A fiber misplacement detection method based on fiber output light spot image

Abstract

The application discloses a kind of based on optical fiber output light spot image optical fiber misplacement detection method, comprising: (1) laser to the end of the optical fiber to be detected axial emission laser signal;(2) optical camera receives the light spot image of the end of the optical fiber to be detected;(3) the light spot image obtained is processed, and its corresponding radial energy density curve is obtained;(4) according to the shift state of radial energy density curve main peak, obtain optical fiber misplacement detection result.The application can be applied in some inconvenient adjustment, detection of optical fiber transmission structure, using this method, whether the fracture of optical fiber, the misplacement condition between optical fiber etc. can be analyzed and checked from output end in the process of optical fiber transmission.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber sensing technology and image processing, and particularly relates to a method for detecting optical fiber misalignment based on an optical fiber output light spot image. BACKGROUND

[0002] To meet the growing demand for data transmission, optical fiber communication technology is constantly improving and developing. Through time division, wavelength division, polarization multiplexing and multi-level modulation and other technical means, a single conventional single-mode optical fiber has achieved 100 Tb / s high-capacity transmission, but is limited by nonlinear noise, optical fiber fusion damage phenomenon and amplifier bandwidth, and has reached the physical limit of its transmission. The capacity of single-mode optical fiber transmission system has reached the Shannon limit, thereby limiting the further increase of system bandwidth. With the rapid development of optical fiber manufacturing technology, a few-mode optical fiber is manufactured by designing appropriate parameters (such as optical fiber diameter and refractive index distribution) to support specific mode transmission. Compared with single-mode optical fiber, few-mode optical fiber can allow more transmission modes and has advantages such as large mode field area and low nonlinear effect. It can effectively reduce the crosstalk caused by the mutual coupling of high-order modes. While avoiding the interference of nonlinear effects on the system, it can also reduce transmission loss. Compared with multi-mode optical fiber, few-mode optical fiber supports fewer transmission modes and has clear mode parameters. By precisely controlling the excitation mode, different mode groups in the few-mode optical fiber are used as independent channels to simultaneously transmit multiple signals, realizing mode division multiplexing, which can significantly improve the transmission capacity.

[0003] At present, the single-mode-few-mode optical fiber butt joint structure is used for detection in the following application occasions:

[0004] Optical fiber communication system: In the optical fiber communication system, the connection of optical fibers is essential. Different optical fiber interface adapters need to be used for connection according to different types of optical fiber interfaces. In order to ensure transmission efficiency and quality, a single-mode-few-mode optical fiber butt joint structure and a corresponding detector need to be used for accurate testing and calibration when performing single-mode-few-mode optical fiber butt joint.

[0005] Industrial automation control system: In the industrial automation control system, the single-mode-few-mode optical fiber butt joint structure is used for the connection of sensors, measuring instruments and image recognition equipment, etc. Some industrial automation equipment needs to transmit signals to remote places in harsh environments. The high transmission capacity of the single-mode-few-mode optical fiber butt joint structure makes it the best connection solution.

[0006] Medical equipment: In medical equipment, the single-mode-few-mode optical fiber butt joint structure is mainly used for the connection of laser surgery equipment, optical microscopes, endoscopes and other light wave equipment. These devices have very high precision and reliability requirements, and the high transmission speed and low loss characteristics of the single-mode-few-mode optical fiber butt joint structure can ensure the quality and efficiency of signal transmission.

[0007] Smart home: In smart home, single-mode-few-mode fiber interface structure is used for the connection of audio and video equipment such as TV, sound and multimedia player, etc. Its high definition and stable transmission performance makes these devices can quickly and effectively connect and communicate with other home devices.

[0008] In summary, single-mode-few-mode fiber interface structure can be applied in many fields such as communication, industry, medical treatment and home entertainment, etc. It has powerful functions and wide application prospects.

[0009] Single-mode fiber and few-mode fiber are two different types of optical fibers commonly used in optical fiber communication. Single-mode fiber is suitable for high-speed transmission and long-distance communication, with low signal attenuation, thin fiber, high bandwidth and large information capacity. Few-mode fiber is suitable for short-distance and low-speed data transmission, such as communication within office, campus or data center.

[0010] In practical application, since the fiber core diameters of single-mode fiber and few-mode fiber are different, when the two interfaces need to be connected, misalignment may occur. At this time, single-mode-few-mode fiber misalignment detection instrument is needed for detection and calibration to ensure the quality and stability of communication.

[0011] At present, single-mode-few-mode fiber misalignment detection instrument can detect the misalignment of optical fiber by using special optical probe. The probe can test and calibrate different optical fiber interfaces, and the test parameters that can be detected include fiber coupling loss, test distance, wavelength, end face geometry, etc., so as to realize accurate calibration and optimization of different types of optical fiber interfaces.

[0012] However, the introduction of optical probe will increase the cost and complicate the experimental steps, and the present application mainly studies the output spot image of the fiber end face, which can detect the misalignment degree between the fiber and the light and the energy transmission distribution without using the optical probe. SUMMARY

[0013] Based on the current status and theory of optical fiber, the present application provides an optical measurement technology based on the output spot image of optical fiber, which realizes a method of calculating the misalignment fusion value of different types of optical fiber with known output spot image information.

[0014] Taking single-mode-few-mode as an example, a single-mode-few-mode optical fiber fusion structure is selected, and an offset is introduced between the single-mode optical fiber and the few-mode optical fiber as a micro displacement to become an eccentric fusion structure. When the few-mode optical fiber is offset, the center excitation characteristics of the light field are destroyed, so a large number of high-order modes can be excited in the few-mode optical fiber. The interference between the high-order modes causes the output spot image of the few-mode optical fiber to have sharp change characteristics and exhibit complex texture characteristics. The present application is based on the above principle.

[0015] To achieve the above purpose, the technical scheme of the present application is as follows:

[0016] A method for detecting the misalignment state of an optical fiber, comprising:

[0017] (1) a laser emits a laser signal axially to one end of the optical fiber to be detected;

[0018] (2) an optical camera receives the spot image output from the end of the optical fiber to be detected;

[0019] (3) the obtained spot image is processed to obtain a corresponding radial energy density curve;

[0020] (4) the misalignment detection result of the optical fiber is obtained according to the offset state of the main peak of the radial energy density curve.

[0021] As a preferred embodiment, the coordinate system corresponding to the radial energy density curve is as follows: the origin corresponds to the starting point of the target radial line segment, the horizontal coordinate is the normalized radial displacement value of the pixel point on the target radial line segment, and the vertical coordinate is the normalized energy density value of the pixel point; the target radial line segment is a diameter line segment in the spot image along the energy dispersion direction, and the energy density values of the pixel points in the spot image are approximately symmetrically distributed along the straight line corresponding to the diameter line segment. The present application has found that, in the case where no misalignment occurs, the main peak on the radial energy density curve is generally one, and the center is located at the center of the coordinates of the normalized radial displacement value. When misalignment occurs, the main peak position is displaced, and the main peak energy is dispersed to form a secondary peak, etc. Based on the above findings, the present application selects the target radial direction as the energy dispersion direction to maximize the influence of the main peak displacement caused by misalignment, thereby realizing quantitative and directional detection.

[0022] As a preferred embodiment, in step (4), the peak with the highest energy density in the radial energy density curve is the main peak (or main lobe), and if the center of the full width at half maximum corresponding to the main peak does not coincide with the normalized radial displacement center value, it is determined that the optical fiber has misaligned. This can realize quantitative measurement. When quantitative measurement is performed, it is not necessary to construct a data relationship in advance.

[0023] As preferred, in step (4), the difference between the center of the full width at half maximum corresponding to the main peak in the radial energy density curve and the center of the normalized radial displacement coordinate is obtained, and the micro displacement value of the fiber misalignment is obtained according to the relationship between the difference and the micro displacement value of the fiber center.

[0024] As preferred, the relationship between the difference and the micro displacement value of the fiber center is as follows:

[0025] y=kx

[0026] In the formula:

[0027] k is a ratio coefficient k;

[0028] y is the difference between the center of the full width at half maximum corresponding to the main peak and the center of the radial displacement coordinate;

[0029] x is the micro displacement value of the fiber misalignment.

[0030] As preferred, the misalignment is the misalignment of the two-to-two connection ports of single-mode, few-mode and multi-mode fibers; in this case, it is mainly applied to laboratory scientific research detection to ensure the center alignment of the two-to-two connection ports of single-mode, few-mode and multi-mode fibers.

[0031] Or the misalignment is the misalignment of any position in the single-mode, few-mode and multi-mode fibers; this case is mainly applied to engineering detection to determine the misalignment of a certain position in the fiber.

[0032] As preferred, before detection, the relationship between the difference and the micro displacement value of the fiber center is constructed for single-mode-single-mode, single-mode-few-mode, single-mode-multi-mode, few-mode-few-mode, few-mode-multi-mode, and multi-mode-multi-mode models; during actual detection, the micro displacement value of the fiber misalignment is obtained according to the above relationship. During actual detection, the mode of the fiber can be determined according to the actual application occasion, and then the corresponding relationship function is selected to determine the misalignment amount.

[0033] As preferred, the data set required for constructing the relationship between the difference and the micro displacement value of the fiber center is obtained by using simulation software or a detection platform.

[0034] As preferred, the software is Rsoft software.

[0035] As preferred, the detection platform comprises:

[0036] An excitation light source for providing the required laser;

[0037] An input fiber I connected to the excitation light source;

[0038] The input end can be connected with the optical fiber II output end in any misalignment mode;

[0039] An optical camera connected with the optical fiber II output end signal, used for acquiring the light spot image of the optical fiber II output end;

[0040] An image processing device, receiving the light spot image collected by the optical camera, acquiring the radial energy density curve of the light spot image, and acquiring the data group required for constructing the relationship between the difference value and the numerical value of the fiber center micro displacement.

[0041] The optical fiber I and the optical fiber II each independently support different mode types of optical fibers.

[0042] The optical fiber I and the optical fiber II can be connected through a fiber fusion machine or a heat shrink tube.

[0043] By using the principle of beam propagation method, the incident light generated by the excitation light source enters the optical fiber II (such as a few-mode optical fiber) through the optical fiber I (such as a single-mode optical fiber), and forms an output light spot at the output end face thereof, and the output light spot is imaged by using an optical camera and finally processed.

[0044] The excitation light source can be a narrow-band light source or a single-wavelength light source, and the center wavelength is 1.55 microns.

[0045] The optical fiber I and the optical fiber II are made of high-purity silica and are fused and drawn, with a radius of 4 microns, a length of more than 3 centimeters, and a core and cladding refractive index of n1=1.476 and n2=1.466.

[0046] The few-mode optical fiber supporting different mode types is made of high-purity silica and is fused and drawn, with a mode number of 2-9 modes, a radius of 7-17 microns, a length of more than 3 centimeters, and a core and cladding refractive index of n1=1.444 and n2=1.44.

[0047] Preferably, the few-mode optical fiber supporting different mode types supports a mode number of 2, 4, 6, or 9 modes, and the corresponding fiber radius is 7, 10, 14, or 17 microns.

[0048] The optical camera is a charge-coupled device, and the semiconductor material used by the charge-coupled device has high photosensitivity, can convert light information into charge information, and then convert it into a digital signal using an analog-to-digital converter, and the digital signal can be compressed and saved using a memory or a hard disk, and then transmitted to a computer.

[0049] Taking a single-mode-few-mode structure as an example, the relationship between the offset and the micro displacement of the single-mode-few-mode optical fiber misalignment fusion structure is obtained by the following method:

[0050] Take a single-mode optical fiber, and take a few-mode optical fiber with mode number of 2-9 modes, after the different mode few-mode optical fiber is fused with the single-mode optical fiber, the change of the light spot image generated at the output end face is studied under the action of the excitation light source. According to the relationship between the fiber cutoff frequency and the mode number, the different mode few-mode optical fiber is misaligned and fused with the single-mode optical fiber, and the lower limit of the offset of the misaligned and fused structure is 0 μm, and the upper limit is the size of the few-mode optical fiber radius.

[0051] Under the action of the excitation light source, an output light spot is generated at the output end face, and an energy density curve is obtained through image processing. The full width at half maximum interval constituted by the peak-to-peak 3dB drop of the energy density curve is used to find the offset of the energy density curve, and the relationship between the offset and the micro-displacement of the single-mode-few-mode optical fiber misaligned and fused structure is found out. Thus, in the case of known output light spot, the numerical value of the micro-displacement of the single-mode-few-mode optical fiber misaligned and fused structure can be deduced. Replace the single-mode optical fiber and the few-mode optical fiber with different lengths, and repeat the above experiment to further verify the conclusion.

[0052] Specifically, the method for constructing the relationship between the difference value and the numerical value of the micro-displacement of the fiber center corresponding to the single-mode-single-mode, single-mode-few-mode, single-mode-multiple-mode, few-mode-few-mode, few-mode-multiple-mode, and multiple-mode-multiple-mode models is as follows:

[0053] According to the same method of steps (1)-(3) in the above detection method, the radial energy density curve of the fiber I-fiber II structure misaligned and connected according to the set micro-displacement numerical value of the fiber center is obtained, the center of the full width at half maximum corresponding to the main peak in the corresponding radial energy density curve is further obtained, the difference between the center of the normalized radial displacement coordinate and the difference value is obtained, and the data group composed of the difference value and the numerical value of the micro-displacement of the fiber center is obtained. Linear fitting is performed to obtain the relationship between the difference value and the numerical value of the micro-displacement of the fiber center;

[0054] The fiber I-fiber II structure is selected from one of the following structures: single-mode optical fiber-single-mode optical fiber, single-mode optical fiber-few-mode optical fiber, single-mode optical fiber-multiple-mode optical fiber, few-mode optical fiber-few-mode optical fiber, few-mode optical fiber-multiple-mode optical fiber, and multiple-mode optical fiber-multiple-mode optical fiber.

[0055] The beneficial effects of the present application are:

[0056] The application provides a fiber misalignment detection method based on an output light spot image of an optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0057] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0058] Figure 1 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0059] Figure 2 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0060] Figure 3 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0061] Figure 4 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0062] Figure 5 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0063] Figure 6 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0064] Figure 7 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0065] Figure 8 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0066] Figure 9 The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0067] Figure 10The energy density curve of the single-mode optical fiber and the few-mode optical fiber with a mode number of 2 is (7 / 12)*10 μm;

[0068] Figure 11 The interval (x2-x1) corresponding to the position where the output spot energy density curve decays by 3dB from the maximum energy density is defined as the full width at half maximum of the spot energy curve.

[0069] Figure 12 The relationship between the micro-displacement of the few-mode optical fiber misalignment fusion and the full width at half maximum of the spot energy curve. DETAILED DESCRIPTION

[0070] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings, so that the technical solutions of the present application are easy to understand and master. It should be pointed out that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which are also considered within the scope of protection of the present application.

[0071] Reference Figure 1 An optical measurement platform based on a single-mode-few-mode optical fiber output spot image, the measurement device includes an excitation light source, a single-mode optical fiber, an optical fiber fusion machine, a heat shrink tube, a few-mode optical fiber (or a multi-mode optical fiber) supporting different modes, an optical camera, and an image processing device (generally a computer). Taking the few-mode optical fiber as an example, the single-mode optical fiber and the few-mode optical fiber supporting different modes are misaligned and fused by the optical fiber fusion machine and the heat shrink tube, forming a single-mode-few-mode (or multi-mode, the same below) structure.

[0072] Before detecting the actual single-mode-few-mode structure, the measurement platform described in the embodiment can be used to detect the data relationship of the single-mode-few-mode structure corresponding to the structure to be detected (mainly the relationship between the micro-displacement value of the single-mode-few-mode structure axis and the difference between the center of the full width at half maximum of the spot energy curve and the radial coordinate center). During measurement, the laser emitted by the excitation light source passes through the single-mode-few-mode structure and outputs an optical image at the output end face of the few-mode optical fiber. The optical image is received by the optical camera, and the optical image representing the energy density information is collected by the optical camera. By analyzing the energy density along the radial direction of the image, the radial energy density curve of the output spot is obtained, and the interval range corresponding to the 3dB drop of the energy density curve peak value, i.e. the full width at half maximum, can obtain the relationship between the micro-displacement value of the misaligned fusion of the single-mode optical fiber and the few-mode optical fiber and the output spot energy.

[0073] The excitation light source is a narrow-band light source or a single-wavelength light source, and a laser with a center wavelength of 1.55 microns can be used.

[0074] The single-mode optical fiber is fused and drawn by high-purity silica, has a radius of 4 microns, a length of 4 cm, and a refractive index of n1=1.476 and n2=1.466 of the core and cladding.

[0075] The few-mode optical fiber or the multi-mode optical fiber supporting different mode types is generally fused and drawn by high-purity silica, has a mode number of 2-9 modes, a radius of 7-17 microns, preferably 7, 10, 14 and 17 microns, and a length of 5 cm, and a refractive index of n1=1.444 and n2=1.44 of the core and cladding.

[0076] Figure 2 The basic structure of the optical fiber is shown in the figure. The basic structure of the optical fiber is generally divided into three parts: the core, the cladding and the coating. The core and the cladding are composed of glasses with different refractive indexes, the core is high-refractive-index glass (such as germanium-doped silica), and the cladding is low-refractive-index glass (such as pure silica). Light is incident into the optical fiber at a certain incident angle, and total reflection occurs between the optical fiber and the cladding (because the refractive index of the cladding is slightly lower than that of the core), so that the light can propagate in the optical fiber. The main function of the coating is to protect the optical fiber from damage from the outside world, while increasing the flexibility of the optical fiber. As described above, the core and the cladding are both glass materials, which cannot be bent and are fragile. The use of the coating can protect and prolong the service life of the optical fiber.

[0077] Figure 3 The structure and light spot of the single-mode optical fiber and the few-mode optical fiber in the case of no misalignment fusion and misalignment fusion are shown in the figures. When the single-mode optical fiber and the few-mode optical fiber are fused at the axis, the energy of the few-mode optical output end light spot image is concentrated at the axis without dispersion, as shown in detail in (a) of FIG. 4. Figure 3 When the single-mode optical fiber and the few-mode optical fiber are misaligned and fused at the axis, the energy of the few-mode optical fiber output end light spot image is dispersed from the axis, as shown in detail in (b) of FIG. 4. Figure 3

[0078] Figure 4 The figure is a schematic diagram of a misalignment fusion structure model shown in the simulation. According to the relationship between the cutoff frequency of the optical fiber and the mode number, the normalized frequency V=2.3 of the single-mode optical fiber, the normalized frequency V=3.0 of the 2-mode few-mode optical fiber, the normalized frequency V=4.5 of the 4-mode few-mode optical fiber, the normalized frequency V=6.0 of the 6-mode few-mode optical fiber, and the normalized frequency V=7.6 of the 9-mode few-mode optical fiber are selected. The supported modes of the 2-mode are LP 01 , LP 11 , the supported modes of the 4-mode are LP 01 , LP 11 , LP 02 , LP 21 , and the supported modes of the 6-mode are LP 01 , LP​11 LP 21 LP 02 LP 31 LP 12 The mode supported by the 9-mode fiber is: LP 01 LP 11 LP 21 LP 02 LP 31 LP 12 LP 41 LP 22 LP 03 .

[0079] To verify the feasibility of the present application, the present application uses Rsoft software to perform simulation experiments. The excitation light source wavelength used is 1.55 microns, and the refractive index of the core and cladding of the single-mode fiber is n1=1.476, n2=1.466. For the four kinds of fibers of 2-mode to 9-mode, the refractive index of the core and cladding of the fiber is n1=1.444, n2=1.44. According to the normalization formula:

[0080]

[0081] In the formula, λ is the wavelength; a is the radius of the few-mode fiber; n1 and n2 are the refractive indexes of the core and cladding of the few-mode fiber.

[0082] By transforming the above formula, the following formula can be obtained:

[0083]

[0084] Therefore, by substituting the relevant physical parameters of the single-mode fiber, the 2-mode, 4-mode, 6-mode, and 9-mode few-mode fiber into the above formula, the following results can be obtained:

[0085] Single-mode: V=2.3,

[0086] 2-mode: V=3.0,

[0087] 4-mode: V=4.5,

[0088] 6-mode: V=6.0,

[0089] 9-mode: V=7.6,

[0090] By inputting the fiber radius value, the corresponding laser wavelength, and the refractive index corresponding to the material and other parameters into the Rsoft software, the software automatically identifies the mode corresponding to the fiber according to the above formula.

[0091] The few-mode fiber described in this invention, based on its radius, is divided into 12 equal parts, with 0 as the lower limit for the micro-displacement of the misaligned fusion splice and the radius as the upper limit, for gradient-type uniform misaligned fusion splicing. Simulation using Rsoft software, for a few-mode fiber with 2 modes, yields the following results: Figure 5 As shown. Similarly, for few-mode fibers with 4, 6, and 9 modes, the results are as follows. Figure 6 , Figure 7 , Figure 8 As shown, as the value of the misaligned fusion splice micro-displacement (the radial distance between the center points of the single-mode fiber and the few-mode fiber) increases uniformly from 0 to a value equal to the radius, the energy deviates further from the center position and gradually decreases. With the increase of the misaligned fusion splice micro-displacement, the loss of the excitation source from the fiber core center to the edge increases, and the energy gradually decreases.

[0092] Get as Figures 5 to 8 After obtaining the light spot image, this invention establishes a rectangular coordinate system for the output light spot image. The light spot image is processed along the radial direction to obtain an energy density curve diagram. Specifically: First, the target radial position is determined: For cases without misalignment, any direction passing through the image center point can be used as the target radial direction (generally, the horizontal direction is chosen to establish the x-axis, and the vertical direction to establish the y-axis); for cases with misalignment, energy is dispersed, and the dispersed energy distribution is still symmetrically distributed along a certain radial straight line. This invention selects the aforementioned radial straight line direction as the target radial direction, that is, the direction in which the light spot energy is dispersed, i.e., the energy is symmetrically distributed along this radial straight line, which actually corresponds to the direction of misalignment, such as... Figure 3 As shown in (b); then establish a coordinate system with the origin at the position corresponding to the starting point of the target's radial direction, the x-axis as the normalized radial displacement corresponding to the target's radial direction, and the y-axis as the energy density value corresponding to the pixel point on the x-axis. Figure 9 This is a schematic diagram of the energy density curve of a few-mode fiber with a mode number of 2 at a misalignment micro-displacement of (7 / 12)*0μm (i.e., no misalignment occurs). Figure 10 This is a schematic diagram of the energy density curve of a few-mode fiber with 2 modes at a misalignment micro-displacement of (7 / 12)*10μm. Under the same mode, an increase in misalignment micro-displacement leads to a decrease in the main lobe energy and an increase in the side lobe energy of the energy density curve, while the main lobe shifts. Specifically, an increase in misalignment micro-displacement causes a shift in the maximum value of the energy density curve within the range corresponding to a 3dB decrease, i.e., a shift in the full width at half maximum (FWHM). The degree of shift increases with the degree of misalignment fusion splicing. Figure 11 This is a schematic diagram of the range corresponding to the first 3dB decay of the output spot energy density curve after the maximum energy density.

[0093] After obtaining the radial energy density curve, the shift change of the full width at half maximum of the energy density curve corresponding to the output spot of the few-mode fiber is recorded, and several parameters such as the single-mode-few-mode fiber micro-displacement value, the full width at half maximum, the center of the full width at half maximum, and the difference between the center of the full width at half maximum and the radial coordinate center are recorded. The difference between the center of the full width at half maximum and the radial coordinate center and the micro-displacement value are processed to obtain a scatter plot of the micro-displacement value of the 2-9 mode few-mode fiber and the difference between the center of the full width at half maximum and the radial coordinate center. In this embodiment, we analyze the 2-mode, 4-mode, 6-mode and 9-mode cases. The abscissa is the micro-displacement value of the 2-mode, 4-mode, 6-mode and 9-mode few-mode fiber (i.e. the fiber center misregistration value), and the ordinate is the difference between the center of the full width at half maximum and the radial coordinate center. After data fitting by the least square method, the following is obtained Figure 12 .

[0094] It can be seen from Figure 12 that within the allowable error range, the single-mode-few-mode fiber misregistration displacement and the difference between the center of the full width at half maximum and the radial coordinate center of the spot energy curve have a linear relationship. The slope k value of different mode few-mode fibers is different. Based on the above conclusion, the present application can obtain the k value by pre-acquiring the above linear relationship. Then in actual detection, the difference between the center of the full width at half maximum and the radial coordinate center of the spot energy curve obtained by detection and the corresponding k value are used to quickly obtain the corresponding fiber misregistration value.

[0095] When the number of modes supported by a certain few-mode fiber (assuming n modes) is known, the corresponding slope ratio coefficient k of the few-mode fiber is obtained by the above detection platform or simulation software n , then

[0096] y n = k n x n

[0097] In the formula, y m is the difference between the center of the full width at half maximum and the radial coordinate center of the spot energy curve;

[0098] x n is the micro-displacement of the single-mode fiber and the few-mode fiber;

[0099] In actual detection, laser is emitted along the axial direction of the fiber to be detected, the energy distribution (i.e. the spot image) of the output spot of the fiber to be detected is obtained by using an optical camera, and the center of the full width at half maximum of the radial energy density curve is calculated by using a computer to process the output spot image and establishing a rectangular coordinate system along the radial direction of the fiber. The specific value x of the micro-displacement of the single-mode-few-mode fiber misregistration fusion joint structure can be obtained by using the above formula.

[0100] For example, for a few-mode fiber with 2 modes, we found a misalignment of (7 / 12)*8μm in our experiment, which is 4.667μm. Through... Figure 12 The corresponding k value can be obtained approximately as k = 0.040 through linear fitting. Then, a similar system can be built. Figure 1 The structure shown uses an optical camera to obtain the energy density curve of the 2-mode fiber. When the difference between the center of the full width at half maximum (FWHM) and the radial coordinate center is y = 0.187, the following formula can be used to calculate:

[0101]

[0102] Substituting the data, we get:

[0103] Clearly, within the allowable error range, the actual misalignment value of 4.667 μm is consistent with the x value of 4.675 μm obtained from the energy density curve, thus effectively verifying the feasibility of our method.

[0104] Similarly, the principles and methods are the same for other modes.

[0105] The single-mode-few-mode structures studied above are mainly used for misalignment detection at single-mode-few-mode ports in the laboratory or for other applicable single-mode-few-mode structure detection.

[0106] For common fiber misalignment detection in practical engineering, the same method can be used. For different multimode or few-mode structures, data sets (difference between the center of the full width at half maximum (FWHM) of the beam energy curve and the center of the radial coordinates, and micro-displacement) corresponding to multimode-multimode and few-mode-few-mode structures are constructed, and the corresponding ratio coefficient k is obtained. Then, using the obtained ratio coefficient k, combined with the actual detected radial energy density curve, the misalignment state and misalignment displacement at a certain position of the fiber can be quickly detected. For example, for a specific multimode fiber to be tested, its mode type is first determined. Using the test platform of this invention or existing simulation software, the relationship curve between the difference between the center of the full width at half maximum (FWHM) of the beam energy curve and the center of the radial coordinates and displacement under its corresponding mode structure is constructed, and the corresponding coefficient k is obtained. Then, k is applied to the actual detection, and the corresponding micro-displacement value can be directly obtained by detecting the difference between the center of the full width at half maximum (FWHM) of the beam energy curve and the center of the radial coordinates in the beam energy curve image. An optical measurement technology based on the output beam image of single-mode-few-mode fiber is summarized in this invention as follows:

[0107] Taking few-mode fiber as an example, before actual testing, the first step is to utilize... Figure 1The platform or simulation software shown, according to the radius size of the common few-mode fiber, carries out gradient misalignment fusion (x) and standard spot image collection, then a series of spot images obtained by an optical camera are used to obtain the difference y of the full width at half maximum of the radial energy density curve by a computer, and finally a plurality of (x, y) data sets in each mode are obtained, the (x, y) data sets are used to obtain the k value corresponding to the different mode fibers by linear fitting;

[0108] 1. For the fiber to be detected, a single-mode fiber can be fused with the input end of the fiber to be detected by using the prior art to form a single-mode-few-mode fiber misalignment fusion structure, then laser is emitted axially, and the spot image of the output end face of the single-mode-few-mode fiber misalignment fusion structure is collected by an optical camera, and the spot image is read by a computer, a rectangular coordinate system is established along the radial direction, the radial direction is taken as the x direction, and the vertical direction of the x direction is taken as the normalized energy density value.

[0109] 2. For the few-mode fiber supporting different modes, the energy density curve output by the few-mode fiber end is obtained, and the full width at half maximum y of the energy density curve is calculated.

[0110] 3. According to the full width at half maximum y of the energy density curve and the coefficient k corresponding to different types of few-mode fibers, the numerical value of the single-mode fiber-few-mode fiber misalignment fusion micro-displacement is obtained.

[0111] Through experimental research, an optical measurement technology based on single-mode-few-mode fiber output spot image is obtained. Under the condition that the spot image is known, the difference between the full width at half maximum center of the spot image energy density curve and the radial coordinate center and the coefficient corresponding to different types of few-mode fibers are used to inversely deduce the micro-displacement value of the single-mode-few-mode fiber misalignment fusion structure. The method of the application is applied to the fields of communication, industry, medical treatment, intelligent home and the like, has a wide application prospect, and can play a great role in the field of detecting or identifying whether the fiber is misaligned in the fiber transmission process. By using the output end face spot image, whether damage occurs in the fiber transmission process can be investigated.

Claims

1. A fiber misalignment detection method based on fiber output spot image, characterized in that, The method comprises the following steps: (1) a laser emits a laser signal axially to one end of a fiber to be detected; (2) an optical camera receives a light spot image output by the end of the fiber to be detected; (3) the obtained light spot image is processed to obtain a corresponding radial energy density curve; (4) a fiber misalignment detection result is obtained according to a shift state of a main peak of the radial energy density curve.

2. The fiber misalignment detection method based on fiber output spot image according to claim 1, characterized in that, In step (3), a coordinate system corresponding to the radial energy density curve is as follows: an origin corresponds to a starting point of a target radial line segment, a horizontal coordinate is a normalized radial displacement value corresponding to a pixel point on the target radial line segment, and a vertical coordinate is a normalized energy density value corresponding to the pixel point; the target radial line segment is a diameter line segment in the light spot image along an energy dispersion direction, and energy density values of pixel points in the light spot image are approximately symmetrically distributed along a straight line corresponding to the diameter line segment. 3.The fiber misalignment detection method based on fiber output spot image according to claim 1, characterized in that, In step (4), the highest energy density peak in the radial energy density curve is the main peak, and if a center of a full width at half maximum corresponding to the main peak is inconsistent with a normalized radial displacement center value, it is determined that the fiber is misaligned. 4.The fiber misalignment detection method based on fiber output spot image according to claim 1, wherein, In step (4), a difference between the center of the full width at half maximum corresponding to the main peak in the radial energy density curve and a normalized radial displacement coordinate center is obtained, and a micro displacement value of the misaligned fiber is obtained according to a relationship between the difference and the micro displacement value of the fiber center.

5. The fiber misalignment detection method based on fiber output spot image according to claim 4, characterized in that, The relationship between the difference and the micro displacement value of the fiber center is as follows: y=kx In the formula, k is a ratio coefficient k, y is the difference between the center of the full width at half maximum corresponding to the main peak and the radial displacement coordinate center, and x is the micro displacement value of the misaligned fiber. The misalignment is a misalignment of two-to-two connection ports of single-mode, few-mode and multi-mode fibers, or a misalignment at any position in the single-mode, few-mode and multi-mode fibers. Before detection, a relationship between the difference and the micro displacement value of the fiber center corresponding to single-mode-single-mode, single-mode-few-mode, single-mode-multi-mode, few-mode-few-mode, few-mode-multi-mode and multi-mode-multi-mode models is constructed, and the micro displacement value of the misaligned fiber is obtained according to the relationship during actual detection. A data group required for constructing the relationship between the difference and the micro displacement value of the fiber center is obtained by using simulation software or a detection platform.

6. The fiber misalignment detection method based on fiber output spot image according to claim 4 or 5, characterized in that, The software is Rsoft software, and the detection platform comprises:

7. The fiber misalignment detection method based on fiber output spot image according to claim 5, characterized in that, an excitation light source for providing required laser light; 8.The fiber misalignment detection method based on fiber output spot image according to claim 7, characterized in that, a fiber I connected with the excitation light source at an input end; 9. The fiber misalignment detection method based on fiber output spot image according to claim 8, characterized in that, a fiber II capable of being connected with an output end of the fiber I at an input end in any misaligned manner; an optical camera connected with an output end of the fiber II for obtaining a light spot image output by the output end of the fiber II; an image processing device for receiving the light spot image collected by the optical camera, obtaining a radial energy density curve of the light spot image, and obtaining the data group required for constructing the relationship between the difference and the micro displacement value of the fiber center. The method for constructing the relationship between the difference and the micro displacement value of the fiber center corresponding to single-mode-single-mode, single-mode-few-mode, single-mode-multi-mode, few-mode-few-mode, few-mode-multi-mode and multi-mode-multi-mode models is as follows: ​ ​ 10.The fiber misalignment detection method based on fiber output spot image according to claim 7, wherein, ​ According to the method of steps (1)-(3) in claim 1, the radial energy density curves of the fiber I-fiber II structure with the fiber center misaligned by the set micro-displacement value are obtained respectively, the difference between the center of the full width at half maximum corresponding to the main peak in the corresponding radial energy density curve and the center of the normalized radial displacement coordinate is further obtained, a data group composed of the difference and the fiber center micro-displacement value is obtained, linear fitting is performed, and the relationship between the difference and the fiber center micro-displacement value is obtained. The fiber I-fiber II structure is selected from one of the following structures: single-mode fiber-single-mode fiber, single-mode fiber-few-mode fiber, single-mode fiber-multiple-mode fiber, few-mode fiber-few-mode fiber, few-mode fiber-multiple-mode fiber, and multiple-mode fiber-multiple-mode fiber.

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