Photobleached all-polymer optical waveguide grating sensor and preparation method thereof

Abstract

The invention discloses a photobleached all-polymer optical waveguide grating sensor and a preparation method thereof, and belongs to the technical field of polymer optical waveguide grating sensors. The preparation method comprises the following steps: carrying out hot stamping on a substrate sheet to obtain a substrate sheet with a groove; spin-coating photoresist on the substrate sheet to form a photoresist core layer; photoetching the photoresist core layer through double-beam interference to obtain the photoresist core layer with interference fringes; spin-coating a thermosensitive polymer cladding material on the photoresist core layer, covering the flexible substrate and then carrying out low-temperature thermocuring so as to bond the photoresist core layer and the flexible substrate; stripping the substrate sheet, exposing the photoresist core layer, covering the protective cladding, and curing to obtain a multi-layer composite device; and performing non-uniform post-baking on the multi-layer composite device to obtain the multi-layer composite device. According to the invention, the grating period can be changed under the condition that the grating mask is not replaced, and the cost of spectrum adjustment is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of polymer optical waveguide grating sensor technology, specifically to an optically bleached all-polymer optical waveguide grating sensor and its fabrication method. Background Technology

[0002] Optical sensing technology, as an important field of information science, boasts advantages such as real-time operation, in-situ sensing, non-invasiveness, and non-destructive properties, making it crucial for applications in environmental monitoring, pharmaceutical research and development, food safety, and many other areas. Compared to electrical sensors, optical sensors do not require power lines, do not short-circuit, and do not generate electrical sparks or electromagnetic interference, thus improving detection safety and making them more suitable for detection in specialized fields such as petroleum, batteries, and flammable and explosive gases.

[0003] Existing optical sensors are mainly divided into fiber optic sensors and optical waveguide sensors. Fiber optic sensors primarily use gratings fabricated on silica optical fibers, featuring distributed detection capabilities and suitable for long-distance linear detection. For planar sensing, distributed fiber optic sensing is currently the main method. Distributed fiber optic sensing involves embedding optical fibers in loops on the surface to be measured, and then sensing signals through signal processing. However, fiber optic sensors suffer from three main problems: firstly, low integration density; secondly, the need for different grating periods and wiring, making it difficult to reduce manufacturing costs; and thirdly, the poor bendability and flexibility of silica optical fibers, limiting their application scenarios. While polymer fiber optic sensors can solve the flexibility and bendability issues, they still cannot meet the requirements for large-scale integration in terms of processing costs and integration density, and the fiber wiring also adds to the manufacturing cost.

[0004] Optical waveguide sensors, with their advantages of high sensitivity, resistance to electromagnetic interference, ease of integration, and real-time monitoring, have experienced rapid development and widespread application. Planar optical waveguide gratings can solve the integration problem of fiber optic gratings. Currently, the materials used to fabricate grating substrates are mainly divided into inorganic materials and organic polymer materials. Inorganic materials typically require processes such as masking, photolithography, and etching during fabrication, resulting in high process costs and material costs. Organic polymer optical waveguides, on the other hand, offer flexibility, low cost, and ease of mass production. Furthermore, polymer materials have lower mass compared to inorganic materials, making them particularly suitable for wearable and flexible applications.

[0005] The fabrication of waveguide gratings on all-polymer substrates mainly falls into three categories: etching, photobleaching, and imprinting. Most optical waveguide sensors are fabricated using photolithography and etching, typically producing sidewall gratings on both sides of the waveguide, which is costly. Imprinting is the most efficient fabrication method for polymer optical waveguides, but it can only fabricate sidewall and top gratings, and modifying the grating size after the imprinting template is determined is costly. Photobleaching, on the other hand, achieves a change in refractive index. Due to its high diffraction efficiency, strong Bragg wavelength selectivity and angle selectivity, it can withstand high laser energy densities, thus exhibiting a high damage threshold and good stability. Reflective bulk gratings are widely used in laser mode selection, semiconductor laser wavelength locking, laser beam combining, and filters. For example, when a commonly used single polysilane material is irradiated with ultraviolet light in an air atmosphere, the Si-Si bonds in the main chain break, and it combines with free radicals of oxygen in the air to form siloxane chemical bonds, resulting in a decrease in refractive index. This photobleaching property can be used to fabricate waveguides. However, photobleaching methods usually involve changing the refractive index on the fabricated waveguide to create a grating, or using photolithography to etch the waveguide onto the fabricated grating. Therefore, this method has advantages in fabricating waveguides or gratings alone, but in fabricating integrated waveguide-grating structures, it needs to be combined with other processes such as photolithography. In addition, current photobleaching technology is divided into two-photon excitation and single-photon excitation. Compared with single-photon excitation, two-photon excitation has more advantages, including: higher penetration, smaller photobleaching area, less damage, and higher signal-to-noise ratio.

[0006] However, in the above scheme, once the imprinting template and photobleaching template (photomask or parameters) of the grating are determined, the characteristics of the grating will be determined along with the polymer waveguide cladding material. When adjusting the spectrum of the waveguide grating sensor in the later stage, multiple masks need to be changed, resulting in excessively high cost for adjusting the spectrum. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, one of the objectives of this invention is to provide a method for fabricating a photobleached all-polymer optical waveguide grating sensor. This method enables the grating period to be changed without replacing the grating mask, greatly reducing the cost of adjusting the spectrum and solving the problem of excessively high cost for spectral adjustment of optical waveguide grating sensors obtained by existing optical waveguide grating fabrication methods.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: A method for fabricating an optically bleached all-polymer optical waveguide grating sensor, comprising the following steps: S1. A substrate sheet is provided, and a plurality of grooves are prepared on the substrate sheet by hot pressing to obtain a substrate sheet with grooves; S2. Spin-coat photoresist onto the substrate sheet with grooves and perform thermal curing to form a photoresist core layer; S3. Photolithography is performed on the photoresist core layer by double-beam interference to form alternating bright and dark interference fringes on the photoresist core layer, thus obtaining a photoresist core layer with interference fringes. S4. After adding polymer cladding material to the photoresist core layer with interference fringes, spin-coating is performed. A flexible substrate is then attached to the polymer cladding material and thermally cured at low temperature to form a polymer optical waveguide cladding. S5. Directly peel off the substrate sheet to expose the photoresist core layer, and cover the photoresist core layer with a protective cladding layer to obtain a multilayer composite device; S6. Perform non-uniform post-baking on the multilayer composite device to obtain the optical waveguide grating sensor.

[0009] In a preferred embodiment of the present invention, the conditions for hot pressing in step S1 are: pressing temperature of 90-180℃, holding temperature of 100-190℃, and holding pressure of 2-10 kg / cm². 2 The holding time is 5-60 min. The groove width and depth obtained by hot pressing in step S1 are 1-10 μm.

[0010] In a preferred embodiment of the present invention, the preparation process of the photoresist core layer in step S2 is as follows: the substrate sheet is rotated at a speed of 2000-8000 rpm for coating, and the spin coating time is 30-90 seconds, so that the photoresist fills the groove and covers the surface of the substrate sheet; then it is placed on a hot plate for thermal curing, heated at 55-65℃ for 5-30 minutes and at 85-95℃ for 5-40 minutes to form the photoresist core layer. The maximum thickness of the photoresist core layer is 0.5-10 μm greater than the depth of the groove.

[0011] In a preferred embodiment of the present invention, during photolithography of the photoresist core layer in step S3, the alternating bright and dark stripes formed by the interference of two beams are perpendicular to the grooves of the substrate sheet.

[0012] As a preferred embodiment of the present invention, the photolithography conditions for the two-beam interference in step S3 are as follows: wavelengths of 365nm, 248nm, or 193nm, and light intensities of 10-1000mW / cm². 2 After exposure to ultraviolet light for 1-15 seconds, a photoresist core layer with alternating exposure amounts is obtained. Two-beam interference produces alternating bright and dark fringes, with the exposure amount of the core layer photoresist corresponding to the position of the bright and dark fringes.

[0013] In a preferred embodiment of the present invention, the preparation of the polymer waveguide cladding in step S4 includes: dropping a polymer cladding material onto a photoresist core layer with interference fringes; spin-coating the polymer cladding material on the photoresist core layer at a rotation speed of 2000-8000 rpm for 30-90 seconds; attaching a flexible substrate onto the polymer cladding material; placing it on a hot plate and heating it at a temperature of 90-120°C for 5-30 minutes to thermally cure the polymer cladding material at a low temperature, thereby bonding the flexible substrate and the photoresist core layer. The thickness of the resulting polymer waveguide cladding is 3-100 μm.

[0014] In a preferred embodiment of the present invention, the thickness of the protective cladding in step S5 is 3-100 μm.

[0015] As a preferred embodiment of the present invention, the specific operation of the non-uniform post-baking in step S6 is as follows: the multilayer composite device is divided into at least two temperature regions from the light incident end to the light emitting end, and the post-baking temperature changes from 150°C to 180°C from the light incident end to the light emitting end, with a temperature difference of ≥5°C between each two adjacent regions, and the heating time is 10-30 minutes.

[0016] The second objective of this invention is to provide a photobleached all-polymer optical waveguide grating sensor, which is prepared according to the preparation method described above.

[0017] In a preferred embodiment of the present invention, the optical waveguide grating sensor includes a flexible substrate, a polymer optical waveguide cladding, a photoresist core layer, and a protective cladding layer stacked sequentially from top to bottom; The photoresist core layer includes a flat plate portion and ridge-shaped protrusions disposed on the flat plate portion, giving it an inverted ridge-shaped cross-sectional structure. The polymer waveguide cladding is connected to the side of the photoresist core layer where the flat plate portion is provided, which is used to support the photoresist core layer and bond the flexible substrate to the photoresist core layer. The protective cladding is connected to the side of the photoresist core layer with the ridge protrusion to protect the polymer waveguide cladding.

[0018] In a preferred embodiment of the present invention, the refractive index of the protective cladding is 1.40-1.50@1550nm; the refractive index of the photoresist core layer is 1.52-1.8@1550nm; and the refractive index of the polymer waveguide cladding is 1.40-1.50@1550nm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The fabrication method provided by this invention uses a combination of imprinting, photobleaching, and thermal modulation techniques to fabricate an inverted ridge optical waveguide grating sensor: a bulk grating structure is formed on the photoresist core layer using photobleaching; a waveguide is realized using polymer imprinting; and the grating period is changed by the temperature gradient of the polymer material after baking, utilizing the characteristic that the refractive index changes with the baking temperature. This allows for the adjustment of the optical waveguide grating sensor spectrum without changing the grating period template, improving integration while effectively reducing process costs by replacing the photomask with thermal treatment. It is suitable for large-scale temperature detection on flammable and explosive non-planar substrates, such as in batteries and power systems. Compared with traditional single technologies, it has higher accuracy and can change the grating period without changing the grating mask, greatly saving costs. Furthermore, this invention achieves device packaging while fabricating the cladding.

[0020] (2) The preparation method provided by the present invention utilizes the characteristic of the refractive index of polymer materials changing after baking temperature. The entire device is placed on different thermal field regions for non-uniform post-baking, so that the grating characteristics at different positions of the device are different. The reflection spectrum of the grating in different regions can be adjusted without changing the grating and waveguide template, so that the spectrum is different and it can be prepared into a chirped grating. This effectively reduces the cost of adjusting the spectrum of the optical waveguide grating sensor and has uniqueness.

[0021] (3) The optical waveguide grating sensor provided by the present invention can achieve the shift of the corresponding spectral curve under local heating. Under a temperature change of 20℃, the center wavelength can shift by more than 2nm, and the shift is large and easy to observe.

[0022] (4) The optical waveguide grating sensor provided by the present invention can realize the detection of the entire device in the entire optical domain. Temperature detection can be completed by only one beam of light. Compared with the existing detection technology, its detection time is shorter. Moreover, no electric sparks are generated during the detection process of the all-optical device. The device has fewer environmental requirements than existing devices. It can be used for detection of various types of electrodes. It has a wide range of applications and a broad market. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the fabrication process of the photobleached all-polymer optical waveguide grating sensor described in this invention. Figure 2 This is a schematic diagram illustrating the fabrication of the photobleached all-polymer optical waveguide grating sensor described in this invention. Figure 3 This is a schematic diagram of the fabrication of the photobleached all-polymer optical waveguide grating sensor described in this invention from a side view angle. Figure 4 This is a schematic diagram of the post-baking temperature distribution of the hot plate during the uneven post-baking process described in this invention. Figure 5 This is a front view of the optically bleached all-polymer optical waveguide grating sensor described in this invention. Figure 6 This is a left-side structural view of the photobleached all-polymer optical waveguide grating sensor described in this invention. Figure 7 This is a three-dimensional structural diagram of the photobleached all-polymer optical waveguide grating sensor described in this invention.

[0024] Explanation of reference numerals: 1. Substrate sheet; 2. Photoresist core layer; 21. Flat plate section; 22. Ridge protrusion; 3. Photoresist core layer with interference fringes; 4. Polymer waveguide cladding; 5. Flexible substrate; 6. Protective cladding. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0026] like Figures 1-3 As shown, the fabrication method of the photobleached all-polymer optical waveguide grating sensor of the present invention includes the following steps: S1. Provide a substrate sheet 1, with a pressurization temperature of 90-180℃, a holding temperature of 100-190℃, and a holding pressure of 2-10 kg / cm². 2 The substrate sheet 1 is hot-pressed under a holding pressure time of 5-60 min to prepare several grooves with a width of 1-10 μm and a depth of 1-10 μm on the substrate sheet 1, thereby obtaining a substrate sheet 1 with grooves.

[0027] S2. Apply photoresist to the substrate thin film 1 with grooves, and spin the substrate thin film 1 at a speed of 2000-8000 rpm for 30-90 seconds to fill the grooves with photoresist and cover the surface of the substrate thin film 1. Then place it on a hot plate for thermal curing: first heat at 55-65℃ for 5-30 minutes, then heat at 85-95℃ for 5-40 minutes to form the photoresist core layer 2. The refractive index of the photoresist core layer is 1.51-1.8@1550nm.

[0028] S3. Photolithography of the photoresist core layer 2 using double-beam interference: The double beams are perpendicular to the grooves of the substrate thin film 1, at a wavelength of 350nm and a light intensity of 20-30mW / cm². 2 Exposure to ultraviolet light for 5-15 seconds forms alternating bright and dark interference fringes on the photoresist core layer 2, resulting in a photoresist core layer 32 with alternating exposure and interference fringes. The two-beam interference forms alternating bright and dark fringes; where the fringes are bright, the core layer photoresist material receives a large exposure, and where the fringes are dark, the core layer material receives little or no exposure; that is, the exposure amount matches the brightness of the alternating bright and dark fringes.

[0029] S4. A polymer cladding material is dropped onto the photoresist core layer 32 with interference fringes. The polymer cladding material on the photoresist core layer 32 is spin-coated at 2000-8000 rpm for 30-90 seconds. A flexible substrate 5 is then attached to the polymer cladding material. The substrate is placed on a hot plate and heated at 90-120℃ for 5-30 minutes to thermally cure the polymer cladding material at a low temperature, forming a polymer waveguide cladding layer 4 with a thickness of 3-100 μm. This cladding layer is then used to bond the flexible substrate 5 and the photoresist core layer 2. The polymer cladding material is either AB adhesive or PDMS.

[0030] S5. Directly peel off the substrate sheet 1 to expose the photoresist core layer 2, and cover the photoresist core layer 2 with a protective cladding layer 6 material. Perform low-temperature thermal curing of the protective cladding layer 6 material at 90-120℃ to obtain a multilayer composite device. The protective cladding layer 6 material is AB glue or PDMS, and the thickness of the protective cladding layer 6 is 3-100μm.

[0031] S6. Place the multilayer composite device on a hot plate or use infrared light for uneven post-baking. The specific operation is as follows: Figure 4 As shown, the multilayer composite device is divided into at least two temperature regions from the light incident end to the light emitting end, from the light incident end (end A) to the light emitting end (end B). The post-baking temperature varies from 150℃ to 180℃, with a temperature difference of ≥5℃ between any two adjacent regions. The heating time is 10-30 minutes, thus obtaining the optical waveguide grating sensor. It should be noted that the post-baking temperature must be lower than the decomposition temperature of the polymer optical waveguide cladding 4.

[0032] Of course, the following heating method can also be used: expose different regions of infrared light of different intensities along the vertical long side for 1-30 minutes to obtain different temperature ranges from 150℃ to 180℃. The number of regions corresponds to the number of gratings with different reflection wavelengths.

[0033] like Figures 5-7 As shown, the photobleached all-polymer optical waveguide grating sensor prepared by the above method includes a flexible substrate 5, a polymer optical waveguide cladding 4, a photoresist core layer 2, and a protective cladding 6 stacked sequentially from top to bottom. The photoresist core layer 2 includes a flat plate portion 21 with a thickness of 0.2-5μm and ridge-shaped protrusions 22 disposed on the flat plate portion 21, so that its cross-sectional structure is an inverted ridge shape. The polymer waveguide cladding 4 is connected to the side of the photoresist core layer 2 where the flat plate portion 21 is provided, which is used to support the photoresist core layer 2 and to bond the flexible substrate 5 to the photoresist core layer 2. The protective cladding 6 is connected to the side of the photoresist core layer 2 where the ridge protrusion 22 is provided, in order to protect the photoresist core layer 2.

[0034] In the aforementioned all-polymer optical waveguide grating sensor, the photoresist is a photosensitive photoresist material, and its refractive index changes with the heating temperature after exposure. Furthermore, its photochemical reaction temperature is higher than the curing temperature of the polymer optical waveguide cladding 4 material. The refractive index of the protective cladding 6 is 1.40-1.50@1550nm; the refractive index of the photoresist core layer 2 is 1.52-1.8@1550nm; and the refractive index of the polymer optical waveguide cladding 4 is 1.40-1.50@1550nm.

[0035] Specifically, the length L of the photoresist core layer 2 is 2000-50000μm (length equal to the substrate sheet 1), the width D is 2000-50000μm, the thickness of the ridge plate 21 is 0.5-10μm, the width L1 of the ridge protrusion 22 is 1-10μm, the height D1 is 1-10μm, and there can be multiple parallel ridge protrusions 22 in the same direction. The distance D2 between two adjacent ridge protrusions 22 is 15-2000μm. The wavelength of the optical waveguide test is 1550nm, but it can also be 980nm, 1310nm, 650nm, etc. The above refractive indices should correspond to the relevant wavelengths. The flexible substrate 5 is preferably a polyimide substrate or a high-temperature resistant polymer.

[0036] Example 1 A photobleached all-polymer optical waveguide grating sensor is fabricated according to the following method: S1. A PMMA substrate sheet is provided, which is a cuboid structure with a thickness of 1 mm, a length of 10000 μm, and a width of 5000 μm; the sheet is subjected to a pressurization temperature of 110℃, a holding temperature of 120℃, and a holding pressure of 3 kg / cm². 2 The substrate sheet was hot-pressed under a holding pressure time of 5 min to prepare two grooves with a length of 10000 μm, a width of 5 μm, and a height of 5 μm on the substrate sheet. The interval between the two grooves was 500 μm, resulting in a substrate sheet with grooves.

[0037] S2. Apply Microchem SU-8-2005 photoresist (USA) to a substrate with grooves. Spin-coat the substrate at 7000 rpm for 40 seconds to fill the grooves with the photoresist and cover the surface of the substrate. Then place it on a hot plate for thermal curing: first heat at 60°C for 10 minutes, then heat at 90°C for 10 minutes to form a photoresist core layer.

[0038] S3. Photolithography is performed on the photoresist core layer using double-beam interference, ensuring that the two beams are perpendicular to the grooves of the substrate thin film: at a wavelength of 365nm and a light intensity of 30mW / cm². 2Expose the photoresist core layer to ultraviolet light for 8 seconds to form alternating bright and dark interference fringes, resulting in a photoresist core layer with alternating exposure and interference fringes.

[0039] S4. Drop a thermosensitive polymer cladding material onto the photoresist core layer with interference fringes. Spin-coat the thermosensitive polymer cladding material on the photoresist core layer at a speed of 6000 rpm for 90 seconds. Place the flexible substrate onto the polymer cladding material. Place it on a hot plate and heat it at 90°C for 20 minutes to allow the polymer cladding material to be thermally cured at low temperature, forming a polymer optical waveguide cladding, and then use it to bond the flexible substrate and the photoresist core layer.

[0040] S5. Directly peel off the substrate thin film to expose the photoresist core layer, and cover the photoresist core layer with PDMS (8:1 ratio) protective cladding material. Bake the protective cladding material at 90℃ for 30 minutes to perform low-temperature thermal curing to obtain a multilayer composite device. S6. Place the multilayer composite device on a hot plate for uneven post-baking. Specifically, divide the multilayer composite device into 6 temperature zones from the light incident end to the light emitting end. From the light incident end (end A) to the light emitting end (end B), the post-baking temperature changes from 150℃ to 180℃, with a temperature difference of 5℃ between each two adjacent zones. The heating time is 20 minutes, thus obtaining the optical waveguide grating sensor.

[0041] The optical waveguide grating sensor fabricated in Example 1 underwent grating center wavelength testing. Light from one side of the optical fiber was coupled into the waveguide using a six-dimensional fine-tuning frame at the short side position, and coupled out of the waveguide from the other side using an optical fiber. A broadband optical signal was input to the input fiber using a broadband light source, and the output signal was detected using a spectrometer at the output waveguide. When the temperature or stress at the corresponding grating position in the chip changes, the spectral lines of the corresponding grating drift.

[0042] As can be seen, the present invention can realize gratings with different spectral lines on a single waveguide (through the photobleaching effect of the waveguide core layer), that is, the refractive index of the core layer can be changed at different post-baking temperatures, replacing the traditional solution that uses multiple grating masks.

[0043] Example 2 A photobleached all-polymer optical waveguide grating sensor is fabricated according to the following method: S1. A polycarbonate (PC) substrate sheet is provided, wherein the PC substrate sheet is a cuboid structure with a thickness of 1 mm, a length of 20000 μm, and a width of 5000 μm; the pressing temperature is 150℃, the holding temperature is 160℃, and the holding pressure is 4 kg / cm². 2The substrate sheet was hot-pressed under a holding pressure time of 10 min to prepare two grooves with a length of 20000 μm, a width of 5 μm, and a height of 5 μm on the substrate sheet. The interval between the two grooves was 1000 μm, resulting in a substrate sheet with grooves.

[0044] S2. Apply EPO-core photoresist to the substrate thin film with grooves, and spin the substrate thin film at a speed of 5000 rpm for 30 seconds to fill the grooves with photoresist and cover the surface of the substrate thin film. Then place it on a hot plate for thermal curing: first heat at 60℃ for 10 minutes, then heat at 90℃ for 20 minutes to form a photoresist core layer.

[0045] S3. Photolithography is performed on the photoresist core layer using double-beam interference, ensuring that the two beams are perpendicular to the grooves of the substrate thin film: at a wavelength of 365nm and a light intensity of 40mW / cm². 2 Expose the photoresist core layer to ultraviolet light for 8 seconds to form alternating bright and dark interference fringes, resulting in a photoresist core layer with alternating exposure and interference fringes.

[0046] S4. Drop a thermosensitive polymer cladding material onto the photoresist core layer with interference fringes. Spin-coat the thermosensitive polymer cladding material on the photoresist core layer at a speed of 6000 rpm for 60 seconds. Place the flexible substrate onto the polymer cladding material. Place it on a hot plate and heat it at 90°C for 20 minutes to allow the polymer cladding material to be thermally cured at low temperature, forming a polymer optical waveguide cladding, and then use it to bond the flexible substrate and the photoresist core layer.

[0047] S5. Directly peel off the substrate thin film to expose the photoresist core layer, and cover the photoresist core layer with PDMS (8:1 ratio) protective cladding material. Bake the protective cladding material at 90℃ for 30 minutes to perform low-temperature thermal curing to obtain a multilayer composite device. S6. Place the multilayer composite device in an infrared exposure device for regional exposure. The specific operation is as follows: Divide the multilayer composite device into 5 temperature regions from the light incident end to the light emitting end. From the light incident end (end A) to the light emitting end (end B), the baking temperature during the exposure process changes from 150℃ to 180℃. Use infrared light of different intensities to expose the regions for 5 minutes along the vertical long side to obtain different temperature ranges from 150℃ to 180℃. The 5 temperature regions correspond to 5 gratings with different reflection wavelengths.

[0048] The optical waveguide grating sensor fabricated in Example 2 underwent grating center wavelength testing. Light from one side of the optical fiber was coupled into the waveguide using a six-dimensional fine-tuning frame at the short side position, and coupled out of the waveguide from the other side using an optical fiber. A broadband optical signal was input to the input fiber using a broadband light source, and the output signal was detected using a spectrometer. When the temperature or stress at the corresponding grating position in the chip changes, the spectral lines of the corresponding grating drift.

[0049] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method of fabricating a photobleaching all-polymer optical waveguide grating sensor, characterized by, The method comprises the following steps: S1, providing a substrate sheet, preparing a plurality of grooves on the substrate sheet by hot stamping to obtain a substrate sheet with grooves; S2, spin coating photoresist on the substrate sheet with grooves and performing thermal curing to form a photoresist core layer; S3, performing photoetching on the photoresist core layer by double-beam interference to form interference fringes on the photoresist core layer to obtain a photoresist core layer with interference fringes; S4, spin coating polymer cladding material on the photoresist core layer with interference fringes, pasting a flexible substrate on the polymer cladding material, and performing low-temperature thermal curing to form a polymer optical waveguide cladding layer; S5, directly peeling off the substrate sheet to expose the photoresist core layer, and covering a protective cladding layer on the photoresist core layer to obtain a multilayer composite device; S6, performing non-uniform post-baking on the multilayer composite device to obtain the optical waveguide grating sensor.

2. The method for fabricating the photobleached all-polymer optical waveguide grating sensor according to claim 1, characterized in that, The conditions for the hot embossing in step S1 are a press temperature of 90 to 180°C, a holding temperature of 100 to 190°C, a holding pressure of 2 to 10 kg / cm2, and a holding time of 5 to 60 min. 2 , a holding temperature of 100 to 190°C, a holding pressure of 2 to 10 kg / cm2, and a holding time of 5 to 60 min.

3. The method for fabricating the photobleached all-polymer optical waveguide grating sensor according to claim 1, characterized in that, In step S2, the photoresist core layer is prepared as follows: spin coating the substrate sheet at a speed of 2000-8000 rpm for 30-90 s to fill the grooves with photoresist and cover the substrate sheet surface; then, placing it on a hot plate for thermal curing, heating at 55-65 ℃ for 5-30 min and at 85-95 ℃ for 5-40 min to form the photoresist core layer.

4. The method for fabricating the photobleached all-polymer optical waveguide grating sensor according to claim 1, characterized in that, In step S3, the light and dark interference fringes formed by double-beam interference are perpendicular to the grooves of the substrate sheet.

5. The method of claim 1, wherein the photobleaching is performed by irradiating the full polymer optical waveguide grating sensor with a light source having a wavelength of 405 nm. The lithography condition of the double-beam interference in step S3 is as follows: after exposure under ultraviolet light with a wavelength of 365 nm, 248 nm or 193 nm and an optical intensity of 10-1000 mW / cm 2 for 1-15 s, an exposed photoresist core layer with an alternating exposure is obtained.

6. The method for fabricating a photobleached all-polymer optical waveguide grating sensor according to claim 1, characterized in that, In step S4, the preparation of the polymer optical waveguide cladding layer comprises: dropping polymer cladding material on the photoresist core layer with interference fringes, spin coating the polymer cladding material on the photoresist core layer at a speed of 2000-8000 rpm for 30-90 s, pasting a flexible substrate on the polymer cladding material; placing it on a hot plate and heating at a temperature of 90-120 ℃ for 5-30 min to thermally cure the polymer cladding material to bond the flexible substrate and the photoresist core layer.

7. The method of claim 1, wherein the photobleaching is performed by irradiating the polymer waveguide grating sensor with a light source having a wavelength of 405 nm. In step S6, the specific operation of the non-uniform post-baking is as follows: dividing the multilayer composite device into at least two temperature regions from the light incident end to the light emitting end, and changing the post-baking temperature from 150 ℃ to 180 ℃ from the light incident end to the light emitting end, with a temperature difference of ≥5 ℃ between every two adjacent regions, and a heating time of 10-30 min.

8. A photo-bleached all-polymer optical waveguide grating sensor, characterized in that, The optical waveguide grating sensor is prepared by the preparation method of any one of claims 1-7.

9. The optically bleached, all-polymer optical waveguide grating sensor of claim 8, wherein, The optical waveguide grating sensor comprises a flexible substrate, a polymer optical waveguide cladding layer, a photoresist core layer, and a protective cladding layer which are sequentially stacked from top to bottom; The photoresist core layer comprises a flat plate part and a ridge-shaped protrusion arranged on the flat plate part, and the cross-sectional structure is inverted ridge-shaped; The polymer optical waveguide cladding layer is connected to one side of the photoresist core layer provided with the flat plate part, for supporting the photoresist core layer and bonding the flexible substrate and the photoresist core layer; The protective cladding layer is connected to one side of the photoresist core layer provided with the ridge-shaped protrusion, for protecting the polymer optical waveguide cladding layer.

10. The optically bleached, all-polymer optical waveguide grating sensor according to claim 8 or 9, characterized in that, The refractive index of the protective cladding is 1.40-1.50@1550nm; the refractive index of the photoresist core layer is 1.52-1.8@1550nm; and the refractive index of the polymer optical waveguide cladding is 1.40-1.50@1550nm.

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