CN103344316A - Sound wave sensor probe of asymmetric structure and hydrophone - Google Patents

Abstract

Provided is a sound wave sensor probe of an asymmetric structure. The sound wave sensor probe of the asymmetric structure comprises an external protective sleeve. The sound wave sensor probe of the asymmetric structure is characterized in that pierced sound wave windows are formed in the surface of the external protective sleeve, a silencing sleeve is arranged inside the external protective sleeve, a fiber bragg grating portion of a distributed feedback type fiber laser penetrates through the silencing sleeve to be fixedly installed inside the external protective sleeve, the position of the end face of the free end of the silencing sleeve aligns to the central symmetry axis of a phase shift grating of the distributed feedback type fiber laser, the fiber bragg grating portion of the distributed feedback type fiber laser is divided into a left grating area and a right grating area according to the position of phase shift, the left grating area is completely inserted into the silencing sleeve, and the right grating area is completely exposed in a sound wave field. provided is a hydrophone. The hydrophone is characterized by comprising a working light path of the distributed feedback type fiber laser, wherein the working light path of the distributed feedback type fiber laser is composed of a pump light source, a wavelength division multiplexer and the sound wave sensor probe of the asymmetric structure, wherein the pump light source is connected with a WDM pump end, a WDM public end is connected with the sound wave sensor probe of the asymmetric structure, and generated laser is output to an interrogator through a WDM output end.

Description

Asymmetric structure-acoustic sensor probe and hydrophone

technical field

The present invention relates to an asymmetric optical fiber hydrophone probe package structure, which is used to realize high-sensitivity sound wave detection.

Background technique

A hydrophone is an instrument that detects signals such as pressure and sound in a liquid by using the characteristics of the material and various modulation effects generated by its interaction with the surrounding environment. Generally, civilian hydrophones are used for seismic detection; in the military, they are used as sonar systems for enemy sniffing of submarines and ships. Therefore, hydrophones are very important for defense and industrial applications.

Due to the advantages of extremely narrow linewidth, high signal-to-noise ratio, linearly adjustable wavelength, low phase noise and stable single-mode output, fiber DFB laser can be used as an extremely superior light source for fiber optic sensing systems for ultra-long-distance , ultra-high precision and ultra-high sensitivity sensing. The active fiber grating sensor composed of DFB fiber laser, in addition to the above advantages, its biggest advantage is that the optical power of the output wavelength is significantly improved, so that compared with the general broadband light source, the intensity signal-to-noise ratio of the sensing signal It has been greatly improved, which provides a good foundation for the detection of wavelength shift. Its ultra-narrow linewidth of 10kHz-50kHz can detect weak Dynamic strain signal. Due to the high sensitivity of DFB fiber lasers to sound waves, they are also used in fiber optic hydrophones, D. Thingbo et al. used the signal of the sound pressure field to modulate the length and refractive index of the DFB fiber laser sensor head, and demodulated it with an unbalanced interferometer device, and obtained a flat gain response of the sound wave signal frequency up to 800kHz. Domestic research on DFB-FL hydrophones started relatively late due to limitations in the development of doped optical fiber manufacturing technology and phase-shift grating writing technology. , National University of Defense Technology and our unit have achieved certain results in the aspects of probe sensitization package, demodulation, multiplexing array and test respectively. Among them, the most important research focus is still how to improve the sensitivity of the sensor. Traditionally, the distributed feedback fiber laser is used as the sensing component, and it is packaged in a tubular or other shaped airtight space. When the sound wave acts on the sensor shell When it is on, it will cause the deformation of the shell, which will be transmitted to the laser, so that the wavelength will be shifted. In addition, there are also structures that allow the laser to experience acoustic disturbances, resulting in wavelength changes.

In short, so far almost all fiber optic hydrophone probes based on DFB fiber lasers at home and abroad have symmetrical structures, and no sensor design schemes that use asymmetric structures to achieve sensitivity enhancement have been found.

Contents of the invention

This scheme proposes a design scheme of an asymmetric structure optical fiber hydrophone sensing probe, which increases the sensitivity of acoustic wave detection through asymmetric structure, thereby realizing high-sensitivity acoustic wave detection.

The technical measures adopted in this plan are: an asymmetric structure acoustic wave sensor probe, which includes an external protective casing, which is characterized in that a hollow sound wave window is arranged on the surface of the external protective casing, and a sound-absorbing casing is arranged inside the external protective casing , the fiber grating part of the distributed feedback fiber laser is installed and fixed inside the outer protective sleeve through the silencer sleeve, and the end face position of the free end of the silencer sleeve is aligned with the central symmetry axis of the phase shift grating of the distributed feedback fiber laser; the fiber of the distributed feedback fiber laser The grating part is divided into a left grating area and a right grating area according to the phase shift position. The left grating area is completely inserted into the sound-absorbing sleeve, and the right grating area is completely exposed to the sound wave field.

The specific features of this scheme are that the sound-absorbing casing is made of multiple layers of materials with different densities, and from the outside to the inside are metal tubes, sound-absorbing cotton layers, and vacuum quartz casings. The vacuum quartz casing includes quartz inner tubes and quartz The outer tube, the quartz inner tube and the quartz outer tube are connected together at the opening to form a closed vacuum sleeve, and a through hole for passing through the optical fiber is arranged in the center of the vacuum quartz sleeve. In order to achieve the sound attenuation effect. The metal tube is used to protect the sound-absorbing tube. The sound-absorbing cotton layer can absorb the sound waves transmitted from the outside to the tube core. The quartz outer tube and the quartz inner tube together form a vacuum quartz sleeve. The interlayer is sealed and vacuumed, so that the sound waves and vibration signals cannot pass through Penetrating into, so as to achieve the sound wave shielding effect. Due to the high density of the metal tube and vacuum quartz sleeve, and the very small density of the sound-absorbing cotton layer and the vacuum area, a multi-layer sound wave reflection section is formed, which is beneficial to sound wave reflection and sound reduction.

The structure of the fiber grating part of the distributed feedback fiber laser is shown in Figure 3. It is realized by writing a phase shift grating on a section of erbium-doped fiber with a length of several centimeters by ultraviolet laser. The phase shift of the phase shift grating is π/2, and the phase shift The position is in the middle of the grating.

The present invention also provides a hydrophone, which is characterized in that it includes a distributed feedback optical fiber laser working optical path composed of a pump light source, a WDM and an asymmetric structure acoustic wave sensor probe; the pump light source is connected to the WDM pump end, and the WDM The common end is connected to the probe of the asymmetric structure acoustic wave sensor, and the generated laser is output to the demodulator through the WDM output end.

The specific feature of this solution is that the asymmetric structure acoustic wave sensor probe includes an external protective sleeve, which is characterized in that a hollow sound wave window is arranged on the surface of the external protective sleeve, and a sound-absorbing sleeve is arranged inside the external protective sleeve. The fiber grating part of the distributed feedback fiber laser is installed and fixed inside the outer protective sleeve through the sound-absorbing sleeve. The part is divided into left grid area and right grid area according to the phase shift position, the left grid area is completely inserted into the muffler sleeve, and the right grid area is completely exposed to the sound wave field;

The sound-absorbing sleeve is made of multiple layers of materials with different densities. From the outside to the inside, there are metal tubes, sound-absorbing cotton layers, and vacuum quartz sleeves. The vacuum quartz sleeves include quartz inner tubes and quartz outer tubes, quartz inner tubes and quartz tubes. The outer tubes are connected together at the openings to form a closed vacuum sleeve, and a through hole for passing through the optical fiber is arranged in the center of the vacuum quartz sleeve. In order to achieve the sound attenuation effect. The metal tube is used to protect the sound-absorbing tube. The sound-absorbing cotton layer can absorb the sound waves transmitted from the outside to the tube core. The quartz outer tube and the quartz inner tube together form a vacuum quartz sleeve. The interlayer is sealed and vacuumed, so that the sound waves and vibration signals cannot pass through Penetrating into, so as to achieve the sound wave shielding effect. Due to the high density of the metal tube and vacuum quartz sleeve, and the very small density of the sound-absorbing cotton layer and the vacuum area, a multi-layer sound wave reflection section is formed, which is beneficial to sound wave reflection and sound reduction.

The structure of the fiber grating part of the distributed feedback fiber laser is shown in Figure 3. It is realized by writing a phase-shifting grating on a section of erbium-doped fiber with a length of several centimeters (generally between 1-10cm) by ultraviolet laser. The phase-shifting grating phase The shift amount is π/2, and the phase shift position is the middle of the grating.

When the pumping light source produces enough pumping laser light to pass through the WDM into the fiber grating part of the distributed feedback fiber laser, the optical fiber in the fiber grating part of the distributed feedback fiber laser will absorb the pumping light energy and generate The new narrow-linewidth single-frequency stable laser is transmitted to both ends respectively, and the backward laser is output from the WDM output end after passing through the WDM. The fiber grating part of the distributed feedback fiber laser passes through the holes at both ends of the sensor housing. The noise-absorbing sleeve covers the left grid area of the distributed feedback fiber laser, and the right grid area of the distributed feedback fiber laser is exposed to the acoustic field. Phase shift The zone is located just near the right end face of the muffler sleeve. When the acoustic radiation enters the sensor, the right grid area of the distributed feedback fiber laser is fully exposed to the acoustic wave field, while the left grid area is silenced due to the existence of the sound-absorbing sleeve, so that the distributed feedback fiber laser is asymmetrically affected. Disturbance of the sound field.

The sensor shell is made of metal material or other hard materials, which protects the sensor and also serves as the base of the sensor. There are multiple groups of hollows engraved on the sensor shell, mainly to prevent the shell from hindering the sound wave from entering the sensor. The sound wave enters the sensor through the hollow window and acts on the exposed part of the fiber grating part of the distributed feedback fiber laser, thereby changing the characteristics of the laser. And then realize the acoustic wave detection.

The patent of the present invention is mainly designed based on the change of the wavelength of the fiber laser caused by the sound wave and the strong enhancement effect of the asymmetric disturbance compared with the traditional symmetrical disturbance.

The external acoustic disturbance will cause the change of the refractive index of the fiber, which will lead to the movement of the center wavelength λ _FL of the laser produced by the fiber laser. Due to the photoelastic effect, the effective refractive index of the fiber laser will change in the acoustic field. Taking a distributed feedback fiber laser with a central wavelength around 1550nm as an example, in a uniformly distributed acoustic wave field (both the left and right gates of the fiber laser are disturbed by the same intensity of the acoustic wave field), the corresponding relationship between the refractive index and the wavelength is shown in Figure 6;

When the packaging structure designed by this patent is adopted, the fiber laser will be disturbed by asymmetrical acoustic waves, so that the refractive index caused by the photoelastic effect will be asymmetrical, and the corresponding relationship between the refractive index change and the wavelength obtained is shown in Figure 7. The amplitude (sensitivity) of the center wavelength change of the distributed feedback fiber laser caused by the acoustic wave is enhanced.

The beneficial effect of the solution is that the sensitivity of the distributed feedback fiber laser for underwater acoustic detection can be greatly increased through the sensor structure designed in the patent. As shown in Figure 6, when the asymmetric structure designed by the present invention is not adopted, the acoustic wave causes the change of the refractive index of the optical fiber to affect the laser wavelength. The sensitivity (slope) is about 0.065; Figure 8 shows the sensitivity coefficient of the sensor structure sensitization designed in the present invention, and the sensitivity coefficient can reach up to 350; through comparison, it can be found that the present invention greatly increases the detection sensitivity of acoustic waves.

Description of drawings

Figure 1: Structural diagram of the sensing probe of an asymmetric optical fiber hydrophone; Figure 2: Structural diagram of the silencer tube; Figure 3: Schematic diagram of the fiber grating part of the distributed feedback fiber laser; Figure 4: The working optical path diagram of the distributed feedback fiber laser; 5: Schematic diagram of the assembly of the fiber laser and the probe housing; Figure 6: Correspondence between the change in the refractive index of the fiber and the wavelength of the laser in the symmetrical acoustic wave field; Figure 7: The corresponding figure between the change in the refractive index of the fiber and the wavelength of the laser in the asymmetrical acoustic wave field; Figure 8: Acoustic detection Sensitization effect diagram.

In the figure: 1-optical fiber pigtail protector; 2-external protective sleeve; 3-hollow acoustic window; 4-fiber entry hole; 5-silence sleeve; 6-free end; 7-erbium-doped fiber; 8-right Gate area; 9-left gate area; 10-backward laser of distributed feedback fiber laser; 11-fiber grating of distributed feedback fiber laser; 12-WDM pump end; 13-WDM common end; 14-central line; 15- Through hole; 16-quartz inner tube; 17-quartz outer tube; 18-metal tube; 19-muffling cotton layer; 20-central axis of silencing tube; 21-vacuum chamber; 22-pump light source; 23-wavelength division multiplexing device (WDM); 24-demodulator; 25-sound wave.

Detailed ways

Example 1

As shown in Figure 1, an asymmetric structure acoustic wave sensor probe includes an outer protective sleeve 2, a hollow acoustic window 3 is arranged on the surface of the outer protective sleeve 2, and a sound-absorbing sleeve 5 is arranged inside the outer protective sleeve 2, The fiber grating part 11 of the distributed feedback fiber laser passes through the sound-absorbing sleeve 5 and is installed and fixed inside the outer protective sleeve 2. The end face position of the free end 6 of the sound-absorbing sleeve 5 and the center of the phase-shifted fiber grating part 11 of the distributed feedback fiber laser The line 14 is aligned; the fiber grating part 11 of the distributed feedback fiber laser is divided into a left grid area 9 and a right grid area 8 according to the phase shift position, the left grid area 9 is completely inserted into the sound-absorbing sleeve 5, and the right grid area 8 is completely exposed to the sound In the field; the sound-absorbing sleeve 5 is formed by stacking multiple layers of materials with different densities. From the outside to the inside, there are metal tube 18, sound-absorbing cotton layer 19 and vacuum quartz sleeve, wherein the vacuum quartz sleeve includes quartz inner tube 16 and quartz outer tube. The tube 17, the quartz inner tube 16 and the quartz outer tube 17 are connected together at the opening to form a closed vacuum quartz sleeve, and the center of the vacuum quartz sleeve is provided with a through hole 15 for passing through the optical fiber to achieve the sound-absorbing effect. The metal tube 18 is used to provide protection for the vacuum quartz casing. The sound-absorbing cotton layer 19 can absorb the sound waves transmitted from the outside to the tube core. The interlayer of the quartz outer tube 17 and the quartz inner tube 16 is sealed and evacuated, so that the sound waves and vibration signals cannot pass through. Penetrating into, so as to achieve the sound wave shielding effect. Because the metal tube 18 and the vacuum quartz casing have a relatively high density, while the sound-absorbing cotton layer 19 and the vacuum zone have a very small density, a multi-layer sound wave reflection section is formed, which is beneficial to sound wave reflection and noise reduction.

The structure of the fiber grating portion 11 of the distributed feedback fiber laser is shown in Figure 3, which is achieved by writing a phase shift grating on a section of erbium-doped optical fiber 7 with a length of several centimeters by ultraviolet laser. The phase shift grating is written on the optical fiber, the phase shift amount of the phase shift grating is π/2, and the phase shift position is the middle of the grating.

The fiber grating length of the distributed feedback fiber laser is 1cm, or 10cm, etc., which can achieve the same effect as above.

The sensor probe solution designed in this patent consists of two parts: a mechanical shell and a distributed feedback fiber laser. The mechanical shell is used to fix the fiber grating of the distributed feedback fiber laser, and the disturbance effect of the external sound wave on the laser is increased through the structural design. Sensitive effect; the distributed feedback fiber laser is used to sense the sound wave, and converts the change of the external sound wave signal into the change of the intensity and wavelength of the laser, so as to realize the function of fiber optic sensing.

The grating part of the distributed feedback fiber laser is fixed inside the probe housing, and passes through the sensor housing shown in Figure 1 through the fiber hole 4; the outer protective sleeve 2 is used to protect the distributed feedback fiber laser inside the probe; the fiber pigtail protector 1 It is used to fix and protect the optical fiber, prevent the optical fiber from being broken due to large shear force, and play a buffering and protective role; the sound-absorbing sleeve 5 is used to absorb and reflect sound waves, so that the sound waves entering the tube disappear or are greatly lost, thereby reducing the transmission of sound waves The hollowed-out sound wave window 3 allows the inside of the sensor to be fully exposed to the sound wave field, and the sound wave can enter the inside of the sensor through the window and act on the distributed feedback fiber laser grating.

The sensor is assembled as shown in Figure 1, the optical fiber pigtail protector 1 is installed on the two ends of the outer protective sleeve 2, the sound-absorbing sleeve 5 is installed on one side of the sensor, and the free end 6 of the sound-absorbing sleeve is suspended inside the outer protective sleeve; The fiber grating part 11 of the distributed feedback fiber laser passes through the sensor shell through the fiber inlet hole 4, and the relative position of the fiber grating part 11 of the fiber laser and the noise-absorbing sleeve 5 of the sensor is shown in Figure 5, so that the central symmetry axis 14 of the phase shift grating is in line with the noise-absorbing sleeve Align the end faces of the free end 6 of the tube; fix the two ends of the fiber grating part 11 of the distributed feedback fiber laser with the sensor housing, and use soft elastic materials such as rubber to protect the fiber pigtail at the fiber pigtail protector 1 at both ends of the sensor.

Example 2

The similarities between this embodiment and Embodiment 1 will not be repeated. The difference is that a hydrophone is also provided, which includes a distributed feedback optical fiber composed of a pump light source 22, a WDM23 and an asymmetric structure acoustic wave sensor probe. The working optical path of the laser; the pump light source 22 is connected to the WDM pump port 12, the WDM common port 13 is connected to the asymmetric structure acoustic wave sensor probe, and the generated laser is output to the demodulator 24 through the WDM output port.

The distributed feedback fiber laser is mainly composed of pump light source, WDM and distributed feedback fiber laser grating. The laser is output through the WDM output port. The 980nm pump involved in this scheme is a common semiconductor pump light source, and the output laser wavelength is 980nm. Since the grating area of the distributed feedback fiber laser involved in the invention is an erbium-doped fiber, the common 800nm semiconductor pump light source and 1480nm semiconductor pump The pump light source can also be used as an alternative to the pump light source in the present invention. The WDM involved in the present invention is a common optical communication wavelength division multiplexer, which is determined and used in conjunction with the wavelength of the pump light source. For example, when the wavelength of the pump light source is 980nm, the WDM requires the use of a device with a specification of 980/1550, that is, the pump The terminal wavelength is required to be 980nm, and the common terminal and output terminal are 1550nm. The above WDMs are common common devices in optical communication and optical sensing.

It is necessary to build a demodulator when used for sound wave detection. Commonly used demodulation schemes have been reported, such as Tan Bo et al., Dynamic characteristics of distributed feedback fiber lasers, Optical Precision Engineering, 2009, Volume 17, Issue 8, 1832- 1838; Jiang Qi et al., Design and Experiment of Distributed Feedback Fiber Laser Hydrophone, Acta Photonica Sinica, 2009, Volume 38, No. 11, 2795-2799; Ma Lina, Optical Laser Hydrophone Technology, Ph.D., Graduate School of National University of Defense Technology Paper, 2010). The above solutions can all realize the demodulation of the sensor probe designed by the patent of the present invention. The present invention adopts a traditional Michelson interferometer as a demodulator during specific implementation, and is used for implementing dynamic demodulation of the dynamic change of the laser wavelength of a distributed feedback fiber laser, thereby realizing acoustic wave detection. In addition, the same acoustic detection effect can also be achieved by using the Mach-Zehnder interferometer instead of the Michelson interferometer.

Claims (7)

1. a unsymmetric structure sonic sensor is popped one's head in, it comprises the exterior protection sleeve pipe, it is characterized in that externally the protection tube surface is provided with hollow out sound wave window, externally protection tube inside arranges the noise reduction sleeve pipe, distributed feed-back formula fiber laser fiber grating portion passes the noise reduction sleeve pipe and is fixed on the exterior protection inside pipe casing, and the free-ended endface position of noise reduction sleeve pipe is alignd with distributed feed-back formula fiber laser phase-shifted grating central symmetry axes; Distributed feed-back formula fiber laser fiber grating portion is divided into left grid region and right grid region according to the phase shift position, and left grid region is inserted in the noise reduction sleeve pipe fully, and right grid region is exposed in the acoustic wavefield fully.

2. unsymmetric structure sonic sensor according to claim 1 is popped one's head in, it is characterized in that the noise reduction sleeve pipe adopts nestable the forming of multilayer different densities material, ecto-entad is followed successively by metal tube, the cotton layer of noise reduction, the vitreosil sleeve pipe, wherein the vitreosil sleeve pipe comprises quartz inner pipe and quartz outer tube, quartz inner pipe and quartz outer tube are joined together to form closed vacuum sleeve at opening part, and vitreosil sleeve pipe central authorities are provided be used to the through hole that passes optical fiber.

3. unsymmetric structure sonic sensor according to claim 1 is popped one's head in, it is characterized in that distributed feed-back formula fiber laser fiber grating portion inscribes phase-shifted grating by Ultra-Violet Laser at the Er-doped fiber of one section several centimeter length to realize, the phase-shifted grating phase-shift phase is pi/2, and phase shift is set to the grating middle.

4. a nautical receiving set is characterized in that it comprises by pump light source, the distributed feed-back formula fiber laser working light path that wavelength division multiplexer (WDM) and unsymmetric structure sonic sensor probe are formed; Pump light source is connected with WDM pumping end, and the WDM common port is connected with unsymmetric structure sonic sensor probe, and the laser of generation exports (FBG) demodulator to by the WDM output terminal.

5. nautical receiving set according to claim 4, it is characterized in that described unsymmetric structure sonic sensor probe, it comprises the exterior protection sleeve pipe, externally the protection tube surface is provided with hollow out sound wave window, externally protection tube inside arranges the noise reduction sleeve pipe, distributed feed-back formula fiber laser fiber grating portion passes the noise reduction sleeve pipe and is fixed on the exterior protection inside pipe casing, and the free-ended endface position of noise reduction sleeve pipe is alignd with distributed feed-back formula fiber laser phase-shifted grating central symmetry axes; Distributed feed-back formula fiber laser fiber grating portion is divided into left grid region and right grid region according to the phase shift position, and left grid region is inserted in the noise reduction sleeve pipe fully, and right grid region is exposed in the acoustic wavefield fully.

6. nautical receiving set according to claim 5, it is characterized in that the noise reduction sleeve pipe adopts nestable the forming of multilayer different densities material, ecto-entad is followed successively by metal tube, the cotton layer of noise reduction, the vitreosil sleeve pipe, wherein the vitreosil sleeve pipe comprises quartz inner pipe and quartz outer tube, quartz inner pipe and quartz outer tube are joined together to form closed vacuum sleeve at opening part, and vitreosil sleeve pipe central authorities are provided be used to the through hole that passes optical fiber.

7. nautical receiving set according to claim 4, it is characterized in that distributed feed-back formula fiber laser fiber grating portion inscribes phase-shifted grating by Ultra-Violet Laser at the Er-doped fiber of one section several centimeter length to realize, the phase-shifted grating phase-shift phase is pi/2, and phase shift is set to the grating middle.

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