Long-period waveguide grating type sensor and manufacturing method thereof

Abstract

A long-period waveguide grating type sensor comprises a glass substrate, a waveguide core layer extending linearly is arranged in the glass substrate, and a wrapping layer is arranged on the periphery of the waveguide core layer. The waveguide core layer is sequentially composed of a first cylindrical core layer, a long-period grating core layer and a second cylindrical core layer from front to back, and the radius of the long-period grating core layer changes in a sine period mode from front to back. The first cylindrical core layer is an optical signal input end, and the second cylindrical core layer is an optical signal output end. The high-sensitivity rapid measurement of the gas is realized by utilizing the high-sensitivity response of the characteristic absorption peak wavelength of the transmission spectrum trough to the refractive index disturbance of the external environment, and meanwhile, the manufacturing method is simple and the cost is low.

Description

Technical Field

[0001] The invention belongs to the field of integrated optics, and in particular relates to a glass-based gradient long-period waveguide grating sensor and a manufacturing method thereof. Background Art

[0002] A gas sensor is an electronic device that can detect and measure the composition or concentration of a gas. It is usually used to detect the presence or concentration change of a specific gas and convert this information into an electrical signal output. Gas sensors are widely used, from gas leak detection in industrial environments to air quality monitoring in daily life.

[0003] There are three main types of gas sensors currently available on the market: Electrochemical sensors generate current through chemical reactions between gas and electrodes, and are used to detect gases such as oxygen and carbon monoxide. They require initialization startup time, have a short service life (2-3 years), good sensitivity and selectivity, and moderate power consumption and cost. Catalytic combustion sensors detect the presence of combustible gases through combustion reactions and are often used for safety monitoring in industry. They have a small detection range (0-4%) and are prone to secondary disasters. They have high power consumption and a short service life (2-3 years). They are widely used for all combustible gas detection. MEMS oxide sensors detect gases through changes in the conductivity of oxide materials in a specific gas environment. They take up to several minutes to start up, have poor sensitivity and selectivity, high power consumption, and low cost.

[0004] In addition, infrared gas measurement sensing is a commonly used optical gas sensing technology. However, the sensitivity of the sensor is greatly affected by environmental factors such as temperature and humidity, and the gas molecules being measured must have corresponding infrared absorption capabilities.

[0005] Long period grating is a periodic structure engraved on the core of an optical fiber with a long grating period (usually in the range of 100 microns to hundreds of microns). This periodic structure couples the guided mode light in the fiber core to the cladding mode, resulting in resonant loss in a specific wavelength range, leading to spectral attenuation. These resonant wavelengths are very sensitive to changes in the refractive index of the surrounding environment and can therefore be used for gas detection. Summary of the invention

[0006] In view of the above problems, the present invention proposes a long period waveguide grating type sensor and a manufacturing method thereof, the design concept of which is to utilize the highly sensitive response of the absorption peak wavelength in the transmission spectrum trough to the refractive index disturbance of the external environment to achieve high-sensitivity and rapid measurement of gas.

[0007] The long period waveguide grating type sensor comprises a glass substrate 1, a cladding 2, a waveguide core layer 3, a first cylindrical core layer 4, a second cylindrical core layer 5 and a long period grating core layer 6;

[0008] A waveguide core layer 3 extending in a straight line is provided in the glass substrate 1, and a cladding layer 2 is provided around the waveguide core layer 3; the extension direction of the waveguide core layer 3 is defined as the front-to-back direction, and the waveguide core layer 3 comprises, from front to back, a first cylindrical core layer 4, a long-period grating core layer 6, and a second cylindrical core layer 5, and the radius of the long-period grating core layer 6 changes sinusoidally from front to back; the first cylindrical core layer 4 is an optical signal input end, and the second cylindrical core layer 5 is an optical signal output end.

[0009] More specifically, the waveguide core layer 3 has a radius ranging from 3.0 to 5.0 μm and a length ranging from 100 to 2500 μm.

[0010] More specifically, the refractive index of the waveguide core layer 3 presents a Gaussian distribution, and the difference between the refractive index of the waveguide core layer 3 and the substrate is 0.005-0.010.

[0011] More specifically, the thickness of the cladding layer 2 is 0 to 2 μm.

[0012] More specifically, the radius of the front end of the long-period grating core layer 6 is equal to that of the first cylindrical core layer (4), which is 3.5 μm; the length of the long-period grating core layer 6 is 1500-4000 μm.

[0013] More specifically, the radius of the long-period grating core layer 6 at its narrowest point is 3.0-3.5 μm, the radius at its widest point is 3.5-4.0 μm, and the variation period is 50-500 μm.

[0014] The manufacturing method of the long period waveguide grating type sensor comprises the following steps:

[0015] 1) coating, photolithography and etching are performed on the upper surface of the glass substrate 1;

[0016] 2) transferring the waveguide pattern that changes sinusoidally from front to back to a mask previously plated on the glass substrate 1 to serve as a barrier film for the optical waveguide during the ion exchange process;

[0017] 3) immersing the glass substrate 1 with the mask into a low-concentration silver ion exchange molten salt for heat exchange, so that a surface optical waveguide is formed in the waveguide pattern on the mask;

[0018] 4) A first electrode and a second electrode are added to the front and rear sides of the glass substrate 1, and an electric plant-assisted exchange process is performed, so that the optical waveguide is buried into the glass substrate under the action of the electric field to form a buried waveguide core layer 3, and the glass substrate 1 left above the waveguide core layer 3 due to the burial constitutes a cladding 2.

[0019] When light passes through a long-period waveguide grating, coupling occurs between the two optical waveguide propagation modes. The use of long-period waveguide gratings for refractive index sensing is mainly based on the premise that the wavelength of its coupled absorption peak moves observably with the change of the refractive index of the external environment. According to the phase matching formula, the absorption peak wavelength in the transmission spectrum is:

[0020] λ res =(N0-N m )Λ

[0021] λ res is the absorption peak wavelength, N0 and N m are the effective refractive indexes of the core fundamental mode and the higher-order mode, respectively. Λ is the sinusoidal variation period of the long-period waveguide grating. The variation of the refractive index of the external environment has a certain influence on the effective refractive index and field distribution of the higher-order mode, thus causing the resonant wavelength to change accordingly. Therefore, the effective refractive index of the higher-order mode can be written as:

[0022] N m =N m (n ex )

[0023] where n ex is the refractive index of the external environment. Under normal circumstances, the core layer fundamental mode and the period of the grating will not be affected by the change of the external refractive index. The change of the external refractive index Δn ex The corresponding shift of the coupling absorption peak wavelength is Δλ res Can be written as:

[0024]

[0025] When the external gas concentration changes, the external refractive index changes. By monitoring the wavelength drift of the spectral absorption peaks and valleys, information on the change in external gas concentration can be obtained, thus achieving a detection effect.

[0026] The technical effect of the present invention is that the waveguide core layer with a radius that changes in a sinusoidal periodic manner enhances its sensitivity as a sensor, and the manufacturing method of the sensor is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural diagram of the long period waveguide grating type sensor of the present invention.

[0028] Figure 2 It is a schematic cross-sectional view of the long-period waveguide grating sensor of the present invention.

[0029] Figure 3 It is a schematic diagram of the core layer of the long period waveguide grating sensor of the present invention.

[0030] Figure 4This is the transmission spectrum of the long period waveguide grating sensor prepared according to the parameters of Example 2 at 1450-1650nm when the external refractive index range is 1.0000-1.0003.

[0031] Figure 5 This is a relationship diagram between the absorption peak wavelength of the long period waveguide grating sensor prepared by the parameters of Example 2 and the external refractive index in the external refractive index range of 1.0000-1.0003.

[0032] Figure 6 This is the transmission spectrum of the long period waveguide grating sensor prepared according to the parameters of Example 3 at 1450-1650nm when the external refractive index range is 1.0000-1.0003.

[0033] Figure 7 This is a relationship diagram between the absorption peak wavelength and the external refractive index of the long period waveguide grating sensor prepared by the parameters of Example 3 in the external refractive index range of 1.0000-1.0003.

[0034] Figure 8 This is the transmission spectrum of the long period waveguide grating sensor prepared according to the parameters of Example 4 at 1450-1650nm when the external refractive index range is 1.0000-1.0003.

[0035] Fig. 9 This is a relationship diagram between the absorption peak wavelength and the external refractive index of the long period waveguide grating sensor prepared by the parameters of Example 4 in the external refractive index range of 1.0000-1.0003.

[0036] Fig.10 This is the transmission spectrum of the long period waveguide grating sensor prepared according to the parameters of Example 5 at 1450-1650nm when the external refractive index range is 1.0000-1.0003.

[0037] Fig.11 This is a relationship diagram between the absorption peak wavelength and the external refractive index of the long period waveguide grating sensor prepared according to the parameters of Example 5 in the external refractive index range of 1.0000-1.0003. DETAILED DESCRIPTION

[0038] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0039] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0041] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0042] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0043] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0044] The present invention will be described in detail below in conjunction with exemplary embodiments with reference to the accompanying drawings.

[0045] Example 1

[0046] according to Figure 1 , Figure 2 , the long period waveguide grating type sensor comprises a glass substrate 1, a cladding 2, a waveguide core layer 3, a first cylindrical core layer 4, a second cylindrical core layer 5 and a long period grating core layer 6;

[0047] A waveguide core layer 3 extending in a straight line is provided in the glass substrate 1, and a cladding layer 2 is provided around the waveguide core layer 3; the extension direction of the waveguide core layer 3 is defined as the front-to-back direction, and the waveguide core layer 3 comprises, from front to back, a first cylindrical core layer 4, a long-period grating core layer 6, and a second cylindrical core layer 5, and the radius of the long-period grating core layer 6 changes sinusoidally from front to back; the first cylindrical core layer 4 is an optical signal input end, and the second cylindrical core layer 5 is an optical signal output end.

[0048] When light passes through a long-period waveguide grating, coupling occurs between the two optical waveguide propagation modes. The use of long-period waveguide gratings for refractive index sensing is mainly based on the premise that the wavelength of its coupled absorption peak moves observably with the change of the refractive index of the external environment. According to the phase matching formula, the absorption peak wavelength in the transmission spectrum is:

[0049] λ res =(N0-N m )Λ

[0050] λ res is the absorption peak wavelength, N0 and N m are the effective refractive indexes of the core fundamental mode and the higher-order mode, respectively. Λ is the sinusoidal variation period of the long-period waveguide grating. The variation of the refractive index of the external environment has a certain influence on the effective refractive index and field distribution of the higher-order mode, thus causing the resonant wavelength to change accordingly. Therefore, the effective refractive index of the higher-order mode can be written as:

[0051] Nm =N m (n ex )

[0052] where n ex is the refractive index of the external environment. Under normal circumstances, the core layer fundamental mode and the period of the grating will not be affected by the change of the external refractive index. The change of the external refractive index Δn ex The corresponding shift of the coupling absorption peak wavelength is Δλ res Can be written as:

[0053]

[0054] When the external gas concentration changes, the external refractive index changes. By monitoring the wavelength drift of the spectral absorption peaks and valleys, information on the change in external gas concentration can be obtained, thus achieving a detection effect.

[0055] Example 2

[0056] A long period waveguide grating type sensor based on Example 1, wherein the first cylindrical core layer 4 and the second cylindrical core layer 5 have a radius of 3.5 μm and a length of 4000 μm;

[0057] The refractive index of the waveguide core layer 3 is Gaussian distributed, and the difference between the refractive index of the peak of the refractive index distribution and that of the substrate is 0.005;

[0058] The thickness of cladding 2 is 2.0 μm;

[0059] The radius of the starting node of the long-period grating core layer 6 is equal to that of the first cylindrical core layer 4, which is 3.5 μm, and the length is 3750 μm;

[0060] The radius of the long-period waveguide grating 6 has a sinusoidal periodic change. The narrowest part of the core radius in the change period is 3.0 μm, the widest part is 3.5 μm, and the change period is 50 μm.

[0061] The refractive index distribution of the long period grating core layer 6 is the same as that of the first cylindrical core layer 4, and the refractive index difference with the substrate is 0.005.

[0062] like Figure 3 , 4 As shown, the present invention is simulated by Rsoft optical simulation software, the input light source is a wide-band light source centered at a wavelength of 1550nm, and the simulation is performed in the range of environmental refractive index 1.0000-1.0003 to obtain different environmental transmission spectra. The simulation results show that this structural sensor can achieve a good sensing effect within the gas refractive index range, and the sensitivity can reach 4000nm / RIU.

[0063] Example 3

[0064] A long period waveguide grating type sensor based on Example 1, wherein the first cylindrical core layer 4 and the second cylindrical core layer 5 have a radius of 3.5 μm and a length of 2000 μm;

[0065] The refractive index of the waveguide core layer 3 is Gaussian distribution, and the difference between the refractive index of the peak of the refractive index distribution and that of the substrate is 0.008;

[0066] The thickness of cladding 2 is 0.5 μm;

[0067] The radius of the starting node of the long-period grating core layer 6 is equal to that of the first cylindrical core layer 4, which is 3.5 μm, and the length is 2000 μm;

[0068] The radius of the long-period waveguide grating 6 has a sinusoidal periodic change. The narrowest part of the core radius in the change period is 3.5μm, the widest part is 3.75μm, and the change period is 150μm.

[0069] The refractive index distribution of the long period grating core layer 6 is the same as that of the first cylindrical core layer 4, and the refractive index difference with the substrate is 0.008.

[0070] like Figure 5 , 6 As shown, the present invention is simulated by Rsoft optical simulation software, the input light source is a wide-band light source centered at a wavelength of 1550nm, and the simulation is performed in the range of environmental refractive index 1.0000-1.0003 to obtain different environmental transmission spectra. The simulation results show that this structural sensor can achieve a good sensing effect within the gas refractive index range, and the sensitivity can reach 8032nm / RIU.

[0071] Example 4

[0072] A long period waveguide grating type sensor based on Example 1, wherein the first cylindrical core layer 4 and the second cylindrical core layer 5 have a radius of 3.5 μm and a length of 750 μm;

[0073] The refractive index of the waveguide core layer 3 is Gaussian distributed, and the difference between the refractive index of the peak of the refractive index distribution and that of the substrate is 0.015;

[0074] The thickness of cladding 2 is 1.0 μm;

[0075] The radius of the starting node of the long-period grating core layer 6 is equal to that of the first cylindrical core layer 4, which is 3.5 μm, and the length is 5000 μm;

[0076] The radius of the long-period waveguide grating 6 has a sinusoidal periodic change. The narrowest part of the core radius in the change period is 3.5 μm, the widest part is 4.0 μm, and the change period is 200 μm.

[0077] The refractive index distribution of the long period grating core layer 6 is the same as that of the first cylindrical core layer 4, and the refractive index difference with the substrate is 0.015.

[0078] like Figure 7 , 8 As shown, the present invention is simulated by Rsoft optical simulation software, the input light source is a wide-band light source centered at a wavelength of 1550nm, and the simulation is performed in the range of environmental refractive index 1.0000-1.0003 to obtain different environmental transmission spectra. The simulation results show that this structural sensor can achieve a good sensing effect within the gas refractive index range, and the sensitivity can reach 7632nm / RIU.

[0079] Example 5

[0080] A long period waveguide grating type sensor based on Example 1, wherein the first cylindrical core layer 4 and the second cylindrical core layer 5 have a radius of 3.5 μm and a length of 500 μm;

[0081] The refractive index of the waveguide core layer 3 is Gaussian distribution, and the difference between the refractive index of the peak of the refractive index distribution and that of the substrate is 0.008;

[0082] The thickness of cladding 2 is 0.5 μm;

[0083] The radius of the starting node of the long-period grating core layer 6 is equal to that of the first cylindrical core layer 4, which is 3.5 μm, and the length is 12500 μm;

[0084] The radius of the long-period waveguide grating 6 has a sinusoidal periodic change. The narrowest part of the core radius in the change period is 3.5 μm, the widest part is 4.0 μm, and the change period is 500 μm.

[0085] The refractive index distribution of the long period grating core layer 6 is the same as that of the first cylindrical core layer 4, and the refractive index difference with the substrate is 0.008.

[0086] like Fig. 9 , 10 As shown, the present invention is simulated by Rsoft optical simulation software, the input light source is a wide-band light source centered at a wavelength of 1550nm, and the simulation is performed in the range of environmental refractive index 1.0000-1.0003 to obtain different environmental transmission spectra. The simulation results show that this structural sensor can achieve a good sensing effect within the gas refractive index range, and the sensitivity can reach 4100nm / RIU.

[0087] The technical effect of the present invention is that the waveguide core layer with a radius that changes in a sinusoidal periodic manner enhances its sensitivity as a sensor, and the manufacturing method of the sensor is simple and low-cost.

[0088] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A long period waveguide grating type sensor, characterized in that: It comprises a glass substrate (1), a cladding layer (2), a waveguide core layer (3), a first cylindrical core layer (4), a second cylindrical core layer (5) and a long-period grating core layer (6); A waveguide core layer (3) extending in a straight line is provided in the glass substrate (1), and a cladding layer (2) is provided around the waveguide core layer (3); the extension direction of the waveguide core layer (3) is defined as the front-to-back direction, and the waveguide core layer (3) comprises, from front to back, a first cylindrical core layer (4), a long-period grating core layer (6), and a second cylindrical core layer (5), and the radius of the long-period grating core layer (6) changes sinusoidally from front to back; the first cylindrical core layer (4) is an optical signal input end, and the second cylindrical core layer (5) is an optical signal output end.

2. A long period waveguide grating sensor according to claim 1, characterized in that: The radius of the waveguide core layer (3) is in the range of 3.0 to 5.0 μm, and the length is in the range of 100 to 2500 μm.

3. A long period waveguide grating sensor according to claim 1, characterized in that: The refractive index of the waveguide core layer (3) is Gaussian distributed, and the difference between the refractive index of the waveguide core layer (3) and the substrate is 0.005-0.

010.

4. A long period waveguide grating type sensor according to claim 1, characterized in that: The thickness of the cladding (2) is 0 to 2 μm.

5. A long period waveguide grating type sensor according to claim 1, characterized in that: The radius of the front end of the long-period grating core layer (6) is equal to that of the first cylindrical core layer (4), which is 3.5 μm; the length of the long-period grating core layer (6) is 1500-4000 μm.

6. A long period waveguide grating sensor according to claim 1, characterized in that: The narrowest radius of the long-period grating core layer (6) is 3.0-3.5 μm, the widest radius is 3.5-4.0 μm, and the variation period is 50-500 μm.

7. A method for manufacturing the long period waveguide grating type sensor of claim 1, comprising the steps of: 1) performing coating, photolithography and etching on the upper surface of the glass substrate (1); 2) transferring the waveguide pattern that changes sinusoidally from front to back to a mask previously plated on a glass substrate (1) to serve as a barrier film for the optical waveguide during the ion exchange process; 3) immersing the glass substrate (1) with the mask in a low-concentration silver ion exchange molten salt for heat exchange, so that a surface optical waveguide is formed in the waveguide pattern on the mask; 4) A first electrode and a second electrode are added to the front and rear sides of the glass substrate (1), and an electric field assisted exchange process is performed, so that the optical waveguide is buried into the glass substrate under the action of the electric field to form a buried waveguide core layer (3), and the glass substrate (1) left above the waveguide core layer (3) due to the burial constitutes a cladding layer (2).

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