Returning light monitoring device and monitoring and adjusting method thereof

Abstract

The invention relates to a return light monitoring device and a monitoring and adjusting method thereof. The return light monitoring device comprises a forward and reverse light separator, a return light power attenuator and a control circuit system, the forward and reverse light separator used for separating forward and reverse laser comprises three ports, the laser enters from an input port Port1 of the forward and reverse light separator and then is output from an output port Port2, return light is output from a side port Port3 from the output port Port2 and then enters the return light power attenuator, and the return light power attenuator carries out power attenuation on the return light and sends the light to the control circuit system for monitoring. Light paths of forward laser and reverse laser are separated by adjusting the length of a fusion coupling part of the optical fiber, power attenuation is carried out on return light by adopting a diffuse reflection principle, the bearable rated optical power of the attenuator is flexibly changed by adjusting the attenuation rate on line, and the attenuator has the characteristics of simple structure, low cost, high reliability and the like. The intensity of the return light can be accurately monitored, protection measures can be taken in time, and laser damage caused by the return light is effectively avoided.

Description

[0001] This application is a divisional application of the invention patent application entitled “Return light monitoring device and its monitoring and adjustment method” filed with the China National Intellectual Property Administration on January 28, 2022 with application number 202111327647.1. Technical Field

[0002] The invention relates to a laser technology, and in particular to a return light monitoring device and a monitoring and adjustment method thereof. Background Art

[0003] With the development of laser technology, the output power of fiber lasers continues to increase, and the application scenarios are becoming more and more complex, and the requirements for the anti-reflection ability of fiber lasers have become higher. During the normal operation or application of the laser, part of the laser will be reflected back along the original path to act on the core components inside the laser. When the intensity of the reflected light reaches a certain threshold, it will cause the laser to operate unstably or be irreversibly damaged. Therefore, accurately monitoring the intensity of the reflected light and taking protective measures in time can effectively avoid damage to the laser due to excessive reflected light.

[0004] In order to solve the above problems, the prior art CN 111106512 A provides a monitoring device, a fiber laser and a method for processing return light, including an attenuation unit, a photoelectric monitor, a temperature monitor and a processor, wherein the attenuation unit is used to attenuate the return light entering the fiber laser, the processor is used to receive and determine whether the photoelectric signal output by the photoelectric monitor and the temperature signal output by the temperature monitor are greater than a first preset threshold, and is also used to control the fiber laser to stop working when it is determined that the photoelectric signal and the temperature signal are greater than the first preset threshold. The prior art solution solves the problem of damage to the fiber laser caused by the return light, but the light power that the attenuation unit can withstand is relatively limited. When the return light power exceeds its rated power, it will cause irreversible damage to the attenuation unit, resulting in the return light monitoring device not being able to work normally. Summary of the invention

[0005] Aiming at the problem of processing the returned light of fiber laser, a returned light monitoring device and its monitoring and adjustment method are proposed. The optical paths of the forward and reverse lasers are separated by adjusting the length of the optical fiber fusion coupling part, and the power of the returned light is attenuated by the diffuse reflection principle. The rated optical power that the attenuator can withstand can be flexibly changed by adjusting the attenuation rate online. The intensity of the returned light can be accurately monitored and protective measures can be taken in time.

[0006] The technical solution of the present invention is: a return light monitoring device, including a forward and reverse light separator, a return light power attenuator and a control circuit system; the forward and reverse light separator for separating forward and reverse lasers includes three ports Port1, Port2, and Port3. After the laser enters from the input port Port1 of the forward and reverse light separator, it is output from the output port Port2. After the return light enters the forward and reverse light separator from the output port Port2, it is output from the reverse light side port Port3 and then enters the return light power attenuator. The return light power attenuator attenuates the power of the return light and then outputs it to the control circuit system to be monitored.

[0007] Preferably, the forward and reverse optical separator is formed by melt-drawing two double-clad optical fibers; the double-clad optical fibers are respectively a main optical fiber and a side arm optical fiber branched from the main optical fiber.

[0008] Preferably, the center of the main optical fiber is the main optical fiber core, the main optical fiber core is wrapped by the main optical fiber cladding, the main optical fiber cladding is coated with a main optical fiber coating layer, and along the forward light path, there is a main optical fiber cladding light leakage section at the front end of the side arm optical fiber.

[0009] Preferably, the return light power attenuator includes a return light reflection module, a return light output fiber and a return light detection module, wherein the return light output fiber is the output port Port3 in the forward and reverse light separator, and the return light output fiber outputs the return light to the return light reflection module. After the return light reflection module reflects and attenuates the return light, it is detected by the return light detection module and then output to the control circuit system.

[0010] Preferably, the surface of the reflected light reflection module is roughened to attenuate the reflected light based on diffuse reflection principle. The attenuation coefficient α is expressed by the relational formula: α∝κ·l f ·θ f , where l f is the vertical distance between the end face of the return light output fiber and the surface of the return light reflection module, θ f is the angle between the return light output fiber and the surface of the return light reflection module 20, κ is the roughness of the surface of the return light reflection module; the received diffuse reflection light power P s Relational formula: Among them, l p is the vertical distance between the return light detection module and the return light reflection module surface, θ p is the angle between the surface of the returned light detection module and the surface of the returned light reflection module.

[0011] A forward and reverse light separator for laser forward and reverse light separation is formed by melting and drawing two double-clad optical fibers, including a main optical fiber and a side arm optical fiber branched from the main optical fiber. The center of the main optical fiber is the main optical fiber core, the main optical fiber core is wrapped by the main optical fiber cladding, and the main optical fiber coating layer is coated on the outside of the main optical fiber cladding. Along the forward light path, there is a main optical fiber cladding light leakage section at the front end of the side arm optical fiber; the fusion coupling length of the main optical fiber and the side arm optical fiber is l r , the length of the main fiber cladding light leakage section is l x , the diameter of the main optical fiber core 100 is d1, and the diameter of the main optical fiber cladding is d2; the laser is input from Port1 at one end of the main optical fiber and output from Port2 at the other end of the main optical fiber; the return light enters from Port2 at the output end of the main optical fiber and outputs from Port3 at the side arm optical fiber port.

[0012] Preferably, the forward light isolation of the forward and reverse light separator is IS 1-2 , I.S. 1-2 Relational formula:

[0013]

[0014] Among them, P 1-3 is the optical power from Port1 to Port3, P1 is the total forward laser power injected into Port1 at the main fiber input end, including the main fiber cladding optical power and the fiber core optical power; l x The longer, the 1-3 The smaller the IS 1-2 The higher;

[0015] The reverse laser transmittance T of the forward and reverse light separator 2-3 Relational formula: Among them, P 2-3 is the optical power from Port2 to Port3, and P2 is the total power of the returned light injected from Port2; r The longer, the 2-3 The larger the T 2-3 The higher.

[0016] Preferably, the forward laser isolation IS of the forward and reverse light separator is 1-2 >20dB, reverse laser transmittance T of forward and reverse optical separator 2-3 >97%.

[0017] Preferably, the main optical fiber is a double-clad passive optical fiber that matches the laser optical path, and the side arm optical fiber is a multi-mode or single-mode double-clad optical fiber.

[0018] A return light monitoring and adjustment method includes a return light monitoring device, and the adjustment steps are as follows:

[0019] S1, the return light is coupled into the return light monitoring device and transmitted in reverse to the forward and reverse light separator; the forward and reverse light separator separates the optical paths of the forward laser and the reverse laser of the laser;

[0020] S2, the reversely transmitted return light is coupled to Port 3 and enters the return light output fiber of the return light power attenuator, and is led out from the return light monitoring device and monitored. The monitoring and adjustment steps are as S201 to S203;

[0021] S201, adjusting the angle and distance between the return light output optical fiber and the return light reflection module; adjusting the attenuation coefficient α online;

[0022] S202, the returning light reflection module attenuates the power of the returning light;

[0023] S203, the return light detection module receives the return light after diffuse reflection and performs photoelectric signal conversion; and online adjusts the power of the received return light;

[0024] S3, the control circuit system reads the electrical signal of the return light monitor and controls the working state of the laser; when the electrical signal exceeds the threshold, the laser is turned off.

[0025] The beneficial effects of the present invention are as follows: the return light monitoring device and the monitoring and adjustment method thereof of the present invention separate the optical paths of the forward and reverse lasers by adjusting the length of the optical fiber fusion coupling part, and use the diffuse reflection principle to attenuate the power of the return light. The rated optical power that the attenuator can withstand can be flexibly changed by adjusting the attenuation rate online. The device has the characteristics of simple structure, low cost and high reliability, and can accurately monitor the intensity of the return light and take protective measures in time, thereby effectively avoiding damage to the laser caused by the return light. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the structure of the return light monitoring device of the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of the forward and reverse light separator of the present invention;

[0028] Figure 3 It is a schematic diagram of the forward light isolation of the forward and reverse light separator of the present invention;

[0029] Figure 4 It is a schematic diagram of the forward light transmittance of the forward and reverse light separator of the present invention;

[0030] Figure 5 A schematic diagram of the reverse light transmission path of the forward and reverse light separator of the present invention;

[0031] Figure 6 It is a schematic diagram of the reverse light transmittance of the forward and reverse light separator of the present invention;

[0032] Figure 7 This is a working principle diagram of the return light power attenuator of the present invention;

[0033] Figure 8 The figure is a flow chart of the return light monitoring and adjustment method of the present invention.

[0034] Figure symbols: 1. Forward and reverse light separator; 10. Main optical fiber; 100. Main optical fiber core; 101. Main optical fiber cladding; 102. Main optical fiber coating; 103. Main optical fiber cladding light leakage section; 11. Side arm optical fiber; 2. Return light power attenuator; 20. Return light reflection module; 21. Return light output optical fiber; 22. Return light detection module; 3. Control circuit system. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0036] like Figure 1 The schematic diagram of the structure of the return light monitoring device is shown, and the device includes a forward and reverse light separator 1, a return light power attenuator 2 and a control circuit system 3. The forward and reverse light separator 1 is used to separate forward and reverse lasers, and includes three ports Port1, Port2 and Port3. The laser enters from the input port Port1 of the forward and reverse light separator 1 and is output from the output port Port2. The return light enters from the output port Port2 and is output from the side port Port3 and enters the return light power attenuator 2. After the power is reduced, it is sent to the control circuit system 3 for monitoring.

[0037] like Figure 2 The schematic diagram of the forward and reverse light separator is shown in the figure. The forward and reverse light separator is used to separate the optical paths of forward and reverse lasers. It is formed by melting and drawing two double-clad optical fibers. It includes a main optical fiber 10 and a side arm optical fiber 11 branching from the main optical fiber 10. The main optical fiber 10 is a double-clad optical fiber with a main optical fiber core 100 at the center. The main optical fiber core 100 is wrapped by a main optical fiber cladding 101. A main optical fiber coating 102 is coated on the outside of the main optical fiber cladding. Along the forward light path, there is a main optical fiber cladding light leakage section 103 at the front end of the side arm optical fiber 11. r is the length of the fusion-coupled portion between the main optical fiber 10 and the side arm optical fiber 11, l x is the length of the main optical fiber cladding light leakage section 103, d1 is the diameter of the main optical fiber core 100, and d2 is the diameter of the main optical fiber cladding 101; the solid arrow represents the forward laser transmission optical path and direction (Port1 to Port2), and the dotted arrow represents the reverse laser transmission optical path and direction (Port2 to Port3).

[0038] The forward laser includes laser signal light, pump light, etc. Most of the signal light is transmitted in the main fiber core 100, and a small amount of high-order mode signal light and residual pump light not absorbed by the gain medium are transmitted in the main fiber cladding 101. In order to improve the separation of forward and reverse lasers, it is necessary to prevent the forward laser from being transmitted from Port 1 to Port 3. Here, the laser power ratio from Port 1 to Port 3 is defined as the forward light isolation IS 1-2 , I.S. 1-2 Relational formula:

[0039]

[0040] Among them, P 1-3 is the optical power from Port1 to Port3, and P1 is the total forward laser power injected into Port1 at the main fiber input end (including the main fiber cladding optical power and the fiber core optical power). Figure 3 As shown, θ1 represents the incident light angle entering the main optical fiber cladding 101, and θ2 represents the incident light angle entering the main optical fiber core 100. According to the light transmission principle (total reflection), the laser whose incident light angle meets the core NA (numerical aperture) is transmitted in the main optical fiber core 100, that is, it is transmitted from Port1 to Port2; the laser whose incident light angle meets the cladding NA is transmitted in the main optical fiber cladding 101, incident from Port1, transmitted to Port2, and may also be transmitted to Port3. In order to improve the forward laser isolation IS 1-2 , the main optical fiber is subjected to cladding light leakage treatment, such as Figure 4 As shown in the figure, when the light angle θ1 injected into Port1 is constant, P 1-3 The length l of the main optical fiber cladding light leakage section 103 x Related: x The longer, the 1-3 The smaller the IS 1-2 The higher.

[0041] Reverse laser includes the reflected light from the end face of the laser output fiber and the reflected light from the surface of the material when the laser is processing the material. Figure 5 As shown in the figure, the reverse laser is coupled into the optical fiber through the fiber end face. Since d2>d1, the return light power coupled into the cladding is significantly greater than the return light power coupled into the fiber core. In order to improve the separation of forward and reverse lasers, it is necessary to avoid the reverse laser from being transmitted from Port2 to Port1 ( Figure 5 ), improve the transmittance from Port2 to Port3 ( Figure 6 ). Reverse laser transmittance T 2-3 Relational formula: Among them, P 2-3 is the optical power from Port2 to Port3, and P2 is the total power of the returned light injected from Port2. Figure 6As shown in the figure, when the light injection angle θ3 at Port2 (i.e. the return light injection angle) is constant, P 2-3 With l r The length of: l r The longer, the 2-3 The larger the T 2-3 The higher.

[0042] In the manufacturing process of the forward and reverse light separator, by monitoring P 1-3 and P 2-3 , online adjustment of the length l of the main optical fiber cladding light leakage section 103 x and the length l of the two optical fiber fusion coupling parts r , to prepare forward and reverse light separators that meet application requirements, requiring forward laser isolation IS 1-2 >20dB, reverse laser transmittance T 2-3 >97%; the main optical fiber can be a double-clad passive optical fiber that matches the laser optical path, including but not limited to 10 / 125, 20 / 400, 30 / 250, 50 / 400, etc., and the side arm optical fiber can be a multi-mode or single-mode double-clad optical fiber, including but not limited to 10 / 125, 20 / 130, 105 / 125, 135 / 155, 200 / 220, etc.

[0043] Return optical power attenuator 2, such as Figure 7 As shown, the return light output optical fiber 21 is the output port Port3 in the forward and reverse light separator 1, and the return light of the laser is output to the return light reflection module 20. The total power of the return light received by the return light reflection module 20 is P3; the surface of the return light reflection module 20 needs to be roughened, and the received return light is reflected by the principle of diffuse reflection. The power of the P3 return light is attenuated after passing through the return light reflection module 20. The attenuation coefficient α is expressed by the following relationship: α∝κ·l f ·θ f , where l f is the vertical distance between the end face of the return light output optical fiber 21 and the surface of the return light reflection module 20, θ f is the angle between the return light output optical fiber 21 and the surface of the return light reflection module 20, κ is the roughness of the surface of the return light reflection module 20, if l f ,θ f The larger the κ is, the larger the α is. Correspondingly, the attenuation of the returning light power by the returning light reflection module 20 is greater. The attenuated optical power is P r The reflected light from the return light reflection module 20 is received by the return light detection module 22, and the received diffuse reflected light power P s Relational formula: Among them, l p is the vertical distance between the return light detection module 22 and the surface of the return light reflection module 20, θp is the angle between the surface of the returning light detection module 22 and the surface of the returning light reflection module 20, if l p ,θ p The larger α is, the greater P s The smaller; In summary, by adjusting l f ,θ f , l p ,θ p Parameters such as power attenuation rate β=(P3-P s ) / P3, when P s When (P s ≤the damage threshold optical power of the return light detection module 22), the greater the attenuation rate β is, the greater the total return light power P3 received by the return light reflection module 20 is, that is, the rated optical power that the attenuator can withstand increases.

[0044] The control circuit system 3 is connected to the return light detection module 22 in the return light power attenuator 2, and is used to determine whether the electrical signal exceeds a threshold value, and turn off the laser when the determination condition is met, thereby protecting the laser from damage by the return light.

[0045] like Figure 8 As shown, a flow chart of a return light monitoring and adjustment method includes:

[0046] S1, the return light is coupled into the return light monitoring device and transmitted in reverse to the forward and reverse light separator; the forward and reverse light separator 1 separates the optical paths of the forward laser and the reverse laser of the laser;

[0047] S2, the reversely transmitted return light is coupled to Port 3 and enters the return light output fiber 21 of the return light power attenuator, and is led out from the return light monitoring device and monitored. The monitoring and adjustment steps are as S201 to S203.

[0048] S201, adjusting the angle and distance between the return light output optical fiber 21 and the return light reflection module 20; and adjusting the attenuation coefficient α online.

[0049] S202: the returning light reflection module 20 attenuates the power of the returning light.

[0050] S203, the return light detection module 22 receives the return light after diffuse reflection, performs photoelectric signal conversion, and online adjusts the power of the received return light.

[0051] S3, the control circuit system 3 reads the electrical signal of the return light detection module 22, controls the working state of the laser, and turns off the laser when the electrical signal exceeds the threshold.

[0052] Example:

[0053] Forward and reverse light separator: used to separate the optical paths of forward and reverse lasers, and export the return light of reverse transmission to the laser through Port3; this embodiment uses 30 / 250 (d1 = 30um, d2 = 250um) passive optical fiber as the main optical fiber, 105 / 135 (d1 = 105um, d2 = 135um) passive optical fiber as the side arm optical fiber, and the process control parameter l x , l r By monitoring the power of Port3, the isolation and transmittance are controlled to meet IS 1-2 >25dB、T 2-3 >98%, and the final structure is as follows Figure 1 The forward and reverse light separator 1 shown;

[0054] Return light power attenuator: This embodiment uses a frosted, black-painted aluminum block as a 20° return light reflection module; in this embodiment, when l f =1cm,θ f =6°; l p =3cm,θ p =10°, the attenuator can withstand >10W return optical power and achieve >20dB power attenuation; when l f =2cm,θ f =10°; l p =3cm,θ p =12°, the attenuator can withstand >25W return optical power and achieve >30dB power attenuation.

[0055] Control circuit system: connected to the return light detection module, used to read the electrical signal of the return light detection module and determine whether it exceeds the threshold value, and activate the protection mechanism to turn off the laser when the electrical signal exceeds the threshold value, thereby protecting the laser from damage by the return light; in this embodiment, the maximum return light power threshold that the laser can withstand is 30W, and the voltage value measured by the return light detection module is 0.245V. This value is set as the voltage threshold. When the return light power is greater than 30W, the control circuit system triggers the protection mechanism to turn off the laser.

[0056] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A return light monitoring device, characterized in that: It includes a forward and reverse optical separator, a return optical power attenuator and a control circuit system; The forward and reverse optical separator for separating forward and reverse lasers comprises a first port, a second port and a third port. After the laser enters from the first port of the forward and reverse optical separator, it is output from the second port. After the return light enters the forward and reverse optical separator from the second port, the reverse light is output from the third port on the side and enters the return light power attenuator. The return light power attenuator attenuates the power of the return light and then outputs it to the control circuit system to be monitored. The return light power attenuator comprises a return light reflection module, a return light output fiber and a return light detection module. The return light output fiber is the third port in the forward and reverse light separator. The return light output fiber guides the return light to the return light reflection module. After the return light is reflected and attenuated by the return light reflection module, it is detected by the return light detection module and then output to the control circuit system. The surface of the reflected light reflection module is roughened to attenuate the reflected light based on the diffuse reflection principle. The attenuation coefficient α is expressed by the relationship: α∝κ·l f ·θ f , where l f is the vertical distance between the end face of the return light output fiber and the surface of the return light reflection module, θ f is the angle between the return light output fiber and the return light reflection module surface, κ is the roughness of the return light reflection module surface; the received diffuse reflection light power P s Relational formula: in, l p is the vertical distance between the return light detection module and the return light reflection module surface, θ p is the angle between the surface of the returned light detection module and the surface of the returned light reflection module.

2. The return light monitoring device according to claim 1, characterized in that: The forward and reverse light separator is formed by melting and drawing two double-clad optical fibers, including a main optical fiber and a side arm optical fiber branched from the main optical fiber. The center of the main optical fiber is the main optical fiber core, the main optical fiber core is wrapped by the main optical fiber cladding, and the main optical fiber coating layer is coated on the outside of the main optical fiber cladding. Along the forward light path, there is a main optical fiber cladding light leakage section at the front end of the side arm optical fiber; the fusion coupling length of the main optical fiber and the side arm optical fiber is l r , the length of the main fiber cladding light leakage section is l x , the laser is input from the first port at one end of the main optical fiber and output from the second port at the other end of the main optical fiber; the return light enters from the second port and outputs from the third port of the side arm optical fiber; the forward light isolation of the forward and reverse light separator is IS 1-2 , I.S. 1-2 Relational formula: Among them, P 1-3 is the optical power from the first port to the third port, P1 is the total forward laser power injected into the first port of the main optical fiber, including the main optical fiber cladding optical power and the core optical power; l x The longer, the 1-3 The smaller the IS 1-2 The higher; The reverse laser transmittance T of the forward and reverse light separator 2-3 Relational formula: Among them, P 2-3 is the optical power from the second port to the third port, and P2 is the total power of the returned light injected from the second port; r The longer, the 2-3 The larger the T 2-3 The higher.

3. The return light monitoring device according to claim 2, characterized in that: Control parameters x , l r By monitoring the power of the third port, the isolation and transmittance are controlled to meet IS 1-2 >20dB、T 2-3 >97%.

4. The return light monitoring device according to claim 1 or 2, characterized in that: The main optical fiber is a double-clad passive optical fiber that matches the optical path of the laser, and the side arm optical fiber is a multi-mode or single-mode double-clad optical fiber.

5. The return light monitoring device according to claim 2, characterized in that: By adjusting l f ,θ f , l p ,θ p Parameters, online adjustment of power attenuation rate β = (P3-Ps) / P3, where P3 is the total power of the returned light received by the returned light reflection module; so that Ps is less than the damage threshold optical power of the returned light detection module.

6. A method for adjusting return light monitoring for a return light monitoring device according to any one of claims 1 to 5, characterized in that: The adjustment steps are as follows: The return light is coupled into the return light monitoring device and transmitted in reverse to the forward and reverse light separator; the forward and reverse light separator separates the optical paths of the forward laser and the reverse laser of the laser; The reversely transmitted return light is coupled to the third port and enters the return light output optical fiber of the return light power attenuator; Directing the return light outputted by the return light output optical fiber to the return light reflection module; Online adjustment of the attenuation coefficient α of the return light reflection module; The returned light reflection module attenuates the power of the returned light; Online adjustment of the return light power P received by the return light detection module s , further attenuating the power of the returned light reaching the returned light detection module; The return light detection module converts the return light after power attenuation into a photoelectric signal; The control circuit system reads the electrical signal of the return light detection module to control the working state of the laser; The laser is turned off when the electrical signal exceeds a threshold.

7. The return light monitoring and adjustment method according to claim 6, characterized in that: Control parameters x , l r By monitoring the power of the third port, the isolation and transmittance are controlled to meet IS 1-2 >20dB、T 2-3 >97%.

8. The return light monitoring and adjustment method according to claim 6 or 7, characterized in that: The return light power attenuator uses a frosted aluminum block coated with black paint as a return light reflection module; When adjusting l f =1cm,θ f =6°; l p =3cm,θ p =10°, the attenuator can withstand >10W return optical power and achieve power attenuation of α>20dB; or When adjusting l f =2cm,θ f =10°; l p =3cm,θ p When α=12°, the attenuator can withstand >25W return optical power and achieve a power attenuation of α>30dB.

9. The return light monitoring and adjustment method according to claim 6, characterized in that: The following steps are also included: By adjusting the angle θ between the return light output fiber and the return light reflection module f The vertical distance l between the end face of the return light output fiber and the surface of the return light reflection module f , adjust the attenuation coefficient α online; By adjusting the angle θ between the return light detection module and the return light reflection module surface p The vertical distance l between the return light detection module and the return light reflection module surface p Online adjustment of the received return light power P s .

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