CN212363082U

CN212363082U - Quick frequency sweep OCT system of frequency sweep light source

Info

Publication number: CN212363082U
Application number: CN202022110426.6U
Authority: CN
Inventors: 秦玉伟
Original assignee: Weinan Teachers College
Current assignee: Weinan Teachers College; Weinan Normal University
Priority date: 2020-09-23
Filing date: 2020-09-23
Publication date: 2021-01-15
Anticipated expiration: 2030-09-23

Abstract

The utility model belongs to the technical field of photoelectric detection, a quick frequency sweep OCT system of frequency sweep light source is related to, include: a swept-frequency laser; and the first optical fiber coupler is used for dividing the light wave signal into reference light and sample light, one end of the first optical fiber coupler is connected with the optical fiber of the sweep laser, and the other end of the first optical fiber coupler is connected with the optical fiber of the third optical fiber coupler. The reference light is collimated by the first lens to become parallel light, and the parallel light is incident on the second lens to be focused and then coupled into the third optical fiber coupler; the sample light is collimated by the third lens to become parallel light, the parallel light is incident to a conversion light path on the scanning galvanometer, the reflected light is focused by the fourth lens and then projected onto a sample to be detected for beam scanning, and the scanning galvanometer is electrically connected with a computer through the first data acquisition circuit; and the input end of the balance detector is connected with the third optical fiber coupler through an optical fiber, and the output end of the balance detector is electrically connected with the computer through a second data acquisition circuit. The utility model discloses the mechanical inertia who produces when having eliminated laser instrument mechanical scanning has improved the stability and the scanning speed of system.

Description

Quick frequency sweep OCT system of frequency sweep light source

Technical Field

The utility model belongs to the technical field of photoelectric detection, concretely relates to quick frequency sweep OCT system of frequency sweep light source.

Background

Optical Coherence Tomography (OCT) is a non-invasive, non-contact Optical tomography with extremely high resolution. The frequency-sweeping OCT technology belongs to the third generation OCT technology, and the sensitivity and the signal-to-noise ratio of the frequency-sweeping OCT technology are obviously superior to those of the traditional OCT technology; and the depth information acquisition process of the frequency-sweeping OCT technology does not need axial mechanical scanning, so that the imaging speed of the OCT system can be obviously improved, and the stability of the system is enhanced. The frequency-sweeping OCT system scans the fast wavelength of the frequency-sweeping laser, detects the intensity of the interference signal of the wavelength by using the point detector, and finally obtains the microstructure information of the object by Fourier of the interference spectrum signal to obtain the chromatographic image of the sample to be detected. The axial scanning speed of the system depends on the wavelength scanning speed of the frequency-scanning laser, so that the imaging speed of the system can be greatly improved. The frequency-sweeping OCT has higher rapid imaging capability than spectral domain OCT and time domain OCT, has the point detection advantage of time domain OCT, and can provide larger detection depth and higher sensitivity.

In practical use, to obtain real-time high-resolution two-dimensional tomographic images and three-dimensional surface topography images, a swept-frequency laser is required to have a fast wavelength sweep and a wide spectrum characteristic, but the requirement cannot be met in the existing OCT system.

SUMMERY OF THE UTILITY MODEL

In view of the above, the present invention provides a fast frequency-sweeping OCT system using a swept-source to solve the above-mentioned technical problems.

The technical scheme of the utility model is that:

a swept source fast swept OCT system, comprising:

the frequency-sweeping laser is used for providing a light wave signal;

the first optical fiber coupler is used for dividing the light wave signal into reference light and sample light, one end of the first optical fiber coupler is connected with the optical fiber of the sweep laser, and the other end of the first optical fiber coupler is connected with the optical fiber of the third optical fiber coupler;

the reference light is collimated by the first lens to become parallel light, and the parallel light is incident on the second lens to be focused and then coupled into the third optical fiber coupler;

the sample light is collimated by the third lens to become parallel light, the parallel light enters the conversion light path on the scanning galvanometer, the reflected light is focused by the fourth lens and then projected on a sample to be detected to carry out light beam scanning, and the scanning galvanometer is electrically connected with a computer through the first data acquisition circuit.

And the input end of the balance detector is connected with the third optical fiber coupler through an optical fiber, and the output end of the balance detector is electrically connected with the computer through a second data acquisition circuit.

Preferably, the swept-frequency laser includes:

the optical fiber coupler comprises a first single-mode optical fiber, a polarization controller, an optical fiber amplifier, a second optical fiber coupler, a second single-mode optical fiber, a polarization sensitive isolator and a spectrum delay line which are sequentially connected through optical fibers and used for realizing unidirectional transmission isolation of light waves;

one end of the dispersion compensation optical fiber is connected with one end of the second optical fiber coupler, the other end of the dispersion compensation optical fiber is connected with the second polarization controller, and the second polarization controller is connected with the first optical fiber coupler.

Preferably, the first fiber coupler has a splitting ratio of 80: 20.

Preferably, the third fiber coupler has a splitting ratio of 50: 50.

Preferably, the first data acquisition circuit and the second data acquisition circuit are respectively a data acquisition card.

Preferably, the fiber amplifier is an erbium doped fiber amplifier.

The utility model provides a pair of frequency sweep light source's quick frequency sweep OCT system, based on can realize that quick frequency sweep have wide spectral characteristic and initiative mode locking technique 7.5MHz, 1550nm sweep frequency laser, this quick broadband sweeps frequency laser, can realize 10dB wavelength sweep range 95nm, linear bandwidth range 76nm, scanning frequency is 7.5 MHz's scanning. The utility model discloses the Spectral Delay Line (SDL) that utilizes the single grating structure realizes that dispersion compensation and wavelength scanning range to the sweep frequency laser are adjustable to the dispersion compensation optic fibre (DCF) that uses high dispersion coefficient carries out the time stretch, can realize quick high resolution formation of image, and can effectively improve the system detection degree of depth, and its beneficial effect has:

1. the axial resolution of the sweep-frequency Optical Coherence Tomography (OCT) system is utilized, so that the imaging speed and the imaging quality are greatly improved;

2. the utility model can realize deep detection, and is very suitable for nondestructive testing of micro devices and microstructures;

3. the utility model can obviously reduce the diffraction times of the grating to the laser resonant cavity light in the dispersion compensation process, reduce the optical power loss caused by multiple diffraction, effectively improve the dispersion compensation efficiency, realize the high-power output of the frequency-swept laser, simultaneously reduce the offset between the incident light and the output light, reduce the light path adjustment and improve the system stability;

4. the utility model discloses have quick wavelength scanning and wide spectrum characteristic concurrently, effectively eliminated the mechanical inertia that the mechanical scanning in-process of laser instrument produced, improved the stability and the scanning speed of system, the practicality is strong, is worth promoting.

Drawings

FIG. 1 is the overall structure of the present invention;

fig. 2 shows a Spectral Delay Line (SDL) dispersion compensation structure according to the present invention.

Reference numerals:

1. optical Fiber Amplifier (OFA); 2. a first Polarization Controller (PC); 3. a first Single Mode Fiber (SMF); 4. spectral Delay Line (SDL); 41. a grating; 42. a focusing lens; 43. a mirror; 5. polarization sensitive isolator (PISO); 6. a second Single Mode Fiber (SMF); 7. a second fiber Coupler (Coupler); 8. dispersion Compensation Fiber (DCF); 9. a second Polarization Controller (PC); 10. a first fiber Coupler (Coupler); 11. a first lens; 12. a second lens; 13. a third fiber Coupler (Coupler); 14. a balance detector; 15. a third lens; 16. a fourth lens; 17. a sample to be tested; 18. a data acquisition card; 19. a computer; 20. and (4) scanning a galvanometer.

Detailed Description

The utility model provides a quick frequency sweep OCT system of frequency sweep light source, it is right to combine the schematic structure drawing of fig. 1 to fig. 2 below the utility model discloses explain.

Example 1

As shown in fig. 1, the utility model provides a quick frequency-sweeping OCT system of a frequency-sweeping light source, including the following structure:

the swept-frequency laser is an optical fiber type fast swept-frequency laser with a 1550nm wave band, the working central wavelength of which is 1550nm, and the swept-frequency laser is used for realizing the scanning of a linear scanning bandwidth range of 76nm and the scanning frequency of 7.5 MHz.

The swept-frequency laser structure is shown in fig. 1, and comprises a first single-mode fiber 3, a polarization controller 2, a fiber amplifier 1, a second fiber coupler 7, a second single-mode fiber 6, a polarization sensitive isolator 5 and a spectral delay line 4, which are sequentially connected through optical fibers and used for realizing unidirectional transmission isolation of light waves. One end of the dispersion compensation fiber 8 is connected with one end of the second fiber coupler 7, the other end of the dispersion compensation fiber is connected with the second polarization controller 9, and the second polarization controller 9 is connected with the first fiber coupler 10.

The optical fiber amplifier 1 is an Erbium-doped optical fiber amplifier OFA for realizing optical amplification, and the Erbium-doped optical fiber is used for acquiring a working medium.

The polarization sensitive isolator 5 realizes self-mode locking, ensures that the active mode-locking erbium-doped fiber ring cavity laser is in one-way operation, and realizes unidirectional transmission isolation of light waves.

Wherein the second fiber coupler 7 has a splitting ratio of 50:50 for directing the optical pulse out of the laser cavity.

The second polarization controller 9 is configured to control a polarization state of the optical wave, implement mode locking, obtain an optical wave with broadband output, and obtain a large optical power output.

Specifically, the internal structure of the swept-frequency laser is divided according to the realized functions: a cavity dispersion compensation section and a wavelength scanning section.

(1) The structure and the working principle of the resonant cavity dispersion compensation part are described as follows:

the ring formed by the optical fiber amplifier 1, the second optical fiber coupler 7, the second single-mode optical fiber 6, the polarization sensitive isolator 5, the spectrum delay line 4, the first single-mode optical fiber 3 and the polarization controller 2 is a laser resonant cavity, and the spectrum delay line 4 in the laser resonant cavity is used for realizing the dispersion compensation of the resonant cavity.

The swept-frequency laser of the present invention uses the single-grating structure based spectrum delay line 4 to realize the cavity dispersion compensation, such as the structure shown in fig. 2, a single grating 41, a single focusing lens 42 and a single reflector 43 constitute a 2-f system.

As shown in fig. 2, the grating 41 is a near-infrared reflection type diffraction grating DG, the focusing lens 42 is a convex lens tri L3, the convex lens tri L3 is an achromatic lens, and the reflecting mirror 43 is a plane reflecting mirror M.

The near-infrared reflection type diffraction grating DG and the plane mirror M are both placed at the focal plane of the convex lens III L3, the plane mirror M is obliquely placed at an inclination angle theta, and the near-infrared reflection type diffraction grating DG is obliquely arranged at an inclination angle theta g.

The plane mirror M and the three L3 convex lenses are respectively fixed on the support, so that the positions between the plane mirror M and the three L3 convex lenses are relatively fixed, the guide device convenient for the support to move is arranged below the support, the guide device is fixed on a box body of the laser, and when the support moves along the guide device, the plane mirror M and the three L3 convex lenses can realize synchronous displacement.

The guiding device comprises a nut seat fixed below the support, the nut seat is sleeved on the screw rod, one end of the screw rod is erected on the support through a bearing, the other end of the screw rod is connected with an output shaft of the motor, the motor is fixed on a box body of the laser, a block body is further fixed on the box body of the laser, a sliding groove is formed in the upper surface of the block body, the lower end of the nut seat is clamped in the sliding groove, and the nut seat can move along the sliding groove.

The motor is started, the screw rod can be driven to rotate synchronously, so that the nut seat synchronously drives the support to move along the sliding groove, synchronous movement of the plane reflector M and the convex lens three L3 is achieved, the distance between the near-infrared reflection type diffraction grating DG and the convex lens three L3 is changed, the dispersion value of the resonant cavity is changed by changing the distance between the near-infrared reflection type diffraction grating DG and the convex lens three L3, and the bandwidth range of the frequency-swept laser is adjustable.

As another embodiment, the plane mirror M and the three convex lenses L3 may be directly fixed on the micro-displacement platform, respectively, the positions of the plane mirror M and the three convex lenses L3 are relatively fixed, and the micro-displacement platform is fixed on the laser box.

The micro displacement platform moves to drive the plane mirror M and the convex lens three L3 to synchronously move, the distance between the near infrared reflection type diffraction grating DG and the convex lens three L3 is changed, the dispersion value of the resonant cavity is changed by changing the distance between the near infrared reflection type diffraction grating DG and the convex lens three L3, and the bandwidth range of the swept-frequency laser can be adjusted.

In the laser resonant cavity, an optical fiber emergent beam from the focus of the first convex lens L1 is collimated by the first convex lens L1 and then parallelly incident to the near-infrared reflection type diffraction grating DG for diffraction. After the diffracted light is focused by the convex lens tri L3, fan-shaped diffracted light beams with different wavelengths are focused on the plane mirror M at the focal plane of the convex lens tri L3 for reflection. The reflected beam is refocused on the near infrared reflection type diffraction grating DG through the third convex lens L3 to generate the second diffraction, and the diffracted light is recoupled into the laser resonant cavity through the second convex lens L2.

Because the near-infrared reflection type diffraction grating DG and the plane reflector M are both arranged at the focal plane of the convex lens III L3, and the inclination angle theta of the plane reflector M is smaller, the emergent light beams secondarily diffracted by the near-infrared reflection type diffraction grating DG are converged again and then are emergent approximately in parallel with the incident light beams.

Compared with the traditional 4-f dispersion compensation system with a double-diffraction grating structure by a grating, in the dispersion compensation system with the 2-f structure by a single grating, incident light is diffracted by a near-infrared reflection type diffraction grating DG only twice, so that the light beam separation and the light wave scattering loss are effectively reduced, and the optical power output of the laser is improved. The Group Velocity Dispersion (GVD) produced by the spectral delay line is expressed as:

wherein GVD is the group velocity dispersion generated by the spectral delay line, m is the number of diffraction orders, p is the diffraction grating spacing, theta_gIs the included angle between the normal of the near infrared reflection type diffraction grating DG and the optical axis of the convex lens three L3, theta is the inclined angle of the plane mirror M, Delta z represents the distance between the near infrared reflection type diffraction grating DG and the convex lens three L3, f is the focal length of the convex lens three L3, k is the focal length of the convex lens three L3₀Is the wave number.

Therefore, while maintaining the inclination angles of the plane mirror M and the near-infrared reflection type diffraction grating DG unchanged, the distance Δ z between the near-infrared reflection type diffraction grating DG and the three convex lenses L3 is changed by the synchronous displacement of the plane mirror M and the three convex lenses L3, thereby generating a spectral delay, and realizing dispersion compensation.

The utility model discloses use the adjustable compensation system of chromatic dispersion that the spectral delay line of single grating constitutes, it is different to the method that carries out chromatic dispersion compensation with the tradition utilizes the grating, and this laser instrument chromatic dispersion compensation part only uses single grating, and light just can realize chromatic dispersion compensation through twice grating diffraction at the laser instrument resonant cavity. The method can obviously reduce the diffraction times of the grating to the laser resonant cavity light in the dispersion compensation process, reduce the optical power loss caused by multiple diffraction, effectively improve the dispersion compensation efficiency and realize the high-power output of the swept-frequency laser. Meanwhile, the deviation between incident light and output light is reduced, the light path adjustment is reduced, and the system stability is improved.

The dispersion compensation method of the swept-frequency laser can also reduce the volume of the laser, reduce the production cost and is easy to integrate. The swept-frequency laser can realize the quick swept-frequency output in a wide spectral range, can be used for a swept-frequency Optical Coherence Tomography (OCT) system light source, can obviously improve the axial resolution of the system, and greatly improves the imaging speed and the imaging quality.

(2) The structure and the working principle of the wavelength scanning part are described as follows:

the wavelength scanning part is arranged at the other output end of a second optical fiber coupler 7 of the laser resonant cavity, and a dispersion compensation optical fiber 8 with large dispersion coefficient and reverse compensation characteristic is used for delaying the output pulse of the laser to realize spectrum scanning.

After the narrow pulse light wave of the broadband and time domain space output by the laser passes through the dispersion compensation fiber 8, each wavelength component is subjected to time delay, so that the narrow pulse light wave of the time domain space is widened. The use of the dispersion compensating fiber 8 enables the reduction in the volume of the fiber laser and the reduction in the laser cost. Each optical pulse signal of the spectral components undergoes time domain conversion and group velocity dispersion in the dispersion compensating fiber 8.

A1550 nm swept laser utilizes a time stretch-stretch technology to realize rapid wavelength scanning, a broadband narrow pulse optical wave generated by the laser generates Group Velocity Dispersion, GVD after passing through a Dispersion compensation optical fiber 8, each wavelength component experiences a characteristic Group delay depending on the wavelength, the broadband narrow pulse is broadened, and the spectral information of the optical wave is mapped into a time domain.

The working principle of the frequency-sweeping laser part is as follows:

the spectrum delay line 4 in the optical fiber amplifier 1 generates light waves, the light waves are connected to the second single-mode fiber 6 through one output end of the second fiber coupler 7 and pass through the polarization sensitive isolator 5, the active mode-locked erbium-doped fiber annular cavity laser is ensured to be in one-way operation, and one-way transmission isolation of the light waves is realized.

The laser resonant cavity is subjected to dispersion compensation through a spectrum delay line 4, the laser resonant cavity returns to the optical fiber amplifier 1 through a first single mode fiber 3 and a first polarization controller 2 with a splitting ratio of 50:50 to realize optical amplification, finally, an optical pulse is led out from the laser resonant cavity through a second optical fiber coupler 7, and the output pulse of the laser is subjected to time delay through a dispersion compensation fiber 8 with a large dispersion coefficient and a reverse compensation characteristic to realize spectrum scanning.

The first polarization controller 2 is used for controlling the polarization state of the light wave to realize mode locking and obtain the light wave with broadband output, and the light wave enters the interferometer light path after passing through the second polarization controller 9.

The frequency-sweeping laser adopts an active mode-locking mode APM, and is matched with components such as a polarization sensitive isolator 5, a second optical fiber coupler 7, a first polarization controller 2, a frequency spectrum delay line 4 and the like to output light waves generated by an optical fiber amplifier 1 into stable frequency-sweeping laser output with the central wavelength of 1550 nm.

The frequency-swept laser is an optical fiber frequency-swept laser, is compact in structure and easy to integrate, achieves compact frequency-swept lasers, and reduces cost.

The utility model discloses a narrow pulse light wave of laser instrument output utilizes the time stretch technique to realize the quick wavelength scanning of laser instrument, and this technique belongs to passive wavelength scanning technique, is accomplished by dispersion compensation optical fiber 8 that has high scattering coefficient. The narrow pulse light wave of the broadband that the laser produces and produces the group velocity dispersion after the dispersion compensation fiber, every wavelength component all experiences a characteristic group delay that depends on wavelength, and the pulse is stretched, maps the spectral information of light wave to the time domain, realizes the quick wavelength scanning of swept-frequency laser time domain space. Compared with the prior art, the technology has the characteristics of rapid wavelength scanning and wide frequency spectrum, effectively eliminates the mechanical inertia generated in the mechanical scanning process of the laser, improves the stability and the scanning speed of the system, does not sacrifice the tuning range, the instantaneous line width and the output optical power, reduces the volume of the laser, reduces the production cost and is beneficial to the integration of compact lasers.

The optical path structure of the interferometer part of the system for swept-frequency OCT is shown in fig. 1:

the light wave emitted by the frequency-sweeping laser is divided into two parts of a sample light and a reference light path by a first optical fiber coupler 10 with a splitting ratio of 80: 20:

after the sample light passes through the optical fiber, the emergent light beam is collimated by the third lens 15, is emitted to the scanning galvanometer 20, and is focused on the sample 17 to be measured by the fourth lens 16 to be scanned;

the reference light is collimated by the first lens 11, focused by the second lens 12 and coupled into the third fiber coupler 13.

The light beam at the other port of the first optical fiber coupler 10 is recoupled with the reference light by the third optical fiber coupler 13 and then interferes to obtain an interference spectrum signal containing the structural information of the sample to be detected, the interference spectrum signal is converted into an electric signal by the balance detector 14, the electric signal is collected by the data acquisition card 18 of the signal processing module and is processed by the computer 19 to realize image reconstruction.

The swept-frequency OCT system employs a balanced detector 14 that eliminates most of the dc terms of the interference signal, thereby reducing dc noise in the OCT image. Because the interference frequency spectrum contains the depth information of the sample to be detected, the interference frequency spectrum signal is subjected to inverse Fourier transform processing, interference noise such as mirror image, autocorrelation and the like in an OCT image is eliminated, the depth information of the sample to be detected is obtained, and after the scattering potential is endowed with a gray value, image reconstruction is carried out by software, so that the chromatographic image of the sample to be detected can be reconstructed.

The reference arm light path adopts a spatial light path structure of double lenses, and the first lens 11 and the second lens 12 are arranged in parallel to realize light ray coaxiality. Emergent parallel beams of optical fiber emergent light of the reference arm after being collimated by the first lens 11 are focused by the second lens 12 and then are coupled into the optical fiber again, the optical path of the reference arm is adjusted by adjusting the distance between the first lens 11 and the second lens 12, the optical path of the reference arm is matched with the optical path of the sample arm to be detected, and the purpose of interference of the sample light and the reference light is achieved.

The structure eliminates the reference mirror of the reference arm in the traditional OCT system interferometer, effectively reduces the optical path loss, improves the system stability, is beneficial to the adjustment of the optical path of the reference arm, reduces the interference of the reflected light of the reference mirror on the frequency-swept laser, and improves the signal-to-noise ratio of the system.

The above disclosure is only for the preferred embodiments of the present invention, however, the present invention is not limited thereto, and any changes that can be considered by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A swept source fast swept OCT system, comprising:

the frequency-sweeping laser is used for providing a light wave signal;

the first optical fiber coupler (10) is used for dividing the light wave signal into reference light and sample light, one end of the first optical fiber coupler is connected with the optical fiber of the sweep laser, and the other end of the first optical fiber coupler is connected with the optical fiber of the third optical fiber coupler (13);

the reference light is collimated by the first lens (11) to become parallel light, and the parallel light is incident on the second lens (12) to be focused and then coupled into the third optical fiber coupler (13);

the sample light is collimated by the third lens (15) to become parallel light, the parallel light enters a conversion light path on the scanning galvanometer (20), the reflected light is focused by the fourth lens (16) and then projected onto a sample (17) to be detected to perform light beam scanning, and the scanning galvanometer (20) is electrically connected with the computer (19) through the first data acquisition circuit;

and the input end of the balance detector (14) is electrically connected with the third optical fiber coupler (13), and the output end of the balance detector is electrically connected with the computer (19) through the second data acquisition circuit.

2. A swept source fast swept OCT system as claimed in claim 1, wherein said swept laser comprises:

the optical fiber coupler comprises a first single-mode optical fiber (3), a polarization controller (2), an optical fiber amplifier (1), a second optical fiber coupler (7), a second single-mode optical fiber (6), a polarization sensitive isolator (5) and a spectrum delay line (4), which are sequentially connected through optical fibers and used for realizing unidirectional transmission isolation of light waves;

and one end of the dispersion compensation optical fiber (8) is connected with one end of the second optical fiber coupler (7) through an optical fiber, the other end of the dispersion compensation optical fiber is connected with the second polarization controller (9) through an optical fiber, and the second polarization controller (9) is connected with the first optical fiber coupler (10) through an optical fiber.

3. A swept frequency source fast swept frequency OCT system according to claim 1, where the first fiber coupler (10) has a split ratio of 80: 20.

4. A swept frequency source fast swept frequency OCT system according to claim 1, wherein the third fiber coupler (13) has a splitting ratio of 50: 50.

5. A swept frequency source fast swept frequency OCT system according to claim 1, where the first and second data acquisition circuits are data acquisition cards (18), respectively.

6. A swept frequency source fast swept frequency OCT system according to claim 2, characterized in that the fiber amplifier (1) is an erbium doped fiber amplifier.