CN108593089B - Optical vibration sensor based on birefringence resonance effect and sensing method - Google Patents

Abstract

The invention discloses an optical vibration sensor and a sensing method based on the birefringence resonance effect. The optical vibration sensor includes a laser emitting unit, a vibration induction amplifying unit, a laser receiving unit and a standard waveform unit which are connected in sequence. The laser emitting unit modulates the light emitted by the light source; the vibration induction amplifying unit introduces the modulated optical signal into the polarization-maintaining ring cavity, and the optical signal resonates to obtain two intrinsic polarization states; the laser receiving unit converts the optical signal into an electrical signal, and the The resonance demodulation curves and slope characteristics of ESOPs with two intrinsic polarization states are obtained, and the vibration induction is realized by the phase difference between the two polarization states; the standard waveform unit performs unified modulation and demodulation on the transmission signal. The invention utilizes the birefringent resonance effect to amplify the sensitivity of light to vibration, thereby realizing vibration induction with high sensitivity and a large measurement space range.

Description

Optical vibration sensor and sensing method based on birefringence resonance effect

technical field

The invention relates to a vibration sensor, in particular to an optical vibration sensor and a sensing method based on the birefringence resonance effect.

Background technique

In the past few decades, optical vibration sensors have developed rapidly due to their high sensitivity, large measurement spatial range, and electromagnetic insensitivity. Existing optical vibration sensors mainly include distributed vibration sensors and point vibration sensors. The distributed vibration sensor is based on the Rayleigh scattering effect in the optical fiber, and realizes continuous vibration field measurement on one optical fiber. It has the advantage of measuring in a large spatial range, but the sensitivity is poor, and it is not suitable for vibration in high sensitivity and extreme environments. Measurement. Although the point-type vibration sensor has a small measurement space, it has excellent vibration measurement capabilities. It is difficult to achieve a balance between sensitivity and measurement spatial range for both conventional optical vibration sensors.

SUMMARY OF THE INVENTION

In order to solve the deficiencies in the prior art, the present invention provides an optical vibration sensor based on the birefringence resonance effect, which uses the birefringence resonance effect to amplify the sensitivity of light to vibration, thereby realizing vibration sensing with high sensitivity and a large measurement space. .

In order to achieve the above object, the concrete scheme adopted in the present invention is:

An optical vibration sensor based on birefringence resonance effect, an optical vibration sensor based on birefringence resonance effect, comprising a laser emitting unit, a vibration induction amplifying unit, a laser receiving unit and a standard waveform unit connected in sequence; the laser emitting unit It includes a laser and a phase modulator that are connected to each other; the vibration induction amplifying unit includes a polarization-maintaining annular cavity, and the input end of the polarization-maintaining annular cavity is connected to the output end of the phase modulator through a polarization-maintaining fiber, and the connection point adopts 45 ° direction rotation welding; the laser receiving unit includes a photodetector, a lock-in amplifier and a signal processor connected in sequence, wherein the photodetector is connected to the output end of the polarization-maintaining ring cavity, and the signal processor is connected to the laser The standard waveform unit includes a signal generator, and the signal generator is connected with the phase modulator and the lock-in amplifier.

As a preferred solution, the laser is connected to the phase modulator through an isolator.

As a preferred solution, the polarization-maintaining annular cavity has a first input port, a second input port, a first output port and a second output port, wherein the second input port and the second output port are reflected into a ring through 0° fusion. .

As a preferred solution, the output end of the phase modulator is connected to the first input port.

As a preferred solution, the signal generator outputs a sine wave or a square wave.

As a preferred solution, the laser is set as a narrow linewidth high coherence laser.

A sensing method of an optical vibration sensor based on a birefringent resonance effect, comprising the following steps:

S1, the laser outputs a laser and transmits it to the phase modulator, while the signal generator sends out a modulation waveform and a demodulation waveform and transmits it to the phase modulator;

S2. The phase modulator modulates the phase of the primary laser according to the modulation waveform, and the modulated laser is output to the polarization-maintaining ring cavity;

S3. A laser excites two resonances of ESOPs with intrinsic polarization states in the polarization-maintaining annular cavity;

S4, the external vibration acts on the polarization-maintaining annular cavity to affect the phase difference between the resonance points of the two ESOPs resonance, and obtains a secondary laser;

S5. The polarization-maintaining ring cavity transmits the secondary laser light to the photodetector and the lock-in amplifier in sequence, and the signal generator transmits the demodulated waveform to the lock-in amplifier at the same time;

S6, the photodetector demodulates the secondary laser to obtain an electrical signal and amplifies it through a lock-in amplifier, and the electrical signal includes the slope characteristics of the resonance of two ESOPs;

S7. The lock-in amplifier transmits the amplified electrical signal to the signal processor, and the signal processor outputs the phase difference between the resonances of the two ESOPs, so that the vibration information can be obtained according to the phase difference.

As a preferred solution, in S7, the method for the signal processor to obtain the phase difference between the resonances of two ESOPs is:

S7.1, the signal processor outputs a sawtooth wave to scan the laser;

S7.2, the signal processor obtains the slope characteristics of the resonance of two ESOPs from the lock-in amplifier;

S7.3. The signal processor calculates the phase difference between the resonances of the two ESOPs according to the slope characteristics of the two resonances.

其中，ΔA是振动信息，k₀是真空下的波数，l是传输波导的长度，

是双折射差的振动系数，φ为谐振点的相差。As a preferred solution, in S7, the calculation method of the vibration information is:

where ΔA is the vibrational information, _k0 is the wavenumber in vacuum, l is the length of the transmission waveguide,

is the vibration coefficient of the birefringence difference, and φ is the phase difference of the resonance point.

Beneficial effects: the invention adopts the resonance effect of multi-turn transmission of light in the polarization-maintaining annular cavity to amplify and detect birefringence vibration, thereby greatly improving the sensitivity to vibration. With two orthogonal polarization modes propagating in the same waveguide, much of the noise is canceled due to reciprocity (common mode), enabling extremely sensitive vibration detection.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the present invention;

2 is a schematic structural diagram of a polarization-maintaining annular cavity of the present invention;

Fig. 3 is the resonance demodulation curve of two ESOPs in the present invention;

Figure 4 is a schematic diagram of the relationship between the resonance characteristics of two ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, and the birefringence phase difference is 0;

Figure 5 is a schematic diagram of the relationship between the resonance characteristics of two ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, and the birefringence phase difference is 0.5π;

Figure 6 is a schematic diagram of the relationship between the resonance characteristics of two ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, and the birefringence phase difference is π;

Figure 7 is a schematic diagram of the relationship between the resonance characteristics of two ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, and the birefringence phase difference is 1.5π;

Fig. 8 is a schematic diagram showing the relationship between the phase difference between two resonance points and the phase difference of birefringence in one cycle of transmission in the cavity, and the range of the phase difference of birefringence is 0～2π;

FIG. 9 is a schematic diagram of the relationship between the phase difference between two resonance points and the phase difference of birefringence in one cycle of transmission in the cavity, and the range of the phase difference of birefringence is 0-0.07π.

Reference numerals: 1, first input port, 2, second input port, 3, first output port, 4, second output port, 5, coupler.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Please refer to FIGS. 1 to 9. FIG. 1 is a schematic diagram of the overall structure of the present invention, FIG. 2 is a schematic diagram of the structure of a polarization-maintaining ring cavity of the present invention, FIG. 3 is the resonant demodulation curve of two ESOPs in the present invention, and FIG. Schematic diagram of the relationship between the resonance characteristics of ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, the birefringence phase difference is 0, Figure 5 is a schematic diagram of the relationship between the resonance characteristics of the two ESOPs and the phase difference of birefringence one cycle of transmission in the cavity, the birefringence phase difference is 0.5π, Figure 6 is a schematic diagram of the relationship between the resonance characteristics of two ESOPs and the birefringence phase difference of one cycle of transmission in the cavity, and the birefringence phase difference is π. The phase difference is 1.5π. Figure 8 is a schematic diagram of the relationship between the phase difference between the two resonance points and the birefringence phase difference of one cycle of transmission in the cavity. The range of the birefringence phase difference is 0～2π. Schematic diagram of the relationship between the birefringence phase difference of one cycle of transmission in the cavity, the range of the birefringence phase difference is 0～0.07π.

An optical vibration sensor based on birefringence resonance effect comprises a laser emitting unit, a vibration induction amplifying unit, a laser receiving unit and a standard waveform unit which are connected in sequence.

The laser emitting unit is connected to a laser, an isolator and a phase modulator in sequence. The laser is set to a high-coherence laser with a narrow linewidth, which can be a YAG laser, a gas laser, a semiconductor laser or a fiber laser. The laser is connected to the phase modulator through an isolator. connect.

The vibration induction amplifying unit includes a polarization-maintaining annular cavity, and the polarization-maintaining annular cavity has a first input port 1, a second input port 2, a first output port 3 and a second output port 4, wherein the second input port 2 and the second output port 4 Reflected into a ring by 0° fusion. The first input port 1 of the polarization-maintaining annular cavity is connected with the output end of the phase modulator through a polarization-maintaining fiber, and the connection point is spliced by 45° rotation.

The laser receiving unit includes a photodetector, a photodetector and a signal processor connected in sequence, wherein the photodetector is connected to the output end of the polarization-maintaining ring cavity, and the signal processor is connected to the laser.

The standard waveform unit includes a signal generator, the signal generator is connected with the phase modulator and the photodetector, and the standard waveform output by the signal generator is a sine wave or a square wave.

All devices can be integrated on the semiconductor, or can be realized by combining discrete components.

Based on the above optical vibration sensor, the present invention also provides a sensing method of the optical vibration sensor based on the birefringent resonance effect, including S1 to S7.

S1. The laser outputs a laser and transmits it to the phase modulator, and at the same time, the signal generator sends out modulation and demodulation waveforms and transmits them to the phase modulator.

S2. The phase modulator modulates the phase of the primary laser according to the modulation waveform, and the modulated laser is output to the polarization-maintaining ring cavity.

S3. The primary laser excites two resonances with intrinsic polarization states in the polarization-maintaining annular cavity.

S4. The external vibration acts on the polarization-maintaining ring cavity to affect the phase difference between the resonance points of the two ESOPs, and a secondary laser is obtained.

S5. The polarization-maintaining ring cavity transmits the secondary laser light to the photodetector and the lock-in amplifier in sequence, and the signal generator transmits the demodulated waveform to the lock-in amplifier at the same time.

S6. The photodetector demodulates the secondary laser to obtain an electrical signal and amplifies it through a lock-in amplifier. The electrical signal includes the slope characteristics of the resonance of two ESOPs.

其中，ΔA是振动信息，k₀是真空下的波数，l是传输波导的长度，

是双折射差的振动系数，φ为谐振点的相差。S7. The lock-in amplifier transmits the amplified electrical signal to the signal processor, and the signal processor outputs the phase difference between the two ESOPs, and the vibration information can be obtained according to the phase difference. The calculation method of vibration information is

where ΔA is the vibrational information, _k0 is the wavenumber in vacuum, l is the length of the transmission waveguide,

is the vibration coefficient of the birefringence difference, and φ is the phase difference of the resonance point.

The specific method for the signal processor to obtain the phase difference between the resonance points of the two ESOPs includes S7.1-S7.3.

S7.1, the signal processor outputs the sawtooth wave scanning laser.

S7.2, the signal processor obtains the slope characteristics of the two ESOPs from the lock-in amplifier.

S7.3. The signal processor calculates the phase difference between the two ESOPs according to the slope characteristics of the two resonances.

The working principle of the present invention is as follows.

First, a laser is input into the polarization-maintaining annular cavity from the first input port 1, and then enters the polarization-maintaining annular cavity from the second output port 4 after passing through the coupler 5. The matrix for one round transmission in the polarization-maintaining annular cavity is:

Among them, α is the loss of light traveling in the cavity for one cycle, which mainly includes the transmission loss of the optical waveguide and the insertion loss of the coupler; k is the coupling coefficient; β and Δβ are the average propagation constant and birefringence, respectively. difference; θ _t represents the equivalent angular alignment error, which is used to describe the polarization crosstalk at the straight end of the coupler; l is the length of the waveguide ring resonator.

The eigenvalue λ _m and the eigenvector v _m are the two key parameters of the matrix S, they satisfy

Sv _m =λ _m v _m (m=1,2); (2)

Among them, the eigenvector _vm represents such a polarization state: the light starts from the second output port 4 of the coupler 5, and after a week of transmission in the cavity, the polarization state returns to the starting state, which is what we often call the eigenstate The polarization state of ESOPs; and the eigenvalue λ _m represents the transmission coefficient of the ESOPs resonance in the cavity for one cycle, and the eigenvalue λ _m is a complex number, not a matrix, which greatly reduces the difficulty of polarization analysis.

The calculation method of the eigenvalue λ _m can be obtained from formula (1) and formula (2):

where ξ satisfies:

Generally speaking, the polarization extinction ratio of the waveguide coupler is high, that is, θ _t is small, so when Δβ _l <θ _t , the above formula (4) can be simplified as:

Assuming that the light field of the primary laser is E1, it is injected from the first input port 1 of the coupler 5, and then coupled to the second output port 4, and the output light field is E4, which is projected onto two ESOPs respectively:

where a and b are the amplitudes of the intrinsic polarization states v1 and v2, respectively; V is the combined matrix of ESOPs, V=(ν1,ν2); C _k is the coupling matrix:

where θ _k is used to describe the equivalent angular misalignment error at the crossover end of the coupler.

The incident light is transmitted in multiple circles in the cavity, and the accumulated light fields of the two ESOPs are:

It can be known from formula (8) and formula (3) that two resonance states will be excited in the cavity, and the difference between the resonance points is: φ=2ξ. (9)

It can be known from formula (5) that when Δβ _l >> θ _t ,

φ=Δβl. (10)

It can be known from formula (10) that the phase difference between the two resonance points is the birefringence phase difference of the polarization-maintaining annular cavity for one transmission cycle.

When the vibration changes, the birefringence vibration effect of the polarization-maintaining optical waveguide is as follows:

是双折射差的振动系数。因此，通过探测两个谐振点的相差(双折射相差)，就能检测振动：where ΔA is the vibrational information, _k0 is the wavenumber in vacuum, l is the length of the transmission waveguide,

is the vibration coefficient of the birefringence difference. Therefore, by detecting the phase difference (birefringence phase difference) of the two resonance points, the vibration can be detected:

According to the above theoretical analysis, the relationship between the resonance characteristics and the birefringence phase difference of one cycle of transmission in the cavity is obtained by simulation, as shown in Figures 4 to 7. In order to excite the resonance of two ESOPs simultaneously in the cavity, the linearly polarized light is incident on the polarization-maintaining ring cavity at a direction of 45° with respect to the slow axis. When the birefringence difference of one cycle in the cavity is zero, the resonances of the two ESOPs are very close, and the distance between the two resonance points increases with the increase of the phase difference.

The relationship between the phase difference between the two resonance points and the phase difference of the birefringence for one cycle of transmission in the cavity is shown in Figures 8 and 9. When the birefringence difference is large (>0.1πrad), the relationship between the two is approximately linear, and this area can be used to measure the change of vibration; but when the birefringence difference is small, the relationship between the two is not linear. The phase difference tends to 2θ _t as the birefringence phase difference decreases, and the change in vibration cannot be measured in this region.

The invention adopts the resonant effect of multi-turn transmission of light in the annular polarization-maintaining annular cavity to amplify and detect birefringence vibration, thereby greatly improving the sensitivity of vibration, and realizes continuous vibration field measurement on one optical fiber, and the measurement space Great range. With two orthogonal polarization modes propagating in the same waveguide, much of the noise is canceled due to reciprocity (common mode), enabling extremely sensitive vibration detection.

It should also be noted that in this document, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply those entities or operations There is no such actual relationship or order between them. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that a process, method, article or device that includes a list of elements includes not only those elements, but also includes not explicitly listed or other elements inherent to such a process, method, article or apparatus. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (6)

1. An optical vibration sensor based on birefringence resonance effect, characterized in that: the vibration sensing and amplifying device comprises a laser emitting unit, a vibration sensing and amplifying unit, a laser receiving unit and a standard waveform unit which are connected in sequence;

the laser emission unit comprises a laser and a phase modulator which are connected with each other;

the vibration induction amplifying unit comprises a polarization-maintaining ring cavity, the input end of the polarization-maintaining ring cavity is connected with the output end of the phase modulator through a polarization-maintaining optical fiber, and the connection point adopts a 45-degree direction for rotary welding;

the laser receiving unit comprises a photoelectric detector, a phase-locked amplifier and a signal processor which are sequentially connected, wherein the photoelectric detector is connected with the output end of the polarization-maintaining annular cavity, and the signal processor is connected with the laser;

the standard waveform unit comprises a signal generator which is connected with the phase modulator and the phase-locked amplifier; the sensing method of the optical vibration sensor based on the birefringence resonance effect comprises the following steps:

s1, outputting primary laser by the laser and transmitting the primary laser to the phase modulator, and simultaneously sending out a modulation waveform and a demodulation waveform by the signal generator and transmitting the modulation waveform and the demodulation waveform to the phase modulator;

s2, the phase modulator modulates the phase of the primary laser according to the modulation waveform, and the modulated laser is output to the polarization-maintaining ring cavity;

s3, exciting two ESOPs resonances with intrinsic polarization states in the polarization-maintaining annular cavity by primary laser;

s4, external vibration acts on the polarization-maintaining annular cavity to influence the phase difference between resonance points of two ESOPs resonances, and secondary laser is obtained;

s5, the polarization-maintaining ring cavity transmits the secondary laser to the photoelectric detector and the phase-locked amplifier in sequence, and the signal generator transmits the demodulation waveform to the phase-locked amplifier;

s6, demodulating the secondary laser by the photoelectric detector to obtain an electric signal and amplifying the electric signal by a phase-locked amplifier, wherein the electric signal comprises slope characteristics of two ESOPs resonances;

s7, the phase-locked amplifier transmits the amplified electric signal to the signal processor, and the signal processor outputs the phase difference between two ESOPs resonances, so that vibration information can be obtained according to the phase difference;

s7.1, the signal processor outputs sawtooth waves to scan the laser;

s7.2, the signal processor obtains slope characteristics of two ESOPs resonances from the lock-in amplifier;

s7.3, calculating the phase difference between the two ESOPs resonances by the signal processor according to the slope characteristics of the two resonances;

s7.4, the calculation method of the vibration information comprises

Where Δ A is vibration information, k₀Is the wave number under vacuum, l is the length of the transmission waveguide,

is the vibration coefficient of birefringence difference, phi is the phase difference of the resonance point.

2. An optical vibration sensor based on birefringence resonance effect as claimed in claim 1, wherein: the laser is connected with the phase modulator through an isolator.

3. An optical vibration sensor based on birefringence resonance effect as claimed in claim 1, wherein: the polarization-maintaining ring cavity is provided with a first input port (1), a second input port (2), a first output port (3) and a second output port (4), wherein the second input port (2) and the second output port (4) are reflected into a ring through 0-degree welding.

4. An optical vibration sensor based on birefringence resonance effect as set forth in claim 3, wherein: the output end of the phase modulator is connected with the first input port (1).

5. An optical vibration sensor based on birefringence resonance effect as claimed in claim 1, wherein: the signal generator outputs a sine wave or a square wave.

6. An optical vibration sensor based on birefringence resonance effect as claimed in claim 1, wherein: the laser is configured as a narrow linewidth, high coherence laser.

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