CN201814557U - Mirror image-free optical frequency domain imaging system based on chromatic dispersion modulation - Google Patents

Abstract

The utility model discloses a mirrorless optical frequency-domain imaging system based on dispersion modulation. A transmission-type optical scanning delay line is set in a reference arm for modulation of dispersion and ensures the identity of axial positions of samples in different dispersion states. . By changing the rotation angle of the vibrating mirror in the transmission optical scanning delay line, the fast modulation of the dispersion is realized, thereby obtaining two sets of interference spectrum signals of the same sample in two dispersion states. The collected two sets of interference spectrum signals are multiplied by corresponding dispersion compensation factors, so that the corresponding imaginary part dispersion after Fourier transform can be accurately compensated. Subtracting the above two sets of interference spectrum signals after dispersion compensation, the imaginary part of the corresponding complex reflection signal disappears, while the real part still contains the dispersion factor. Dispersion compensation is performed on the subtracted interference spectrum signal again, and then inverse Fourier transform is performed to obtain the real reflection signal of the sample, which can be used for mirrorless reconstruction of the sample image.

Description

A mirrorless optical frequency-domain imaging system based on dispersion modulation

technical field

The utility model relates to an optical coherence tomography (OCT) technology, in particular to a mirrorless optical frequency domain imaging system based on dispersion modulation. the

Background technique

Optical coherence tomography (OCT) imaging technology is a new type of optical imaging technology that can perform non-invasive, non-contact, high-resolution in vivo imaging of the tissue structure and physiological functions inside the tested living sample. It has broad application prospects in the field of early diagnosis of diseases and in vivo biopsy. the

The optical frequency domain imaging system is a type of optical coherence tomography system. It uses a high-speed frequency-swept laser source and a point detector to collect axial interference spectral signals of the sample. The reference arm is composed of a fixed plane mirror and does not require axial scanning. , the axial depth information of the sample can be obtained by performing inverse Fourier transform on the axial interference spectrum signal, which has the characteristics of high speed and high sensitivity. However, optical frequency domain imaging also has its inherent shortcomings. While collecting the interference signal carrying the depth information of the sample, it also collects the mutual interference signal between the layers of the sample, the self-coherent interference signal of each layer of the sample itself, and the reference light itself. Coherent noise such as self-coherent interference signals. And because what is collected is the real part of the interference spectrum signal, not the complex interference spectrum signal, the result obtained by inverse Fourier transform of the real part of the interference spectrum signal is Hermitian conjugated, resulting in superposition in the image The complex conjugate image that is completely symmetrical about the zero optical path position on the real image of the sample. the

In order to distinguish the real image of the sample, the zero optical path point is usually moved outside the sample surface by adjusting the optical path of the reference arm, so that the real image and the complex conjugate image do not overlap on the image, but due to the fringes near the zero optical path The highest visibility, that is, the highest image sensitivity, the high-sensitivity image area cannot be used by removing the zero optical path, and because the zero optical path is outside the sample, only half of the imaging depth of the OFDI system is used. Eliminating the complex conjugate image of Fourier domain OCT can make better use of the high-sensitivity area near zero optical path and double the imaging depth. Many foreign scientific research institutions have carried out research in this area. M.Wojtkowski and others proposed the method of using the piezoelectric ceramic driver to move the mirror of the reference arm, the Zhongping Chen group of the University of California, Irving proposed the method of using the electro-optic phase modulator, and the Izatt group of Duke University proposed the use of the 3×3 fiber coupler In this method, by introducing a fixed additional phase between adjacent axial interference spectrum signals, the complex interference spectrum recovery algorithm is used to reconstruct the complex form of the interference spectrum signal, and then the Fourier inverse transform is performed to eliminate the complex conjugate image. The G.J.Tearney group of Harvard Medical School in the United States proposed the method of using an acousto-optic phase modulator to carry out carrier frequency and polarization encoding on the interference spectrum signal to remove the complex conjugate image. Hofer et al. proposed a method of using dispersion material to provide dispersion and using a complex iterative algorithm to eliminate complex conjugate images. S.Witte et al. also used dispersion material for dispersion coding and proposed a simplified peak elimination algorithm to remove complex conjugate images. the

The above-mentioned methods all have their inherent shortcomings. For example, the method of multi-step phase shifting using piezoelectric ceramic drivers requires multiple measurements of the same position, which reduces the imaging speed and requires high phase stability, which is susceptible to various The influence of environmental disturbance on the phase; the method of using electro-optic phase modulator and acousto-optic phase modulator needs to introduce more complex and expensive instruments and equipment, and puts forward strict requirements on the data acquisition speed of the system; the use of 3×3 fiber coupler The method is susceptible to the influence of temperature on the coupling coefficient, resulting in the inaccuracy of restoring the complex interference spectrum, which affects the overall complex conjugate suppression rate; the existing method of using dispersion to remove complex conjugate images needs to rely on complex iterative algorithms. The simplification of also reduces complex conjugate suppression. Therefore, it is necessary to study an image elimination method that is easy to implement and has a high complex conjugate suppression rate. the

Utility model content

The purpose of the utility model is to provide a mirrorless optical frequency-domain imaging system based on dispersion modulation for the deficiencies of the prior art. A transmissive optical scanning delay line is set on the reference arm of the optical frequency domain imaging system to realize dispersion modulation while maintaining the optical path of the reference arm unchanged, ensuring the identity of the axial position of the sample under different dispersion states. By rapidly changing the rotation angle of the galvanometer in the transmission optical scanning delay line, two sets of interference spectrum signals of the same sample in two dispersion states are obtained. The dispersion of the corresponding imaginary part is compensated by multiplying the corresponding dispersion compensation factor, subtracting the two sets of interference spectra after dispersion compensation, performing dispersion compensation again, and then performing inverse Fourier transform to obtain the real reflection signal of the sample. Due to the mirrorless reconstruction of the sample image, the imaging depth of the system is doubled. the

The purpose of this utility model is achieved through the following technical solutions:

A mirrorless optical frequency-domain imaging system based on dispersion modulation, which includes: a swept light source, a first broadband fiber coupler, a second broadband fiber coupler, a sample arm optical circulator, a reference arm optical circulator, a sample arm polarization Controller, sample arm collimating mirror, reference arm polarization controller, reference arm collimating mirror, reference arm focusing lens, reference arm plane mirror, sample arm scanning galvanometer, sample arm focusing lens, third broadband fiber coupler, transmissive Optical scanning delay line, balanced detector, Mach-Zehnder interferometer, data acquisition card, computer. Wherein, the frequency-sweeping light source is connected with the first broadband fiber coupler; the first broadband fiber coupler is respectively connected with the second broadband fiber coupler and the Mach-Zehnder interferometer; the second broadband fiber coupler is respectively connected with the sample arm optical circulator and the reference The arm optical circulator; the sample arm optical circulator is connected to the sample arm polarization controller and the sample arm collimator in turn; the parallel beam emitted by the sample arm scanning galvanometer and the sample arm collimator is placed at 45 degrees, and the refracted beam passes through the sample The focusing lens of the arm is irradiated on the sample; the optical circulator of the reference arm is connected with the polarization controller of the reference arm, the collimating mirror of the reference arm, the focusing lens of the reference arm, and the plane mirror of the reference arm in sequence; the output port of the optical circulator of the reference arm is connected with the transmission optical Scanning delay line connection, transmissive optics The output ports of the scanning delay line and the sample arm optical circulator are respectively connected to the third broadband fiber coupler, and the two output ports of the third broadband fiber coupler are connected to the two input ports of the balanced detector The output ports of the balance detector and the Mach-Zehnder interferometer are respectively connected with the data acquisition card, and the data acquisition card is connected with the computer. the

Compared with the background technology, the utility model has the following technical effects:

1. Fast mirror elimination algorithm. In the transmission optical scanning delay line, by changing the rotation angle of the galvanometer, the fast modulation of the dispersion is realized, thereby obtaining two sets of interference spectrum signals of the same sample in two dispersion states. By compensating the dispersion of the two sets of interference spectral signals, subtracting the imaginary part of the common complex reflection signal, and then performing a second dispersion compensation on the residual dispersion of the interference spectral signal corresponding to the real part, the complex interference spectral signal can be obtained, and finally the The complex interference spectrum signal is subjected to Fourier inverse transformation, and a full-range mirrorless optical coherence tomography image is obtained. the

2. The rapid modulation of dispersion can be realized under the condition that the optical path of the reference arm remains unchanged. By adjusting the lateral offset y ₀ between the rotating axis of the galvanometer and the optical axis of the Fourier transform lens in the transmissive optical scanning delay line, the optical path length of the reference arm can be kept constant when the rotation angle of the galvanometer in the transmissive scanning delay line changes. change; adjusting the angle θ _g between the normal line of the grating and the optical axis can realize rapid modulation of dispersion by changing the rotation angle of the galvanometer in the transmission optical scanning delay line, and keep the optical path of the reference arm unchanged, ensuring that the The identity of the axial position of the sample in different dispersion states. By introducing a transmissive optical scanning delay line to realize zero group delay and dispersion modulation at the same time, it is easy to implement and ensures the compactness and reliability of the optical frequency domain imaging system.

Description of drawings

Fig. 1 is the system schematic diagram of the specific embodiment of the mirrorless optical frequency domain imaging method based on dispersion modulation described in the utility model;

Fig. 2 is the structural representation of the transmissive optical scanning delay line in the mirrorless optical frequency domain imaging system based on dispersion modulation described in the utility model;

Fig. 3 is the timing control diagram of the mirrorless optical frequency domain imaging system based on dispersion modulation described in the utility model;

Fig. 4 is the algorithm flowchart of the mirrorless optical frequency domain imaging system based on dispersion modulation described in the utility model;

In the figure: 1. Sweep frequency light source, 2. Broadband fiber coupler, 3. Optical circulator, 4. Polarization controller, 5. Sample arm collimating mirror, 6. Sample arm scanning galvanometer, 7. Focusing lens, 8 , sample, 9, reference arm collimating mirror, 10, focusing lens, 11, plane mirror, 12, collimating mirror, 13, blazed grating, 14, Fourier transform lens, 15, vibrating mirror, 16, rectangular prism, 17 . Receiving reflector, 18. Receiving collimating mirror, 19. Balance detector, 20. Mach-Zehnder interferometer, 21. Data acquisition card, 22. Computer, 23. Transmissive optical scanning delay line. the

Detailed ways

The utility model will be further described below in conjunction with the accompanying drawings and embodiments, and the purpose and effect of the utility model will become more obvious. the

Figure 1 is a structural diagram of a specific embodiment of a mirrorless optical frequency-domain imaging system based on dispersion modulation, including a frequency-sweeping light source 1, a first broadband fiber coupler 2, a second broadband fiber coupler 3, and a sample arm halo Linear device 4, reference arm optical circulator 5, sample arm polarization controller 6, sample arm collimator mirror 7, reference arm polarization controller 8, reference arm collimator mirror 9, reference arm focusing lens 10, reference arm plane mirror 11, Sample arm scanning galvanometer 19, sample arm focusing lens 20, sample 21, third broadband fiber coupler 22, transmission optical scanning delay line 23, balance detector 24, Mach-Zehnder interferometer 25, data acquisition card 26, computer 27. the

Wherein, the frequency-sweeping light source 1 is connected to the first broadband fiber coupler 2; the first broadband fiber coupler 2 is respectively connected to the second broadband fiber coupler 3 and the Mach-Zehnder interferometer 25; the second broadband fiber coupler 3 is connected to the sample The arm optical circulator 4 and the reference arm optical circulator 5; the sample arm optical circulator 4 is connected with the sample arm polarization controller 6 and the sample arm collimating mirror 7 in sequence; the sample arm scanning galvanometer 19 and the sample arm collimating mirror 7 exit The parallel light beam is placed at 45 degrees, and the refracted light beam is irradiated on the sample 21 through the sample arm focusing lens 20; the reference arm optical circulator 5 and the reference arm polarization controller 8, the reference arm collimating mirror 9, the reference arm focusing lens 10, The reference arm plane mirror 11 is connected successively; the output port of the reference arm optical circulator 5 is connected with the transmissive optical scanning delay line 23 again, and the output ports of the transmissive optical scanning delay line 23 and the sample arm optical circulator 4 are respectively connected with the third broadband optical fiber The coupler 22 is connected, and the two output ports of the third broadband fiber coupler 22 are connected with the two input ports of the balance detector 24; the output ports of the balance detector 24 and the Mach-Zehnder interferometer 25 are connected with the data acquisition card 26 respectively , the data acquisition card 26 is connected with the computer 27. the

As shown in Figure 1, the low-coherent light emitted from the frequency-sweeping light source 1 enters the calibration optical path and the main interferometer optical path respectively through the first broadband fiber coupler 2, and the light entering the calibration optical path passes through the Mach-Zehnder interferometer 25 to generate a calibration path. The light that enters the main interferometer optical path enters the reference arm and the sample arm respectively after being split by the second broadband fiber coupler 3, and the light in the reference arm enters the transmissive optical scanning delay line 23 after being collimated by the collimating mirror 12, and transmitted The sample light returned by the third broadband fiber coupler 22 and the sample arm merges and interferes, and enters the balance detector 24. The OCT interference spectrum signal formed and the calibration signal generated by the Mach-Zehnder interferometer 25 are collected by the data acquisition card 26 at the same time. Finally, these interference spectrum signals are sent to the computer 27 for data processing and image reconstruction. the

The mirrorless optical frequency domain imaging method based on dispersion modulation of the present invention comprises the following steps: 1. Setting a transmission optical scanning delay line in the reference arm of the optical frequency domain imaging system to provide dispersion. the

The optical path traveled by the light in the sample arm in Figure 1 is a constant, represented by L _sam in the derivation of the following formula, and the optical path traveled by the light in the reference arm can be divided into two parts: except for the transmission optical scanning delay line 23 The optical path other than is represented by _Lref , and the optical path in the transmission optical scanning delay line 23 is represented by _Lrsod , then the phase difference of the interference spectrum signal can be expressed as:

Φ＝kL _sam -kL _ref -kL _rsod (1)

where k is the wavenumber of light and k=2π/λ,. The light passes through the transmission optical scanning delay line 23, and its phase change can be expressed as:

k·L _rsod ＝φ _R +k·l (2)

Wherein, l is the optical path when both the galvanometer rotation angle γ and the grating defocus (Lf) in the transmission optical scanning delay line 23 are zero. The galvanometer rotation angle γ in the φ _R transmissive optical scanning delay line 23 and the additional phase under the condition that the grating defocus (Lf) is not zero, then the expression of this additional phase φ _R is:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&omega;\&gamma;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; L\&omega;\&gamma;</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; L\&omega;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; f\&omega;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; \&pi;m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; p</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; f\&omega;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Wherein ω is the optical frequency and ω=k c, y ₀ is the lateral offset of the galvanometer 15 rotating shafts from the optical axis, γ is the rotation angle of the galvanometer 15, and L is the distance between the blazed grating 13 and the Fourier transform lens 14 Distance, f is the focal length of Fourier transform lens 14, β is determined by psinβ=m(λ-λ ₀ ), p is a grating constant, m is a diffraction order, λ ₀ is a central wavelength, and α is determined by α=β+θ _g , θ _g is the angle formed between the normal of the blazed grating 13 and the optical axis. The Taylor expansion of φ _R (ω) is:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; !</span>}{{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them, φ _R (ω ₀ ) is the phase delay, φ _R ′(ω ₀ ) is the group delay, and φ _R ″(ω ₀ ) is the group velocity dispersion. The expressions are:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; \&pi;mL\&gamma;</span>}}{{\mathrm{<span\; class="notranslate">\; p\&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

${{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; 16</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}\mathrm{<span\; class="notranslate">\; L\&gamma;</span>}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="p"\; filenames="HSA00000041372400011.png"\; state="\{\{state\}\}">p</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="cos"\; filenames="HSA00000041372400011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; 16</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="p"\; filenames="HSA00000041372400011.png"\; state="\{\{state\}\}">p</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="cos"\; filenames="HSA00000041372400011.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Considering only the second-order terms of φ _R (ω) Taylor expansion, substituting equations (2) and (4) into equation (1), the expression of the interference spectrum phase difference can be obtained as:

$\mathrm{<span\; class="notranslate">\; \&Phi;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; sam</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; l</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

2. Adjust the transmission optical scanning delay line to generate dispersion that changes with the rotation angle of the vibrating mirror 15, and keep the reference arm optical path constant. the

Adjust the lateral offset between the galvanometer 15 rotating shaft and the optical axis as the following expression:

${\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

Then the group delay φ _R ′(ω ₀ ) does not change with the change of the rotation angle γ of the vibrating mirror 15 . And because the optical path l is constant when the rotation angle γ of the vibrating mirror 15 in the delay line 23 of the transmissive optical scanning and the defocus (Lf) of the blazed grating 13 are all zero, and in the reference arm except the transmissive optical scanning The optical path length L _ref outside the delay line 23 is constant, so the first item in the formula (8) is only related to the sample depth z, which is set as:

z=L _sam -L _ref -l-φ _R ′(ω ₀ )·c (10)

The group velocity dispersion φ _R ″(ω ₀ ) of the second term in the formula (8) changes with the change of the rotation angle γ of the scanning galvanometer 15, that is, the quantitative dispersion caused by the transmissive optical scanning delay line 23 can be The variable phase φ _d , its expression is:

${\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \&prime;</span><span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

The OCT interference signal formed after the sample light returned by the sample arm interferes with the reference light returned by the reference arm, the expression of the interference spectrum signal collected by the data acquisition card 21 is:

3. Collect interference spectrum signals in two dispersion states, use dispersion compensation and subtraction algorithms to eliminate mirror images, and obtain full-range mirror-free sample images. the

The vibrating mirror 15 in the transmissive optical scanning delay line 23 is controlled by a synchronous timing signal. Corresponding to different rotation angles of the vibrating mirror 15, the transmissive optical scanning delay line 23 provides two different dispersions respectively, and the computer 21 generates two acquisition triggers respectively. The signal triggers the data acquisition card 20 to collect data, and the two interference spectrum signals collected are:

可以通过在样品臂放置平面镜通过相位解包裹算法求得，样品各层的自相干 

由于强度很小可以忽略，参考臂强度|E_r|²可以通过平衡探测器去除直流项。对干涉光谱信号乘以色散补偿因子 

可以得到补偿色散的干涉光谱信号I_c(ω)： due to dispersion phase

It can be obtained by placing a plane mirror on the sample arm and using the phase unwrapping algorithm. The self-coherence of each layer of the sample

Since the intensity is negligibly small, the reference arm intensity | _Er | ² can be used to remove the DC term by balancing the detector. Multiply the interference spectrum signal by the dispersion compensation factor

The dispersion-compensated interference spectrum signal I _c (ω) can be obtained:

By subtracting the formulas (6) and (7) obtained by dispersion compensation, the interference spectrum signal that eliminates the imaginary part of the corresponding complex reflection signal can be obtained:

可以得到复数形式的干涉光谱信号为： Divide (8) by the difference of the square of the two dispersion compensation factors

The complex interference spectrum signal can be obtained as:

Finally, performing Fourier transform on the obtained complex interference spectrum signal can obtain an axial scanning depth information that eliminates the mirror image, which can realize better utilization of the high-sensitivity area at the zero optical path and double the detection depth. the

Figure 2 is a schematic diagram of a transmissive optical scanning delay line. Wherein the normal line of the blazed grating 13 and the optical axis of the Fourier transform lens 14 form an included angle θ _g , the light of the reference arm is collimated by the collimating mirror 12 and then enters the transmissive optical scanning delay line, and the collimated beam passes through the reflective blazed grating 13 light splitting, each spectral component after the splitting is focused on the vibrating mirror 15 through the Fourier transform lens 14, after being reflected by the vibrating mirror 15, it returns to the blazed grating 13 through the Fourier transform lens 14, and is diffracted again by the blazed grating 13 and merged into one The beam collimated light is projected onto the right-angle prism 16, after the light passing through the right-angle prism 16 is staggered in the direction perpendicular to the plane where the optical table is located, it returns to the blazed grating 13 along the original direction, and then passes through the Fourier transform lens 14 and the vibrating mirror 15 to be After being reflected by the vibrating mirror 15, it passes through the Fourier transform lens 14 and the blazed grating 13 again, and after being diffracted four times by the blazed grating 13, it is recombined into outgoing light, and finally the outgoing beam reflected by the receiving mirror 17 enters the receiving collimating mirror 18.

Figure 3 shows the timing control diagram of the mirrorless optical frequency domain imaging system based on dispersion modulation. The computer 27 generates synchronous timing signals to control the galvanometer 15 in the transmissive optical scanning delay line 23 and the galvanometer 19 in the sample arm. The computer 27 generates a triangular wave signal to drive the scanning galvanometer 19 in the sample arm, and the computer 27 generates a square wave signal to drive the galvanometer 15 in the transmission optical scanning delay line 23 . The low level and high level of the square wave driving signal of the oscillating mirror 15 in the transmission optical scanning delay line 23 respectively correspond to two different dispersion states. Utilize computer 27 to generate synchronous timing, the rising segment of the triangular wave driving signal of the scanning vibrating mirror 19 in the sample arm corresponds to the low level segment in the square wave driving signal of the vibrating mirror 15 of 23 in the transmission optical scanning delay line, The falling segment of the triangular wave driving signal of the scanning vibrating mirror 19 in the sample arm corresponds to the high level segment of the square wave driving signal of the vibrating mirror 15 in the transmission optical scanning delay line 23 . The computer 27 generates a collection trigger signal for triggering the data acquisition card 26 to collect data, collects two sets of interference spectrum signals corresponding to the same sample in two dispersion states, and finally transmits them to the computer 27 for data processing. the

Fig. 4 shows the algorithm flow chart of the mirrorless optical frequency domain imaging system based on dispersion modulation. The collected interference spectrum signal 1 and interference spectrum signal 2 are respectively multiplied by the corresponding dispersion compensation factor, so that the corresponding imaginary part dispersion after Fourier transform is accurately compensated, and the interference spectrum signal 1 after dispersion compensation and the interference spectrum after dispersion compensation are obtained For signal 2, after subtracting the above two sets of interference spectrum signals after dispersion compensation, the imaginary part of the corresponding complex reflection signal disappears, while the real part still contains the dispersion factor. Dispersion compensation is performed on the subtracted interference spectrum signal again to obtain a complex interference spectrum signal, and finally the real reflection signal of the sample can be obtained by Fourier transform, which can be used to reconstruct a mirror-free full-range optical coherence tomography image. the

Claims (1)

1. one kind based on the synthetic non-mirror image optimal frequency domain imaging system of chromatic dispersion, it is characterized in that it comprises: swept light source (1), first broadband optical fiber coupler (2), second broadband optical fiber coupler (3), sample ami light circulator (4), reference arm light circulator (5), sample arm Polarization Controller (6), sample arm collimating mirror (7), reference arm Polarization Controller (8), reference arm collimating mirror (9), reference arm condenser lens (10), reference arm plane mirror (11), sample arm scanning galvanometer (19), sample arm condenser lens (20), the 3rd broadband optical fiber coupler (22), transmission-type optical scan delay-line (23), balance detection device (24), Mach-Zehnder interferometers (25), data collecting card (26), computer (27); Wherein, swept light source (1) links to each other with first broadband optical fiber coupler (2); First broadband optical fiber coupler (2) connects second broadband optical fiber coupler (3) and Mach-Zehnder interferometers (25) respectively; Second broadband optical fiber coupler (3) connects sample ami light circulator (4) and reference arm light circulator (5) respectively; Sample ami light circulator (4) links to each other successively with sample arm Polarization Controller (6), sample arm collimating mirror (7); Sample arm scanning galvanometer (19) is 45 degree placements with the collimated light beam of sample arm collimating mirror (7) outgoing, and the light beam of turning back is radiated on the sample (21) by sample arm condenser lens (20); Reference arm light circulator (5) links to each other successively with reference arm Polarization Controller (8), reference arm collimating mirror (9), reference arm condenser lens (10), reference arm plane mirror (11); The output port of reference arm light circulator (5) is connected with transmission-type optical scan delay-line (23) again, the output port of transmission-type optical scan delay-line (23) and sample ami light circulator (4) links to each other with the 3rd broadband optical fiber coupler (22) respectively, and two output ports of the 3rd broadband optical fiber coupler (22) link to each other with two input ports of balance detection device (24); The output port of balance detection device (24), Mach-Zehnder interferometers (25) links to each other with data collecting card (26) respectively, and data collecting card (26) links to each other with computer (27).

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