CN117723144A - Polarization modulation type underwater sound detection device, method and hydrophone - Google Patents
Polarization modulation type underwater sound detection device, method and hydrophone Download PDFInfo
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Abstract
The invention belongs to the technical field of hydrophones, and discloses a polarization modulation type underwater sound detection device, a method and a hydrophone. The invention adopts the sensitive element made of transparent crystal or liquid crystal material with double refraction characteristic, modulates the underwater sound signal to the polarized light signal through the polarization state change of the double refraction transparent crystal or liquid crystal polarized light when the sensitive element is deformed, and realizes the detection of the underwater sound signal through the demodulation of the polarized state change signal. The device comprises a linear polarized light source, a sensitive element, a light polarization state detector, a photoelectric converter array and a signal filtering processing circuit, wherein linear polarized light emitted by the linear polarized light source is incident to the sensitive element, the light polarization state detector is used for unbiasing polarized light emitted by the sensitive element, demodulating an underwater sound signal modulated into the light polarization state by the sensitive element, the photoelectric converter array is used for converting the detected underwater sound signal into an electric signal, and finally the signal filtering processing circuit is used for filtering the electric signal to obtain the underwater sound signal. The invention has low self-noise level and high sensitivity.
Description
Technical Field
The invention belongs to the technical field of hydrophones, and particularly relates to a polarization modulation type underwater sound detection device and method and a hydrophone.
Background
As an important device for detecting underwater acoustic signals, the hydrophone is widely used for underwater detection, target positioning, communication, tracking, sound field measurement and the like, and is a key device for human insight into the sea. Existing hydrophones can be divided into two types, circuit type and optical path type.
The circuit type hydrophone comprises magneto-electric type hydrophones, piezoelectric type hydrophones, piezoresistive type hydrophones and capacitive type hydrophones, sensitive elements and conditioning circuits of the hydrophones are sensitive to temperature, and the self-noise lowest level of the circuit is determined by circuit thermal noise; since thermal noise is determined by the temperature of the hydrophone, it is very difficult to further reduce the self-noise level of the circuit type hydrophone based on the existing level, as known from the working principle thereof.
The optical path type hydrophone mostly uses different types of optical fibers as sensitive elements, and although the electromagnetic interference resistance is strong, the signal conditioning and demodulation processes based on the optical path are complex, and the improvement of the sensitivity is required to break through the constraint of the mechanism of the existing hydrophone. In recent years, although the research of the optical path hydrophone has made considerable progress, researchers still do not find a hydrophone design scheme with high sensitivity and low noise level, so as to meet the water hearing requirement of weak underwater sound signals under the condition of increasingly enhanced background noise of the ocean.
In summary, the existing hydrophone, whether it is a circuit hydrophone or an optical path hydrophone, encounters technical bottlenecks in terms of increasing the sensitivity of the hydrophone and reducing self-noise, so that a novel underwater sound detection device is urgently needed to be provided.
Disclosure of Invention
The invention aims to provide a polarization modulation type underwater sound detection device, which adopts a sensitive element made of transparent crystal or liquid crystal material with birefringence characteristics, modulates an underwater sound signal onto a polarized light signal through the polarization state change of the crystal or liquid crystal polarized light with the birefringence characteristics when the sensitive element is deformed, and realizes the detection of the underwater sound signal by demodulating the polarized state signal.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a polarization-modulated acoustic detection device, comprising:
a sensing element made of transparent crystal or liquid crystal material having birefringence characteristics, the sensing element being for converting an underwater acoustic signal into a polarization state variation signal of polarized light;
the narrow-band linear polarized light source is used for generating linear polarized light, wherein the linear polarized light can be incident into the sensitive element in a direction with an angle theta with a main optical axis of the sensitive element, and the angle range of theta is as follows: θ is more than 0 and less than 90 degrees;
a light polarization state detector for demodulating the modulated polarized light emitted from the sensing element into light intensity stripes;
the photoelectric detector array is used for collecting light intensity stripes emitted by the light polarization state detector and converting the light intensity stripes into electric signals;
the signal filtering processing circuit is used for collecting the electric signal obtained by the photoelectric detector array, filtering the electric signal, eliminating high-frequency interference and direct current signals in the electric signal and obtaining a detected underwater sound signal;
when the sensitive element is in a water-free sound environment, linearly polarized light emitted by the narrow-band linearly polarized light source is incident into the sensitive element, and the light polarization detector is adjusted in advance, so that the light intensity stripe contrast output by the light polarization detector is maximum;
when the sensitive element is in the underwater sound field, the narrow-band linear polarized light source and the light polarization state detector are not regulated, so that the underwater sound signal is converted into a polarization state change signal of light transmitted by the sensitive element, and the polarization state change signal is demodulated by the light polarization state detector.
In addition, on the basis of the polarization modulation type underwater sound detection device, the invention also provides a polarization modulation type underwater sound detection method which is suitable for the polarization modulation type underwater sound detection device, and the polarization modulation type underwater sound detection method adopts the following technical scheme:
a polarization modulation type underwater sound detection method adopts the polarization modulation type underwater sound detection device, which comprises the following steps:
step 1, placing a sensitive element in an underwater sound field;
step 2, linearly polarized light emitted by the narrow-band linearly polarized light source enters the sensitive element, the direction of the linearly polarized light entering the sensitive element forms an angle theta with a main optical axis of the sensitive element, and the polarization state modulation of the polarized light by the underwater sound signal is completed;
step 3, demodulating the modulated polarized light emitted by the sensitive element into light intensity stripes by the light polarization state detector;
step 4, collecting light intensity stripes formed by the light polarization state detector by the photoelectric detector array and converting the light intensity stripes into electric signals;
step 5, the signal filtering processing circuit collects the electric signals obtained by the photoelectric detector array, and carries out filtering processing on the electric signals to eliminate high-frequency interference and direct current signals, so as to obtain detected underwater sound signals;
before the detection of the underwater acoustic signal by using the polarization modulation type underwater acoustic detection device, firstly placing a sensitive element in a non-underwater acoustic environment, and enabling linearly polarized light emitted by a narrow-band linearly polarized light source to be incident into the sensitive element, and pre-adjusting an optical polarization detector to enable the contrast of light intensity stripes output by the optical polarization detector to be maximum;
when the sensitive element is in the underwater sound field, the narrow-band linear polarized light source and the light polarization state detector are not regulated, so that the underwater sound signal is converted into a polarization state change signal of light transmitted by the sensitive element and is demodulated by the light polarization state detector.
In addition, the invention also provides a hydrophone based on the polarization modulation type underwater sound detection device, wherein the hydrophone comprises the underwater sound detection device, and the polarization modulation type underwater sound detection device is adopted by the underwater sound detection device.
The invention has the following advantages:
the invention relates to a polarized modulation type underwater sound detection device, which utilizes transparent crystal or liquid crystal material with special optical characteristics (birefringence characteristics) to realize the modulation of underwater sound on polarized light and can obtain a higher underwater sound signal-to-noise ratio than other detection methods. The device of the invention not only avoids the defects of the traditional circuit hydrophone such as piezoelectricity, piezoresistance, capacitance, electromagnetic signals and the like in the aspect of electromagnetic interference resistance, but also avoids the influence of the circuit hydrophone (circuit type underwater sound detection device) caused by sensitive elements, thermal noise of a pre-amplifying circuit and the like, and has lower self-noise level; the device is different from the traditional optical path hydrophone (optical path underwater sound detection device), the wavelength, frequency, intensity or phase of light is not used as a key intermediate parameter during the detection of the underwater sound signal, the sensitive element does not directly convert the underwater sound signal into the variable quantity of the wavelength, frequency, intensity or phase, but uses the polarization state of light as a key intermediate parameter, and the sensitive element directly converts the underwater sound signal into the polarization state variable quantity of light at first, so that the device has higher sensitivity than the traditional optical fiber detection device. The conditioning light path and the underwater sound demodulation light path of the device are simpler, the number of optical elements is reduced, the insertion loss and noise superposition are reduced, and the technical space for reducing the self-noise level is increased.
Drawings
FIG. 1 is a schematic diagram of a polarization modulation type underwater sound detection device according to an embodiment of the present invention;
FIG. 2 is an exploded view of a light polarization detector according to an embodiment of the present invention;
FIG. 3 is a flow chart of a method for detecting polarized modulated underwater sound according to an embodiment of the present invention;
reference numerals illustrate:
the device comprises a 1-narrow-band linear polarized light source, a 2-sensitive element, a 3-light polarization state detector, a 4-photoelectric detector array, a 5-signal filtering processing circuit, a 6-antireflection film, a 7-second polarization grating, a 8-third polarization grating, a 9-half wave plate and a 10-opaque film.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and detailed description:
example 1
In this embodiment 1, a polarization modulation type underwater sound detection device is described, which uses a sensing element made of transparent crystalline material with birefringence characteristics, directly uses the polarization state of light as a parameter, modulates an underwater sound signal onto a polarized light signal through the polarization state change of the transparent crystalline polarization material with birefringence characteristics when the sensing element is deformed, and realizes the detection of the underwater sound signal by demodulating the polarized state signal.
As shown in fig. 1, the polarization modulation type underwater sound detection device in this embodiment includes a narrow-band linear polarized light source 1, a sensitive element 2, a light polarization state detector 3, a photodetector array 4, and a signal filtering processing circuit 5.
The narrow-band linearly polarized light source 1 is used for providing a polarized light source with small wavelength range (ideal range is single wavelength), small noise and high polarization degree for the polarized modulation type underwater sound detection device so as to generate linearly polarized light.
Specifically, the narrowband linearly polarized light source 1 comprises a laser light source and a first polarization grating matched with the laser light source.
The laser light source outputs light with the line width range not more than 2nm, the central wavelength (such as 1550 nm) of the matched polarization grating is the same as that of the laser light source, the light source is used for polarizing the light, and the light source filtered by the polarization grating is changed into linearly polarized light.
The linearly polarized light generated by the narrow-band linearly polarized light source 1 can be incident into the sensing element 2 in a direction of an angle θ with respect to a main optical axis of the sensing element 2, and in this embodiment, the angle range θ is as follows: θ is more than 0 and less than 90 degrees.
The sensor 2 is made of transparent crystalline material with birefringence characteristics, is sensitive to the acoustic signal, and is capable of converting the acoustic signal into a signal of change of polarization state of linearly polarized light passing through it, and its basic principle is:
when linearly polarized light is incident on the sensor 2, if the vibration direction and the crystal optical axis are included by an angle theta (theta not equal to 0), the incident light vibration is decomposed into two components perpendicular to the optical axis (o vibration) and parallel to the optical axis (e vibration), and the o light and the e light in the crystal are corresponding.
Since the transparent crystal material having the birefringent characteristic has different refractive indexes in the o-direction and the e-direction, the light generates an optical path difference in both directions, and the polarization state of the synthesized light is changed from that of the incident light.
Wherein the amount of change of the polarization state delta is proportional to the distance d the light travels in the sensor 2. The sensitive element 2 in the underwater acoustic field will deform under the stress generated by the underwater sound to change the size and dimension by deltal。
If the linearly polarized light enters the sensitive element 2 at an angle theta with the optical axis, the crystal size changes due to the underwater acoustic signalConversion of deltalConverted into a signal delta of the change in the transmission distance of light in the sensor 2dThe polarization state of the light is caused to change by an amount of delta.
When the original size of the sensor 2 and the angle of incidence of the linearly polarized light are fixed, Δδ is proportional to the intensity of the water sound. When the stress caused by the underwater sound disappears, the deformation of the sensing element 2 disappears, and the size of the sensing element is restored to the original state, namely, when the underwater sound acts on the sensing element, the underwater sound signal is converted into a polarization state change signal delta of the transmitted light of the sensing element 2.
Here, stress due to the underwater sound disappears, that is, the underwater sound signal is zero, hereinafter referred to as "static".
Further, the angle range of θ in this embodiment is 30+.ltoreq.θ+.ltoreq.60°. Since the same deformation of the sensor 2 will produce o-light and e-light of equal intensity at θ=45°, the contrast of the light intensity fringes formed by the light polarization detector 3 is maximized, and therefore, it is generally chosen that the linearly polarized light is incident into the sensor 2 at 45 ° to the principal optical axis of the crystal.
Among them, transparent crystals having birefringent properties include, for example, transparent crystal materials such as mica, calcite, quartz, and the like.
Of course, the sensor element 2 may also be made of a transparent liquid crystal material having birefringent properties.
For example, the sensor 2 is made of a nematic liquid crystal elastomer.
The nematic liquid crystal elastomer is formed by crosslinking a nematic liquid crystal material and an elastomer material, and the nematic liquid crystal is used for converting an underwater sound signal into a polarization state change signal; an elastomeric material for providing a supporting framework for the nematic liquid crystal.
Of course, the above nematic liquid crystal elastomer is merely exemplary and is not limiting to the transparent liquid crystal material having a birefringent property, and the transparent liquid crystal material having a birefringent property includes, for example, blue-phase liquid crystal and the like.
The light polarization state detector 3 is used for extracting a polarization state change signal delta of polarized light emitted by the sensitive element 2, demodulating the modulated polarized light emitted by the sensitive element 2 into light intensity stripes, and further completing underwater sound signal demodulation.
As shown in fig. 2, the light polarization detector 3 includes an antireflection film 6, a second polarization grating 7, a third polarization grating 8, a half-wave plate 9, and an opaque film 10 having two parallel slits.
Wherein polarized light incident on the light polarization detector 3 passes through the antireflection film 6, then passes through the second polarization grating 7 and the third polarization grating 8, and then light coming out of the third polarization grating 8 passes through the half wave plate 9, then passes through the opaque film 10 having two parallel slits together with light coming out of the second polarization grating 7, and then comes out.
The antireflection film 6 in this embodiment has a unidirectional light transmission characteristic, the extinction ratio of which is relatively large, and the antireflection film 6 is used to ensure that polarized light emitted from the sensor 2 is not reflected back to the sensor 2.
The antireflection film 6 adopts a five-layer sub-film structure, and the materials of the sub-films are TiO respectively from top to bottom 2 、Al 2 O 3 、TiO 2 、Al 2 O 3 And TiO 2 The thickness is 6, 26, 6, 89 and 76nm respectively, and the extinction ratio of the antireflection film 6 is more than 1000.
The second polarization grating 7 and the third polarization grating 8 are used to separate the o-light and e-light components. Wherein the polarization angle of the second polarization grating 7 differs from the polarization angle of the third polarization grating 8 by 90 °.
The polarization angles of the second polarization grating 7 and the third polarization grating 8 can be adjusted simultaneously by rotating the light polarization detector 3.
The half wave plate 9 is used for converting the polarization direction of the emergent light of the third polarization grating 8 into the same polarization direction as the emergent light of the second polarization grating 7, and is used for forming an interference phenomenon with the emergent light of the second polarization grating 7.
An opaque film 10 having two parallel slits is used to form an interference double slit.
Since the o light is perpendicular to the e light and the polarization directions of the second polarization grating 7 and the third polarization grating 8 are perpendicular, the second polarization grating 7, the third polarization grating 8, the half-wave plate 9 and the opaque film 10 are adhered together to form the light polarization detector 3 (for convenience in showing the respective structures of the light polarization detector, an exploded view of the light polarization detector is provided in fig. 2), when the light polarization detector 3 is rotated, the second polarization grating 7, the third polarization grating 8, the half-wave plate 9 and the opaque film 10 are all rotated along with the rotation. When the second polarization grating 7 is oriented in line with the o/e light, the third polarization grating 8 must be oriented in line with the e/o light. The half wave plate 9 has the function of converting the emergent light of the third polarization grating 8 into the light with the same direction as the emergent light of the second polarization grating 7, so that the polarization direction of the light reaching the double slits is ensured to be consistent.
In static state, the underwater sound intensity p is 0, linear polarized light emitted by the narrow-band linear polarized light source 1 is incident to the sensitive element 2, the light polarization state detector 3 is rotated, the angles of the second polarization grating 7 and the third polarization grating 8 are adjusted along with the light polarization state detector 3, so that the polarization direction of the second polarization grating 7 is consistent with the polarization direction of e/o light, the polarization direction of the third polarization grating 8 is consistent with the polarization direction of o/e light at the moment, the contrast of light intensity stripes output by the opaque film 10 is strongest, the contrast of the light incident to the photoelectric detector array 4 is strongest, and the detection error of the detection device is minimum.
If the underwater sound intensity p is not 0, the optical polarization state detector 3 outputs a light intensity stripe change signal caused by the underwater sound signal in the underwater sound field, wherein the light intensity stripe signal is determined by the polarization state change signal of the polarized light emitted by the sensitive element 2.
The operating band of the antireflection film 6, the second polarization grating 7, the third polarization grating 8, and the half-wave plate 9 of the light polarization detector 3 in this embodiment includes the linearly polarized light band emitted from the narrowband linearly polarized light source 1.
The photodetector array 4 collects the light intensity fringe signal emitted from the light polarization detector 3 and converts it into an electrical signal.
The photodetector array 4 is a linear array composed of a plurality of photodetectors, such as a CCD linear array (a common CCD linear array includes, for example, a PCL52 type CCD linear array, etc.), which is perpendicular to the double slit formed by the light polarization detector 3.
And the signal filtering processing circuit 5 is used for collecting the electric signal obtained by the photoelectric detector array 4, filtering the electric signal, eliminating high-frequency interference and direct current signals in the electric signal and obtaining a detected underwater sound signal.
It should be noted that, the signal filtering processing circuit 5 in this embodiment is relatively mature, and will not be described here again.
Before the underwater acoustic signal is detected, firstly, when the sensitive element 2 is in an underwater acoustic environment (namely, the underwater acoustic signal), linearly polarized light emitted by a narrow-band linearly polarized light source is incident into the sensitive element 2, and the light polarization state detector 3 is adjusted in advance, so that the contrast of light intensity stripes output by the light polarization state detector 3 is maximum. At this time, the output signal of the optical polarization detector 3 does not contain the static polarization state variation of the sensing element 2 any more, and is only related to the polarization state variation signal caused by the underwater sound signal.
When the sensitive element is in the underwater sound field, the narrow-band linearly polarized light source 1 and the light polarization state detector 3 are not regulated any more, so that the underwater sound signal is converted into a polarization state change signal of light transmitted by the sensitive element and demodulated by the light polarization state detector.
Here, the narrow-band linearly polarized light source 1 and the light polarization detector 3 are not adjusted any more, which means that the linearly polarized light emitted by the narrow-band linearly polarized light source 1 is kept unchanged, the angle θ at which the linearly polarized light enters the sensitive element 2 is unchanged, and the light polarization detector 3 is not rotated any more.
The invention not only avoids the shortages of the circuit type hydrophone in the aspect of electromagnetic interference resistance, but also avoids the influence of the circuit type hydrophone due to the thermal noise of the sensitive element and the pre-amplifying circuit, and the like, thereby having lower self-noise level.
The invention uses the polarization state of light as a key intermediate parameter, adopts a sensitive element made of transparent crystals with double refraction characteristics, directly converts the underwater sound signal into the polarization state variation of light, and has higher sensitivity than the existing optical fiber detection device.
In addition, compared with the existing optical fiber detection device, the device has the advantages that the conditioning optical path and the underwater sound demodulation optical path are simpler, the number of optical elements is reduced, the insertion loss and the noise superposition are reduced, and the technical space for reducing the self-noise level is increased.
The invention can be realized by adopting an optical chip process, and has better application prospect and potential for reducing cost compared with other detection devices.
Example 2
This embodiment 2 describes a polarization-modulated underwater sound detection method based on the polarization-modulated underwater sound detection device in the above embodiment 1.
As shown in fig. 3, the polarization modulation type underwater sound detection in this embodiment includes the following steps:
and 1, placing the sensitive element 2 in the underwater sound field.
And 2, linearly polarized light emitted by the narrow-band linearly polarized light source 1 enters the sensitive element 2, the direction of the linearly polarized light entering the sensitive element 2 forms an angle theta with the main optical axis of the sensitive element, and the polarization state modulation of the polarized light by the underwater sound signal is completed.
In the present embodiment, the angle range of θ is 0 < θ < 90 °, more specifically, the angle range of θ may be defined in the [30 °,60 ° ] range, for example, the angle of θ takes a value of 45 °.
And 3, demodulating the modulated polarized light emitted by the sensitive element into light intensity stripes by the light polarization state detector 3.
And 4. The photodetector array 4 collects the light intensity stripes generated by the light polarization state detector 3 and converts the light intensity stripes into electric signals.
And 5, the signal filtering processing circuit 5 collects the electric signal obtained by the photoelectric detector array 4, and performs filtering processing on the electric signal to eliminate high-frequency interference and direct current signals, so as to obtain a detected underwater sound signal.
Wherein the following pretreatment is performed before the detection of the underwater acoustic signal by the device of the present invention:
when the sensitive element 2 is placed in a non-underwater sound environment (i.e. no underwater sound signal exists), linear polarized light emitted by the narrow-band linear polarized light source 1 enters the sensitive element 2, the light polarization state detector 3 is adjusted in a rotating mode, so that the polarization direction of the second polarization grating 7 is consistent with the polarization direction of e/o light, at the moment, the polarization direction of the third polarization grating 8 is consistent with the polarization direction of o/e light, the opaque film 10 with two parallel slits outputs interference fringes with the strongest contrast of light intensity fringes, and the output signal of the light polarization state detector 3 does not contain static polarization state variation quantity of the sensitive element 2 any more and is only related to the polarization state variation signal caused by the underwater sound signal.
When the sensing element 2 is in the underwater acoustic field, the narrow-band linearly polarized light source 1 and the light polarization state detector 3 are not adjusted any more, so that the underwater acoustic signal is converted into a polarization state change signal of the light transmitted by the sensing element and demodulated by the light polarization state detector.
Example 3
This embodiment 3 describes a hydrophone comprising a hydrophone assembly employing a polarization-modulated hydrophone assembly as described in embodiment 1 above.
Because the hydrophone adopts the polarization modulation type underwater sound detection device in the embodiment 1, the hydrophone has lower self-noise level compared with the traditional circuit type hydrophone and higher sensitivity compared with the traditional optical path type hydrophone.
In addition, the adjusting light path and the underwater sound demodulation light path in the underwater sound detection device of the hydrophone are simpler, and the number of optical elements is reduced, so that the insertion loss and noise superposition are reduced, and the technical space for reducing the self-noise level is increased.
The foregoing description is, of course, merely illustrative of preferred embodiments of the present invention, and it should be understood that the present invention is not limited to the above-described embodiments, but is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
Claims (10)
1. A polarization-modulating type underwater sound detection device, comprising:
a sensing element made of transparent crystal or liquid crystal material having birefringence characteristics, the sensing element being for converting an underwater acoustic signal into a polarization state variation signal of polarized light;
the narrow-band linear polarized light source is used for generating linear polarized light, wherein the linear polarized light can be incident into the sensitive element in a direction with an angle theta with a main optical axis of the sensitive element, and the angle range of theta is as follows: θ is more than 0 and less than 90 degrees;
a light polarization state detector for demodulating the modulated polarized light emitted from the sensing element into light intensity stripes;
the photoelectric detector array is used for collecting light intensity stripes formed by the light polarization state detector and converting the light intensity stripes into electric signals;
the signal filtering processing circuit is used for collecting the electric signal obtained by the photoelectric detector array, filtering the electric signal, eliminating high-frequency interference and direct current signals in the electric signal and obtaining a detected underwater sound signal;
when the sensitive element is in a water-free sound environment, linearly polarized light emitted by the narrow-band linearly polarized light source is incident into the sensitive element, and the light polarization detector is adjusted in advance, so that the light intensity stripe contrast output by the light polarization detector is maximum;
when the sensitive element is in the underwater sound field, the narrow-band linear polarized light source and the light polarization state detector are not regulated, so that the underwater sound signal is converted into a polarization state change signal of light transmitted by the sensitive element, and the polarization state change signal is demodulated by the light polarization state detector.
2. The polarization-modulated underwater sound detection device as claimed in claim 1, wherein,
the angle range of theta is as follows: θ is more than or equal to 30 degrees and less than or equal to 60 degrees.
3. The polarization-modulated underwater sound detection device as claimed in claim 1, wherein,
the narrow-band linearly polarized light source comprises a laser light source and a first polarization grating matched with the laser light source;
wherein the laser light source outputs light with a linewidth range not more than 2 nm; the center wavelength of the first polarization grating is the same as the center wavelength of the laser light source, and the light source filtered by the first polarization grating is changed into linearly polarized light.
4. The polarization-modulated underwater sound detection device as claimed in claim 1, wherein,
the light polarization state detector includes:
the anti-reflection film is used for ensuring that polarized light emitted by the sensitive element is not reflected back to the sensitive element;
a second polarization grating and a third polarization grating for separating light components of o light and e light; the polarization angle of the second polarization grating is 90 degrees different from the polarization angle of the third polarization grating, and can be adjusted simultaneously;
the half wave plate is used for converting the polarization direction of the emergent light of the third polarization grating into the same polarization direction as the emergent light of the second polarization grating;
and an opaque film having two parallel slits for forming an interference double slit.
5. The polarization-modulated underwater sound detection device as set forth in claim 4, wherein,
the extinction ratio of the anti-reflection film is more than 1000; the operating band of the anti-reflective film, the second polarization grating, the third polarization grating, and the half wave plate comprises a linearly polarized light band emitted by a narrowband linearly polarized light source.
6. The polarization-modulated underwater sound detection device as set forth in claim 4, wherein,
when the sensitive element is in a water-free sound environment, linearly polarized light emitted by the narrow-band linearly polarized light source is incident into the sensitive element, and the light polarization detector is rotated, so that the contrast of light intensity stripes output by the opaque film is maximum;
when the sensitive element is in the underwater sound field, the narrow-band linear polarized light source and the light polarization state detector are not regulated, the output signal of the light polarization state detector does not contain the static polarization state variation quantity of the sensitive element, and only contains the polarization state variation signal caused by the underwater sound.
7. The polarization-modulated underwater sound detection device as claimed in claim 1, wherein,
the photodetector array is composed of a plurality of photodetectors, which are perpendicular to the double slit formed by the light polarization state detectors.
8. A polarization-modulated acoustic detection method based on the polarization-modulated acoustic detection device according to any one of claims 1 to 7, characterized in that the polarization-modulated acoustic detection comprises the steps of:
step 1, placing a sensitive element in an underwater sound field;
step 2, linearly polarized light emitted by the narrow-band linearly polarized light source enters the sensitive element, the direction of the linearly polarized light entering the sensitive element forms an angle theta with a main optical axis of the sensitive element, and the polarization state modulation of the polarized light by the underwater sound signal is completed;
step 3, demodulating the modulated polarized light emitted by the sensitive element into light intensity stripes by the light polarization state detector;
step 4, the photoelectric detector array collects light intensity stripes formed by the light polarization state detector and converts the light intensity stripes into electric signals;
and 5, acquiring an electric signal obtained by the photoelectric detector array by a signal filtering processing circuit, and filtering the electric signal to eliminate high-frequency interference and direct current signals and obtain a detected underwater sound signal.
9. The method of claim 8, wherein,
before the detection of the underwater acoustic signal by using the polarization modulation type underwater acoustic detection device, firstly placing a sensitive element in a non-underwater acoustic environment, and enabling linearly polarized light emitted by a narrow-band linearly polarized light source to be incident into the sensitive element, and pre-adjusting an optical polarization detector to enable the contrast of light intensity stripes output by the optical polarization detector to be maximum;
when the sensitive element is in the underwater sound field, the narrow-band linear polarized light source and the light polarization state detector are not regulated, so that the underwater sound signal is converted into a polarization state change signal of light transmitted by the sensitive element and is demodulated by the light polarization state detector.
10. A hydrophone comprises a water sound detection device, which is characterized in that,
the acoustic detection apparatus employs the polarization modulation type acoustic detection apparatus according to any one of claims 1 to 7.
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