High-symmetry large-bandwidth flexible array waveguide grating chip for fiber bragg grating demodulation system

Abstract

The invention discloses a high-symmetry large-bandwidth flexible array waveguide grating chip for a fiber bragg grating demodulation system, and belongs to the technical field of planar optical waveguide devices. The polymer optical waveguide is composed of a polymer flexible substrate layer, a polymer lower cladding layer, a polymer optical waveguide core layer and a polymer upper cladding layer, the refractive index of materials of the polymer upper cladding layer and the polymer lower cladding layer is lower than that of materials of the polymer optical waveguide core layer, and the polymer optical waveguide core layer is of an optical waveguide structure integrated by two AWGs and two MMI units. According to the invention, the defects of demodulation blind area and one-way transmission of the existing array waveguide grating in an FBG demodulation system are overcome, the wide dynamic range and high resolution demodulation of reflection wavelength are realized, the bidirectional signal input and output of left and right ports are supported, the system flexibility is improved, and in addition, the system performance is improved. Compared with an inorganic material system, the optical waveguide device prepared from a polymer material has the remarkable advantages of good flexibility, simple process, low cost, high efficiency and the like, and is suitable for a dynamic deformation environment or a biological integration scene.

Description

Technical Field

[0001] The present invention belongs to the technical field of planar optical waveguide devices, and particularly relates to a high-symmetry large-bandwidth flexible arrayed waveguide grating chip for a fiber Bragg grating (FBG) demodulation system. Background Art

[0002] As a breakthrough technology in the field of optoelectronic sensing, fiber Bragg grating sensors have significant technical advantages in distributed monitoring networks, deformation detection of industrial facilities, monitoring of oil and gas pipelines, and safety monitoring of power facilities due to their small size, strong corrosion resistance, and excellent electromagnetic interference resistance. Among them, the FBG demodulation system based on an arrayed waveguide grating (AWG), as the core device of fiber optic sensors, has been widely used in related fields.

[0003] The FBG demodulation system utilizes the powerful wavelength division multiplexing ability of the AWG chip to diffract the reflected light of the FBG into different output channels of the AWG, demodulate multiple sensing signals simultaneously, and then obtain the corresponding central wavelength of the FBG according to the intensity ratio of the output signal light of adjacent channels of the AWG chip, which has the advantages of high precision and high speed. However, due to the spectral transmission characteristics of the AWG, when the central wavelength reflected by the FBG is close to the central wavelength of the AWG channel, only one channel can output optical power, resulting in a demodulation blind area and being unable to achieve a wide dynamic range and high resolution simultaneously. In addition, the existing AWG demodulation method is unidirectional transmission, lacking flexibility, and the materials used to prepare AWG devices are mainly inorganic rigid material systems including silicon nitride, III-V compound semiconductors, and silicon-on-insulator, which limit the actual application scenarios of AWG devices in the FBG demodulation system. Summary of the Invention

[0004] Aiming at the deficiencies of unidirectional transmission and the existence of demodulation blind areas in the AWG device in the existing FBG demodulation system, the present invention proposes a high-symmetry large-bandwidth flexible arrayed waveguide grating chip for a fiber Bragg grating (FBG) demodulation system.

[0005] The present invention proposes a high-symmetry large-bandwidth flexible arrayed waveguide grating chip. This device is based on a polymer material platform and has a certain flexibility. By integrating two wavelength-independent 1×2 multimode interferometers (MMIs) and two spectrally adjacent AWGs, on the one hand, it realizes a highly symmetric structure, enabling the flexible interchange of the input and output left and right ports; on the other hand, it effectively expands the working bandwidth and eliminates the demodulation blind area problem existing in the traditional design. This device has significant application prospects.

[0006] The present invention integrates two AWGs with the same structure and two 1×2 MMI structures with the same structure. Each AWG has N output channels, and the center wavelength of each output channel of the right AWG is designed to be located between the center wavelengths of two adjacent output channels of the left AWG. During the operation of the device, the FBG sensor reflects light of a specific wavelength and inputs it from any one of the 1×2 MMIs, and then the light is evenly divided into two paths and enters the left AWG and the right AWG. According to the known mathematical relationship between the logarithm ratio of the optical intensities between adjacent output channels of the two AWGs' spectra and the center wavelength of the light reflected by the FBG sensor, the center wavelength value reflected by the sensor is demodulated. The present invention solves the problems of demodulation blind spots and unidirectional transmission defects existing in the existing arrayed waveguide gratings in the FBG demodulation system, realizes the demodulation of the reflected wavelength with a wide dynamic range and high resolution, and supports the bidirectional signal input and output of the left and right ports, significantly improving the flexibility of the system. In addition, the optical waveguide device prepared by using polymer materials has significant advantages such as good flexibility, simple process, low cost, and high efficiency compared with the inorganic material system, and is particularly suitable for dynamic deformation environments or bio-integration scenarios. The device shows good flexibility and flexibility during operation, effectively solving the problems of narrow dynamic detection range and insufficient accuracy in the existing technology, and has broad practical application prospects.

[0007] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0008] A high-symmetry large-bandwidth flexible arrayed waveguide grating chip for an FBG demodulation system according to the present invention is shown in the attached Figure 1 (corresponding to Figure 2 the cross-sectional view A-A' in

[0009] The structure of the polymer waveguide core layer 43 is shown in the attached Figure 2As shown, it is composed of a first 1×2 MMI unit 8, a second 1×2 MMI unit 38, a left AWG, and a right AWG. The size parameters and structures of the first 1×2 MMI unit 8 and the second 1×2 MMI unit 38 are the same and are symmetrically arranged front and back. The size parameters and structures of the left AWG and the right AWG are the same and are symmetrically arranged left and right with respect to the first 1×2 MMI unit 8 and the second 1×2 MMI unit 38, and the whole device has central symmetry. The first 1×2 MMI unit 8 is composed of a first 1×2 MMI unit input single-mode straight waveguide 1, a first 1×2 MMI unit input linear tapered waveguide 2, a first 1×2 MMI unit multimode planar waveguide 3, a first 1×2 MMI unit first output linear tapered waveguide 4 and a first 1×2 MMI unit second output linear tapered waveguide 6 with the same size parameters and structures, and a first 1×2 MMI unit first output bent waveguide 5 and a first 1×2 MMI unit second output bent waveguide 7 with the same size parameters and structures. The second 1×2 MMI unit 38 is composed of a second 1×2 MMI unit input single-mode straight waveguide 31, a second 1×2 MMI unit input linear tapered waveguide 32, a second 1×2 MMI unit multimode planar waveguide 33, a second 1×2 MMI unit first output linear tapered waveguide 34 and a second 1×2 MMI unit second output linear tapered waveguide 36 with the same size parameters and structures, and a second 1×2 MMI unit first output bent waveguide 35 and a second 1×2 MMI unit second output bent waveguide 37 with the same size parameters and structures. The left AWG is composed of a first output waveguide array 11 and a second output waveguide array 27 with the same size parameters and structures and a waveguide number of N, a first linear tapered waveguide array 13 and a second linear tapered waveguide array 25 with the same size parameters and structures and a waveguide number of N, a first planar waveguide 15 and a second planar waveguide 23 with the same size parameters, a third linear tapered waveguide array 17 and a fourth linear tapered waveguide array 21 with the same size parameters and structures and a waveguide number of n > N, and a first bent waveguide array 19 with a waveguide number of n > N. The first output waveguide array 11, the first linear tapered waveguide array 13, the first planar waveguide 15, the third linear tapered waveguide array 17, the first bent waveguide array 19, the fourth linear tapered waveguide array 21, the second planar waveguide 23, the second linear tapered waveguide array 25, and the second output waveguide array 27 are connected in sequence;The right AWG consists of a third output waveguide array 12 and a fourth output waveguide array 28 with the same size parameters and structure and a wave derivative of N, a fifth linear tapered waveguide array 14 and a sixth linear tapered waveguide array 26 with the same size parameters and structure and a wave derivative of N, a third planar waveguide 16 and a fourth planar waveguide 24 with the same size parameters and structure, a seventh linear tapered waveguide array 18 and an eighth linear tapered waveguide array 22 with the same size parameters and structure and a wave derivative of n > N, and a second bent waveguide array 20 with a wave derivative of n > N. The third output waveguide array 12, the fifth linear tapered waveguide array 14, the third planar waveguide 16, the seventh linear tapered waveguide array 18, the second bent waveguide array 20, the eighth linear tapered waveguide array 22, the fourth planar waveguide 24, the sixth linear tapered waveguide array 26, and the fourth output waveguide array 28 are connected in sequence. The first 1×2 MMI unit 8 is connected to the first planar waveguide 15 of the left AWG through the first bent waveguide 9 and to the third planar waveguide 16 of the right AWG through the second bent waveguide 10. The second 1×2 MMI unit 38 is connected to the second planar waveguide 23 of the left AWG through the third bent waveguide 39 and to the fourth planar waveguide 24 of the right AWG through the fourth bent waveguide 40. The input single-mode straight waveguide 1 of the first 1×2 MMI unit and the input single-mode straight waveguide 31 of the second 1×2 MMI unit form the input ports of the high-symmetry large-bandwidth flexible arrayed waveguide grating chip. The N waveguides in the first output waveguide array 11, the N waveguides in the second output waveguide array 27, the N waveguides in the third output waveguide array 12, and the N waveguides in the fourth output waveguide array 28 form the output ports of the high-symmetry large-bandwidth flexible arrayed waveguide grating chip, where N is an integer greater than or equal to 4.

[0010] Among them, the width W of a single waveguide in the input single-mode straight waveguide 1 of the first 1×2 MMI unit, the first output bent waveguide 5 of the first 1×2 MMI unit, the second output bent waveguide 7 of the first 1×2 MMI unit, the input single-mode straight waveguide 31 of the second 1×2 MMI unit, the first output bent waveguide 35 of the second 1×2 MMI unit, the second output bent waveguide 37 of the second 1×2 MMI unit, the first bent waveguide 9, the second bent waveguide 10, the third bent waveguide 39, the fourth bent waveguide 40, and the first output waveguide array 11, the second output waveguide array 27, the third output waveguide array 12, the fourth output waveguide array 28, the first bent waveguide array 19, and the second bent waveguide array 20 1 is the same, which is 2 - 10 μm. The array length L of the first output waveguide array 11, the second output waveguide array 27, the third output waveguide array 12, and the fourth output waveguide array 28 3 is the same, which is 1000 - 8000 μm, and the array width W 7 is the same, which is 500 - 8000 μm. The spacing W between single waveguides in the array 2The same is 10 to 150 μm; the lengths L of the individual linear tapered waveguides in the first 1×2 MMI unit input linear tapered waveguide 2, the first 1×2 MMI unit first output linear tapered waveguide 4, the first 1×2 MMI unit second output linear tapered waveguide 6, the second 1×2 MMI unit input linear tapered waveguide 32, the second 1×2 MMI unit first output linear tapered waveguide 34, the second 1×2 MMI unit second output linear tapered waveguide 36, and the first linear tapered waveguide array 13, the second linear tapered waveguide array 25, the third linear tapered waveguide array 17, the fourth linear tapered waveguide array 21, the fifth linear tapered waveguide array 14, the sixth linear tapered waveguide array 26, the seventh linear tapered waveguide array 18, and the eighth linear tapered waveguide array 22 2 The same is 100 to 500 μm, and the narrow port width W of the individual linear tapered waveguides 1 The same is 2 to 10 μm, and the wide port width W 3 The same is 4 to 20 μm; the wide ports of the linear tapered waveguides are at the joints of the first 1×2 MMI unit input linear tapered waveguide 2, the first 1×2 MMI unit first output linear tapered waveguide 4, the first 1×2 MMI unit second output linear tapered waveguide 6, the second 1×2 MMI unit input linear tapered waveguide 32, the second 1×2 MMI unit first output linear tapered waveguide 34, the second 1×2 MMI unit second output linear tapered waveguide 36 and the first 1×2 MMI unit multimode slab waveguide 3, the second 1×2 MMI unit multimode slab waveguide 33; the wide ports of the linear tapered waveguides are at the joints of the first linear tapered waveguide array 13, the second linear tapered waveguide array 25, the third linear tapered waveguide array 17, the fourth linear tapered waveguide array 21, the fifth linear tapered waveguide array 14, the sixth linear tapered waveguide array 26, the seventh linear tapered waveguide array 18, the eighth linear tapered waveguide array 22 and the first slab waveguide 15, the second slab waveguide 23, the third slab waveguide 16, the fourth slab waveguide 24 of the slab waveguide, and W 3 >W 1 ; the center spacing W of the wide ports of adjacent linear tapered waveguides in the first linear tapered waveguide array 13, the second linear tapered waveguide array 25, the third linear tapered waveguide array 17, the fourth linear tapered waveguide array 21, the fifth linear tapered waveguide array 14, the sixth linear tapered waveguide array 26, the seventh linear tapered waveguide array 18, the eighth linear tapered waveguide array 22 6 The same, is 4 to 30 μm, and W 6 ≥W 3 ; the widths W of the first 1×2 MMI unit multimode slab waveguide 3 and the second 1×2 MMI unit multimode slab waveguide 33 5 The same is 25 to 70 μm, and the length L 1The same is 450 to 1500 μm; the waveguide center distance between the first output linear tapered waveguide 4 and the second output linear tapered waveguide 6 of the first 1×2 MMI unit, and the waveguide center distance W between the first output linear tapered waveguide 34 and the second output linear tapered waveguide 36 of the second 1×2 MMI unit 4 The same is 10 to 20 μm; the Rowland circle diameters R of the first slab waveguide 15, the second slab waveguide 23, the third slab waveguide 16, and the fourth slab waveguide 24 are the same, being 500 to 8000 μm; the channel input angle formed by the extension line of the waveguide center at the connection of the first curved waveguide 9 and the first slab waveguide 15 and the center line of the first slab waveguide 15, and the channel input angle formed by the extension line of the waveguide center at the connection of the third curved waveguide 39 and the second slab waveguide 23 and the center line of the second slab waveguide 23 are the same as θ 1 , and the channel input angle formed by the extension line of the waveguide center at the connection of the second curved waveguide 10 and the third slab waveguide 16 and the center line of the third slab waveguide 16, and the channel input angle formed by the extension line of the waveguide center at the connection of the fourth curved waveguide 40 and the fourth slab waveguide 24 and the center line of the fourth slab waveguide 24 are the same as θ 2 , θ 1 is not equal to θ 2 , and (where m is the grating diffraction order, n s is the effective refractive index of the slab waveguide, and Δλ is the center wavelength difference between adjacent output channels of the AWG); the length L of the shortest curved waveguide in the first curved waveguide array 19 and the second curved waveguide array 20 4 is the same, being 1000 to 5000 μm, and the length L of the longest curved waveguide 5 is the same, being 1300 to 30000 μm; the length difference ΔL between adjacent waveguides is the same, being 10 to 200 μm, and L 5 = L 4 +(n - 1)×ΔL. The length of all waveguides is defined as the projection length of the waveguide along the center connection line of the input single-mode straight waveguide 1 of the first 1×2 MMI unit and the input single-mode straight waveguide 31 of the second 1×2 MMI unit

[0011] A high-symmetry large-bandwidth flexible arrayed waveguide grating chip for an FBG demodulation system according to the present invention. When the single-mode straight waveguide 1 of the first 1×2 MMI unit is used as the input channel for the FBG reflected light, and the N waveguides in the second output waveguide array 27 and the N waveguides in the fourth output waveguide array 28 are used as the output channels, after the signal light passes through the input linear tapered waveguide 2 of the first 1×2 MMI unit and is input into the wavelength-independent first 1×2 MMI unit multimode slab waveguide 3, it is evenly divided into two identical signal lights, which are respectively input into the first slab waveguide 15 of the left AWG by the first output linear tapered waveguide 4 of the first 1×2 MMI unit, the first output bent waveguide 5 of the first 1×2 MMI unit, and the first bent waveguide 9, and are input into the third slab waveguide 16 of the right AWG by the second output linear tapered waveguide 6 of the first 1×2 MMI unit, the second output bent waveguide 7 of the first 1×2 MMI unit, and the second bent waveguide 10. According to the grating formula (1), due to the designed difference in the incident angles θ i i.e., θ 1 , θ 2 , the central wavelengths of the output channels that are not adjacent in space in the left AWG and the right AWG are close, forming adjacent spectra, that is, the central wavelength of each output channel in the fourth output waveguide array 28 is correspondingly located between the central wavelengths of the two output channels in the second output waveguide array 27 in the spectrum. When the central wavelength of the FBG reflected signal light to be demodulated is located between the central wavelengths of any two adjacent output channels in the second output waveguide array 27 of the left AWG, different from the case where there is only one channel output in a single AWG, there will definitely be two signal lights with different light intensities detected and output respectively in any output channel in the second output waveguide array 27 of the left AWG and the corresponding output channel in the fourth output waveguide array 28 of the right AWG. Then, according to the relationship between the logarithm ratio of the light intensities of the adjacent spectra channels output by the demodulation formula (2) and the central wavelength of the FBG reflected signal light, the wavelength λ FBG of the FBG reflected light can be obtained, where Δλ is the central wavelength interval between adjacent spectra channels, Δλ FBG is the full width at half maximum of the FBG reflected light. When the central wavelength of the FBG reflected signal light is within the range of the central wavelength of any output waveguide channel in the second output waveguide array 27 of the left AWG and the central wavelength of the corresponding adjacent spectra output waveguide channel in the fourth output waveguide array 28 of the right AWG in the output spectrum, P i in the demodulation formula (2) is the signal light power output by the corresponding output waveguide channel in the second output waveguide array 27 of the left AWG, Δλ i and λ i are respectively the full width at half maximum and the central wavelength of the spectrum of this channel, P i+1 is the signal light power output by the corresponding adjacent spectra output waveguide channel in the fourth output waveguide array 28 of the right AWG, and λ i+1is the central wavelength of the channel spectrum. When the central wavelength of the FBG reflected signal light is within the range of the central wavelength of any output waveguide channel in the fourth output waveguide array 28 of the right AWG and the central wavelength of the corresponding spectral adjacent output waveguide channel in the second output waveguide array 27 of the left AWG, P in the demodulation formula (2) i is the optical power of the signal light output from the corresponding output waveguide channel in the fourth output waveguide array 28 of the right AWG, Δλ i and λ i are the full width at half maximum and the central wavelength of the channel spectrum respectively, P i+1 is the optical power of the signal light output from the corresponding spectral adjacent output waveguide channel in the second output waveguide array 27 of the left AWG, λ i+1 is the central wavelength of the channel spectrum. Therefore, when the device works, the logarithmic ratio of the optical intensities of the spectral adjacent channels in the demodulation function is linear with the central wavelength of the FBG reflected signal light and is continuous in the spectrum, with high detection resolution, solving the problems of demodulation blind area and narrow dynamic detection range existing in the traditional single AWG. When the single-mode straight waveguide 31 at the input of the second 1×2 MMI unit is used as the input channel of the FBG reflected light and the N waveguides in the first output waveguide array 11 and the N waveguides in the third output waveguide array 12 are used as the output channels, the working principle is the same as above and can be connected with both ends swapped.

[0012] n s W 6 sinθ i +n s W 6 sinθ o +n c ΔL=mλ (1)

[0013]

[0014] where n s is the effective refractive index of the mode of the AWG array waveguide, n c is the effective refractive index of the mode of the AWG planar waveguide, θ i is the incident angle of the signal light, θ o is the exit angle of the signal light.

[0015] In the high-symmetry large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system described in the present invention, the left and right AWGs are flat or Gaussian arrayed waveguide gratings, and the two 1×2 MMI units are broadband wavelength-independent 1×2 uniform optical splitters.

[0016] A highly symmetric large-bandwidth flexible arrayed waveguide grating chip for an FBG demodulation system according to the present invention. The material of the polymer flexible substrate 41 is polymer PDMS, and the thickness is 0.5 to 1 mm. The materials of the polymer lower cladding 42 and the polymer upper cladding 44 are any one of a series of polymer materials with good transparency, including fluorinated bisphenol A phenolic resin cladding (F-SU8Clad), polyethylene (PE), polystyrene (PS), polycarbonate (PC), polymethyl methacrylate (PMMA), P(MMA-co-GMA), and EpoClad (in the same device, the material of the polymer upper cladding 44 above the polymer core layer 33 and the material of the polymer lower cladding 42 can be the same or different), and the thickness is 5 to 15 μm (the thickness of the polymer upper cladding 44 above the polymer core layer 33 and the thickness of the polymer lower cladding 42 can be the same or different). The material of the polymer core layer 43 is a series of ultraviolet direct writing photoresist materials with a refractive index greater than that of the polymer cladding material, including fluorinated bisphenol A phenolic resin core (F-SU8Core), SU-8 2002, SU-8 2005, and EpoCore, and the thickness is 3 to 8 μm.

[0017] Compared with the existing device structure and manufacturing technology, the beneficial effects of the present invention are as follows:

[0018] (1) The present invention designs a wavelength-independent 1×2 MMI waveguide structure at the input end, so that the input signal light is evenly divided into two uniform signal lights. At the same time, the designed tapered waveguide connection reduces the device loss. More importantly, the optical fields transmitted in the MMI and tapered region waveguides at the input end undergo mode integration, thereby making the output spectrum of the AWG more flattened, significantly broadening the output spectral bandwidth, reducing the crosstalk between channels, and obtaining a more ideal Gaussian spectral response, covering a wider wavelength demodulation range;

[0019] (2) The present invention uses two AWGs with exactly the same structural parameters. By designing different channel input angles θ 1 and θ 2 of the left and right AWGs, the central wavelengths of the output channels of the two AWGs are different, and the output channel spectra are adjacent, forming a continuous spectral band, so that at least two output channels have effective signals at any FBG reflection light wavelength, and the peak position can be controlled by controlling the input angles θ 1 and θ 2 to achieve. It has both the high speed and high precision characteristics of the traditional AWG demodulation method and the working flexibility, effectively solves the problem of the existence of demodulation blind areas, realizes continuous demodulation, and greatly improves the dynamic demodulation range of FBG sensors;

[0020] (3) Compared with the AWG for wavelength demodulation of traditional FBG sensors, the input / output ends of the demodulation signal of the present invention can be interchangeably connected at the left and right ports, with reciprocity, greatly improving the flexibility of use; at the same time, based on the polymer material platform, the preparation process is simple, the cost is low, and the device has good flexibility, can achieve ultra-thinness and certain bending deformation, is not easy to break under repeated bending, and can still maintain the optical transmission stability under dynamic deformation, having significant advantages in dynamic deformation environments or bio-integration scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. is a schematic cross-sectional structure diagram of a high-symmetry large-bandwidth flexible arrayed waveguide grating chip for an FBG demodulation system according to the present invention (corresponding to Figure 2 the cross-sectional view A-A' in

[0022] Figure 2 FIG. is a schematic core layer structure diagram of a high-symmetry large-bandwidth flexible arrayed waveguide grating chip for an FBG demodulation system according to the present invention;

[0023] Figure 3 FIG. is a single-mode transmission optical field diagram of the input waveguide cross-section of the device described in Example 1 (corresponding to the position of B-B' in Figure 2 the attached

[0024] Figure 4 (a) FIG. is a schematic diagram of a 1×2 MMI structure according to the present invention; Figure 4 (b) FIG. is an output optical power diagram of the two output channels (CH1 and CH2, i.e., the first output linear tapered waveguide 4 and the second output linear tapered waveguide 6 of the first 1×2 MMI unit) of the first 1×2 MMI according to the present invention in the O band;

[0025] Figure 5 (a) FIG. is a schematic diagram of the spectral distribution of the device according to the present invention in the O band; Figure 5 (b) FIG. is a process curve of the device for FBG wavelength demodulation by using adjacent channels of the central wavelength (O 1 、O 9 、O 2 、O 10 ); Figure 5 (c) FIG. is a relationship curve diagram between the logarithmic ratio of the output optical power of adjacent channels of the device center wavelength (O 1 、O 9 、O 2 、O 10 ) and the FBG reflection wavelength;

[0026] Figure 6 FIG. is a process flow chart of the device preparation in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be introduced more clearly and perfectly in conjunction with the accompanying drawings. It should be noted that those skilled in the art will have a deeper understanding of the advantages and functions of the present invention under this description. However, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0028] Embodiment 1:

[0029] In this embodiment, the selected polymer flexible substrate 41 is a PDMS polymer flexible substrate with a thickness of 0.5 mm.

[0030] In this embodiment, the polymer upper cladding 44 (the thickness of the polymer upper cladding above the polymer waveguide core layer 43) and the polymer lower cladding 42 of the device are F-SU8Clad with a thickness of 6 μm (refractive index n = 1.4942 @ 1310 nm).

[0031] In this embodiment, the polymer waveguide core layer 43 of the device is F-SU8Core with a thickness of 3 μm and a width (W 1 ) of 3 μm (refractive index n = 1.515 @ 1310 nm).

[0032] In this embodiment, the demodulation signal band is selected as the O band (1260 nm - 1360 nm).

[0033] In this embodiment, the optical field diagram of the highly symmetric large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system at the input waveguide (corresponding to the waveguide cross-section at the B-B' position in the attached Figure 2 figure) is simulated by COMSOL Mutiphysics software. To ensure that the signal light for demodulation is input into the chip in the fundamental mode, as shown in the attached Figure 3 figure, the simulated structural dimensions of the polymer waveguide core layer of the designed device should be 3 μm × 3 μm. At this size, the signal light can achieve low-loss single-mode transmission.

[0034] As shown in the attached Figure 4 figure, in this embodiment, a 1×2 MMI device independent of the O-band wavelength in the highly symmetric large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system is simulated and designed by Rsoft software. To better improve the bandwidth of the AWG and obtain a more ideal Gaussian spectral response, as shown in the attached Figure 4 (a) and (b), the width W 3 of the linear tapered waveguide wide port is designed and optimized to be 6 μm in Rsoft software, and the structural length L 1 of the multimode interference region of the MMI device is 28.1 μm, and the width W 5is 520.0 μm, and the center distance W between the one-to-two output waveguides 4 When it is 15.1 μm, the 1×2 MMI device has the lowest transmission loss, the signal optical powers output by the two channels are consistent, and the transmission characteristics within the O band are independent of wavelength.

[0035] In this embodiment, for the high-symmetry large-bandwidth flexible arrayed waveguide grating chip structure for the FBG demodulation system, the number of waveguides N in the first output waveguide array 11, the second output waveguide array 27, the third output waveguide array 12, and the fourth output waveguide array 28 is 8, the number of bent waveguides n in the first bent waveguide array 19 and the second bent waveguide array 20 is 40, the grating diffraction order m is 41, the center wavelength difference Δλ between adjacent output channels of the AWG is 1.6 nm, the width W of a single waveguide in the input single-mode straight waveguide 1 of the first 1×2 MMI unit, the first output bent waveguide 5 of the first 1×2 MMI unit, the second output bent waveguide 7 of the first 1×2 MMI unit, the input single-mode straight waveguide 31 of the second 1×2 MMI unit, the first output bent waveguide 35 of the second 1×2 MMI unit, the second output bent waveguide 37 of the second 1×2 MMI unit, the first bent waveguide 9, the second bent waveguide 10, the third bent waveguide 39, the fourth bent waveguide 40, and the first output waveguide array 11, the second output waveguide array 27, the third output waveguide array 12, the fourth output waveguide array 28, the first bent waveguide array 19, and the second bent waveguide array 20 1 is 3 μm; the array length L of the first output waveguide array 11, the second output waveguide array 27, the third output waveguide array 12, and the fourth output waveguide array 28 3 is 1500 μm, and the array width W 7 is 3500 μm. For the convenience of FA array coupling, the distance W between waveguides in the array 2 is 127 μm; the length L of a single linear tapered waveguide in the input linear tapered waveguide 2 of the first 1×2 MMI unit, the first output linear tapered waveguide 4 of the first 1×2 MMI unit, the second output linear tapered waveguide 6 of the first 1×2 MMI unit, the input linear tapered waveguide 32 of the second 1×2 MMI unit, the first output linear tapered waveguide 34 of the second 1×2 MMI unit, the second output linear tapered waveguide 36 of the second 1×2 MMI unit, and the first linear tapered waveguide array 13, the second linear tapered waveguide array 25, the third linear tapered waveguide array 17, the fourth linear tapered waveguide array 21, the fifth linear tapered waveguide array 14, the sixth linear tapered waveguide array 26, the seventh linear tapered waveguide array 18, and the eighth linear tapered waveguide array 22 2 is 300 μm, and the narrow-port width W of a single linear tapered waveguide 1 is 3 μm, and the wide-port width W 3is 6 μm; the center-to-center spacing W of adjacent linear tapered waveguides in the first linear tapered waveguide array 13, the second linear tapered waveguide array 25, the third linear tapered waveguide array 17, the fourth linear tapered waveguide array 21, the fifth linear tapered waveguide array 14, the sixth linear tapered waveguide array 26, the seventh linear tapered waveguide array 18, and the eighth linear tapered waveguide array 22 6 is 6 μm; the width W of the first 1×2 MMI unit multimode planar waveguide 3 and the second 1×2 MMI unit multimode planar waveguide 33 5 is 28.1 μm, and the length L 1 is 520 μm; the waveguide center-to-center spacing between the first output linear tapered waveguide 4 and the second output linear tapered waveguide 6 of the first 1×2 MMI unit, and the waveguide center-to-center spacing between the first output linear tapered waveguide 34 and the second output linear tapered waveguide 36 of the second 1×2 MMI unit W 4 is 15.1 μm; the Rowland circle diameter length R of the first planar waveguide 15, the second planar waveguide 23, the third planar waveguide 16, and the fourth planar waveguide 24 is 1150 μm; the channel input angle formed by the waveguide center extension line at the connection of the first curved waveguide 9 and the first planar waveguide 15 and the center line of the first planar waveguide 15, and the channel input angle θ formed by the waveguide center extension line at the connection of the third curved waveguide 39 and the second planar waveguide 23 and the center line of the second planar waveguide 23 1 is 16.3°, the channel input angle formed by the waveguide center extension line at the connection of the second curved waveguide 10 and the third planar waveguide 16 and the center line of the third planar waveguide 16, and the channel input angle θ formed by the waveguide center extension line at the connection of the fourth curved waveguide 40 and the fourth planar waveguide 24 and the center line of the fourth planar waveguide 24 2 is 16.9°, the total length L of the shortest curved waveguides in the first curved waveguide array 19 and the second curved waveguide array 20 4 is 1000 μm, and the total length L of the longest curved waveguides 5 is 2392.3 μm, and the length difference ΔL between adjacent waveguides is the same at 35.7 μm.

[0036] In this embodiment, the high-symmetry large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system has a transmission spectrum in the O band as shown in the appendix Figure 5As shown in (a), the solid and dashed lines respectively represent the upper and lower output channel spectra. It can be seen that the maximum insertion loss of the device is about -4 dB, the wavelength interval between single AWG channels is 1.6 nm, and the 1×2 MMI device and linear tapered waveguide design make the spectrum of the AWG more flat-topped, increase the bandwidth, and reduce the crosstalk between adjacent channels in the single AWG space. The crosstalk < -27 dB. At the same time, it can be seen that at any demodulation wavelength, there are effective output signals of two output channels, and there is no demodulation blind area. As attached Figure 5 As shown in (b), assume that the wavelength of the FBG reflected light is λ shown in the figure FBG , at this time, input the FBG reflected light into the arrayed waveguide grating of this embodiment. At the output end of the device, channels O 1 and O 9 , two effective signals with optical powers of P 1 and P 9 can be detected. Then, according to the linear relationship between the logarithm ratio of O 1 and O 9 and λ FBG in the demodulation formula (2) , λ FBG can be demodulated. Similarly, λ FBG can be demodulated at any position in the spectrum in attachment Figure 5 (b). As shown in attachment Figure 5 (c), the calculation lists the linear relationships between the wavelength ranges of λ FBG 1.3048 - 1.3056, 1.3056 - 1.3064, 1.3064 - 1.3072, 1.3072 - 1.3082 and respectively, that is, the demodulation function. It can be seen that continuous demodulation can be achieved with high demodulation accuracy. At the same time, when the input and output of the left and right ports are interchanged, the working effect is the same.

[0037] Embodiment 2:

[0038] The preparation method of the high-symmetry large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system described in this embodiment is as shown in attachment Figure 6 and is specifically described as follows:

[0039] A. Clean the PDMS polymer flexible substrate 41: Perform ultrasonic cleaning on the polymer flexible substrate with acetone solution for 15 min; then use a cotton ball soaked with acetone to wipe the surface of the PDMS polymer flexible substrate in a single direction for four rounds, and then use a cotton ball soaked with ethanol to repeat the above wiping process to remove acetone residues; after multi-channel rinsing with deionized water, use nitrogen purging technology to achieve surface dehydration; transfer the clean polymer flexible substrate to a constant temperature oven for drying treatment (temperature 120 °C, time 30 min); finally, perform plasma surface treatment for 90 s;

[0040] B. Spin-coating the F-SU8 Clad polymer lower cladding 42: On the surface of the treated PDMS polymer flexible substrate, use the spin-coating process to prepare an F-SU8 thin film. Select a rotation speed of 2500 r / min and a time of 20 s. Then perform pre-baking, with the temperature / time being: 60°C / 5 min, 90°C / 10 min, 120°C / 10 min, to volatilize the organic solvent, and wait for it to cool naturally to room temperature. After cooling to room temperature, expose it to ultraviolet light with a wavelength of 350 - 400 nm for 110 s, and then perform post-baking at 60°C / 5 min, 90°C / 10 min, 120°C / 10 min, and wait for it to cool naturally to obtain an F-SU8 Clad polymer lower cladding with a thickness of 5 μm. Finally, perform plasma surface treatment for 90 s;

[0041] C. Spin-coating the F-SU8 Core core layer film 43’: On the surface of the treated polymer lower cladding F-SU8 Clad film, use the spin-coating process to prepare an F-SU8 core layer film. Select a rotation speed of 3000 r / min and a time of 20 s. Then perform baking with the temperature / time being: 60°C / 5 min, 90°C / 10 min, 120°C / 10 min to volatilize the organic solvent, and then wait for it to cool naturally to room temperature to obtain a negative F-SU8 Core core layer film 43’ with a thickness of 3 μm;

[0042] D. Lithography of the core layer F-SU8 Core film 43’: Cover the designed device structure (corresponding to the attached Figure 2 ) lithography mask 45 (the structure is complementary to the prepared core layer structure) on the negative F-SU8 Core film and closely adhere it to its surface. Perform ultraviolet light exposure with a wavelength of 350 - 400 nm for 111 s through an ultraviolet lithography machine. After exposure, perform baking with the temperature / time being: 120°C / 10 min, and then cool naturally to room temperature;

[0043] E. Development of the core layer F-SU8 Core core layer 43 structure: Use the developer PGMEA for wet etching to etch away the unexposed core layer film, obtaining a clearly visible device polymer waveguide core layer F-SU8 Core structure morphology. Then wash the surface developer with isopropyl alcohol solution, and then wash the surface isopropyl alcohol solution with deionized water and dry it with nitrogen. Then perform baking with the temperature / time being: 120°C / 10 min to harden the film, and then wait for it to cool naturally to room temperature to complete the preparation of the polymer waveguide core layer F-SU8 Core structure 43. Finally, perform plasma surface treatment for 120 s;

[0044] F. Spin-coating the F-SU8 Clad polymer upper cladding 44: On the surface of the prepared polymer waveguide core layer F-SU8 Core structure 43, the F-SU8 Clad polymer upper cladding is prepared by spin-coating. The rotation speed is selected as 2500 r / min and the time is 20 s. Then pre-bake, the temperature / time is: 60 °C / 5 min, 90 °C / 10 min, 120 °C / 10 min to volatilize the organic solvent, and then wait for it to cool naturally to room temperature. After cooling to room temperature, use a lithography machine to perform ultraviolet light blank exposure with a wavelength of 350 - 400 nm for 110 s, and then perform post-bake and film hardening at 60 °C / 5 min, 90 °C / 10 min, 120 °C / 10 min, and wait for natural cooling to obtain a 5-μm-thick F-SU8 Clad polymer upper cladding; finally, obtain a high-symmetry large-bandwidth flexible arrayed waveguide grating chip for the FBG demodulation system described in the present invention.

Claims

1. A highly symmetrical, large-bandwidth flexible arrayed waveguide grating chip for FBG demodulation system, characterized by: From bottom to top, it is composed of a polymer flexible substrate (41), a polymer lower cladding (42), a polymer waveguide core layer (43) and a polymer upper cladding (44); the polymer waveguide core layer (43) and the polymer upper cladding (44) are located together on the polymer lower cladding (42), and the polymer waveguide core layer (43) is completely covered in the polymer upper cladding (44); the effective refractive index of the polymer waveguide core layer is higher than the effective refractive index of the polymer upper cladding and the polymer lower cladding; the polymer waveguide core layer (43) is composed of a first 1×2 MMI unit (8), a second 1×2 MMI unit (38), a left AWG and a right AWG; the first 1×2 MMI unit (8) and the second 1×2 MMI unit (38) have the same size parameters and structure and are symmetrically arranged front to back; the left AWG and the right AWG have the same size parameters and structure and are symmetrically arranged with respect to the first 1×2 MMI unit (8) and the second 1×2 The MMI unit (38) is arranged symmetrically on the left and right, and the whole device has central symmetry; the left AWG and the right AWG are flat or Gaussian waveguide gratings, and the two 1×2 MMI units are wide-band wavelength-independent one-to-two uniform optical splitters; the first 1×2 MMI unit (8) is composed of a first 1×2 MMI unit input single-mode straight waveguide (1), a first 1×2 MMI unit input linear tapered waveguide (2), a first 1×2 MMI unit multimode planar waveguide (3), a first 1×2 MMI unit first output linear tapered waveguide (4) and a first 1×2 MMI unit second output linear tapered waveguide (6) having the same size parameters and structure, a first 1×2 MMI unit first output curved waveguide (5) and a first 1×2 MMI unit second output curved waveguide (7) having the same size parameters and structure; the second 1×2 MMI unit (38) is composed of a second 1×2 MMI unit input single-mode straight waveguide (31), a second 1×2 MMI unit input linear tapered waveguide (2), a first 1×2 MMI unit multimode planar waveguide (3), and a first 1×2 MMI unit first output linear tapered waveguide (4) and a first 1×2 MMI unit second output linear tapered waveguide (6) having the same size parameters and structure. The invention is composed of an MMI unit input linear tapered waveguide (32), a second 1×2 MMI unit multimode planar waveguide (33), a second 1×2 MMI unit first output linear tapered waveguide (34) and a second 1×2 MMI unit second output linear tapered waveguide (36) having the same size parameters and structure, a second 1×2 MMI unit first output curved waveguide (35) and a second 1×2 MMI unit second output curved waveguide (37) having the same size parameters and structure;The left AWG is composed of a first output waveguide array (11) and a second output waveguide array (27) having the same size parameters and structure and a waveguide number of N, a first linear tapered waveguide array (13) and a second linear tapered waveguide array (25) having the same size parameters and structure and a waveguide number of N, a first slab waveguide (15) and a second slab waveguide (23) having the same size parameters and structure, a third linear tapered waveguide array (17) and a fourth linear tapered waveguide array (21) having the same size parameters and structure and a waveguide number of n>N, and a first curved waveguide array (19) having a waveguide number of n>N. The first output waveguide array (11), the first linear tapered waveguide array (13), the first slab waveguide (15), the third linear tapered waveguide array (17), the first curved waveguide array (19), the fourth linear tapered waveguide array (21), the second slab waveguide (23), the second linear tapered waveguide array (25) and the second output waveguide array (27) are connected in sequence; the right AWG is composed of a first output waveguide array (11), a first linear tapered waveguide array (13), a first slab waveguide (15), a third linear tapered waveguide array (17), a first curved waveguide array (19), a fourth linear tapered waveguide array (21), a second slab waveguide (23), a second linear tapered waveguide array (25) and a second output waveguide array (27) are connected in sequence; The WG is composed of a third output waveguide array (12) and a fourth output waveguide array (28) having the same size parameters and structure and a waveguide number of N, a fifth linear tapered waveguide array (14) and a sixth linear tapered waveguide array (26) having the same size parameters and structure and a waveguide number of N, a third slab waveguide (16) and a fourth slab waveguide (24) having the same size parameters and structure, a seventh linear tapered waveguide array (18) and an eighth linear tapered waveguide array (22) having the same size parameters and structure and a waveguide number of n>N, and a second curved waveguide array (20) having a waveguide number of n>N. The third output waveguide array (12), the fifth linear tapered waveguide array (14), the third slab waveguide (16), the seventh linear tapered waveguide array (18), the second curved waveguide array (20), the eighth linear tapered waveguide array (22), the fourth slab waveguide (24), the sixth linear tapered waveguide array (26) and the fourth output waveguide array (28) are connected in sequence; a first 1×2 The MMI unit (8) is connected to the first slab waveguide (15) of the left AWG through the first curved waveguide (9), and is connected to the third slab waveguide (16) of the right AWG through the second curved waveguide (10); the second 1×2 MMI unit (38) is connected to the second slab waveguide (23) of the left AWG through the third curved waveguide (39), and is connected to the fourth slab waveguide (24) of the right AWG through the fourth curved waveguide (40); the first 1×2 MMI unit input single-mode straight waveguide (1) and the second 1×2 MMI unit input single-mode straight waveguide (31) constitute an input port of a high-symmetry large-bandwidth flexible array waveguide grating chip, and the N waveguides in the first output waveguide array (11), the N waveguides in the second output waveguide array (27), the N waveguides in the third output waveguide array (12), and the N waveguides in the fourth output waveguide array (28) constitute an output port of the high-symmetry large-bandwidth flexible array waveguide grating chip, where N is an integer greater than or equal to 4.; 2. A highly symmetrical, large bandwidth flexible arrayed waveguide grating chip for a FBG demodulation system as claimed in claim 1, characterized in that: The first 1×2 MMI unit input single-mode straight waveguide (1), the first 1×2 MMI unit first output curved waveguide (5), the first 1×2 MMI unit second output curved waveguide (7), the second 1×2 MMI unit input single-mode straight waveguide (31), the second 1×2 MMI unit first output curved waveguide (35), the second 1×2 The width W1 of a single waveguide in the second output curved waveguide (37), the first curved waveguide (9), the second curved waveguide (10), the third curved waveguide (39), and the fourth curved waveguide (40) of the MMI unit is the same as that in the first output waveguide array (11), the second output waveguide array (27), the third output waveguide array (12), the fourth output waveguide array (28), the first curved waveguide array (19), and the second curved waveguide array (20), which is 2 to 10 μm; the array length L3 of the first output waveguide array (11), the second output waveguide array (27), the third output waveguide array (12), and the fourth output waveguide array (28) is the same as that in the range of 1000 to 8000 μm, the array width W7 is the same as that in the range of 500 to 8000 μm, and the spacing W2 between the single waveguides in the array is the same as that in the range of 10 to 150 μm; the first 1×2 MMI unit input linear tapered waveguide (2), the first 1×2 MMI unit first output linear tapered waveguide (4), the first 1×2 The length L2 of the second output linear tapered waveguide (6) of the MMI unit, the input linear tapered waveguide (32) of the second 1×2 MMI unit, the first output linear tapered waveguide (34) of the second 1×2 MMI unit, the second output linear tapered waveguide (36) of the second 1×2 MMI unit, and the length L2 of the single linear tapered waveguide in the first linear tapered waveguide array (13), the second linear tapered waveguide array (25), the third linear tapered waveguide array (17), the fourth linear tapered waveguide array (21), the fifth linear tapered waveguide array (14), the sixth linear tapered waveguide array (26), the seventh linear tapered waveguide array (18), and the eighth linear tapered waveguide array (22) are the same, which is 100 to 500 μm, and the narrow port width W1 of the single linear tapered waveguide is the same, which is 2 to 10 μm, and the wide port width W3 is the same, which is 4 to 20 μm; the first 1×2 The connection points of the MMI unit input linear tapered waveguide (2), the first 1×2 MMI unit first output linear tapered waveguide (4), the first 1×2 MMI unit second output linear tapered waveguide (6), the second 1×2 MMI unit input linear tapered waveguide (32), the second 1×2 MMI unit first output linear tapered waveguide (34), the second 1×2 MMI unit second output linear tapered waveguide (36) and the first 1×2 MMI unit multimode planar waveguide (3) and the second 1×2 MMI unit multimode planar waveguide (33) are wide ports of the linear tapered waveguides;The first linear tapered waveguide array (13), the second linear tapered waveguide array (25), the third linear tapered waveguide array (17), the fourth linear tapered waveguide array (21), the fifth linear tapered waveguide array (14), the sixth linear tapered waveguide array (26), the seventh linear tapered waveguide array (18), the eighth linear tapered waveguide array (22) and the first slab waveguide (15), the second slab waveguide (23), the third slab waveguide (16), and the fourth slab waveguide (24) are connected to each other in a linear tapered manner. The first linear tapered waveguide array (13), the second linear tapered waveguide array (25), the third linear tapered waveguide array (17), the fourth linear tapered waveguide array (21), the fifth linear tapered waveguide array (14), the sixth linear tapered waveguide array (26), the seventh linear tapered waveguide array (18), and the eighth linear tapered waveguide array (22) have the same center spacing W6 of the wide ports of adjacent linear tapered waveguides, which is 4 to 30 μm, and W6 ≥ W3; the first 1×2 The width W5 of the MMI unit multimode planar waveguide (3) and the second 1×2 MMI unit multimode planar waveguide (33) are the same, which is 25 to 70 μm, and the length L1 is the same, which is 450 to 1500 μm; the waveguide center distance between the first 1×2 MMI unit first output linear tapered waveguide (4) and the first 1×2 MMI unit second output linear tapered waveguide (6), and the waveguide center distance between the second 1×2 MMI unit first output linear tapered waveguide (34) and the second 1×2 The waveguide center distance W4 of the second output linear tapered waveguide (36) of the MMI unit is the same, which is 10 to 20 μm; the Rowland circle diameter length R of the first slab waveguide (15), the second slab waveguide (23), the third slab waveguide (16), and the fourth slab waveguide (24) is the same, which is 500 to 8000 μm; the channel input angle formed by the waveguide center extension line of the first curved waveguide (9) at the connection with the first slab waveguide (15) and the center line of the first slab waveguide (15), and the channel input angle formed by the waveguide center extension line of the first curved waveguide (9) at the connection with the first slab waveguide (15) and the center line of the first slab waveguide (15), and the channel input angle formed by the waveguide center extension line of the third curved waveguide (39) at the connection with the second slab waveguide (15). The channel input angle formed by the waveguide center extension line at the connection of the waveguide (23) and the center line of the second slab waveguide (23) is the same as θ1, the channel input angle formed by the waveguide center extension line at the connection of the second curved waveguide (10) and the third slab waveguide (16) and the center line of the third slab waveguide (16), and the channel input angle formed by the waveguide center extension line at the connection of the fourth curved waveguide (40) and the fourth slab waveguide (24) and the center line of the fourth slab waveguide (24) are the same as θ2, θ1 is not equal to θ2, and; Where m is the grating diffraction order, n s is the effective refractive index of the planar waveguide, Δλ is the difference in the center wavelengths of adjacent output channels of the AWG; the length L4 of the shortest curved waveguide in the first curved waveguide array 19 and the second curved waveguide array 20 is the same, 1000-5000 μm, and the length L5 of the longest curved waveguide is the same, 1300-30000 μm; the length difference ΔL between adjacent waveguides is the same, 10-200 μm, and L5=L4+(n-1)×ΔL. All waveguide lengths are defined as the projected length of the waveguide along the center line connecting the first 1×2 MMI unit input single-mode straight waveguide 1 and the second 1×2 MMI unit input single-mode straight waveguide 31.

3. The highly symmetric, large bandwidth flexible arrayed waveguide grating chip for FBG demodulation system according to claim 1, characterized in that: When the first 1×2 MMI unit input single-mode straight waveguide (1) is used as the input channel of the FBG reflected light, and the N waveguides in the second output waveguide array (27) and the N waveguides in the fourth output waveguide array (28) are used as the output channels, the signal light is input into the first 1×2 MMI unit multimode planar waveguide (3) through the first 1×2 MMI unit input linear tapered waveguide (2), and then is evenly divided into two identical signal lights, which are respectively input into the first planar waveguide (15) of the left AWG by the first output linear tapered waveguide (4) of the first 1×2 MMI unit, the first output curved waveguide (5) of the first 1×2 MMI unit, and the first curved waveguide (9), and are respectively input into the first planar waveguide (15) of the left AWG by the second output linear tapered waveguide (6) of the first 1×2 MMI unit, the first 1×2 The second output bending waveguide (7) and the second bending waveguide (10) of the MMI unit are input into the third planar waveguide (16) of the right AWG; due to the difference in the designed signal light incident angles θ1 and θ2, the center wavelengths of the output channels of the left AWG and the right AWG that are not adjacent in space are close to each other, forming spectral adjacency, that is, the center wavelength of each output channel in the fourth output waveguide array (28) is respectively located between the center wavelengths of the two output channels in the second output waveguide array (27) in the spectrum; when the center wavelength of the FBG reflected signal light to be demodulated is located between the center wavelengths of any two adjacent output channels in the second output waveguide array (27) of the left AWG, two signal lights with different light intensities are detected in any output channel of the second output waveguide array (27) of the left AWG and the corresponding output channel of the fourth output waveguide array (28) of the right AWG; then, according to the relationship between the logarithmic ratio of the light intensities of adjacent channels in the output spectrum and the center wavelength of the FBG reflected signal light in the demodulation formula (2), the wavelength λ of the FBG reflected light can be obtained. FBG ; Where Δλ is the center wavelength interval of adjacent channels in the spectrum, Δλ FBG is the half-maximum full width of the FBG reflected light. When the central wavelength of the FBG reflected signal light is within the range of the central wavelength of any output waveguide channel in the second output waveguide array (27) of the left AWG in the output spectrum and the central wavelength interval of the corresponding spectral adjacent output waveguide channel in the fourth output waveguide array (28) of the right AWG, P in the demodulation formula (2) is i is the signal optical power outputted by the corresponding output waveguide channel in the second output waveguide array (27) of the left AWG, Δλ i and λ i are the half-maximum full width and central wavelength of the channel spectrum, P i+1 is the signal optical power outputted by the corresponding spectrally adjacent output waveguide channel in the fourth output waveguide array (28) of the right AWG, λ i+1 is the central wavelength of the channel spectrum; when the central wavelength of the FBG reflected signal light is within the range of the central wavelength of any output waveguide channel in the fourth output waveguide array (28) of the right AWG in the output spectrum and the central wavelength interval of the corresponding spectrum adjacent output waveguide channel in the second output waveguide array (27) of the left AWG, P in the demodulation formula (2) is i is the signal optical power outputted by the corresponding output waveguide channel in the fourth output waveguide array (28) of the right AWG, Δλ i and λ i are the half-maximum full width and central wavelength of the channel spectrum, P i+1 is the signal optical power outputted by the corresponding spectrally adjacent output waveguide channel in the second output waveguide array (27) of the left AWG, λ i+1 is the central wavelength of the channel spectrum.

4. A highly symmetrical, large bandwidth flexible arrayed waveguide grating chip for FBG demodulation system according to claim 1, 2 or 3, characterized in that: The material of the polymer flexible substrate (41) is polymer PDMS, with a thickness of 0.5 to 1 mm; the material of the polymer lower cladding (42) and the material of the polymer upper cladding (44) are fluorinated bisphenol A phenolic resin package, polyethylene, polystyrene, polycarbonate, polymethyl methacrylate, P (MMA-co-GMA) or EpoClad, with a thickness of 5 to 15 μm; the material of the polymer core layer (43) is a fluorinated bisphenol A phenolic resin core, SU-8 2002, SU-82005 or EpoCore with a refractive index greater than that of the polymer cladding material, with a thickness of 3 to 8 μm.

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