A gain flattening filter

Abstract

The utility model discloses a kind of gain flatness filters, it is related to gain flatness filter technical field, the gain flatness filter includes shell, optical fiber head, collimator, filter piece and total reflection light ware, shell is formed with the installation cavity with opening;Optical fiber head is inserted in opening, and incident fiber and emergent fiber are worn on optical fiber head;Collimator is located in installation cavity and is connected with optical fiber head, collimator is oppositely arranged with incident fiber and emergent fiber;Filter piece is oppositely arranged collimator and is located the side of collimator back to optical fiber head;Total reflection light ware is located the side of filter piece back to collimator. By being simultaneously provided with incident fiber and emergent fiber on the optical fiber head located in one end of gain flatness filter, and make optical fiber head, collimator and filter piece are sequentially connected, then total reflection light ware is set on the side of filter piece back to collimator, in this way, incident light signal passes through filter piece twice in round trip process, while meeting miniaturization design, modulation depth is improved.

Description

Technical Field

[0001] This utility model relates to the field of gain-flat filter technology, and in particular to a gain-flat filter. Background Technology

[0002] Erbium-doped fiber amplifiers (EDFAs) are crucial components in DWDM (wavelength division multiplexing), offering advantages such as high gain, large bandwidth, low noise, insensitivity to optical polarization, transparency to data rate and format, and negligible crosstalk in multi-channel systems. In DWDM systems, due to the dense multiplexing of channel wavelengths and the uniform broadening characteristics of EDFAs, intense competition exists between different channels. When multiple wavelengths of optical signals pass through the EDFA, the gain of different channel wavelengths will vary. Furthermore, EDFAs are often cascaded in DWDM networks, and the gain fluctuations of each EDFA accumulate and exacerbate the overall DWDM gain fluctuations. This exacerbates signal power imbalances in the network, causing the BER (bit error rate) to fail to meet system requirements. Therefore, flattening the gain spectrum of EDFAs becomes a practical problem in DWDM system applications, and GFF (gain flattening filter) is a passive device for flattening the gain of EDFAs.

[0003] Modulation depth is a crucial metric for evaluating GFF (Glass Filter) devices. Conventional GFF devices consist of a signal transmitter and a signal receiver housed within a single package, with a filter assembly connected to the transmitter positioned between them. This filter assembly includes a TFF (Thin Film Filter) to flatten input optical signals of various wavelengths. The modulation depth of such GFFs is typically below 10 dB. However, with increasingly demanding requirements for lasers and EDFAs (Electronic Digital Facilitators), GFFs with a modulation depth below 10 dB are no longer sufficient.

[0004] In related technologies, in order to achieve a modulation depth greater than 10dB, another set of filter components is symmetrically arranged in the same GFF package tube. The problem is that the package space required by the two sets of filter components increases, thus increasing the space occupied by the entire GFF device, making it difficult to meet the miniaturization requirements. Utility Model Content

[0005] The main objective of this invention is to propose a gain-flat filter that aims to improve modulation depth while meeting the requirements of miniaturization design.

[0006] To achieve the above objectives, the gain-flattening filter proposed in this utility model includes a housing, an optical fiber head, a collimator, a filter element, and a total reflector. The housing forms a mounting cavity with an opening. The optical fiber head is inserted into the opening, and an incident optical fiber and an outgoing optical fiber pass through the optical fiber head. The collimator is disposed in the mounting cavity and connected to the optical fiber head, and the collimator is disposed opposite to the incident optical fiber and the outgoing optical fiber. The filter element is disposed opposite to the collimator and located on the side of the collimator facing away from the optical fiber head. The total reflector is disposed on the side of the filter element facing away from the collimator.

[0007] In one embodiment, an access channel, a first fixing hole, and a second fixing hole are formed inside the optical fiber head; the access channel is disposed at the end of the optical fiber head away from the mounting cavity, and the first fixing hole and the second fixing hole both connect the access channel and the mounting cavity; the incident optical fiber and the outgoing optical fiber pass through the access channel and are respectively inserted into the first fixing hole and the second fixing hole.

[0008] In one embodiment, the optical fiber head includes a connecting sleeve, an access component, and a fixing component. The connecting sleeve is inserted into the opening, the access component is inserted into the end of the connecting sleeve away from the outer shell, and the fixing component is inserted into the end of the connecting sleeve away from and close to the outer shell. An access channel is formed within the access component, and a guide channel, a first fixing hole, and a second fixing hole are formed within the fixing component. The access channel communicates with the guide channel, and both the first fixing hole and the second fixing hole communicate with the guide channel and the mounting cavity. The guide channel gradually narrows along the direction from the access channel to the mounting cavity. The incident optical fiber and the outgoing optical fiber pass through the access channel and the guide channel and are respectively inserted into the first fixing hole and the second fixing hole.

[0009] In one embodiment, the gain flattening filter further includes a first connector, which is sleeved on the fiber optic head, and the outer shell is sleeved on the first connector, wherein the first connector connects the fiber optic head and the outer shell.

[0010] In one embodiment, a boss is formed on the outer peripheral wall of the first connector, the boss abutting against the end of the housing near the optical fiber head, and the boss gradually expands along the direction from the optical fiber head to the housing.

[0011] In one embodiment, the gain flattening filter further includes a connecting tube, which is located on the side of the collimator opposite to the fiber optic head and is sleeved on the collimator; the filter element and the total reflector are sequentially fixed on the side of the connecting tube opposite to the collimator.

[0012] In one embodiment, the gain-flattening filter further includes a second connector and a third connector; the second connector is sleeved at the connection between the connecting cylinder and the filter and connects the connecting cylinder and the filter, and the third connector is sleeved at the connection between the filter and the total reflector and connects the filter and the total reflector.

[0013] In one embodiment, a first inclined surface is formed at the end of the optical fiber head near the collimator, and a second inclined surface adapted to the first inclined surface is formed at the end of the collimator near the optical fiber head, with the first inclined surface and the second inclined surface being disposed opposite to each other.

[0014] In one embodiment, the gain-flattening filter further includes a fourth connector, which is sleeved at the connection between the fiber optic head and the collimator and connects the fiber optic head and the collimator.

[0015] In one embodiment, the total reflector includes a transmissive portion and a reflective coating, the transmissive portion being connected to the side of the filter facing away from the collimator, and the reflective coating being applied to the side of the transmissive portion facing away from the filter.

[0016] The gain-flattening filter proposed in this utility model includes a housing, an optical fiber head, a collimator, a filter element, and a total reflector. The housing forms a mounting cavity with an opening. The optical fiber head is inserted into the opening, and an incident optical fiber and an outgoing optical fiber are threaded through the optical fiber head. The collimator is located in the mounting cavity and connected to the optical fiber head, and the collimator is positioned opposite to the incident optical fiber and the outgoing optical fiber. The filter element is positioned opposite to the collimator and located on the side of the collimator facing away from the optical fiber head. The total reflector is located on the side of the filter element facing away from the collimator. This invention simultaneously sets up an incident fiber and an exit fiber at the fiber optic head of a gain-flattening filter, and connects the fiber optic head, collimator, and filter in sequence. Then, a total reflector is set on the side of the filter facing away from the collimator. In this way, the incident light signal enters from the incident fiber, passes through the collimator and filter in sequence, is reflected by the total reflector and refracted back, and then passes through the filter and collimator in sequence before exiting from the exit fiber. That is, the incident light signal passes through the filter twice during its round trip. The modulation depth of each pass is less than 10dB, and the modulation depth after the two passes is greater than 10dB. Compared with the method of setting filter components at both ends separately, the gain-flattening filter of this invention is smaller in size, achieving both miniaturization and increased modulation depth. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 An exploded view of an embodiment of the gain-flattening filter provided by this utility model; Figure 2 A front view of an embodiment of the gain-flattening filter provided by this utility model; Figure 3 for Figure 2 Cross-sectional view along line A-A'; Figure 4 A top view of an embodiment of the gain-flattening filter provided by this utility model; Figure 5 for Figure 4 Cross-sectional view along line B-B'; Figure 6 for Figure 5 A schematic diagram of the structure after hiding some parts of the structure; Figure 7 for Figure 1 A schematic diagram of the middle section structure; Figure 8 for Figure 5 A schematic diagram of the middle section structure; Figure 9 for Figure 7 Right view of the middle structure; Figure 10 Loss spectrum diagram of an embodiment of the gain flattening filter provided by this utility model; Figure 11 The loss spectrum diagram of another embodiment of the gain-flattening filter provided by this utility model.

[0019] Explanation of icon numbers: 100. Gain-flattening filter; 1. Housing; 1a. Mounting cavity; 2. Fiber optic head; 21. Access component; 21a. Access channel; 22. Connecting sleeve; 23. Fixing component; 231. First bevel; 23a. Guide channel; 23b. First fixing hole; 23c. Second fixing hole; 31. Incident fiber; 32. Outgoing fiber; 4. Collimator; 41. Second bevel; 5. Filter component; 6. Total reflector; 71. First connector; 711. Boss; 72. Second connector; 73. Third connector; 74. Fourth connector; 8. Connecting cylinder.

[0020] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0021] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.

[0022] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0023] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0024] This invention proposes a gain-flattening filter 100.

[0025] Please see Figure 1 , Figure 4 and Figure 5 In one embodiment of this utility model, the gain-flattening filter 100 includes a housing 1, an optical fiber head 2, a collimator 4, a filter element 5, and a total reflector 6. The housing 1 forms a mounting cavity 1a with an opening. The optical fiber head 2 is inserted into the opening, and an incident optical fiber 31 and an outgoing optical fiber 32 are threaded through the optical fiber head 2. The collimator 4 is disposed in the mounting cavity 1a and connected to the optical fiber head 2. The collimator 4 is disposed opposite to the incident optical fiber 31 and the outgoing optical fiber 32. The filter element 5 is disposed opposite to the collimator 4 and is located on the side of the collimator 4 away from the optical fiber head 2. The total reflector 6 is disposed on the side of the filter element 5 away from the collimator 4.

[0026] In this embodiment, the gain-flattening filter 100 is coaxially packaged, and the outer shell 1 is made of glass. Inside, along the central axis of the gain-flattening filter 100 from the opening end inward, the fiber optic head 2, collimator 4, filter element 5, and total reflector 6 are arranged sequentially. The fiber optic head 2 is located at the opening of the outer shell 1 and is fixed thereto by laser welding or bonding. Its end face simultaneously passes through the incident fiber 31 and the outgoing fiber 32. The fiber optic head 2 can be made of ceramic material, and the two fibers are arranged in parallel inside the ceramic fiber optic head 2 with coplanar end faces. The collimator 4 can be directly bonded or connected to the side of the fiber optic head 2 facing the mounting cavity 1a through a mounting kit. It is used to collimate the diverging light from the incident fiber 31 into a parallel beam and refocus the reflected parallel beam onto the outgoing fiber 32, thereby achieving bidirectional transmission on the same optical path. The filter element 5 can be a single-piece thin-film filter, and the total reflector 6 can be a gold-plated plane mirror. It can be fixed to the closed end of the tube shell by laser welding, or connected to the side of the filter element 5 facing away from the collimator 4 by connecting sleeve 22 or adhesive parts. Its reflective surface faces the filter element 5 and is perpendicular to the central axis of the gain flat filter 100, so that the beam after passing through the filter is reflected back.

[0027] In summary, the gain-flattening filter 100 in this embodiment forms the optical path from fiber optic head 2 to collimator 4 and then to the filter. After reflection by the mirror, it passes through the filter and collimator 4 again before finally returning to fiber optic head 2. The beam undergoes a first spectral shaping during its single-pass passage through the filter, and after being reflected by the mirror, it passes through the same filter again, achieving a second spectral shaping. Due to the superposition of the two shaping effects, the overall modulation depth is increased from less than 10dB in a single pass to meet the high-requirement EDFA link's gain flatness requirement, which is greater than 10dB. Please refer to [reference needed]. Figures 10 to 11 All functional components are arranged sequentially along the central axis of the same gain-flat filter 100 within a single housing, eliminating the need for two sets of filter components symmetrically arranged at both ends. As a result, the package length is shortened by about half, and the space occupied is the same as or close to that of a conventional GFF with a modulation depth of less than 10dB. Therefore, the gain-flat filter 100 of this embodiment achieves improved modulation depth while meeting the requirements of miniaturization design.

[0028] Please see Figure 5 , Figure 7 , Figure 8 and Figure 9 In one embodiment of the present invention, an access channel 21a, a first fixing hole 23b, and a second fixing hole 23c are formed inside the optical fiber head 2; the access channel 21a is disposed at the end of the optical fiber head 2 away from the mounting cavity 1a, and the first fixing hole 23b and the second fixing hole 23c are both connected to the access channel 21a and the mounting cavity 1a; the incident optical fiber 31 and the outgoing optical fiber 32 pass through the access channel 21a and are respectively inserted into the first fixing hole 23b and the second fixing hole 23c.

[0029] In this embodiment, a structure for positioning and fixing the optical fiber is provided inside the optical fiber head 2, thereby eliminating the need for an additional metal tail and further shortening the overall length of the device. Specifically, the optical fiber head 2 can be made of ceramic material, such as zirconia ceramic integrally molded. The outer shell 1 can be made of glass material. The outer shell 1 is tubular and forms an installation cavity 1a inside. One end of the outer shell 1 is closed, and the other end has an opening communicating with the installation cavity 1a. The optical fiber head 2 is at least partially inserted into the opening and bonded to the inner wall of the opening of the outer shell 1 with adhesive. An access channel 21a is opened in the center of the end face of the optical fiber head 2 facing away from the installation cavity 1a. The aperture of this channel is slightly larger than the sum of the outer diameters of the two optical fibers, allowing the incident optical fiber 31 and the outgoing optical fiber 32 to pass through side by side. Two parallel micro-holes extend from the bottom of the access channel 21a toward the installation cavity 1a, namely the first fixing hole 23b and the second fixing hole 23c. Both holes communicate with the access channel 21a, and their apertures are tightly fitted to the bare optical fiber. During assembly, the coatings of the two optical fibers are first stripped off, and the bare fiber portions are inserted side-by-side into the access channel 21a. Then, they are pushed into the first fixing hole 23b and the second fixing hole 23c respectively, until the fiber end faces are flush with the end face of the fiber head 2 near the mounting cavity 1a. Subsequently, epoxy resin or other sealing agents can be potted into the opening of the access channel 21a to achieve lateral fixation and sealing of the incident fiber 31 and the outgoing fiber 32. Since the center distance between the first fixing hole 23b and the second fixing hole 23c is ensured by a one-time ceramic molding process, the relative positional accuracy of the two optical fibers is higher than that of the traditional metal tailstock fixing scheme, thus ensuring consistent reciprocating coupling efficiency of the collimator 4. Simultaneously, since the access channel 21a and the fixing holes are all located inside the fiber head 2, the axial length of the device is reduced, resulting in a more compact overall structural layout, which is beneficial for miniaturization design.

[0030] Further, please refer to Figure 2 , Figure 3 and Figure 5 In one embodiment of this utility model, the optical fiber head 2 includes a connecting sleeve 22, an access member 21, and a fixing member 23. The connecting sleeve 22 is inserted into the opening, the access member 21 is inserted into the end of the connecting sleeve 22 away from the outer shell 1, and the fixing member 23 is inserted into the end of the connecting sleeve 22 away from and close to the outer shell 1. An access channel 21a is formed in the access member 21, and a guide channel 23a, a first fixing hole 23b, and a second fixing hole 23c are formed in the fixing member 23. The access channel 21a communicates with the guide channel 23a, and the first fixing hole 23b and the second fixing hole 23c both communicate with the guide channel 23a and the mounting cavity 1a. The guide channel 23a is gradually narrowed along the direction from the access channel 21a to the mounting cavity 1a. The incident optical fiber 31 and the outgoing optical fiber 32 pass through the access channel 21a and the guide channel 23a and are respectively inserted into the first fixing hole 23b and the second fixing hole 23c.

[0031] In this embodiment, the fiber optic connector 2 comprises three separate parts: a connecting sleeve 22, an access component 21, and a fixing component 23. This combination allows for more flexible fiber guidance and positioning while retaining the advantage of miniaturization. The connecting sleeve 22 can be made of a thin-walled metal cylinder. The outer wall of the connecting sleeve 22 is inserted into the opening of the outer shell 1. For example, the outer wall of the connecting sleeve 22 can be press-fitted with the inner wall of the opening of the outer shell 1. The inner wall of the connecting sleeve 22 has insertion ports at both ends. The access component 21 can be made of materials such as zirconia ceramic. The outer wall of the access component 21 is inserted into the insertion port at the end of the connecting sleeve 22 furthest from the outer shell 1. A straight access channel 21a is formed in the center of the access component 21, with a channel diameter slightly larger than the sum of the outer diameters of the two bare fibers, facilitating initial fiber insertion. The fixing component 23 can also be made of materials such as zirconia ceramic. The outer wall of the fixing component 23 is inserted into the connecting sleeve 22. The socket at one end of the outer shell 1 is inserted. The center of the fixing member 23 is first provided with a guide channel 23a in the shape of a cone, hemisphere, or trapezoid, etc. That is, the guide channel 23a gradually narrows from the access member 21 toward the mounting cavity 1a. The first fixing hole 23b and the second fixing hole 23c can be flush with the narrowest part of the guide channel 23a, or communicate with the guide channel 23a at the narrowest part of the guide channel 23a. The first fixing hole 23b and the second fixing hole 23c continue to extend to the end face of the fixing member 23 near the mounting cavity 1a, forming a precision micro hole that communicates with the mounting cavity 1a. The hole diameter is tightly fitted with the bare optical fiber.

[0032] During assembly, the incident fiber 31 and the outgoing fiber 32 are first passed side-by-side through the access channel 21a of the access component 21. Guided by the flared end of the guide channel 23a, they automatically converge and approach the first fixing hole 23b and the second fixing hole 23c. Then, the incident fiber 31 and the outgoing fiber 32 are respectively inserted into the first fixing hole 23b and the second fixing hole 23c until the end faces of the incident fiber 31 and the outgoing fiber 32 are flush with the end faces of the fixing component 23 near the mounting cavity 1a. After the fiber threading is completed, low-stress epoxy resin can be applied at the junction of the access channel 21a and the guide channel 23a to achieve lateral fixation and sealing of the optical fibers. The shrinkage design of the guide channel 23a serves as a self-centering mechanism for the optical fiber, reducing the difficulty of manual fiber threading and preventing damage to the bare fiber at the entrance of the fixing hole. The connecting sleeve 22 can be made of metal, while the access piece 21 and fixing piece 23 can be made of ceramic. This balances welding sealing and optical fiber positioning accuracy. Furthermore, the combined length of the three pieces can be adjusted by turning the length of the connecting sleeve 22 to accommodate the tail size requirements of different EDFA modules without the need for re-molding. The incident fiber 31 and the outgoing fiber 32 remain at the same end, maintaining the miniaturization effect and further improving compatibility.

[0033] Further, please refer to Figure 1 and Figure 6In one embodiment of the present invention, the gain flattening filter 100 further includes a first connector 71, which is sleeved on the fiber optic head 2 and the outer shell 1 is sleeved on the first connector 71. The first connector 71 connects the fiber optic head 2 and the outer shell 1.

[0034] In this embodiment, a first connector 71 is added between the fiber optic head 2 and the outer shell 1 to achieve welding sealing, anti-torsion, and axial positioning functions. The first connector 71 can be a cylindrical structure made of engineering plastic. The outer diameter of the first connector 71 is clearance-fitted or interference-fitted with the inner hole of the opening end of the outer shell 1. The gap between the first connector 71 and the outer shell 1 can be further sealed with a sealant to achieve airtightness. The end of the first connector 71 away from the outer shell 1 is used to attach the fiber optic head 2. The outer circumferential surface of the fiber optic head 2 and the first connector 71 can also be further bonded with epoxy adhesive, forming a sealed connection after curing. The wall thickness of this component can be machined and adjusted to adapt to different wall thicknesses of the outer shell 1 without changing the size of the ceramic fiber optic head 2, further improving compatibility with different models of outer shell 1.

[0035] Further, please refer to Figure 1 and Figure 6 In one embodiment of the present invention, a boss 711 is formed on the outer peripheral wall of the first connector 71. The boss 711 abuts against the end of the outer shell 1 near the optical fiber head 2. The boss 711 gradually expands along the direction from the optical fiber head 2 to the outer shell 1.

[0036] In this embodiment, a boss 711 is provided around the center of the outer periphery of the first connector 71. One side of the boss 711 abuts against the outer shell 1 to prevent the first connector 71 from being further inserted into the outer shell 1, thereby providing an axial mounting reference for the fiber optic head 2 and avoiding over-insertion or under-insertion into the outer shell 1. The outer wall of the boss 711 gradually expands from the fiber optic head 2 toward the outer shell 1, forming a conical stop structure. The cross-section of this structure is triangular, which reduces the volume of the boss 711 while providing sufficient stop strength, saving material usage, and allowing the outer shell 1 and fiber optic head 2 to transition smoothly without sharp edges.

[0037] Further, please refer to Figure 1 , Figure 3 and Figure 5 In one embodiment of the present invention, the gain flat filter 100 further includes a connecting tube 8, which is located on the side of the collimator 4 away from the fiber head 2 and is sleeved on the collimator 4; the filter element 5 and the total reflector 6 are sequentially fixed on the side of the connecting tube 8 away from the collimator 4.

[0038] In this embodiment, a connecting cylinder 8 is provided on the side of the collimator 4 facing away from the fiber optic head 2, so that the mounting reference of the filter 5 and the total reflector 6 is transferred from the inner cavity of the housing 1 to the end face of the connecting cylinder 8. This reduces the dependence on the machining accuracy of the inner diameter of the housing 1 and facilitates the connection and fixation of the collimator 4, filter 5, and total reflector, as well as the alignment of the central axis of the gain flattening filter 100, before being installed into the housing 1. The connecting cylinder 8 can be made of metal. One end of the connecting cylinder 8 is coaxially sleeved with the outer wall of the collimator 4; the other end of the connecting cylinder 8 is narrowed to form a step, and the step surface is set perpendicular to the central axis of the gain flattening filter 100. The filter 5 is in close contact with the step surface, which ensures that the central axis of the gain flattening filter 100 is perpendicular to the filter 5. Similarly, the two sides of the filter 5 are also set as parallel planes. When the total reflector is in close contact with the filter 5, the reflecting surface of the total reflector 6 is perpendicular to the central axis of the gain flattening filter 100.

[0039] Further, please refer to Figure 1 , Figure 3 and Figure 5 In one embodiment of the present invention, the gain flat filter 100 further includes a second connector 72 and a third connector 73; the second connector 72 is sleeved at the connection between the connecting cylinder 8 and the filter element 5 and connects the connecting cylinder 8 and the filter element 5, and the third connector 73 is sleeved at the connection between the filter element 5 and the total reflector 6 and connects the filter element 5 and the total reflector 6.

[0040] In this embodiment, for example, both the second connector 72 and the third connector 73 are heat-shrink tubing made of low-shrinkage polyolefin. The second connector 72 is pre-fitted onto the outer step of the connecting cylinder 8. After the filter with the metal ring is placed into the step, heating causes the tubing to shrink, uniformly clamping the outer wall of the metal ring to the outer wall of the step of the connecting cylinder 8, forming a radial fixation. Its shrinkage force is sufficient to resist daily vibration without generating lateral compression that could deform the filter. The third connector 73 is similar and will not be described in detail. For example, the second connector 72 and the third connector 73 are made of room temperature curing epoxy. The third connector 73 is applied to the outer wall between the end face of the filter 5 and the total reflector. After curing, the total reflector is bonded to the filter 5. The second connector 72 is similar and will not be described in detail. In this way, the axial connection and radial positioning of the connecting cylinder 8, the filter 5, and the total reflector 6 are achieved.

[0041] Further, please refer to Figure 3 In one embodiment of the present invention, a first inclined surface 231 is formed at the end of the fiber optic head 2 near the collimator 4, and a second inclined surface 41 adapted to the first inclined surface 231 is formed at the end of the collimator 4 near the fiber optic head 2. The first inclined surface 231 and the second inclined surface 41 are arranged opposite to each other.

[0042] In this embodiment, a first inclined plane 231 and a second inclined plane 41 that are parallel to each other are respectively provided on the mating end faces of the fiber optic head 2 and the collimator 4. The two inclined planes form an angle with the gain flattening filter 100, and the angles formed by the two inclined planes and the gain flattening filter 100 are complementary, that is, the first inclined plane 231 and the second inclined plane 41 are parallel to each other. In this way, the reflected light from the fiber end face and the collimator 4 lens will no longer return to the incident fiber 31 along the original path, but will be deflected by the inclined planes to the cladding and the surrounding space, thereby reducing the return reflection power and significantly increasing the overall return loss of the device. The first bevel 231 is directly formed on the end face of the ceramic fiber head 2 near the mounting cavity 1a, and the second bevel 41 is formed on the end face of the collimator 4 away from the filter 5. The angles of the two are complementary. During assembly, the first bevel 231 and the second bevel 41 are kept parallel and cured by a sleeve structure or adhesive dispensing. The bevel angle is selected to deviate from the return path of the optical fiber numerical aperture, ensuring that after the round-trip optical signal passes through the filter twice, the remaining reflected light is refracted and absorbed by the bevel, avoiding interference with the laser source. This bevel fit does not introduce additional components; high return loss can be achieved simply by changing the end face shape, while maintaining the original miniaturized single-end folded optical path structure.

[0043] Further, please refer to Figure 3 In one embodiment of the present invention, the gain flattening filter 100 further includes a fourth connector 74, which is sleeved at the connection between the fiber optic head 2 and the collimator 4 and connects the fiber optic head 2 and the collimator 4.

[0044] In this embodiment, the fourth connector 74 is made of plastic heat-shrink tubing or flexible adhesive. Exemplarily, the fourth connector 74 is a section of polyolefin heat-shrink tubing, pre-fitted onto the outer wall of the fiber optic head 2. After the first inclined surface 231 and the second inclined surface 41 are accurately aligned, the heat-shrink tubing is moved above the joint between the fiber optic head 2 and the collimator 4, and heated with hot air to shrink it, evenly covering the transition area between the ceramic ferrule and the metal jacket of the collimator 4, forming a flexible clamp. The shrinkage force is sufficient to resist daily insertion and removal and vibration, without causing ferrule cracking or lens displacement due to hard compression; simultaneously, the inner wall of the heat-shrink tubing has a hot-melt adhesive layer, which, after cooling, forms a seal with the two covered surfaces, preventing moisture from entering the optical path along the joint. Exemplarily, the fourth connector 74 can also use low-shrinkage UV adhesive, with three small adhesive spots applied to the outer perimeter of the joint. After UV curing, a stable connection is formed, similarly serving the functions of connection, fixation, and sealing.

[0045] Furthermore, in one embodiment of the present invention, the total reflector 6 includes a transmission part and a reflective coating. The transmission part is connected to the side of the filter 5 that is away from the collimator 4, and the reflective coating is applied to the side of the transmission part that is away from the filter 5.

[0046] In this embodiment, the total reflector 6 has a sheet-like structure, unlike traditional independent reflectors, which shortens the optical path and reduces assembly difficulty. The total reflector 6 includes a transmitting part and a reflective coating. The transmitting part is made of glass of the same material as the substrate of the filter element 5, and its thickness is much smaller than that of traditional reflectors. Its side near the filter element 5 is directly bonded to the end face of the filter element 5 via a third connector 73, avoiding scratches caused by contact between the coating and the filter element 5. The entire side of the transmitting part facing away from the filter element 5 is coated with a high-reflectivity metal or dielectric reflective coating. The film layer has a reflectivity of more than 98% in the C-band, achieving total internal reflection. By integrating the reflective surface on the back of the transmitting part, the air gap between the filter and the reflective surface is reduced from the traditional hundreds of micrometers to the thickness of the adhesive layer. The round-trip beam does not need to cross the air gap again after passing through the filter twice, reducing one interface reflection and thus reducing insertion loss.

[0047] Please refer to Figures 10 to 11 In one embodiment, the collimator 4 is a C-lens prism, with one end face of the C-lens prism being inclined, i.e., at an angle to the central axis of the gain-flattening filter 100, and the other end face being curved. The connecting cylinder 8 is a hollow metal component, fitted over the curved end face of the C-lens prism. The total reflection filter is a GFF filter, with its reflecting surface facing the connecting cylinder 8. The C-lens prism, connecting cylinder 8, and GFF filter are sequentially connected and coaxially arranged to form a first type of semi-finished product. When testing the first type of semi-finished product, the optical signal enters from the inclined end face of the C-lens prism, passes through the C-lens prism, connecting cylinder 8, and GFF filter sequentially, and then exits. Figure 10 As shown, the spectral diagram was obtained by testing the first type of semi-finished product. Figure 10 As can be seen, the modulation depth of the first type of semi-finished product is less than 10dB.

[0048] Based on the first type of semi-finished product, a total reflection device is glued to the side of the GFF filter facing away from the connecting cylinder 8. The total reflection device uses a total reflection coated filter, with the reflecting surface of the total reflection coated filter facing the GFF filter. The C-lens prism, connecting cylinder 8, GFF filter, and total reflection coated filter are sequentially connected and coaxially arranged to form the second type of semi-finished product. When testing the second type of semi-finished product, the light signal enters from the inclined end face of the C-lens prism, passes through the C-lens prism, connecting cylinder 8, and GFF filter in sequence, and is reflected by the total reflection coated filter. The light signal returns and passes through the GFF filter, connecting cylinder 8, and C-lens prism in sequence, and exits from the inclined end face of the C-lens prism. Figure 11 As shown, the spectral diagram was obtained by testing the second type of semi-finished product. Figure 11 As can be seen, the modulation depth of the second type of semi-finished product is less than 10dB.

[0049] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A gain-flattening filter, characterized in that, The gain-flattening filter includes: The outer casing (1) has a mounting cavity (1a) with an opening. Fiber optic head (2), the fiber optic head (2) is inserted into the opening, and an incident fiber (31) and an outgoing fiber (32) are threaded through the fiber optic head (2). Collimator (4), the collimator (4) is disposed in the mounting cavity (1a) and connected to the fiber head (2), the collimator (4) is disposed opposite to the incident fiber (31) and the outgoing fiber (32); Filter (5), the filter (5) being disposed relative to the collimator (4) and located on the side of the collimator (4) facing away from the fiber head (2); and Total reflector (6), the total reflector (6) is disposed on the side of the filter (5) facing away from the collimator (4); The fiber optic head (2) has an access channel (21a), a first fixing hole (23b) and a second fixing hole (23c). The access channel (21a) is located at the end of the fiber optic head (2) away from the mounting cavity (1a), and the first fixing hole (23b) and the second fixing hole (23c) are both connected to the access channel (21a) and the mounting cavity (1a). The incident optical fiber (31) and the outgoing optical fiber (32) pass through the access channel (21a) and are respectively inserted into the first fixing hole (23b) and the second fixing hole (23c).

2. The gain-flattening filter as described in claim 1, characterized in that, The fiber optic head (2) includes a connecting sleeve (22), an access piece (21), and a fixing piece (23). The connecting sleeve (22) is inserted into the opening, the access piece (21) is inserted into the end of the connecting sleeve (22) away from the outer shell (1), and the fixing piece (23) is inserted into the end of the connecting sleeve (22) away from and close to the outer shell (1). The access member (21) has an access channel (21a) formed therein, and the fixing member (23) has a guide channel (23a), a first fixing hole (23b) and a second fixing hole (23c) formed therein. The access channel (21a) is connected to the guide channel (23a). The first fixing hole (23b) and the second fixing hole (23c) are both connected to the guide channel (23a) and the mounting cavity (1a). The guide channel (23a) is gradually narrowed along the direction from the access channel (21a) to the mounting cavity (1a). The incident optical fiber (31) and the outgoing optical fiber (32) pass through the access channel (21a) and the guide channel (23a) and are respectively inserted into the first fixing hole (23b) and the second fixing hole (23c).

3. The gain-flattening filter as described in claim 1, characterized in that, The gain flattening filter further includes a first connector (71), which is sleeved on the fiber head (2), and the outer shell (1) is sleeved on the first connector (71). The first connector (71) connects the fiber head (2) and the outer shell (1).

4. The gain-flattening filter as described in claim 3, characterized in that, The outer peripheral wall of the first connector (71) is formed with a boss (711), which abuts against the end of the outer shell (1) near the optical fiber head (2), and the boss (711) gradually expands along the direction from the optical fiber head (2) to the outer shell (1).

5. The gain-flattening filter as described in claim 1, characterized in that, The gain flat filter also includes a connecting tube (8), which is located on the side of the collimator (4) facing away from the fiber head (2) and is sleeved on the collimator (4). The filter (5) and the total reflector (6) are fixedly disposed on the side of the connecting cylinder (8) opposite to the collimator (4).

6. The gain-flattening filter as described in claim 5, characterized in that, The gain-flattening filter also includes a second connector (72) and a third connector (73); The second connector (72) is sleeved at the connection between the connecting cylinder (8) and the filter (5) and connects the connecting cylinder (8) and the filter (5). The third connector (73) is sleeved at the connection between the filter (5) and the total reflector (6) and connects the filter (5) and the total reflector (6).

7. The gain-flattening filter as described in claim 1, characterized in that, The fiber optic head (2) has a first inclined surface (231) formed at one end near the collimator (4), and the collimator (4) has a second inclined surface (41) that is adapted to the first inclined surface (231) at one end near the fiber optic head (2). The first inclined surface (231) and the second inclined surface (41) are arranged opposite to each other.

8. The gain-flattening filter as described in claim 1, characterized in that, The gain flattening filter further includes a fourth connector (74), which is sleeved at the connection between the fiber head (2) and the collimator (4) and connects the fiber head (2) and the collimator (4).

9. The gain-flattening filter as described in claim 1, characterized in that, The total reflector (6) includes a transmission part and a reflective coating. The transmission part is connected to the side of the filter (5) facing away from the collimator (4), and the reflective coating is applied to the side of the transmission part facing away from the filter (5).

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