Three-section type optical fiber probe and polarized optical coherence tomography system

Abstract

The invention relates to the technical field of optical fiber optics, and discloses a three-section optical fiber probe and a polarization optical coherence tomography system.The three-section optical fiber probe comprises a first optical fiber section, a second optical fiber section and a third optical fiber section which are sequentially connected; the fiber core diameter of the first optical fiber is larger than that of the third optical fiber, and the fiber core diameter of the third optical fiber section is matched with the fiber core radius of a polarization maintaining optical fiber in the polarization optical coherence tomography system; the second optical fiber section comprises a gradual change fiber core, and the radius of the gradual change fiber core is gradually reduced from the fiber core diameter of the first optical fiber section to the fiber core diameter of the third optical fiber section. The optical signal receiving energy of the three-section type optical fiber probe can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber optics, and in particular to a three-section optical fiber probe and a polarization optical coherence tomography system. Background Art

[0002] As a light transmission medium, optical fiber has the advantages of low loss, wide bandwidth, easy integration, and strong anti-interference ability. It is an indispensable optical component.

[0003] In the polarization optical coherence tomography system, the use of polarization-maintaining fiber devices makes the imaging system stable, anti-interference and easy to operate. However, due to the small core size of the polarization-maintaining fiber, when the optical fiber probe adapted to the polarization-maintaining fiber is used to receive the optical signal, the energy of the received optical signal is small. Summary of the invention

[0004] In view of this, the present invention provides a three-section optical fiber probe and a polarization optical coherence tomography system to solve or partially solve the technical problem that the existing polarization optical coherence tomography system uses polarization-maintaining optical fiber to receive low energy optical signals.

[0005] The technical solution proposed by the present invention is as follows:

[0006] A first aspect of the present invention provides a three-section fiber optic probe, which is applied to a polarization optical coherence tomography system, and includes a first fiber optic segment, a second fiber optic segment, and a third fiber optic segment connected in sequence; the core diameter of the first fiber optic segment is larger than the core diameter of the third fiber optic segment, and the core diameter of the third fiber optic segment is adapted to the core radius of the polarization-maintaining fiber in the polarization optical coherence tomography system; the second fiber optic segment includes a gradient core, and the radius of the gradient core gradually decreases from the core diameter of the first fiber optic segment to the core diameter of the third fiber optic segment.

[0007] Optionally, it also includes air holes, which are arranged in parallel with the gradient fiber core, and the air holes include a first air hole and a second air hole symmetrically arranged along a first direction with the gradient fiber core as the symmetry axis, and a third air hole and a fourth air hole symmetrically arranged along a second direction with the gradient fiber core as the symmetry axis, the first direction is perpendicular to the second direction, and the radii of the first air hole, the second air hole, the third air hole and the first half of the fourth air hole all increase synchronously with the decrease of the diameter of the gradient fiber core, the radii of the second half of the first air hole and the second air hole remain unchanged, and the radii of the second half of the third air hole and the fourth air hole gradually decrease until they disappear.

[0008] Optionally, the first optical fiber segment is a multimode optical fiber.

[0009] Optionally, the third optical fiber segment is a Panda-type polarization-maintaining optical fiber.

[0010] Optionally, the first optical fiber segment is connected to a fiber collimator in a sample arm of a polarization optical coherence tomography system, the third optical fiber segment is connected to a PANDA-type polarization-maintaining optical fiber in the polarization optical coherence tomography system, and the first air hole and the second air hole are coaxially arranged with two stress regions of the PANDA-type polarization-maintaining optical fiber in the polarization optical coherence tomography system, respectively.

[0011] Optionally, the front half of the first air hole is conical, the rear half of the first air hole is cylindrical, and the structure of the second air hole is the same as that of the first air hole; the front half and the rear half of the third air hole are both conical, and the fourth air hole has the same structure as the third air hole.

[0012] Optionally, the cone is a convex cone.

[0013] Optionally, the cone is a flat cone.

[0014] Optionally, the cone is a concave cone.

[0015] A second aspect of the present invention provides a polarization optical coherence tomography system, comprising a three-section optical fiber probe as described in any one of the first aspects.

[0016] It can be seen from the above technical solutions that the present invention has the following advantages:

[0017] The present invention provides a three-section optical fiber probe and a polarization optical coherence tomography system. The optical fiber probe is divided into a first optical fiber section, a second optical fiber section and a third optical fiber section which are connected in sequence. The first optical fiber section serves as the starting section of the optical fiber probe. When the optical fiber receives light from the outside, the energy of the light that can be collected is proportional to the core area. Since the core diameter of the first optical fiber section is larger than the core diameter of the third optical fiber section, the ability of the optical fiber probe to receive optical signals can be improved. The third optical fiber section serves as the terminating section. The core diameter of the third optical fiber section is compatible with the polarization-maintaining optical fiber in the polarization optical coherence tomography system, which is conducive to the efficient connection between the three-section optical fiber probe and other optical fiber devices. The gradient structure of the second optical fiber section can make the optical signal collected by the first optical fiber section smoothly transition to the third optical fiber section for transmission, and then be transmitted to the polarization-maintaining optical fiber in the polarization optical coherence tomography system. The energy of the optical signal received by the three-section optical fiber probe can be improved by the first optical fiber section, the second optical fiber section and the third optical fiber section which are connected in sequence.

[0018] By setting four air holes, the radii of the first air hole, the second air hole, the third air hole and the first half of the fourth air hole are all increased synchronously with the decrease of the diameter of the gradient core, so that the optical fiber has the same binding force on the light linearly deflected along the first direction or the second direction, the radii of the second half of the first air hole and the second air hole remain unchanged, and the radii of the second half of the third air hole and the fourth air hole gradually decrease until they disappear, so that the light loss linearly deflected along the second direction is reduced, and the difference between the light loss linearly deflected along the first direction is reduced, so that the three-section optical fiber probe has a good collection ability for the light linearly deflected along the first direction and the second direction, reduces the difference between the coupling efficiencies of light in two orthogonal directions, and further reduces the difference in intensity of data obtained by the dual channels of the polarization optical coherence tomography system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly express the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 Schematic diagram of the structure of a three-section optical fiber probe in an embodiment of the present invention;

[0021] Figure 2 Schematic diagram of a longitudinal section of a three-section optical fiber probe at x=0 in an embodiment of the present invention;

[0022] Figure 3 Schematic diagram of a longitudinal section of a three-section optical fiber probe at y=0 in an embodiment of the present invention;

[0023] Figure 4 A schematic diagram of a longitudinal section of another three-section optical fiber probe at x=0 in an embodiment of the present invention;

[0024] Figure 5 A schematic diagram of another longitudinal section of a three-section optical fiber probe at y=0 in an embodiment of the present invention;

[0025] Figure 6 is a schematic diagram of a longitudinal section of another three-section optical fiber probe at x=0 in an embodiment of the present invention;

[0026] Figure 7 is a schematic diagram of a longitudinal section of another three-section optical fiber probe at y=0 in an embodiment of the present invention;

[0027] Figure 8 Schematic diagram of the structure of a polarization optical coherence tomography system in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0030] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, it can also be the internal connection of two components, it can be a wireless connection, or it can be a wired connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] At present, in polarization optical coherence tomography systems, the use of polarization-maintaining fiber devices makes the imaging system stable, anti-interference and easy to operate. However, due to the small core size of the polarization-maintaining fiber, when a fiber probe adapted to the polarization-maintaining fiber is used to receive the optical signal, the energy of the received optical signal is small.

[0033] In addition, due to the existence of fast and slow dual axes in polarization-maintaining optical fiber, light with polarization directions parallel to the fast axis and slow axis respectively has different refractive indices, numerical apertures and coupling coefficients, and the light energy coupling efficiency in the two orthogonal directions is quite different, resulting in large differences in the intensity of the data obtained by the dual channels of the polarization optical coherence tomography system.

[0034] Based on this, an embodiment of the present invention provides a three-section optical fiber probe, which is applied to a polarization optical coherence tomography system, such as Figure 1 , Figure 2 and Figure 3As shown, the three-section optical fiber probe includes a first optical fiber section, a second optical fiber section, and a third optical fiber section which are connected in sequence; the core diameter of the first optical fiber is larger than the core diameter of the third optical fiber, and the core diameter of the third optical fiber section is adapted to the core radius of the polarization-maintaining optical fiber in the polarization optical coherence tomography system; the second optical fiber section includes a gradient core, and the radius of the gradient core gradually decreases from the core diameter of the first optical fiber section to the core diameter of the third optical fiber section.

[0035] The three-section optical fiber probe is located before the collimating lens in the sample arm of the polarization optical coherence tomography system and is connected to the optical fiber coupler. The section next to the collimating lens is the first optical fiber section, and its larger core enables more backscattered light from the sample to be coupled into the three-section optical fiber probe.

[0036] Exemplarily, the first fiber segment is used as the starting segment of the three-segment fiber optic probe, and a multimode fiber is used. The core diameter of the multimode fiber is 30 microns, which is three times the core diameter of the polarization-maintaining fiber of 10 microns. The core area of ​​this segment of multimode fiber is nine times the core area of ​​the polarization-maintaining fiber. When the fiber receives light from the outside, the energy of the light that can be collected is proportional to the core area. The multimode fiber of the starting segment uses a larger diameter core, which improves the ability of the three-segment fiber optic probe to collect light signals.

[0037] The third fiber segment is used as the termination segment of the three-segment fiber probe, and adopts a panda-type polarization-maintaining fiber. The panda-type polarization-maintaining fiber is a stress-type polarization-maintaining fiber, and its stress area is two panda-eye-shaped areas.

[0038] The internal structure of the third optical fiber segment is consistent with the internal structure of the polarization-maintaining optical fiber used in other optical fiber devices in the polarization optical coherence tomography system, that is, the polarization-maintaining optical fiber used in other optical fiber devices is also a panda-type polarization-maintaining optical fiber and has a matching size, which is conducive to efficient connection between the optical fiber probe and other optical fiber devices.

[0039] The second optical fiber segment uses a graded-index fiber core, the core diameter of which gradually decreases along the axial direction from 30 microns to 10 microns. This graded-index structure is designed to allow the optical signal collected by the starting multimode optical fiber to smoothly transition to the polarization-maintaining optical fiber for transmission.

[0040] The core parts of the first optical fiber segment, the second optical fiber segment and the third optical fiber segment are all formed of fused silica doped with germanium dioxide and are prepared in sections. The first optical fiber segment is a multimode optical fiber with a core diameter of 30 microns.

[0041] The second optical fiber segment is processed on the basis of single-mode optical fiber through laser micromachining technology, and the third optical fiber segment is polarization-maintaining optical fiber, which is then fused using a fusion splicer.

[0042] A three-section optical fiber probe according to an embodiment of the present invention is divided into a first optical fiber section, a second optical fiber section and a third optical fiber section which are connected in sequence. The first optical fiber section serves as the starting section of the optical fiber probe. When the optical fiber receives light from the outside, the energy of the light that can be collected is proportional to the core area. Since its core diameter is larger than the core diameter of the third optical fiber section, the ability of the optical fiber probe to receive optical signals can be improved. The third optical fiber section serves as the terminating section. Its core diameter is compatible with the polarization-maintaining optical fiber in the polarization optical coherence tomography system, which is conducive to the efficient connection between the three-section optical fiber probe and other optical fiber devices. The gradient structure of the second optical fiber section can make the optical signal collected by the first optical fiber section smoothly transition to the third optical fiber section for transmission, and then be transmitted to the polarization-maintaining optical fiber in the polarization optical coherence tomography system. By connecting the first optical fiber section, the second optical fiber section and the third optical fiber section in sequence, the energy of the optical signal received by the three-section optical fiber probe can be improved.

[0043] In some embodiments, the three-section fiber optic probe also includes air holes, and the air holes and the gradient fiber core are arranged in parallel. The air holes include a first air hole and a second air hole symmetrically arranged along a first direction with the gradient fiber core as the symmetry axis, and a third air hole and a fourth air hole symmetrically arranged along a second direction with the gradient fiber core as the symmetry axis. The first direction is perpendicular to the second direction. The radii of the first air hole, the second air hole, the third air hole and the first half of the fourth air hole all increase synchronously with the decrease in the diameter of the gradient fiber core, the radii of the second half of the first air hole and the second air hole remain unchanged, and the radii of the second half of the third air hole and the fourth air hole gradually decrease until they disappear.

[0044] Specifically, the air hole is arranged in the core cladding of the three-section optical fiber probe, and spans the second optical fiber segment and the third optical fiber segment in the third direction. The third direction is the length direction of the core of the three-section optical fiber probe, and the first direction, the second direction and the third direction correspond to the y-axis, the x-axis and the z-axis in the three-axis vertical coordinate system, respectively, and the z-axis coincides with the axis of the core.

[0045] The first optical fiber segment is connected to the optical fiber collimator in the sample arm of the polarization optical coherence tomography system, the third optical fiber segment is connected to the panda-type polarization-maintaining optical fiber in the polarization optical coherence tomography system, and the first air hole and the second air hole are coaxially arranged with two stress areas of the panda-type polarization-maintaining optical fiber in the polarization optical coherence tomography system respectively.

[0046] On the longitudinal section at x=0 and y=0, the gradient curve of the graded-index fiber core presents a funnel shape. In order to reduce the loss of light energy in the funnel-shaped area, four gradually larger air holes appear around the graded-index fiber core as the graded-index fiber core becomes smaller, which enhances the ability of the optical fiber to bind light, and the sizes of the four air holes are synchronously increased, so that the optical fiber has the same binding force on light deflected along the x or y direction.

[0047] When the core transitions from 30 microns to 10 microns, the same size as the core of the polarization-maintaining optical fiber, the four air holes around the core increase to their maximum size, at which point the diameter of the air holes is 20 microns.

[0048] Then, along the z direction, the first and second air holes coaxial with the two panda eyes, i.e., the stress zone, of the panda-type polarization-maintaining fiber remain unchanged in size. The third and fourth air holes arranged in the vertical direction gradually decrease in diameter until they disappear after growing to a maximum value of 20 microns, completely transitioning to the panda-type polarization-maintaining fiber.

[0049] Specifically, the front half of the first air hole is conical, the rear half of the first air hole is cylindrical, and the structure of the second air hole is the same as that of the first air hole; the front half and the rear half of the third air hole are both conical, and the structure of the fourth air hole is the same as that of the third air hole.

[0050] By setting the first air hole and the second air hole to be conical first and then cylindrical, and the third air hole and the fourth air hole to be bidirectionally conical, the optical loss along the x-direction linear deflection is reduced, and the difference between the optical loss along the y-direction linear deflection is reduced, so that the optical fiber probe has a good collection ability for the light along the x-direction or y-direction linear deflection, reduces the difference between the coupling efficiency of the light in the two orthogonal directions, and enables the light components polarized in the two orthogonal directions to be efficiently collected, thereby improving the intensity of the optical signal received by the polarization optical coherence tomography imaging system.

[0051] The boundary between the fiber core in the middle section of the optical fiber probe or the air holes around the fiber core and the fused silica cladding of the optical fiber can be formed by rotating a parabola around its central axis. The cone shape of the air holes distributed in the three-section optical fiber probe can be a concave cone, a flat cone or a convex cone. The three cone shapes can improve the ability of the optical fiber probe to receive optical signals and reduce the coupling efficiency difference between linear polarizations along two orthogonal directions.

[0052] in Figure 2 and Figure 3 The light energy collected by the three-section optical fiber probe including the convex cone air hole distribution is 4.5 times that collected by the ordinary polarization-maintaining optical fiber, and the difference between the light energy coupling efficiency in two orthogonal directions is reduced by 52%.

[0053] Figure 4 and Figure 5 The light energy collected by the three-section optical fiber probe including the flat-cone air hole distribution is 3.9 times that of the light energy collected by the ordinary polarization-maintaining optical fiber, and the difference between the light energy coupling efficiencies in two orthogonal directions is reduced by 43%.

[0054] Figure 6 and Figure 7The light energy collected by the three-section optical fiber probe including the concave cone air hole distribution is 3.1 times that of the light energy collected by the ordinary polarization-maintaining optical fiber, and the difference between the light energy coupling efficiency in two orthogonal directions is reduced by 29%.

[0055] The present invention also provides a polarization optical coherence tomography system, comprising a three-section optical fiber probe as described in any one of the above embodiments.

[0056] In one example, a polarization optical coherence tomography system equipped with the optical fiber probe is as follows: Figure 8 As shown, Figure 8 Except for the three-section fiber probe, other fiber components are polarization-maintaining fiber components. In the figure, SL is a frequency-sweeping laser that can emit frequency-sweeping laser; PC is a polarization controller that is used to adjust the polarization state of the frequency-sweeping laser to linear polarization, and the linear polarization direction coincides with the fast axis or slow axis of the polarization-maintaining fiber; Coupler1 and Coupler2 are 50 / 50 couplers that are used to split light to produce Michelson interference; TSF is the three-section fiber probe in the above embodiment, which is used to increase the energy of the collected optical signals in the two polarization directions; PMF is a section of polarization-maintaining fiber with the same length as TSF, which is used to synchronize the optical paths of the signal arm and the reference arm of the Michelson interference part; CL1 and CL2 are collimating lenses; QWP1 and QWP2 are Quarter wave plate, where the angle between QWP1 and the deflection direction of the swept laser line is 22.5°, and the angle between QWP2 and the deflection direction of the swept laser line is 45°; M is a reflector used to reflect the reference light back to the Michelson interferometer, and there are light polarization components with equivalent energy in the fast and slow axes of the polarization-maintaining fiber; GM is a scanning galvanometer pair that enables the laser to scan the area of ​​interest of the sample; Lens is a scanning lens that focuses the laser into the sample; PBS1 and PBS2 are polarization beam splitters that separate the light energy deflected along the fast and slow axes of the polarization-maintaining fiber, which are detected by two balanced detectors, PD1 and PD2, respectively.

[0057] A three-section optical fiber probe and a polarization optical coherence tomography system according to an embodiment of the present invention divide the optical fiber probe into a first optical fiber section, a second optical fiber section and a third optical fiber section which are connected in sequence. The first optical fiber section serves as the starting section of the optical fiber probe. When the optical fiber receives light from the outside, the energy of the light that can be collected is proportional to the core area. Since its core diameter is larger than the core diameter of the third optical fiber section, the ability of the optical fiber probe to receive optical signals can be improved. The third optical fiber section serves as the terminating section. Its core diameter is compatible with the polarization-maintaining optical fiber in the polarization optical coherence tomography system, which is conducive to the efficient connection between the three-section optical fiber probe and other optical fiber devices. The gradient structure of the second optical fiber section can make the optical signal collected by the first optical fiber section smoothly transition to the third optical fiber section for transmission, and then be transmitted to the polarization-maintaining optical fiber in the polarization optical coherence tomography system. By connecting the first optical fiber section, the second optical fiber section and the third optical fiber section in sequence, the energy of the optical signal received by the three-section optical fiber probe can be improved.

[0058] By setting four air holes, the radii of the first air hole, the second air hole, the third air hole and the first half of the fourth air hole are all increased synchronously with the decrease of the diameter of the gradient core, so that the optical fiber has the same binding force on the light linearly deflected along the first direction or the second direction, the radii of the second half of the first air hole and the second air hole remain unchanged, and the radii of the second half of the third air hole and the fourth air hole gradually decrease until they disappear, so that the light loss linearly deflected along the second direction is reduced, and the difference between the light loss linearly deflected along the first direction is reduced, so that the three-section optical fiber probe has a good collection ability for the light linearly deflected along the first direction and the second direction, reduces the difference between the coupling efficiencies of light in two orthogonal directions, and further reduces the difference in intensity of data obtained by the dual channels of the polarization optical coherence tomography system.

[0059] Although example embodiments and their advantages have been described in detail, those skilled in the art may make various changes, substitutions and modifications to these embodiments without departing from the spirit and defined scope of the present invention, and such modifications and variations are all within the defined scope.

Claims

1. A three-section optical fiber probe, applied to a polarization optical coherence tomography system, characterized in that: comprising a first optical fiber segment, a second optical fiber segment and a third optical fiber segment connected in sequence; The core diameter of the first optical fiber is greater than the core diameter of the third optical fiber, and the core diameter of the third optical fiber segment is compatible with the core radius of the polarization-maintaining optical fiber in the polarization optical coherence tomography system; The second optical fiber segment includes a graded-index core, the radius of which gradually decreases from the core diameter of the first optical fiber segment to the core diameter of the third optical fiber segment.

2. The three-section optical fiber probe according to claim 1, characterized in that: It also includes air holes, which are arranged in parallel with the gradient fiber core. The air holes include a first air hole and a second air hole symmetrically arranged along a first direction with the gradient fiber core as the symmetry axis, and a third air hole and a fourth air hole symmetrically arranged along a second direction with the gradient fiber core as the symmetry axis. The first direction is perpendicular to the second direction. The radii of the first air hole, the second air hole, the third air hole and the first half of the fourth air hole increase synchronously with the decrease of the diameter of the gradient fiber core, the radii of the second half of the first air hole and the second air hole remain unchanged, and the radii of the second half of the third air hole and the fourth air hole gradually decrease until they disappear.

3. The three-section optical fiber probe according to claim 1, characterized in that: The first optical fiber segment is a multimode optical fiber.

4. The three-section optical fiber probe according to claim 1, characterized in that: The third optical fiber segment is a Panda-type polarization-maintaining optical fiber.

5. The three-section optical fiber probe according to claim 2, characterized in that: The first optical fiber segment is connected to the optical fiber collimator in the sample arm of the polarization optical coherence tomography system, the third optical fiber segment is connected to the PANDA-type polarization-maintaining optical fiber in the polarization optical coherence tomography system, and the first air hole and the second air hole are respectively coaxially arranged with two stress regions of the PANDA-type polarization-maintaining optical fiber in the polarization optical coherence tomography system.

6. The three-section optical fiber probe according to claim 2, characterized in that: The front half of the first air hole is conical, the rear half of the first air hole is cylindrical, and the structure of the second air hole is the same as that of the first air hole; The front half and the rear half of the third air hole are both tapered, and the fourth air hole has the same structure as the third air hole.

7. The three-section optical fiber probe according to claim 6, characterized in that: The cone is a convex cone.

8. The three-section optical fiber probe according to claim 6, characterized in that: The cone is a flat cone.

9. The three-section optical fiber probe according to claim 6, characterized in that: The cone is a concave cone.

10. A polarization optical coherence tomography system, characterized in that: It comprises a three-section optical fiber probe as described in any one of claims 1 to 9.

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