Optical fiber distributed temperature sensing passive multichannel multiplexing system

Abstract

The invention discloses an optical fiber distributed temperature sensing passive multichannel multiplexing system, which is characterized in that a beam of probe light emitted by a DTS host is equally divided into N paths by an optical coupler and is transmitted in N multiplexing channels, and then N-1 shunt delay devices are used for separating and delaying light beams in N-1 multiplexing channels to avoid overlapping with light beams in other multiplexing channels, so that N paths of temperature sensing optical fibers can synchronously acquire optical fiber signals and do not influence each other.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensing, and particularly to an optical fiber distributed temperature sensing passive and passive multi-channel multiplexing system. Background Art

[0002] A distributed optical fiber temperature sensing system based on Raman scattering (hereinafter referred to as a distributed temperature sensing system or DTS system) injects a detection pulse light into a fiber to be measured, receives and analyzes the Raman scattered light at each point of the sensing optical fiber, and obtains the temperature information at each position along the optical fiber. Its temperature measurement accuracy is high, the coverage length is long, the measurement points are dense, and it is less affected by interference, and it has played an important role in the feedback control and operation status monitoring in fields and industries such as integrated pipe galleries, petroleum refining, and power transmission cables.

[0003] A large number of practical applications require monitoring the temperature information of multiple segments of optical fiber dispersed from a certain node. For example, starting from an equipment machine room, multiple paths of optical fiber are branched out to monitor whether there is a fire in each refined oil storage tank. This requires the DTS system to have multi-channel multiplexing capabilities, that is, to be able to distinguish the scattered signals of multiple branched optical fibers and separately demodulate the temperature information along each branched optical fiber.

[0004] The most common solution is to install a 1*N optical switch at the branch node (controlled electrically, select one of the N outputs to connect to the 1 input), where the DTS measurement host is connected to the 1 input, and each branched optical fiber is connected to the N outputs. Through switch control, time-division multiplexing is realized, and the DTS measurement host polls the temperature information of each branched optical fiber, as shown in the invention patent CN106989843A and the like. This method has small optical power loss and good adaptability, but the monitoring of each branched optical fiber is discontinuous, and information is easily missed. Moreover, additional energy and control signals need to be provided to the multiplexing device (i.e., the optical switch), and the system complexity is higher; the switching speed of the optical switch is slow and the switching life is limited, which affects the system performance and long-term stability.

[0005] As an improvement, the utility model CN221571701U proposes to introduce a 1*N optical splitter inside the DTS measurement host, evenly divide the detection pulse light into N paths, and inject them into N branched temperature-sensitive optical fibers at the same time, and set up N groups of receiving systems in the measurement host to independently receive the Raman scattered signals of each branched temperature-sensitive optical fiber. This solution can achieve uninterrupted monitoring of all branches and avoid the service life problem of the optical switch, but the N groups of receiving systems greatly increase the system cost.

[0006] Furthermore, the invention patent CN107990998A cascades several 2*2 optical couplers, and leads out multiple sensing optical fibers from the optical fiber trunk to access branches. An excitation light delivery optical fiber with an appropriate length is connected between the couplers to increase the signal delay of the sensing optical fibers of the farther branches, so that the optical signals of the farther branches are not aliased in time with those of the nearer branches, and they can be acquired simultaneously and synchronously. However, in this method, the excitation light delivery optical fiber will also generate Raman scattering signals, which, as noise and interference, are superimposed on the Raman signals of the temperature sensing optical fibers of the nearer branches, forming cross-interference in each temperature sensing channel and reducing the temperature demodulation accuracy. At the same time, in order to ensure that the detection light energy divided among the branches is roughly equal, it is necessary to carefully adjust the splitting ratio of each stage of the coupler, and the manufacturability of the system is low.

[0007] In addition, the invention patent CN105136337A proposes to combine few-mode optical fibers and mode division multiplexing technology to inject different transmission modes into each branch optical fiber; the invention patent CN104567958B proposes to introduce microstructures into the optical fiber to endow the scattered light with coding capabilities in the time domain, frequency domain and wavelength domain to realize multi-channel multiplexing of the system. Both of these methods must use special optical fibers, which affects the versatility of the DTS system.

[0008] In summary, the current multi-channel multiplexing technologies or systems of DTS cannot simultaneously achieve the following: continuous monitoring of each branch optical fiber, no use of active switching devices such as switches, no interference between channels, no significant increase in system complexity, and compatibility with common types of optical fibers. Summary of the Invention

[0009] In view of this, the present invention provides a fiber optic distributed temperature sensing passive and passive multi-channel multiplexing system. The system uses an optical coupler to evenly divide a beam of detection light emitted by a DTS host into N paths for transmission in N multiplexing channels, and then uses N-1 beam splitting and delay devices to separate and delay the light beams in N-1 multiplexing channels respectively to avoid overlapping with the light beams in other multiplexing channels, so as to ensure that N temperature sensing optical fibers can synchronously acquire optical fiber signals and do not affect each other.

[0010] A fiber optic distributed temperature sensing passive and passive multi-channel multiplexing system includes a DTS host, a connecting optical fiber, an optical coupler, N-1 beam splitting and delay devices, and N temperature sensing optical fibers;

[0011] The DTS host is used for emitting detection light and receiving and processing Raman scattered light carrying temperature information. The DTS host is connected to the optical coupler through a connecting optical fiber.

[0012] The optical coupler is used to evenly divide a received detection light into N light beams. The optical coupler has N multiplexing channel ports, one of the multiplexing channel ports is directly connected to one of the temperature sensing optical fibers, and the remaining N - 1 multiplexing channel ports are respectively connected with a splitting and delaying device for separating and delaying the light beam in its multiplexing channel to avoid overlapping with the light beams in other multiplexing channels. Each splitting and delaying device is connected to one temperature sensing optical fiber. The temperature sensing optical fibers are all used to sense temperature and generate Raman scattered light carrying temperature information. N is a positive integer not less than 2.

[0013] Preferably, the structures of the N - 1 splitting and delaying devices are the same, and each includes a housing, a first wavelength division multiplexer and a second wavelength division multiplexer arranged in the housing. An input port and an output port are arranged on the housing. The input port is connected to one end of an input combining optical fiber, and the other end of the input combining optical fiber is connected to the combining optical port of the first wavelength division multiplexer. The Raman Stokes scattered light port of the first wavelength division multiplexer is connected to the Raman Stokes scattered light port of the second wavelength division multiplexer through a Raman Stokes scattered light transmission optical fiber. The Raman anti - Stokes scattered light port of the first wavelength division multiplexer is connected to the Raman anti - Stokes scattered light port of the second wavelength division multiplexer through a Raman anti - Stokes scattered light transmission optical fiber. The detection light port of the first wavelength division multiplexer is connected to the detection light port of the second wavelength division multiplexer through a detection light transmission optical fiber. The combining optical port of the second wavelength division multiplexer is connected to the output port through an output combining optical fiber.

[0014] Preferably, the length of the Raman Stokes scattered light transmission optical fiber is equal to the length of the Raman anti - Stokes scattered light transmission optical fiber.

[0015] Preferably, the lengths of the input combining optical fiber and the output combining optical fiber are in the range of 0.1m - 10m.

[0016] Preferably, the optical round - trip transmission distances of the N - 1 splitting and delaying devices are different from each other.

[0017] Preferably, the optical round - trip transmission distance of the splitting and delaying device on the latter multiplexing channel is greater than the sum of the optical round - trip transmission distance of the splitting and delaying device on the previous multiplexing channel and the length of the temperature sensing optical fiber.

[0018] Preferably, the optical fiber types of the N temperature sensing optical fibers are the same.

[0019] Preferably, the working bandwidth of the optical coupler covers the wavelengths of the detection light and the Raman scattered light.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention uses an optical coupler to divide a beam of detection light emitted by the DTS host into N paths for transmission in N multiplexing channels, and then uses N-1 branch delay devices to separate and delay the light beams in the N-1 multiplexing channels respectively to avoid overlapping with the light beams in other multiplexing channels, so as to ensure that the N-path temperature sensing optical fibers can synchronously obtain optical fiber signals without affecting each other.

[0022] 2. The present invention arranges a branch delay device that does not require energy and drive on N-1 channels of the N multiplexed channels, so that the Raman scattering signals generated by the N temperature sensing optical fibers do not overlap in time and can be acquired at one time by the DTS detection host 100, thereby realizing the synchronous and continuous acquisition of temperature information at each point along the N temperature sensing optical fibers without cross interference between the sensing optical fibers.

[0023] 3. The system of the present invention has a simple composition and simple operation. It does not require a control unit or additional power supply. It can continuously monitor all multiplexed channels simultaneously without mutual interference between the channels. It is compatible with common optical fiber types and has a wide range of applications without the need for special optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the system composition of the optical fiber distributed temperature sensing passive multi-channel multiplexing system.

[0026] Figure 2 It is a structural diagram of a branch delay device.

[0027] The meanings of the numbers in the figure are:

[0028] 100 is a DTS host, 101 is a connecting optical fiber, 102 is an optical coupler, 103 is a branch delay device, and 104 is a temperature sensing optical fiber;

[0029] 201 is the first wavelength division multiplexer, 202 is the optical combining port of the first wavelength division multiplexer, 203 is the Raman Stokes scattering light port of the first wavelength division multiplexer, 204 is the probe light port of the first wavelength division multiplexer, 205 is the Raman anti-Stokes scattering light port of the first wavelength division multiplexer, 206 is the second wavelength division multiplexer, 207 is the Raman Stokes scattering light port of the second wavelength division multiplexer, 208 is the probe light port of the second wavelength division multiplexer, 209 is the Raman anti-Stokes scattering light port of the second wavelength division multiplexer, 210 is the input optical combining optical fiber, 211 is the probe light transmission optical fiber, 212 is the output optical combining optical fiber, 213 is the Raman Stokes scattering light transmission optical fiber, 214 is the Raman anti-Stokes scattering light transmission optical fiber, 215 is the optical combining port of the second wavelength division multiplexer;

[0030] 220 is the input port and 221 is the output port. Detailed implementation manners

[0031] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary and do not limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0032] The terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit this disclosure. The singular forms "a", "the" and "said" used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0033] It should be understood that although the terms first, second, etc. may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of this disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "when" or "while" or "in response to determining".

[0034] In the description of the present invention, unless otherwise specified and defined, it should be noted that the terms "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the communication inside two components. It can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] The present invention provides a fiber optic distributed temperature sensing passive and passive multi-channel multiplexing system. The system uses an optical coupler to evenly divide a beam of detection light emitted by the DTS host into N paths for transmission in N multiplexing channels, and then uses N-1 demultiplexing and delay devices to separate and delay the light beams in N-1 multiplexing channels respectively to avoid overlapping with the light beams in other multiplexing channels, so as to ensure that N temperature sensing optical fibers can synchronously obtain optical fiber signals and do not affect each other.

[0036] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0037] As Figure 1 shown, the present invention provides a fiber optic distributed temperature sensing passive and passive multi-channel multiplexing system, including a DTS host 100, a connecting optical fiber 101, an optical coupler 102, N-1 demultiplexing and delay devices 103, and N temperature sensing optical fibers 104.

[0038] The DTS host 100 (fiber optic distributed temperature sensing detection host) is used to emit detection light pulses and can receive Raman scattered light carrying temperature information. The Raman scattered light includes Raman Stokes scattered light and Raman anti-Stokes reflected light. The temperature is accurately measured by analyzing the intensity ratio of the Raman Stokes scattered light and the Raman anti-Stokes reflected light. The DTS host 100 is connected to the optical coupler 102 through the connecting optical fiber 101.

[0039] One end of the connecting optical fiber 101 is connected to the light output port of the DTS host 100, and the other end is connected to the connection port of the optical coupler 102.

[0040] The optical coupler 102 is used to evenly divide a received beam of detection light into N light beams, and its working bandwidth covers the wavelengths of the detection light and the Raman scattered light. Since the Raman scattered light includes Raman Stokes scattered light and Raman anti-Stokes reflected light, the working bandwidth of the optical coupler 102 needs to cover the wavelengths of the detection light, Raman Stokes scattered light, and Raman anti-Stokes reflected light.

[0041] The optical coupler 102 is a 1xN optical coupler, having one connection port and N multiplexing channel ports. One of the multiplexing channel ports of the optical coupler 102 is directly connected to one of the temperature sensing optical fibers, and the remaining N - 1 multiplexing channel ports are respectively connected with a beam splitting and delaying device 103 for separating and delaying the light beam in its corresponding multiplexing channel to avoid overlapping with the light beams in other multiplexing channels. Each beam splitting and delaying device 103 is connected to one path of temperature sensing optical fiber. The temperature sensing optical fibers are all used to sense temperature and generate Raman scattering light carrying temperature information. N is a positive integer not less than 2.

[0042] As Figure 1 shown, the left port of the optical coupler 102 is the connection port for connecting with the connecting optical fiber 101, and there are N ports on its right side, numbered as multiplexing channel port 1, multiplexing channel port 2... multiplexing channel port N from top to bottom. Among them, multiplexing channel port 1 is directly connected to the temperature sensing optical fiber 104 - 1, and multiplexing channel port 2... multiplexing channel port N are all first connected to the beam splitting and delaying devices, and then the beam splitting and delaying devices are connected to the temperature sensing optical fibers. That is, multiplexing channel port 2 is connected to the input port of the beam splitting and delaying device 103 - 2, and the output port of the beam splitting and delaying device 103 - 2 is connected to the temperature sensing optical fiber 104 - 2; multiplexing channel port 3 is connected to the input port of the beam splitting and delaying device 103 - 3, and the output port of the beam splitting and delaying device 103 - 3 is connected to the temperature sensing optical fiber 104 - 3... multiplexing channel port N is connected to the input port of the beam splitting and delaying device 103 - N, and the output port of the beam splitting and delaying device 103 - N is connected to the temperature sensing optical fiber 104 - N.

[0043] The beam splitting and delaying devices 103 - 2, 103 - 3... 103 - N are all used to separate and delay the light beams (detection signals and temperature sensing signals) in their corresponding multiplexing channels to avoid overlapping with the light beams in other multiplexing channels.

[0044] The structures of the above N - 1 beam splitting and delaying devices 103 are the same, but the internal optical round - trip transmission distances are different.

[0045] The detection optical pulses emitted by the DTS host 100 are transmitted through the connecting optical fiber 101 to the optical coupler 102. The optical coupler 102 evenly divides the received detection light into N sub-beams. One of the sub-beams is directly transmitted from the multiplexing channel port 1 to the temperature sensing optical fiber 104-1, and the remaining N-1 sub-beams are transmitted from their respective corresponding multiplexing channel ports N to their respective corresponding temperature sensing optical fibers 104-N through the splitting delay devices 103-N. Since the optical round-trip transmission distances inside the N-1 splitting delay devices 103 are different, each splitting delay device 103 can separate and delay the detection light transmitted on its multiplexing channel from the detection light on other multiplexing channels, so that the N sub-beams (detection light) evenly divided by the optical coupler 102 reach the N-channel temperature sensing optical fibers 104-N successively. After the temperature sensing optical fibers 104-1…104-N synchronously sense the temperature, Raman scattered light is generated (the Raman scattered light generated by the temperature sensing optical fibers 104-1…104-N does not overlap in time). The Raman scattered light carrying temperature information is transmitted back in the reverse direction along the multiplexing channel where it is located and finally reaches the DTS host 100 successively. The Raman scattered light generated by the N-channel temperature sensing optical fibers is obtained by the DTS host 100 at one time, so as to accurately analyze and determine the measured temperatures of each channel of temperature sensing optical fibers.

[0046] As Figure 2 shown, the above N-1 splitting delay devices all include a housing, a first wavelength division multiplexer 201 and a second wavelength division multiplexer 206 arranged inside the housing. Both the first wavelength division multiplexer 201 and the second wavelength division multiplexer 206 include a light combining port, a Raman Stokes scattered light port, a Raman anti-Stokes scattered light port and a detection light port.

[0047] Specifically, an input port 220 and an output port 221 are arranged on the housing. The input port 220 is connected to one end of the input light combining optical fiber 210, and the other end of the input light combining optical fiber 210 is connected to the light combining port 202 of the first wavelength division multiplexer 201. The Raman Stokes scattered light port 203 of the first wavelength division multiplexer 201 is connected to the Raman Stokes scattered light port 207 of the second wavelength division multiplexer 206 through the Raman Stokes scattered light transmission optical fiber 213. The Raman anti-Stokes scattered light port 205 of the first wavelength division multiplexer 201 is connected to the Raman anti-Stokes scattered light port 209 of the second wavelength division multiplexer 206 through the Raman anti-Stokes scattered light transmission optical fiber 214. The detection light port 204 of the first wavelength division multiplexer 201 is connected to the detection light port 208 of the second wavelength division multiplexer 206 through the detection light transmission optical fiber 211. The light combining port 215 of the second wavelength division multiplexer 206 is connected to the output port 221 through the output light combining optical fiber 212.

[0048] The first wavelength division multiplexer 201 and the second wavelength division multiplexer 206 are both conventional devices that do not require external power supply or control. Both the first wavelength division multiplexer 201 and the second wavelength division multiplexer 206 are used to combine or separate Raman Stokes light, Raman reflected light, and probe light, and they restrict each type of light to only be transmitted between specified ports, that is:

[0049] The probe light can only be transmitted bidirectionally between the light combining port 202 of the first wavelength division multiplexer 201 and the probe light port 204, and between the light combining port 215 of the second wavelength division multiplexer 206 and the probe light port 208, and cannot be transmitted between other port combinations.

[0050] The Raman Stokes scattered light can only be transmitted bidirectionally between the light combining port 202 of the first wavelength division multiplexer 201 and the Raman Stokes scattered light port 203, and between the light combining port 215 of the second wavelength division multiplexer 206 and the Raman Stokes scattered light port 207, and cannot be transmitted between other port combinations.

[0051] The Raman anti-Stokes scattered light can also only be transmitted bidirectionally between the light combining port 202 of the first wavelength division multiplexer 201 and the Raman anti-Stokes scattered light port 205, and between the light combining port 215 of the second wavelength division multiplexer 206 and the Raman anti-Stokes scattered light port 209, and cannot be transmitted between other port combinations.

[0052] When the probe light enters from the input port 220 of a certain optical fiber delay device and is transmitted through the input light combining optical fiber 210, it reaches the light combining port 202 of the first wavelength division multiplexer 201, and then is coupled to the probe light port 204 of the first wavelength division multiplexer 201. After being output from the probe light port 204, it is transmitted along the probe light transmission optical fiber 211 to the probe light port 208 of the second wavelength division multiplexer 206, and then is coupled to the light combining port 215 of the second wavelength division multiplexer 206 and further input into the output light combining optical fiber 212. After being transmitted through the output light combining optical fiber 212 to the output port 221, it then enters the temperature sensing optical fiber;

[0053] After the temperature-sensing optical fiber generates Raman scattered light, the Raman scattered light enters from the output port 221 of the demultiplexing and delaying device, propagates leftward along the output combining optical fiber 212, and then enters the combining port 215 of the second wavelength division multiplexer 206. Subsequently, the Raman Stokes scattered light is output from its Raman Stokes scattered light port 207 and transmitted along the Raman Stokes scattered light transmission optical fiber 213 and then enters the Raman Stokes scattered light port 203 of the first wavelength division multiplexer 201. At the same time, the Raman anti-Stokes scattered light is output from its Raman anti-Stokes scattered light port 209 and transmitted along the Raman anti-Stokes scattered light transmission optical fiber 214 and then enters the Raman anti-Stokes scattered light port 205 of the first wavelength division multiplexer 201. The Raman Stokes scattered light and the Raman anti-Stokes scattered light entering the first wavelength division multiplexer 201 are coupled into the input combining optical fiber 210 from its combining port 202, are combined and transmitted leftward in the input combining optical fiber 210, and then are output from the input port 220 of the device, enter from the corresponding multiplexing channel port of the optical coupler 102, are output from the left port of the optical coupler 102, and are transmitted to the DTS host 100 along the connection optical fiber 101.

[0054] The lengths of the Raman Stokes scattered light transmission optical fiber 213 and the Raman anti-Stokes scattered light transmission optical fiber 214 in each demultiplexing and delaying device are equal.

[0055] For a single demultiplexing and delaying device, since the lengths of its input combining optical fiber 210 and output combining optical fiber 212 are very short, the generated Raman Stokes scattered light and Raman anti-Stokes scattered light can be ignored. When the probe light propagates rightward in the probe light transmission optical fiber 211, although a certain amount of leftward (backward) Raman Stokes scattered light and Raman anti-Stokes scattered light are generated, the two kinds of scattered light cannot reach the input combining optical fiber 210 through the first wavelength division multiplexer 201. Therefore, the entire demultiplexing and delaying device will not generate additional Raman Stokes scattered light and Raman anti-Stokes scattered light.

[0056] In this embodiment, the lengths of the input combining optical fiber 210 and the output combining optical fiber 212 in the demultiplexing and delaying device can be designed in the range of 0.1 m - 10 m.

[0057] When setting the above N - 1 demultiplexing and delaying devices 103, in order to separate the light beams in the N multiplexing channels and avoid signal overlap and cross-interference of the N temperature-sensing optical fibers, the optical round-trip transmission distance of the demultiplexing and delaying device on the subsequent multiplexing channel should be greater than the sum of the optical round-trip transmission distance of the demultiplexing and delaying device on the previous multiplexing channel and the length of the temperature-sensing optical fiber.

[0058] Assume that the fiber lengths of the N temperature-sensing optical fibers 104-1…104-N are respectively L 1 、L2 …L N Let the optical round-trip transmission distance of the optical path delay device 103-2 be d 2 d 2 is the sum of the lengths of the input combined optical fiber 210, the detection optical transmission fiber 211, the output combined optical fiber 212, and the Raman Stokes optical transmission fiber 213 in the optical path delay device 103-2. Similarly, let the optical round-trip transmission distance of the optical path delay device 103-3 be d 3 …The optical round-trip transmission distance of the optical path delay device 103-N is d N Then, when setting the above N-1 optical path delay devices 103, their fiber lengths should meet the following conditions:

[0059]

[0060]

[0061] The fiber types of the above N temperature sensing optical fibers 104 should be the same and match the fiber compatibility of the ports and devices. In actual use, according to actual needs, communication single-mode fibers, multi-mode fibers, microstructured fibers, or other types of fibers can be uniformly used.

[0062] The fiber distributed temperature sensing passive passive multi-channel multiplexing system constructed in the above manner can achieve non-overlapping Raman scattering signals generated by the temperature sensing optical fibers 104-1, 104-2…104-N in time without power supply and drive, and can be obtained by the DTS detection host 100 at one time, realizing synchronous and continuous acquisition of temperature information at each point along the temperature sensing optical fibers 104-1, 104-2…104-N, and there is no cross-interference between the sensing optical fibers.

[0063] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

Claims

1. A passive multi-channel multiplexing system for distributed optical fiber temperature sensing, characterized in that: It comprises a DTS host (100), a connecting optical fiber (101), an optical coupler (102), N-1 branch delay devices (103) and N temperature sensing optical fibers (104); The DTS host (100) is used to transmit detection light and receive and process Raman scattered light carrying temperature information. The DTS host (100) is connected to the optical coupler (102) via a connecting optical fiber (101). The optical coupler (102) is used to divide a received detection light into N light beams. The optical coupler (102) has N multiplexing channel ports, one of which is directly connected to one of the temperature sensing optical fibers. The remaining N-1 multiplexing channel ports are respectively connected to a branch delay device (103) for separating and delaying the light beams in the multiplexing channel to avoid overlapping with the light beams in other multiplexing channels. Each branch delay device (103) is connected to a temperature sensing optical fiber. The temperature sensing optical fibers are used to sense temperature and generate Raman scattered light carrying temperature information. N is a positive integer not less than 2.

2. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 1 is characterized in that: The N-1 branch delay devices (103) have the same structure and all include a housing, a first wavelength division multiplexer (201) and a second wavelength division multiplexer (206) arranged in the housing, an input port (220) and an output port (221) are arranged on the housing, the input port (220) is connected to one end of an input light combining optical fiber (210), the other end of the input light combining optical fiber (210) is connected to the light combining port of the first wavelength division multiplexer (201), and the Raman-Stokes scattered light port of the first wavelength division multiplexer (201) is connected to the second wavelength division multiplexer (206) via a Raman-Stokes scattered light transmission optical fiber (213). The Raman-Stokes scattered light port of the wavelength division multiplexer (206) is connected, the Raman anti-Stokes scattered light port of the first wavelength division multiplexer (201) is connected to the Raman anti-Stokes scattered light port of the second wavelength division multiplexer (206) via a Raman anti-Stokes scattered light transmission optical fiber (214), the detection light port of the first wavelength division multiplexer (201) is connected to the detection light port of the second wavelength division multiplexer (206) via a detection light transmission optical fiber (211), and the light combining port of the second wavelength division multiplexer (206) is connected to the output port (221) via an output light combining optical fiber (212).

3. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 2 is characterized in that: The length of the Raman-Stokes scattered light transmission optical fiber (213) is equal to the length of the Raman anti-Stokes scattered light transmission optical fiber (214).

4. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 2 is characterized in that: The lengths of the input light-combining optical fiber (210) and the output light-combining optical fiber (212) are in the range of 0.1 m to 10 m.

5. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 1 or 2, characterized in that: The optical round-trip transmission distances of the N-1 branch delay devices (103) are different.

6. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 5, characterized in that: The optical round-trip transmission distance of the branch delay device on the subsequent multiplexing channel is greater than the sum of the optical round-trip transmission distance of the branch delay device on the previous multiplexing channel and the length of the temperature sensing optical fiber.

7. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 1, characterized in that: The N temperature sensing optical fibers (104) are of the same optical fiber type.

8. The optical fiber distributed temperature sensing passive multi-channel multiplexing system according to claim 1, characterized in that: The working bandwidth of the optical coupler (102) covers the wavelengths of both the detection light and the Raman scattered light.

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