CN210433462U - Optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on Qiongsi matrix - Google Patents

Abstract

The utility model discloses an optical fiber type frequency sweep polarization sensitive OCT imaging system based on qiong si matrix. In a swept-frequency polarization-sensitive optical coherence tomography system, the polarization state of light is represented by a Jones matrix. The delay unit is utilized to enable two incident linearly polarized lights with mutually vertical polarization directions to generate a certain optical path difference, the optical path difference is transmitted to a sample arm with phase modulation through an optical fiber, the influence of the optical fiber is eliminated through data processing in the later period, and OCT imaging with full depth range and high sensitivity is realized. The utility model discloses utilize degree of depth multiplexing and phase modulation to realize two polarization state simultaneous imaging of horizontal direction and vertical direction, obtain the image that information is more perfect, high sensitivity to the algorithm is simple, the system is light and handy, can realize real-time image and rebuild.

Description

Optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on Qiongsi matrix

Technical Field

The utility model relates to an OCT imaging technique and frequency sweep OCT imaging system especially relate to an optical fiber type frequency sweep polarization sensitive OCT imaging system based on jones matrix.

Background

The Optical Coherence Tomography (OCT) imaging technology is a novel Optical imaging technology, can carry out non-invasive, non-contact and high-resolution in-vivo imaging on the tissue structure and the physiological function in a tested living body sample, and has wide application prospect in the fields of early diagnosis of diseases and in-vivo biopsy. Experiments prove that the OCT technology has important application value in the researches of ophthalmology, dentistry, early diagnosis of cardiovascular diseases and skin cancer, developmental biology and the like.

The traditional OCT considers that the refractive index of a sample changes along with the depth of the sample, and the light characteristics reflected back to a detector at different depths are different, so that the internal structure information of the sample is obtained by utilizing the principle. Hee et al, 1992, have proposed a polarization Sensitive OCT (polarization Sensitive Optical Coherence tomography) in which the refractive index of a sample is different at different depths and also different at different directions at the same depth, i.e., the sample has birefringence, to obtain not only reflected light intensity information of ordinary OCT but also polarization state information of reflected light, particularly birefringence information of biological tissues, at the same time, to determine the polarization characteristics of a subject. At present, the PS-OCT has made remarkable research progress in the directions of skin burn detection, caries discrimination, glaucoma and diabetic edema diagnosis, coronary heart disease monitoring and the like.

The system structure of the polarization sensitive OCT comprises space PS-OCT and all-fiber PS-OCT. The space PS-OCT is relatively simple to analyze, easy to realize and low in cost, but the space PS-OCT is relatively large in volume and not compact due to the existence of the space light path. In all-fiber PS-OCT, in order to make the structure compact and practical, optical fibers are introduced into the optical path, and all light propagation is performed in the optical fibers. This allows on the one hand a reduction in the system volume, but on the other hand the introduction of optical fibers also brings about an additional polarization effect, Park et al 2004 propose to compare the reflected light from the sample surface with the sample interior to compensate for the effect of the optical fibers.

The polarization sensitive OCT analysis method mainly comprises a Jones matrix analysis method and a Stokes component analysis method. Jiao et al 2002 verified that the internal polarization information of a sample can be characterized by a jones matrix. And an experimental system based on a space light path is designed, two super-radiation light-emitting diode light sources are used, the polarization states are horizontal and vertical, two detectors are used for detecting respectively, and two function generators of the light sources are controlled to be the same at the same time and in the same time sequence. In 2005, a light source arm was proposed to use a polarization modulator to continuously modulate the polarization state of incident light, and two detectors respectively detect the horizontal and vertical components, so as to achieve the purpose of only requiring a single light source and a single scanning depth. Yasuno et al, 2012 proposed that a delay element using a davit prism be incorporated into the sample arm to produce two input beams with relative delays and orthogonal polarization states. The detection arm is used for detecting the polarization states in the horizontal direction and the vertical direction respectively by using a balanced detector. In the same year, Fan et al propose to add phase modulation to the sample arm to cause the reflection position to deviate slightly from the axis of rotation of the galvanometer, eliminating the mirror image, and achieving full-range detection. However, the prior method still has the defects of complex algorithm, large system volume, poor stability, limitation of imaging depth and signal-to-noise ratio and the like, and needs to be solved urgently.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide an optical fiber type frequency sweep polarization sensitive OCT imaging system based on qiong si matrix has overcome the not enough of prior art. The utility model discloses do not need expensive electrooptical modulation device, it is with low costs, but to the input of two polarization states simultaneously, high sensitivity formation of image.

The technical solution of the utility model is as follows:

an optical fiber type frequency-sweeping polarization-sensitive optical coherence tomography system based on an Qiongsi matrix is characterized in that: in a sweep-frequency polarization-sensitive OCT imaging system, representing the polarization state of light by using a Jones matrix; the delay unit is utilized to enable two incident linearly polarized lights with mutually vertical polarization directions to generate a certain optical path difference; full optical fiber transmission is adopted; the method of depth multiplexing and phase modulation is adopted to realize simultaneous and high-sensitivity imaging of two input polarization states; the algorithm is simple, the system is light and handy, and real-time image reconstruction can be realized.

The utility model discloses a polarization sensitive optical coherence tomography system's concrete step is as follows:

① in the sweep-frequency optical coherence tomography system, a first polarizer (4) is used to change the incident light of a sample arm into linearly polarized light with an angle of 45 degrees with the horizontal direction, the intensity of the linearly polarized light is maximized by adjusting a first polarization controller (3), the incident light is divided into two linearly polarized lights with mutually perpendicular polarization states and equal intensity by a first polarization beam splitter (504), in order to realize simultaneous imaging of the sample after the sample is irradiated by the incident light with mutually perpendicular polarization states, a depth multiplexing method is adopted, a delay unit is used, and the optical path difference of two arms in the delay unit is adjusted to ensure that the two incident lights have a certain optical path difference:

wherein k is the wave number, d is half of the optical path difference of the two arms of the delay unit, and the middle is taken as the zero optical path position;

② optical signals are transmitted through optical fibers, and polarization information is described by Jones matrix, J is the Jones matrix from the delay system to the sample surface, back and forth in the sample, and from the sample surface to the detector_in、J_samp、J_outAnd finally, the measured jones matrix is:

jones matrix J for measuring the surface of a sample in advance_surfTo eliminate the influence of the optical fiber through the later data processing;

③ to realize high-sensitivity imaging, the incident linear polarized light with two polarization directions perpendicular to each other is irradiated to the sample and imaged on both sides of the zero optical path on the basis of the polarized optical coherence tomography methodIn the sample arm, a certain offset is set for the scanning galvanometer (802), and linear phase modulation is introduced

f_mThe modulation coefficient is adopted, x is the transverse scanning position, and the mirror image is eliminated through linear phase modulation, so that two polarization states are imaged on two sides of a zero optical path simultaneously, and full-depth range and high-sensitivity imaging are realized;

④, the first balanced detector (907) and the second balanced detector (908) respectively detect the interference signals of the two channels of horizontal polarization and vertical polarization, which contain linear phase modulation terms:

wherein, I_h(k, x) is the interference signal of the horizontal polarization channel; i is_v(k, x) is the interference signal of the vertical polarization channel; s (k) is the low coherence light source power spectral density distribution; e_S、E_RReal amplitude of the sample and reference arm light; z is a radical of_samp、z_refIs the optical path length of the sample arm and the reference arm;

taking the coherent terms of the interference signals:

⑤ Fourier transforming the coherent terms along x-axis, filtering out negative frequency part, and inverse Fourier transforming;

⑥ Fourier transform along the k-axis:

wherein Γ (z) is Fourier transform of S (k), and intensity information is extracted to obtain J₁₁，J₁₂，J₂₁，J₂₂。

⑦ data processing, the information returned from the sample surface can be measured as J_surfAnd is and

J_surf＝J_outJ_in

from the above formula, one can obtain:

let be J_T

Wherein:

additionally, J can be obtained by comparing the states of the input and output_T

The two formulae are equal, and can be obtained:

obtaining J by solving the above formula_samp。

The optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on the Jones matrix comprises a frequency-sweeping light source, wherein incident light is divided into a light beam in a sample arm and a light beam in a reference arm after passing through a first optical fiber coupler; the light beam in the sample arm sequentially passes through the first polarization controller, the first polarizer and the delay unit, then enters the sample unit, irradiates to a sample, and then returns to enter the detection unit through the second optical fiber coupler; incident light of the reference arm enters the detection unit through the second polarization controller to be converged with reflected light of the sample arm, enters the detection unit for detection, and transmits data into the computer. In the delay unit, linearly polarized light forming an included angle of 45 degrees with the horizontal direction enters a first polarization beam splitter through a first collimating mirror, is divided into two beams of light, then respectively passes through a first quarter-wave plate and a second quarter-wave plate, is reflected by a first plane reflector and a second plane reflector, then is converged in the first polarization beam splitter, and then enters an optical fiber through a second collimating mirror. In the sample unit, incident light is irradiated to the two-dimensional scanning galvanometer by the third collimating mirror, and then is irradiated to the sample by the telescope system consisting of the first lens and the second lens, and reflected light with sample information returns to the second optical fiber coupler. In the detection unit, reference light enters the beam splitter through the fourth collimating mirror and the second polarizer, sample light enters the beam splitter through the fifth collimating mirror, the interference signal is divided into two beams by the beam splitter, and the two beams pass through the second polarization beam splitter and the third polarization beam splitter respectively and then are measured by the first balance detector and the second balance detector to obtain intensity information. The system is characterized in that: the system is compact, flexible and stable by adopting all-fiber transmission; a time delay unit is arranged, so that two incident linearly polarized lights with the same intensity and mutually vertical polarization directions generate a certain optical path difference, and a depth multiplexing method is adopted to realize simultaneous imaging of two polarization states; incident light of the sample arm irradiates on a scanning galvanometer with certain offset, linear phase modulation is generated, and space carrier frequency is added to interference signals while the galvanometer rotates so as to eliminate mirror images and realize high-sensitivity imaging of two polarization states.

The light source is a wavelength scanning laser light source.

The sample is a sample having birefringent properties.

The delay unit can change the optical path difference of the linearly polarized light with the two polarization directions perpendicular to each other by changing the optical paths of the two arms.

The two-dimensional galvanometer of the sample arm sets a certain offset for incident light to generate linear phase modulation.

The beam splitter in the delay unit is a polarizing beam splitter.

The two quarter-wave plates in the delay unit form an angle of 45 degrees with the horizontal direction.

The beam splitter in the detection unit is a non-polarizing beam splitter.

The Michelson interferometer is characterized by comprising two interference light paths with approximate equal optical paths, namely a reference arm and a sample arm, and is an optical fiber optical system.

The system works as follows:

light emitted by the swept-frequency light source is coupled into the Michelson interferometer through the first fiber coupler and is divided into a sample arm and a reference arm. Incident light of the sample arm becomes linearly polarized light forming an included angle of 45 degrees with the horizontal direction after passing through the first polarizer, and the light intensity of the linearly polarized light is maximized through the first polarization beam splitter. The sample light path passes through a delay unit, linearly polarized light forming an included angle of 45 degrees with the horizontal direction is divided into linearly polarized light in the horizontal direction and the vertical direction by a first polarization beam splitter, the linearly polarized light respectively enters two arms of the delay unit with different optical paths, the linearly polarized light respectively passes through a first quarter-wave plate, a second quarter-wave plate, a first plane reflector and a second plane reflector for reflection, the polarization direction returns to the first polarization beam splitter after rotating for 90 degrees and is converged to form two beams of incident light with a certain optical path difference and mutually vertical polarization directions, the incident light irradiates a sample through the phase modulation of a two-dimensional scanning galvanometer, returns to a second optical fiber coupler and reaches a detection unit; the reference light enters the detection unit through the second polarization controller and the second polarizer. The reference light and the sample light are converged in the detection unit and are divided into two beams through the beam splitter, mutual interference terms in interference signals are obtained through the balance detector, intensity information is extracted from the interference signals, and the interference signals enter the computer through the image acquisition card to obtain the measured Jones matrix. A jones matrix of the sample surface was obtained in advance to compensate for the effect of the fiber.

Compared with the prior art, the utility model has the advantages of it is following:

the utility model discloses abandoned bulky, not compact, the poor space type light path of stability, adopted full optical fiber to realize, guaranteed compact, nimble, the stability of system.

The utility model discloses do not need expensive polarization modulator, and realize the input of polarization direction mutually perpendicular's two incident linearly polarized light through the time delay unit, adopt the multiplexing mode of degree of depth to realize imaging when to two polarization state inputs.

The utility model discloses sensitive OCT imaging system of optical fiber type frequency sweep polarization based on qiong si matrix's characteristics are used for polarization frequency domain optical coherence tomography with linear phase modulation, the incident light shines to the scanning that has certain offset shakes on the mirror, produce linear phase modulation, when shaking mirror pivoted, space carrier frequency has been added to interference signal, in order to eliminate the mirror image, make two polarization direction mutually perpendicular's incident line polarization, shine to the reverberation formation of image on the both sides of zero optical path behind the sample, and be close to zero optical path, realize the full range high sensitivity formation of image.

Drawings

Fig. 1 is a system structure diagram of the optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on the qiong matrix of the present invention.

Fig. 2 is a schematic structural diagram of the polarization modulator replaced by the middle delay unit according to the present invention.

Fig. 3 is a schematic diagram of a sample unit structure of a two-dimensional galvanometer with phase modulation according to the present invention.

Fig. 4 is a schematic structural diagram of a detection unit with a beam splitter and a balanced detector according to the present invention.

Fig. 5 is a comparison between the principle schematic diagram of the imaging of two orthogonal polarization components simultaneously and with high sensitivity and the schematic diagram of the predecessor method by using the depth multiplexing and linear phase modulation method in the present invention.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the scope of the present invention should not be limited by these examples.

Please refer to fig. 1. Fig. 1 is the structure diagram of the optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on the qiong matrix of the present invention. The optical fiber type sweep frequency polarization sensitive optical coherence tomography system based on the Jones matrix comprises a sweep frequency light source 1, wherein incident light is divided into a light beam in a sample arm and a light beam in a reference arm 6 after passing through a first optical fiber coupler 2; the light beam in the sample arm sequentially passes through the first polarization controller 3, the first polarizer 4 and the delay unit 5, then enters the sample unit 8, irradiates to a sample, and then returns to enter the detection unit 9 through the second optical fiber coupler 7; incident light of the reference arm 6 enters the detection unit 9 through the second polarization controller 10, is merged with reflected light of the sample arm, enters the detection unit 9 for detection, and transmits data to the computer 11.

Please refer to fig. 2. Fig. 2 is a schematic diagram of the structure of the middle delay unit of the present invention. Linearly polarized light forming an included angle of 45 degrees with the horizontal direction enters a first polarization beam splitter 504 through a first collimating mirror 501, is divided into two beams, then respectively passes through a first quarter-wave plate 502 and a second quarter-wave plate 506, is reflected by a first plane mirror 503 and a second plane mirror 507, then is converged by the first polarization beam splitter 504, and then enters an optical fiber through a second collimating mirror 505.

Please refer to fig. 3. Fig. 3 is a schematic diagram of a sample unit structure of a two-dimensional galvanometer with linear phase modulation according to the present invention. Incident light is irradiated to the two-dimensional scanning galvanometer 802 by the third collimating mirror 801, and is irradiated to a sample 805 by a telescope system consisting of the first lens 803 and the second lens 804, and reflected light with sample information returns to the second optical fiber coupler 7.

Please refer to fig. 4. Fig. 4 is a schematic structural diagram of a detection unit with a beam splitter and a balanced detector according to the present invention. The reference light enters the beam splitter 905 through the fourth collimating mirror 901 and the second polarizer 902, the sample light enters the beam splitter 905 through the fifth collimating mirror 903, the interference signal is split into two beams by the beam splitter 905, and the intensity information is measured by the first balance detector 907 and the second balance detector 908 after passing through the second polarization beam splitter 904 and the third polarization beam splitter 906 respectively.

Please refer to fig. 5. Fig. 5 is a comparison between the principle schematic diagram of the imaging of two orthogonal polarization components simultaneously and with high sensitivity and the schematic diagram of the predecessor method by using the depth multiplexing and linear phase modulation method in the present invention. (a) For the prior schematic diagram of the imaging deghosting of the predecessor method, sacrifice the degree of depth when realizing two orthogonal polarization states simultaneous imaging, (b) do the utility model discloses in adopt the multiplexing method of degree of depth and set up the offset and introduce the schematic diagram that linear phase modulation accomplished the deghosting in the mirror that shakes, realized two orthogonal polarization states simultaneously and big degree of depth, high sensitivity imaging.

The incident linearly polarized light with the two polarization states vertical to each other is as follows:

after passing through the delay system, the incident light of the sample arm is:

wherein k is the wave number, d is half of the optical path difference of the two arms of the delay unit, and the middle is taken as the zero optical path position.

Optical signals are transmitted through optical fibers, and the Jones matrices from the time delay system to the surface of the sample, back and forth in the sample and from the surface of the sample to the detector are respectively J_in、J_samp、J_outAnd finally, measuring the Jones matrix as follows:

jones matrix J for measuring the surface of a sample in advance_surfAnd then the influence of the optical fiber is eliminated through later data processing.

The light field vectors of the sample arm and the reference arm are respectively:

wherein z is_samp、z_refIs the optical path of the sample arm to the reference arm, E_S、E_RThe real amplitudes of the sample and reference arm light.

Is the introduced phase modulation.

In the detection arm, the horizontal direction in the formula (4) is taken, and the light field vector is expressed as:

the interference signal obtained from equation (5) is:

taking the mutual interference terms of the interference signals in the formula (6):

fourier transform is carried out on the mutual interference terms in the formula (7) along the x axis, and the negative frequency part is filtered out:

and (3) performing inverse Fourier transform on the formula (8):

fourier transform equation (9) along k-axis:

similarly, the vertical direction is:

where Γ (z) is the Fourier transform of S (k).

Extracting intensity information in formulas (10) and (11), respectively, to obtain J₁₁，J₁₂，J₂₁，J₂₂Then, the formula (3) was obtained.

The information returned from the sample surface can be measured as J_surfAnd is and

J_surf＝J_outJ_in(12)

from (12), it can be obtained:

let be J_T(13)

Wherein:

additionally, J can be obtained by comparing the states of the input and output_T

Obtaining by solution:

equation (13) is equal to equation (17), and the following can be obtained:

substituting expressions (14) and (15) into expression (18) can obtain:

to obtain J_samp。

Claims (5)

1. An optical fiber type frequency-sweeping polarization-sensitive OCT imaging system based on a Jones matrix is characterized in that in the frequency-sweeping polarization-sensitive OCT imaging system, the polarization state of light is represented by the Jones matrix; the delay unit is utilized to enable two incident linearly polarized lights with mutually vertical polarization directions to generate a certain optical path difference; full optical fiber transmission is adopted; the method is characterized in that: the depth multiplexing method is realized by introducing a delay unit (5) module, and eliminates mirror images by adopting a linear phase modulation method, so that two input polarization states can be imaged at the same time and high sensitivity.

2. The Jones matrix-based fiber-optic swept-polarization-sensitive OCT imaging system of claim 1, wherein: the device comprises a sweep frequency light source (1), wherein incident light is divided into a sample arm and a reference arm (6) through a first optical fiber coupler (2); the sample arm is connected to a first polarization controller (3) through an optical fiber, the light intensity of the input sample arm can be adjusted to be maximum by adjusting the first polarization controller (3), the light enters a time delay unit (5) with two arms having different optical paths and respectively arranged at two sides of a zero optical path after passing through a first polarizer (4), two beams of incident linearly polarized light with a certain optical path difference and mutually vertical polarization directions are generated, then the incident linearly polarized light enters a sample unit (8), irradiates to a sample and then returns to enter a detection unit (9) with two paths of balance detectors through a second optical fiber coupler (7); incident light of the reference arm (6) enters the detection unit (9) through the second polarization controller (10) to be merged with reflected light of the sample arm, enters the detection unit (9) for detection, and transmits data to the computer (11).

3. The optical fiber type swept-frequency polarization-sensitive OCT imaging system based on the qiong matrix of claim 2, wherein: in the delay unit (5), linearly polarized light forming an included angle of 45 degrees with the horizontal direction enters a first polarization beam splitter (504) through a first collimating mirror (501), is divided into two beams of light, then respectively passes through a first quarter-wave plate (502) and a second quarter-wave plate (506), is reflected by a first plane reflector (503) and a second plane reflector (507), then is converged in the first polarization beam splitter (504), and enters an optical fiber through a second collimating mirror (505).

4. The optical fiber type swept-frequency polarization-sensitive OCT imaging system based on the qiong matrix of claim 2, wherein: in the sample unit (8), incident light is irradiated to the two-dimensional scanning galvanometer (802) through the third collimating mirror (801), and then is irradiated to the sample (805) through a telescope system consisting of the first lens (803) and the second lens (804), and reflected light with sample information returns to the second optical fiber coupler (7).

5. The optical fiber type swept-frequency polarization-sensitive OCT imaging system based on the qiong matrix of claim 2, wherein: in the detection unit (9), reference light enters a beam splitter (905) through a fourth collimating mirror (901) and a second polarizer (902), sample light enters the beam splitter (905) through a fifth collimating mirror (903), an interference signal is divided into two beams by the beam splitter (905), and intensity information is measured by a first balance detector (907) and a second balance detector (908) after passing through a second polarization beam splitter (904) and a third polarization beam splitter (906) respectively.

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