Space angle measuring device based on tilted fiber grating-surface plasma resonance sensor

Abstract

The invention discloses a space angle measuring device based on a tilted fiber grating-surface plasma resonance sensor, which belongs to the technical field of optical fiber sensing and comprises a broadband light source, a polarizer, a polarization controller, a sensor, a spectrometer and a computer. The broadband light source, the polarizer, the polarization controller, the sensor and the spectrograph are sequentially connected through single-mode optical fibers, and the other end of the spectrograph is connected with the computer through a data line; after passing through the polarizer and the polarization controller, light emitted from the broadband light source is changed into transverse magnetic waves from full polarization waves and then enters the sensor to perceive space angle changes, the spectrograph receives optical signals, and finally the computer demodulates the direction and the size of a bending angle. According to the space angle measuring device based on the tilted fiber grating-surface plasma resonance sensor, the bending direction and the bending angle of the sensor can be detected at the same time, and the sensitivity and the precision are high.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to a spatial angle measuring device based on a tilted optical fiber grating-surface plasma resonance sensor. Background Art

[0002] Angle sensors are widely used in industries such as robot motion status monitoring, building structure monitoring, and civil engineering surveying. Taking robots as an example, the high-precision control of their joint freedom depends on the accurate measurement of the bending angle and bending direction. Common angle sensors mainly use the principles of capacitance, inductance, Hall effect, photoelectric effect, etc. for measurement. Such sensors will have defects such as narrow bandwidth, susceptibility to electromagnetic interference, and susceptibility to temperature interference in some complex and harsh environments. The development of fiber optic sensor technology has changed this situation. Fiber optic sensors have the advantages of high precision, small size, easy integration, insensitivity to flammable and explosive gases, and resistance to electromagnetic interference. At present, fiber optic sensors have been widely used in aerospace, biomedical diagnosis, chemical detection and other fields.

[0003] At present, fiber optic angle sensors are mainly divided into two categories: those based on grating structure and those based on micro-interferometer structure. At present, most sensors based on grating structure can only detect bending angle, but not bending direction. Fiber optic angle sensors based on micro-interferometer structure are easy to break and have a small measurement range. Summary of the invention

[0004] The purpose of the present invention is to provide a spatial angle measurement device based on a tilted fiber grating-surface plasmon resonance sensor, aiming to solve the problems that the existing sensors have limited measurement range, measurement accuracy that does not meet the requirements, and cannot simultaneously measure the size and direction of the bending angle.

[0005] To achieve the above object, the present invention provides a spatial angle measurement device based on a tilted fiber Bragg grating-surface plasmon resonance sensor, comprising a broadband light source, a polarizer, a polarization controller, a sensor, a spectrometer and a computer, wherein the broadband light source, the polarizer, the polarization controller, the sensor and the spectrometer are connected in sequence through a single-mode optical fiber, and the other end of the spectrometer is connected to the computer through a data line;

[0006] The light emitted from the broadband light source passes through the polarizer and polarization controller, and then changes from a fully polarized wave to a transverse magnetic wave, and then enters the sensor to sense the change in spatial angle. The light signal is received by the spectrometer, and finally the direction and size of the bending angle are demodulated by the computer.

[0007] Preferably, the sensor is a tilted fiber Bragg grating-surface plasmon resonance sensor, which is made by engraving a small-angle tilted fiber Bragg grating on a single-mode optical fiber, coating a gold film covering the entire grating area on the surface of the optical fiber cladding, and encapsulating and protecting the entire sensing area with polydimethylsiloxane.

[0008] Preferably, the tilted fiber grating is written by a phase mask method, the angle between the grating plane and the fiber axis is 80°-84°, the grating region length is 10mm-15mm, and the grating axial period is 25μm-30μm.

[0009] Preferably, the gold film is coated by magnetron sputtering or evaporation coating method, the film thickness is 30nm-60nm, and the gold film coating range is 10mm-15mm, which is the same as the gate area length.

[0010] Preferably, the thickness of the polydimethylsiloxane film layer is 5 mm-10 mm, and the length of the polydimethylsiloxane film layer is 50 mm-100 mm.

[0011] Preferably, the tilted fiber grating is sensitive to the bending direction and bending angle of the sensing area, and the change in the sensor transmission spectrum corresponding to the change in the bending direction and bending angle is the vector angular sensitivity of the sensor; the vector angular sensitivity of the tilted fiber grating in the direction of the grating slow axis is the largest, and the vector angular sensitivity of the tilted fiber grating in the direction of the grating fast axis is the smallest.

[0012] Preferably, the sensor is insensitive to the bending direction of the sensing area, but is sensitive to the bending angle of the sensing area, and the change in the bending angle is within the angle response range of the sensor.

[0013] Preferably, after the incident light passes through the polarizer and enters the tilted fiber grating-surface plasmon resonance sensor, the tilted fiber grating will destroy the fundamental mode field propagating in the fiber core and form a cladding mode and a Bragg core mode propagating in the opposite direction. When the sensor is bent in different directions, it will cause the Bragg reflection wavelength and the cladding mode resonance wavelength to drift, wherein the Bragg reflection wavelength and the cladding mode resonance wavelength are respectively:

[0014]

[0015] Where ξ is the angle between the grating plane and the perpendicular plane of the optical fiber, n eff,core and n eff,cloadding,i are the effective refractive indices of the core mode and the i-th cladding mode, respectively, and Λ is the nominal period of the tilted grating.

[0016] Preferably, the relationship between Λ and the grating period Λg along the fiber direction can be expressed as:

[0017] Λ=Λ g cosξ;

[0018] When the optical fiber is bent in different directions, Λ will change to different degrees, resulting in a significant drift in the Bragg reflection wavelength and the cladding mode resonance wavelength.

[0019] Preferably, the propagation region of the cladding mode is located in the optical fiber cladding, which will induce an evanescent field on the sensor surface. The evanescent field and the gold film on the sensor surface are mutually coupled to stimulate the surface plasmon resonance phenomenon. The wavelength λ of the surface plasmon resonance wave is:

[0020]

[0021] in, is the effective refractive index of the evanescent field, is the effective refractive index of the surface plasmon, ε m is the dielectric constant of the metal layer, ε d is the dielectric constant of polydimethylsiloxane, and the above four variables are all functions of the resonance wavelength λ.

[0022] Therefore, the present invention adopts the above-mentioned spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor, which has the following beneficial effects: utilizing the electric field sensitive characteristics of the surface plasmon resonance exciton to detect the bending angle of the sensor; utilizing the asymmetry of the tilted fiber Bragg grating to detect the bending direction of the sensor; combining the intrinsic response of the core film in the tilted fiber Bragg grating to temperature changes to calibrate the influence of external temperature changes on the sensor, so that the sensor can simultaneously detect the bending direction and bending angle of the sensor.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a spatial angle measurement device based on a tilted fiber Bragg grating-surface plasmon resonance sensor according to an embodiment of the present invention;

[0025] Figure 2 A schematic diagram of a tilt angle measuring sensor probe according to an embodiment of the present invention;

[0026] Figure 3 This is an experimental diagram of the transmission spectrum variation when measuring different inclination angles according to an embodiment of the present invention;

[0027] Figure 4 The vector angle measurement result of the embodiment of the present invention, the red dots are the true values, and the blue dots are the demodulated values;

[0028] Reference numerals

[0029] 1. Broadband light source; 2. Polarizer; 3. Polarization controller; 4. Sensor; 41. Tilted fiber grating; 42. Gold film; 43. Polydimethylsiloxane; 5. Spectrometer; 6. Computer. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0032] Example

[0033] like Figure 1 As shown, the present invention provides a spatial angle measurement device based on a tilted fiber grating-surface plasmon resonance sensor.

[0034] The invention comprises a broadband light source 1, a polarizer 2, a polarization controller 3, a sensor 4, a spectrometer 5 and a computer 6. The broadband light source 1, the polarizer 2, the polarization controller 3, the sensor 4 and the spectrometer 5 are connected in sequence through a single-mode optical fiber. The other end of the spectrometer 5 is connected to the computer 6 through a data line.

[0035] Sensor 4 is a tilted fiber grating-surface plasma resonance sensor. The tilted fiber grating-surface plasma resonance sensor is formed by sequentially writing a small-angle tilted fiber grating 41 on a single-mode optical fiber, coating a certain thickness of gold film 42 on the outer layer of the grating, and then immersing the entire sensing area in polydimethylsiloxane 43, so that the polydimethylsiloxane 43 is hardened as a protective layer to complete the encapsulation. The tilted fiber grating 41 is written by the phase mask method, the angle between the grating plane and the fiber axis is 80°-84°, the grating area length is 10mm-15mm, and the grating axial period is 25μm-30μm. The gold film 42 is coated by magnetron sputtering or evaporation coating method, the film thickness is 30nm-60nm, and the coating range of the gold film 42 is 10mm-15mm, which is the same as the grating area length. The film thickness of polydimethylsiloxane 43 is 5mm-10mm, and the film length of polydimethylsiloxane 43 is 50mm-100mm.

[0036] The tilted fiber Bragg grating 41 is sensitive to the bending direction and bending angle of the sensing area, and the change in the transmission spectrum of the sensor 4 corresponding to the change in the bending direction and bending angle is called the vector angle sensitivity of the sensor 4. The vector angle sensitivity of the tilted fiber Bragg grating 41 is directional, with the largest vector angle sensitivity in the direction of the grating slow axis and the smallest vector angle sensitivity in the direction of the grating fast axis.

[0037] The tilted fiber Bragg grating-surface plasmon resonance sensor is insensitive to the bending direction of the sensing area, but sensitive to the bending angle of the sensing area, and the bending angle change is within the angle response range of the tilted fiber Bragg grating-surface plasmon resonance sensor.

[0038] The sensing mechanism of the tilted fiber Bragg grating-surface plasmon resonance sensor is as follows: the light emitted from the broadband light source 1 is converted from a fully polarized wave to a transverse magnetic wave after passing through the polarizer 2 and the polarization controller 3, and then enters the tilted fiber Bragg grating-surface plasmon resonance sensor to sense the change in spatial angle, the optical signal is received by the spectrometer 5, and finally the direction and size of the bending angle are demodulated by the computer 6.

[0039] Working principle: The 2 cm length area where the tilted fiber grating-surface plasmon resonance sensor is located is the sensing area. During measurement, one end of the sensor 4 is fixed on the device and remains unchanged, and the other end of the sensor 4 can be bent freely to achieve changes in any tilt angle, and changes in any direction and any tilt angle. Due to the protective effect of polydimethylsiloxane 43 as a packaging layer, the sensor 4 will not be broken or damaged due to changes in bending stress. After the incident light passes through the polarizer 2 and enters the tilted fiber grating-surface plasmon resonance sensor, the tilted fiber grating 41 will destroy the fundamental mode field propagating in the core, and form a cladding mode and a Bragg core mode that propagate in the opposite direction. When the sensor 4 is bent in different directions, it will cause its Bragg reflection wavelength and cladding mode resonance wavelength to drift. The Bragg reflection wavelength and the cladding mode resonance wavelength are:

[0040]

[0041] Where ξ is the angle between the grating plane and the perpendicular plane of the optical fiber, n eff,core and n eff,cloadding,i are the effective refractive indices of the core mode and the i-th cladding mode, respectively. Λ corresponds to the nominal period of the tilted fiber grating 41, and its relationship with the grating period Λg along the fiber direction can be expressed as:

[0042] Λ=Λgcosξ;

[0043] When the optical fiber is bent in different directions, Λ will change to different degrees, resulting in a significant drift in the Bragg reflection wavelength and the cladding mode resonance wavelength.

[0044] In addition, the propagation area of ​​the cladding mode is located in the optical fiber cladding. This mode will induce an evanescent field on the surface of the sensor 4. The evanescent field is coupled with the metal layer (i.e., the gold film 42) on the surface of the sensor 4 to stimulate the surface plasmon resonance phenomenon. The wavelength λ of the surface plasmon resonance wave is:

[0045]

[0046] in, is the effective refractive index of the evanescent field, is the effective refractive index of the surface plasmon, ε m is the dielectric constant of the metal layer, ε d is the dielectric constant of polydimethylsiloxane 43, and the above four variables are all functions of the resonance wavelength λ.

[0047] When the sensor 4 is bent, the evanescent field on the surface of the optical fiber cladding A corresponding change will occur, and this change is independent of the bending direction of the sensor 4. Therefore, the bending angle of the sensor 4 can be inferred by detecting the change in the resonant wavelength of the sensor 4.

[0048] The tilted fiber grating-surface plasmon resonance structure used can simultaneously excite the cladding mode and the surface plasmon. Since the tilted fiber grating 41 is an asymmetric structure, and the surface plasmon is a symmetric structure. Therefore, the size of the inclination angle and the direction of the bending process of the sensor 4 will have different effects on the cladding mode and the plasmon resonance. The drift of the plasmon resonance wavelength is only related to the size of the inclination angle, and the change of the cladding mode is related to the size and direction of the inclination angle at the same time, so that the size and direction of the inclination angle can be measured simultaneously. In addition, the Bragg core mode can be used as a reference wavelength to eliminate the temperature cross-sensitive response in the sensing measurement.

[0049] Therefore, the present invention adopts the above-mentioned spatial angle measurement device based on the tilted fiber grating-surface plasmon resonance sensor, which has a simple structure, is easy to manufacture, has high sensitivity and accuracy, and can simultaneously detect the bending direction and bending angle of the sensor.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A spatial angle measurement device based on a tilted fiber Bragg grating-surface plasmon resonance sensor, characterized in that: It includes a broadband light source, a polarizer, a polarization controller, a sensor, a spectrometer and a computer, wherein the broadband light source, the polarizer, the polarization controller, the sensor and the spectrometer are connected in sequence through a single-mode optical fiber, and the other end of the spectrometer is connected to the computer through a data line; The light emitted from the broadband light source passes through the polarizer and polarization controller, and then changes from a fully polarized wave to a transverse magnetic wave, and then enters the sensor to sense the change in spatial angle. The light signal is received by the spectrometer, and finally the direction and size of the bending angle are demodulated by the computer.

2. The spatial angle measurement device based on the tilted fiber grating-surface plasmon resonance sensor according to claim 1, characterized in that: The sensor is a tilted fiber Bragg grating-surface plasmon resonance sensor, which is made by writing a small-angle tilted fiber Bragg grating on a single-mode optical fiber, coating a gold film on the surface of the optical fiber cladding to wrap the entire grating area, and encapsulating and protecting the entire sensing area with polydimethylsiloxane.

3. The spatial angle measurement device based on the tilted fiber grating-surface plasmon resonance sensor according to claim 2, characterized in that: The tilted fiber grating is written by a phase mask method, the angle between the grating plane and the fiber axis is 80°-84°, the grating region length is 10mm-15mm, and the grating axial period is 25μm-30μm.

4. The spatial angle measurement device based on the tilted fiber grating-surface plasmon resonance sensor according to claim 2, characterized in that: The gold film is coated by magnetron sputtering or evaporation coating method, the film thickness is 30nm-60nm, and the gold film coating range is 10mm-15mm, which is the same as the gate area length.

5. The spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor according to claim 2, characterized in that: The thickness of the polydimethylsiloxane film layer is 5mm-10mm, and the length of the polydimethylsiloxane film layer is 50mm-100mm.

6. The spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor according to claim 2, characterized in that: The tilted fiber Bragg grating is sensitive to the bending direction and bending angle of the sensing area. The change in the sensor transmission spectrum corresponding to the change in the bending direction and bending angle is the vector angle sensitivity of the sensor. The vector angle sensitivity of the tilted fiber Bragg grating in the direction of the grating slow axis is the largest, and the vector angle sensitivity of the tilted fiber Bragg grating in the direction of the grating fast axis is the smallest.

7. The spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor according to claim 2, characterized in that: The sensor is insensitive to the bending direction of the sensing area, but is sensitive to the bending angle of the sensing area, and the change of the bending angle is within the angle response range of the sensor.

8. The spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor according to claim 2, characterized in that: After the incident light passes through the polarizer and enters the tilted fiber Bragg grating-surface plasmon resonance sensor, the tilted fiber Bragg grating will destroy the fundamental mode field propagating in the fiber core and form the reverse propagating cladding mode and Bragg core mode. When the sensor is bent in different directions, it will cause the Bragg reflection wavelength and the cladding mode resonance wavelength to drift, where the Bragg reflection wavelength and the cladding mode resonance wavelength are: Where ξ is the angle between the grating plane and the perpendicular plane of the optical fiber, n eff,core and n eff,cladding,i are the effective refractive indices of the core mode and the i-th cladding mode, respectively, and Λ is the nominal period of the tilted grating.

9. The spatial angle measurement device based on the tilted fiber grating-surface plasmon resonance sensor according to claim 8, characterized in that: Λ and the grating period Λ along the fiber g The relationship can be expressed as: L=L g cosξ; When the optical fiber is bent in different directions, Λ will change to different degrees, resulting in a significant drift in the Bragg reflection wavelength and the cladding mode resonance wavelength.

10. The spatial angle measurement device based on the tilted fiber Bragg grating-surface plasmon resonance sensor according to claim 9, characterized in that: The propagation area of ​​the cladding mode is located in the optical fiber cladding, which will induce an evanescent field on the sensor surface. The evanescent field is coupled with the gold film on the sensor surface, exciting the surface plasmon resonance phenomenon. The wavelength λ of the surface plasmon resonance wave is: in, is the effective refractive index of the evanescent field, is the effective refractive index of the surface plasmon, ε m is the dielectric constant of the metal layer, ε d is the dielectric constant of polydimethylsiloxane, and the above four variables are all functions of the resonance wavelength λ.

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