Apparatus and method for high speed and long depth range imaging using optical coherence tomography

Abstract

An exemplary apparatus may be provided that may include a laser arrangement configured to provide laser radiation and including an optical cavity. The optical cavity may include a first arrangement of a dispersion light guide having a first side and a second side and configured to (i) receive at least one first electromagnetic radiation at the first side so as to provide at least one second electromagnetic radiation, and (ii) receive at least one third electromagnetic radiation at the second side so as to provide at least one third electromagnetic radiation at the second side so as to provide at least one second electromagnetic radiation. So as to provide at least one fourth electromagnetic radiation. The first side and the second side are different from each other, and the second radiation and the third radiation are related to each other. The optical cavity may also include an active optical modulator second arrangement, which may be configured to receive and modulate the fourth radiation so as to provide the first electromagnetic radiation to the first arrangement.

Description

This application is a divisional application filed again for the divisional application 202210142915.0. 202210142915.0 is a divisional application of the invention patent application with PCT international application number PCT / US2017 / 017664, international application date 2017-02-13, application number 201780023073.4 entering the Chinese national phase, and titled "Device and method for high-speed and long depth range imaging using optical coherence tomography". CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is related to and claims priority to U.S. Patent Application Serial No. 62 / 294,822 filed on February 12, 2016 and U.S. Patent Application Serial No. 62 / 310,365 filed on March 18, 2016, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to optical imaging systems and, more particularly, to apparatus and methods relating to high speed imaging of three-dimensional scattering properties of a sample located within a large imaging volume, and especially to rapid depth resolved imaging of a sample having a geometry that causes the distance of each region of the sample relative to the imaging system to vary across the sample and over time. Background Art

[0003] Optical coherence tomography (OCT) provides cross-sectional images of biological specimens with resolution on the scale of a few microns to tens of microns. Conventional OCT, known as time-domain OCT ("TD-OCT"), can use low-coherence interferometry techniques to achieve depth ranging. In contrast, Fourier domain OCT ("FD-OCT") techniques can use spectroscopic radar techniques to achieve depth ranging. FD-OCT techniques have been shown to facilitate higher imaging speeds through improved signal-to-noise performance and elimination of the mechanically scanned interferometer reference arm.

[0004] FD-OCT systems typically operate by separating a light source into a sample beam and a reference beam. The sample beam can be directed to the sample to be imaged, and the reflected light from the sample is recombined with the light from the reference beam (i.e., returned from the reference arm), resulting in an interference signal that can provide information about, for example, the structure, composition, and state of the sample. The light in the sample path and / or the light in the reference path can be modified by, for example, a phase modulator or frequency shifter that changes the characteristics of the interference and enhances the information content of the signal or makes the signal easier to detect. The FD-OCT system can sample the interference signal as a function of wavelength.

[0005] In one exemplary embodiment of an FD-OCT system, an interference signal as a function of wavelength can be obtained by using a light source having an output wavelength that is swept, varied, or stepped as a function of time. Thus, detection of the interference signal as a function of time can produce an interference signal as a function of wavelength. This exemplary embodiment can be referred to as an optical frequency domain imaging ("OFDI") technique.

[0006] In another exemplary embodiment of the FD-OCT system, the interference signal as a function of wavelength can be obtained by using a broadband light source and a spectral dispersion unit or spectrometer that spatially separates the recombined sample light and reference light according to wavelength so that a one-dimensional or two-dimensional camera can sample the signal as a function of wavelength. This exemplary embodiment may be referred to as spectral domain OCT technology. In both exemplary embodiments, the detected interference signal as a function of wave number k (k=1 / wavelength) can be used to provide information about the scattering depth distribution in a turbid or semi-turbid sample or a transparent sample. Such information may include information about, for example, the structure, composition, state, flow, and birefringence of the sample.

[0007] Scatterers at a given depth can cause modulation of the amplitude or polarization of the interference signal. The frequency of this modulation in wavenumber space can be related to the location of the scattering or the time delay of the light reflected from the scattering relative to the time delay of the light in the reference arm. Scatterers located at a depth that causes no net time delay in the reflected signal relative to the reference arm light can cause an interference signal that may not be modulated with wavenumbers. As the location of the scatterer moves from this zero delay point, the amplitude of the frequency can increase. In order to image over a large delay window, for example, to detect and localize reflections within a large time delay window, the interference signal can often be sampled in wavenumber space with a sufficiently high resolution to facilitate clear detection of the range of modulation frequencies associated with the large delay window.

[0008] To accommodate sampling at higher resolutions in wavenumbers, faster and faster analog-to-digital converters ("ADCs") may be used in OFDI systems, and higher and higher pixel count cameras may be used in SD-OCT systems. In both OFDI and SD-OCT systems, the increased amount of data resulting from imaging over a large area may generally result in the use of higher and higher bandwidth data transmission buses and data storage units.

[0009] Optical domain subsampling can be used to increase the depth range of an OFDI or SD-OCT system without increasing the number of spectral measurements performed. Additionally, optical domain subsampling can be used to increase imaging speed without increasing the electrical bandwidth of the imaging system. In this way, an optical domain subsampling OCT system can interrogate a greater amount of physical space with a given number of measurements than an FD-OCT or SD-OCT system operating with the same number of measurements.

[0010] In high-speed optical-domain subsampling OCT systems, imaging across a large depth range can be performed at extremely high speeds, resulting in video-rate volumetric microscopy of samples that are not precisely positioned relative to the imaging system and that contain surfaces at varying distances to the imaging system across the field of view.

[0011] Therefore, there is a need to address and / or overcome at least some of the deficiencies described above. Overview of Exemplary Embodiments

[0012] In particular, at least some of the deficiencies of conventional systems and methods may be addressed with an exemplary apparatus that may include a laser arrangement configured to provide laser radiation and including an optical cavity. The optical cavity may include a first arrangement of dispersive optical waveguides having a first side and a second side and configured to (i) receive at least one first electromagnetic radiation at the first side to provide at least one second electromagnetic radiation, and (ii) receive at least one third electromagnetic radiation at the second side to provide at least one fourth electromagnetic radiation. The first side and the second side are different from each other, and the second radiation and the third radiation are related to each other. The optical cavity may also include a second arrangement of active optical modulators that may be configured to receive and modulate the fourth radiation to provide the first electromagnetic radiation to the first arrangement. The laser radiation may be associated with at least one of the first radiation, the second radiation, the third radiation, or the fourth radiation.

[0013] In one exemplary embodiment, the first arrangement may be a fiber Bragg grating (FBG), a chirped FBG and / or an array of FBGs. The FBG may be provided in a polarization-maintaining fiber and / or a non-polarization-maintaining fiber. The first arrangement may also be configured to cause a group delay that varies linearly with the optical frequency of the first radiation and / or the third radiation. According to another exemplary embodiment, the first arrangement may include (i) at least one first circulator that receives the first radiation and transmits the second radiation, and / or (ii) at least one second circulator that receives the third radiation and transmits the fourth radiation. The optical cavity may include at least one third arrangement of optical amplifiers, which may be configured to amplify at least one of the first radiation, the second radiation, the third radiation, or the fourth radiation. The optical amplifier arrangement may include a semiconductor amplifier, a Raman amplifier, a parametric optical amplifier, and / or a fiber amplifier. The optical cavity may also include a fourth arrangement of additional active optical modulators, which may be configured to receive and modulate the second radiation so as to provide the third electromagnetic radiation to the first arrangement. For example, the fourth arrangement of additional active optical modulators may be configured to suppress optical radiation traveling through the first arrangement, which is different from the second radiation. Additionally or alternatively, the fourth arrangement of further active optical modulators may be a further active optical amplifier arrangement.

[0014] According to further exemplary embodiments of the present disclosure, the optical cavity may include at least one fifth arrangement of optical polarizers configured to block optical radiation transmitted through the first arrangement. The optical cavity may also include a dispersion compensation arrangement and / or a fixed periodic spectral filter arrangement. The fixed periodic spectral filter arrangement may include (i) a Fabry-Perot etalon filter having a finesse between 3 and 25, and / or (ii) an optical interleaver. The Fabry-Perot etalon filter may be an air gap etalon filter.

[0015] In yet further exemplary embodiments of the invention, the laser radiation may have a wavelength that varies in time, for example continuously and / or discretely.For example, the action of the first arrangement and the second arrangement may cause the wavelength to change at a rate faster than 80 nm / microsecond.

[0016] In a further alternative embodiment, the first arrangement may include a fiber Bragg grating (FBG) provided in a polarization maintaining optical waveguide, the first radiation may be emitted along a first birefringence axis of the optical waveguide, and the third radiation may be emitted along a second birefringence axis of the optical waveguide, the first birefringence axis and the second birefringence axis being different from each other. The second electromagnetic radiation may be a reflection of the first electromagnetic radiation, and the fourth electromagnetic radiation may be a reflection of the third electromagnetic radiation.

[0017] According to yet another exemplary embodiment of the present disclosure, an exemplary device may be provided, which may include a laser arrangement configured to provide laser radiation and including an optical cavity. The optical cavity may include: a dispersive first arrangement, which may be configured to receive at least one first electromagnetic radiation to provide at least one second electromagnetic radiation; and a dispersive second arrangement, which is configured to receive at least one third electromagnetic radiation to provide at least one fourth electromagnetic radiation, but the second radiation and the third radiation are related to each other. The optical cavity may also include an active optical modulator second arrangement, which may be configured to receive and modulate the fourth radiation to provide electromagnetic radiation to the first arrangement, wherein the laser radiation is associated with at least one of the first radiation, the second radiation, the third radiation, or the fourth radiation. The laser arrangement may also include an interferometer arrangement, which is configured to generate (i) a fifth electromagnetic radiation from the laser radiation in the sample arm, (ii) a sixth electromagnetic radiation from the laser radiation in the reference arm, and (iii) an interference signal based on interference between the fifth electromagnetic radiation and the sixth electromagnetic radiation. The laser arrangement may also include a beam scanning arrangement, which is configured to scan the fifth electromagnetic radiation across at least one portion of at least one sample. The interaction between the laser arrangement, the interferometer arrangement and the beam scanning arrangement provides three-dimensional measurement of optical properties of portion(s) of sample(s).

[0018] For example, according to an exemplary embodiment, the laser arrangement may further comprise: an analog to digital acquisition arrangement configured to obtain an interference signal based on an electronic clock signal; and an electronic signal generator configured to drive the second arrangement, and the electronic clock signal may be phase locked to the electronic signal generator. The first arrangement and the second arrangement may comprise a fiber Bragg grating or a portion of the same fiber Bragg grating. The second electromagnetic radiation may be a reflection of the first electromagnetic radiation, and the fourth electromagnetic radiation may be a reflection of the third electromagnetic radiation. The laser radiation may be an optical frequency comb.

[0019] According to yet another exemplary embodiment of the present disclosure, an exemplary apparatus may be provided, which may include a laser radiation configured to generate a specific number (N) of discrete optical frequencies. The exemplary apparatus may also include: an interferometer arrangement configured to generate an interference signal from the laser radiation; and a beam scanning arrangement configured to scan at least one portion of the laser radiation across at least one portion of at least one sample. The line width of each of the discrete optical frequencies may be less than 10 GHz, and the interval between each of the discrete optical frequencies may be greater than 20 GHz. The laser radiation may step between discrete optical frequencies at a rate greater than 20 million discrete optical frequency steps per second. In another exemplary embodiment of the present invention, the laser arrangement may include a continuous fiber Bragg grating having a length greater than 2 meters, and / or a fiber Bragg grating array having a length greater than 2 meters.

[0020] According to yet another exemplary embodiment of the present disclosure, a method computer-accessible medium (e.g., having software stored on the medium to be executed by a computer) can be provided for displaying a video stream about at least one structure. For example, using this method and computer-accessible medium, four-dimensional interferometric data about different parts of at least one structure at different time points can be measured, wherein the four-dimensional data describes at least one optical property of the at least one structure. In addition, the four-dimensional interferometric data can be transformed into two-dimensional video data, and the video stream of different parts of the structure can be displayed using the two-dimensional video data. The waiting time for performing the measurement and display is less than 1 second.

[0021] The exemplary process performed by this exemplary method and computer is completed in a medical procedure, and can also enable the use of a video stream to interactively guide the procedure. Additionally, the measurement can be performed using a frequency comb light source. Alternatively or additionally, the measurement can be performed using a laser arrangement as described in the various embodiments above.

[0022] According to yet another exemplary embodiment of the present disclosure, a method computer-accessible medium (e.g., having software stored on the medium executed by a computer) can be provided for use in a medical procedure on at least one anatomical structure. Using this exemplary method and computer, single-dimensional interferometric measurement data describing at least one optical property of a structure can be measured at a rate greater than 5 megahertz. In addition, four-dimensional interferometric measurement data can be constructed from one-dimensional interferometric data about different parts of at least one structure at different time points, and the four-dimensional interferometric measurement data can be used in a medical procedure. For example, measurements can be performed using a frequency comb light source. Alternatively or additionally, measurements can be performed using a laser arrangement as described in the various embodiments above.

[0023] According to yet another exemplary embodiment of the present disclosure, a method computer-accessible medium (e.g., having software stored on the medium to be executed by a computer) can be provided for displaying a video stream about at least one structure. For example, using this method and computer-accessible medium, four-dimensional interferometric measurement data about different parts of at least one structure at different points in time can be measured, but the four-dimensional data describes at least one optical property of the structure, and the four-dimensional interferometric measurement data can be cyclically wrapped in a specific spatial dimension. Additionally, the exemplary method and computer can transform the four-dimensional interferometric measurement data into two-dimensional video data by compressing the specific spatial dimension, and use the two-dimensional video data to display a video stream of different parts of the structure.

[0024] For example, compression may include (i) locating the position of the structure surface within the four-dimensional interferometry data, and (ii) using the position to control the compression. Furthermore, the measurements may be performed using a frequency comb light source and / or a laser arrangement as described in various embodiments above.

[0025] These and other objects, features and advantages of the present disclosure will become apparent when the following detailed description of exemplary embodiments of the present disclosure is read in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other objects, features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings which show illustrative embodiments of the present disclosure, in which:

[0027] Figure 1 is an exemplary graphical representation of the relationship between frequency content and time for an exemplary wavelength stepping laser;

[0028] Figure 2 is a block diagram of an exemplary optical subsampling (OS-OCT) imaging system according to an exemplary embodiment of the present disclosure;

[0029] Figure 3 is a diagram illustrating aliasing of a depth signal in an exemplary OS-OCT system according to an exemplary embodiment of the present disclosure;

[0030] Figure 4 is a set of exemplary illustrations of annular packages imaged in an exemplary OS-OCT system according to an exemplary embodiment of the present disclosure;

[0031] Figure 5 is a set of illustrations of an imaging probe used in an exemplary OS-OCT system and exemplary images obtained for a tilted sample according to an exemplary embodiment of the present disclosure;

[0032] Figure 6 is a set of illustrations of an exemplary high-speed wavelength stepping source according to an exemplary embodiment of the present disclosure, and graphs of exemplary outputs produced thereby;

[0033] Figure 7 is a diagram of an exemplary high-speed OS-OCT imaging system according to an exemplary embodiment of the present disclosure;

[0034] Figure 8 is a diagram of an exemplary quadrature demodulation system according to an exemplary embodiment of the present disclosure;

[0035] Fig. 9 is a set of exemplary OS-OCT images obtained without and with orthogonal demodulation according to an exemplary embodiment of the present disclosure;

[0036] Fig.10 is a flow chart providing an exemplary method of quadrature demodulation and OS-OCT signal processing including techniques for correcting quadrature errors in an optical demodulator according to an exemplary embodiment of the present disclosure;

[0037] Fig.11 is a block diagram of a system for providing an exemplary timing scheme for control electronics in an exemplary OS-OCT imaging system according to an exemplary embodiment of the present disclosure;

[0038] Fig.12 is a diagram of an imaging microscope used in an exemplary OS-OCT system according to an exemplary embodiment of the present disclosure;

[0039] Fig.13 is a set of exemplary wide-field OS-OCT images according to an exemplary embodiment of the present disclosure;

[0040] Fig.14 is a set of exemplary images of the high-speed OS-OCT system;

[0041] Fig.15 is a set of exemplary images of a video sequence acquired from an exemplary high-speed OS-OCT system according to an exemplary embodiment of the present disclosure;

[0042] Fig.16 is another set of exemplary images provided by an exemplary video sequence generated by an exemplary high-speed OS-OCT system showing polarization-dependent image contrast according to an exemplary embodiment of the present disclosure;

[0043] Fig.17 is a block diagram of an apparatus for interleaving laser output pulses from adjacent A-lines to fill time gaps in the laser output, and a graphical representation of exemplary outputs from various components, according to an exemplary embodiment of the present disclosure;

[0044] Fig.18 is an exemplary illustration of a fiber Bragg grating array according to an exemplary embodiment of the present disclosure, and an exemplary graph of an output provided from one of its components;

[0045] Fig.19 is a set of diagrams of an exemplary laser source utilizing a fiber Bragg grating according to an exemplary embodiment of the present disclosure;

[0046] Fig. 20 is a set of diagrams of an exemplary laser source utilizing a continuously chirped fiber Bragg grating according to an exemplary embodiment of the present disclosure;

[0047] Fig.21is an exemplary illustration of an exemplary grating design arrangement in a fiber Bragg grating array used in a laser source according to an exemplary embodiment of the present disclosure;

[0048] Fig. 22 is a diagram of an exemplary laser source utilizing active polarization control according to an exemplary embodiment of the present disclosure;

[0049] Fig.23 is a diagram of an exemplary laser source including a frequency shifter or a phase shifter to restrict the circulation of light in a particular path according to an exemplary embodiment of the present disclosure;

[0050] Fig.24 is a diagram of an exemplary laser source including optical interleavers and deinterleavers to generate different group delays across wavelength channels (with exemplary power diagrams) according to an exemplary embodiment of the present disclosure;

[0051] Fig.25 is a diagram of an exemplary time domain detection scheme of a non-monotonic wavelength signal and its recombination in a computational arrangement prior to a Fast Fourier Transform (FFT) according to an exemplary embodiment of the present disclosure;

[0052] Fig.26 is a diagram of an exemplary system for generating additional optical frequencies from an input set of frequencies using frequency shifting (and an exemplary illustration of wavelengths) according to an exemplary embodiment of the present disclosure;

[0053] Fig. 27 is a set of graphs illustrating exemplary polarization modulated source outputs according to exemplary embodiments of the present disclosure;

[0054] Fig.28 is an exemplary illustration of a dispersive element provided by combining a set of continuously chirped fiber Bragg gratings according to an exemplary embodiment of the present disclosure;

[0055] Fig.29 is a diagram of an exemplary imaging interferometer that uses phase modulation to perform quadrature demodulation according to an exemplary embodiment of the present disclosure;

[0056] Fig.30 is a set of exemplary graphs that provide exemplary schemes for phase shifting light as a function of time and wave number to perform quadrature demodulation in accordance with exemplary embodiments of the present disclosure;

[0057] Fig.31 is a diagram of an exemplary system and exemplary acquisition of a signal into a register having a greater depth using an 8-bit digitizer and fringe averaging according to an exemplary embodiment of the present disclosure;

[0058] Fig.32is a diagram of an exemplary laser source providing modulation in a cavity, the laser source being configured to suppress light circulation in a particular path (and providing an exemplary diagram of its output) according to an exemplary embodiment of the present disclosure;

[0059] Fig.33 is a diagram of an exemplary OS-OCT system using a comb source including multiple wavelengths and a wavelength demultiplexer to spatially separate each wavelength signal prior to detection according to an exemplary embodiment of the present disclosure;

[0060] Fig.34 is a diagram of an exemplary OS-OCT laser including optical gain within a reflective dispersive element according to an exemplary embodiment of the present disclosure;

[0061] Fig.35 is a diagram of an exemplary OS-OCT laser including a polarizer and configured by a polarization controller to suppress light circulation in a particular subcavity according to an exemplary embodiment of the present disclosure;

[0062] Fig.36 is a diagram of an exemplary OS-OCT source provided by a dispersive pulse broadband laser source according to an exemplary embodiment of the present disclosure;

[0063] Fig.37 is a set of exemplary illustrations of exemplary configurations, operations / functions, and timings of exemplary OS-OCT sources according to exemplary embodiments of the present disclosure;

[0064] Fig.38 is a set of graphs providing exemplary measurements of spectral output of an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure;

[0065] Fig.39 is a set of graphs providing exemplary measurements of temporal output of an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure;

[0066] Fig.40 is a set of graphs providing exemplary measurements of coherence length of an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure; and

[0067] Fig.41 is a graph providing exemplary measurements of noise for an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure.

[0068] Throughout the drawings, the same reference numerals and characters, unless otherwise stated, are used to represent the same features, elements, components, or portions of the illustrated embodiments. Moreover, although the subject disclosure will now be described in detail with reference to the drawings, this description is done in conjunction with the illustrative embodiments. Changes and modifications may be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure and the appended claims. Detailed Description of Exemplary Embodiments

[0069] Optical domain sub-sampling OCT is hereinafter referred to as optical sub-sampling OCT (OS-OCT). In an exemplary embodiment of the present disclosure, an imaging system based on optical frequency domain imaging (OFDI) may be provided. Unlike conventional OCT systems that utilize a wavelength swept source in which the wavelength of the light source varies substantially continuously over time, OS-OCT may use a wavelength stepped source having a wavelength that varies in a stepwise manner, with the wavelength discretely jumping in wavelength-separated periods in which the wavelength is substantially constant.

[0070] Figure 1 An exemplary diagram illustrating the relationship between frequency content and time for an exemplary wavelength-stepping laser. Figure 1 This exemplary illustration of shows the output wavenumber as a function of time for an exemplary wavelength stepping source 100. The source may include an optical output 110 that may vary in wavenumber over time. A trace of an exemplary wavenumber 132 versus time 131 is provided in curve 130. The exemplary trace may be characterized by periods of stability in k of the laser 133a-133f separated by periods during which the source wavenumber is rapidly switching 135a-135f. The step size in wavenumber space may be given as Δk 134. Alternatively or additionally, the wavelengths may not necessarily be equally spaced in wavenumber, and there may be a series of Δk intervals in the source. Each of the stability periods 133a-133f may define wavenumber values ​​k_a to k_f (137a-137f) for a particular channel of the source. The stability period may occupy a variable percentage of the time interval between adjacent wavenumbers; for example, it may fill the entire time gap, and the laser may jump directly from one wavenumber to the next, or it may be a short pulse in which the laser power is turned off until the next wavenumber. The exemplary curve 130 includes 6 channels, which may be a subset of the total channel count of the source, or the source may include fewer different wave number outputs, such as, for example, two. The output power of the source is designed to produce appreciable power in each of the channels.

[0071] The power trace may be flat (as a function of wavelength) and / or may vary depending on, for example, the spectral response of the gain medium used in the source, or may be made to follow a particular profile. During times 135a-135f between wavelengths, the power of the exemplary laser source may be modulated and / or turned off. Figure 1 The wavenumber output shown in indicates monotonically increasing wavenumbers, but the wavenumbers 137a-137f can follow a non-monotonic order, such as, for example, the output wavenumbers can occur in a descending monotonic order, or in a non-monotonic order, such as, for example, in the following order: 137a, then 137d, then 137f, then 137e, then 137b, then 137c. In an exemplary embodiment of the present disclosure, the source output wavelength in the OCT imaging band can be approximately centered at 800nm, 1.0μm, 1.3μm, 1.5μm, 1.6μm, or 1.7μm. In other exemplary embodiments, it can be operated in any optical range, including those in the UV and visible bands. In another exemplary embodiment of the present disclosure, the source can output wavelengths grouped into two or more spectral regions. For example, wavelengths within 1.0μm-1.1μm can be output, and then wavelengths of 1.3-1.4μm can be output. Alternatively, an exemplary source that produces multiple wavenumber stepped outputs in each of the red, green, and blue visible spectrums may be used in accordance with exemplary embodiments of the present disclosure.

[0072] exist Figure 2 In another exemplary embodiment of the exemplary optical double sampling (OS-OCT) imaging system shown in , the wavelength step source 200 can be divided into a sample arm 220 and a reference arm 210 by a beam splitter 205. The light or other electromagnetic radiation in the reference arm 210 can be directed to a first port 240a of a composite demodulator 240. The light or other electromagnetic radiation in the sample arm 220 can be directed to the sample and collected from the sample. For example, this can be achieved by directing the sample arm light to a first port 230a of an optical circulator, which can preferentially direct the light or other electromagnetic radiation to port 230b. The light or other electromagnetic radiation from port 230b can be directed toward the sample 250 by an optical fiber 235. The optical fiber 235 can include, but is not limited to, various probes, catheters, endoscopes, and microscopes, which are known in the art, for controlling the position and other characteristics of the sample arm light on the sample. The backscattered light or other electromagnetic radiation from the sample 250 can be collected by the optical fiber 235 and returned to the port 230b of the circulator 230 and preferentially directed to the port 230c. The light or other electromagnetic radiation may then be directed to port 240b of a composite demodulator 240. Composite demodulator 240 may include, for example, optical components, a digitizer, and digital processing. For each wave number channel, the composite demodulator may be used to measure a signal associated with the interference between sample arm 220 and reference arm 210. For example, the composite demodulator may provide a complex signal S (composed of a combination of 270 and 280) corresponding to each wave number channel that is proportional to the composite reflected sample field, Where P(ki ) corresponds to wave number k i The reflected signal power, and θ(k i ) is the reference arm light and corresponds to wave number k i The complex signal S (comprising, for example, a combination of 270 and 280) may be forwarded to a data processing and recording unit 260 (which may include one or more computers or one or more processors).

[0073] In an exemplary embodiment of the present disclosure, the complex demodulator 240 may be based on a polarization-based demodulation arrangement, such as described in, for example, Vakoc, Optics Letters 31(3)362-364 (2006) U.S. Patent Publication No. 2007 / 0035743. In another exemplary embodiment of the present disclosure, a phase modulator may be placed in the reference arm 210 or the sample arm 220. The exemplary phase modulator may be provided, configured and / or constructed to induce a phase shift of, for example, π / 2 radians or 0 radians, such that two measurements may be made at each of these phase shifts for each wave number channel, thereby providing the time multiplexed in-phase and quadrature signals required to construct the complex signal S. In another exemplary embodiment of the present disclosure, the complex demodulator may be based on the use of 3×3 pairs, such as described in, for example, Choma, Optics Letters 28(22)2162-2164.

[0074] Figure 3 Depicted is a diagram illustrating aliasing of a depth signal in an exemplary OS-OCT system according to an exemplary embodiment of the present disclosure. Figure 3 As shown, the frequency conversion can be achieved by i The interference at the location is sub-sampling. Figure 3 An exemplary graph of provides the frequency of the complex signal S as a function of the delay between the sample arm and the reference arm. The solid curve 300 shows an exemplary frequency of a continuously swept wavelength source, while the dashed curve 310 shows the frequency of a complex signal S using a wave number k. i The measured frequencies are optically subsampled at the frequencies centered at zero delay 340. In the frequency range centered at zero delay 340, no conversion can be induced. At frequency ranges corresponding to delays of larger magnitudes, the frequencies can be down-converted to baseband signals. For example, frequencies that appear in the delay range 320 between +F / 5 and +3*F / 5 when a wavelength swept source is used can be down-sampled to a range of -F / 5 to F / 5 using optical subsampling. By detecting only a limited frequency range, for example, from -F / 5 to F / 5, the frequencies obtained in the range defined by the wavelength sweep source can be acquired with a reduced amount of data. arrive Characterize the signal over the entire depth.

[0075] In the above exemplary embodiment, the data processing and data storage unit 260 (see Figure 2 ) can be obtained from the complex signal array S by using the discrete Fourier transform method i Each of the generates a depth scattering distribution, which is known in the art. These exemplary distributions can be concatenated to generate an image. Figure 4 A set of exemplary diagrams illustrating circular packages imaged in an exemplary OS-OCT system according to exemplary embodiments of the present disclosure. Figure 4 As shown, a subsampled image is generated from samples spanning a greater extent than the depth range of the subsampled image. An exemplary sample arranged at an angle depicted in exemplary image 400 can be utilized, which can be acquired with an exemplary OFDI system that provides complex demodulation and, for example, without subsampling. By, for example, discarding some of the sampled data points within each A-line, a subsampled image can be generated and shown in exemplary image 410. The image depth range can be significantly reduced, and signals occurring outside the baseband can be down-converted to appear within the reduced depth range. By tiling the image, i.e., vertically concatenating copies of the image, an initial structure 420 can be identified. Using a surface search routine, a single representation of the object can be isolated from the replicated representation 430, thereby restoring an image of the sample. Note that imaging is effectively achieved within a range sufficient to encompass the tilted sample, but with a reduced amount of data corresponding to the depth range depicted in 410.

[0076] Use subsampled optical imaging to increase the effective depth range in Figure 5 is shown in the figure, Figure 5A set of illustrations of imaging probes used in an exemplary OS-OCT system and exemplary images obtained for tilted samples according to exemplary embodiments of the present disclosure are shown. The imaging instrument 500 may include an endoscope 501 that can transmit imaging light or other electromagnetic radiation from a system 502 to a sample 510 and return backscattered light or other electromagnetic radiation to the system 502. The endoscope 501 may be provided by or include the use of a single bidirectional waveguide such as an optical fiber, or alternatively may be provided by the use of two or more waveguides. One of the waveguides may propagate light or other electromagnetic radiation from the system 502 to the sample 510, and another of the waveguides may return scattered or reflected light or other electromagnetic radiation from the sample 510 to the system 502. The endoscope 501 may include, for example, a beam scanner 540 near its distal end that is capable of scanning an angle 530 of light leaving the endoscope 501. The beam scanner 540 may be based on a micro-electromechanical scanner, such as described in Kim et al., Opt. Express 15, 18130-18140 (2007). For samples oriented at an angle to the endoscope, the distance from the beam scanner 540 to the sample surface may be relatively short for one angle, such as d1 520a, and relatively long for another angle, such as d2 520b.

[0077] Using conventional OCT or OFDI techniques, the imaging system 500 can acquire data over the entire depth range (d2-d1+δ), where the parameter δ522 describes the imaging depth into the sample. Conventional OCT or OFDI images 550 provide images as a function of depth 521 and angle 523. The exemplary image occupies a depth range given by d2-d1+δ. Acquiring data over this large area in a short time requires fast digitization and data transmission capabilities. Such exemplary images can also indicate that acquisition may be inefficient. This may be because, in a large area of ​​the acquired image, there is little or no information content at a depth greater than δ above the tissue surface 533a or below the tissue surface 533b. The use of subsampled optical frequency domain imaging or subsampled SD-OCT can facilitate the acquisition of the same information content and has higher efficiency. Exemplary subsampled OFDI images 560 are provided as a function of depth 561 and angle 564. The exemplary imaging system 500 can be configured to provide an imaging range of δ562. The exemplary imaging range need not be greater than the imaging penetration depth into the sample, and may instead be smaller if information is desired on shallower regions. The wrapping nature of the exemplary subsampling imaging procedure may facilitate capturing information from the surface depth δ of the sample at all angles. Furthermore, the exemplary imaging acquisition bandwidth may not be dedicated to empty space above the tissue surface, or below imaging penetration into tissue.

[0078] Tissue surface 570 may be located or otherwise determined using a surface finding procedure, including, for example, a snake procedure as described in Yezzi et al., IEEE TranMed Imag 16, 2 99-209 (1997), and the exemplary image expanded to generate image 590 in which the tissue is shown having a surface of approximately constant depth. Exemplary Embodiment of a High-Speed ​​OS-OCT Imaging System

[0079] Exemplary embodiments of a high-speed optical subsampling imaging system and an image display device and method according to the present disclosure are described below and are described in Figure 6-16 Medium picture.

[0080] For example, Figure 6 An exemplary embodiment of a high-speed laser source and exemplary outputs provided by one or more components thereof according to the present disclosure is shown. Figure 6 As shown in , an exemplary laser device 600 includes a ring cavity including an intensity modulator 610, a set of semiconductor optical amplifiers (611 and 614), a first dispersive fiber 615, a set of wavelength selective filters based on a fixed Fabry-Perot etalon 613, an output coupler 616 and a second dispersive fiber 612. Laser or other electromagnetic radiation can circulate in a clockwise direction in the laser cavity. The negative dispersion element can be generated or otherwise made by a dispersion compensating fiber that provides a total dispersion of approximately -700ps / nm at 1550nm, for example. The positive dispersion element can be generated or otherwise made by a standard single-mode fiber that provides a total dispersion of +700ps / nm at 1550nm, for example. Such an exemplary standard fiber can be operated in a double-pass configuration using a Faraday rotator mirror to reduce the effects of polarization mode dispersion. The exemplary laser can operate with a central wavelength o (e.g., approximately 1550nm) and a laser bandwidth 632a from 1522nm to 1590nm. It should be understood that lasers may operate at additional wavelengths and bandwidths.

[0081] Light or other electromagnetic radiation from a dispersion compensating fiber can be amplified by, for example, a broadband semiconductor optical amplifier (614, 611), which can include an optical isolator to prevent light / radiation from passing in the counterclockwise direction. The amplified light passes through a set of two identical FP etalons 613 with a 200GHz FSR. The laser can be operated with one etalon or multiple etalons. (Multiple) exemplary etalons can transmit light or other electromagnetic radiation at approximately equally spaced wave numbers. For example, two FP etalons can be used in an exemplary embodiment to narrow the optical transmission spectrum of the combined filter and improve noise performance and reduce nonlinear interactions in the amplifier and the optical fiber. The output coupler 616 can be placed after the filter 613 and direct approximately 20% of the light out of the cavity. The exemplary coupling ratio of the output coupler 616 can be set within a wide range. In such exemplary embodiments of the present disclosure, the length of each dispersive element can be selected to be roughly matched in amplitude and also have opposite signs across the operating bandwidth.

[0082] The intensity modulator 610 can be driven by a pulse generator 622 that produces pulses of tunable length and tunable repetition rate. In an exemplary embodiment, the pulse length can be between 0.05ns and 5ns, although other ranges of pulse lengths are possible. Such exemplary pulse lengths can provide a time window with high light transmission through the modulator 610. The intensity modulator 610 can also provide a high switch extension ratio (approximately 30dB) by optimizing the lithium niobate waveguide properties, which can be used to limit the transmitted light when in the "off" state. Alternatively or additionally, an electro-optic intensity modulator can be used, or the semiconductor gain element can be current modulated to provide this intensity modulation function. A polarizer can be included before the modulator 610 to compensate for modulators with polarization-dependent operation, and a polarization controller can be placed between the polarizer and the modulator to align the returned light polarization state with the optimal axis of the modulator. For example, a polarization controller can be included throughout the laser cavity to align the light polarization state at each element.

[0083] In an exemplary embodiment of the present disclosure, the pulse generator 622 can be driven at, for example, about 18.9 MHz, which can be the 4336th harmonic of the fundamental cavity frequency given by the inverse of the cavity round trip time. By operating at this exemplary harmonic, the pulse returned to the intensity modulator can be matched to the transmission window and passed through the exemplary modulator. At the modulator, most or all of the laser wavelength pulses can temporarily overlap within a single multi-wavelength pulse. After passing through a dispersive fiber, these pulses can be separated in time. Then, a second dispersive fiber can recompress these pulses. Each pulse at the modulator can be stretched to produce a pulse train, each pulse in the pulse train having a separate wavelength. At any given time, there are multiple pulse trains in the cavity.

[0084] A laser output may be provided from an output coupler 616. The output may be passed through an additional optical amplifier to increase the power, and / or it may be further filtered through one or more wavelength selective filters (such as, for example, an FP etalon 619) for improving the line width and / or reducing ASE light transmission. The output pulse train may be stretched or compressed in time using a dispersion compensating element (or positive dispersion element) 618, which may be or include, for example, a dispersion compensating fiber or a fiber Bragg grating array operating in a reflection mode, or a chirped fiber Bragg grating operating in a reflection mode. An external dispersion element 618 may be used to modify the A-line duration and the associated desired digitization speed externally without modifying the laser cavity.

[0085] Additional amplifiers 617, 620 may be included to increase power and improve linewidth. These amplifiers may be based on semiconductor optical amplifiers, but may be constructed, for example, from doped fibers or utilize Raman gain. Filters used outside the laser cavity 619 may remove background amplified spontaneous emission light and narrow the linewidth of each wavelength pulse. Amplification and filtering may be repeated in multiple stages to further increase power and optimize linewidth.

[0086] In an exemplary embodiment of the present disclosure, the laser output may include a pulse train 640, each pulse having a different wavelength corresponding to the transmission passband of the filters 613, 619. This can be visualized by a high-speed photoelectric receiver and captured on a high-speed oscilloscope. The length of such an exemplary pulse train 641 according to an exemplary embodiment of the present disclosure may be set to approximately 50ns, although other settings are contemplated within the scope of the present disclosure. Each pulse train represents an "A line" in OCT imaging and may contain different pulses, each of which may have a unique wavelength approximately equally spaced in wavenumber and matching the wavelength selective filter transmission peak. The spectrum of the output laser 630 may be a comb-like structure with substantially different output wavelength bands 631.

[0087] An exemplary spectral output 630 is Figure 6 Graphs of optical power 632b, 631b as a function of wavelength 632a, 631a are shown in FIG. A zoomed image of a smaller wavelength range is shown in FIG. 631, while a larger range is shown in FIG. 632. Time output 640 plots received voltage 640b as a function of time 640a.

[0088] The effective A-line rate of the laser can be varied by operating the intensity modulator at different harmonics of the fundamental cavity round-trip frequency (or equivalently at different pulse repetition times that are subharmonics of the cavity round-trip time). This can facilitate the A-line repetition rate to be varied electronically. The amplitude of the dispersion can be adjusted to modify the A-line length by adjusting the time interval between each wavelength pulse. Although these elements are Figure 6 Although a particular organization and / or order is shown in the drawings, it should be apparent to one skilled in the art that there are alternative orderings and / or organizations that may be used and are within the scope of the present disclosure.

[0089] In an exemplary embodiment of the present disclosure, the output of the high-speed laser source 700 may be directed to the input of an interferometer 701 (eg, Figure 7). The interferometer 701 can split or separate the output of the laser source 700 into a sample arm 703 and a reference arm 704. The sample arm 703 can include an electro-optic modulator (EOM) 710 for polarization modulation, which can be used to improve polarization-sensitive imaging. The EOM 710 can be configured to modulate the polarization state of each wavelength pulse, each A-line, each imaging frame, each imaging volume, or any time block of data. The EOM 710 can be placed in the sample arm 703 before an optical circulator 711 and in the optical path of the optical circulator 711, and the optical circulator 711 can guide the light or other electromagnetic radiation to a double-pass optical fiber 717, which provides the light or other electromagnetic radiation to the sample 714. Alternatively or additionally, a modulator (e.g., EOM 710) can be placed before the coupler 702 and in the optical path of the coupler 702 to modulate the sample arm light and the reference arm light or other electromagnetic radiation. Alternatively or additionally, such an exemplary modulator can be located in the double-pass optical fiber 717. The double pass fiber may include a beam splitter 712 that directs a portion of the light to a structure such as a mirror 713 that is used to calibrate the system. The sample arm 703 may also provide light or other electromagnetic radiation to the sample 714. The reference arm light may pass through a circulator 705 to a double pass fiber 718 leading to a mirror 706. The position of the mirror 76 may be adjusted to modify the optical delay of the reference arm. Polarization controllers 707, 708, 715 may be provided in the reference arm 704 and / or the sample arm 703. A polarizer 709 may be provided before the EOM 710 and in the optical path of the EOM 710 to set the input polarization state into the modulator. The light or other electromagnetic radiation provided from the reference arm 703 and the sample arm 704 may be combined at an optical demodulator 716.

[0090] Figure 8 The exemplary embodiment according to the present disclosure is shown in more detail. Figure 7804. For example, light(s) or other electromagnetic radiation from sample 801 and reference 802 are provided to a polarization beam combiner (PBC) 804, which splits or otherwise separates the received light or other electromagnetic radiation into two orthogonal polarization states. The polarization state of the light or other electromagnetic radiation from reference arm 802 can be controlled with a polarization controller 803, which can be configured to split the reference arm light, for example, approximately equally to each output port of PBC 804 for polarization-diverse detection, or primarily in one output port if polarization-diverse detection is not used. In each output port of PBC 804, a system of optical components can be configured to generate, for example, a shift in one in-phase channel (MI) detected on signal 809a relative to another orthogonal channel (MQ) detected on signal 809b. In this exemplary embodiment, polarization controllers 806a, 806b, 806c, 806d can provide different phase delays in light or other electromagnetic radiation from the sample arm 801 relative to light or other electromagnetic radiation from the reference arm 802, and thereby cause controllable phase shifts in the interference fringes generated by polarization beam splitters 807a, 807b, 807, 807d.

[0091] Alternatively or additionally, such an exemplary optical circuit can be constructed in free space using a bulk beam splitter and a polarization rotator. The output of each polarization beam splitter can be passed to an input of opposite sign of a balanced receiver 808a, 808b, 808c, 808d for reducing intensity noise. The signal can be low pass filtered using filters 809a, 809b, 809c, 809d. The cutoff frequency of these low pass filters can be set to match the frequency bandwidth of the baseband window used for optical subsampling of the laser, which can be approximately 1 / (2*dT), where dT is the time interval of the wavelength pulses from the laser, and / or can be approximately the minimum time interval of the wavelength pulses from the laser if the time interval is unequal across the A line. For example, 50 / 50 optical couplers 805a, 805b can be included in the exemplary system.

[0092] When the MI and MQ signals are added in a quadrature manner, there can be a reduction in complex conjugate artifacts resulting from conjugate ambiguity in the measurement of one signal. For example, the amount of reduction in conjugate artifacts is related to how closely the relationship between MI and MQ is in perfect quadrature (e.g., about 90 degrees phase separation). To reduce the number of RF channels, a demodulator can be provided that creates the information needed to generate MI and MQ by sequential phase modulation in the reference arm or sample arm of the interferometer using, for example, a lithium niobate phase modulator or an acousto-optic modulator.

[0093] Imperfections in the orthogonal relationship between the detected interference fringes MI (e.g., detected on signal 809a) and MQ (e.g., detected on signal 809b) can result in imperfect separation of the signals from the positive delay space and the negative delay space. In this exemplary embodiment, the measured signal can be modified after being acquired by digital converters 810a, 810b and the digitized signal is transmitted to a computing arrangement (e.g., a computer, a processor and / or multiples or combinations thereof). These exemplary modifications can be used to correct these errors using known techniques, such as those described in Siddiqui et al., Optics Express 23, 5 5508-5520 (2015). Such exemplary corrections can be performed using a set of mirrors such as (see Figure 7 The correction may be performed using predetermined data acquired from a separate sample of the signal from the mirror 713 in the image acquisition system, and / or may optionally be derived from the signal in the sample itself. The correction may remove errors that occur as a function of the measured wavelength (i.e., spectral errors), as well as errors that occur as a function of the RF frequency (i.e., RF errors). RF errors may become significant at high speed imaging due to the higher RF frequencies involved in the system. Such an exemplary procedure may utilize data from Figure 7 The signal of the sample calibration mirror 713 at various depth positions and the residual peak at all depth positions is minimized simultaneously. The exemplary procedure can be used to apply a frequency response function (H(Δ)) in the RF frequency domain to correct frequency-related errors. Amplitude and phase error corrections can be applied in the RF time domain. These errors can be calculated or otherwise determined once per system (e.g., by a computational arrangement) and applied to all subsequent images if the system (e.g., by a computational arrangement) does not significantly change its state. The spectral error can be calculated and applied separately from the RF error (e.g., by a computational arrangement) so that changes in state that only affect the spectral error can be calibrated independently of the RF error.

[0094] The exemplary demodulation circuit may operate on a subsampled measurement similar to a conventional Fourier domain measurement, as described in Siddiqui et al., Optics Express 23, 5 5508-5520 (2015). Fig. 9 In an example shown, Fig. 9 1 illustrates a set of exemplary OS-OCT images obtained without and with quadrature demodulation according to an exemplary embodiment of the present disclosure. Fig. 9 As shown, a subsampled image of a finger is provided without quadrature demodulation 900, and the overlap of the image with its complex conjugate is illustrated, resulting in artifacts in the image. As described herein, this problem can be solved with demodulation and error correction illustrated in display 901. For example, Figure 8The exemplary configuration shown in can be used to generate two phase-shifted interference fringes for the X polarization state of the digitizer 810a (e.g., I on the first channel (channel 1) of the digitizer 810a, and Q on the second channel (channel 2)), and by using a 1×N beamsplitter instead of the 1×2 beamsplitter 805a, additional phase-shifted interference signals can be generated. For example, in one exemplary configuration, the polarization-based demodulation system can provide three phase-shifted interference signals at relative phase shifts of 0 degrees, +60 degrees, and +120 degrees. The exemplary use of three or more phase-shifted interference channels can be utilized, for example, to improve orthogonal demodulation accuracy, or to reduce the presence of signal artifacts at DC.

[0095] An exemplary procedure for processing acquired signals from a mirror structure to derive post-processing correction factors is described below and in Fig.10 It is shown in Fig.10 A flow chart is shown that provides an exemplary method of quadrature demodulation and OS-OCT signal processing according to an exemplary embodiment of the present disclosure, the signal processing including techniques for correcting quadrature errors in an optical demodulator. Fig.10 As indicated, in procedure 1010, the detected signals MI and MQ may be obtained, and in procedure 1020 the signals are Fourier transformed (FT) processed using a Hanning window, and then in procedure 1030 the signals are coherently averaged across the fringes to improve the signal-to-noise ratio (e.g., using a computational arrangement). Next, the signal peak in the Fourier domain may be found in procedure 1040. Thereafter, in procedure 1050, RF error correction may be performed, as described in Siddiqui et al., Optics Express 23, 5 5508-5520 (2015), followed by spectral error correction in procedure 1060, again as described in Siddiqui et al., Optics Express 23, 5 5508-5520 (2015). After several iterations through the optimization loop (black dashed box), the error function may be used to update and optimize the correction factors H(Δ) and α(k) and β(k) in process 1070.

[0096] Exemplary embodiments of a high-speed optical subsampling OCT system may utilize a phase synchronized clock system across many system modules, such as Fig.11 As shown in the figure, Fig.11 A block diagram of a system for providing an exemplary timing scheme for control electronics in an exemplary OS-OCT imaging system according to an exemplary embodiment of the present disclosure is shown. Fig.11As provided, a signal generator 1108 may be used as a clock for a pattern / pulse generator 1105 to drive an intensity modulator 1104. The internal clock of the signal generator 1108 may be shared across several electronic subsystems to synchronize and phase lock the exemplary system, including a first signal generator 1101 that controls the EOM 1100, a second signal generator 1102 that controls the fast axis beam scanner 1103, a third signal generator 1107 that controls the slow axis beam scanner 1106, and a fourth signal generator 1111 that controls the acquisition clock of high speed digitizers 1112, 1113 to acquire interferometer fringe data. The pattern / pulse generator 1105 may utilize a binary data pattern that may be set by a computer arrangement 1109. The trigger output signal from the signal generator 1108 may be passed to a delay generator 1110 to generate a trigger signal for the high speed digitizers 1112, 1113. It should be understood that the exemplary embodiments described above are merely exemplary and that a person skilled in the art may appreciate multiple organizations of clock electronics and signal paths to achieve similar effects within the scope of the present disclosure. The exemplary timing configuration has been configured to facilitate highly phase stable measurements across the A-line with short or long separations.

[0097] The clock frequency for the exemplary digitizers 1112, 1113 may be configured as an integer multiple of the laser A-line rate, which produces an integer number of digitized samples for each A-line. This may facilitate multiple A-lines to be directly averaged (i.e., in the fringe domain of the measurement or as a composite A-line after an FFT) without taking into account A-line phase shifts. For example, in this exemplary system, the pattern / pulse generator 1105 may be driven by a 3.64437734 GHz signal, for example, from the signal generator 1108; the pattern generator 1105 is set by the computer 1109 to generate 192 bits at this frequency and remain "on" for one bit in the 192 bit sequence, thereby producing an A-line rate of 3.64437734 GHz / 192 = 18.9811319791667 MHz. The digitizer clock is set by the external clock 1111 to, for example, 1.23377357865 GHz to provide, for example, exactly 65 measurements per A-line. For example, a set of consecutive acquisitions can be combined to generate a coherently averaged A-line with improved SNR and additional fringe signal. Exemplary coherent averaging of A-lines can be performed using a processor located on a digitizer board, such as a field programmable gate array (FPGA), or using a computer arrangement.

[0098] Fig.12 A diagram of an imaging microscope used in an exemplary OS-OCT system according to an exemplary embodiment of the present disclosure is shown. In this exemplary embodiment, Fig.12The imaging system of the present invention can include a scanning beam probe including large angle galvanometer mirrors 1202, 1203 that can scan a beam across the x and y dimensions, respectively. A collimator 1200 can create a collimated beam 1208 that can be directed to the beam scanners 1202, 1203 (e.g., approximately 7 mm beam size) and a focusing lens 1201 having, for example, a 250 mm focal length that can be placed before the scanners 1202, 1203 and in the optical path of the scanners 1202, 1203 to create a fan-beam imaging geometry. The exemplary system can facilitate wide-field depth-resolved images of a sample of, for example, a human face at a field of view 1204, 1205, 1206 that expands as the sample 1207 moves away from the exemplary probe.

[0099] Fig.13 A set of exemplary widefield OS-OCT images according to an exemplary embodiment of the present disclosure is illustrated. For example, a three-dimensional data set can be visualized by examining a single depth plane of the exemplary image 1301, an average intensity projection across the depth of the exemplary image 1300, or other display modes such as a single cross-sectional image. The exemplary images 1300 and 1301 demonstrate the large depth field and widefield capabilities of the exemplary system. In these exemplary images 1300, 1301, a depth of field greater than 3 cm can be obtained. When acquiring this image, the exemplary laser was operated at an A-line rate of approximately 18.9 MHz, and the image displayed 2000×2000 lateral pixels (across a 9 cm×9 cm area), using a fast axis scanner operating at 16.5925 Hz and a slow axis scanner operating at 0.008296 Hz and measured using a 250 mm focusing lens. Since the speed of this exemplary laser far exceeds the scanning speed, it is possible to average adjacent A lines in a single frame, between two frames, or between volumes to improve the SNR of the exemplary image.

[0100] Additional exemplary imaging microscopes may also be provided by using, for example, a 3.9 kHz resonant beam scanner and a slower galvanometer scanner. A 250 mm focusing lens may be used. Using an exemplary 3.9 kHz resonant fast scanner, approximately 8 volumes per second may be acquired while measuring ~2428 pixels in the fast frame and 1000 pixels in the slow frame. This procedure and arrangement facilitates volumetric imaging of a sample, with each volume acquired at video rate (e.g., at 8 volumes per second). The exemplary volume acquisition rate may be significantly increased by reducing the number of A-lines in the fast frame direction, the slow frame direction, and by increasing the speed of the scanner. The imaging was performed using an 18.9 MHz A-line rate source. Due to the sinusoidal nature of the resonant scanner, such as Fig.14As shown, sinusoidal interpolation may be performed in the process to remove this spatial disruption in the horizontal direction from the original image 1400 to create the undistorted image 1401. Fig.14 The 219th cross-sectional image 1403 of the first volume at location 1404 in the exemplary undistorted image 1401 is shown in FIG. 1 and demonstrates how sub-surface features appear in the recorded baseband window. For example, the baseband window size can be changed by changing the FSR of the intracavity / exocavity filter. Images 1400 and 1401 are exemplary average intensity projection images across the depth axis.

[0101] In another exemplary embodiment of a system according to the present disclosure, polarization-differential volumetric tissue imaging is used to measure optical birefringence and the optical axis of the birefringence within a tissue field, and these volumetric measurements are acquired using video-rate microscopy to allow video-rate birefringence imaging of the surgical field. In such an exemplary embodiment, four digitizer channels (e.g., Figure 8 810a, 810b), providing I / Q measurements for each of the X and Y polarization diverse detection channels. The trigger output of the first digitizer board 810a can be used to trigger the start of acquisition on the second digitizer board 810b. The lengths of the optical paths and cables after the interferometric PBC 804 are maximally balanced to avoid differential delays that can cause modulation or PS errors. For polarization sensitive (PS) measurements, for example, frequency-dependent phase shifts between the X and Y channels can produce artificial birefringence measurements by causing the Y channel phase to increase significantly relative to the X channel with depth. Such artifacts are further removed by delaying the X channel signal relative to the Y channel signal in post-processing performed in the computer arrangements 810a, 810b.

[0102] Fig.15 A set of exemplary images from a video sequence acquired from an exemplary high-speed OS-OCT system in accordance with an exemplary embodiment of the present disclosure is shown, including snapshots of videos acquired using an exemplary embodiment of the present system. Fig.15 The exemplary images provided in illustrate a mouse sciatic nerve resting on a silicon phantom using average intensity projections across depth at three time points (1500, 1501, 1502). During this exemplary time period, the nerve was crushed with a pair of forceps. The optical birefringence axis was extracted using a known procedure, and a median optical axis projection was performed to generate optical axis images 1503, 1504, 1505. Cross-sectional images 1506 and 1507 of the optical axis data are presented at lines 1508 and 1509, respectively. The optical axis data is displayed with the angle of the optical axis mapped to the color in images 1503, 1504, 1505, 1506, 1507. In this exemplary data set, the recording lasted approximately 9 seconds and contained 54 complete volumes.

[0103] In this example, the fast scanner operates at 3.945 kHz and modulates between input polarization 1 during the forward scan and input polarization 2 during the backward scan (e.g., the EOM modulation speed is 3.945 kHz). The slow axis scanner has a speed of 6.514083 Hz and is driven with a ramp waveform, thus providing 600 lateral forward (fast axis) scans and 600 backward (fast axis) scans in one volume. A lateral field of 1.2 cm x 1 cm is measured. The depth range of the exemplary subsampled OCT system is approximately 5 centimeters. Such exemplary data were acquired using a 200 GHz output wavenumber spacing, resulting in a baseband imaging window depth of approximately 500 μm in tissue.

[0104] In an exemplary embodiment, polarization data may be displayed by mapping the three optical axis parameters of the Stokes representation of polarization to red, green, and blue shades, and then median projecting these color volume images across depth to generate two-dimensional maps 1503, 1504, 1505, 1506, 1507 of tissue optical birefringence.

[0105] Alternatively, if Fig.16 As shown, an average structural (intensity) projection 1600, or a weighted projection 1601 with optical axis, delay and / or depolarization information can be displayed using exemplary embodiments of systems and methods according to the present disclosure. The exemplary image illustrates a surgically exposed rat sciatic nerve 1603 being manipulated by forceps 1604 in situ with surrounding muscles 1605a, 1605b, 1605c. The exemplary birefringent projection image 1601 shows the optical axis angle mapped onto a circular color map 1602, where the color / hue represents the optical axis angle in a linear plane orthogonal to the imaging beam propagation direction 1606. Here, the hue / color values ​​are weighted by the intensity and delay values ​​across depth. This single on-surface projection is a single capture within a video acquisition, with the same Fig.15 1607. Samples with low birefringence are displayed with low values ​​(such as, for example, forceps 1607) and those with high birefringence can be displayed with high value colors. Embedded nerve / tissue features (such as 1608) can be visualized in this 3D to 2D projection. It should be understood that there are a variety of methods for displaying three-dimensional data, and for converting / transferring such exemplary three-dimensional data to a two-dimensional image. Additional Light Source Embodiments

[0106] Figure 6The exemplary laser source shown in and described above relates to one exemplary embodiment of the present disclosure. In further exemplary embodiments, the laser source may include an optical gain based on a fiber amplifier, a parametric amplifier, a nonlinear amplifier, and / or a Raman amplifier, etc.

[0107] Fig.17 A block diagram of an apparatus for interleaving laser output pulses from adjacent A-lines to fill time gaps in the laser output is shown, along with illustrations of exemplary outputs from various components, in accordance with an exemplary embodiment of the present disclosure. In this exemplary embodiment including a laser source, the temporal duration of each wavelength pulse 1717 can be configured by controlling the signal to the intensity modulator to be less than the temporal interval of the pulse after being stretched by the dispersion element in the cavity. This can be performed to limit overlap of different wavelength pulses in the amplifier or other laser cavity elements, which can also cause a lower laser duty cycle by creating off times 1718 between pulses. Due to these off times, the power of the laser can be concentrated in short pulses 1715, creating higher instantaneous power, which can be disadvantageous by generating nonlinear effects or saturating the boost amplifier. In an exemplary embodiment, this exemplary low duty cycle pulse train can pass through a multipath optical circuit including a coupler 1710, a first arm 1718, a delay 1711 including a delay fiber, and a polarization controller 1712, and can be recombined using, for example, a coupler 1713. The delay 1711 can be configured to be, for example, approximately equal to the A-line repetition rate plus half the time interval between pulses. This exemplary configuration can interleave adjacent A-lines together without overlapping pulses 1716 in time.

[0108] Alternatively or additionally, repeated dispersive elements may be used to temporally disperse each of the wavelength pulses without affecting the temporal separation of the pulses. For example, a Gires-Tournois etalon having an FSR that matches the FSR of the wavelength selective filter or an FSR at an integer multiple of the wavelength selective filter of the laser may be utilized at the laser output to create large dispersion within the limited bandwidth of each pulse, resulting in pulse stretching. An exemplary group delay response of such a filter may be periodic 1715 such that each pulse is temporally widened (or compressed if configured in this exemplary manner) without causing significant modification of the pulse-to-pulse spacing. As Figure 6 The exemplary lasers shown may include Fig.17 1700 , 1703 , 1706 , 1709 , dispersion elements 1705 , 1702 , 1707 , spectral filters 1704 , 1708 and intensity modulator 1701 are shown in FIG.

[0109] In another exemplary embodiment of the present disclosure, the wavelength selective filter can be composed of an air cavity Fabry-Perot etalon, which has the advantages of not using a dispersive medium in the etalon and maintaining a constant free spectral range across a large bandwidth. Alternative wavelength filter configurations can include fiber-based Fabry-Perot etalons, virtual imaging phase array gratings, fiber Bragg gratings or other waveguide Bragg gratings, arrayed waveguide gratings, circular arrayed waveguide gratings, or optical interleavers and deinterleavers, etc.

[0110] According to yet another exemplary embodiment, the dispersion element ( Figure 6 The spectral dispersion (shown as components 612, 615) may be based on a fiber Bragg grating (FBG) array or a long chirp fiber Bragg grating. For example, dispersion is created by the different spatial locations of the reflection of each wavelength. Fig.18 An exemplary diagram of a fiber Bragg grating array according to an exemplary embodiment of the present disclosure is illustrated, along with an exemplary diagram of an output provided from one of its components. Fig.18 In the exemplary FBG array configuration shown, a group of individual FBGs 1800a-1800h can be positioned along the fiber separated by a distance Δx 1806 such that the reflected pulses from each consecutive grating are separated in time by (c / (2nΔx))^-1, where c is the speed of light and n is the refractive index of the fiber. For example, the individual FBGs 1800a-h can be used as wavelength selective filters such that an FP etalon or similar periodic filter is not required and the FBG reflection wavelength defines the lasing wavelength. Alternatively or additionally, the spectral position of the FBG reflectivity can be aligned with the wavelength passed by a wavelength selective filter (such as an intracavity FP etalon).

[0111] An exemplary reflection bandwidth of the FBG can be wide so that the laser linewidth is determined by the etalon linewidth. A variable optical attenuator 1805 can be included in the array to, for example, limit the number of reflected pulses to reduce the number of lasing wavelengths. Input light from one side 1801a can be reflected to create output light 1801b where each wavelength provides a different group delay based on the position of the FBG that is aligned with its wavelength or with the first FBG encountered by light matched to its wavelength. The exemplary FBG array configuration can also be used from both sides where light emitted from the other end 1802c reflects off the same grating and returns to 1802d and since the input light 1802a sees the FBG in a reversed order the FBG can have the opposite dispersion to that achieved in the reflected light 1801b. Alternatively or additionally, a second FBG array can be used to create the opposite dispersion where the order of the gratings in the array is reversed. The FBG reflectivity 1804 versus wavelength 1803 can be customized through a grating writing process to configure its linewidth, reflectivity, phase response, and center wavelength, as Fig.18 As shown in the figure.

[0112] In further exemplary embodiments, chirped FBGs may be used that provide continuous wavelength reflectivity along the length of the fiber. For example, a wavelength selective filter in the cavity may define the laser emission wavelength, and the chirped FBG may create (multiple) positive and negative dispersions. As with the exemplary FBG array, the same chirped FBG may be used to create (multiple) positive and negative dispersions by emitting from opposite sides. The reflectivity of the chirped FBG may be designed to induce a specific laser output distribution and / or compensate for wavelength-dependent losses or gains in the cavity. The exemplary laser may be configured without a wavelength selective filter in the cavity to, for example, generate a continuous wavelength swept output, thereby providing a laser source for high-speed conventional FD-OCT.

[0113] The spacing of an exemplary FBG in an FBG array may be, for example, about 5 cm in optical fiber (Δx=5 cm), resulting in a 0.5 ns time displacement between light reflections at wavelengths corresponding to adjacent FBGs. For example, the FBGs may be placed closer together to shorten the time interval, and further apart to lengthen it. FBG arrays of tens of centimeters to hundreds of meters may be provided.

[0114] To reduce or otherwise minimize light transmission through an FBG array or a continuously chirped FBG dispersive element, the reflectivity of the grating can be made close to 100%, thereby significantly limiting the transmission. For example, this can be done to prevent laser emission paths within the laser cavity from bypassing the intensity modulator.

[0115] Fig.19 A set of diagrams showing an exemplary laser source utilizing a fiber Bragg grating according to an exemplary embodiment of the present disclosure. In particular, Fig.19 1900, an exemplary embodiment of a laser including a single FBG array or a continuously chirped FBG and an exemplary embodiment providing a pair of FBG arrays or continuously chirped FBGs are shown. For example, in a single FBG array / continuously chirped FBG configuration 1900, an intensity modulator 1902, circulators 1906, 1907, optional wavelength selective filters 1903, 1905, and an optical amplifier 1904 and an output coupler 1910 are provided in Fig.19. For example, light or other electromagnetic radiation is output at port 1911. The wavelength selective filter may be or include, for example, a Fabry-Perot etalon or other periodic spectral filter. Positive dispersion may be generated by light entering the FBG array and / or the continuously chirped FBG 1908 from the left, and compensating negative dispersion may be created by light entering the FBG array or the continuously chirped FBG 1908 from the right. Alternatively or additionally, the exemplary FBG device / configuration 1900 may be configured to generate negative dispersion for light entering from the left and positive dispersion for light entering from the right. An exemplary single FBG 1909 is provided within the FBG array and provides a reflection path for light from the left and the right. It should be understood that this may be one of many FBGs that may be located in the optical fiber 1908, such as Fig.18 shown.

[0116] exist Fig.19 In an alternative exemplary embodiment of the present disclosure to the exemplary configuration 1901 shown in , the exemplary laser may include the same intensity modulator 1950, circulators 1951, 1952, wavelength selective filters (optional) 1953, 1955, optical amplifier 1954, and output coupler 1956, where light or other electromagnetic radiation exits on optical fiber 1957. For example, gratings 1958, 1959 may be used, and there may be no transmission path from grating 1958 to grating 1959. Grating 1958 may be configured or constructed to create positive dispersion, and grating 1959 may be configured or constructed to create negative dispersion, such as the negative dispersion matching the positive dispersion grating 1958 in amplitude, or vice versa. Drive signals 1912, 1960 may be used to actuate intensity modulators 1902, 1950, respectively. These drive signals may be generated from a pulse generator or a computing arrangement. This exemplary embodiment and further described exemplary embodiments of laser systems according to the present disclosure may include more or fewer wavelength selective filters and gain media, and the exemplary components may be organized in different configurations or ways within this exemplary cavity.

[0117] exist Fig. 20 In the exemplary embodiment of the laser system shown in , the exemplary laser can utilize a continuously chirped FBG 2008, as well as an intensity modulator 2000 driven by a drive signal 2010, circulators 2001, 2007, (optional) wavelength selective filters 2002, 2004, an optical amplifier 2003, and an output coupler 2005. Light or other electromagnetic radiation can be output on an optical fiber 2006. A dispersion compensation element / configuration 2009 can be provided to correct for the mismatched dispersion created by the exemplary FBG system 2008.

[0118] In further exemplary embodiments, an array of FBGs or a continuously chirped FBG may be provided from a polarization maintaining fiber to ensure that reflected light or other electromagnetic radiation from all wavelengths is in approximately the same polarization state. An exemplary array of FBGs or a continuously chirped FBG may additionally be provided in a reduced cladding mode fiber to remove side modes in the FBG reflectivity.

[0119] In another exemplary configuration, the FBG array or the continuously chirped FBG can be based on a polarization-maintaining (PM) fiber, and the light or other electromagnetic radiation entering from one side can be emitted along the fast axis, and the light emitted from the other side can be emitted along the slow axis. In this exemplary configuration using the FBG array, the offset of the reflectivity of each grating in the fast and slow axes can be configured to match the wavelength spacing of the laser. Using such an exemplary embodiment, the laser emission due to light transmission through the grating can be prevented by, for example, placing a polarizer on one or both sides of the grating 2011. For example, polarizers 2012a, 2012b can be used together with polarization controllers 2013a, 2013b. Light or other electromagnetic radiation emitted from the left side through the polarizer 2012a in the fast axis and transmitted through the grating 2014 can be blocked by the polarizer 2012b. The reflectivity of the FBG can be configured to cause a specific laser output distribution and / or compensate for wavelength-related losses or gains in the cavity.

[0120] In yet further exemplary embodiments, the WSF element can be omitted from the cavity and the FBG array can define the lasing wavelengths, and the linewidth of each lasing wavelength depends on the bandwidth of the reflectivity of each FBG. Alternatively or additionally, a continuously chirped FBG array can be used as a dispersive element without additional wavelength selective elements and create a continuously swept wavelength source.

[0121] In another exemplary embodiment, an array of FBGs may be used and configured to limit transmission through the array, which may be used to prevent light from circulating in unintended paths. Fig.21 An exemplary diagram showing an exemplary grating design arrangement in a fiber Bragg grating array used in a laser source according to an exemplary embodiment of the present disclosure is shown. Fig.21As shown, the individual FBGs 2106a-2106j can be positioned along the position axis 2102 according to their reflection wavelengths 2100 so that each grating reflection profile can occupy two laser wavelengths λ1-λ10. For example, grating 2106b reflects light at λ2 and λ1. However, the light at λ1 on the left is mostly reflected by the previous grating 2106a. Therefore, grating 2106b can provide a primary reflection point for the light at λ2 and serve to reduce the transmission of the light at λ1 that is transmitted through grating 2106a. From the right, 2106b can provide a primary reflection of the light at λ1, and 2106a reduces the transmission of the light at λ1. Because the light from the left and right sides is primarily reflected from different gratings, the grating positions can be spaced apart at a consistent interval Δx2104 so that the total cavity group delay experienced by each wavelength is approximately the same.

[0122] In an alternative exemplary embodiment, the FBG array used to create dispersion may include two or more gratings at each wavelength 2101 and position 2103, such as Fig.21 2190. For example, the first grating 2166a reflects light from λ1 on the left, and the second grating 2166b suppresses transmission by reflecting the small light that is transmitted through 2166a. The spacing of the grating pairs 2166a, 2166b and 2166c, 2166d, etc. can be, for example, half the spacing of the gratings 2166a, 2166c, for example, Δx / 2 2170 compared to Δx 2105. For example, Δx can be 5 centimeters. In these examples, if each grating has a reflectivity of 90%, approximately 10% of the light is transmitted. Therefore, the second grating 2166b further reduces the transmittance to about 10%, resulting in a transmittance of approximately 1%.

[0123] Fig. 22 1 illustrates a diagram of an exemplary laser source utilizing active polarization control according to an exemplary embodiment of the present disclosure. In this exemplary embodiment, an exemplary configuration is provided to minimize the effect of polarization rotation of each wavelength in the FBG configuration. Fig. 22As shown in , the laser cavity includes an intensity modulator 2230, a circulator 2231, 2232, a FBG dispersion element 2233, a wavelength selective filter (optional) 2235, 2236, an optical amplifier 2234, and also includes active polarization modulators 2210a, 2210b. These modulators 2210a, 2210b can be used to align the polarization state of each wavelength pulse to a predetermined state using control signals 2203, 2202, respectively. The laser output from the coupler 2237 can be directed to a computing / controller arrangement 2200, which can include a tap coupler 2204 to direct the laser output power to a detector 2205 and an additional optical output 2206, and can adjust the polarization drive signal for each pulse by, for example, maximizing the output power. This exemplary optimization can be performed on a pulse-by-pulse basis, thereby providing an exemplary correction waveform that can be transmitted to the polarization modulators 2210a, 2210b. For example, this exemplary computational arrangement 2200 may be the same arrangement used to generate a drive signal 2201 for an intensity modulator 2230 .

[0124] Fig.23 A diagram showing yet another exemplary laser source including a frequency shifter or phase shifter to restrict the circulation of light in a particular path according to an exemplary embodiment of the present disclosure. Fig.23 As shown in , a laser cavity is provided, which includes an intensity modulator 2300 (driven by a signal 2301 from a computing arrangement or pulse generator), circulators 2302a, 2302b, wavelength selective filters 2304a, 2304b, an optical amplifier 2305, an output coupler 2307 and a bidirectional dispersive element 2303 (such as, for example, an FBG array or a continuously chirped FBG), and the laser cavity may also include optical frequency shifters 2306, 2307, which can be used to suppress the propagation of light or radiation on the path from 2302b through the bidirectional dispersive element 2303 to the circulator 2302a to the optical amplifier 2305 and back to the circulator 2302b (bypassing the modulator 2300). The first frequency shifter 2306 can cause a frequency shift of +F, and the second frequency shifter can cause a frequency shift of -F.

[0125] Thus, light / radiation passing through the first frequency shifter 2306 and the second frequency shifter 2307 may not have a net frequency shift. However, light / radiation circulating without seeing the intensity modulator is continuously shifted upward by +F for each round trip. +F can be, for example, 1 GHz, and the line width of the wavelength selective filters 2304a, 2304b can be, for example, 1 GHz. This can cause the light / radiation to be separated from the passband of the wavelength selective filter and suppress the light circulation in this path. In the exemplary case of an FBG array, the line width of the bidirectional dispersion element 2303 can be configured to be sufficiently broadband to reflect light that is shifted upward by +F once by the frequency shifter 2306. The frequency shifters 2306, 2307 can be constructed, for example, using an acousto-optic frequency shifter or an electro-optic modulator, and can additionally be or include a phase modulator. In another exemplary embodiment configured to use a phase modulator, the second phase modulator 2307 can cause a phase modulation opposite to the phase modulation caused by the first phase modulator 2306. In this exemplary approach, a first phase modulator can spectrally broaden the light, while a second phase modulator compensates for this broadening and allows the light to pass through the wavelength selective filter passband. Laser output 2308 is provided by output coupler 2309.

[0126] exist Fig.34 In a similar exemplary embodiment illustrated, a frequency shifter may be placed in the path of a circulator 3402a that is not placed in the path of another circulator 3402b. The frequency shifter 3409 may cause a shift of +F during each pass through it. When light passes through the preferred cavity (via the intensity modulator 3400), the double pass frequency shifter 3409 may cause a shift of +2F, which will align with the passband of the wavelength selective filters 3404a, b. The bidirectional dispersion element will have a reflection aligned with the passband of the wavelength selective filters 3404a, 3404b plus +F. The second frequency shifter 3410 may cause a shift of -2F, so the light / radiation directed toward the intensity modulator 3400 may have a zero net frequency shift. However, the path from circulator 3402b through bidirectional dispersive element 3403 to circulator 3402a to optical amplifier 3405 and back to circulator 3402b may have a +F shift with each round trip through the path and may cause a walk-off from the passband of wavelength selective filters 3404a, 2404b. Fig.34 As shown in , the exemplary system may include an optical amplifier 3405, an output coupler 3407 that provides a light output 3408, and a modulator 3400 that may be driven by a drive signal 3401.

[0127] Fig.35A diagram showing an exemplary OS-OCT laser including a polarizer and configured by a polarization controller to suppress light circulation in a particular subcavity according to an exemplary embodiment of the present disclosure. For example, such an exemplary system can be configured to limit light circulation in unintended paths, with component 3509 placed in the path of circulator 3502a, which is not placed in the path of 3502b ( Fig.35 ). A preferred cavity traveling through the intensity modulator 3500 will travel twice through the component, while light / radiation travels through an unintended path (bypassing the intensity modulator 3500) and through a single pass. For example, Fig.35 The exemplary laser cavity shown in includes an intensity modulator 3500 (driven by a signal 3501 from a computing arrangement or pulse generator), circulators 3502a, 3502b, wavelength selective filters 3504a, 3504b, an optical amplifier 3505, an output coupler 3507 and a bidirectional dispersive element 3503, such as an FBG array or a continuously chirped FBG, and may also include a non-isolated gain medium 3509 placed in the double-pass path of the circulator 3502a. The gain of the cavity traveling through the intensity modulator 3500 in the cavity path 3500 can exceed the gain of the path from the circulator 3502b through the bidirectional dispersive element 3503 to the circulator 3502a to the optical amplifier 3505 and back to the circulator 3502b, which passes through the gain medium 3509, for example once instead of twice. Polarization controllers 3510a-3510d can be placed at various locations within the cavity to maximize / minimize the transmission or gain through the components within the cavity.

[0128] In another exemplary embodiment, an exemplary system can be provided to limit the circulation of light / radiation in an unintended path, so component 3509 can be a polarizer. The light / radiation traveling in the path can be set to an X polarization state by a polarization controller 3510b, and the polarizer 3509 can be set to pass through the polarization state. The light / radiation reflected from the two-way dispersive element 3503 can be configured to return in an X polarization state using a polarization controller and pass through the polarizer 3509. In particular, the light / radiation 3503 that is being transmitted through the two-way dispersive element can be configured to have an orthogonal Y polarization state (as set by the polarization controller 3510d) using a polarization controller and can be attenuated by the polarizer 3509. The polarizer 3509 can be placed anywhere in the path connecting components 3502a, 3505, 3502b and 3503. For example, the optical amplifier 3505 can be used as a polarizer because of its polarization-dependent gain.

[0129] In further exemplary embodiments, an optical interleaver / deinterleaver is used to generate additional dispersion. In particular, Fig.24A diagram illustrating an exemplary laser source including optical interleavers and deinterleavers to generate different group delays across wavelength channels (with exemplary power diagrams) according to an exemplary embodiment of the present disclosure. In particular, Fig.24 As shown, an exemplary laser cavity can be provided, which includes an intensity modulator 2400 driven by a drive signal 2401, circulators 2402a, 2402b, a dispersion element 2404, a wavelength selective filter 2417a, 2417b, an optical amplifier 2408, and an output fiber 2409. The laser additionally includes circulators 2403a, 2403b and optical interleavers 2405a, 2405b. Interleaving 2403a, 2405b can separate the even channels and odd channels input on i to port a (odd) and port b (even). For example, if filters 2417a, 2417b create a set of wavelengths (λ1, λ2, λ3, .....), then the odd wavelength group (λ1, λ3, λ5, ...) can be emitted on port a and the even wavelength group (λ2, λ4, λ5, ...) can be emitted on port b. In this exemplary manner, by adjusting the length difference of the fiber mirror path 2406a relative to the port 2407a, the pulses of the even wavelengths can be separated in time from the pulses of the odd wavelengths. This time displacement of the even and odd wavelengths can be compensated by the interleaver 2405b by reversing the length difference in the output ports 2406b, 2407b.

[0130] In this exemplary embodiment, the dispersion used by element 2404 can be reduced enough to separate the dispersion of even wavelengths or odd wavelengths by itself, and interleaving 2405a, 2405b can be used to shift the even / odd wavelength groups. The input power at the intermediate layer 2405a, 2405b can be shown, for example, in 2410, and the output power on port a is shown in 2411, while the output power on port b is shown in 2412. The communication interval of the optical interleaving can be designed to match the interval of the laser set by the wavelength selective filters 2417a, 1417b. According to such an exemplary configuration, the laser output is not monotonically in wavelength, but first passes through the odd wavelengths and then passes through the even wavelengths, for example, in the following order for a ten-wavelength laser: [λ1, λ3, λ5, λ7, λ9, λ2, λ4, λ6, λ8, λ10]. An exemplary OS-OCT imaging system using such an exemplary digitizer and computer arrangement 2501 can acquire these signals 2502 in time and reorganize the measurements in a memory 2503 before processing by, for example, a Fourier transform 2404, as shown in FIG. Fig.25 As shown in the picture.

[0131] In further exemplary embodiments, the source dispersion properties may be configured to generate a sequence of output pulses that are substantially uniformly spaced in time by, for example, controlling the dispersion profile in an intracavity dispersive element.

[0132] Fig.26 A diagram of an exemplary system for generating additional optical frequencies from an input set of frequencies using frequency shifting (and an exemplary illustration of wavelengths) according to an exemplary embodiment of the present disclosure is illustrated. In this exemplary embodiment, the output pulse train of a first wavelength group 2610 (e.g., [λ1, λ2, λ3, λ4, ...]) of a laser 2600 can be divided into optical paths 2603a and 2603b, and one path can pass through an optical frequency shifter 2602. The light / radiation from these paths can also be delayed, for example, by using fiber length, and the two paths are recombined so that the pulses do not overlap. The combined light / radiation 2604 can include new wavelength groups 2611, including, for example, the group [λ1, λ1+Δλ, λ2, λ2+Δλ, λ3, λ3+Δλ, λ4, λ4+Δλ, ...]. This exemplary configuration can be used to expand the number of wavelengths provided by a source. The optical frequency shifter can be, for example, an acousto-optic frequency shifter and / or a phase modulator that can be driven with a periodic linear phase ramp that is aligned with the pulses arriving at the modulator. The drive signal 2620 can control the frequency shifter 2602 and can be connected to, for example, a computer arrangement that can additionally control the exemplary laser and imaging system.

[0133] In further exemplary embodiments, the exemplary laser source can be configured to include source polarization modulation between two polarization states (SOPs). For example, the output of a wavelength stepping laser can be split into two paths, and the polarization is rotated in one path, and the two beams are recombined to create a dual polarization state source.

[0134] Fig. 27 A set of graphs illustrating exemplary polarization modulated source outputs according to exemplary embodiments of the present disclosure are shown. Fig. 27 In another exemplary configuration, the light / radiation in one path can be delayed relative to the light / radiation in the second path to avoid overlapping, and this delay can be, for example, half of the interval between the input pulses to produce the output 2700 of the SOP with each pulse cycle. In another exemplary configuration, SOP modulation can be performed in adjacent A lines 2702. In another exemplary configuration, SOP modulation can be performed between any number of adjacent A lines (for example, between the number of A rows in a single B scan frame or a whole C scan). In another exemplary configuration, for example, electro-optic modulators, waveguide modulators and / or acousto-optic frequency shifters can be used to actively modulate the laser output polarization.

[0135] Fig.28An exemplary illustration of a dispersive element provided by combining a set of continuously chirped fiber Bragg gratings according to an exemplary embodiment of the present disclosure is illustrated. Fig.28 As shown in , an exemplary laser source can use a dispersive element 2880 constructed by connecting a series of chirped FBGs. For example, a first chirped FBG 2800a can be spliced ​​into a spliced ​​arrangement 2801a to a second chirped FBG 2800b, and a grating-free fiber can be included between the chirped FBGs. A third chirped FBG 2800c can splice a spliced ​​arrangement 2802b to a second grating 2800b. Each of the gratings 2800a-2800c can be configured to reflect a limited bandwidth. For example, a first grating 2800a can have a reflectivity profile 2805a, a second grating 2800b can have a reflectivity profile 2805b, and a third grating 2800c can have a reflectivity profile 2805c. The exemplary reflectivity profiles of the gratings 2800a-2800c can overlap. The group delay distributed by gratings 2800a-2800c may be given by delay profiles 2806a-2806c, respectively.

[0136] Fig.32 A diagram of an exemplary laser source providing modulation in a cavity, configured to suppress light circulation in a particular path (and providing an exemplary diagram of its output) is shown according to an exemplary embodiment of the present disclosure, wherein the exemplary laser can be configured to avoid light circulation in unwanted paths by using a modulator. In particular, the exemplary laser can be configured to include a modulator 3230, circulators 3231, 3232, a reflective dispersion arrangement 3233, an optical group of additional modulatable loss or gain elements 3251, wavelength selective filters 3235, 3236, an optical amplifier 3234, and an output coupler 3237 that creates a light output 3238. For example, an exemplary laser may be configured to preferentially emit laser light in cavity path A defined by light passing through the components in the following order: 3230-3231-3233-3231-3250-3235-3234-3236-3237-3232-3233-3230, and further configured to not emit laser light in cavity path B defined by light passing through the components in the following order: 3234-3236-3237-3232-3233-3231-3250-3235-3234.

[0137] Fig.32The exemplary system shown in can be configured to provide a lower gain in the path B by, for example, modulating the loss in the cavity path B using, for example, a modulator 3250, or by modulating the gain of the optical amplifier 3234 using a drive signal 3240. The modulation of the loss / gain can be periodic in the diagram 3260 with a timing frequency (T1+T2). The cycle of light through path B can be configured as (N+0.5)*(T1+T2), where N is an integer. As shown in Figure 3260, the light / radiation circulating in path B can successively encounter a time with low loss (or high gain) 3262a, 3262b, followed by a time with high loss (or low gain) 3261a, 3261b. This can increase the overall loss of the path across multiple cycles and reduce the accumulation of light. By, for example, adding optical fiber to the modulator 3230, the cycle time of path A can be set separately from the cycle time of path B. The exemplary timing can be configured as N*(T1+T2), where N is an integer. For example, light / radiation circulating in path B can provide a consistent state of low loss (or high gain) that produces laser emission, or can experience a state of high loss (or low gain) with suppressed laser emission. The drive signal 3241 to the modulator can be configured to provide a laser duty cycle of 50% or less and aligned with the timing of the low loss (or high gain) cycle. In this exemplary approach, the exemplary laser can be configured to output light / radiation 3238 having periods of laser output (3271a, 3271b) separated by periods of finite light / radiation output (3272a, 3272b), as shown in Figure 3270.

[0138] In this exemplary configuration, light / radiation from path B can be suppressed. Time T2 can be, for example, equal to T1, or can be less than T1. It can be understood that the modulation pattern in 3260 can be, for example, a smooth modulation, such as a sinusoidal modulation. The dispersion element 3233 can be configured to produce a wavelength at a gain peak during a time when cavity path A has the lowest total gain (such as at the edge of time windows 3262a, 3262b), and to produce a wavelength at the edge of the gain peak during a time when the gain is the highest (such as in the central region of time windows 3262a, 3262b). Modulation of loss and gain can be performed, for example, by modulating the current 3240 used in the semiconductor optical amplifier 3234, and / or by inserting an additional modulator or gain element 3250 controlled by a signal 3251. For example, the control signals 3240 and 3251 can be synchronized with the drive signal 3241, for example. The duty cycle of the output light 3238 can be increased by splitting the light into two paths and delaying one path relative to the other path by approximately the length of an A line and recombining. In this second path, the light / radiation may, for example, be polarization rotated to create adjacent A lines with different polarizations, such as Fig. 27 as shown in .

[0139] Fig.36 A diagram showing an exemplary OS-OCT source provided by a dispersive pulsed broadband laser source according to an exemplary embodiment of the present disclosure. In addition to the laser cavity, the exemplary source can have a non-cavity configuration. In this exemplary embodiment, light / radiation from a broadband light source 3600 can be pulsed in time by an intensity modulator 3601 (e.g., driven by a signal 3605 from a computing arrangement or pulse generator). The light / radiation can enter a circulator 3602, which guides such light / radiation toward a dispersive element 3603 (such as an FBG array or a continuously chirped FBG). The dispersed light / radiation returns from the dispersive element 3603 and travels through a wavelength selective filter 3604 (e.g., the number of filters in this path ranges from zero to multiple). The light / radiation can be amplified in several stages by optical amplifiers 3606a, 3606b. If a wavelength selective comb filter 3604 is used, or if an FBG array is used as a dispersive element 3603, the output of the exemplary laser can be wavelength stepped. The output of the laser can be wavelength swept if a continuously chirped FBG 3603 is used without a wavelength selective filter 3604. These exemplary components can be arranged in a different order to achieve the same output. Additional Interferometer Embodiments

[0140] Fig.29 A diagram of an exemplary imaging interferometer using phase modulation to perform quadrature demodulation according to an exemplary embodiment of the present disclosure is illustrated. In this exemplary embodiment, an exemplary OS-OCT system can be configured to perform complex demodulation of fringes by phase modulating light in the reference arm or the sample arm. Fig.29As shown in FIG. 2 , a laser source 2900 may send light / radiation to an interferometer 2901 that includes a sample arm 2903 and a reference arm 2904 created by an optical coupler 2902. The light / radiation in the reference arm 2904 may pass through a phase modulator 2950 that may be driven by a signal 2951 generated by a computer arrangement in synchronization with the laser 2900. The phase modulator 2950 may be constructed using an electro-optic modulator, an acousto-optic frequency shifter, and / or other arrangements for modulating the phase of a light beam. The light / radiation from the reference arm 2904 and the sample arm 2903 may be combined at an interference coupler 2930, and the output signals may be detected by a digitizer 2931 and a computer arrangement 2932. The reference arm phase shift may be configured to facilitate detection of the in-phase (I) and quadrature (Q) components of the interference fringes and allow complex conjugate ambiguity removal. The reference may include a circulator 2905 that directs and receives light from a reference mirror 2906 through an optical fiber path 2918. The sample arm 2903 may include an electro-optic modulator 2910 and a polarizer 2909 for controlling the polarization of the light. The circulator 2911 may direct light / radiation through an optical coupler 2912 to a sample calibration mirror 2913 and a sample 2914, and receive reflected light / radiation from these paths along an optical fiber 2917. Polarization controllers 2907, 2915, 2908 may be provided to control the polarization state of the light / radiation.

[0141] The phase shifting that can be performed by the modulator 2950 can be configured to phase shift adjacent light pulses from an exemplary source, such as Fig.30 As shown in Figure 3000, for example, phase 1 is applied to the first pulse of wave number k1, and the second phase 2 is used for the second pulse of wave number k1, and the operation is repeated for subsequent pulses. Alternatively or additionally, the phase state can be modulated between the A lines (3010). Alternatively, the phase modulator can be operated within the pulse to generate a phase shift in the front of the pulse and a second phase shift in the back half (3020). Although a two-state phase shift device is described, which nominally provides 0 degree and 90 degree phase states, multiple phase states can be generated by the phase modulator so that, for example, a three-state configuration is used to provide a phase of 0 degree, +60 degree, +120 degree. Alternatively or additionally, established techniques based on acousto-optic frequency shifters or N×N interference couplers (where, for example, N is not equal to 2) can be used to create orthogonal or phase-shifted signals for complex conjugate removal.

[0142] Fig.33 A diagram illustrating an exemplary OS-OCT system using a comb source including multiple wavelengths and a wavelength demultiplexer to spatially separate each wavelength signal before detection according to another exemplary embodiment of the present disclosure. Fig.33As shown in , a comb light source 3300 can be used, which can provide a continuous or nearly continuous light / radiation output of a set of wavelengths λ1 to λn. Such an exemplary source 3300 can be input into an interferometer, which includes a split coupler 3301, which separates the light / radiation into a reference arm 3370a and a sample arm 3370b. The reference arm 3370b can use a coupler 3303 to guide the light to an optical fiber 3307, which can be coupled to a mirror 3306. The reflected light / radiation returns to the coupler 3303 and can be transmitted to a phase modulator or an acousto-optic frequency shifter 3304. The sample arm light / radiation can be guided to a coupler 3302, which further guides the light / radiation to an optical fiber 3308, which forwards the light / radiation to the sample, and the reflected light / radiation can return to the interference coupler 3305. Interference fringes appear on output ports 3309a and 3309b. Interference fringes of wavelength λ1 may be isolated using demultiplexers 3310a and 3310b, which may be or include, for example, a grating or arrayed waveguide grating (AWG). The optical signal of λ1 may be directed to output 3311a. A similar output for demultiplexer 3310b may be directed to output 3311b, and signals 3311a, 3311b may be input to a balanced optical receiver to perform intensity noise subtraction.

[0143] The detected signal 3311d may then be sent or otherwise provided to a computing arrangement 3311e, which is shown in detail as a computer arrangement 3340. For example, the signal 3341 may be digitized by an analog-to-digital converter 3342 provided in the computer arrangement 3340, and such signal information 3343 may be separated into I 3345 and Q 3346 components using, for example, a demodulator 3344. When the device 3304 is, for example, a frequency shifter (such as an acousto-optic frequency shifter), such an exemplary demodulator 3344 may be or include an I / Q demodulator based on mixing using known techniques. The signals 3345, 3346 may define a composite interference signal of λ1, and may be part of the input to a Fourier transform engine 3347, a portion of which (along with information from other wavelengths) may be used to calculate or otherwise determine a depth-resolved scattered signal 3348 using known Fourier domain OCT processing. Additional wavelength signals may be analyzed in a similar manner using additional output ports of the demultiplexers 3310a, 3310b using similar exemplary embodiments described herein for the λ1 systems and methods. Optical receiver, digitizer and computer embodiments

[0144] Fig.31An exemplary system and diagram illustrating exemplary acquisition of signals into a register with greater depth using an 8-bit digitizer and fringe averaging according to an exemplary embodiment of the present disclosure is shown. For example, an OS-OCT system may include a digitizer 3100 for acquiring interferometric fringe signals, which may be configured to perform on-board averaging of fringes. Fig.31 As shown, the digitizer 3100 may digitize the analog signal 3101 using an 8-bit analog-to-digital converter 3102. The 8-bit digital word from sample 1 may then be passed to an averaging engine 3107, which may first convert the word to 16 bits 3103 and then add the word 3105 with the existing value in register 3104. Such an exemplary procedure may be repeated for sample 2 in a separate averaging engine 3108.

[0145] In an exemplary configuration of N points in the A line / stripes, there may be N averaging engines. The N+1 sample may then be returned to the first averaging engine 3107. Such an exemplary procedure may be repeated for i iterations, and the value after the i iterations may be output 3107a from the averaging engine 3107 as a 16-bit word. The group of 16-bit words 3107a, 3108a, 3109a, etc. may define average stripes, where 3108a may be generated by the averaging engine 3108, and 3109a may be generated by the averaging engine 3109. Here we note that the digitizer 3102 may operate at a higher bit depth. The digitizer arrangement 3100 allows the use of a lower bit depth digitizer while improving dynamic range and signal fidelity by stripe averaging. The exemplary digitizer system may be partially executed on a computer or field programmable gate array. For example, the digitizer clock input 3180 may be synchronized with the laser so that the digitizer clock, the laser A line, and the resulting stripes remain highly synchronized. The onboard processor may also perform core signal processing, such as FFT. This may facilitate the optical subsampling system to perform real-time processing and image display. Additionally, the digitizer may be configured to continuously stream the acquired data to the computing arrangement to allow continuous imaging or real-time continuous imaging. The signal may be digitized at a bit depth other than 8 bits, such as 10 bits, and may be converted to another bit depth other than 16 bits, such as 12 bits or 14 bits.

[0146] In another exemplary embodiment of the present disclosure, the digitizer may utilize a sample and hold integrate and hold function that accumulates the signal over the pulse duration and returns the accumulated measurement as an alternative to conventional digitizers used with low pass filters. In another exemplary embodiment, signal roll-off that occurs as frequencies near the Nyquist edge of a subsampled baseband image may be offset by amplifying the signal as a function of depth and selecting such amplification to match the roll-off of the OS-OCT system. Alternative embodiments of imaging probes

[0147] In further exemplary embodiments of the present disclosure, an optical subsampling imaging system may be operated with a small scanning beam probe that can be used to image internal parts. The exemplary scanning probe may be based on a fiber scanning architecture, based on a small MEMs-based mirror, based on a rotating prism or a rotating probe design. In addition, the probe may be configured to provide forward and lateral imaging. For example, a microscope may be configured to include optical elements required to dynamically adjust the focal plane to the sample position. This may be performed, for example, by mechanically moving the lens position and / or by using a variable optical lens (such as voltage-controlled liquid lens technology). Additionally or alternatively, such an exemplary probe or microscope system may include a non-Gaussian imaging beam profile characterized by an extended depth of focus. Such an exemplary beam profile may, for example, be a Bessel beam, which may be generated, for example, by using a circular aperture or by an axicon lens. Additional Light Source Designs and Exemplary Embodiments

[0148] Fig.37A set of exemplary diagrams illustrating exemplary configurations, operations / functions, and timing of an exemplary OS-OCT source 3700 according to exemplary embodiments of the present disclosure are illustrated. For example, an electrical pulse 3701 of approximately 525 ps from a pattern generator 3712 can drive an electro-optic lithium niobate intensity modulator 3713 and repeat at the resonance of the cavity round trip time. The gain medium can be or include a semiconductor optical amplifier (SOA) 3721 with a 3 dB bandwidth of 102 nm. A continuously chirped fiber Bragg grating 3714 can be placed between two circulators 3715a, 371b to facilitate access to both positive and negative dispersion. The length of the grating can be, for example, 8.3 meters with a continuous reflection bandwidth of 1522 nm to 1605 nm. The grating can be designed to produce a linear group delay with respect to the optical frequency, for example, to produce a dispersion of + / -930 ps / nm at 1550 nm. The same grating can be used for both positive and negative dispersion. The insertion loss of the grating used in the reflection mode is 1.36 dB for the near side reflection wavelength and 1.71 dB for the wavelength reflected from the far end of the grating. In order to obtain higher stability and lower noise level, the dispersion in the laser cavity caused by the single mode fiber can be matched by inserting 9m dispersion compensating fiber (DCF) 3720 with a dispersion parameter of -38.5ps / nm / km at λ=1550nm. In addition, 20% of the light in the laser cavity can be separated via an 80 / 20 output optical coupler 3718 to generate an optical output 3719. A digital delay generator 3711 can be used to modulate the SOA current drive 3710. The delay generator can be driven by a mode generator 3712.

[0149] Because the fiber Bragg grating can be partially transmissive, there can be three separate cavities in the laser. These cavities can be labeled in the order in which the circulating light passes through points A 3717a and B 3717b. The longest cavity that provides the desired laser emission can pass through two points (cavity ABABA). The non-zero transmission of the CFBG also creates two short cavities (cavity AAAAA, cavity BBBBB). Within the CFBG passband, approximately 30% of the light can be reflected. In addition, wavelengths outside the grating reflection bandwidth are transmitted through the grating with approximately 100% efficiency. Because cavity BBBBB has no optical gain, it may not be a laser emission cavity but can create reflections. Cavity AAAAA can contain an SOA and can emit lasers, which can affect the laser emission in cavity ABABA.

[0150] Laser emission in cavity AAAAA can be suppressed by modulating the SOA and controlling the round trip time of each of cavities ABABA, AAAAA, and BBBBB. In this exemplary configuration, the round trip time of cavity ABABA can be approximately twice the round trip time of cavities AAAAA and BBBBB (see 3702). An exemplary modulation of SOA 3731 and EOM 3730 can be suppressed light circulation in these short cavities, as shown in Figure 3703. Light / radiation circulating in cavity AAAAA can be blocked by EOM 3732. Light / radiation circulating in cavity BBBBB can be blocked by SOA modulation 3733 for all wavelengths of CFBG. Light / radiation circulating in cavity ABABA can reach SOA through EOM when current is high, and then return to pass through EOM 3734.

[0151] To generate a wavelength stepped (frequency comb) output, a fixed fused silica FP etalon 3716 with an 80 GHz FSR (~0.64 nm) and low finesse (~5) can be provided. In an exemplary embodiment, an etalon with a FSR between 25 GHz and 400 GHz can be used. When the FP is removed, continuous wavelength sweep operation can be achieved. In an exemplary embodiment of system 3700, the SOA can be driven with a current pulse of, for example, 61 ns. The round trip of the long cavity (ABABA) is 244.75 ns (approximately 50.1 m), for example, almost 4 times larger than the SOA current pulse. This can produce a duty cycle of approximately 25% at the laser output. To increase the A-line rate, a 4x copy and paste buffered delay line 3704 can be used to create an A-line rate of 16.3 MHz. An enhancer SOA 3742 is used after the copy and paste delay line. The delay line includes a set of 50 / 50 couplers (3741a, 3741b, 3741c) and delay fibers (3743a, 3743b). A polarization controller is included in the path to align the polarization state with the enhancer SOA 3742.

[0152] In this exemplary embodiment, a FP etalon with a fineness value between 3 and 25 is used to provide low noise operation. In this laser embodiment, a FP etalon with a linewidth wider than the desired laser emission linewidth is used. The laser emission provides linewidth narrowing, while the wider FP passband can produce lower noise performance. For example, the FP can be a solid etalon, or can be constructed of two partial mirrors with an air space between the mirrors. Using air-spaced mirrors can facilitate the FSR of the etalon to be dynamically changed.

[0153] It should be understood by those skilled in the art that the output coupler (e.g. Fig.37The output coupler 3718 shown in can be located anywhere within the laser cavity to provide laser output light. In further exemplary embodiments, the optical frequency comb source can provide light / radiation at discrete optical frequencies spaced greater than 20 GHz and an instantaneous linewidth of less than 10 GHz for each optical frequency.

[0154] Fig.38 A set of graphs providing exemplary measurements of the spectral output of an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure is shown. For example, for continuous (3800a, 3801a) and frequency comb (3800b, 3801b) configurations, in Fig.38 The following diagram illustrates the copy and paste operation at 4x. Fig.37 Output spectra 3800, 3801 of the laser after the delay line 3704 of (a) a delay line 3704 of (b) a delay line 3704 of (c) a delay line 3704 of (d) a delay line 3704 of (c) a delay line 3704 of (d) a delay line 3704 of (e) a delay line 3704 of (f ...

[0155] Fig.39 A set of graphs showing exemplary measurements of the temporal output of an exemplary OS-OCT source are shown according to an exemplary embodiment of the present disclosure. In particular, Fig.39 As shown, output traces for the laser in both CW (3900) and frequency comb (3901) configurations are provided, measured with an 8 GHz optical receiver and a 2 GHz oscilloscope. In an exemplary frequency comb configuration, the EOM can be driven with 525 ps electrical pulses, and the CFBG dispersion at 1550 nm is 930 ps / nm, resulting in approximately 600 ps spacing between 80 GHz spaced pulses. This pulse structure is difficult to detect, in part due to the 2 GHz oscilloscope bandwidth. A second CFBG can be provided to stretch the laser output post-cavity (without copy and paste buffering) to further separate the optical pulses 3902 in the time domain.

[0156] Fig.40A set of graphs illustrating exemplary measurements of the coherence length of an exemplary OS-OCT source according to an exemplary embodiment of the present disclosure are illustrated, including the coherence properties of a continuous sweep configuration and a frequency comb configuration. For each such exemplary configuration, a laser is output to a Mach-Zehnder interferometer to generate interference fringes. For the continuous wavelength sweep configuration 4000, an 8 GHz optical receiver is used to detect the fringe signal, and an RF spectrum analyzer is used to measure the fringe amplitude. The fringe amplitude is measured as a function of the mirror position relative to the zero delay point. Since the frequency comb configuration generates RF frequencies within a restricted baseband, an 800 MHz optical receiver and a high-speed digitizer can be used to run at speeds greater than 1 GS / sec to capture fringes as a function of the mirror position. The reference arm measurements are subtracted from these fringes, and the amplitude of the fringes is calculated as a function of the mirror position. As shown in 4001, the frequency comb configuration provides a much longer coherence length.

[0157] Fig.41 A graph is shown providing exemplary measurements of noise for an exemplary OS-OCT source, including the relative intensity noise (RIN) of a laser source, according to an exemplary embodiment of the present disclosure. The RIN was measured using an 800 MHz optical receiver and a digitizer greater than 2 GS / sec. RIN levels of -140 dB / Hz and -145 dB / Hz were obtained for a continuous swept laser and a frequency comb laser.

[0158] The foregoing merely illustrates the principles of the present disclosure. Various modifications and alternatives to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. In fact, arrangements, systems, and methods according to exemplary embodiments of the present disclosure may be used and / or implemented with any OCT system, OFDI system, SD-OCT system, SECM system, OBM system, or other imaging system capable of imaging in vivo or in fresh tissue, such as those described in the following patent applications: International Patent Application PCT / US2004 / 029148 filed on September 8, 2004 (which was filed as International Patent Publication No. WO on May 26, 2005). No. 2005 / 047813, U.S. Patent Application No. 11 / 266,779, filed on November 2, 2005 (published as U.S. Patent Publication No. 2006 / 0093276 on May 4, 2006), and U.S. Patent Application No. 10 / 501,276, filed on July 9, 2004 (published as U.S. Patent Publication No. 2005 / 0018201 on January 27, 2005), U.S. Patent Publication No. 2002 / 0122246, published on May 9, 2002, U.S. Patent Application No. 61 / 649,546, U.S. Patent Application No. 11 / 625,135, U.S. Patent Application No. 61 / 589,083, and International Application No. PCT / US2014 / 048256, the disclosures of which are incorporated herein by reference in their entirety. It will therefore be appreciated that those skilled in the art will be able to conceive of many systems, arrangements and methods that, although not explicitly shown or described herein, still embody the principles of the present invention and are therefore within the spirit and scope of the present disclosure. In addition, as will be appreciated by those of ordinary skill in the art, the various exemplary embodiments described herein may be used interchangeably with all other exemplary described embodiments. In addition, to the extent that prior art knowledge is not expressly incorporated herein by reference above, it is expressly incorporated herein in its entirety. All publications cited above are incorporated herein by reference in their entirety.

Claims

1. A device comprising: a laser arrangement configured to generate laser radiation at a specific number (N) of discrete optical frequencies; an interferometer arrangement configured to generate an interference signal from said laser radiation, and a beam scanning arrangement configured to scan at least a portion of the laser radiation across at least a portion of at least one sample, wherein the line width of each of the discrete optical frequencies is less than 10 GHz, and wherein the spacing between each of the discrete optical frequencies is greater than 20 GHz, and wherein the laser radiation steps between the discrete optical frequencies at a rate greater than 20 million discrete optical frequency steps per second.

2. The apparatus of claim 1, wherein the laser arrangement comprises a continuous fiber Bragg grating having a length greater than 2 meters.

3. The apparatus of claim 1, wherein the laser arrangement comprises a fiber Bragg grating array having a length greater than 2 meters.

4. A method for displaying a video stream about at least one structure, comprising: a) measuring four-dimensional interferometry data about different parts of at least one structure at different points in time, wherein the four-dimensional data describes at least one optical property of the at least one structure, wherein the four-dimensional interferometry data is cyclically wrapped in a specific spatial dimension; b) using a computer, transforming the four-dimensional interferometry data into two-dimensional video data by compressing the specific spatial dimension; and c) displaying video streams of different portions of the at least one structure using the two-dimensional video data.

5. The method of claim 4, wherein the compressing comprises (i) locating a position of a surface of the at least one structure within the four-dimensional interferometry data, and (ii) using the position to control the compression.

6. The method of claim 4, wherein step (a) is performed using a frequency comb light source.

7. The method according to claim 4, wherein step (a) is performed using a laser arrangement configured to provide laser radiation and comprising an optical cavity comprising: a first arrangement of a dispersive optical waveguide having a first side and a second side and configured to receive and disperse (i) at least one first electromagnetic radiation received at the first side so as to provide at least one second electromagnetic radiation, and (ii) at least one third electromagnetic radiation received at the second side so as to provide at least one fourth electromagnetic radiation, wherein the first side and the second side are different from each other and wherein the second radiation and the third radiation are correlated with each other, and a second arrangement of active optical modulators configured to receive and modulate said fourth radiation so as to provide said at least one first electromagnetic radiation to said first arrangement, and Wherein the laser radiation is associated with at least one of the first radiation, the second radiation, the third radiation or the fourth radiation.

8. A computer accessible medium comprising software thereon for displaying a video stream about at least one structure, wherein: When the computer executes the software, the computer is configured to execute a program including: a) measuring four-dimensional interferometry data about different parts of at least one structure at different points in time, wherein the four-dimensional data describes at least one optical property of the at least one structure; b) using a computer to transform the four-dimensional interferometry data into two-dimensional video data; as well as c) displaying video streams of different portions of said at least one structure using said two-dimensional video data, wherein said measuring and said displaying are performed with a latency of less than 1 second.

9. A computer accessible medium comprising software thereon for displaying a video stream about at least one structure, wherein: When the computer executes the software, the computer is configured to execute a program including: a) measuring four-dimensional interferometry data about different parts of at least one structure at different points in time, wherein the four-dimensional data describes at least one optical property of the at least one structure, wherein the four-dimensional interferometry data is cyclically wrapped in a specific spatial dimension; b) transforming the four-dimensional interferometry data into two-dimensional video data by compressing the specific spatial dimension; and c) displaying video streams of different portions of the at least one structure using the two-dimensional video data.

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