阅读说明：本技术 基于光电振荡器的加速度测量仪器 (Acceleration measuring instrument based on photoelectric oscillator ) 是由 于晋龙 毛新丹 王菊 马闯 于 2020-05-14 设计创作，主要内容包括：本发明公开了一种基于光电振荡器的加速度测量仪器,包括由宽谱光源、调制器、光纤光栅、微波放大器,微波滤波器、光电探测器构成的光电振荡回路。该结构通过粘贴在悬臂梁上的光纤光栅来感知加速度变化：加速度变化引起光纤光栅的形变,引起其中心波长变化,中心波长决定了光电振荡回路谐振腔的基频f<Sub>0</Sub>,此时基频的检测精度就是加速度测量精度。再利用累积放大原理,当谐振腔振荡在高次谐波时,实际谐振频率f<Sub>N</Sub>＝Nf<Sub>0</Sub>,则基频的变化就被放大了N倍,可以达到很高的测量精度。本发明有益效果：具有极简单的结构和极好的相位噪声性能；利用OEO将光纤光栅波长变化转换为微波信号频率变化并利用累积放大原理,能够达到较高的传感分辨率,且可靠性较高。(The invention discloses an acceleration measuring instrument based on a photoelectric oscillator, which comprises a photoelectric oscillation loop consisting of a wide-spectrum light source, a modulator, a fiber bragg grating, a microwave amplifier, a microwave filter and a photoelectric detector. The structure senses acceleration change through the fiber bragg grating pasted on the cantilever beam: the acceleration change causes the deformation of the fiber grating, which causes the change of the central wavelength thereof, which determines the fundamental frequency f of the resonant cavity of the photoelectric oscillation circuit 0 At this time, the detection accuracy of the fundamental frequency is the acceleration measurement accuracy. Then, by using the accumulation amplification principle, when the resonant cavity oscillates at higher harmonic, the actual resonant frequency f N ＝Nf 0 The change of the fundamental frequency is amplified by N times, and high measurement accuracy can be achieved. The invention has the beneficial effects that: has an extremely simple structure and excellent phase noise performance; the OEO is utilized to convert the wavelength change of the fiber bragg grating into the frequency change of a microwave signal, and the accumulation amplification principle is utilized, so that the high sensing resolution can be achieved, and the reliability is high.)

1. An acceleration measuring instrument based on a photoelectric oscillator comprises a modulator (2) arranged along the emitting direction of a wide-spectrum light source (1), wherein an optical signal output by the modulator (2) enters a fiber bragg grating (9) after passing through a first port (3a) and a second port (3b) of a three-port circulator (3); it is characterized in that the preparation method is characterized in that,

and a photoelectric oscillation loop is arranged between the third port (3c) of the three-port optical circulator (3) and the modulator (2), and the light reflected from the fiber grating (9) passes through the third port (3c) of the three-port optical circulator (3) and is fed back to the microwave modulation port of the modulator (2) through the photoelectric oscillation loop.

2. The optoelectronic oscillator-based acceleration measuring instrument according to claim 1, characterized by, that the optoelectronic oscillation loop is composed of a photodetector (4), a first microwave amplifier (5), a microwave filter (6), a second microwave amplifier (7) and an electric coupler (8) arranged between the third port (3c) of the three-port optical circulator (3) and the modulator (2);

the light reflected back from the fiber grating (9) passes through the third port (3c) of the three-port circulator (3) and is fed back to the microwave modulation port of the modulator (2) through the photoelectric oscillation loop, and the light reflected back from the fiber grating (9) passes through the third port (3c) of the three-port circulator (3) and enters the photoelectric detector (4); the optical signal is converted into an electric signal through the photoelectric detector (4), then the electric signal is amplified through the first microwave amplifier (5), the amplified electric signal is amplified through the second microwave amplifier (7) after passing through the microwave filter (6), and the amplified electric signal is fed back to a microwave modulation port of the modulator (2) through the electric coupler (8).

3. The acceleration measuring instrument based on the optoelectronic oscillator of claim 1, wherein the fiber grating (9) is adhered to a cantilever beam, and a weight is connected to a free end of the cantilever beam, and an external force is applied to the weight to accelerate the weight, so as to cause deformation of the cantilever beam, and then cause a change in a central wavelength of the fiber grating (9), and finally change a fundamental frequency f of a resonant cavity of the optoelectronic oscillation circuit₀(ii) a One end of the electric coupler (8) is connected with the modulator (2), the other end of the electric coupler (8) is connected with an external electric spectrometer, and output microwave signals are observed through the electric spectrometer.

4. Optoelectronic oscillator-based accelerometer according to claim 1, characterized in that the broad spectrum light source (1) is a semiconductor broad spectrum light source or an EDFA-based broad spectrum light source.

5. The optoelectronic oscillator-based accelerometer according to claim 1, wherein the fiber grating (9) is used as both a sensing element and a filtering unit in the optoelectronic oscillation circuit, and the central wavelength of the fiber grating (9) is calculated as:

λ＝2n_effΛ (1)

in the formula (1), λ is the center wavelength of the fiber grating, Λ is the grating period, n_effIs the effective refractive index of the fiber grating;

when the external acceleration a to be measured changes, the fiber bragg grating (9) deforms, and the formula (4) is obtained according to the formula (2) and the formula (3):

in the formulas (2), (3) and (4), λ is the central wavelength of the fiber grating, PThe elasto-optic coefficient of the optical fiber is the stress of the fiber bragg grating, a is the acceleration to be tested, F is the external force applied to the test weight, m is the mass of the test weight, E is the elastic modulus of the cantilever beam, and S is the sectional area of the cantilever beam;

actual resonant frequency f of the opto-electronic resonant circuit_NThe mode selection is carried out through a microwave filter (6), and the following conditions are met:

f_N＝Nf₀(5)

in the formula (5), N is a natural number; f. of₀Is the resonant cavity fundamental frequency of the photoelectric oscillation circuit, and f is obtained by observing the output microwave signal with an external spectrometer_NThe change of the central wavelength of the fiber grating is obtained by using the relation between the frequency and the wavelength, and the acceleration a to be measured is obtained by using the formula (4).

Technical Field

The present invention relates to acceleration measurement systems, and in particular to an acceleration measurement instrument based on an optoelectronic oscillator (OEO).

Background

Acceleration measurement is generally to measure acceleration change indirectly through the vibration of proof mass, converts the vibration information that acceleration change arouses into other parameters, extracts it again, and traditional acceleration sensor has multiple types such as piezoelectricity formula, piezoresistive formula, capacitanc, but traditional acceleration sensor sensitivity is low, easily receives electromagnetism, the interference of temperature, introduces some errors easily, so hardly realize the accurate measurement to acceleration. With the development of optical fiber technology, acceleration measurement based on fiber bragg gratings can effectively solve the problems, so that the fiber bragg gratings have important application in the fields of automobiles, ships, bridges, aerospace, military and the like.

The fiber grating is a reflection type grating, the central wavelength of the fiber grating is sensitive to the change of factors such as external temperature, stress strain and the like, acceleration information can be obtained through central wavelength modulation, and then the wavelength change is demodulated out, but optical demodulation equipment (such as a spectrometer and the like) is expensive and is generally commonly used in a laboratory and limits the wide application of the optical demodulation equipment, so that how to demodulate the wavelength change of the fiber grating becomes a research focus at home and abroad. Currently, the commonly used fiber grating wavelength demodulation technologies are mainly classified into two types: filtering methods and interference methods. The filtering method is to convert the wavelength change into the intensity change and construct a tunable optical filter, and mainly comprises a matched grating detection method, a tunable filtering detection method, an edge filter detection method, a charge coupler array method, a wavelength tunable light source demodulation method and the like. Although this method is relatively simple, it is difficult to further improve the sensing accuracy. The interference method uses the coherence of light waves, that is, converts the drift amount of the wavelength into the phase change amount to measure, and the actual application thereof mainly includes unbalanced mach-zehnder interference method, michelson interference method, and the like. The method has high detection sensitivity and resolution, but is easily interfered by the change of the external temperature environment and vibration or jitter, and has strict requirements on the demodulation working environment. The two types of demodulation methods mainly aim at signals with relatively low frequency (within KHz), but in some special fields, signals with high-speed change (mHz level) need to be measured, and the requirement on sensing resolution is relatively high. Therefore, in recent years, researchers have proposed some new demodulation methods to convert the optical domain sensing information to the microwave domain, and there are two main methods: one converts fiber grating wavelength variations into microwave signal frequency variations and the other converts fiber grating wavelength variations into intensity variations. In comparison, the method for converting the wavelength change of the fiber bragg grating into the frequency change of the microwave signal can achieve higher sensing resolution and higher reliability.

An optoelectronic oscillator (OEO) is a novel oscillator developed in recent years, can generate microwave signals with ultralow phase noise, has high output spectral purity which can reach the mHz magnitude, and therefore acceleration change is converted into the change of the frequency of the generated microwave signals by utilizing an OEO structure, and the sensing resolution is favorably improved.

Disclosure of Invention

Aiming at the prior art, the invention provides an acceleration measuring instrument based on an optoelectronic oscillator (OEO), which utilizes the change sensitivity of the resonant wavelength of a fiber grating to the external temperature, strain, refractive index, concentration and the like, simultaneously uses the fiber grating as a sensing element and a filter unit in the OEO, establishes a most basic optoelectronic oscillator (OEO) structure, when the external acceleration to be measured is changed, the wavelength of the fiber grating is changed along with the change, and the central wavelength determines the fundamental frequency f of the resonant cavity₀At this time, the detection accuracy of the fundamental frequency is the acceleration measurement accuracy. Then, by using the accumulation amplification principle, when the resonant cavity oscillates at higher harmonic, the actual resonant frequency f_N＝Nf₀The change of the fundamental frequency is amplified by N times, and the acceleration to be measured can be calculated by observing the output microwave signal.

In order to solve the technical problem, the acceleration measuring instrument based on the photoelectric oscillator comprises a modulator arranged along the emission direction of a wide-spectrum light source, wherein an optical signal output by the modulator enters a fiber bragg grating after passing through a first port and a second port of a three-port circulator; and a photoelectric oscillation circuit is arranged between the third port of the three-port optical circulator and the modulator, and light reflected from the fiber bragg grating passes through the third port of the three-port optical circulator and is fed back to the microwave modulation port of the modulator through the photoelectric oscillation circuit.

Furthermore, the acceleration measuring instrument based on the photoelectric oscillator of the invention is characterized in that the photoelectric oscillation circuit is composed of a photoelectric detector, a first microwave amplifier, a microwave filter, a second microwave amplifier and an electric coupler, wherein the photoelectric detector, the first microwave amplifier, the microwave filter, the second microwave amplifier and the electric coupler are arranged between a third port of the three-port optical circulator and the modulator; the light reflected back from the fiber grating passes through the third port of the three-port circulator and is fed back to the microwave modulation port of the modulator through the photoelectric oscillation loop, and the light reflected back from the fiber grating enters the photoelectric detector through the third port of the three-port circulator; the photoelectric detector converts the optical signal into an electric signal, the electric signal is amplified by the first microwave amplifier, the amplified electric signal is amplified by the second microwave amplifier after passing through the microwave filter, and the amplified electric signal is fed back to the microwave modulation port of the modulator through the electric coupler.

The fiber bragg grating is adhered to a cantilever beam, a weight is connected to the free end of the cantilever beam, external force is applied to the weight, the weight is accelerated, accordingly, the cantilever beam is deformed, the central wavelength of the fiber bragg grating is changed, and finally, the resonant cavity fundamental frequency f of the photoelectric oscillation circuit is changed₀(ii) a One end of the electric coupler is connected with the modulator, the other end of the electric coupler is connected with an external electric spectrum instrument, and the output microwave signals are observed through the electric spectrum instrument.

The wide-spectrum light source is a semiconductor wide-spectrum light source or an EDFA-based wide-spectrum light source.

In the invention, the fiber grating is simultaneously used as a sensing element and a filtering unit in a photoelectric oscillation circuit, wherein the central wavelength calculation formula of the fiber grating is as follows:

λ＝2n_effΛ (1)

in the formula (1), λ is the center wavelength of the fiber grating, Λ is the grating period, n_effIs the effective refractive index of the fiber grating;

when the external acceleration a to be measured changes, the fiber bragg grating deforms, and the formula (4) is obtained according to the formula (2) and the formula (3):

in the formulas (2), (3) and (4), λ is the central wavelength of the fiber grating, PThe elasto-optic coefficient of the optical fiber is the stress of the fiber bragg grating, a is the acceleration to be tested, F is the external force applied to the test weight, m is the mass of the test weight, E is the elastic modulus of the cantilever beam, and S is the sectional area of the cantilever beam;

actual resonant frequency f of the opto-electronic resonant circuit_NThe mode selection is carried out through a microwave filter, and the following conditions are met:

f_N＝Nf₀(5)

in the formula (5), N is a natural number; f. of₀Is the resonant cavity fundamental frequency of the photoelectric oscillation circuit, and f is obtained by observing the output microwave signal with an external spectrometer_NThe change of the central wavelength of the fiber grating is obtained by using the relationship between the frequency and the wavelength, and finally, the acceleration a to be measured is obtained by using the formula (4).

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention adopts an optoelectronic oscillator (OEO) structure, utilizes the advantage of high measurement resolution of microwave signals generated by the optoelectronic oscillator, applies the accumulation amplification principle to acceleration measurement, and amplifies the measured change by 10⁵～10⁶And the high sensing resolution is achieved, and the reliability is high.

(2) The invention converts the wavelength change of the fiber bragg grating into the frequency change of the microwave signal, can carry out rapid information extraction and processing on an electric domain, and can realize high-resolution and high-speed sensing demodulation.

(3) The measuring instrument is simple and easy to operate, has lower cost compared with optical demodulation equipment, and is suitable for large-scale popularization.

Drawings

FIG. 1 is a schematic diagram of an acceleration measuring instrument based on an optoelectronic oscillator (OEO) according to the present invention;

in the figure:

1-wide spectrum light source 2-modulator 3-three-port optical circulator 4-photoelectric detector

5-first microwave amplifier 6-microwave filter 7-second microwave amplifier 8-electric coupler

9-fiber grating.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, which are not intended to limit the invention in any way.

As shown in fig. 1, the acceleration measuring instrument based on an optoelectronic oscillator (OEO) according to the present invention includes a modulator 2 disposed along an emitting direction of a wide-spectrum light source 1, a direct current optical signal output by the wide-spectrum light source 1 is injected into the modulator 2, and an optical signal output by the modulator 2 enters a fiber grating 9 after passing through a first port 3a and a second port 3b of a three-port circulator 3; a photoelectric oscillation circuit is arranged between the third port 3c of the three-port optical circulator 3 and the modulator 2, and light reflected from the fiber grating 9 passes through the third port 3c of the three-port circulator 3 and is fed back to the microwave modulation port of the modulator 2 through the photoelectric oscillation circuit.

The photoelectric oscillation circuit consists of a photoelectric detector 4, a first microwave amplifier 5, a microwave filter 6, a second microwave amplifier 7 and an electric coupler 8 which are arranged between a third port 3c of the three-port optical circulator 3 and the modulator 2; the light reflected from the fiber grating 9 is fed back to the microwave modulation port of the modulator 2 through the third port 3c of the three-port circulator 3 by the photoelectric oscillation circuit, and the light reflected from the fiber grating 9 enters the photoelectric detector 4 through the third port 3c of the three-port circulator 3; the optical signal is converted into an electrical signal by the photoelectric detector 4 and then amplified by the first microwave amplifier 5, the amplified electrical signal is amplified by the second microwave amplifier 7 after passing through the microwave filter 6, and the amplified electrical signal is fed back to the microwave modulation port of the modulator 2 through the electric coupler 8, so that a closed photoelectric oscillation loop is formed.

The fiber bragg grating 9 is adhered to a cantilever beam, a weight is connected to the free end of the cantilever beam, external force is applied to the weight, the weight generates acceleration, and accordingly deformation of the cantilever beam is caused, the fiber bragg grating 9 is adhered to the cantilever beam to sense acceleration change, so that central wavelength change of the fiber bragg grating 9 is caused, and finally resonant cavity fundamental frequency f of the photoelectric oscillation circuit is changed₀(ii) a One end of the electric coupler 8 is connected with the modulator 2, the other end of the electric coupler 8 is connected with an external electric spectrometer, and output microwave signals are observed through the external electric spectrometer connected with the other end of the electric coupler.

In the invention, the wide-spectrum light source 1 may be a semiconductor wide-spectrum light source or an EDFA-based wide-spectrum light source, and the small signal gains of the first microwave amplifier 5 and the second microwave amplifier 6 are both 30dB to provide sufficient gain for the oscillation starting of the photoelectric oscillation circuit.

The design concept of the invention is to convert the wavelength change of the fiber bragg grating into the frequency change of a microwave signal, construct a most basic optoelectronic oscillator (OEO) structure, and simultaneously use the fiber bragg grating 9 as a sensing element and a filtering unit in the OEO, wherein the central wavelength calculation formula of the fiber bragg grating 9 is as follows:

λ＝2n_effΛ (1)

in the formula (1), λ is the center wavelength of the fiber grating, Λ is the grating period, n_effIs the effective refractive index of the fiber grating;

when the external acceleration to be measured changes, the fiber grating 9 deforms, the grating constant Λ of the fiber grating 9 changes, so that the output wavelength of the fiber grating changes, and according to the relation between the grating wavelength and the strain change and the relation between the acceleration and the strain in the elastic system:

according to the formulas (2) and (3), it is possible to obtain:

in the formulas (2), (3) and (4), λ is the central wavelength of the fiber grating, PThe elasto-optic coefficient of the optical fiber is the stress of the fiber bragg grating, a is the acceleration to be tested, F is the external force applied to the test weight, m is the mass of the test weight, E is the elastic modulus of the cantilever beam, and S is the sectional area of the cantilever beam; the change of the fiber grating wavelength is linearly related to the acceleration, so that the change of the fiber grating wavelength is measured, and the central wavelength of the fiber grating determines the fundamental frequency f of the resonant cavity₀Due to f in the oscillator₀The integral multiple frequency can satisfy the oscillation condition of the photoelectric oscillation circuit OEO, and the actual resonant frequency f of the OEO_NThe microwave filter 6 is used for mode selection, and the following conditions are met:

f_N＝Nf₀(5)

in the formula (5), N is a natural number, f₀Is the fundamental frequency of the resonant cavity of the photoelectric oscillation circuit, and the actual resonant frequency f_NAt a fundamental frequency f₀By this relationship, the variation of the fundamental frequency caused by the acceleration variation is amplified by N times, so that it can be seen that: under the same observation condition and test precision, directly measuring f₀Is far less than the value of measurement f_NAnd N and f₀The obtained precision is high, and the measurement error is greatly reduced; i.e. f is obtained by observing the output microwave signal by an external spectrometer_NBy variation of (a) using_NAnd N and f₀Then, the relationship between the frequency and the wavelength is used to obtain the change Δ λ of the central wavelength of the fiber grating, and the acceleration a to be measured is obtained by using the formula (4).