A fiber optic microring hydrophone based on composite film sensitivity enhancement

Abstract

The present invention discloses an optical fiber microring hydrophone based on composite film sensitization, wherein the hydrophone is composed of an optical fiber microring made of a single-mode optical fiber and a composite film. When an underwater low-frequency sound wave hits the microring, due to the influence of external pressure, the refractive index and circumference of the optical fiber microring change, which in turn causes the resonance spectrum to shift, and the intensity of the same wavelength point changes. The frequency and amplitude of the external sound wave signal are detected by the intensity change of the wavelength point, thereby realizing the detection of the external sound wave. The main function of the composite film is to resonate with the external sound wave, and the resonant deformation of the composite film is used to increase the deformation of the optical fiber microring, thereby further improving the sound pressure sensitivity. The hydrophone of the present invention can avoid electromagnetic interference, has good stability, and is miniaturized; in addition, the resonance point can be tuned by changing the thickness and radius of the composite film, thereby realizing the tunability of the sound wave frequency point detection, and at the same time, the sound pressure sensitivity can be further improved.

Description

Technical Field

[0001] The invention relates to the field of sensors, and in particular to an optical fiber micro-ring hydrophone based on composite film sensitization. Background Art

[0002] Fiber-optic hydrophones are devices that use fiber-optic technology to detect underwater low-frequency sound waves. They detect the frequency and amplitude of sound waves by changing their optical signals. With the advantages of small size, strong anti-electromagnetic interference ability and high sensitivity, they are gradually replacing piezoelectric acoustic sensors in the fields of sound wave detection, submarine detection, marine resource exploration and passive sonar.

[0003] Nowadays, in the field of underwater low-frequency sound wave sensing, most fiber-optic hydrophones are Fabry-Perot (FP) acoustic wave sensors, but the sensor manufacturing process is complicated and expensive. As for fiber-optic microring hydrophones, they have become a new research trend due to their advantages of simple and convenient manufacturing, low cost, and high quality factor. Therefore, fiber-optic microring hydrophones have high research value. The present invention combines the fiber-optic microring with the composite film, which greatly improves the sensitivity of underwater low-frequency sound wave detection. Summary of the invention

[0004] In view of the fact that most traditional hydrophones are piezoelectric acoustic sensors, which are easily affected by electromagnetic interference and are not suitable for harsh environments, the present invention proposes an optical fiber microring hydrophone based on composite thin film sensitization, which has a simple manufacturing process, low cost, high sensitivity, and can achieve tunable detection of sound wave frequency points.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a composite film-based sensitization optical fiber microring hydrophone, characterized in that the hydrophone comprises: an optical fiber microring and a composite film; the composite film is plasma bonded to a bottom glass substrate with a certain diameter, the optical fiber microring is solidified and packaged in the middle of the composite film, and the corresponding optical fiber microring is just above the through hole; when underwater low-frequency sound waves hit the composite film, the composite film resonance is used to increase the deformation of the optical fiber microring, so that a sensitization effect is achieved for underwater low-frequency sound wave detection; the production process and packaging process of the hydrophone include:

[0007] The single-mode optical fiber is tapered and knotted into an optical fiber micro-ring;

[0008] Glass spacers of a certain thickness are fixed on both sides of the bottom glass substrate with holes, and the bottom PDMS film is plasma bonded to the bottom glass substrate with holes;

[0009] Place the optical fiber microring on the bottom PDMS film, with the through hole of the bottom holed glass substrate directly below it, and then drop low refractive index glue MY-132-A on the optical fiber microring and wrap it around;

[0010] Then the two ends of the optical fiber microring were encapsulated with PDMS solution and sealed with blocks on both sides to prevent the solution from overflowing;

[0011] The top PDMS film is plasma bonded to the top perforated glass cover plate, and then covered on the glass gasket together. In an oxygen-free environment, the low-refractive index glue MY-132-A is cured using a UV lamp, and finally the top glass cover plates on both sides are fixed to the block blocks on both sides.

[0012] Furthermore, the diameter of the optical fiber microring is 200-800 μm, and the diameter of the micro-nano optical fiber is 2-4 μm.

[0013] Furthermore, the composite film is composed of three layers of films, namely a bottom PDMS film, a low refractive index glue MY-132-A, and a top PDMS film.

[0014] Furthermore, the PDMS film is colorless, odorless, corrosion-resistant, has good material chemical properties, and has a refractive index lower than that of the optical fiber core, which can prevent a large amount of light leakage in the optical fiber microring; the low-refractive index glue MY-132-A has a refractive index of 1.32 and is a very good optical packaging material. Under oxygen-free conditions, it can be cured by irradiation with ultraviolet light to encapsulate the optical fiber microring, forming a protective layer and preventing light leakage.

[0015] Furthermore, the sensing principle of the hydrophone is based on the change of the refractive index and circumference of the optical fiber microring. Since the resonant wavelength of the optical fiber microring must satisfy the condition λ=2πn eff R / m, when external sound waves hit the composite film, the composite film will resonate, which will make the effective refractive index of the optical fiber microring n eff And the radius R will change, causing the resonant wavelength λ of the fiber microring to shift.

[0016] Furthermore, the demodulation algorithm of the hydrophone is based on intensity demodulation. When the resonant wavelength shifts, the intensity of the same wavelength point before and after the shift will change, and then compared with the reference hydrophone, the frequency and sensitivity of the external sound wave are demodulated through the change in intensity.

[0017] Furthermore, the demodulation algorithm of the hydrophone takes into account the thermal noise of the tunable laser and other devices, which leads to unstable working wavelength and working point offset. Therefore, it is necessary to measure the working point wavelength through the DC output of the photodetector to determine, and compare the DC component obtained by signal processing with a preset range. If the DC component is between the preset range, the output wavelength of the laser is not changed. Otherwise, the output wavelength of the laser is changed to lock the working point.

[0018] Compared with the prior art, the present invention has the following beneficial effects: it provides an optical fiber microring hydrophone based on composite film sensitization, which has the characteristics of anti-electromagnetic interference, good stability, high sensitivity, simple manufacturing process and low cost; the hydrophone combines the optical fiber microring with the composite film, and when underwater low-frequency sound waves hit the composite film, the deformation of the optical fiber microring is increased by utilizing the resonant deformation of the composite film, thereby further improving the sound pressure sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of a process for manufacturing an optical fiber microring hydrophone based on composite thin film sensitization according to an embodiment of the present invention.

[0020] Figure 2 It is an isometric view of an optical fiber microring hydrophone based on composite thin film sensitization according to an embodiment of the present invention.

[0021] Figure 3 It is an exploded view of the structure of an optical fiber microring hydrophone based on composite thin film sensitivity enhancement according to an embodiment of the present invention.

[0022] Figure 4 4 is a diagram of an experimental device for underwater low-frequency sound wave detection according to an embodiment of the present invention.

[0023] Figure 5 It is a time domain and frequency domain response diagram of the optical fiber microring hydrophone based on composite thin film sensitization according to an embodiment of the present invention and a reference hydrophone to a sound wave signal with a frequency of 1.6 kHz.

[0024] Figure 6 The figure is the relationship between the output voltage and the sound pressure of the optical fiber microring hydrophone based on composite thin film sensitivity enhancement at a sound wave frequency of 1 kHz in an embodiment of the present invention.

[0025] Description of Reference Numerals

[0026] 1- bottom glass substrate with holes, 2- glass gasket, 3- bottom PDMS film, 4- optical fiber microring, 5- low refractive index glue MY-132-A, 6- PDMS solution, 7- blockers on both sides, 8- top PDMS film, 9- top glass cover with holes, 10- top glass cover plates on both sides, 11- computer, 12- data acquisition card, 13- photodetector, 14- vibration table, 15- rigid wall circular tube, 16- water, 17- reference hydrophone, 18- power amplifier, 19- signal generator, 20- polarizer, 21- tunable laser DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "include" and / or "comprising" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] like Figure 1 As shown, this embodiment provides a flow chart of a process for manufacturing an optical fiber microring hydrophone based on composite thin film sensitization, including:

[0031] Step S1: The single-mode optical fiber is tapered and knotted into an optical fiber micro-ring 4.

[0032] Take a 30cm long single-mode optical fiber, and use optical fiber strippers to remove a 5cm long coating in the middle of the single-mode optical fiber. Then, place the single-mode optical fiber on the clamps at both ends of the taper platform, align the portion without the coating with the oxyhydrogen flame, adjust the distance and height between the oxyhydrogen flame and the optical fiber, and then set the parameters of the stepper motor, slowly drive the optical fiber to both ends, gradually pull the optical fiber diameter to 2-4μm, and then turn off the oxyhydrogen flame and the stepper motor; remove the optical fiber, manually make a ring with a diameter of 2cm, and then place the optical fiber on the clamps at both ends to fix it, adjust the parameters of the stepper motor, and slowly drive the optical fiber to both ends until the diameter of the optical fiber microring 4 is pulled into 200-800μm.

[0033] Step S2: glass spacers 2 of a certain thickness are fixed on both sides of the bottom glass substrate 1 with holes, and the bottom PDMS film 3 is plasma bonded to the bottom glass substrate 1 with holes.

[0034] A through hole with a certain diameter is punched in the glass substrate, and then the surface of the bottom holed glass substrate (1) is cleaned, and glass gaskets of a certain thickness are fixed on both sides thereof with UV curing adhesive. After that, the bottom holed glass substrate 1 and the bottom PDMS film 3 are put into a plasma cleaning machine together, and after plasma treatment, the bottom holed glass substrate 1 and the bottom PDMS film 3 are bonded together.

[0035] Step S3: Place the optical fiber microring 4 on the bottom PDMS film 3, with the through hole of the bottom porous glass substrate 1 directly below it, and then drop the low refractive index glue MY-132-A5 on the optical fiber microring 4 and wrap the optical fiber microring 4.

[0036] The optical fiber microring 4 is placed on the bottom PDMS 3 film. Since the refractive index of PDMS is about 1.40, which is slightly smaller than the refractive index of the optical fiber core, it can prevent a large amount of light leakage. The through hole of the bottom perforated glass substrate 1 is just below the optical fiber microring 4. This is mainly to cause the deformation of the bottom PDMS film 3 caused by sound waves to drive the refractive index and circumference of the optical fiber microring 4 to change, thereby improving the sound pressure sensitivity. Then, low-refractive-index glue MY-132-A is dripped on the optical fiber microring 4. Its refractive index is 1.32, which is also a good optical packaging glue. The optical fiber microring 4 is wrapped to prevent light leakage.

[0037] Step S4: Then the two ends of the optical fiber microring 4 are placed in the PDMS solution 6 for encapsulation and sealed with stoppers 7 on both sides to prevent the solution from overflowing.

[0038] The mass ratio of PDMS to curing agent is 10:1, and then the mixture is stirred evenly and vacuumed to eliminate bubbles in the solution. The PDMS solution 6 is then used to cover both ends of the optical fiber microring 4 for packaging, and sealed with blocks 7 on both sides to prevent the solution from overflowing.

[0039] Step S5: The top PDMS film 8 is plasma bonded to the top perforated glass cover plate 9, and then covered on the glass gasket 2 together. In an oxygen-free environment, the low refractive index glue MY-132-A5 is cured using an ultraviolet lamp, and finally the top glass cover plates 10 on both sides are fixed on the two side blocks 7.

[0040] like Figure 2 As shown, an embodiment of the present invention provides an isometric view of a fiber optic microring hydrophone based on composite thin film sensitization.

[0041] like Figure 3As shown, an embodiment of the present invention provides an exploded diagram of a fiber optic microring hydrophone structure based on composite thin film sensitization.

[0042] like Figure 4 As shown, an embodiment of the present invention provides an experimental device diagram for underwater low-frequency sound wave detection.

[0043] The two ends of the optical fiber microring 4 are connected to the polarizer 20 and the photodetector 13 respectively through a fiber fusion machine; first, the tunable laser 21 outputs a wavelength of a certain band, passes through the polarizer 20, and passes through the optical fiber microring 4 to excite the resonance mode and generate a resonance wavelength. When the sound wave hits the composite film, the resonance wavelength of the optical fiber microring 4 is shifted. The photodetector 13 converts the optical signal into an electrical signal, transmits it to the data acquisition card 12 for storage, and connects to the computer terminal 11 to perform intensity demodulation on the signal, demodulates the frequency and amplitude of the corresponding sound wave, and then compares it with the signal of the reference hydrophone 17 to obtain the corresponding sound pressure sensitivity.

[0044] The underwater low-frequency sound waves are generated by a signal generator 19 that emits a sinusoidal signal of a certain frequency, which passes through a power amplifier 18 and then drives the vibration table 14 to generate vibrations, so that sound waves of corresponding frequencies are generated in the water 16 of the rigid-walled circular tube 15. The reference hydrophone 17 is calibrated according to the national standard, and the signal is directly transmitted to the data acquisition card 12.

[0045] When the signal generator 19 drives the vibration table 14 to emit sound waves of a certain frequency, when the sound waves hit the composite film, the composite film produces resonance deformation, causing the refractive index and circumference of the optical fiber microring 4 to change, and the resonant wavelength to shift. The intensity of the same wavelength point before and after the shift will change, and the frequency and amplitude of the corresponding sound wave can be demodulated by the intensity.

[0046] In order to better demodulate the frequency and amplitude of the sound wave, the tunable laser 21 is first used to perform spectrum scanning, and the wavelength corresponding to the middle voltage value is approximately selected as the working wavelength, because the amplitude change of this wavelength is relatively most obvious when subjected to sound waves.

[0047] Taking into account the thermal noise of the tunable laser 21 and other devices, which causes the working wavelength to be unstable and the working point to be offset, it is necessary to measure the working point wavelength by judging the DC output by the photodetector 13, and compare the DC component obtained by signal processing with the preset range. If the DC component is between the preset range, the output wavelength of the tunable laser 21 will not be changed. Otherwise, the output wavelength of the tunable laser 21 will be changed to lock the working point.

[0048] like Figure 5 As shown, the embodiment of the present invention provides a time domain and frequency domain response diagram of a fiber optic microring hydrophone based on composite thin film sensitization and a reference hydrophone to a sound wave signal with a frequency of 1.6 kHz.

[0049] like Figure 6 As shown, the embodiment of the present invention provides the relationship between the output voltage and the sound pressure of the optical fiber microring hydrophone based on composite thin film sensitization at a sound wave frequency of 1 kHz.

[0050] The above is a detailed introduction to a composite thin film-sensitized optical fiber microring hydrophone provided by the present invention. The description of the specific embodiment is only used to help understand the structure and design of the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. An optical fiber microring hydrophone based on composite film sensitization, characterized in that: The hydrophone comprises: an optical fiber microring (4) and a composite film; the composite film is plasma bonded to a bottom glass substrate (1) with a certain diameter and having a hole; the optical fiber microring (4) is solidified and packaged in the middle of the composite film, and the corresponding optical fiber microring (4) is just above the through hole; when underwater low-frequency sound waves hit the composite film, the composite film resonance is used to increase the deformation of the optical fiber microring (4), so that a sensitivity enhancement effect is achieved for underwater low-frequency sound wave detection; the production process and packaging process of the hydrophone comprise: The single-mode optical fiber is tapered and knotted into an optical fiber micro-ring (4); Glass gaskets (2) of a certain thickness are fixed on both sides of the bottom glass substrate with holes (1), and the bottom PDMS film (3) is plasma bonded to the bottom glass substrate with holes (1); The optical fiber microring (4) is placed on the bottom PDMS film (3), with the through hole of the bottom holed glass substrate (1) directly below, and then the low refractive index glue MY-132-A (5) is dripped on the optical fiber microring (4) and wrapped around the optical fiber microring (4); Then, both ends of the optical fiber microring (4) are encapsulated with a PDMS solution (6) and sealed with stoppers (7) on both sides to prevent the solution from overflowing; The top PDMS film (8) is plasma bonded to the top perforated glass cover plate (9), and then covered on the glass gasket (2). In an oxygen-free environment, the low refractive index glue MY-132-A (5) is cured using an ultraviolet lamp, and finally the top glass cover plates (10) are fixed on the two side blocks (7).

2. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 1, characterized in that: The diameter of the optical fiber micro-ring (4) is 200-800 μm, and the diameter of the micro-nano optical fiber is 2-4 μm.

3. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 1, characterized in that: The composite film is composed of three layers of films, namely a bottom PDMS film (3), a low refractive index glue MY-132-A (5), and a top PDMS film (8).

4. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 3, characterized in that: The PDMS film is colorless, odorless, corrosion-resistant, has good material chemical properties, and has a refractive index lower than that of the optical fiber core, thereby preventing a large amount of light leakage in the optical fiber microring (4); the low-refractive-index glue MY-132-A (5) has a refractive index of 1.32 and is a good optical packaging material. Under oxygen-free conditions, it can be cured by irradiation with ultraviolet light to encapsulate the optical fiber microring (4), form a protective layer and prevent light leakage.

5. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 1, characterized in that: The sensing principle of the hydrophone is based on the change of the refractive index and circumference of the optical fiber microring (4). Since the resonant wavelength of the optical fiber microring must satisfy the condition λ=2πn eff R / m, when external sound waves hit the composite film, the composite film will resonate, which will cause the effective refractive index n of the optical fiber microring (4) to eff And the radius R will change, causing the resonant wavelength λ of the fiber microring to shift.

6. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 1, characterized in that: The demodulation algorithm of the hydrophone is based on intensity demodulation. When the resonant wavelength shifts, the intensity of the same wavelength point before and after the shift will change. Then, compared with the reference hydrophone, the frequency and sensitivity of the external sound wave are demodulated through the change in intensity.

7. The optical fiber microring hydrophone based on composite thin film sensitization according to claim 6, characterized in that: The demodulation algorithm of the hydrophone takes into account the thermal noise of the tunable laser and other devices, which leads to unstable working wavelength and working point offset. Therefore, it is necessary to measure the working point wavelength through the direct current output by the photodetector to determine, and compare the direct current component obtained by signal processing with the preset range. If the direct current component is between the preset range, the output wavelength of the laser is not changed, otherwise, the output wavelength of the laser is changed.

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