Optical fiber side light extraction structure and method

Abstract

The application discloses a kind of optical fiber side light extraction structure and method, belong to optical fiber side light extraction technical field, structure has including femtosecond grating light extraction component, filter component including filter layer and with slit light shielding layer, and detection component.The method includes: with grating diffraction separation optical signal in fiber core, with filter component filters optical signal, with detector receives signal.The application is by femtosecond laser in fiber core and writes small refractive index modulation area, with diffraction effect will transport light be introduced with specific angle to side, again cooperate external filter and metal slit and constitute spatial filter, physically block the stray light deviating from preset angle.This internal diffraction+external filter synergic mechanism avoids physical damage optical fiber surface, and realizes high purity, high directional signal extraction under micro size.

Description

Technical Field

[0001] This invention relates to the field of optical fiber lateral light extraction technology, specifically to an optical fiber lateral light extraction structure and method. Background Technology

[0002] In the operation and maintenance of optical fiber communication networks, it is usually necessary to extract a small amount of optical signal as a monitoring sample without interrupting the transmission of the main optical signal. This sample is used to analyze parameters such as the quality, type, and attenuation of the optical signal, and to locate faults in combination with physical location information.

[0003] Currently, existing light extraction solutions mainly rely on two types of technologies: planar lightwave circuit (PLC) splitters or fused biconical taper (FBT) splitters, and fiber side polishing technology. While PLC splitters and FBT splitters are mature technologies, their device package sizes are typically in the centimeter range, making them bulky and difficult to integrate into confined spaces such as fiber optic patch cords or flanges. Furthermore, these devices usually have a clear distinction between the main optical path and sub-paths, making it difficult to meet the service requirements of simultaneous light extraction in both directions, and they also have high insertion loss, hindering their application in cost-sensitive large-scale deployment scenarios.

[0004] While V-groove or U-groove fiber side polishing reduces size, it suffers from severe optical matching defects. Due to the linear transmission characteristics of light, the angle between the polished light and the fiber axis is extremely small, typically less than 30°, causing the optical signal to be incident on the monitoring chip attached to the side at a very high angle. This large-angle incident light easily causes total internal reflection on the chip surface, preventing most of the light energy from entering the chip and resulting in extremely low monitoring efficiency. Moreover, existing monitoring chips are mostly designed for vertical incident light and lack adaptation solutions for large-angle incident light. Furthermore, polishing extracts light across the entire wavelength range, making it difficult to select specific wavelengths for large-angle light using conventional coating techniques. In terms of manufacturing, uncontrollable factors such as polishing material loss, processing pressure, speed, and fiber core position deviation result in extremely poor consistency of product optical parameters, making standardized mass production difficult and keeping manufacturing costs high. Summary of the Invention

[0005] In view of the above-mentioned problems, the present invention provides a fiber optic lateral light extraction structure and method.

[0006] Therefore, the technical problem solved by this invention is: addressing the problems of existing optical fiber light extraction technologies, such as side polishing and beam splitters, including uncontrollable light extraction angle, low optical signal-to-noise ratio, large device size, and difficulty in achieving standardized manufacturing.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a fiber optic side-mounted light extraction structure, comprising a light extraction component, including an optical fiber having a core and a plurality of discrete refractive index modulation regions distributed along the axial direction of the core, wherein the refractive index modulation regions are located inside the core and the radial cross-sectional area of ​​the refractive index modulation regions is smaller than the radial cross-sectional area of ​​the core; a filter component disposed on the side of the light extraction component, including a filter layer and a light-shielding layer having a light-transmitting slit, wherein the light-transmitting slit is spatially aligned with the refractive index modulation regions; and a detection component disposed on the side of the filter component away from the light extraction component, for receiving optical signals passing through the filter component.

[0008] As a preferred embodiment of the optical fiber lateral light extraction structure described in this invention, the refractive index modulation region is an ellipsoidal structure formed by femtosecond laser processing, and multiple refractive index modulation regions are periodically arranged along the central axis of the fiber core.

[0009] As a preferred embodiment of the optical fiber lateral light extraction structure of the present invention, the refractive index modulation region is configured to make the optical signal present an arc-shaped distribution on the radial cross section of the optical fiber, and the divergence angle corresponding to the arc-shaped distribution is 15 degrees to 20 degrees.

[0010] As a preferred embodiment of the optical fiber lateral light extraction structure described in this invention, the light-shielding layer includes a metal plate, the light-transmitting slit is a through hole opened on the metal plate, and the through hole is configured to filter out light signals propagating at a non-normal incident angle, thereby allowing the light signals to enter the detection component at a normal incident angle.

[0011] In a preferred embodiment of the optical fiber lateral light extraction structure described in this invention, the filter layer is located between the optical fiber and the light-shielding layer; the filter layer is configured to filter out stray light whose propagation direction is perpendicular to the axial direction of the optical fiber and deviates from a preset direction.

[0012] As a preferred embodiment of the optical fiber lateral light extraction structure of the present invention, the fixed base has a positioning groove for accommodating the optical fiber. The filter assembly covers the opening of the positioning groove, encapsulating the optical fiber within the positioning groove.

[0013] In a preferred embodiment of the optical fiber lateral light extraction structure of the present invention, the light extraction component further includes a connecting layer, which is disposed between the optical fiber and the filter component to fix the relative positions of the optical fiber and the filter component.

[0014] As a preferred embodiment of the optical fiber lateral light extraction structure described in this invention, the axial distribution period of the refractive index modulation region is set according to the center wavelength of the optical signal, so that the optical signal diffracts along a preset direction.

[0015] To solve the above-mentioned technical problems, the present invention also provides the following technical solution: a method for lateral light extraction from an optical fiber, comprising: transmitting an optical signal in the core of an optical fiber; using multiple discrete refractive index modulation regions located inside the core and having a radial cross-sectional area smaller than the radial cross-sectional area of ​​the core to diffract the transmitted optical signal, thereby separating the optical signal propagating along a preset direction laterally in the optical fiber; using a light-shielding layer in a filter assembly to filter the optical signal, blocking stray light deviating from the preset direction, and allowing the optical signal to pass through a light-transmitting slit in the light-shielding layer; and using a detection assembly to receive the optical signal passing through the light-transmitting slit.

[0016] As a preferred embodiment of the optical fiber lateral light extraction method of the present invention, the method further includes the step of preparing a refractive index modulation region before transmitting the optical signal: focusing a femtosecond laser inside the fiber core, controlling the effective range of the laser focus to be smaller than the radial cross-sectional dimension of the fiber core; setting the pulse writing period of the femtosecond laser according to the center wavelength of the optical signal, inducing the periodically distributed refractive index modulation region in the fiber core, so that the diffraction angle generated by the refractive index modulation region matches the spatial position of the light-transmitting slit.

[0017] The beneficial effects of this invention are as follows: This invention utilizes the diffraction principle of a femtosecond grating within the fiber core to achieve lateral light extraction while preserving the mechanical strength of the optical fiber. Experimental data shows that this structure has extremely low optical insertion loss, with additional loss controllable to within -0.3dB, reaching -0.2dB under optimized processes, and potentially even optimized to -0.1dB, with almost no impact on the main optical path communication. Compared to polishing solutions, its output angle is precisely controlled by the grating period, and combined with dual spatial filtering by the filter layer and the slit, it can effectively eliminate stray light that is not normally incident, significantly improving the monitoring signal-to-noise ratio. Compared to beam splitter solutions, this structure is extremely small in size and easy to integrate; moreover, the grating structure supports bidirectional light transmission monitoring. Furthermore, the use of automated femtosecond laser fabrication solves the problem of poor consistency in traditional polishing processes, enabling low-cost, standardized mass production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a side view of an optical fiber lateral light extraction structure.

[0020] Figure 2 This is a schematic diagram of the cross-section of an optical fiber in a lateral light extraction structure.

[0021] Figure 3 This is a side view of an optical fiber lateral light extraction structure.

[0022] Figure 4 This is a flowchart of a fiber optic lateral light extraction method.

[0023] Figure 5 This is a top view of a fiber optic side-extraction structure.

[0024] In the diagram: 100, light-collecting component; 101, optical fiber; 102, fiber core; 103, refractive index modulation region; 104, connecting layer; 200, filter component; 201, filter layer; 202, light-shielding layer; 300, detection component; 400, fixing base; L, optical signal. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0026] Example 1, referring to Figures 1 to 3 As one embodiment of the present invention, a fiber optic lateral light extraction structure is provided, including a light extraction component 100, a filter component 200 and a detection component 300, which can realize non-invasive lateral extraction and monitoring of optical signals transmitted in optical fibers.

[0027] The light extraction assembly 100 includes an optical fiber 101, which has a core 102 and a plurality of discrete refractive index modulation regions 103 distributed along the axial direction of the core 102. The refractive index modulation regions 103 are located inside the core 102, and the radial cross-sectional area of ​​the refractive index modulation regions 103 is smaller than the radial cross-sectional area of ​​the core 102.

[0028] The light-collecting assembly 100 is the core component for achieving optical signal separation. The optical fiber 101 of the light-collecting assembly 100 has a core 102, within which multiple discrete refractive index modulation regions 103 are distributed along its axial direction. The refractive index modulation region 103 is a region where the physical properties of the core material are locally altered. The refractive index of this region differs from the surrounding unmodified core material, thus disrupting the total internal reflection condition for optical signal transmission within the fiber and diffracting a portion of the optical signal out of the fiber's side. The radial cross-sectional area of ​​the refractive index modulation region 103 is smaller than that of the core 102. This feature ensures that the refractive index modulation region 103 occupies only a small portion of the core cross-section, guaranteeing that the vast majority of the main optical signal can still be transmitted normally, and keeping insertion loss within an extremely low range.

[0029] In this embodiment of the application, optical fiber 101 is a conventional single-mode quartz optical fiber; As a specific example of this embodiment, optical fiber 101 is a standard G.652 single-mode communication optical fiber with a core diameter of approximately 9 micrometers.

[0030] In an alternative implementation, optical fiber 101 may also be a multimode optical fiber; In another alternative embodiment, the optical fiber 101 may also be a special optical fiber such as a multimode polymer optical fiber or a chalcogenide glass optical fiber.

[0031] In this embodiment of the application, the process for forming the refractive index modulation region 103 is femtosecond laser-induced modification; In an alternative implementation, the refractive index modulation region 103 may also be used to create tiny scattering centers by irradiating the interior of the fiber core with a high-energy particle beam. In another alternative implementation, the refractive index modulation region 103 can also be used to create tiny scattering centers inside the fiber core by ion implantation local diffusion.

[0032] The refractive index modulation region 103 is a tiny modified point suspended in the center of the fiber core, with its diameter controlled between 1 and 3 micrometers. This ensures effective light extraction while avoiding excessive disturbance to the main mode field.

[0033] The filter assembly 200 is disposed on the side of the light-collecting assembly 100 and includes a filter layer 201 and a light-shielding layer 202 with a light-transmitting slit, the light-transmitting slit being spatially aligned with the refractive index modulation region 103.

[0034] The filter assembly 200 is used to purify and filter the extracted light.

[0035] The filter layer 201 is responsible for filtering the spectral dimensions, eliminating ambient light interference or light signals in non-working wavelengths.

[0036] The light-transmitting slit is precisely aligned with the refractive index modulation region 103 in spatial position for spatial filtering: the light-shielding layer 202 is responsible for blocking most of the scattered stray light, allowing only the portion of light that passes vertically through the light-transmitting slit to pass through.

[0037] In this embodiment, the light-shielding layer 202 can be a material with high light absorption or high reflectivity, such as a thin metal sheet like stainless steel, copper, or aluminum foil. In an alternative embodiment, the light-shielding layer 202 may also be a polymer film coated with a black light-absorbing coating, such as a PI film. In another alternative implementation, the light-shielding layer 202 may also be a metal coating deposited directly on the surface of the optical fiber.

[0038] In this embodiment of the application, the shape of the light-transmitting slit can be rectangular; In one alternative implementation, the shape of the light-transmitting slit can also be circular; In another alternative implementation, the shape of the light-transmitting slit can also be elliptical.

[0039] The shape of the light-transmitting slit depends specifically on the required light-emitting aperture.

[0040] In this embodiment, the filter layer 201 is a multilayer dielectric interference film; In an alternative embodiment, the filter layer 201 may also be an absorptive colored glass.

[0041] In this specific embodiment, a stacked structure of "optical fiber-filter layer-shielding layer" is adopted. The filter layer 201 is a multilayer dielectric film bonded or coated on the surface of the optical fiber 101; the shielding layer 202 is a metal shielding sheet, such as a stainless steel sheet, covering the filter layer 201. The light-transmitting slit 203 is a through hole opened on the metal shielding sheet. The shielding layer 202 is located on the outermost layer and can physically block most stray light, while the dielectric film filter layer 201 located in the middle further filters out background noise of specific wavelengths. The two work together to significantly improve the signal-to-noise ratio. The detection component 300 is disposed on the side of the filter component 200 away from the light-collecting component 100 and is used to receive the optical signal L passing through the filter component 200.

[0042] The detection component 300 is disposed on the side of the light filter component 200 away from the light acquisition component 100, and is used to receive the light signal L passing through the light filter component 200.

[0043] The detection component 300 serves as a photoelectric conversion or light collection terminal, used to receive the light signal passing through the filter light component 200, and is also responsible for responding to the side-emitted light signal.

[0044] The detection component 300 can be selected from different types of photodetectors according to monitoring requirements. In this embodiment, the detection component 300 is selected as a PIN photodiode. In an alternative implementation, the detection component 300 may also be an avalanche photodiode (APD). In another alternative implementation, the detection component 300 may also be a CCD / CMOS image sensor.

[0045] In some scenarios where it is necessary to extract optical signals over long distances, the detection component 300 can also be another coupled optical fiber or optical guide for collecting optical energy.

[0046] In the specific scenario of this embodiment, a highly sensitive photodiode is attached to the outside of the light-transmitting slit to convert the received weak light signal into a current signal in real time for subsequent optical power analysis.

[0047] Example 2, Reference Figures 1 to 5 As an embodiment of the present invention, an optical fiber lateral light extraction structure is provided based on the previous embodiment, which also includes a light extraction component 100, a filter component 200 and a detection component 300.

[0048] like Figure 3 As shown, specifically, the refractive index modulation region 103 is an ellipsoidal structure formed by femtosecond laser processing, and multiple refractive index modulation regions 103 are arranged periodically along the central axis of the fiber core 102.

[0049] The formation of this structure is based on the nonlinear interaction between a femtosecond laser and a transparent medium. When the femtosecond laser is focused inside the fiber core 102, it typically exceeds... The peak power density induces a nonlinear multiphoton absorption effect, causing changes in the material of the focal region, resulting in a permanent abrupt change in refractive index within the originally homogeneous quartz glass matrix. This ellipsoidal shape is determined by the Rayleigh length of the focused laser beam. With waist radius The proportional relationship determines the amount of change in refractive index. Follow the empirical formula: in For laser pulse energy, To increase writing speed, This represents the laser pulse width.

[0050] In this embodiment, the refractive index modulation amount is adjusted by controlling the above parameters. Precise control in The magnitude is sufficient to disrupt the total internal reflection condition, while avoiding a significant decrease in the mechanical strength of the optical fiber due to excessive damage.

[0051] like Figure 2 As shown, specifically, the refractive index modulation region 103 is configured to make the optical signal L present an arc-shaped distribution on the radial cross section of the optical fiber 101, and the divergence angle corresponding to the arc-shaped distribution is 15 degrees to 20 degrees.

[0052] Since the characteristic size of the refractive index modulation region 103 in this embodiment is typically 1 to 3 micrometers, which is on the same order of magnitude as the wavelength of the transmitted optical signal (1.31 micrometers or 1.55 micrometers), its scattering characteristics are between Rayleigh scattering and geometric optical scattering. The radius of curvature of the ellipsoidal structure causes the scattered light to form an anisotropic distribution on the radial cross section. By controlling the numerical aperture NA of the processing laser and optimizing the ratio of the major and minor axes of the ellipsoid, the distribution pattern of the scattering phase function can be changed, concentrating the scattered light energy within a specific arc angle of 15 to 20 degrees. This ensures that the light energy density is sufficient to be recognized by subsequent detection components, avoiding both excessive light energy divergence leading to a decrease in the signal-to-noise ratio and overly concentrated beams that are difficult to align.

[0053] like Figure 1 and Figure 5 As shown, specifically, the light-shielding layer 202 includes a metal plate, and the light-transmitting slit is a through hole opened on the metal plate. The through hole is configured to filter out light signals propagating at non-normal incident angles, thereby allowing the light signal L to enter the detection component 300 at a normal incident angle.

[0054] The slit in the metal plate is the entrance pupil of the optical system, and its physical dimensions determine the effective receiving field of view of the system. Let the width of the light-transmitting slit be... The thickness of the metal plate is Then only the angle of incidence is considered. Light rays that meet the following conditions can pass directly through the aperture to reach the detector: In this embodiment, the ratio of the metal plate thickness to the slit width is set. This constructs an extremely narrow receiving field of view, physically blocking all cladding mode noise and ambient stray light propagating at non-normal incident angles, significantly improving the signal-to-noise ratio.

[0055] Specifically, the filter layer 201 is located between the optical fiber 101 and the light-shielding layer 202; the filter layer 201 is configured to filter out stray light whose propagation direction is perpendicular to the axis of the optical fiber 101 and deviates from a preset direction.

[0056] This achieves dual filtering in both the spectral and spatial dimensions. The filter layer 201 is made of a dielectric film or colored glass transparent to a specific wavelength, used in conjunction with the spatial filtering function of the aforementioned metal plate. When the optical signal passes through the fiber cladding, it may contain multi-band background noise caused by Rayleigh scattering. The filter layer 201 first selectively absorbs light in the non-operating wavelength band according to the wavelength, and then the metal plate further cuts off light rays deviating from the preset optical path according to the angle. The combination of these two ensures that the wavelength and direction of the final optical signal entering the detector are correct.

[0057] Specifically, the fixed base 400 has a positioning groove for accommodating the optical fiber 101; the filter assembly 200 covers the opening of the positioning groove and encapsulates the optical fiber 101 within the positioning groove.

[0058] The geometric center line of the positioning slot serves as the reference axis. When the optical fiber 101 is placed into the slot and pressed by the filter assembly 200, the optical fiber will automatically align, thereby ensuring that the refractive index modulation region 103 in the fiber core is always located on the optical axis of the light-transmitting slit. This sandwich-style encapsulation structure provides extremely high mechanical stability, maintaining the accuracy of optical path alignment even when vibration or temperature changes cause minor deformation of the material.

[0059] Specifically, the light-collecting component 100 also includes a connecting layer 104, which is disposed between the optical fiber 101 and the filter component 200 to fix the relative positions of the optical fiber 101 and the filter component 200.

[0060] Preferably, the connecting layer 104 is made of a transparent optical adhesive material, the refractive index of which matches the surface materials of the optical fiber 101 and the filter assembly 200 to reduce interface reflection loss. After curing, the connecting layer 104 forms a stable physical connection, ensuring the positional accuracy between the optical fiber and the filter assembly, and enhancing the overall structure's vibration resistance and environmental adaptability. Simultaneously, this connecting layer also acts as a stress buffer, preventing thermal expansion differences caused by temperature changes from affecting optical path alignment.

[0061] Preferably, the connecting layer 104 uses 353 adhesive, which has a refractive index as low as 1.46 and a high light transmittance of greater than 95% at 1550 nm. This adhesive achieves mechanical fixation between the optical fiber 101 and the filter component 200 while avoiding the introduction of additional light absorption or scattering losses. Its viscosity parameter is controlled between 500-800 cP to ensure that the gap of less than 10 micrometers between the optical fiber and the filter layer can be uniformly filled during coating. After curing, a transparent adhesive layer with a thickness of about 5 micrometers is formed, which not only meets the structural stability requirements but also controls the interface reflection to below 0.5%.

[0062] Besides its mechanical fixing function, the connecting layer 104 also serves the purpose of refractive index matching. To minimize Fresnel reflection loss, the refractive index of the connecting layer 104 is... The refractive index was chosen to be close to that of the fiber cladding, approximately 1.45. The connecting layer fills the tiny air gap between the cylindrical surface of the fiber and the plane of the filter assembly, minimizing the reflection coefficient at the interface when the optical signal exits the fiber and enters the filter assembly, thereby improving the transmission efficiency of optical energy.

[0063] like Figure 3 As shown, specifically, the axial distribution period of the refractive index modulation region 103 is set according to the center wavelength of the optical signal L, so that the optical signal L diffracts along a preset direction.

[0064] This is the core physical mechanism for achieving lateral light extraction in this embodiment; its essence is the construction of a volumetric Bragg grating. According to the grating diffraction equation, in order to achieve the center wavelength... The optical signal is at a preset angle relative to the optical fiber axis. Diffraction occurs, and the axial period of the refractive index modulation region is observed. Phase matching conditions must be met: in The effective refractive index is the fundamental mode of the optical fiber. This embodiment calculates and verifies the optimal period parameters for different communication bands, as shown in the table below: Table 1: Validation Table of Optimal Periodic Parameters

[0065] By setting a specific axial period according to the table above, it is possible to precisely control the emission of light signals of different wavelengths along a preset diffraction angle, thereby achieving wavelength-selective lateral light extraction.

[0066] To further verify the impact of multi-point processing on optical signal transmission loss, this embodiment conducted multiple sets of grating cascade tests.

[0067] In the experiment, a C-band broadband light source was used. Three refractive index modulation regions (labeled FBG1, FBG2, and FBG3) were sequentially fabricated in the same optical fiber as light-collecting points, with corresponding center reflection wavelengths of 1535 nm, 1549 nm, and 1564 nm, respectively. The additional insertion loss introduced by the light-collecting structure was evaluated by measuring the changes in reflection intensity at each wavelength before and after each fabrication. Specific test data are shown in Table 2 below: Table 2: Multi-point processing reflection intensity loss test table

[0068] As shown in Table 2, the signal strength attenuation of the preceding grating is minimal as the number of subsequent gratings (i.e., light-collecting points) increases. Specifically, when the second light-collecting point (FBG2) is inserted, the reflected light loss of the first light-collecting point (FBG1) is approximately 0.3 dB; when the third light-collecting point (FBG3) is inserted, the cumulative loss of the first light-collecting point (FBG1) increases by only about 0.22 dB, while the loss of the second light-collecting point (FBG2) increases by only 0.24 dB.

[0069] The above data shows that the femtosecond laser micromachining technology described in this invention can stably control the single-point additional loss within the range of 0.2dB to 0.3dB. This means that even if multiple light-collecting points are deployed on the same optical fiber for multi-wavelength monitoring, the overall impact on the main communication optical path is negligible, fully demonstrating the low-intrusion advantage of this solution in online monitoring of optical communication networks.

[0070] Example 3, referring to Figure 4 As one embodiment of the present invention, a fiber optic side-light extraction method is provided, which is based on the fiber optic side-light extraction structure in the aforementioned embodiment.

[0071] S1. Preparation of the refractive index modulation region.

[0072] Before transmitting optical signals, an optical field manipulation mechanism must be pre-established within the fiber core. Specifically, a femtosecond laser is focused inside the fiber core, and the movement of the fiber relative to the laser focus is controlled by a precision displacement platform. During this process, the effective range of the laser focus must be strictly controlled, ensuring its radial dimension is smaller than the radial cross-sectional dimension of the fiber core, typically controlled within 1 to 3 micrometers, to ensure the integrity of the fiber's waveguide structure is not compromised. This is based on the center wavelength of the optical signal to be monitored. Setting the pulse writing period of the femtosecond laser The period is calculated based on the phase matching condition, which is given by the formula: in The expected lateral exit angle is determined by inducing periodically distributed refractive index modulation regions within the fiber core, ensuring that the angle of the diffracted light generated by these regions accurately matches the spatial position of the subsequent light-transmitting slit.

[0073] S2, transmission and lateral separation of optical signals.

[0074] The main optical signal is transmitted within the core of the optical fiber. When the light wave propagates to a region containing multiple discrete refractive index modulation regions, the light interacts with the material. By utilizing the refractive index modulation regions located inside the fiber core, whose radial cross-sectional area is smaller than that of the fiber core, the condition for total internal reflection is broken. Based on the aforementioned periodic structure, the transmitted light signal undergoes diffraction as it passes through this region. This physical process strips a very small proportion of the light energy from the main mode field, forming a diffraction pattern along a predetermined direction. The monitoring light propagates. At this time, due to the ellipsoidal morphology of the refractive index modulation region, the monitoring light exhibits a specific divergence angle of 15 to 20 degrees and an arc-shaped distribution on the radial cross section, providing a favorable light field shape for subsequent efficient collection.

[0075] S3, Spatial filtering of monitoring light.

[0076] The monitoring light is filtered using a light-shielding layer in the filter assembly. When the light field emitted from the side of the optical fiber reaches the filter assembly, it contains effective monitoring light propagating along a preset diffraction direction, as well as stray light caused by fiber micro-bending or impurities. The light-shielding layer, acting as a spatial filter, physically blocks all stray light deviating from the preset direction. Simultaneously, a light-transmitting slit aligned with the refractive index modulation region allows only normally or nearly normally incident monitoring light to pass through. In this process, a filter layer located between the light-shielding layer and the optical fiber can also be used to filter out background light whose propagation direction is perpendicular to the fiber axis but whose wavelength does not meet the requirements, thereby purifying the signal in both the spatial and frequency domains.

[0077] S4. Reception and detection of optical signals.

[0078] The detection component receives the monitoring light passing through the light-transmitting slit. After the aforementioned diffraction separation and spatial filtering, the light signal reaching the photosensitive surface of the detection component has an extremely high signal-to-noise ratio. The detection component converts the received light intensity signal into an electrical signal, the amplitude of which is precisely proportional to the power of the main optical signal transmitted within the optical fiber. By analyzing this electrical signal, real-time, online monitoring of the optical fiber link status can be achieved.

[0079] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A fiber optic lateral light extraction structure, characterized in that: include, The light-collecting assembly (100) includes an optical fiber (101) having a core (102) and a plurality of discrete refractive index modulation regions (103) distributed along the axial direction of the core (102), the refractive index modulation regions (103) being located inside the core (102), and the radial cross-sectional area of ​​the refractive index modulation regions (103) being smaller than the radial cross-sectional area of ​​the core (102); A filter assembly (200) is disposed on the side of the light-collecting assembly (100) and includes a filter layer (201) and a light-shielding layer (202) having a light-transmitting slit, wherein the light-transmitting slit is spatially aligned with the refractive index modulation region (103). A detection component (300) is disposed on the side of the filter component (200) away from the light-collecting component (100) and is used to receive the light signal (L) passing through the filter component (200).

2. The optical fiber lateral light extraction structure as described in claim 1, characterized in that: The refractive index modulation region (103) is an ellipsoidal structure formed by femtosecond laser processing, and multiple refractive index modulation regions (103) are arranged periodically along the central axis of the fiber core (102).

3. The optical fiber lateral light extraction structure as described in claim 2, characterized in that: The refractive index modulation region (103) is configured such that the optical signal (L) is distributed in an arc shape on the radial section of the optical fiber (101), and the divergence angle corresponding to the arc shape distribution is 15 degrees to 20 degrees.

4. The optical fiber lateral light extraction structure as described in claim 1, characterized in that: The light-shielding layer (202) includes a metal plate, and the light-transmitting slit is a through hole opened on the metal plate. The through hole is configured to filter out light signals propagating at a non-normal incident angle, thereby allowing the light signal (L) to enter the detection component (300) at a normal incident angle.

5. The fiber optic lateral light extraction structure as described in claim 4, characterized in that: The filter layer (201) is located between the optical fiber (101) and the light-shielding layer (202); the filter layer (201) is configured to filter out stray light whose propagation direction is perpendicular to the axis of the optical fiber (101) and deviates from a preset direction.

6. The optical fiber lateral light extraction structure as described in any one of claims 1 to 5, characterized in that: It also includes, A fixed base (400) having a positioning groove for accommodating the optical fiber (101); The filter assembly (200) covers the opening of the positioning groove and encapsulates the optical fiber (101) inside the positioning groove.

7. A fiber optic lateral light extraction structure as described in any one of claims 1 to 5, characterized in that: The light-collecting component (100) further includes a connecting layer (104), which is disposed between the optical fiber (101) and the filter component (200) to fix the relative position of the optical fiber (101) and the filter component (200).

8. A fiber optic lateral light extraction structure as described in any one of claims 1 to 5, characterized in that: The axial distribution period of the refractive index modulation region (103) is set according to the center wavelength of the optical signal (L) so that the optical signal (L) diffracts along a preset direction.

9. A method for lateral light extraction from an optical fiber, employing an optical fiber lateral light extraction structure as described in any one of claims 1 to 8, characterized in that, include: Transmit optical signals in the core of an optical fiber; By utilizing multiple discrete refractive index modulation regions located inside the fiber core and having a radial cross-sectional area smaller than that of the fiber core, the transmitted optical signal is diffracted, thereby separating the optical signal propagating in a preset direction in the lateral direction of the optical fiber. The light signal is filtered by the light-shielding layer in the light-filtering assembly, blocking stray light that deviates from the preset direction, and allowing the light signal to pass through the light-transmitting slit of the light-shielding layer; The light signal passing through the light-transmitting slit is received using a detection component.

10. The optical fiber lateral light extraction method as described in claim 9, characterized in that: Before transmitting the optical signal, the process also includes the step of preparing a refractive index modulation region: The femtosecond laser is focused inside the fiber core, and the effective range of the laser focus is controlled to be smaller than the radial cross-sectional dimension of the fiber core; The pulse writing period of the femtosecond laser is set according to the center wavelength of the optical signal, and the periodically distributed refractive index modulation region is induced in the fiber core, so that the diffraction angle generated by the refractive index modulation region matches the spatial position of the light-transmitting slit.

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