CN107064001A - Monochromatic light spectrometer polarization domain optical coherence tomography system based on photoswitch - Google Patents

Abstract

The present invention relates to the field of polarization frequency domain optical coherence tomography system, especially the polarization frequency domain optical coherence tomography system based on optical switch. The channel selection of the optical switch realizes the time-sharing detection of the horizontal polarization and vertical polarization two-channel interference signals by a single spectrometer, and the detected two-channel polarization signals can be calculated to obtain the intensity image, fast axis image and delay image of the sample with birefringence properties. The invention has a simple structure, does not need to use a beam splitting prism, greatly reduces the difficulty of adjusting the optical path, and avoids the intermode interference caused by the polarization beam splitter, and realizes polarization imaging without complicated phase modulation equipment and algorithms.

Description

Polarization-frequency-domain optical coherence tomography system with single spectrometer based on optical switch

technical field

The invention relates to the field of polarization frequency-domain optical coherence tomography systems, in particular to a single-spectrometer polarization frequency-domain optical coherence tomography system based on an optical switch.

Background technique

Polarization-sensitive optical coherence tomography (OCT) is a new imaging method developed on the basis of traditional OCT imaging technology. polarization information. The development of polarization OCT has always been accompanied by the development of traditional OCT technology. At present, it has changed from time-domain polarization OCT with slower scanning speed to frequency domain polarization (OCT spectrum domain optical coherence tomography, SDOCT) with faster scanning speed, including spectral polarization OCT and swept polarization OCT. When polarized light is incident on the sample to be tested, the polarization properties of the returned light are changed due to the birefringence properties of the sample. By detecting the polarization properties of the returned light, the polarization properties of the sample to be tested, such as the phase delay diagram and the fast axis pattern, etc. can be obtained. , while providing the same intensity structure information as conventional OCT. To obtain the polarization information of the sample, the polarization interference information in the vertical direction and the polarization interference information in the horizontal direction of the sample must be measured.

In the traditional polarized OCT system, the linearly polarized light is divided into two beams through a non-polarizing beam splitter, and one of the beams passes through a 1/4 wave plate placed at an appropriate angle to become a linearly polarized light with an angle of 45° to the incident polarization direction. Another beam of light passes through a 1/4 wave plate whose fast axis is at a 45° angle to its polarization direction and enters the sample as circularly polarized light. The light returning to the sample becomes elliptically polarized light after passing through the wave plate again. Coherent superposition occurs when the beam splitter is used, and then the coherent light is split into two mutually orthogonal beams by a polarization beam splitter and detected by two detectors respectively. When the broadband light is split by the polarization beam splitter, the two orthogonal polarized lights cannot be completely separated, resulting in crosstalk between the two polarized light information and affecting the imaging quality. In addition, due to the use of the beam-splitting prism, it is difficult to adjust the optical path to obtain a relatively ideal imaging signal-to-noise ratio. In spectral polarization OCT, the price of the spectrometer CCD detector is expensive, and there are high synchronization requirements for the two spectrometers during two-way detection. To realize polarized OCT with a single spectrometer without using a polarizing beam splitter, it is necessary to improve the reference arm or the detection end. Fan et al. constructed two reference arms and introduced a certain optical path difference between them combined with a full-range imaging algorithm to separate the two quadrature signals. This method requires additional phase modulation equipment and more complex algorithms, and this method The images formed by the two reference light signals have different system sensitivities at the same depth of the sample, resulting in measurement errors, and the use of non-polarizing beam splitters for light splitting increases the difficulty of optical path adjustment. Bernhard et al. used a grating at the detection end to inject two beams of orthogonally polarized light into different areas of the CCD at different diffraction angles to achieve polarization detection. This method reduced the diffraction efficiency and the system signal-to-noise ratio, and the system adjustment was difficult.

Therefore, it is necessary to propose a single-spectrometer polarization-frequency-domain optical coherence tomography system based on an optical switch to address the above problems.

Contents of the invention

Aiming at the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a single spectrometer polarization frequency domain optical coherence tomography system based on an optical switch, which adopts a single detector and uses a high-speed 1-point 2-way optical switch to perform orthogonally polarized light The channel selection does not use beam splitters and polarizing beam splitters, which simplifies the system structure and adjustment difficulty, and improves the system stability and signal-to-noise ratio.

Single spectrometer polarization frequency domain optical coherence tomography system based on optical switch, including low coherence broadband light source, optical fiber polarizer, optical fiber coupling splitter, optical switch, first optical fiber mirror, optical fiber polarization controller, second optical fiber Reflecting mirror, collimating mirror, 1/4 wave plate, three-dimensional scanning galvanometer, focusing objective lens, sample to be tested, spectrometer and computer data acquisition equipment, the low coherence broadband light source is connected to the fiber coupling splitter through the fiber polarizer, The optical fiber coupling splitter is distributedly connected to an optical switch, a collimating mirror and a spectrometer, and the optical switch is respectively connected to the first optical fiber reflecting mirror and the second optical fiber reflecting mirror through the optical fiber polarization controller, and the collimating mirror is sequentially passed through 1 The /4 wave plate, the three-dimensional scanning vibrating mirror and the focusing objective lens are connected to the sample to be tested, and the spectrometer is connected to a computer data acquisition device.

Preferably, the optical switch adopts a 1-point 2-way optical switch or a multi-point multi-way optical switch.

Preferably, the low-coherence broadband light source is equipped with a linear array CCD detector or the broadband-swept low-coherence light source is equipped with a photodetector or a photoelectric balance detector.

Preferably, the low-coherence broadband light source has a bandwidth ranging from tens of nanometers to hundreds of nanometers.

Preferably, the low-coherence broadband uses light-emitting diodes, superluminescent light-emitting diodes, frequency-swept broadband light sources, femtosecond lasers, or supercontinuum light sources.

Preferably, the spectrometer is a Michelson interferometer or a Mach-Zehnder interferometer.

Preferably, the optical fiber polarization controller can use a wave plate, and the first optical fiber reflective mirror and the second optical fiber reflective mirror are both collimating mirrors and plane reflective mirrors.

The working process of the single-spectrometer polarization-frequency-domain optical coherence tomography system based on an optical switch is as follows: (1) The light emitted by a low-coherence broadband light source passes through a polarizer and becomes linearly polarized light, which is coupled into a Michelson interferometer and divided into a reference optical path and sample light; (2) The reference light is divided into two paths by a 1-to-2 optical switch, one of which passes through a fiber optic polarization controller and a fiber optic reflector, and the polarization direction of the light is turned 90° compared with the incident light ; (3) The other path is reflected by the fiber optic mirror and returned to the original path. After adjustment, the optical paths of the two reference lights and the sample light are equal, and the slight difference can be easily compensated by software. The sample light passes through a fiber optic polarization controller so that the light incident on the sample is circularly polarized light. After the light is internally reflected by the sample, it carries the polarization information of the sample and becomes elliptically polarized light through the fiber optic polarization controller. Coupled into the Michelson interferometer and two channels The reference light interferes; (4) The two reference lights interfere with the sample light and carry the polarization information of the horizontal and vertical directions of the sample respectively, and the separate detection of the polarization information of the horizontal and vertical directions is respectively denoted by controlling the optical channel selection by controlling the light on and off. I _H and I _V , the spectrometer collects the recorded interference spectrum signals through the video acquisition card and sends them to the computer for data processing, transforms the two signals into K space, interpolates, subtracts DC, and performs Fourier inverse transformation to obtain each channel The intensity information and phase information of the signal are recorded as A _H (z), φ _H , A _V (z), φ _V respectively. After calculation, the intensity diagram, phase delay diagram and fast axis direction diagram of the measured sample are obtained,

Due to the adoption of the above technical solution, the present invention does not use a polarization beam splitter, avoids intermode interference, and does not use a beam splitting prism, which reduces the difficulty of system adjustment, increases the system signal-to-noise ratio, and uses a single detector to simplify the structure and reduce costs. Purpose, without adding additional phase modulation equipment and complex reconstruction algorithms, improves the calculation speed, and has strong practicability at the same time.

Description of drawings

Fig. 1 is a schematic diagram of the system structure of the present invention.

detailed description

The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways defined and covered by the claims.

As shown in Figure 1, the single spectrometer polarization frequency domain optical coherence tomography system based on an optical switch includes a low-coherence broadband light source 1, a fiber polarizer 2, a fiber-coupled splitter 3, an optical switch 4, and a first fiber reflector Mirror 5, fiber optic polarization controller 6, second fiber optic mirror 7, collimating mirror 8, 1/4 wave plate 9, three-dimensional scanning galvanometer 10, focusing objective lens 11, sample to be tested 12, spectrometer 13 and computer data acquisition equipment 14. The low-coherence broadband light source 1 is connected to a fiber-coupled splitter 3 through a fiber-optic polarizer 2, and the fiber-coupled splitter 3 is respectively connected to an optical switch 4, a collimating mirror 8, and a spectrometer 13, and the optical switch 4 Respectively connect the first fiber optic mirror 5 and the second fiber optic mirror 7 through the fiber optic polarization controller 6, and the collimating mirror 8 is sequentially connected with the 1/4 wave plate 9, the three-dimensional scanning vibrating mirror 10 and the focusing objective lens 11 to be tested Sample 12, the spectrometer 13 is connected to a computer data acquisition device 14.

Further, the optical switch 4 adopts a 1-point 2-way optical switch or a multi-point multi-channel optical switch, and the low-coherence broadband light source 1 is equipped with a linear array CCD detector or a broadband sweeping low-coherence light source is equipped with a photodetector or a photoelectric balance detection device.

Further, the low-coherence broadband light source 1 has a bandwidth ranging from tens of nanometers to hundreds of nanometers, and the low-coherence broadband light source 1 adopts light-emitting diodes, superluminescent light-emitting diodes, frequency-swept broadband light sources or femtosecond lasers or supercontinuum spectrum light source.

Further, the spectrometer 13 is a Michelson interferometer or a Mach-Zehnder interferometer, the fiber polarization controller 6 can use a wave plate, and the first fiber mirror 5 and the second fiber mirror 7 are collimated mirror plus a flat mirror.

The working process of the single-spectrometer polarization-frequency-domain optical coherence tomography system based on an optical switch is as follows: (1) The light emitted by a low-coherence broadband light source passes through a polarizer and becomes linearly polarized light, which is coupled into a Michelson interferometer and divided into a reference optical path and sample light; (2) The reference light is divided into two paths by a 1-to-2 optical switch, one of which passes through a fiber optic polarization controller and a fiber optic reflector, and the polarization direction of the light is turned 90° compared with the incident light ;(3) The other path is reflected by the fiber optic mirror and returns to the original path. After adjustment, the optical paths of the two paths of reference light and sample light are equal. The slight difference can be easily compensated by software, and the sample light passes through a fiber optic polarization controller. The light incident on the sample is circularly polarized light, and after the light is internally reflected by the sample, it carries the polarization information of the sample and becomes elliptically polarized light through the fiber polarization controller again, coupled into the Michelson interferometer and interferes with the two reference lights; (4) The two paths of reference light and sample light interfere with the polarization information in the horizontal and vertical directions of the sample respectively. The optical channel selection is controlled by controlling the light on and off, and the separate detection of the polarization information in the horizontal and vertical directions is recorded as I _H and IV _respectively . The spectrometer will The recorded interference spectrum signal is collected by the video acquisition card and then sent to the computer for data processing. The two signals are transformed into K space, interpolated, DC subtracted, and then inverse Fourier transformed to obtain the intensity information and phase information of each signal. They are recorded as A _H (z), φ _H , A _V (z) and φ _V respectively. After calculation, the intensity diagram, phase delay diagram and fast axis direction diagram of the measured sample are obtained,

The traditional dual-detector system requires strict synchronization when detecting the horizontal and polarization signals, otherwise the time delay between the two detectors detecting the signal will reduce the image quality, and the use of polarization beam splitters (beam splitters) or non-polarization beam splitters The prism splits the light, which introduces noise and increases the difficulty of adjusting the optical path. In this embodiment, only one detector is needed and no polarizing beam splitter and beam splitting prism are used. It can be detected without additional phase modulation equipment and complex algorithms. To the horizontal and vertical two-way signals, the structure of the existing system is simplified, and the system adjustment is simple and easy.

The present invention does not use a polarizing beam splitter, which avoids intermode interference, and does not use a beam splitting prism, which reduces the difficulty of system adjustment and increases the signal-to-noise ratio of the system. A single detector is used to simplify the structure and reduce costs without adding additional Advanced phase modulation devices and complex reconstruction algorithms increase calculation speed.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly or indirectly used in other related All technical fields are equally included in the scope of patent protection of the present invention.

Claims (8)

1. A single spectrometer polarization frequency domain optical coherence tomography system based on an optical switch, characterized in that it includes a low-coherence broadband light source, an optical fiber polarizer, an optical fiber coupling splitter, an optical switch, a first optical fiber mirror, and an optical fiber polarization A controller, a second fiber optic mirror, a collimating mirror, a 1/4 wave plate, a three-dimensional scanning galvanometer, a focusing objective lens, a sample to be tested, a spectrometer and a computer data acquisition device, the low-coherence broadband light source is connected through a fiber optic polarizer A fiber-coupled splitter, the fiber-coupled splitter is respectively connected to an optical switch, a collimating mirror, and a spectrometer, and the optical switch is respectively connected to a first fiber optic reflector and a second fiber optic reflector through a fiber polarization controller. The collimating mirror is connected to the sample to be measured through a 1/4 wave plate, a three-dimensional scanning galvanometer and a focusing objective lens in sequence, and the spectrometer is connected to a computer data acquisition device. 2 . The optical coherence tomography system based on an optical switch with a single spectrometer in the polarization frequency domain according to claim 1 , wherein the optical switch adopts a 1-to-2-way optical switch or a multi-division and multiple-way optical switch. 3 . 3. The single-spectrometer polarization-frequency-domain optical coherence tomography system based on an optical switch according to claim 1, characterized in that: the low-coherence broadband light source is matched with a linear array CCD detector or the broadband-swept low-coherence light source is matched with a photoelectric detector or photoelectric balance detector. 4. The optical switch-based single-spectrometer polarization-frequency domain optical coherence tomography system according to claim 1, characterized in that: the low-coherence broadband light source has a bandwidth ranging from tens of nanometers to hundreds of nanometers. 5. The single spectrometer polarization frequency domain optical coherence tomography system based on optical switch according to claim 1, characterized in that: the low coherence broadband adopts a light source light emitting diode, a superradiant light emitting diode, a frequency-sweeping broadband light source or a flying second laser or supercontinuum light source. 6 . The polarization-frequency-domain optical coherence tomography system based on an optical switch with a single spectrometer according to claim 1 , wherein the spectrometer is a Michelson interferometer or a Mach-Zehnder interferometer. 7. The single spectrometer polarization frequency domain optical coherence tomography system based on optical switch according to claim 1, characterized in that: the optical fiber polarization controller can use a wave plate, the first optical fiber mirror and the second Fiber optic mirrors are collimating mirrors plus plane mirrors. 8. Single spectrometer polarization frequency domain optical coherence tomography system based on optical switch, characterized in that: its working process is as follows: (1) The light emitted by the broadband low-coherence light source passes through the polarizer and then becomes linearly polarized light coupled into the Michelson interferometer and split into reference light path and sample light; (2) The reference light passes through a 1-to-2 optical switch to divide the reference light into two paths, one of which passes through a fiber optic polarization controller and a fiber optic mirror to return, and the polarization direction of the light is turned 90° compared with the incident light; (3) The other path is reflected by the fiber optic mirror and returns to the original path. After adjustment, the optical paths of the two reference lights and the sample light are equal. The slight difference can be easily compensated by software. The sample light passes through a fiber optic polarization controller so that The light incident on the sample is circularly polarized light, and after the light is internally reflected by the sample, it carries the polarization information of the sample and becomes elliptically polarized light through the fiber polarization controller again, coupled into the Michelson interferometer and interferes with the two reference lights; (4) After the interference between the two reference beams and the sample beam, the polarization information in the horizontal and vertical directions of the sample is carried respectively, and the separate detection of the polarization information in the horizontal and vertical directions is denoted as I _H and IV respectively by controlling the optical channel selection and control of the light _switch , the spectrometer collects the recorded interference spectrum signal through the video acquisition card and sends it to the computer for data processing, transforms the two signals into K space, interpolates, subtracts DC, and performs Fourier inverse transform to obtain the intensity information and The phase information is recorded as A _H (z), φ _H , A _V (z), and φ _V respectively. 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