A high-speed swept source optical coherence tomography wave number linearization system and method

Abstract

This invention provides a high-speed swept-frequency optical coherence tomography (OCT) wavenumber linearization system and method. The proposed system and method introduce a Mach-Zehnder interferometer module with embedded dual fiber Bragg gratings into the high-speed swept-frequency OCT. The fiber Bragg gratings intercept interference signals within a certain wavelength range to obtain the phase correction vector required for wavenumber linearization in high-speed OCT. This vector is then used to perform linear interpolation on the high-speed OCT signal. This invention effectively solves the trigger jitter problem of the swept-frequency light source in different swept-frequency cycles, achieves wavenumber linearization resampling of the high-speed OCT signal, ensures the axial resolution of high-speed OCT, and significantly improves the imaging capability and practicality of the OCT system.

Description

Technical Field

[0001] This invention belongs to the field of performance enhancement technology for swept-frequency optical coherence tomography. Specifically, it relates to a method for acquiring the phase correction vector required for high-speed swept-frequency optical coherence tomography based on a Mach-Zehnder interferometer signal with an embedded dual-fiber Bragg grating, thereby achieving wavenumber linear resampling. Background Technology

[0002] Optical coherence tomography (OCT) is a non-invasive, non-contact, high-resolution biomedical optical imaging method with important applications in cell analysis, materials detection, and blood flow imaging. Swept Source OCT (SS-OCT), based on a swept-source light source, is a typical Fourier domain optical coherence tomography technique. However, the trigger jitter and sweep nonlinearity issues inherent in high-speed sweep source scanning severely affect the imaging performance of high-speed SS-OCT. Therefore, a phase correction vector is necessary to address the trigger jitter of the swept source and to linearly resample the acquired signal in wavenumber space during frequency domain optical coherence tomography.

[0003] General methods for obtaining phase correction vectors are mainly divided into hardware methods and software methods. Hardware methods include the plane mirror reference method and the conventional Mach-Zehnder interferometry. The plane mirror reference method distributes a small amount of light from the sample arm to a stationary plane mirror, and detects the interference signals of the reflected light from the plane mirror and the backscattered light from the sample with the reference light to obtain the correction vector. The conventional Mach-Zehnder interferometry, after the output of the swept frequency source, allows a portion of the light to pass through a Mach-Zehnder interferometer (MZI). The Mach-Zehnder interferometer interference signal and the optical coherence tomography (OCT) signal are detected simultaneously, achieving phase correction of the OCT signal. However, the plane mirror reference method can only correct phase jumps within a small range of integer sampling points and may introduce artifacts, reducing imaging performance; the conventional Mach-Zehnder interferometry can correct the phase but does not solve the trigger jitter problem of each scan of the swept frequency source. Besides hardware methods, current software methods for obtaining correction vectors are either computationally intensive and time-consuming, or easily interfered with and cannot operate stably. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a high-speed swept-frequency optical coherence tomography wavenumber linearization method. Two fiber Bragg gratings are used in the Mach-Zehnder interferometer module of the swept-frequency optical coherence tomography system to align the spectral fringe signals of different laser scans, and linear sampling of the optical coherence tomography signal is achieved using the Mach-Zehnder interference signal between the reflection peaks of the two fiber Bragg gratings.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A high-speed swept-frequency optical coherence tomography wavenumber linearization system includes a swept-frequency light source, a Mach-Zehnder interferometer module, a detector module, and a data acquisition and data processing program.

[0007] The output port of the frequency sweep light source is connected to the first port of the first coupler. The first coupler splits the light into a first signal light and a second signal light. The first signal light enters the Mach-Zehnder interferometer module. The second signal light enters the input port of the second coupler. The second coupler splits the light into a first incident light and a second incident light. The first incident light enters the reference arm, and the second incident light enters the sample arm.

[0008] The reference arm includes a collimating mirror and a plane mirror. The first incident light enters the reference arm, is reflected back by the collimating mirror and the plane mirror, and then enters the first input port of the third coupler. The sample arm includes a scanning galvanometer and a collimating mirror. The second incident light enters the sample arm, is reflected back by the scanning galvanometer and the collimating mirror, and then enters the sample.

[0009] The first and second output ports of the third coupler are respectively connected to the two ports of the first balanced detector, and the first and second output ports of the Mach-Zehnder interferometer module are respectively connected to the two ports of the second balanced detector. The data acquisition card acquires the output signals of the first and second balanced detectors, and the computer program processes the data stream acquired by the data acquisition card.

[0010] The Mach-Zehnder interferometer module includes two fiber couplers, a lens, a polarization controller, and two fiber Bragg gratings with different operating frequencies. The first fiber coupler splits the light incident on the Mach-Zehnder interferometer module into two beams, which pass through the lens and polarization controller respectively before being recoupled at the second fiber coupler. The two fiber Bragg gratings with different operating frequencies are inserted into the first and second output ports of the second fiber coupler, respectively. The second fiber coupler splits the light into two beams again, and the two beams pass through the two fiber Bragg gratings before exiting the Mach-Zehnder interferometer module.

[0011] A high-speed swept-frequency optical coherence tomography wavenumber linearization method, applicable to the aforementioned high-speed swept-frequency optical coherence tomography wavenumber linearization system, includes the following steps:

[0012] S1: Start the sweep frequency optical coherence tomography system. 5% of the output light of the first coupler is split into two beams as the first signal light when it passes through the first fiber coupler at the end of the Mach-Zehnder interferometer module. The two beams pass through the two fiber Bragg gratings with different operating frequencies and enter the two ports of the second balanced detector.

[0013] S2: The computer-controlled data acquisition card acquires the signals from the first and second balanced detectors, and uses a computer program to perform registration of the second balanced detector signal, so that the laser scan aligns with the reflection peaks of the two fiber Bragg gratings to capture the Mach-Zehnder interferometer module signal within a certain wavelength range.

[0014] S3: The Mach-Zehnder interferometer signal has two fiber Bragg grating reflection peaks. The signal between the reflection peaks is used to obtain the phase correction vector required for the wavenumber linearization of the first balanced detector signal.

[0015] S4: Using the phase correction vector obtained in S3, linear interpolation is performed on the synchronously acquired optical coherence tomography signal to achieve linear resampling of wavenumber.

[0016] The beneficial effects of this invention are:

[0017] (1) The phase correction vector acquisition method is based on independent interference and signal channels, which will not affect the main part of the swept frequency optical coherence tomography, nor will it be affected by the main part of the swept frequency optical coherence tomography, and can stably acquire the phase correction vector.

[0018] (2) Since two fiber Bragg gratings of different frequencies are used, the optical signal of each frequency sweep will be aligned with the reflection peak of the fiber Bragg grating and the signal between the two frequencies will be intercepted, thereby aligning the spectra of different laser frequency sweep cycles and solving the trigger jitter problem of high-speed frequency sweep light source.

[0019] (3) The Mach-Zehnder interferometer signal and the optical coherence tomography signal are acquired simultaneously by the high-speed acquisition device in each laser frequency sweep, and the frequency sweep range is the same, which ensures that an accurate phase correction vector is obtained. Attached Figure Description

[0020] Figure 1 This is an experimental schematic diagram of the high-speed swept-frequency optical coherence tomography system built according to the present invention.

[0021] Figure 2 This is a schematic diagram of the Mach-Zehnder interferometer module with embedded dual fiber Bragg gratings built according to the present invention.

[0022] Figure 3The embodiments of the present invention utilize the Mach-Zehnder interferometer signal and the high-speed optical coherence tomography signal acquired synchronously by the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be clearly and completely described below with reference to embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The present invention can replace two fiber Bragg gratings with different operating frequencies in the Mach-Zehnder interferometer module to realize a high-speed frequency-sweeping optical coherence tomography system with different sweep frequency ranges. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1 , Figure 1 This is an experimental schematic diagram of the high-speed swept-frequency optical coherence tomography system constructed according to the present invention. The output port of the swept-frequency light source 1 is connected to the first port of the first coupler 2. The first coupler splits the light into two beams, one of which enters the Mach-Zehnder module 4, and the two outputs of the Mach-Zehnder module 4 enter the second balanced detector 6. The other beam enters the input port of the second coupler 301. The second coupler 301 splits the light into two beams, one of which enters the reference arm and the other enters the sample arm. The light from the reference arm passes through the fiber optic circulator 302 and the collimating mirror 304, and is then reflected back by the plane mirror 309 to enter the first input port of the third coupler 305. The light from the sample arm passes through the fiber optic circulator 303 and the scanning galvanometer 306, and then passes through the collimating mirror 307 before entering the sample 308, and is then reflected back to enter the second input port of the third coupler 305. The first and second output ports of the third coupler 305 are respectively connected to the two ports of the first balanced detector 5. The data acquisition card 8 acquires the output signals of the first balance detector 5 and the second balance detector 6, and the computer 7 processes the data stream acquired by the data acquisition card 8.

[0025] Please see Figure 2 , Figure 2 This is a schematic diagram of the Mach-Zehnder interferometer module with embedded dual fiber Bragg gratings constructed according to the present invention. Light from the second output port of fiber coupler 2 enters the Mach-Zehnder interferometer module 4 with embedded dual fiber Bragg gratings, and is incident on the first input port of fiber coupler 401. It is split into two beams. One beam passes through lenses 402 and 404, then through polarization controller 406, and enters the first input port of fiber coupler 408. The other beam passes through lenses 403 and 405, then through polarization controller 407, and enters the second input port of fiber coupler 408. The first and second output ports of the fiber coupler serve as the two outputs of the Mach-Zehnder interferometer module 4 with embedded dual fiber Bragg gratings.

[0026] The present invention provides a high-speed swept-frequency optical coherence tomography wavenumber linearization method comprising the following steps:

[0027] S1: A Mach-Zehnder interferometer is introduced into the sweep frequency optical coherence tomography system. The output light of the sweep frequency laser is split into two paths by the first coupler 2. 95% of the light enters the optical coherence tomography system 3, and 5% of the light signal enters the Mach-Zehnder interferometer module 4.

[0028] S2: Two fiber Bragg gratings (FBGs) 409 and 410 with different operating frequencies are inserted into the two output ports of the fiber coupler 408 at the end of the Mach-Zehnder interferometer module 4, respectively, to realize the construction of the Mach-Zehnder interferometer module 4 with embedded dual fiber Bragg gratings.

[0029] S3: The two outputs of the Mach-Zehnder interferometer module 4 with embedded dual fiber Bragg gratings are connected to the two input ports of the second balanced detector 6, and are connected to the computer 7 through the data acquisition card 8.

[0030] S4: Start the swept-frequency optical coherence tomography system. 95% of the light from the first coupler 2 enters the main part 3 of the swept-frequency optical coherence tomography system. The remaining 5% of the output light is split into two paths when passing through the fiber coupler 408 at the end of the Mach-Zehnder interferometer. The two paths pass through the two fiber Bragg gratings 409 and 410 with different operating frequencies, respectively, and enter the two ports of the second balanced detector 6.

[0031] S5: Computer 7 controls data acquisition card 8 to input signals from the first balance detector 5 and the second balance detector 6.

[0032] The system collects data and uses a computer program to perform signal registration with the second balanced detector, aligning the laser scan with the reflection peak of the fiber Bragg grating to capture Mach-Zehnder interferometer signals within a certain wavelength range. Ultimately, the Mach-Zehnder interferometer spectral signals from different laser scans are aligned.

[0033] S6: The aligned Mach-Zehnder interferometer signal has two fiber Bragg grating reflection peaks. The signal between the reflection peaks is used to obtain the phase correction vector required for wavenumber linearization of the first balanced detector signal (which is the optical coherence tomography signal).

[0034] S7: Using the phase correction vector obtained above, linear interpolation is performed on the synchronously acquired optical coherence tomography signal to achieve linear resampling of wavenumber.

[0035] In this example, the swept-frequency light source uses a MEMS-VCSEL SL132121 swept-frequency laser from Thor Labs, USA, with a center wavelength of 1300 nm, a sweep rate of 200 kHz, and a sweep range of 100 nm. The fiber coupler is model TW1300R2A2. The fiber Bragg grating used in this embodiment is an O / E LAND OEPBG-1310 with a center wavelength of 1310 nm and a narrow bandwidth of 0.5 nm. Considering the sweep rate of the swept-frequency light source, the balanced detector used in this embodiment is a THORLABS PDB480C-AC with a bandwidth of 1.6 GHz, which meets the imaging bandwidth requirements. To achieve wavenumber linearization, the optical coherence tomography signal and the Mach-Zehnder interferometer signal must be acquired simultaneously by a high-speed data acquisition card. This embodiment uses a Teledyne ADQ-7 high-speed data acquisition card, which has two channels and a maximum sampling rate of 10 GS / s.

[0036] Please see Figure 3 The Mach-Zehnder interferometer signals synchronously acquired by the high-speed acquisition card are as follows: Figure 3 As shown in (a), the acquired optical coherence tomography signals are as follows: Figure 3 (b) Two fiber Bragg grating reflection peaks in the acquired Mach-Zehnder interferometer signals serve as trigger signals. Within each scan cycle, the signal between these two fiber Bragg grating signals is always truncated as the phase correction vector for wavenumber linearization, thus resolving the trigger jitter problem inherent in frequency-scanning light sources. Further, using the acquired phase correction vector in conjunction with a linear interpolation algorithm, wavenumber linearization of the optical coherence tomography signal can be achieved.

[0037] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A high-speed swept-frequency optical coherence tomography wavenumber linearization system, characterized in that, Includes a frequency sweep light source, a Mach-Zehnder interferometer module, a detector module, and data acquisition and processing programs; The output port of the swept frequency light source is connected to the first port of the first coupler. The first coupler splits the light into a first signal light and a second signal light. The first signal light enters the Mach-Zehnder interferometer module. The second signal light enters the input port of the second coupler, and the second coupler splits the light into a first incident light and a second incident light. The first incident light enters the reference arm, and the second incident light enters the sample arm. The reference arm includes a collimating mirror and a plane mirror. The first incident light enters the reference arm, is reflected back by the collimating mirror and the plane mirror, and then enters the first input port of the third coupler. The sample arm includes a scanning galvanometer and a collimating mirror. The second incident light enters the sample arm, is reflected back by the scanning galvanometer and the collimating mirror, and then enters the sample. The first and second output ports of the third coupler are respectively connected to the two ports of the first balanced detector, and the first and second output ports of the Mach-Zehnder interferometer module are respectively connected to the two ports of the second balanced detector. The data acquisition card acquires the output signals of the first and second balanced detectors, and the computer program processes the data stream acquired by the data acquisition card. The Mach-Zehnder interferometer module includes two fiber couplers, a lens, a polarization controller, and two fiber Bragg gratings with different operating frequencies. The first fiber coupler splits the light incident on the Mach-Zehnder interferometer module into two beams, which pass through the lens and polarization controller respectively before being recoupled at the second fiber coupler. The two fiber Bragg gratings with different operating frequencies are inserted into the first and second output ports of the second fiber coupler, respectively. The second fiber coupler splits the light into two beams again, and the two beams pass through the two fiber Bragg gratings before exiting the Mach-Zehnder interferometer module.

2. A high-speed swept-frequency optical coherence tomography wavenumber linearization method, applicable to the high-speed swept-frequency optical coherence tomography wavenumber linearization system described in claim 1, characterized in that, Includes the following steps: S1: Start the sweep frequency optical coherence tomography system. 5% of the output light of the first coupler is split into two beams as the first signal light when it passes through the first fiber coupler at the end of the Mach-Zehnder interferometer module. The two beams pass through the two fiber Bragg gratings with different operating frequencies and enter the two ports of the second balanced detector. S2: The computer-controlled data acquisition card acquires the signals from the first and second balanced detectors, and uses a computer program to perform registration of the second balanced detector signal, so that the laser scan aligns with the reflection peaks of the two fiber Bragg gratings to capture the Mach-Zehnder interferometer module signal within a certain wavelength range. S3: The Mach-Zehnder interferometer signal has two fiber Bragg grating reflection peaks. The signal between the reflection peaks is used to obtain the phase correction vector required for the wavenumber linearization of the first balanced detector signal. S4: Using the phase correction vector obtained in S3, linear interpolation is performed on the synchronously acquired optical coherence tomography signal to achieve linear resampling of wavenumber.

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