described herein. The reference arm R provides an optical path of a predetermined, fixed length for generating a reference signal for comparison with a reflected optical signal returned from an examination object or sample via the sample arm S, as further described herein.

[0017] In some embodiments, the light source 102 may be a wavelength-tunable, long-coherence light source to provide an optimal imaging depth range. In one embodiment, but not limited to, the coherence length may be greater than 5 mm to achieve a suitable imaging range for the SDM-OCT system 100. Commercially available vertical-cavity surface-emitting laser (VCSEL) diodes, such as, but not limited to, the SL1310V1 from Thorlabs Inc., having a center wavelength of 1310 nm, may be used as the light source for the SDM-OCT system 100. Other suitable center wavelengths may also be used. In one embodiment, the VCSEL laser may have a sweep rate of 100 kHz, a tuning range of 100 nm, and a coherence length greater than 50 mm. The laser output from the light source 102 is 37 mW. VCSEL diodes are essentially semiconductor-based devices that emit light perpendicular to the chip surface. It should be understood that other suitable light source specifications may be used for VCSEL diodes and / or other types of light sources. For example, Fourier Domain Modelocked (FDML) lasers and MEMS tunable lasers from Axsun Technologies, Santec Corporation, Exalos Inc, and Insight Photonics Inc may be used.

[0018] Referring again to FIG. 1, the light beam output from light source 102 is optically coupled to optical coupler 104 for splitting or dividing the single input light into two output light beams. Optical couplers (also known as splitters) are generally passive fiber optic devices operable to combine and distribute light from one or more input fibers to one or more output fibers. Thus, the optical energy input is split into multiple output signals that retain essentially the same characteristics as the input light. Suitable optical couplers include fiber optic couplers available from AC Photonics, Thorlabs, or other suppliers.

[0019] As shown in FIG. 1 , the 5 / 95 coupler 104 is configured to produce a 5 / 95 split of light, with 5% of the light being diverted to a Mach-Zehnder interferometer (MZI) 108, and the remaining 95% of the light being used to perform SDM-OCT imaging, as described below, to perform phase calibration of the OCT signal. In various aspects, any suitable means for performing phase calibration of the OCT signal can be used in the SDM-OCT system 100, including, but not limited to, an MZI. The SDM-OCT system 100 may incorporate any known suitable MZI, without limitation. The MZI signal generated by the MZI is acquired by a balanced detector 126 and, in one embodiment, is used to perform phase calibration of the OCT signal. In other possible embodiments, the MZI signal may be omitted if an optical clock signal is used instead to time the acquisition of the OCT signal. In various aspects, performing phase calibration of the OCT signal is not limited to any of the above-described arrangements. It should be understood that if an optical clock is used, the 5 / 95 optical coupler 104 may be omitted.

[0020] In various embodiments, any suitable optical splitting or splitting of an input light beam, representing a percentage of the incident beam, may be used in an SDM-OCT system without limitation, depending on the intended application and system parameters. Therefore, the present invention is not expressly limited to the optical splitting or splitting ratios disclosed herein; these optical splitting or splitting ratios merely represent some of the many possible designs for the coupler. Those skilled in the art will understand that the optical splitting ratio is determined by how much light is directed into each of the sample and reference arms. It is desirable to apply as much force as possible to the sample while keeping the sample force within a safe range. Meanwhile, sufficient force is required in the reference arm to achieve shot-noise-limited sensitivity.

[0021] 1, the 95% portion of the light that passes through the 5 / 95 optical splitter 104 is transmitted to the 20 / 80 optical splitter 106. In this embodiment, the 20 / 80 optical splitter directs 20% of the input light to the reference arm R (reference channel) and 80% of the light to the sample arm S (detection channel). In other embodiments, a 10 / 90 optical splitter may be used, directing 10% of the input light to the reference arm R (reference channel) and 90% of the light to the sample arm S (detection channel).

[0022] In the reference arm R, input light to the reference arm enters the circulator 110. In various embodiments, an optical circulator is a three-port optical fiber device used to separate optical signals traveling in opposite directions within an optical fiber. Light entering one port (including the incident light and the reflected light traveling in the opposite direction) exits the adjacent port. As shown in FIG. 1 , input light entering port 1 of the optical circulator 110 is directed through port 2 to a collimator lens 112, and the collimated beam is reflected by a reference mirror 114. The reflected reference beam returns to port 2 of the circulator 110 through the collimator lens 112 and exits the circulator 110 through port 3. The light exiting port 3 of the circulator 110 is split into multiple reference beams via an optical splitter 117. Each of the multiple reference beams is directed to a corresponding 50 / 50 optical coupler 132a, 132b, 132c, 132d and combined with the multiple sampling beams to generate an interference signal, as described herein.

[0023] 1 , light directed into the sample arm from 20 / 80 beam splitter 106 is split into multiple sampling beams by optical splitter 116. Each sampling beam passes through a corresponding optical delay 118a, 118b, 118c, 118d and enters port 1 of optical circulators 120a, 120b, 120c, 120d. Optical circulators 120a, 120b, 120c, 120d direct the sampling beams through their respective ports 2 to fiber array 122. The sampling beams pass through fiber array 122, are collimated by collimator 124, and then collected at multiple different spots or sampling locations across the surface of sample 130 using scan lens 140.

[0024] The optical splitter 116, in one embodiment, may be an optical fiber splitting device, and at the output from the device, the sampling beam may be split into at least two or more sampling beams. In one exemplary embodiment, but not limited to, the sample arm light beam may be split via a 1x8 optical splitter and transmitted to eight different optical fibers forming the sampling optical fiber array 122. Each optical fiber of the sampling fiber array 122 represents a sample position S1, S2, S3, ... Sn in the sample or specimen, where n = sample position number. Note that only four optical fibers are shown in FIG. 1 for simplicity and clarity.

[0025] It should be noted that optical splitter 116 may be used to split or divide the incident sampling light into more or less than eight output optical fibers, depending on the intended sampling application, the number of desired sample locations, and other factors. Similarly, optical splitter 117 may be used to split or divide the incident reference light into more or less than eight output optical fibers, depending on the intended sampling application, the number of desired sample locations, and other factors. Thus, the present invention is not limited to a particular number of sampling or reference optical fibers in sampling fiber array 122 or the number of sampling locations (S1...Sn). In various embodiments, optical splitters 116 and 177 split or divide the incident light into 2, 4, 8, 16, 32, 64, 128, 256, or more beams. Numerous variations and configurations are possible.

[0026] Referring again to FIG. 1 , the sample 130 can be simultaneously scanned by the sampling light from the fiber array 122 using the galvanometer scanning mirror 138. The sampling light from the fiber array may be focused into parallel sampling beams using any suitable optical elements, including, but not limited to, a collimator lens 124 disposed between the fiber array 122 and the galvanometer scanning mirror 138, and a scan lens disposed between the galvanometer scanning mirror 138 and the sample 130, as shown in FIG. 1 . The galvanometer scanning mirror 138 comprises a galvo motor with a diagonally positioned, rapidly vibrating or oscillating (e.g., up and down) mirror driven by a motor shaft (not shown). The sampling light beams from the fiber array 122 are independently transmitted and scanned across the surface of the sample 130 by the galvanometer scanning mirror 138, thereby generating discrete, independent illuminated sampling spots or locations, each corresponding to one of the output ports. The scanning mirror 138 may project the sampling beam onto the sample in any suitable pattern to capture the desired image information. Other variations and types of scanning devices may be used without limitation. In some non-limiting examples, the scanning mirror 138 may be a Cambridge Technologies Model 6215H or a Thorlabs GVS102.

[0027] 1, the simultaneously returned reflected sample optical signals from each sampling position on sample 130 are transmitted through scan lens 140, scanning mirror 138, collimator lens 124, and fiber array 122 to second ports of optical circulators 120a, 120b, 120c, and 120d, which direct the reflected sample beams to corresponding 50 / 50 optical couplers 132a, 132b, 132c, and 132d, which combine the reflected sample beams with the multiple reference beams output from optical splitter 117 to generate interference signals.

[0028] Both the reflected interference signals output from the OCT via couplers 132a, 132b, 132c, and 132d and the interference signals generated by MZI 108 are detected by dual-balanced detectors 128 and 126 (e.g., PDB480C-AC, 1.6 GHz, Thorlabs Inc.), respectively, and their outputs are simultaneously acquired by a dual-channel high-speed data acquisition card 134 (e.g., ATS 9373, Alazar Technologies Inc.). The acquired signal data from data acquisition card 134 is continuously streamed to the memory of computer 136 or to memory accessible to another suitable processor-based device or PLC (programmable logic controller) via an appropriately configured port. The signal data may be stored in memory for further processing, display, export, etc.

[0029] As used herein, the term "computer" 136 refers to any suitable computer or server device having a central processing unit (CPU), microprocessor, microcontroller, or other computational data processing device or circuitry configured to execute computer program instructions (e.g., code) and process signal data acquired from the data acquisition card 134. This includes, for example, but is not limited to, desktop computers, personal computers, laptops, notebooks, tablets, and other processor-based devices having suitable processing power and speed. The computer 136 may include all the usual accessories associated with such devices, including, but not limited to, a suitably programmed processor, memory device(s), power supply, video card, visual display device or screen (e.g., for a graphical user interface), firmware, software, user input devices (e.g., keyboard, mouse, touchscreen, etc.), wired and / or wireless output devices, and wired and / or wireless communication devices (e.g., Ethernet, Wi-Fi, Bluetooth, etc.) for transmitting captured sampled images. Accordingly, the present invention is not limited by any particular type of processor-based device.

[0030] The memory may be any suitable non-transitory computer-recordable medium, such as any suitable volatile or non-volatile memory, including, but not limited to, random access memory (RAM) and its various varieties, read-only memory (ROM) and its various varieties, USB flash memory, and magnetic or optical data storage devices (e.g., internal / external hard disks, floppy disks, magnetic tape, CD-ROMs, DVD-ROMs, optical disks, ZIP® drives, Blu-ray disks, etc.), which can be written to and / or read by a processor operatively connected to the medium.

[0031] Furthermore, it should be understood that various aspects of the present embodiments may be implemented in software, hardware, firmware, or a combination thereof. The computer programs described herein are not limited to any particular embodiment and may be implemented in an operating system, an application program, a foreground or background process, a driver, or any combination thereof, and run on a single computer or server processor, or on multiple computer or server processors.

[0032] It should be noted that the optical paths and optical couplings between components shown and described herein may be achieved by any suitable means, including, for example, but not limited to, optical cables or optical fibers, relays, transmission in open space (e.g., air or other medium without physical contact between components), other optical transmission technologies currently available or to be developed, and any combination thereof. Thus, the present invention is not limited to any particular optical coupling means, and many variations are possible. In one embodiment, optical fibers may be used to optically couple components other than lenses, mirrors, and / or objects or samples.

[0033] SDM-OCT photonic chip

[0034] In various embodiments, at least some of the elements of the SDM-OCT system 100, or functional equivalents thereof, are replaced by a photonic chip. FIG. 2 is an illustration of a photonic chip-based SDM-OCT system 100a in one embodiment, including a swept-source laser 102 or other light source optically coupled to an integrated photonic chip 200 configured to perform at least some of the tasks associated with parallel SDM-OCT imaging as described herein. Furthermore, the integrated photonic chip 200 is operably coupled to a series of optical elements arranged to direct and / or scan one or more sampling beams to and from the sample 130, as described above. As shown in FIG. 2, the series of optical elements may include a collimator lens 124, a scanning mirror 138, and a scan lens 140 in one embodiment. The integrated photonic chip may further be operably coupled to a high-speed data acquisition card 134 and a computer 136, which may receive and store detected interference signals based on the reference and sampling beams, as well as an integrated MZI (not shown).

[0035] A schematic layout of a silicon-based photonic chip 200a in one embodiment is shown in FIG. 3. The photonic chip 200a includes a substrate that includes two parallel, opposing major surfaces having a thickness T measured therebetween and four perpendicular sides defining the perimeter of the chip, and in one embodiment, has a generally rectangular prism or cubic configuration. The substrate is formed from a material having an appropriate refractive index. In some embodiments, the substrate may have a thickness of approximately 1-2 mm. However, other thicknesses may be employed for the substrate without limitation. In various other embodiments, the substrate may have a thickness of 0.25 mm-0.75 mm, 0.5 mm-1 mm, 0.75 mm-1.25 mm, 1 mm-1.5 mm, 1.25 mm-1.75 mm, 1.5 mm-2 mm, 1.75 mm-2.25 mm, 2 mm-2.5 mm, 2.25 mm-2.75 mm, or 2.5 mm-3 mm.

[0036] The substrate of the photonic chip 200a may be made of any suitable single material or multi-layered and composite combination of materials conventionally used to construct photonic chips with waveguides, without limitation. Non-limiting examples of materials suitable for fabricating the photonic chip 200a include indium phosphide (InP), lithium niobate (LiNbO), silicon nitride (SiN), gallium arsenide (GaAs), silicon, and silicon-on-insulator (SOI). In one exemplary embodiment, the substrate of the photonic chip 200a comprises silicon nitride.

[0037] As another non-limiting example, the photonic chip 200a may be fabricated from an SOI substrate. An SOI chip typically consists of a silicon (Si) base layer, an intermediate silicon dioxide (SiO2) insulator layer, and a thin top crystalline silicon layer that is typically thinner than the insulator layer. The top silicon layer, which guides the light beam or wave, has a refractive index of n=3.45, and the SiO2 insulator layer has a refractive index of n=1.45.

[0038] Referring again to FIG. 3 , the photonic chip 200a is patterned with a waveguide structure having an array or multiple interconnected branching waveguides, including, but not limited to, a branching on-chip waveguide channel 314 that splits the sample signal S1 into multiple channels, a waveguide channel 324 that directs the sample signal to and from the sample, and a waveguide channel 328 that directs the reflected optical signal S2 from the sample to an interferometer for detection, as described in additional detail below. In various embodiments, the waveguides can be configured to function as waveguide channels, which are configured to form on-chip photonic beam splitters and optical time delay units or regions. The waveguide channels direct an incident beam onto the on-chip 200a and cause it to propagate and follow the optical path shown through the chip, thereby advantageously allowing for the creation of channels of different lengths in the time delay region that creates an optical delay between channels in a parallel OCT system.

[0039] The patterned waveguide channels may be formed in the substrate of chip 200a using any known conventional semiconductor fabrication technique or method known in the art, without limitation. In one illustrative and non-limiting example, the waveguide channels may be formed by doping the substrate using methods well known and used in the art for semiconductor fabrication. Doping includes processes such as diffusion and ion implantation that introduce dopant elements into selected regions of a silicon substrate to form the desired waveguide pattern. The doped channels have a first refractive index that is different from the refractive index of the base silicon material, thereby causing the optical signal or light wave to follow the doped channel pattern. However, other semiconductor fabrication techniques used in silicon photonics may also be used in other embodiments, without limitation.

[0040] Other non-limiting examples of suitable semiconductor methods that may be used to form the waveguide channels include a combination of photolithography or deep UV (ultraviolet) lithography to define the desired waveguide channel pattern, followed by selective etching of the Si top layer in the case of an SOI chip to form the waveguides. The relatively large difference in refractive index between the SiO2 insulator layer (n=1.45) and the Si top layer (n=3.45), as discussed above, confines electromagnetic fields to the Si top layer, allowing electromagnetic optical signals or waves in the optical spectrum to travel within the waveguide channels of the photonic chip 200a.

[0041] 3, chip 200a includes an input port 302 formed in one of its first side surfaces that couples directly to an input optical fiber operably coupled to a light source. Chip 200a further includes a plurality of sampling beam ports 304 formed in its other side surface. In various other embodiments, input port 302 and sampling beam ports 304 may be formed in any two different side surfaces of photonic chip 200a, depending on the placement of these ports desired in the scanning device.

[0042] 3, chip 200a further includes a detector port 306 formed in a surface of a third side of chip 200a that couples the interference signal output from the interferometer directly to a balanced detector array (not shown) located external to chip 200a. Chip 200a further includes an MZI port 308 formed in a surface of a side of chip 200a that couples the interference signal output from the on-chip MZI directly to a balanced detector array (not shown) located external to chip 200a.

[0043] In various aspects, the side of chip 200a selected for input port 302, sampling beam port 304, detector port 306, and MZI port 308 may vary, with the goal of efficient use of chip space to minimize chip size and / or optimize placement relative to the physical device or equipment into which the chip is integrated. Thus, the above configurations are not limiting of the invention, and the illustrated embodiment illustrates one of many possible configurations.

[0044] Referring again to FIG. 3 , input light is split by splitter 316 into MZI branch 318 and OCT branch 320. MZI branch 318 provides input light to on-chip MZI 322, which is used to perform precise phase calibration of the OCT image signal, as described above. Light provided through OCT branch 320 is split by splitter 310 into a reference arm and a sample arm. The sample arm uses sampling beam S1 as input light and sends it to an on-chip splitter and time delay formed by a custom-configured multi-branch waveguide structure created using waveguide channels. In some embodiments, splitter 310 is a 50:50 splitter that directs equal portions of the light provided through OCT branch 320 into the reference arm and the sample arm. In other embodiments, splitter 310 may direct a larger or smaller portion of the light provided through OCT branch 320 into the reference arm relative to the portion directed into the sample arm. In various other aspects, the splitter 310 may be a 5:95 splitter, a 10:90 splitter, a 15:85 splitter, a 20:80 splitter, a 25:75 splitter, a 30:70 splitter, a 35:65 splitter, a 40:60 splitter, a 45:55 splitter, a 50:50 splitter, a 55:45 splitter, a 60:40 splitter, a 65:35 splitter, a 70:30 splitter, a 75:25 splitter, an 80:20 splitter, an 85:15 splitter, a 90:10 splitter, or a 95:5 splitter.

[0045] As shown in FIG. 3, two rows of 1×2 photonic waveguide splitters 312 formed by a plurality of branched on-chip waveguide channels 314 are used to evenly and progressively split the incoming sampling light S1 in each row from an initial unique beam or channel into eight final sample beams or channels. Each waveguide splitter is formed by a branch of a waveguide that splits the input sampling beam S1 equally (i.e., 50:50) into two output sampling light beams. This light beam splitting is conveniently performed sequentially in each of the three rows of waveguide splitters to create eight output sampling beams, as shown in FIG. 3. In various other embodiments, the photonic chip 200a may include fewer or more rows, including, but not limited to, a single splitter row (e.g., a 1×8 splitter in this example) used to split the sampling light S1 into the desired number of sampling beams for scanning the sample. The number of splitter rows used is not a limitation of the present invention and may, in some embodiments, be determined by the shape and / or size of the photonic chip 200a desired for a given application. Furthermore, it should be noted that other embodiments may use more or fewer than eight sampling beams or channels as desired, and the present invention is not expressly limited to the eight-beam prototypical embodiment described herein. In various embodiments, the row or rows of splitters may split or divide the incident light into 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 128, 256, or more sample beams.

[0046] Each sampling beam propagates through a separate waveguide channel 324 passing through the chip 200a, forming multiple output beams or channels that exit the photonic chip 200a through multiple sampling beam ports 304 densely packed on one side of the chip's substrate, as shown in FIG. 3 . In the photonic chip 200a, a physical length (optical delay) difference ΔL between each of the eight waveguide channels 324 is introduced by configuring different termination path lengths or channel lengths for each channel between the photonic splitter in the third row of the three-row cascade and the sampling beam ports 304. The temporal or optical delay introduced by varying the length of the waveguide channels 324 generates multiplexed interference signals, as described above. In various embodiments, the difference ΔL is selected to generate an optical delay between the multiple sampling beams that is shorter than the coherence length of the light source, so that signals from different physical locations are detected in different frequency bands when an image is formed.

[0047] In various other embodiments, the photonic chip may incorporate multiple detection channels, and the DAC or other device used to detect and record OCT signals may include multiple channels, with each OCT signal being directed to a dedicated channel selected from the multiple channels of the DAC or other data collection device. Without being limited to a particular theory, the use of multiple detection channels eliminates the need for different optical path lengths or optical delays for each channel to encode each channel in a multiplexed signal directed to a single channel of the DAC or other data collection device. As a result, the optical path lengths of each OCT channel may be matched to one another in a known pattern or may be randomly varied without affecting the operation of the photonic chip using multi-channel detection.

[0048] In some embodiments, the difference in length ΔL between adjacent waveguide channels 324 may be uniform or equal, providing for transmitting sampling light of all wavelengths in different bands. In other embodiments, the delay need not be uniform. As an example, in some applications, a system designer may intentionally use non-uniform delays to optimize the scanned image returned from the sample, to accommodate the particular shape of the sample being scanned, such as when the sample has a non-uniform and / or non-planar surface shape. Thus, the present invention is not limited to a uniform difference in length ΔL between adjacent waveguide channels 324.

[0049] 3, three cascaded 1×2 (1=input, 2=output) splitters 312 are arranged to split and direct the sampling light S1 beam in a first direction (downward as shown in FIG. 3). In some embodiments, ends of waveguide channels 324 are associated with respective output ports in the time delay region of the chip, and the waveguides have different predetermined lengths to create optical time delays between the sampling beams or channels.

[0050] In various embodiments, the end of the waveguide channel 324 may follow any direction or path relative to other waveguides on the chip, without limitation. In some embodiments, the end of the waveguide channel 324 is positioned generally perpendicular to the waveguide channel 314 in the splitter region, as shown in FIG. 3 . In other embodiments, the incident sampling light S1 following the waveguide path in the time delay region travels generally perpendicular to the sampling light path in the splitter region, advantageously conserving space and minimizing size on the chip 200a, thereby enabling the creation of extremely compact photonic splitter and time delay units. The term “generally” is used to mean that the sampling light S1 in the splitter region does not necessarily travel perfectly perpendicular to the sampling light in the time delay region as it travels through the curved and angled portions of the individual photonic splitters 312; rather, the predominant flow of sampling light through these regions is perpendicular to each other in this non-limiting embodiment. In other embodiments, the flow of sampling light may be oblique or parallel to one another in the splitter region and the time delay region, and therefore the present invention is not limited to the flow of sampling light through chip 200a as shown in FIG.

[0051] It should be understood that in other embodiments beyond the prototype described above, the number of waveguide channels, the length or delay difference between channels, the output spacing, the polishing angle, the chip dimensions, and the waveguide configuration may vary. Furthermore, the splitter formed by the waveguide channels may split the incident beam in any suitable ratio ranging from approximately 5:95 to 95:5. In various other aspects, the splitter formed by the waveguide channels may split the incident beam in ratios of 5:95, 10:90, 15:95, 20:95, 25:95, 30:95, 35:95, 40:95, 45:95, 50:95, 55:95, 60:95, 65:95, 70:95, 75:95, 80:95, 5:95, or 95:5. Therefore, the present invention is not expressly limited to the above-described design and quoted values ​​of these parameters in the prototype demonstration system. Accordingly, other embodiments may differ in these respects and are not intended to limit the invention.

[0052] Generally, when the photonic chip 200a is used to split light from a single fiber into N sampling channels as described above, the intensity of each sampling channel is approximately 1 / N of the input intensity. This allows for an even distribution of light to all output channels of the photonic chip for sampling. If the reflected sampling light is collected and passed back through three photonic splitter cascades to return from the sample, only approximately 1 / N of the sampling beam intensity is returned, generating the OCT signal described above. This insertion loss is proportional to the number of channels into which the photonic chip 101 splits the light.

[0053] To reduce the insertion loss of the reflected sampling beam S2, the sampling beam S1 is split only on its first pass through the photonic chip 200a to the sample. The back-reflected light from the sample results in significantly reduced loss by reducing the number of on-chip optical splitters through which the light passes. Referring again to FIG. 3, the reflected optical signal S2 returning from the sample during the sampling process performed to generate a digitized image of the sample does not pass through the two rows of photonic splitters 312. Instead, it passes through only one row of 2×2 couplers or splitters 326 (2 = input, 1 = output), shown within the rectangular box. The reflected sampling beam S2 passes through a dedicated waveguide channel 328 (shown by a dotted line in FIG. 3) and interferes with the reference light R1 from the reference arm in the interferometer array. In this configuration, the top two rows of optical couplers or splitters 312 (each row introducing a 3 dB loss) are bypassed to avoid optical loss.

[0054] Referring again to Figure 3, interference regions are patterned on chip 200a to receive reference optical signals R1 that interfere with reflected optical signal S2 received from a sampling splitter region that collects reflected light returning from the sample. The single input reference optical signal R1 is split into four reference optical signals R1 by patterning reflected optical waveguide channels 328 with an appropriate number of branches, as shown in Figure 3. In one embodiment, all reference optical R1 waveguide channels may have the same optical path length, while sampling optical waveguide channels 324 have different optical path lengths to generate optical time delays.

[0055] In other embodiments, all of the sampling light S1 waveguide channels may have the same optical path length, while each of the reference light R1 waveguide channels 330 may have a different optical path length similar to the optical delay between the sampling light S1 waveguide channels described above. In various other aspects, a combination of sample and reference arm waveguide layout designs may be used to generate the same differential optical path length delay between different interference signals originating from different imaging channels. The optical path difference is used to shift the frequencies of the interference signals from the different imaging channels to different frequency bands corresponding to different depth ranges within the acquired OCT image. Therefore, the present invention is not limited to having the same optical path length for either the sample arm or the reference arm. The interference signals from different channels are formed in different frequency bands when the optical path difference between the individual sample and reference arms is unique. Because all interference signals are in different frequency bands, a single photodetector may be used to simultaneously detect all signals in parallel.

[0056] FIG. 4 is a schematic diagram of photonic chip 200b in another embodiment. The configuration of elements of photonic chip 200b shown in FIG. 4 is substantially similar to photonic chip 200a shown in FIG. 3 with respect to input port 302, sampling beam port 304, detector port 306, and MZI port 308, as well as the configuration of light guides and splitters for sample arm, interferometer array, and MZI 322. In various embodiments, photonic chip 200b further includes one or more reference arm ports 402 configured to direct light to an external / free-space reference arm (not shown) via waveguide 319 and to direct light from the external / free-space reference arm via waveguide 321. In various embodiments, the external reference arm may include a collimator and a reflecting mirror similar to those shown in FIG. 1 (see collimator 112 and reference mirror 114) and described above. In other aspects, the external reference arm may include additional optical elements, including but not limited to optical splitters, delays, and any other optical elements suitable for a reference arm without any limitation. In some aspects, an external reference arm including free space optics may be used to perform dispersion matching with the sample arm.

[0057] FIG. 5 is a schematic diagram of a photonic chip 200c according to an additional embodiment. The configuration of elements in the photonic chip 200c shown in FIG. 5 is substantially similar to the photonic chip 200a shown in FIG. 3, further incorporating Fabry-Perot-Bragg gratings (FPBGs) in both the OCT (interferometer array) and MZI circuits. In some embodiments, the FPBGs provide registration of the OCT and MZI signals. In other embodiments, at least two Fabry-Perot-Bragg gratings may be integrated into either the OCT channel or the MZI channel to minimize phase jitter caused by the laser source. FIG. 6 is a schematic diagram of a photonic chip 200d substantially similar to the photonic chip 200c of FIG. 5, further including an external / free-space reference arm similar to the external reference arm shown in the photonic chip 200b of FIG. 4.

[0058] FIG. 7 is a schematic diagram of a photonic chip 200e according to an additional embodiment. The configuration of elements of the photonic chip 200e shown in FIG. 7 is substantially similar to that of the photonic chip 200c shown in FIG. 5, and further includes additional on-chip photodetectors 702a and 702b operably coupled to the outputs of the MZI arms and an additional on-chip photodetector array 704 operably coupled to the output of the interferometer array. All photodetectors are indicated by black boxes in FIG. 7. As shown in FIG. 7, the photodetectors 702a and 702b operably coupled to the MZI arms are operably coupled to a DAC or k-clock to facilitate precise phase calibration of the OCT image signal. The photodetector array 704 operably coupled to the output of the interferometer array is configured to detect interference signals related to OCT. As shown in FIG. 7, the signals detected by the photodetector array 7004 may be conditioned by bandpass filters (BPFs) and mixed in a signal mixer / combiner before being passed to a DAC for subsequent multiplexed data acquisition and recording, as described above. FIG. 8 is a schematic diagram of an additional embodiment of a photonic chip 200f that is substantially similar to the photonic chip 200e of FIG. 7, with the addition of an external reference arm similar to the external reference arm of the photonic chip 200d of FIG.

[0059] FIG. 9 is a schematic diagram of a photonic chip 200g according to an additional embodiment. The configuration of elements in the photonic chip 200g shown in FIG. 9 is substantially similar to that of the photonic chip 200e shown in FIG. 7, but eliminates the bandpass filters and signal mixers / conditioners used to condition the OCT signals before recording using a single multiplexed DAC channel. Instead, the OCT signals are sent to separate, dedicated channels in the DAC, eliminating the multiplexing of the OCT signals and the associated elements of the photonic chip used to achieve the multiplexed OCT signals. Note that the separate DAC channels used to individually record the OCT signals do not record the optical delay of the OCT signals used by the previously described systems of FIGS. 1, 2, 3, 4, 5, 6, 7, and 8 due to the multiplexing of the OCT signals into a single DAC channel. FIG. 10 is a schematic diagram of a photonic chip 200h according to an additional embodiment, substantially similar to the photonic chip 200g of FIG. 9, but with the addition of an external reference arm similar to that of the photonic chip 200b of FIG. 4.

[0060] Without being limited to a particular theory, capturing and storing each OCT signal stream on an individual, dedicated DAC channel further eliminates the need to accommodate optical path length / optical delay variations for each OCT channel, as described above. In various embodiments, photonic chips 200g and 200h that include OCT signal capture using multi-channel DACs are compatible with OCT channels that are relatively matched in optical path length or with OCT channels that have different optical path lengths, since each OCT channel is captured and stored individually in parallel.

[0061] The definitions and methods set forth herein are provided to more clearly define the present disclosure and to guide those of ordinary skill in the art in the practice of the present disclosure. Unless otherwise specified, terms are to be understood in accordance with conventional usage by those of ordinary skill in the relevant art.

[0062] In some embodiments, numerical values ​​expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like, used to describe and claim particular embodiments of the present disclosure are to be understood as being optionally modified by the term "about." In some embodiments, the term "about" is used to indicate that a numerical value includes the standard deviation of the mean for the device or method being employed to measure that value. In some embodiments, the numerical parameters set forth in the written description and accompanying claims are approximations that may vary depending on the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the present disclosure are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. The numerical values ​​set forth in some embodiments of the present disclosure may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. The recitation of ranges of values ​​herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated herein as if it were individually set forth herein. The description of discrete values ​​should be understood to include ranges between the values.

[0063] In some embodiments, the terms "a," "an," "the," and similar references used in the context of describing particular embodiments (particularly in the particular context of the claims below) should be construed to cover both the singular and the plural, unless expressly stated otherwise. In some embodiments, the term "or" as used herein, including the claims, is used to mean "and / or" unless expressly indicated to refer to alternatives only or unless the alternatives are mutually exclusive.

[0064] The terms "comprise," "have," and "include" are open-ended linking verbs. One or more forms or tenses of these verbs, such as "comprises," "comprising," "has," "having," "includes," and "including," are also open-ended. For example, a method that "comprises," "has," or "includes" one or more steps is not limited to having only those one or more steps and may include other, unlisted steps. Similarly, a composition or device that "comprises," "has," or "includes" one or more features is not limited to having only those one or more features and may include other, unlisted features.

[0065] All methods described herein may be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Any examples provided herein with respect to specific embodiments, or the use of exemplary language (e.g., "such as"), are intended merely to more clearly explain the disclosure and do not limit the scope of the disclosure as set forth in any other claims. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the disclosure.

[0066] Groupings of alternative elements or embodiments of the disclosure disclosed herein are not to be construed as limitations. Members of each group may be referenced and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group may be included in or deleted from a group for reasons of convenience or patentability. When such inclusions or deletions are made, the specification shall be deemed to include the group as modified so as to satisfy the group description set forth in all Markush format used in the appended claims.

[0067] All publications, patents, patent applications, and other references cited in this application are herein incorporated by reference in their entirety for all purposes to the same extent as if each individual publication, patent, patent application, or other reference was specifically and individually indicated to be incorporated by reference in its entirety for all purposes. The citation of a reference herein should not be construed as an admission that it is prior art to the present disclosure.

[0068] Although the present disclosure has been described in detail, it will be apparent that modifications, variations, and equivalents are possible without departing from the scope of the present disclosure as defined in the appended claims. Furthermore, it should be understood that all examples in this disclosure are provided by way of non-limiting examples.

Claims

1. 1. An integrated photonic chip for parallel optical coherence tomography scanning, comprising: a) an optical input port configured to receive a single input beam from an external light source; b) a plurality of optical output ports configured to transmit a plurality of sampling beams from the tip to a sample and to receive a plurality of sampling beams reflected from the sample; c) a first branch waveguide including an MZI arm, a reference arm, and a sampling arm, and configured to split a single incident beam into an MZI input beam transmitted by the MZI arm, a reference input beam transmitted by the reference arm, and a sampling input beam transmitted by the sampling arm; d) an MZI waveguide structure configured to receive the MZI input beam and then generate an MZI interference signal indicative of the phase of the input beam; e) a multi-branch waveguide structure formed in a substrate and including a plurality of interconnected waveguide channels defining a splitter region configured to optically couple the sampling input beam of the sample arm to each of the output ports and an interferometer region configured to define a plurality of optical interferometers; f) a pair of MZI output ports operatively coupled to the MZI waveguide structure and configured to transmit the MZI interference signal to at least one balanced detector; g) an array of OCT output ports operatively coupled to the optical interferometer and configured to transmit OCT interference signals externally to the array of balanced detectors; (i) the waveguide channels of the splitter region are configured to define a plurality of photonic splitters that split a single incident sampling beam received at the input port into a plurality of sampling beams at the output ports; (ii) a portion of the waveguide channel between the photonic splitter and the output port has a different predetermined length to create an optical time delay between each of a plurality of sampling beams; (iii) the optical interferometer is positioned to receive the reference light and a plurality of reflected optical signals returning from the sample, and is configured to combine the reflected optical signals with the reference light to generate a plurality of the OCT interference signals that are emitted toward the array of OCT output ports.

2. The chip of claim 1 , wherein the at least one balanced detector comprises at least one internal balanced detector or at least one external balanced detector.

3. further comprising a pair of reference arm input / output ports; The chip of claim 1 , wherein a pair of the reference arm input / output ports are operatively coupled to an external reference arm, the external reference arm configured to generate the reference input beam.

4. a) a first balanced photodetector integrated between the MZI waveguide structure and the MZI output port; 10. The chip of claim 1, further comprising: b) an array of balanced photodetectors embedded between a plurality of said optical interferometers and said array of OCT output ports.

5. a) a pair of MZI Fabry-Perot Bragg Gratings (FPBGs) integrated into each output of a pair of MZI output ports and configured to minimize phase jitter generated by the external light source; b) a plurality of interferometric FPBGs integrated into an output of each of the plurality of optical interferometers and configured to register the OCT interference signals transmitted from different optical interferometers.

6. each balanced photodetector in the array of balanced photodetectors configured to direct a stream of the detected OCT interference signal to one channel of a multi-channel DAC; 6. The chip of claim 5, wherein each channel of the multi-channel DAC is configured to receive one stream of the detected OCT interference signals from one balanced photodetector of the array of balanced photodetectors.

7. The chip of claim 5 further comprising an array of bandpass filters operatively coupled to the array of balanced photodetectors.

8. further comprising a signal mixer operatively coupled to the array of bandpass filters; 8. The chip of claim 7, wherein the signal mixer is configured to combine filtered signal streams from the array of bandpass filters into a single multiplexed signal stream for forwarding to a single channel of a DAC.

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