Endoscope based on tail end beveled optical fiber, endoscope navigation device and method

Abstract

The invention discloses an endoscope based on a tail end beveled optical fiber and an endoscope navigation device and method, and relates to the technical field of medical instruments, and the endoscope based on the tail end beveled optical fiber comprises an endoscope body and a multi-core optical fiber; the multi-core optical fiber is embedded into the endoscope body and extends in the length direction of the endoscope body, the end face of the tail end of the multi-core optical fiber is obliquely arranged in the direction perpendicular to the center axis of the multi-core optical fiber, the end face of the tail end is coated with an adhesive layer, and the refractive index of the adhesive layer is matched with the refractive index of a fiber core of the multi-core optical fiber. The end face of the tail end of the multi-core optical fiber is obliquely arranged in the direction perpendicular to the central axis of the multi-core optical fiber and coated with the refractive index matching adhesive layer, so that Fresnel reflected light generated at the tail end deviates from a fiber core transmission path and is greatly attenuated, and meanwhile the refractive index of the provided adhesive layer is matched with the refractive index of the fiber core of the multi-core optical fiber; therefore, the reflection intensity is further reduced, and the shape sensing precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical devices, in particular to an endoscope based on a tail-end bevelled optical fiber, an endoscope navigation device and method. BACKGROUND

[0002] In a gastrointestinal examination operation, such as a small intestine examination operation, the insertion process of a small intestine scope completely depends on the experience, skills and touch of a physician. The small intestine is deep, long (5-7 m), winding, high in free degree and stacked with each other, which leads to a difficult insertion process and a coil knot in the body of the curved section of the scope, causing pain to the patient. When facing a patient with intestinal adhesion or emaciation, the operation difficulty is further increased, and even intestinal rupture and perforation may occur. How to operate the small intestine scope to smoothly reach the target area and minimize the discomfort and complications of the patient is a difficult problem to be solved in the small intestine scope operation process. The traditional shape sensing technology based on CT imaging, electromagnetic positioning and fiber grating array has the disadvantages of large radiation injury, magnetic field sensitivity, low refresh rate and low spatial resolution, and is difficult to meet the real-time and accurate tracking of the posture of the small intestine scope under the condition of large curvature and complex deformation in the operation. Therefore, there is an urgent need for a real-time visual and high-precision shape sensing and tracking means to navigate the endoscope in the operation to assist the physician in the insertion. The distributed optical fiber shape sensing technology is an ideal solution to meet all these needs.

[0003] The optical fiber shape sensing measures the strain of each core of the multicore optical fiber or optical fiber bundle at each position by an optical frequency domain reflectometer (OFDR), to solve the bending direction angle and bending curvature of the optical fiber at each position, and finally reconstruct the shape of the optical fiber through a shape reconstruction algorithm. The optical fiber shape sensing technology has the advantages of electromagnetic immunity, high precision and high sensing resolution, small size and flexibility, corrosion resistance and the like. Therefore, the technology is very suitable for tracking the shape and position of the endoscope in the gastrointestinal examination operation process, to realize the navigation of the endoscope. However, in the multicore optical fiber shape sensing system based on OFDR, the tail end of the multicore optical fiber is generally directly exposed to the air. Due to the mismatch between the refractive index of the optical fiber core and the refractive index of the air, nearly 4% of the incident light power is reflected back into the detector as Fresnel reflection light. While the signal power, i.e. the backscattered Rayleigh scattering light power in the optical fiber, is only 10 -5 % of the incident light power, which will cause the signal to be submerged in the noise of the Fresnel reflection light, seriously affecting the strain demodulation accuracy and further reducing the shape sensing accuracy. SUMMARY

[0004] The present application provides an endoscope based on a tail-end bevelled optical fiber, an endoscope navigation device and method, which can solve the technical problem of low optical fiber shape sensing accuracy in the prior art.

[0005] In a first aspect, an embodiment of the present application provides an endoscope based on a tail-end beveled optical fiber, the endoscope based on the tail-end beveled optical fiber comprising: an endoscope body; and a multicore optical fiber embedded in the endoscope body and extending along a length direction of the endoscope body, a tail-end end face of the multicore optical fiber being arranged in an inclined manner in a direction perpendicular to a central axis of the multicore optical fiber, and the tail-end end face being coated with a glue layer, a refractive index of the glue layer matching a core refractive index of the multicore optical fiber.

[0006] With reference to the first aspect, in an embodiment, an included angle between the tail-end end face and a plane perpendicular to the central axis of the multicore optical fiber is 8° to 45°.

[0007] With reference to the first aspect, in an embodiment, a difference between the refractive index of the glue layer and the core refractive index of the multicore optical fiber is within a preset minimum range.

[0008] With reference to the first aspect, in an embodiment, the glue layer is an ultraviolet glue layer.

[0009] With reference to the first aspect, in an embodiment, the tail-end end face is a smooth plane.

[0010] With reference to the first aspect, in an embodiment, the smooth plane is a plane prepared through an angle-grinding and polishing process, and a surface roughness of the smooth plane is less than a preset minimum value.

[0011] In a second aspect, an embodiment of the present application provides an endoscope navigation device, the endoscope navigation device comprising: The endoscope based on the tail-end beveled optical fiber, the fan-in fan-out device, the optical switch, the optical frequency domain reflectometer, and the data acquisition and processing device in any of the above embodiments; The output end of the endoscope based on the tail-end beveled optical fiber is connected to the optical switch through the fan-in fan-out device, the output end of the optical switch is connected to the optical frequency domain reflectometer, and the optical frequency domain reflectometer is connected to the data acquisition and processing device through a collection channel and a trigger channel respectively.

[0012] With reference to the second aspect, in an embodiment, the endoscope navigation device further comprises a display device connected to an output end of the data acquisition and processing device, and the display device is configured to display a reconstructed shape of the optical fiber shape sensor.

[0013] In a third aspect, an embodiment of the present application provides an endoscope navigation method, which is implemented based on the endoscope based on the tail-end beveled optical fiber in any of the above embodiments, and the endoscope navigation method comprises: Collecting back Rayleigh scattering signals of the multicore optical fiber in a natural straight state as a reference signal and collecting back Rayleigh scattering signals of the multicore optical fiber in a curved state of the endoscope as a measurement signal; Based on the reference signal and the measurement signal, strain distributions of three cores arranged in an equilateral triangle shape on a cross section of the multicore optical fiber along a length direction of the three cores are demodulated; According to the strain distributions, a twist angle, a bending curvature and a bending direction angle of the multicore optical fiber along a length direction of the multicore optical fiber are calculated; According to the twist angle, the bending curvature and the bending direction angle, a three-dimensional shape of the multicore optical fiber is reconstructed by a shape reconstruction algorithm to realize endoscope navigation.

[0014] In combination with the third aspect, in an implementation, in the demodulating of the strain distributions of the three cores arranged in the equilateral triangle shape on the cross section of the multicore optical fiber along the length direction of the three cores based on the reference signal and the measurement signal, for any core in the multicore optical fiber: The reference signal and the measurement signal of the current core are respectively subjected to fast Fourier transform to obtain reference distance domain signals and measurement distance domain signals of the current core along the length direction of the optical fiber; The reference distance domain signals and the measurement distance domain signals are subjected to short-time Fourier transform to obtain reference frequency domain signals and measurement frequency domain signals along the length of the optical fiber; The reference frequency domain signals and the measurement frequency domain signals are demodulated by a cross-correlation algorithm to obtain frequency drifts at positions of the current core; The frequency drifts at the positions of the current core are divided by a conversion constant to obtain strain values at the positions of the current core to obtain the strain distribution of the current core along the length direction of the current core.

[0015] The technical scheme provided by the embodiments of the present application has the following beneficial effects: The endoscope based on the tail end beveling optical fiber provided by the embodiments of the present application, in which the tail end face of the multicore optical fiber is arranged in an inclination in a direction perpendicular to the central axis of the multicore optical fiber and is coated with a refractive index matching glue layer, so that the Fresnel reflection light generated by the tail end deviates from the transmission path of the core and is greatly attenuated. The refractive index of the glue layer provided by the embodiments of the present application matches the refractive index of the core of the multicore optical fiber, thereby further reducing the reflection intensity, thereby significantly reducing the noise level of the return detector. This enables the weak Rayleigh scattering signal to be effectively extracted, improves the accuracy of strain demodulation, and further improves the accuracy of endoscope shape sensing. Further, the multicore optical fiber provided by the embodiments of the present application does not need to be engraved with a fiber grating, thereby reducing the manufacturing cost. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0017] Figure 1 is a structure schematic diagram of an end-tapered fiber based endoscope and a side view of a multi-core fiber; Figure 2 is a structure schematic diagram of an endoscope navigation device; Figure 3(a) is a fiber core strain curve after demodulation without polishing the tail end of a seven-core fiber; Figure 3(b) is a fiber core strain curve after demodulation after polishing the tail end of a seven-core fiber and coating with ultraviolet glue; Figure 4 is a schematic diagram of the position relationship between two adjacent sensing points in a fiber and a cross-sectional view of a multi-core fiber; Figure 5(a) is a reconstructed circular ring shape without polishing the tail end of a seven-core fiber; Figure 5(b) is a reconstructed circular ring shape after polishing the tail end of a seven-core fiber and coating with ultraviolet glue.

[0018] In the figure: 1, endoscope body; 2, multi-core fiber; 3, instrument channel; 4, light guide mirror; 5, objective lens; 6, air and water injection channel; 7, fan-in fan-out device; 8, optical switch; 9, optical frequency domain reflectometer; 10, data acquisition and processing device; 11, single-mode optical fiber. DETAILED DESCRIPTION

[0019] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. In the description of the present application, it should be noted that the terms "upper", "lower", and the like indicate the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the present application and simplify the description, and thus cannot be understood as indicating or implying that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus cannot be understood as limiting the present application. Unless otherwise explicitly specified and limited, the terms "mounting", "connection", and "connection" should be understood broadly, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be direct connection, can also be indirect connection through an intermediate medium, and can be internal communication of two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0020] The present application provides an endoscope based on a tail end beveling optical fiber, an endoscope navigation device and method, which can solve the technical problem of low optical fiber shape sensing precision in the prior art.

[0021] In a first aspect, the embodiments of the present application provide an endoscope based on a tail end beveling optical fiber.

[0022] Figure 1 is a structural schematic view of an endoscope based on a tail end beveling optical fiber and a side view of a multi-core optical fiber. Referring to Figure 1 The endoscope based on the tail end beveling optical fiber includes: an endoscope body 1; and a multi-core optical fiber 2 embedded in the endoscope body 1 and extending along the length direction of the endoscope body 1, the tail end face of the multi-core optical fiber 2 is arranged in an inclined manner in the direction perpendicular to the central axis of the multi-core optical fiber 2, and a glue layer is coated on the tail end face, the refractive index of the glue layer matches the core refractive index of the multi-core optical fiber 2.

[0023] Specifically, the endoscope based on the tail end beveling optical fiber provided by the embodiment of the present application is mainly used for shape sensing and navigation during the body cavity inspection. An encapsulation cavity for integrating instrument channels 3, light guides 4, objective lenses 5, and gas injection and water injection channels 6 is also provided in the endoscope body 1. The instrument channel 3 is a working pipeline that penetrates through the endoscope body 1, allowing treatment instruments such as biopsy forceps to pass through to perform interventional operations. The light guide 4 is used for illumination. The objective lens 5 is used for capturing images. The gas injection and water injection channel 6 is used for injecting gas into the cavity to expand the lumen or injecting water to clean the objective lens 5.

[0024] The multi-core optical fiber 2 serves as a shape sensing unit of the endoscope and is embedded in the wall layer structure of the endoscope body 1 along the length direction of the endoscope body 1, for sensing the spatial shape change of the endoscope in the cavity in real time. The tail end of the multi-core optical fiber 2 is a light signal transmission end. The tail end face of the multi-core optical fiber 2 is inclined relative to a reference plane perpendicular to the central axis of the optical fiber, to form an inclined surface with a specific inclination angle. Thus, when the incident light is reflected on the inclined surface, the direction of the reflected light will change significantly, and the reflected light will no longer return to the fiber core along the original light path, but deviate from the fiber core into the cladding region of the multi-core optical fiber 2. When the light is transmitted in the cladding region, it will rapidly attenuate due to the loss of waveguide constraint, thereby reducing the Fresnel reflection at the tail end of the multi-core optical fiber 2, and greatly reducing the interference of the reflected light on the rear-end signal detection.

[0025] Further, a glue layer is coated on the end face ground into an inclined surface, and the refractive index of the glue layer is close to or matches the refractive index of the fiber core material of the transmitted light signal in the multi-core optical fiber 2. The coating of the refractive index matching glue further reduces the refractive index difference at the tail end face. Even if a small amount of light is reflected on the inclined surface, the reflectivity will be suppressed due to the similar refractive index of the glue layer and the fiber core, further reducing the Fresnel reflectivity, reducing the noise to the back Rayleigh scattering signal, and improving the accuracy of strain demodulation and shape sensing. At the same time, the glue layer can also play a physical protection role for the beveling end face, preventing the multi-core optical fiber 2 from being contaminated or damaged.

[0026] In the embodiment of the present application, the included angle between the tail end face and the plane perpendicular to the central axis of the multi-core optical fiber 2 is 8° to 45°.

[0027] Specifically, when the included angle between the tail end face and the plane perpendicular to the central axis of the multi-core optical fiber 2 is 8° to 45°, most of the Fresnel reflected light is radiated into the cladding and rapidly attenuated, and the reflectivity is close to 0, so it has almost no effect on the accuracy of shape sensing.

[0028] In a specific embodiment, the included angle between the end face and the plane perpendicular to the central axis of the multicore optical fiber 2 can be set to 8°. When the angle is below 8°, the tilt angle is too small, and the tail end face is close to vertical. At this time, most of the Fresnel reflected light will return in a direction close to the original path, and can still be coupled into the core and transmitted reversely to the detector, forming noise interference. If the included angle between the tail end face and the plane perpendicular to the central axis of the multicore optical fiber 2 is above 8°, the processing is difficult and the Fresnel reflected light will not be greatly reduced compared to 8°. Therefore, the included angle between the tail end face and the plane perpendicular to the central axis of the multicore optical fiber 2 is set to about 8° in the embodiments of the present application. On the one hand, it is ensured that the angle is not too small, so that the Fresnel reflected light generated by the tail end face is effectively deflected in a direction, so that it is radiated into the cladding and quickly attenuates. On the other hand, it is ensured that the angle is not too large, so that the tail end face is easy to process, and the overall structure of the multicore optical fiber 2 is stable.

[0029] In the embodiments of the present application, the difference between the refractive index of the glue layer and the refractive index of the core of the multicore optical fiber 2 is within a preset minimum range.

[0030] Specifically, the difference between the refractive index of the glue layer and the refractive index of the core of the multicore optical fiber 2 is within a preset minimum range, which means that the absolute deviation value of the refractive index of the cured glue layer and the refractive index of the core material of the multicore optical fiber 2 is within 0.03. The embodiments of the present application have achieved deflection of most of the reflected light through the beveled tail end face, but a small part of the light may be reflected at the tail end face. According to the Fresnel reflection law in optics, the absolute deviation value of the refractive index of the glue layer and the refractive index of the core of the multicore optical fiber 2 is set within a preset minimum range, and the theoretical reflectivity at the interface between the fiber core and the glue layer is reduced to a very low level, thereby weakening the total power of the reflected light finally returned to the detector. In a specific embodiment, if the multicore optical fiber 2 uses a quartz core, the refractive index of the quartz core is 1.456 to 1.462, and therefore the refractive index of the glue layer should be controlled to be 1.453 to 1.465. Further, the thickness of the glue layer can be 20 to 100 microns, ensuring the formation of a uniform refractive index transition layer at the tail end face.

[0031] In the embodiments of the present application, the glue layer is a ultraviolet glue layer.

[0032] Specifically, the refractive index of the ultraviolet glue can be adjusted by adjusting the ratio of the prepolymer and the monomer to match the refractive index of the quartz core. In some other embodiments of the present application, other materials such as epoxy resin glue and silicon-based glue can also be used to make the glue layer, as long as they can meet the requirements of the refractive index of the glue layer of the present application, which are not limited herein.

[0033] In the embodiments of the present application, the tail end face is a smooth plane.

[0034] Specifically, the smooth plane is a plane prepared by an angle grinding and polishing process, and the surface roughness of the smooth plane is less than a preset minimum value. The preset minimum value can be 0.01 μm. During the grinding process of the tail end face, an angle clamp is used to make the tail end face form a specific angle with the plane perpendicular to the center axis of the optical fiber, so that consistent tilt angles of each optical fiber end face in batch processing can be ensured. After the grinding is completed, finer abrasives or polishing liquid is used to finish the surface after grinding to remove microscopic scratches and further reduce the surface roughness, so that an optical-grade smooth surface is obtained. Finally, the tail end face is checked under a microscope to ensure that the end face is free of scratches, dust, stains, and that the core area of the optical fiber is free of damage, cracks, pits, and process defects.

[0035] In a second aspect, the embodiments of the present application provide an endoscope navigation device.

[0036] Figure 2 Structure diagram of the endoscope navigation device. Referring to Figure 2 The endoscope navigation device comprises: The endoscope based on the tail end beveling optical fiber, the fan-in fan-out device 7, the optical switch 8, the optical frequency domain reflectometer 9 and the data acquisition and processing device 10 in any of the above embodiments; wherein the output end of the endoscope based on the tail end beveling optical fiber is connected to the optical switch 8 through the fan-in fan-out device 7, the output end of the optical switch 8 is connected to the optical frequency domain reflectometer 9, and the optical frequency domain reflectometer 9 is connected to the data acquisition and processing device 10 through the acquisition channel and the trigger channel respectively.

[0037] Specifically, the fan-in fan-out device 7 is used to realize the optical coupling function of a single multi-core optical fiber 2 to multiple single-mode optical fibers 11. The optical switch 8 is used to sequentially switch and query the single-mode optical fibers 11 of the fan-in fan-out device 7. The optical frequency domain reflectometer 9 is used to measure the strain size of each core of the multi-core optical fiber 2 in the endoscope. The data acquisition and processing device 10 is used for data acquisition and processing to obtain the three-dimensional shape of the multi-core optical fiber 2.

[0038] The multi-core optical fiber 2 used in the embodiments of the present application is a seven-core optical fiber. The seven-core optical fiber is fused with the fan-in fan-out device 7, and the single-mode optical fibers 11 at the other end of the fan-in fan-out device 7 are connected to different channels of the optical switch 8, and the other end of the optical switch 8 is connected to the optical frequency domain reflectometer 9. The data acquisition and processing module is responsible for triggering signals to the optical frequency domain reflectometer 9. After the optical frequency domain reflectometer 9 system receives the first trigger signal, the data acquisition and processing module will collect the signal of the first channel of the optical switch 8, that is, the backscattering Rayleigh signal of the first core. After the optical frequency domain reflectometer 9 receives the second trigger signal, the data acquisition and processing module will collect the signal of the second channel of the optical switch 8, that is, the backscattering Rayleigh signal of the second core. In this way, the backscattering Rayleigh signals of all the cores in the seven-core optical fiber are collected.

[0039] In the embodiments of the present application, the endoscope navigation device further comprises a display device connected to the output end of the data acquisition and processing device 10, and the display device is used to display the reconstructed shape of the optical fiber shape sensor. Thus, in the gastroscopy surgery, the three-dimensional shape of the endoscope can be tracked in real time and fed back to the doctor to assist the doctor in inserting the endoscope, so as to realize accurate navigation of the endoscope, thereby reducing the pain of the patient and reducing the risk of postoperative complications.

[0040] In a third aspect, the embodiments of the present application provide an endoscope navigation method, which is based on the endoscope based on the tail end beveling optical fiber in any of the above embodiments, and the endoscope navigation method specifically comprises the following steps: Step S1: respectively collecting the backscattering Rayleigh signals of the multicore optical fiber in a natural straight state as reference signals and the backscattering Rayleigh signals of the multicore optical fiber in a curved state of the endoscope as measurement signals.

[0041] Specifically, the endoscope is kept in a natural straight state, the backscattering Rayleigh signals of the three cores for shape measurement in the seven-core optical fiber are collected by using the optical frequency domain reflectometer as the reference signals, and the endoscope is bent into a specific shape, and the backscattering Rayleigh signals of the three cores for shape measurement in the seven-core optical fiber are collected as the measurement signals.

[0042] Step S2: based on the reference signals and the measurement signals, demodulating the strain distribution of the three cores arranged in an equilateral triangle shape on the cross section of the multicore optical fiber along the length direction of the three cores.

[0043] In the embodiments of the present application, in step S2, for any one of the three cores: Step S21: respectively performing fast Fourier transform on the reference signals and the measurement signals of the current core to obtain the reference distance domain signals and the measurement distance domain signals of the current core along the length direction of the optical fiber.

[0044] Step S22: performing short-time Fourier transform on the reference distance domain signals and the measurement distance domain signals to obtain the reference frequency domain signals and the measurement frequency domain signals along the length of the optical fiber.

[0045] Specifically, in order to analyze the local characteristics of the signals, the long optical fiber needs to be processed in segments. The short-time Fourier transform is performed on a sliding finite length window, the distance domain signals are segmented, and the Fourier transform is performed on the signal segments in each window, so that for each position on the optical fiber, a set of reference frequency domain signals and measurement frequency domain signals can be obtained, which provides a basis for detecting the slight changes of each small segment of the optical fiber.

[0046] Step S23: demodulating the reference frequency domain signals and the measurement frequency domain signals by using a cross-correlation algorithm to obtain the frequency drift of each position of the current core.

[0047] Specifically, the reference frequency domain signal and the measurement frequency domain signal of the frequency domain signal segment of the reference and the measurement signal in the same position window are correlated. When a certain micro-section of the optical fiber is strained, the spacing of the internal scattering points will change by microns, resulting in a small linear drift of the returned Rayleigh scattering spectrum of the section on the frequency axis. By calculating the cross-correlation function of the reference frequency domain signal and the measurement frequency domain signal, and finding the shift of the peak value position relative to the zero point, the frequency drift amount corresponding to the center position of the current window can be demodulated. By repeating this process, the frequency drift sequence of all position points of the fiber core can be obtained.

[0048] Step S24: dividing the frequency drift amount at each position of the current fiber core by a conversion constant to obtain the strain value at each position of the current fiber core, so as to obtain the strain distribution of the current fiber core along the length direction thereof.

[0049] Specifically, the frequency drift amount of each position point demodulated in step S23 is divided by a conversion constant to obtain the strain value at each position of the current fiber core. By performing this operation on all position points, the strain distribution of the fiber core along the length direction is obtained. The conversion constant can be 0.78 v 0, v 0 is the center frequency of the tunable laser in the optical frequency domain reflectometer.

[0050] The embodiments of the present application will only use the three fiber cores arranged in an equilateral triangle on the cross section of the seven-core optical fiber when reconstructing the shape of the endoscope. When reconstructing the shape, the scanning range of the tunable light source in the optical frequency domain reflectometer is 8 nm.

[0051] The tail end of the optical fiber is bent into a 2 cm radius circle to demodulate and generate the fiber core strain curve. FIG. 3(a) is the fiber core strain curve demodulated without polishing the tail end of the seven-core optical fiber. The abscissa of FIG. 3(a) is the fiber length, and the ordinate is the strain value. FIG. 3(b) is the fiber core strain curve demodulated after polishing and coating the tail end of the seven-core optical fiber with ultraviolet glue. The abscissa of FIG. 3(b) is the fiber length, and the ordinate is the strain value. Without polishing and coating the tail end of the seven-core optical fiber with ultraviolet glue, the interference of Fresnel reflection in the three fiber cores in FIG. 3(a) is serious, which significantly reduces the signal-to-noise ratio of the fiber strain demodulation and greatly reduces the measurement accuracy. After polishing and coating the tail end of the seven-core optical fiber with ultraviolet glue, the strain demodulation results of the three fiber cores in FIG. 3(b) can accurately demodulate the strain.

[0052] Step S3: calculating the twist angle, bending curvature and bending direction angle of the multi-core optical fiber along the length direction thereof according to the strain distribution.

[0053] Specifically, according to the strain values of the three cores at the same spatial position point obtained in step S2, the torsion rate of the multicore optical fiber along the length direction thereof is calculated, and the specific calculation method is as follows:

[0054] wherein, represents the torsion strain, , , , represents the strain values of the three cores at the same spatial position point, represents the core intrinsic torsion rate of the multicore optical fiber, represents the distance from the outer core to the middle core of the multicore optical fiber, , represents the torsion rate.

[0055] According to the torsion rate of the multicore optical fiber along the length direction thereof, the torsion angle of the multicore optical fiber along the length direction thereof is calculated, and the specific calculation method is as follows:

[0056] wherein, represents the torsion angle.

[0057] According to the core azimuth angle of the multicore optical fiber, the torsion strain and the distance from the outer core to the middle core of the multicore optical fiber, the bending direction angle and the bending curvature of the multicore optical fiber are calculated, and the specific calculation steps include the following steps: A bending strain equation set is constructed, and the specific equation is as follows:

[0058] wherein, represents the bending curvature, represents the bending direction angle, , , represents the core azimuth angle of the three cores; The bending strain equation set is rewritten in a matrix form, and the specific equation is as follows:

[0059] wherein, , , respectively represents the distance from the three cores to the middle core, represents the component of the bending vector in the X-axis direction, represents the component of the bending vector in the Y-axis direction; Based on the above matrix, the bending direction angle and the bending curvature are solved, and the specific equation is as follows:

[0060] in, Represent the arctangent function in the four quadrants, which can be determined by... and The sign determines the correct quadrant.

[0061] Step S4: Based on the torsion angle, bending curvature and bending direction angle, the three-dimensional spatial shape of the multi-core optical fiber is reconstructed using a shape reconstruction algorithm to achieve endoscope navigation.

[0062] Figure 4 This diagram illustrates the positional relationship between two adjacent sensing points in an optical fiber and provides a schematic of the cross-section of a multi-core optical fiber. (See also...) Figure 4 Specifically, the twist angle, curvature, and direction angle are substituted into a fast shape reconstruction algorithm based on a homogeneous transformation matrix to reconstruct the shape of the seven-core fiber, i.e., the shape of the endoscope. For the first... One sensor point ( Perform iterative calculations: The parameters of the current arc segment are calculated as follows:

[0063]

[0064] in, This represents the central angle corresponding to the fiber segment between adjacent sensing points. Indicates the first The curvature of each sensing point Indicates the distance between sensor points. Indicates the first The bending radius of each sensing point; Construct the transformation matrix components of the current segment as follows:

[0065] in, Indicates the first Rotation matrix of each sensing point Indicates the first The displacement vector of each sensing point Indicates the first The effective bending direction angle of each sensing point ; Figure 4 middle, 、 , Indicates the coordinate system for three-dimensional reconstruction; Calculate the first The global coordinates of each sensor point are as follows:

[0066] in, a global coordinate of a first sensing point, a global coordinate of a first sensing point, a global coordinate of a first sensing point, a global coordinate of a first sensing point.

[0067] After the iteration is completed, an ordered point set is obtained, and the points are sequentially connected, that is, a reconstructed endoscope three-dimensional space shape curve is formed.

[0068] In one specific embodiment, the tail end of the seven-core optical fiber is bent into a circular ring with a radius of 2 cm, and the shape is reconstructed. Figure 5(a) is the circular ring shape of the seven-core optical fiber tail end without grinding and reconstruction, and Figure 5(b) is the circular ring shape of the seven-core optical fiber tail end after grinding and coating with ultraviolet glue and reconstruction, wherein the X axis generally represents the horizontal spatial position, and the Y axis represents the vertical spatial position. It can be seen from Figure 5(a) that it is quite different from the actual circular ring shape, and it can be seen from Figure 5(b) that it conforms to the true shape. Therefore, it can be proved that the shape of the seven-core optical fiber cannot be accurately reconstructed if the end face of the seven-core optical fiber tail end is not ground, and the shape of the endoscope cannot be reconstructed.

[0069] The endoscope based on the tail end beveling optical fiber provided by the embodiment of the present application, wherein the end face of the multi-core optical fiber is arranged in an inclined manner in the direction perpendicular to the central axis of the multi-core optical fiber, and a refractive index matching glue layer is coated, so that the Fresnel reflection light generated by the tail end deviates from the fiber core transmission path and is greatly attenuated. The refractive index of the glue layer provided by the embodiment of the present application matches the refractive index of the fiber core of the multi-core optical fiber, thereby further reducing the reflection intensity, thereby significantly reducing the noise level of the return detector. This enables the weak Rayleigh scattering signal to be effectively extracted, improves the accuracy of strain demodulation, and further improves the accuracy of the endoscope shape sensing. Further, the multi-core optical fiber provided by the embodiment of the present application does not need to be engraved with a fiber grating, thereby reducing the manufacturing cost.

[0070] In the description of the present application, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower" and the like is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise expressly specified and limited, the terms "mounting", "connection", "connection" should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection, or an integral connection; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or a communication between two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0071] It should be noted that, in the present application, the relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another, without necessarily requiring or implying any actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0072] The foregoing is merely illustrative of the principles of the application and various modifications can be made by those skilled in the art without departing from the spirit and scope of the application. The above embodiments are illustrative, and not restrictive, of the scope of the application.

Claims

1. An endoscope based on a tail-end beveled optical fiber, characterized in that, The endoscope based on the tail-end obliquely cleaved optical fiber includes: Endoscope body; and A multi-core optical fiber is embedded in the endoscope body and extends along the length of the endoscope body. The end face of the multi-core optical fiber is inclined in a direction perpendicular to the central axis of the multi-core optical fiber, and the end face is coated with an adhesive layer. The refractive index of the adhesive layer matches the core refractive index of the multi-core optical fiber.

2. The endoscope based on a tail-end obliquely cleaved optical fiber according to claim 1, characterized in that, The angle between the tail end face and the plane perpendicular to the central axis of the multi-core optical fiber is 8° to 45°.

3. The endoscope based on a tail-end beveled optical fiber according to claim 1, characterized in that, The difference between the refractive index of the adhesive layer and the refractive index of the core of the multi-core optical fiber is within a preset minimum range.

4. The endoscope based on a tail-end beveled optical fiber according to claim 3, characterized in that, The adhesive layer is a UV adhesive layer.

5. The endoscope based on a tail-end obliquely cleaved optical fiber according to claim 1, characterized in that, The tail end face is a smooth plane.

6. The endoscope based on a tail-end beveled optical fiber according to claim 5, characterized in that, The smooth plane is a plane prepared by a fixed-angle grinding and polishing process, and the surface roughness of the smooth plane is less than a preset minimum value.

7. An endoscope navigation device, characterized in that, The endoscope navigation device includes: The endoscope, fan-in / fan-out device, optical switch, optical frequency domain reflectometer, and data acquisition and processing device based on the tail-end obliquely cut optical fiber according to any one of claims 1 to 6; The output end of the endoscope based on the tail-end obliquely cut optical fiber is connected to the optical switch through the fan-in fan-out device. The output end of the optical switch is connected to the optical frequency domain reflectometer. The optical frequency domain reflectometer is connected to the data acquisition and processing device through the acquisition channel and the trigger channel, respectively.

8. The endoscope navigation device according to claim 7, characterized in that, The endoscope navigation device also includes a display device connected to the output end of the data acquisition and processing device, which is used to display the reconstructed shape of the fiber optic shape sensor.

9. An endoscope navigation method, implemented using an endoscope based on a tail-end obliquely cleaved optical fiber as described in any one of claims 1 to 6, characterized in that, The endoscopic navigation method includes: Backscattering signals of multi-core optical fibers in their naturally straight state were collected as reference signals, and backscattering signals of multi-core optical fibers in the bent state of the endoscope were collected as measurement signals. Based on the reference signal and the measurement signal, the strain distribution along the length of the three fiber cores arranged in an equilateral triangle shape on the cross-section of the multi-core optical fiber is demodulated. Based on the strain distribution, calculate the twist angle, bending curvature, and bending direction angle of the multi-core optical fiber along its length. Based on the torsion angle, curvature, and bending direction angle, the three-dimensional spatial shape of the multi-core optical fiber is reconstructed using a shape reconstruction algorithm to achieve endoscope navigation.

10. The endoscopic navigation method according to claim 9, characterized in that, In the demodulation of the strain distribution along the length of the three fiber cores arranged in an equilateral triangle shape on the cross-section of the multi-core optical fiber based on the reference signal and the measurement signal, for any one of the fiber cores: Perform Fast Fourier Transform on the reference signal and measurement signal of the current fiber core respectively to obtain the reference distance domain signal and the measurement distance domain signal of the current fiber core along the fiber length direction; The reference distance domain signal and the measured distance domain signal are subjected to short-time Fourier transform to obtain the reference frequency domain signal and the measured frequency domain signal along the fiber length; A cross-correlation algorithm is used to demodulate the reference frequency domain signal and the measured frequency domain signal, and the frequency drift at each position of the current fiber core is obtained by demodulation. Divide the frequency drift at each position of the current fiber core by the conversion constant to obtain the strain value at each position of the current fiber core, so as to obtain the strain distribution of the current fiber core along its length.

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