CN112426129B - Optical fiber probe and variable-focus optical fiber OCT device based on adjustable mode field area - Google Patents

Optical fiber probe and variable-focus optical fiber OCT device based on adjustable mode field area Download PDF

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CN112426129B
CN112426129B CN202011271865.3A CN202011271865A CN112426129B CN 112426129 B CN112426129 B CN 112426129B CN 202011271865 A CN202011271865 A CN 202011271865A CN 112426129 B CN112426129 B CN 112426129B
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CN112426129A (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 adjustable mode field area, wherein the OCT 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 source beam is split by the coupler into a first beam and a second beam; 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, 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, and has the characteristic of adjustable focus; meanwhile, the variable-focus optical fiber OCT device can be used for endoscopy and realizes high-resolution imaging beyond the field depth range.

Description

Optical fiber probe and variable-focus optical fiber OCT device based on adjustable mode field area
Technical Field
The invention relates to the technical field of optical fiber devices, in particular to an optical fiber probe and an optical fiber coherence tomography (OCT) device based on variable-focus optical fiber with adjustable mode field area.
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 that affects 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 use for endoscopic imaging of the interior of tissue due to system composition and volume limitations. The OCT probe with the adjustable working distance can also be used as one of effective means for overcoming the defects, scanning on tissue depth information is realized by changing the focusing position of a light spot, and high-resolution imaging in the working distance adjusting range can be realized. The focus-tunable technology that has been studied for OCT devices includes technologies based on electro-optical, thermo-optical, 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 can be expanded, and the OCT technology based on the optical fiber probe is used for the research of the imaging of body organs in vivo at present. The early fiber OCT probe is to bond the fiber and the graded index lens together, the emergent light of the fiber can generate focusing effect after passing through the graded index lens or the ball lens, and the light beam is reflected by the aid of the all-reverse side processed by the micro reflector or the light-emitting end of the lens, so that the light can be emitted from the side direction 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 focus adjustable fiber OCT apparatus is still in the initial stage of research.
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 mode field area, wherein the variable-focus optical fiber OCT device adopts an all-optical fiber probe structure as a sample arm, is small and exquisite, is easy to package and has the characteristic of adjustable focus; meanwhile, the variable-focus optical fiber OCT device can solve the defect that the transverse resolution and the depth of field are mutually restricted due to the fact that the structure composition and the structure parameters are fixed, so that the variable-focus optical fiber OCT device can be used for endoscopy and high-resolution imaging beyond the depth of field range is achieved.
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 welding a single mode optical fiber, an active optical fiber, a microstructure optical fiber filled with a thermosensitive medium, a coreless optical fiber I, a graded index optical fiber and a coreless optical fiber II; an inclined cutting surface is arranged at the end part of the coreless optical fiber II; the optical fiber probe is fixed in the medical injector to realize encapsulation.
The side surface of the medical injector is provided with an opening, and the optical fiber probe is fixed in the medical injector through ultraviolet gel to realize encapsulation.
And an antireflection film for the pumping light is arranged on the inclined cutting surface of the coreless fiber II.
The utility model provides an adopt optical fiber probe's variable focus optical fiber OCT device based on mode field area 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 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 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 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.
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 GDA0003797170870000031
Figure GDA0003797170870000032
wherein
Figure GDA0003797170870000033
λ and w 0 Respectively the wavelength and mode field radius of emergent light at the end face of the microstructure fiber, n 0 And l 0 Material refractive index and geometric length, n, of the first coreless fiber serving as beam expander g And l g The effective refractive index and the aggregate length of the fiber core of the graded index fiber, g is the refractive index gradient coefficient of the graded index fiber, n s Is the refractive index of the space in which the outgoing light is located, Z w The focal length of the variable-focus optical fiber OCT device; w is the radius of the spot at the focus.
The first coupler is a coupler with 8:2, 1 x 2 fiber coupler.
The second coupler has a 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 microstructure optical fiber enters the graded-index optical fiber after being expanded by the first coreless optical fiber, the graded-index optical fiber with a proper length can play a role in light beam convergence, the direction of the emergent light is changed by the second section of obliquely cut coreless optical fiber, and the final focus is positioned outside the medical injector playing a role in packaging. The pumping light is added, so that the active optical fiber can absorb the pumping light and convert partial light energy into heat energy, the heat energy is transferred to air holes of the microstructure optical fiber connected with the active optical fiber, the refractive index of a thermosensitive medium in the air holes is changed, the diameter of a mode field of the microstructure optical fiber is changed, and the working distance of the optical fiber probe is adjusted; meanwhile, the way of arranging an antireflection film on the inclined cutting surface of the coreless fiber II is adopted, the unabsorbed pump light in the reflected light is attenuated, and the damage of the pump light to biological tissues is prevented.
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 field depth range by combining an image recombination technology.
2. The heat effect of the pump light and the thermal sensitive medium is used as a means for adjusting the focus of the OCT device, so that the light control and the light transmission are combined into a whole, and the limitation of regulation and control modes such as voltage, current and the like in biomedical imaging is avoided.
3. The optical fiber probe of the present invention is used as a sample arm of the device of the present invention, and a microstructure optical fiber filled with a thermosensitive medium is used as a light guide optical fiber. By utilizing the characteristic that the refractive index of the microstructure optical fiber mode field is related to that of the filling medium in the hole, the photothermal effect is generated through external pump light, the photothermal effect directly or indirectly acts on the filling medium to change the effective refractive index of the filling medium, and the mode field diameter of the microstructure optical fiber is further changed, so that the adjustable focus of the OCT device is realized. The whole optical fiber probe is packaged in a medical injector and can be used for endoscopic imaging. In addition, the mode of realizing focus adjustment by changing the structural parameters of the 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.
4. The optical fiber probe with the adjustable focus position comprises a second inclined cutting coreless fiber, so that the light beam deflection effect is achieved, and meanwhile, unabsorbed pump light in reflected light can be attenuated in a mode that an antireflection film is arranged on the inclined cutting surface of the second coreless fiber, so that damage to biological tissues by the pump light is prevented.
Drawings
FIG. 1 is a schematic diagram of a variable focus optical fiber OCT apparatus 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 microstructure optical fiber, 10.4 is a graded index optical fiber, 10.5 is a coreless optical fiber I, 10.6 is a coreless optical fiber II, 10.7 is a medical injector, 11 is a reflector, 12 is a balanced photodetector, 13 is a spectrum analyzer, 14 is a controller, and 15 is a wavelength division multiplexer.
Detailed Description
The invention is described in further detail below with reference to the drawings and the detailed description.
Examples
As shown in figures 1 and 2, the variable-focus optical fiber OCT device based on adjustable mode field area comprises a broadband light source 1, a 980nm laser light source 2, a first coupler 3, 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 an energy of 20% of the source energy and a second beam with an energy of 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 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 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 sequentially welding a single-mode optical fiber 10.1, an active optical fiber 10.2, a microstructure optical fiber 10.3 filled with ethanol, a first coreless optical fiber 10.5, a graded index optical fiber 10.4 and a second coreless optical fiber 10.6, wherein an inclined cutting surface is arranged at the end part of the second coreless optical fiber 10.6, an opening is formed in the side surface of a medical injector 10.7, and the whole optical fiber probe 10 is fixed in the medical injector 10.7 through ultraviolet gel to realize encapsulation.
The variable-focus optical fiber OCT device realizes adjustable focus as follows: emergent light of the microstructure optical fiber 10.3 enters the graded-index optical fiber 10.4 after beam expansion through the first coreless fiber 10.5, the graded-index optical fiber 10.4 with proper length can play a role in light beam convergence, the emergent light direction is changed through the second section of obliquely cut coreless fiber 10.6 again, and the final focus is positioned outside the medical injector 10.7 playing a role in packaging. The addition of the pump light enables the active optical fiber 10.2 to absorb the pump light and convert partial light energy into heat energy, and the heat energy is transferred to the air holes of the micro-structural optical fiber 10.3 connected with the heat energy to cause the refractive index of ethanol in the air holes to change, so that the mode field diameter of the micro-structural optical fiber 10.3 is changed, and the working distance of the optical fiber probe 10 is adjusted; meanwhile, the way of arranging an antireflection film on the inclined cutting surface of the coreless fiber II is adopted, the unabsorbed pump light in the reflected light is attenuated, and the damage of the pump light to biological tissues is prevented.
For a fiber optic OCT device, its focal length Zw and lateral resolution D can be expressed as:
Figure GDA0003797170870000071
Figure GDA0003797170870000072
wherein
Figure GDA0003797170870000073
(wherein λ andw 0 wavelength and mode field radius of emergent light of 10.3 end faces of the microstructure optical fiber respectively), n 0 And l 0 Refractive index of material and geometric length, n, of 10.5 for the beam-expanding coreless fiber, respectively g And l g The effective refractive index of the fiber core and the aggregate length of the graded index fiber 10.4, g is the index gradient coefficient of the graded index fiber 10.4, n s Is the refractive index of the space in which the outgoing light is located, Z w Is the focal length of the variable-focus optical fiber OCT device; w is the radius of the spot at the focus. It can be seen from the formula that when the pump light power changes, the thermal conversion amount of the active optical fiber 10.2 is changed, so that the refractive index of the photosensitive medium (ethanol) in the micro-structured optical fiber 10.3 changes, and the radius w of the emergent optical mode field of the micro-structured optical fiber 10.3 is further changed 0 Finally, the adjustment of the characteristic parameter focal length Zw and the transverse resolution D of the optical fiber OCT device is realized, and the focus is adjustable.
The microstructured optical fiber 10.3 used in this example was a photonic crystal fiber of type SM-7.0-1100-28, the first 10.5 coreless fiber and the second 10.6 coreless fiber were of type FG125LA, and the graded-index fiber 10.4 was a multimode graded-index fiber of type GIF 625. Comsol software is used for simulating the refractive index of a thermosensitive medium (ethanol) in air holes of the microstructure optical fiber at different temperatures, the mode field radius of emergent light of the microstructure optical fiber is calculated, the focal length Zw and the transverse resolution D of the optical fiber OCT device are further calculated, and the result is shown in the table I.
Table showing the mode field area of the microstructured fiber at different temperatures, the focal length Zw and the lateral resolution D of the OCT device
Figure GDA0003797170870000074
Figure GDA0003797170870000081
As can be seen from the data in the table, the focal length of the fiber OCT device is changed from 62.7300 μm to 64.4541 μm and the corresponding lateral resolution is changed from 8.7319 μm to 9.0188 μm when the temperature in the air cavity is changed from 20 ℃ to 75 ℃. The variable-focus optical fiber OCT device based on the adjustable mode field area can realize the adjustment of the focus position through the change of the mode field area.
The embodiments of the present invention are described in detail with reference to the drawings, but the present invention is not limited to the above embodiments, and various changes, such as changing the type of optical fiber used, can be made within the knowledge of those skilled in the art without departing from the gist of the present invention, and a variable focus optical fiber OCT apparatus based on mode field area adjustment can also be implemented.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such modifications are intended to be included in the scope of the present invention.

Claims (10)

1. A fiber optic probe, comprising: the optical fiber probe is formed by sequentially welding a single mode optical fiber, an active optical fiber, a microstructure optical fiber filled with a thermosensitive medium, a coreless optical fiber I, a graded index optical fiber and a coreless optical fiber II; an inclined cutting surface is arranged at the end part of the coreless optical fiber II; the optical fiber probe is fixed in a medical injector to realize encapsulation, wherein the characteristic that the refractive index of a filling medium in a hole is related to the mode field diameter of the micro-structural optical fiber is utilized, and external pump light generates a photothermal effect to directly or indirectly act on the filling medium to change the effective refractive index of the filling medium, so that the mode field diameter of the micro-structural optical fiber is further changed, and the focus of the OCT device is adjustable.
2. The fiber optic probe of claim 1, wherein: the side surface of the medical injector is provided with an opening, and the optical fiber probe is fixed in the medical injector through ultraviolet gel to realize encapsulation.
3. The fiber optic probe of claim 1, wherein: and an anti-reflection film for aiming at the pump light is arranged on the inclined cutting surface of the coreless fiber II.
4. A variable focus optical fiber OCT apparatus based on mode field area adjustment using the optical fiber probe according to any one of claims 1 to 3, 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 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 optical fiber OCT device can be adjusted; 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.
5. The variable focus optical fiber OCT device of claim 4, based on mode field area adjustability, characterized by: 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.
6. The variable focus optical fiber OCT device of claim 4, based on the mode field area being adjustable, wherein: 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.
7. The variable focus optical fiber OCT device of claim 4, based on the mode field area being adjustable, 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.
8. The variable focus optical fiber OCT device of claim 4, based on the mode field area being adjustable, wherein: focal length Z of variable-focus optical fiber OCT device w And the lateral resolution D is expressed as:
Figure FDA0003885878180000021
Figure FDA0003885878180000022
wherein
Figure FDA0003885878180000023
λ and w 0 Respectively the wavelength of emergent light from the end face of the microstructure fiber and the mode field radius, n 0 And l 0 Refractive index of material and geometric length, n, of coreless fiber I for beam expansion g And l g The effective refractive index and the aggregate length of the fiber core of the graded index fiber, g is the refractive index gradient coefficient of the graded index fiber, n s The refractive index coefficient of the space where the emergent light is located; z w The focal length of the variable-focus optical fiber OCT device; w is the radius of the spot at the focus.
9. The variable focus optical fiber OCT device of claim 4, based on mode field area adjustability, characterized by: the first coupler is a coupler with 8:2, 1 x 2 fiber coupler.
10. The variable focus optical fiber OCT device of claim 7, based on mode field area adjustability, wherein: the second coupler has a light splitting ratio of 5:5, 2 x 2 fiber coupler.
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