A dual-band fiber Bragg grating demodulation device with a shared demodulation optical path

Abstract

This application discloses a dual-band fiber Bragg grating demodulation device with a shared demodulation optical path, belonging to the field of fiber optic sensing technology. This application uses a polarization conversion module to convert light from two bands into two orthogonal polarization states, enabling them to share a single demodulation optical path without crosstalk. Simultaneously, this application uses a dispersive element to rationally adjust the incident angles of the two bands, ensuring that the two bands, after incident at different angles, maintain the same diffraction angle upon exiting, thereby further achieving the goal of a shared optical path. This allows this application to achieve dual-band demodulation without reducing demodulation accuracy or maintaining system compactness.

Description

Technical Field

[0001] This application belongs to the field of fiber optic sensing technology, and more specifically, relates to a dual-band fiber optic grating demodulation device with a shared demodulation optical path. Background Technology

[0002] Fiber Bragg gratings (FBGs) are optical components based on optical fibers, widely used in sensing and communication fields. Due to factors such as environmental temperature and stress, the center wavelength of FBGs can drift, necessitating high-precision demodulation instruments to monitor these changes in real time. The C-band and L-band are the main bands for fiber optic communication; however, in current technologies, FBG demodulation systems typically achieve high-precision demodulation only in one band.

[0003] When the demodulation range is extended to two or more bands, problems such as decreased spectral resolution and increased linear array detector size are often encountered. Extending the band range leads to a reduction in spectral resolution, making accurate demodulation of fiber Bragg gratings difficult. This is because, over a wider band, the spectrometer must cover a larger wavelength range within the same detector range, resulting in a decrease in resolution for each wavelength band. To maintain the same resolution, extending the band often requires larger linear array detectors, which not only increases the size and cost of the equipment but also places higher demands on optical path design and optical components. In summary, existing demodulation techniques struggle to simultaneously guarantee high resolution and system compactness when the demodulation range is extended to two or more bands. This limits the application of fiber Bragg grating demodulation systems over a wider band range, especially in sensing applications requiring high precision and high sensitivity. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the prior art, this application provides a dual-band fiber grating demodulation device with a shared demodulation optical path. Its purpose is to solve the technical problem that the existing demodulation technology cannot simultaneously meet the requirements of high resolution and system compactness when the demodulation range is extended to dual bands.

[0005] To achieve the above objectives, this application provides a dual-band fiber Bragg grating demodulation device with a shared demodulation optical path, the dual-band fiber Bragg grating demodulation device comprising:

[0006] The polarization conversion module is used to convert incident light with wavelengths in the first band and incident light with wavelengths in the second band into first polarization state light and second polarization state light respectively before they are emitted to the collimating lens.

[0007] A collimating lens is used to convert light of the first polarization state and light of the second polarization state into parallel light before it is emitted to a dispersive element.

[0008] A dispersive element is used to direct light of different wavelengths in a first polarized state to a focusing lens at different angles; and to direct light of different wavelengths in a second polarized state to a focusing lens at different angles.

[0009] A focusing lens is used to converge the first polarized light separated by the polarization beam splitter to the first linear array detector, and the second polarized light separated by the beam splitter to the second linear array detector.

[0010] A polarization beam splitter is used to reflect light of a first polarization state to a first linear array detector and transmit light of a second polarization state to a second linear array detector.

[0011] The first linear array detector is used to detect the wavelength of light in the first polarization state, and the detection range is the first band;

[0012] The second linear array detector is used to detect the wavelength of light in the second polarization state, and the detection range is the second band.

[0013] Preferably, the dual-band fiber Bragg grating demodulation device further includes:

[0014] A wavelength division multiplexer is used to separate the light in the first band and the light in the second band of the incident broadband light and then input them into an optical fiber coupler collimator.

[0015] The fiber optic coupler is used to collimate light with wavelengths in the first band and light with wavelengths in the second band, and then send them out to the polarization conversion module.

[0016] Preferably, the polarization conversion module includes:

[0017] A birefringent crystal is used to separate incident light with wavelengths in a first band into light with a first polarization state and light with a second polarization state. The light with the first polarization state exits through a first high-transmittance glass, and the light with the second polarization state exits through a first half-wave plate. It is also used to separate incident light with wavelengths in a second band into light with a second polarization state and light with a second polarization state. The light with the second polarization state exits through a second half-wave plate, and the light with the second polarization state exits through a second high-transmittance glass.

[0018] The first half-wave plate is used to convert the second polarized light in the first band into the first polarized light in the first band before it is emitted to the first cylindrical lens.

[0019] The first high-transmittance glass is used to compensate the optical path of the first polarized light in the first band and then project it onto the first cylindrical lens.

[0020] The first cylindrical lens is used to adjust the beam waist of the first polarization state light in the first band;

[0021] The second half-wave plate is used to convert the first polarized light in the second band into the second polarized light in the second band before it is emitted to the second cylindrical lens;

[0022] The second high-transmittance glass is used to allow the second polarized light of the second band to be compensated for the optical path before exiting to the second cylindrical lens;

[0023] The second cylindrical lens is used to adjust the beam waist of the second polarized light in the second band.

[0024] Preferably, the polarization conversion module is also used to adjust the beam waist of the first polarization state light and the second polarization state light before they are emitted.

[0025] Preferably, the dual-band fiber grating demodulation device conforms to the 4f system.

[0026] Preferably, the dual-band fiber grating demodulation device conforms to a 4f system, and the size of the light spot on the first and second linear array detectors is adjusted by controlling the beam waist of the light emitted from the polarization conversion module.

[0027] Preferably, the first polarized light and the second polarized light enter the dispersive element at different incident angles and exit at the same exit angle.

[0028] Preferably, the first polarization state and the second polarization state are orthogonal polarization states.

[0029] Preferably, the dual-band fiber Bragg grating demodulation device further includes:

[0030] The first optical supplementary element is located in front of the first linear array detector and is used to compensate for aberrations and reduce the size of the light spot on the first linear array detector.

[0031] The second optical supplementary element, located in front of the second linear array detector, is used to compensate for aberrations and reduce the size of the light spot on the second linear array detector.

[0032] Preferably, the dual-band fiber Bragg grating demodulation device further includes:

[0033] The data processing unit is used to calculate the center wavelength and bandwidth of the incident light based on the light intensity data of each wavelength channel detected by the first linear array detector and the second linear array detector.

[0034] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0035] (1) This application uses a polarization conversion module to convert light in two bands into two orthogonal polarization states, so that the two can share a demodulation optical path and do not interfere with each other. At the same time, this application reasonably adjusts the incident angle of light in two bands through a dispersive element, so that light in two bands enters the dispersive element at different incident angles and then exits at the same diffraction angle, thereby further realizing the purpose of sharing an optical path. This application achieves dual-band demodulation without reducing demodulation accuracy and maintaining system compactness.

[0036] (2) The device of this application conforms to the 4f system, thereby adjusting the size of the light spot on the linear array detector by controlling the beam waist of the light emitted from the polarization conversion module, thereby enabling the linear array detector to achieve higher precision.

[0037] (3) This application uses a wavelength division multiplexer to separate the light in different wavelength bands in the broadband light in advance, and then input them into the polarization conversion module respectively. This process is more conducive to the polarization conversion module changing the polarization state of light in different wavelength bands. Attached Figure Description

[0038] Figure 1 This application provides a dual-band fiber Bragg grating demodulation device with a shared demodulation optical path.

[0039] Figure 2 This is a schematic diagram of the working principle of the demodulation device based on the 4f system provided in the embodiments of this application;

[0040] Figure 3 This is a schematic diagram of the polarization conversion module provided in an embodiment of this application;

[0041] Figure 4 This is a schematic diagram of the operation of the linear array detector provided in the embodiments of this application;

[0042] Figure 5 This is a schematic diagram of the optical path of the C-band and L-band polarization multiplexing scheme provided in the embodiments of this application;

[0043] Figure 6 This is a schematic diagram of the planar grating optical path for implementing C+L band multiplexing provided in an embodiment of this application.

[0044] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-wavelength division multiplexer, 2-fiber coupled collimator, 3-polarization conversion module, 31-birefringent crystal, 32-K9 glass, 33-half-wave plate, 34-cylindrical lens, 4-collimating lens, 5-dispersive element, 6-focusing lens, 7-polarization beam splitter, 8-optical supplementary element, 81-first optical supplementary element, 82-second optical supplementary element, 9-linear array detector, 91-first linear array detector, 92-second linear array detector, 10-data processing unit. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0046] like Figure 1As shown, this application provides a dual-band fiber grating demodulation device with a shared demodulation optical path for demodulating C+L band wavelengths, wherein:

[0047] Wavelength division multiplexer 1 is used to separate the C-band and L-band of the input broadband light source, and then input them to the two input channels of fiber optic coupler collimator 2 through two fiber optic output channels.

[0048] The fiber optic coupler collimator 2, typically a convex lens with a small focal length, is used to collimate the outgoing light and output it to the polarization conversion module 3 through two output fibers, thereby reducing the divergence angle and avoiding additional losses.

[0049] The polarization conversion module 3 is used to convert C-band and L-band light into two orthogonal polarization states, P-light and S-light, respectively; output the P-light and S-light to the collimating lens 4; and simultaneously control the beam waist of the output P-light and S-light to increase the demodulation spectral resolution.

[0050] Collimating lens 4, typically a cylindrical mirror, converts the P-beam and S-beam after passing through collimating lens 4 into parallel beams, which are preferably incident on dispersive element 5 with a larger beam width to enhance spectral resolution.

[0051] The dispersive element 5 is usually a grating or a prism, or a double grating structure. The prism-grating structure further enhances the dispersive ability and produces diffraction at different angles for light of different wavelengths based on the grating equation. Specifically, it directs light of different wavelengths in P light to the focusing lens 6 at different angles; and directs light of different wavelengths in S light to the focusing lens 6 at different angles.

[0052] Focusing mirror 6, typically a cylindrical mirror, is used to converge the P-light and S-light passing through polarizing beam splitter 7 onto the first linear array detector 91 and the second linear array detector 92, respectively, to compress the spot size.

[0053] The polarization beam splitter 7 is used to separate the P-beam and the S-beam so that they are respectively incident on the first linear array detector 91 and the second linear array detector 92.

[0054] The first optical supplementary element 81 and the second optical supplementary element 82 are located in front of the first linear array detector 91 and the second linear array detector 92, respectively, to compensate for aberrations, maintain the consistency of the light spots on the first linear array detector 91 and the second linear array detector 92, and further compress the light spot width.

[0055] The first linear array detector 91 and the second linear array detector 92 are used to detect the spectral data of P-light and S-light, respectively.

[0056] The data processing unit 10 is used to integrate, process, and analyze the spectral data of P-light and S-light, and to calculate parameters such as the center wavelength and bandwidth of the fiber optic grating.

[0057] The specific process of demodulating the C+L band wavelength using a dual-band fiber grating demodulation device is as follows:

[0058] The wavelength division multiplexer 1 divides the input optical signal into C-band and L-band input optical signals, and outputs them to the corresponding fiber arrays.

[0059] The optical signals output from the fiber arrays corresponding to the C-band and L-band are collimated by the fiber coupler collimator 2. The C-band light is converted into S-polarized signal light by the polarization conversion module 3, and the L-band light is converted into P-polarized signal light by the polarization conversion module 3.

[0060] After polarization conversion, the C-band and L-band optical signals are collimated by collimating lens 4 and then incident on the dispersive element 5. The dispersive element 5 demultiplexes the optical signals of different wavelengths. Dispersion of the C-band and L-band can be completed using only one dispersive element, resulting in a simple and compact structure.

[0061] In the dispersive element 5, the C-band fiber array and the L-band light are incident on the dispersive element 5 at different angles, and the exit angles of the exiting element are basically the same.

[0062] Dispersion spreads different wavelengths at different exit angles, and then the light spot is compressed through the focusing lens 6 and incident on the polarization separation element 7.

[0063] The C-band optical signal, after entering the polarization separating element, is reflected and enters the linear array detector 91. The L-band optical signal, after entering the polarization separating element, is directly projected into the linear array detector 92. An optical compensation element 8 is provided in front of the linear array detector to compensate for system aberrations and further compress the spot size. The final data processing unit 10 integrates, processes, and analyzes the C-band and L-band spectral data, and calculates parameters such as the center wavelength and bandwidth of the fiber Bragg grating.

[0064] This application's dual-band fiber grating demodulation device conforms to a 4f system, and adjusts the size of the light spots on the first and second linear array detectors by controlling the beam waist of the light emitted from the polarization conversion module. For example... Figure 2 The working principle of this application is illustrated in the diagram:

[0065] The input light in two bands is separated into its constituent wavelengths, and the spectrum of each wavelength is detected and processed by the linear array detector 9. The output beam from the polarization conversion module 3 is collimated by the collimating lens 4 and incident parallel to the dispersive element 5, which disperses the beam into its constituent wavelength channels. The dispersed light is focused onto the linear array detector 9 by the focusing lens 6, forming a strip-shaped dispersive spectrum in the effective area of ​​the linear array detector. The pixel regions of different wavelength channels correspond to pixels at different positions on the detector, thereby enabling the detection of the intensity of light in each wavelength channel. The entire system is configured to conform to a 4f system. The spot size on the linear array detector 9 is determined by the spot size of the output light from the front end of the polarization conversion module 3. By controlling the beam waist of the output light spot from the polarization conversion module 3, the spot size on the linear array detector 9 can be precisely adjusted, thereby achieving high-precision detection.

[0066] The polarization conversion module 3 is used to adjust the polarization state of the input optical signal and change the beam waist of the optical signal in the dispersion direction. Figure 3 A detailed structural diagram of polarization conversion module 3 is shown below:

[0067] The C-band optical signal is split into P-light and S-light after passing through the birefringent crystal 31. The P-light is converted into S-light after passing through the half-wave plate 33, and the polarization state of the S-light is unaffected after passing through the K9 glass 32.

[0068] After the L-band optical signal passes through the birefringent crystal 31, the P-band light passes through the K9 glass 32, and the S-band light passes through the half-wave plate 33 to be converted into P-band light.

[0069] At this point, the C-band and L-band light are converted into S-band and P-band light respectively after passing through the polarization module, achieving polarization multiplexing. The optical signal then undergoes beam waist transformation through cylindrical lens 34, and the size of the beam waist on the rear surface of the lens directly determines the beam size of the detector.

[0070] Figure 4 A detailed schematic diagram of the operation of the linear array detector 9 is shown below:

[0071] Because the polarization conversion module 3 performs a separation-focusing transformation on the light beam, perpendicular incidence cannot be achieved on the detection surface. The light beam of the target wavelength band is received through two separate branches. The pixel regions of different wavelength channels correspond to pixels at different positions on the detector, thereby enabling the detection of the light intensity of each wavelength channel.

[0072] Figure 5 Detailed optical path diagrams of C-band and L-band polarization multiplexing schemes are shown:

[0073] The beam, after passing through polarization conversion module 3, is split into two paths and finally converged in the plane by the linear array detector 9 via the 4f system. Polarization diversity reception is achieved through a shared system structure, where the C-band is transmitted via S-polarized light and the L-band is transmitted via P-polarized light.

[0074] Figure 6 A detailed schematic diagram of a planar grating for C+L band multiplexing is shown below:

[0075] By adjusting the incident angles of the two wavebands, the center wavelengths of light in the C-band and L-band are incident at different angles θ. i (θ C ,θ L The incident grating maintains the same diffraction angle at the exit θ. d This achieves the goal of a common optical path. According to the grating equation:

[0076] d sinθ i +d sinθ d =mλ

[0077] Where d is the grating constant; λ is the center wavelength of the incident light in the corresponding band; m = 1.

[0078] This application is primarily used in the field of fiber optic sensing to detect changes in fiber optic grating parameters and to invert changes in environmental factors such as temperature and stress. It can also be applied to spectral analysis, optical signal demodulation, monitoring and regulation of optical communication systems, and spectral coding.

[0079] This application's embodiments are applied to C+L band fiber Bragg grating demodulators, and can also be extended to fiber Bragg grating demodulators of any two different bands such as S+C and S+L. Furthermore, this application can be applied to dual-port input fiber Bragg grating demodulators, where the input light for different bands can be replaced with different external fiber optic interfaces.

[0080] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0081] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. "Fixed connection" refers to a connection where the relative positional relationship remains unchanged after connection. "Rotary connection" refers to a connection where the components can rotate relative to each other after connection. "Sliding connection" refers to a connection where the components can slide relative to each other after connection. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0082] Furthermore, the mathematical concepts mentioned in the embodiments of this application, such as symmetry, equality, parallelism, and perpendicularity, are limitations specific to the current technological level, rather than absolute and strict mathematical definitions. Slight deviations are permissible; approximations of symmetry, equality, parallelism, and perpendicularity are all acceptable. For example, "A and B are parallel" means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. "A and B are perpendicular" means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0083] It is understood that the various numerical designations used in the embodiments of this application are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application.

[0084] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A dual-band fiber optic grating demodulation device with a shared demodulation optical path, characterized in that, The dual-band fiber grating demodulation device includes: The polarization conversion module is used to convert incident light with wavelengths in the first band and incident light with wavelengths in the second band into first polarization state light and second polarization state light respectively before they are emitted to the collimating lens. A collimating lens is used to convert light of the first polarization state and light of the second polarization state into parallel light before it is emitted to a dispersive element. A dispersive element is used to direct light of different wavelengths in a first polarized state to a focusing lens at different angles; and to direct light of different wavelengths in a second polarized state to a focusing lens at different angles. A focusing lens is used to converge the first polarized light separated by the polarization beam splitter to the first linear array detector, and the second polarized light separated by the beam splitter to the second linear array detector. A polarization beam splitter is used to reflect light of a first polarization state to a first linear array detector and transmit light of a second polarization state to a second linear array detector. The first linear array detector is used to detect the wavelength of light in the first polarization state, and the detection range is the first band; The second linear array detector is used to detect the wavelength of light in the second polarization state, and the detection range is the second band; The polarization conversion module includes: A birefringent crystal is used to separate incident light with wavelengths in a first band into light with a first polarization state and light with a second polarization state. The light with the first polarization state exits through a first high-transmittance glass, and the light with the second polarization state exits through a first half-wave plate. It is also used to separate incident light with wavelengths in a second band into light with a second polarization state and light with a second polarization state. The light with the second polarization state exits through a second half-wave plate, and the light with the second polarization state exits through a second high-transmittance glass. The first half-wave plate is used to convert the second polarized light in the first band into the first polarized light in the first band before it is emitted to the first cylindrical lens. The first high-transmittance glass is used to allow the first polarized light of the first band to be compensated for the optical path before being emitted to the first cylindrical lens; The first cylindrical lens is used to adjust the beam waist of the first polarization state light in the first band; The second half-wave plate is used to convert the first polarized light in the second band into the second polarized light in the second band before it is emitted to the second cylindrical lens; The second high-transmittance glass is used to allow the second polarized light of the second band to be compensated for the optical path before exiting to the second cylindrical lens; The second cylindrical lens is used to adjust the beam waist of the second polarized light in the second band.

2. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The dual-band fiber grating demodulation device further includes: A wavelength division multiplexer is used to separate the light in the first band and the light in the second band of the incident broadband light and then input them into an optical fiber coupler collimator. The fiber optic coupler is used to collimate light with wavelengths in the first band and light with wavelengths in the second band, and then send them out to the polarization conversion module.

3. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The polarization conversion module is also used to adjust the beam waist of the first polarized light and the second polarized light before they are emitted.

4. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The dual-band fiber grating demodulation device conforms to the 4f system.

5. The dual-band fiber optic grating demodulation device according to claim 1 or 3, characterized in that, The dual-band fiber grating demodulation device conforms to a 4f system, and adjusts the size of the light spot on the first and second linear array detectors by controlling the beam waist of the light emitted from the polarization conversion module.

6. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The first polarized light and the second polarized light enter the dispersive element at different incident angles and exit at the same exit angle.

7. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The first polarization state and the second polarization state are orthogonal polarization states.

8. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The dual-band fiber grating demodulation device further includes: The first optical supplementary element is located in front of the first linear array detector and is used to compensate for aberrations and reduce the size of the light spot on the first linear array detector. The second optical supplementary element, located in front of the second linear array detector, is used to compensate for aberrations and reduce the size of the light spot on the second linear array detector.

9. The dual-band fiber optic grating demodulation device according to claim 1, characterized in that, The dual-band fiber grating demodulation device further includes: The data processing unit is used to calculate the center wavelength and bandwidth of the incident light based on the light intensity data of each wavelength channel detected by the first linear array detector and the second linear array detector.

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