CN112426128B - Optical fiber probe and variable-focus optical fiber OCT device based on beam expanding length adjustment - Google Patents

Optical fiber probe and variable-focus optical fiber OCT device based on beam expanding length adjustment Download PDF

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CN112426128B
CN112426128B CN202011269324.7A CN202011269324A CN112426128B CN 112426128 B CN112426128 B CN 112426128B CN 202011269324 A CN202011269324 A CN 202011269324A CN 112426128 B CN112426128 B CN 112426128B
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CN112426128A (en
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姬崇轲
高帅
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Foshan University
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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0062—Arrangements for scanning
    • A61B5/0066—Optical coherence imaging
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • A61B1/00163—Optical arrangements
    • A61B1/00165—Optical arrangements with light-conductive means, e.g. fibre optics
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0073—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by tomography, i.e. reconstruction of 3D images from 2D projections
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0075—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0082—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence adapted for particular medical purposes
    • A61B5/0084—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence adapted for particular medical purposes for introduction into the body, e.g. by catheters

Abstract

The invention provides an optical fiber probe and a variable-focus optical fiber OCT device based on beam expanding length adjustment, wherein the OCT device comprises a broadband light source, a laser light source, a first coupler, a reference arm light path structure, a sample arm light path structure and a spectral analysis component; the broadband light source is used for emitting a source light beam, and the source light beam is divided into a first light beam and a second light beam by the coupler; the laser light source is used for emitting pump light; the first light beam is incident into the reference arm light path structure, the second light beam is coupled with the pump light emitted by the laser light source and is incident into the optical fiber probe of the sample arm light path structure, and the adjustable focus of the optical fiber OCT device is realized; the spectral analysis component is configured to receive and analyze a first light beam reflected from the reference arm optical path structure and a second light beam reflected from the sample arm optical path structure. The variable-focus optical fiber OCT device adopts an all-fiber probe structure as a sample arm, is small and exquisite, is easy to package, has the characteristic of adjustable focus, and can realize high-resolution imaging beyond the fixed depth of field range of the traditional probe.

Description

Optical fiber probe and variable-focus optical fiber OCT device based on beam expanding length adjustment
Technical Field
The invention relates to the technical field of optical fiber devices, in particular to an optical fiber probe and an OCT (optical coherence tomography) device based on a variable-focus optical fiber with adjustable beam expanding length.
Background
Due to the unique non-invasive nature, optical coherence tomography is widely used in the biomedical imaging field as an extremely potential imaging means. Resolution, one of the important parameters of OCT systems, is a determining factor affecting the imaging quality. The longitudinal resolution of the OCT device is affected by the central wavelength and bandwidth of the low coherence light source, while the lateral resolution depends on the spot size of the beam focused on the sample to be measured, both independent of each other. However, the lateral resolution and the depth of focus of the OCT device are a pair of mutually restricted parameters, and the lateral resolution rapidly decreases as the tissue to be measured moves away from the focus, which limits the OCT technology to high-quality imaging of tissues beyond the depth of field. In order to obtain high-resolution imaging of a large range of tissues, a plurality of novel imaging technologies are developed, such as a probe made based on a bessel beam, a multi-beam scanning mechanism, a self-focusing technology based on adaptive optics, and the like, but the energy at the focus of the probe made based on the bessel beam principle is too weak, and the energy requirement on a light source is high when the probe is used for imaging; the multi-beam scanning mechanism and the self-focusing technique are difficult to be used for endoscopic imaging of the interior of the tissue due to the system constitution and volume limitation. The OCT probe with the adjustable working distance can also be used as one effective means for overcoming the defects, the scanning on the tissue depth information is realized by changing the focusing position of the light spot, and the high-resolution imaging in the working distance adjusting range can be realized. The currently reported focus-adjustable technologies for OCT devices include technologies based on electro-optic, thermo-optic, electro-mechanical, and acoustic control mechanisms.
The optical fiber is combined with the OCT technology to manufacture the OCT endoscopic probe based on the optical fiber, the structure of a system sample arm can be simplified, the application range of the OCT is expanded, and the OCT technology based on the optical fiber probe is used for the research of body lumen organ imaging at present. The early optical fiber OCT probe is to bond an optical fiber and a graded index lens together, the emergent light of the optical fiber can generate a focusing effect after passing through the graded index lens or a ball lens, and the light beam is reflected by the aid of a total reverse side processed by a micro reflector or a light-emitting end of the lens, so that the light beam is emitted laterally when the probe is used in an endoscope. With the development of optical fiber manufacturing processes, coreless optical fibers and graded-index optical fibers are used in the manufacture of optical fiber OCT probes. Due to the small size and convenient welding of the optical fiber, the all-fiber OCT probe has great progress in the aspects of packaging size, insertion loss and the like. However, the OCT apparatus is still under the initial stage of research for the focus-adjustable optical fiber.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide an optical fiber probe and a variable-focus optical fiber OCT device based on adjustable beam expanding length.
In order to achieve the purpose, the invention is realized by the following technical scheme: a fiber optic probe, comprising: the optical fiber probe is formed by sequentially connecting a single-mode optical fiber, an active optical fiber, a hollow glass tube filled with a thermosensitive medium and a graded-index optical fiber; the optical fiber probe is fixed in the medical injector to realize encapsulation.
Two ends of the active optical fiber are respectively connected with the graded-index optical fiber and the hollow glass tube filled with the thermosensitive medium in a fixing mode of ultraviolet gel gluing; and the single-mode optical fiber is fixedly welded with the active optical fiber through a welding machine.
The utility model provides an adopt optical fiber probe's variable focus optical fiber OCT device based on beam expanding length is adjustable which characterized in that: the device comprises a broadband light source, a laser light source, a coupler I, a reference arm light path structure, a sample arm light path structure and a spectrum analysis component; the broadband light source is used for emitting a source light beam, and the source light beam is divided into a first light beam and a second light beam by the coupler; the laser light source is used for emitting pump light; the sample arm optical path structure adopts an optical fiber probe as a sample arm; the first light beam is incident into the reference arm light path structure, and the second light beam is coupled with a pump light emitted by a laser light source and is incident into the optical fiber probe of the sample arm light path structure, so that the adjustable focus of the optical fiber OCT device is realized; the spectral analysis component is configured to receive and analyze a first light beam reflected from the reference arm optical path structure and a second light beam reflected from the sample arm optical path structure.
The reference arm light path structure comprises a circulator I, a polarization controller I, a beam collimator, a one-dimensional stepping motor and a reflector used as a reference arm; the first light beam is coupled into the light beam collimator through the circulator I and irradiates on the reflector; the reflector is fixed on the one-dimensional stepping motor to adjust the optical path of the reference arm optical path structure.
The sample arm light path structure further comprises a second circulator, a wavelength division multiplexer, a second polarization controller and a three-dimensional stepping motor; the second light beam passes through the second circulator and then is coupled with the pump light emitted by the laser light source through the wavelength division multiplexer, and then enters the optical fiber probe; the optical fiber probe is fixed on the three-dimensional stepping motor so as to adjust the optical path of the sample arm optical path structure.
The optical path of the reference arm optical path structure can be adjusted through the one-dimensional stepping motor, the optical path of the sample arm optical path structure can be adjusted through the three-dimensional stepping motor, so that the optical paths of the sample arm optical path structure and the reference arm optical path structure are basically the same, dispersion caused by different optical fiber lengths of the sample arm and the reference arm is eliminated, in addition, the sample arm optical path structure and the reference arm optical path structure are respectively provided with the polarization controller II and the polarization controller I, and the signal-to-noise ratio of interference signals can be improved through adjusting the polarization controller I and the polarization controller II. The one-dimensional stepping motor and the three-dimensional stepping motor are connected with the controller through circuit connecting lines, so that the movement and data acquisition of the one-dimensional stepping motor and the three-dimensional stepping motor are realized.
The spectral analysis component comprises a second coupler, a balanced photoelectric detector, a spectrum analyzer and a controller; the balance photoelectric detector, the spectrum analyzer and the controller are connected in sequence; and the first light beam reflected from the optical path structure of the reference arm and the second light beam reflected from the optical path structure of the sample arm are coupled through the second coupler to generate interference signals, and the interference signals are recorded through the balanced photoelectric detector and the spectrum analyzer and then are stored in the controller.
Focal length Z of variable-focus optical fiber OCT device w And the lateral resolution D is expressed as:
Figure GDA0003821871990000031
Figure GDA0003821871990000032
wherein
Figure GDA0003821871990000033
λ and w 0 Respectively the wavelength of the emergent light of the active optical fiber end face and the mode field radius, n 0 And l 0 Refractive index and geometric length, n, of the material filled in the hollow glass tube for beam expansion g And l g The effective refractive index and the aggregate length of the fiber core of the graded index fiber respectively, g is the refractive index gradient coefficient of the graded index fiber, n s Is the refractive index coefficient of the space where the emergent light is located.
The first coupler is a coupler with 8:2, 1 x 2 fiber coupler.
The second coupler is a coupler with the light splitting ratio of 5:5, 2 x 2 fiber coupler.
The variable-focus optical fiber OCT device realizes adjustable focus as follows: emergent light of the active optical fiber enters the graded-index optical fiber after being expanded by the hollow glass tube filled with the thermosensitive medium, the graded-index optical fiber with proper length can play a role in converging light beams, and finally the light beams are converged outside the medical injector. The active optical fiber can absorb the pump light and convert partial light energy into heat energy due to the addition of the pump light, and the heat is transferred to the hollow glass tube which is connected with the active optical fiber and filled with the thermosensitive medium, so that the refractive index of the thermosensitive medium in the tube is changed, the beam expanding length of the light beam is changed, the working distance of the optical fiber probe is adjusted, and the function of adjusting the focus of the optical fiber OCT device is achieved.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the variable-focus optical fiber OCT device has the function of adjusting the focus position, can scan biological tissues in the depth direction by changing the focus position of OCT light spots, and can realize high-resolution imaging beyond the depth of field range by combining the image recombination technology.
2. The invention utilizes the heat effect of the pump light and the thermal sensitive medium as the means for adjusting the focus of the optical fiber OCT device, thereby avoiding the limitation of the regulation and control modes such as voltage, current and the like in the biomedical imaging.
3. The optical fiber probe is used as a sample arm of the optical fiber OCT device, and a hollow glass tube filled with a thermosensitive medium is used as a beam expanding structure. The photothermal effect is generated by external pump light, and the photothermal effect directly or indirectly acts on the filled thermosensitive medium to change the effective refractive index of the filled thermosensitive medium, so that the effective beam expanding length of the optical fiber probe is further changed, and the focus of the optical fiber OCT device is adjustable. The whole optical fiber probe is packaged in a medical injector and can be used for endoscopic imaging. In addition, the mode of adjusting the focus by changing the structural parameters of the optical fiber OCT device can realize high-range high-definition imaging with extended depth of field, and has low regulation and control cost and small optimization difficulty.
Drawings
FIG. 1 is a schematic diagram of a variable focus fiber OCT device of the invention;
FIG. 2 is a schematic view of a fiber optic probe of the present invention;
wherein, 1 is a broadband light source, 2 is a laser light source, 3 is a coupler I, 4 is a coupler II, 5.1 is a circulator I, 5.2 is a circulator II, 6.1 is a polarization controller I, 6.2 is a polarization controller II, 7 is a beam collimator, 8 is a one-dimensional stepping motor, 9 is a three-dimensional stepping motor, 10 is an optical fiber probe, 10.1 is a single-mode optical fiber, 10.2 is an active optical fiber, 10.3 is a hollow glass tube filled with ethanol, 10.4 is a graded index optical fiber, 10.5 is a medical injector, 11 is a reflector, 12 is a balanced photoelectric detector, 13 is a spectrum analyzer, 14 is a controller, and 15 is a wavelength division multiplexer.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Examples
As shown in figures 1 and 2, the variable-focus optical fiber OCT device based on adjustable beam expanding length comprises a broadband light source 1, a 980nm laser light source 2, a coupler I3, a reference arm optical path structure, a sample arm optical path structure and a spectrum analysis component. The broadband light source 1 is configured to emit a source light beam, which is split into a first light beam and a second light beam by a coupler one 3. The laser light source 2 is used for emitting pump light, the optical fiber probe 10 is used as a sample arm in the sample arm optical path structure, the first light beam is incident to the reference arm optical path structure, the second light beam is coupled with the pump light emitted by the laser light source 2 and is incident to the optical fiber probe 10 in the sample arm optical path structure, the adjustable focal point of the optical fiber OCT device is achieved, and the spectrum analysis component is used for receiving and analyzing the first light beam reflected back from the reference arm optical path structure and the second light beam reflected back from the sample arm optical path structure.
Specifically, the splitting of the first coupler 3 is 8:2, the source beam is split by a coupler one 3 into a first beam with energy 20% of the source energy and a second beam with energy 80% of the source energy. The reference arm light path structure comprises a circulator I5.1, a polarization controller I6.1, a beam collimator 7, a one-dimensional stepping motor 8 and a reflector 11 serving as a reference arm, wherein a first light beam with energy accounting for 20% of the energy of a light source is coupled into the beam collimator 7 after passing through the circulator I5.1 and irradiates on the reflector 11, and the reflector 11 is fixed on the one-dimensional stepping motor 8 so as to adjust the light path of the reference arm light path structure.
The sample arm light path structure comprises a second circulator 5.2, a wavelength division multiplexer 15, a polarization controller 6.2, a fiber probe 10 and a three-dimensional stepping motor 9, wherein a second light beam with energy accounting for 80% of light source energy passes through the second circulator 5.2 and then is coupled with a pump light emitted by a laser light source 2 through the wavelength division multiplexer 15 and is incident on the fiber probe 10, and the fiber probe 10 is fixed on the three-dimensional stepping motor 9 to adjust the light path of the sample arm light path structure.
The spectral analysis component comprises a second coupler 4, a balanced photoelectric detector 12, a spectrum analyzer 13 and a controller 14, wherein the balanced photoelectric detector 12, the spectrum analyzer 13 and the controller 14 are sequentially connected; the first light beam reflected from the optical path structure of the reference arm and the second light beam reflected from the optical path structure of the sample arm are coupled by the second coupler 4 to generate an interference signal, and the interference signal is recorded by the balanced photodetector 12 and the spectrum analyzer 13 and then stored in the controller 14. The optical path of the reference arm optical path structure can be adjusted through the one-dimensional stepping motor 8, and the optical path of the sample arm optical path structure can be adjusted through the three-dimensional stepping motor 9, so that the optical paths of the sample arm optical path structure and the reference arm optical path structure are basically the same through adjustment, and the dispersion caused by different optical fiber lengths of the sample arm and the reference arm is eliminated. In addition, the sample arm optical path structure and the reference arm optical path structure are respectively provided with a second polarization controller 6.2 and a first polarization controller 6.1, and the signal-to-noise ratio of interference signals can be improved by adjusting the first polarization controller 6.1 and the second polarization controller 6.2. The one-dimensional stepping motor 8 and the three-dimensional stepping motor 9 are connected with the controller 14 through circuit connecting wires, so that the movement and data acquisition of the one-dimensional stepping motor 8 and the three-dimensional stepping motor 9 are realized.
The optical fiber probe 10 is formed by connecting a single mode optical fiber 10.1, an active optical fiber 10.2, a hollow glass tube 10.3 filled with ethanol and a graded index optical fiber 10.4 in sequence, and the optical fiber probe 10 is fixed in a medical injector 10.5 to realize encapsulation. Wherein, the two ends of the active optical fiber 10.2 are respectively connected with the graded index optical fiber 10.4 and the hollow glass tube 10.3 filled with ethanol by adopting a fixing mode of ultraviolet gel gluing, and the single mode optical fiber 10.1 is welded and fixed with the active optical fiber 10.2 by a welding machine.
The variable-focus optical fiber OCT device realizes adjustable focus as follows: emergent light of the active optical fiber 10.2 enters the graded-index optical fiber 10.4 after being expanded by the hollow glass tube 10.3 filled with ethanol, the graded-index optical fiber 10.4 with proper length can play a role in converging light beams, and finally the light beams are converged outside the medical injector 10.5. The pumping light is added, so that the active optical fiber 10.2 can absorb the pumping light and convert partial light energy into heat energy, the heat energy is transferred to the hollow glass tube 10.3 which is connected with the active optical fiber and filled with ethanol, the refractive index of the ethanol in the tube is changed, the beam expanding length of a light beam is changed, the working distance of the optical fiber probe 10 is adjusted, and the function of adjusting the focus of the optical fiber OCT device is achieved.
The focal length Z of the variable-focus optical fiber OCT device w And the lateral resolution D is expressed as:
Figure GDA0003821871990000061
Figure GDA0003821871990000071
wherein
Figure GDA0003821871990000072
λ and w 0 Respectively the wavelength and mode field radius of the emergent light of the active fiber end face, n 0 And l 0 Refractive index and geometric length, n, of the material filled in the hollow glass tube for beam expansion g And l g The effective refractive index and the aggregate length of the fiber core of the graded index fiber respectively, g is the refractive index gradient coefficient of the graded index fiber, n s Is the refractive index coefficient of the space where the emergent light is located.
As can be seen from the formula, when the pump light worksWhen the rate changes, the heat conversion quantity of the active optical fiber is changed, thereby causing the refractive index n of the hollow glass Guan Zhongguang sensitive medium 0 Changes the beam expanding length of the light beam, and finally realizes the characteristic parameter focal length Z of the optical fiber OCT device w And adjusting the transverse resolution D to realize adjustable focus.
The hollow core glass tube used in this embodiment was manufactured by Polymicro corporation under the model number TSP100170, and the graded-index fiber 10.4 was a multimode graded-index fiber under the model number GIF 625. Simulating the refractive index of a thermosensitive medium in an air hole of the hollow glass tube at different temperatures by using Comsol software, and calculating the focal length Z of the optical fiber OCT device w And a lateral resolution D, the results of which are shown in table one.
Table-refractive index of thermosensitive medium (ethanol) and focal length Z of OCT device at different temperatures w And a lateral resolution D
Figure GDA0003821871990000073
Figure GDA0003821871990000081
As can be seen from the data in the table, when the temperature in the air hole changes from 20 ℃ to 75 ℃, the focal length of the optical fiber OCT device changes from 1124.37 μm to 1064.20 μm, and the corresponding transverse resolution changes from 23.55 μm to 22.91 μm. The variable-focus optical fiber OCT device can realize the adjustment of the focus position through the change of the beam expanding length caused by the change of the refractive index of the thermal medium (ethanol).
While the embodiments of the present invention have been described in detail with reference to the drawings, the present invention is not limited to the above embodiments, and it is within the knowledge of those skilled in the art to realize a variable focus optical fiber OCT apparatus adjustable based on the expanded beam length, by changing the type of optical fiber used without departing from the gist of the present invention.

Claims (6)

1. A fiber optic probe, comprising: the optical fiber probe is formed by sequentially connecting a single-mode optical fiber, an active optical fiber, a hollow glass tube filled with a thermosensitive medium and a graded-index optical fiber; the optical fiber probe is fixed in the medical injector to realize encapsulation;
the optical fiber probe is used as a sample arm of the variable-focus optical fiber OCT device, the hollow glass tube filled with the thermosensitive medium is used as a beam expanding structure, and external pump light generates a photothermal effect and directly or indirectly acts on the filled thermosensitive medium to change the effective refractive index of the filled thermosensitive medium, so that the effective beam expanding length of the optical fiber probe is changed, and the focus of the variable-focus optical fiber OCT device is adjustable.
2. The fiber optic probe of claim 1, wherein: one end of the active optical fiber is connected with a hollow glass tube filled with a thermosensitive medium in an ultraviolet gel gluing fixing mode; and the single-mode optical fiber is fixedly welded with the active optical fiber through a welding machine.
3. A variable focus optical fiber OCT apparatus based on beam expansion length adjustability using the fiber-optic probe according to claim 1 or 2, characterized by: the device comprises a broadband light source, a laser light source, a first coupler, a reference arm light path structure, a sample arm light path structure and a spectral analysis component; the broadband light source is used for emitting a source light beam, and the source light beam is divided into a first light beam and a second light beam by the coupler; the laser light source is used for emitting pump light; the sample arm light path structure adopts an optical fiber probe as a sample arm; the first light beam is incident into the reference arm light path structure, and the second light beam is coupled with a pump light emitted by a laser light source and is incident into an optical fiber probe of the sample arm light path structure, so that the focus of the variable-focus optical fiber OCT device can be adjusted; the spectral analysis component is used for receiving and analyzing a first light beam reflected from the reference arm optical path structure and a second light beam reflected from the sample arm optical path structure;
the reference arm light path structure comprises a circulator I, a polarization controller I, a beam collimator, a one-dimensional stepping motor and a reflector used as a reference arm; the first light beam is coupled into the beam collimator through the first circulator and irradiates on the reflector; the reflector is fixed on the one-dimensional stepping motor to adjust the optical path of the reference arm optical path structure;
the sample arm light path structure further comprises a second circulator, a wavelength division multiplexer, a second polarization controller and a three-dimensional stepping motor; the second light beam passes through the second circulator and then is coupled with the pump light emitted by the laser light source through the wavelength division multiplexer, and then enters the optical fiber probe; the optical fiber probe is fixed on the three-dimensional stepping motor so as to adjust the optical path of the sample arm optical path structure;
focal length Z of variable-focus optical fiber OCT device w And the lateral resolution D is expressed as:
Figure 650520DEST_PATH_IMAGE001
wherein the content of the first and second substances,
Figure 226995DEST_PATH_IMAGE002
λ and w 0 Respectively the wavelength of emergent light of the end face of the active optical fiber and the radius of a mode field,n 0 andl 0 respectively the refractive index and the geometric length of the material filled in the hollow glass tube which plays a role of beam expansion,n g andl g the effective refractive index of the core and the geometric length of the graded-index fiber,gis the index gradient coefficient of the graded index fiber,n s is the refractive index coefficient of the space where the emergent light is located.
4. The variable focus optical fiber OCT device of claim 3, based on expanded beam length adjustability, wherein: the spectral analysis component comprises a second coupler, a balanced photoelectric detector, a spectrum analyzer and a controller; the balance photoelectric detector, the spectrum analyzer and the controller are connected in sequence; and a first light beam reflected from the optical path structure of the reference arm and a second light beam reflected from the optical path structure of the sample arm are coupled through the coupler II to generate interference signals, and the interference signals are recorded through the balanced photoelectric detector and the spectrum analyzer and then stored in the controller.
5. The variable focus optical fiber OCT device of claim 3, based on expanded beam length adjustability, wherein: the first coupler is a coupler with 8:2, 1 x 2 fiber coupler.
6. The variable focus optical fiber OCT device of claim 4, wherein: the second coupler has a light splitting ratio of 5:5, 2 x 2 fiber coupler.
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