CN114777823B - FLRD sensor system and FLRD sensing device based on phase drift - Google Patents
FLRD sensor system and FLRD sensing device based on phase drift Download PDFInfo
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Abstract
The invention discloses an FLRD sensor system and an FLRD sensor based on phase driftDevice belongs to optic fibre sensing technical field, and the system includes: signal light generating means for generating signal light and reference light; the FLRD sensor is arranged on a propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries information of the quantity to be detected; the signal light detection module is arranged on an output light path of the FLRD sensor and is used for detecting information signal light carrying the quantity to be detected and converting the information signal light into a first electric signal; the reference light detection module is arranged on a transmission light path of the reference light and is used for detecting the reference light and converting the reference light into a second electric signal; and a demodulation device for extracting phases of the two paths of electric signals respectively and calculating a phase differenceThen according toCalculating a time decay constant tau to complete the measurement; preferably, the signal light and the reference light are extracted via the same modulator. The invention can improve the measurement accuracy of the PS-FLRD system.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to an FLRD sensor system and an FLRD sensing device based on phase drift.
Background
The Cavity Ring Down (CRD) technology is a spectrum detection technology, and compared with the traditional spectrum detection technology, the signal light can be circularly transmitted in the Cavity, so that the absorption of substances to light is greatly enhanced, and the detection sensitivity is greatly improved. And because the CRD technology measures the attenuation rate of the signal, not the attenuation value of the signal, the influence of light source jitter on the result is avoided. The earliest CRD technology adopts a cavity composed of two high-reflection mirrors, couples light modulated by sine waves into the cavity, and measures the intra-cavity loss by detecting the change of the phase of the input and output light. However, the cavities formed by the high-reflection mirrors need to be aligned strictly, and the problems of pattern matching and the like exist. And the optical fiber has low loss and is easy to couple with the optical fiber, so that the optical fiber is introduced into the CRD system, and the ring-down technology of the optical fiber ring-shaped cavity is proposed.
The phase shift fiber loop attenuation (PS-FLRD) method is that two couplers with high coupling ratio are connected to each other to form a loop. The optical signal can repeatedly pass through the detection area in the optical fiber loop, the intensity and phase change of the signal caused by attenuation can be accumulated in the loop, and the loss in the loop cavity can be demodulated by detecting the phase change of the input light and the output light. In PS-FLRD, on the one hand, as light repeatedly passes through the detection area, the influence of the optical fiber loss is amplified, resulting in a very high sensitivity of the whole system, and on the other hand, since the loss is obtained by measuring the phase shift, the detection result is not influenced by the laser power fluctuation, and the whole system is more stable.
Based on the above advantages, PS-FLRD has been widely used for biochemical measurement of gas absorption and solution concentration, but there are problems at present, mainly expressed in the following two aspects:
(1) The PS-FLRD system demodulates the gas concentration mainly by detecting the phase drift, while the laser and Photo Detector (PD) are very sensitive to the phase drift, and the phase of the modulated light is correspondingly shifted due to the shift of the half-wave voltage of the modulator during long-time operation, which greatly affects the stability of the PS-FLRD system. The sensitivity of the system to the phase is seriously related to the measuring range, stability and resolution of the system to the gas concentration.
(2) The mapping from phase drift to loss is derived theoretically, after the phase drift is calculated by the existing method, the optical fiber loss is further obtained by demodulating the existing method by using the formula in the PS-CRD system, the calculation and derivation process adopts the condition of approximate continuous cavity length, and in practical application, the cavity length is several meters to tens of meters or even hundreds of meters in the PS-FLRD, and cannot be ignored, so that only light with integral multiple of the loop length can be output, and the result obtained by demodulating by the existing method has inherent error and affects loss detection precision.
Disclosure of Invention
Aiming at the defects and improvement demands of the prior art, the invention provides an FLRD sensor system and an FLRD sensing device based on phase drift, and aims to improve the measurement accuracy of a PS-FLRD system.
To achieve the above object, according to one aspect of the present invention, there is provided an FLRD sensor system comprising: the device comprises a signal light generating device, an FLRD sensor, a signal light detection module, a reference light detection module and a demodulation device;
signal light generating means for generating reference light and signal light; the reference light and the signal light are modulated sinusoidal light and are generated by the same light source;
the FLRD sensor is arranged on a propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries information of the quantity to be detected;
the signal light detection module is arranged on an output light path of the FLRD sensor and is used for detecting information signal light carrying the quantity to be detected and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
the reference light detection module is arranged on a transmission light path of the reference light and is used for detecting the reference light and converting the reference light into an electric signal, and the electric signal is recorded as a second electric signal;
demodulation device connected to the signal light detection module and the reference light detection module for extracting the phases of the first and second electric signals and calculating the phase differenceThereafter according to->Calculating a time decay constant tau to finish the measurement of the to-be-detected quantity;
where L represents the loop length in the FLRD sensor, Ω represents the angular modulation frequency, v represents the speed of light in the fiber, Δt represents the additional propagation time compared to the propagation time in the fiber, and n represents the number of turns the signal light has propagated along the FLRD sensor.
Further, the signal light generating device includes: a light source, a signal generator, a modulator and a first coupler;
a light source for generating an original light beam;
a signal generator for generating a modulated signal;
the modulator is arranged on the output light path of the light source, connected with the signal generator and used for modulating the original light beam into sine light according to the modulating signal;
and the first coupler is arranged on the output light path of the modulator and is used for dividing the sine light output by the modulator into two parts, wherein the sine light of a larger part is used as signal light, and the sine light of a smaller part is used as reference light.
Further, the signal light detection module and the reference light detection module are the same type of photoelectric detector.
Further, the demodulation device comprises a lock-in amplifier and a demodulation module;
the phase-locked amplifier is connected with the signal light detection module and the reference light detection module and is used for respectively extracting the phases of the first electric signal and the second electric signal and calculating the phase difference
Demodulation module for according toAnd calculating a time decay constant tau to finish the measurement of the to-be-detected quantity.
Further, the FLRD sensor includes: the second coupler, the third coupler and the sensing unit; the second coupler and the third coupler are 1×2 couplers;
the 1 port of the second coupler is connected with the 1 port of the third coupler, and the high coupling ratio end of the second coupler and the high coupling ratio end of the third coupler are respectively connected with the two ends of the sensing unit;
the low coupling ratio end of the second coupler is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler is used as the output end of the FLRD sensor.
According to another aspect of the present invention, there is provided a phase drift based FLRD sensing device comprising: the device comprises a light source, a signal generator, a modulator, a first coupler, an FLRD sensor, a signal light detection module, a reference light detection module and a phase difference calculation module;
a light source for generating an original light beam;
a signal generator for generating a modulated signal;
the modulator is arranged on the output light path of the light source, connected with the signal generator and used for modulating the original light beam into sine light according to the modulating signal;
the first coupler is arranged on the output light path of the modulator and is used for dividing the sine light output by the modulator into two parts, wherein the sine light of a larger part is used as signal light, and the sine light of a smaller part is used as reference light;
the FLRD sensor is arranged on a propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries information of the quantity to be detected;
the signal light detection module is arranged on an output light path of the FLRD sensor and is used for detecting information signal light carrying the quantity to be detected and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
the reference light detection module is arranged on a transmission light path of the reference light and is used for detecting the reference light and converting the reference light into an electric signal, and the electric signal is recorded as a second electric signal;
a phase difference calculation module connected with the signal light detection module and the reference light detection module for respectively extracting phases of the first and second electric signals and calculating a phase difference
Further, the signal light detection module and the reference light detection module are the same type of photoelectric detector.
Further, the phase difference calculation module is a phase-locked amplifier.
Further, the FLRD sensor includes: the second coupler, the third coupler and the sensing unit; the second coupler and the third coupler are 1×2 couplers;
the 1 port of the second coupler is connected with the 1 port of the third coupler, and the high coupling ratio end of the second coupler and the high coupling ratio end of the third coupler are respectively connected with the two ends of the sensing unit;
the low coupling ratio end of the second coupler is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler is used as the output end of the FLRD sensor.
In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:
(1) The invention is based on the light transmission characteristics of FLRD, namely, since the cavity length of FLRD cannot be ignored and only the light with integral multiple of the loop length can be output, the light output by FLRD should be discrete rather than continuous, and the relation between the phase and the loss under the discontinuous condition is deducedIn calculating the phase difference of the signal light relative to the reference light>Thereafter, further according to the formula->The demodulation method in the invention conforms to the transmission characteristic of light in the FLRD, can reduce the inherent error existing when the traditional PS-CRD formula is applied to the PS-FLRD, and effectively improves the measurement accuracy of the PS-FLRD system.
(2) The invention divides the modulated light output by the modulator into the signal light and the reference light, because the two lights pass through the same modulator, the drift of the half-wave voltage of the modulator causes the drift of the whole system under long-time work to simultaneously influence the signal light and the reference light, and the changes are counteracted when calculating the phase difference.
(3) The invention utilizes the photoelectric detector with the same model to finish the detection of the signal light and the reference light, so that the noise floor of the photoelectric detector has the same effect on the signal light and the reference light, thereby eliminating the influence of the noise floor of the photoelectric detector on the measurement result in the process of calculating the phase difference, further improving the measurement precision and effectively improving the stability of the system.
(4) The phase difference calculation method and device can be used for quickly and accurately calculating the phase difference by extracting the phases of two paths of signals and calculating the phase difference by using the Lock-in amplifier (LIA).
Drawings
FIG. 1 is a schematic diagram of an FLRD sensor system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an FLRD sensing device based on phase drift according to an embodiment of the present invention;
the same reference numbers are used throughout the drawings to reference like elements or structures, wherein:
the device comprises a 0-signal light generating device, a 1-light source, a 2-signal generator, a 3-modulator, a 4-first coupler, a 5-second coupler, a 6-third coupler, a 7-sensing unit, an 8-first photoelectric detector, a 9-second photoelectric detector, a 10-lock-in amplifier, an 11-demodulation module and a 12-demodulation device.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
In the present invention, the terms "first," "second," and the like in the description and in the drawings, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order.
In order to solve the technical problem that the existing PS-FLRD system uses a demodulation formula in the PS-CRD system, and has inherent errors, so that the measurement accuracy is low, the invention provides an FLRD sensor system and an FLRD sensing device based on phase drift, and the whole thought of the FLRD sensor system is as follows: based on the transmission characteristic of light in the FLRD, namely, because the cavity length of the FLRD cannot be ignored, only light with the integral multiple of the loop length can be output, the light output by the FLRD is discrete instead of continuous, the relation between the phase and the loss under the discontinuous condition is deduced, after the phase difference between the signal light and the reference light is calculated, the optical fiber loss is demodulated based on the relation between the phase and the loss under the discontinuous condition, thereby eliminating the inherent error in the traditional demodulation equation and improving the measurement precision; on the basis, the optical path structure is adjusted, so that the reference light and the signal light are led out through the same modulator, thereby reducing the phase drift caused by the electro-optical modulator, further improving the measurement accuracy and improving the stability of the system.
Before explaining the technical scheme of the invention in detail, the principle related to signal demodulation of the invention is briefly described as follows:
assume that the modulated optical signal expression is
I out0 (t)＝I 0 (1+γsin(Ωt))
Wherein I is 0 Is the direct current component of the output light, Ω represents the angular modulation frequency, γ represents the modulation depth, and t is the propagation time in the fiber. In PS-CRD where the cavity length is continuous, the total output light can be written as:
τ is the time decay constant caused by the sensing module and Δt is the additional propagation time of the light compared to t. However, in PS-FLRD the cavity length cannot be neglected, only light passing through an integer multiple of the loop length can be output. The output light should be discrete rather than continuous. The additional time Δt is replaced by the following equation:
n represents the number of turns the light has propagated, L represents the loop length, v represents the speed of light in the fiber, and the time decay constant depends on two parts:
wherein τ Optical fiber Represents the time decay constant, τ, of the fiber Coupler Representing a coupler time decay constant; 1/τ Optical fiber Associated with losses of one turn transmitted in the fibre loop, 1/τ Coupler Only with respect to the number of passes. When the loss in the fiber changes, the attenuation caused by the coupler is not affected. Thus, a is defined as the transmittance of one revolution of light propagation, instead of the decay time constant:
α＝α optical fiber ·α Coupler
Wherein alpha is Optical fiber Indicating the optical fiber transmittance, alpha Coupler Indicating the transmittance of the coupler;
based on the definition, the obtained PS-FLRD total output light formula is as follows after taking the discreteness of the output light into consideration:
in order to facilitate deriving the phase and loss relationship under discontinuous conditions, let:
namely:
so that K can be utilized n Calculating the phase differenceThe concrete steps are as follows:
wherein Im (K) n ) And Re (K) n ) Respectively represent K n Imaginary and real parts of (2);
because of
So that the number of the parts to be processed,
since α <1 in FLRD, the above formula can be reduced to:
based on the above calculation formula, under discontinuous conditions, the attenuation caused by the sensing unit can be shifted by the phaseTab listThe calculation method accords with the transmission characteristic of light in the FLRD, eliminates the inherent error existing when the demodulation method of the PS-CRD is applied to the PS-FLRD system, and effectively improves the measurement accuracy of the PS-FLRD system.
The following are examples.
Example 1:
an FLRD sensor system, as shown in fig. 1, comprising: a signal light generating device 0, an FLRD sensor, a first photodetector 8, a second photodetector 9, and a demodulating device 12;
signal light generating means 0 for generating reference light and signal light; the reference light and the signal light are modulated sinusoidal light and are generated by the same light source;
the FLRD sensor is arranged on a propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries information of the quantity to be detected;
the second photoelectric detector 9 is arranged on the output optical path of the FLRD sensor and is used for detecting information signal light carrying the quantity to be detected and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
a first photodetector 8, disposed on the propagation optical path of the reference light, for detecting the reference light and converting it into an electrical signal, denoted as a second electrical signal;
demodulation means 12 connected to the signal light detection module and the reference light detection module for extracting phases of the first electric signal and the second electric signal, respectively, and calculating a phase differenceThereafter according to->And calculating a time decay constant tau to finish the measurement of the to-be-detected quantity.
Based on the analysis, the phase difference of the two signals is calculatedThen, the signal demodulation formula used, i.e. +.>The relation between the phase and the loss under the discontinuous condition is reflected, so that compared with the demodulation method directly utilizing the demodulation formula of the PS-CRD for demodulation, the embodiment can effectively improve the measurement accuracy.
Referring to fig. 1, in the present embodiment, a signal light generating apparatus 0 includes: a light source 1, a signal generator 2, a modulator 3 and a first coupler 4;
a light source 1 for generating an original light beam;
a signal generator 2 for generating a modulated signal;
the modulator 3 is arranged on the output light path of the light source 1, is connected with the signal generator 2 and is used for modulating the original light beam into sine light according to a modulating signal;
a first coupler 4, disposed on the output optical path of the modulator 3, for dividing the sinusoidal light output from the modulator 3 into two parts, wherein a larger part of the sinusoidal light is used as the signal light, and a smaller part of the sinusoidal light is used as the reference light;
in the embodiment, the reference light and the signal light are led out through the same modulator, so that the phase drift caused by the electro-optical modulator can be reduced, the measurement precision is further improved, the stability of the system is improved, and the precision and the stability of the system can be remarkably improved particularly in the application of optical fiber loss and the like in a strong radiation measuring environment, which need long-time measurement; in order to further eliminate the influence of the environment, it is preferable that in the present embodiment, the first photodetector 8 and the second photodetector 9 are the same type of photodetectors, whereby the influence of the noise floor of the photodetectors on the measurement accuracy can be eliminated.
Referring to fig. 1, in the present embodiment, a demodulation apparatus 12 includes a lock-in amplifier 10 and a demodulation module 11;
a lock-in amplifier 10 connected to the signal light detection module and the reference light detection module for extracting phases of the first and second electric signals, respectively, and calculating a phase differenceThe phase-locked amplifier is used for rapidly and accurately completing phase extraction and phase difference calculation;
a demodulation module 11 for according toAnd calculating a time decay constant tau to finish the measurement of the to-be-detected quantity.
Referring to fig. 1, in the present embodiment, the FLRD sensor includes: a second coupler 5, a third coupler 6 and a sensing unit 7; the second coupler 5 and the third coupler 6 are each 1×2 couplers; two ports are arranged on one side of the 1 multiplied by 2 coupler, namely a high coupling ratio end and a low coupling ratio end, and the optical signal energy of the high coupling ratio end is larger than that of the low coupling ratio end; the other side of the 1 x 2 coupler has only one port, namely 1 port;
the 1 port of the second coupler 5 is connected with the 1 port of the third coupler 6, and the high coupling ratio end of the second coupler 5 and the high coupling ratio end of the third coupler 6 are respectively connected with two ends of the sensing unit 7; the sensing unit 7 must be placed on one side of the second coupler 5 connected with the high coupling ratio end of the third coupler 6, and since the sensing unit 7 needs to be disconnected when the initial phase is measured, if the sensing unit 7 is placed on the other side of the ring cavity, the initial phase cannot be measured;
the low coupling ratio end of the second coupler 5 is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler 6 is used as the output end of the FLRD sensor; the low coupling ratio end of the third coupler 6 serves as an output end for introducing light such that a large part of the light can circulate in the ring cavity.
Example 2:
a phase drift based FLRD sensing device, as shown in fig. 2, comprising: the device comprises a light source 1, a signal generator 2, a modulator 3, a first coupler 4, an FLRD sensor, a first photoelectric detector 8, a second photoelectric detector 9 and a phase difference calculation module;
a light source 1 for generating an original light beam;
a signal generator 2 for generating a modulated signal;
the modulator 3 is arranged on the output light path of the light source 1, is connected with the signal generator 2 and is used for modulating the original light beam into sine light according to a modulating signal;
a first coupler 4, disposed on the output optical path of the modulator 3, for dividing the sinusoidal light output from the modulator 3 into two parts, wherein a larger part of the sinusoidal light is used as the signal light, and a smaller part of the sinusoidal light is used as the reference light;
the FLRD sensor is arranged on a propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries information of the quantity to be detected;
the second photoelectric detector 9 is arranged on the output optical path of the FLRD sensor and is used for detecting information signal light carrying the quantity to be detected and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
a first photodetector 8, disposed on the propagation optical path of the reference light, for detecting the reference light and converting it into an electrical signal, denoted as a second electrical signal;
a lock-in amplifier 10 connected to the signal light detection module and the reference light detection module for extracting phases of the first and second electric signals, respectively, and calculating a phase difference
In the embodiment, the reference light and the signal light are led out through the same modulator, so that the phase drift caused by the electro-optical modulator can be reduced, the measurement precision is further improved, the stability of the system is improved, and the precision and the stability of the system can be remarkably improved particularly in the application of optical fiber loss and the like in a strong radiation measuring environment, which need long-time measurement; in order to further eliminate the influence of the environment, it is preferable that in the present embodiment, the first photodetector 8 and the second photodetector 9 are the same type of photodetectors, whereby the influence of the noise floor of the photodetectors on the measurement accuracy can be eliminated.
Referring to fig. 2, in this embodiment, the FLRD sensor includes: a second coupler 5, a third coupler 6 and a sensing unit 7; the second coupler 5 and the third coupler 6 are each 1×2 couplers;
the 1 port of the second coupler 5 is connected with the 1 port of the third coupler 6, and the high coupling ratio end of the second coupler 5 and the high coupling ratio end of the third coupler 6 are respectively connected with two ends of the sensing unit 7;
the low coupling ratio end of the second coupler 5 is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler 6 is used as the output end of the FLRD sensor.
The FLRD sensing device based on phase drift provided by the embodiment is an integrated, miniaturized and high-sensitivity sensing device, and has good application prospect in the sensing field; in practical application, the design can be performed at the sensing unit 7 according to different to-be-detected amounts, so as to realize the measurement of the to-be-detected amounts.
For example, in a strong radiation environment such as space, the fiber loss increases due to the radiation attenuation (RIA) effect, which seriously affects the application of the fiber in the radiation environment, and in order to evaluate the effect of the RIA effect, an accurate measurement of the fiber loss is required. The method of measuring RIA is Optical Time Domain Reflectometry (OTDR), but because of its inherent attenuation dead zone, the optical fiber with a shorter length cannot be detected, the FLRD sensor system provided in this embodiment can be used to accurately measure the optical fiber loss in a strong radiation environment, at this time, the erbium-doped optical fiber is used as a sensing unit, and the FLRD sensor is placed in an irradiation room, the RIA effect is a slow process, which requires tens of thousands to thousands of hours to fully deplete the optical fiber, and this requires a long time to keep stable, because in this embodiment, some drifts caused by the environment affect both the reference signal and the input signal, and these drifts are eliminated to the greatest extent in the calculation process of the phase difference, so as to realize accurate and stable measurement of the production time.
In other applications, the sensing may be designed at the sensing unit according to different utility requirements. If the highly doped optical fiber is placed at the sensing unit, the loss generated by the optical fiber under the strong radiation environment can be detected; the gas chamber can be arranged at the sensing unit, and different kinds of gases or gases with different concentrations are introduced into the gas chamber for gas sensing; the common optical fiber can be placed at the sensing unit, and then the pressure is increased to perform stress sensing; liquid can be placed in the sensing unit part to measure the refractive index; magnetic field measurement, temperature measurement, etc. can also be implemented.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (8)
1. An FLRD sensor system, comprising: the device comprises a signal light generating device, an FLRD sensor, a signal light detection module, a reference light detection module and a demodulation device;
the signal light generating device is used for generating reference light and signal light; the reference light and the signal light are modulated sinusoidal light and are generated by the same light source;
the FLRD sensor is arranged on the propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries the information of the quantity to be detected;
the signal light detection module is arranged on an output light path of the FLRD sensor and is used for detecting information signal light carrying the to-be-detected quantity and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
the reference light detection module is arranged on a transmission light path of the reference light and is used for detecting the reference light and converting the reference light into an electric signal, and the electric signal is recorded as a second electric signal;
the demodulation device comprises a lock-in amplifier and a demodulation module; the phase-locked amplifier is connected with the signal light detection module and the reference light detection module and is used for respectively extracting the phases of the first electric signal and the second electric signal and calculating the phase differenceThe demodulation module is used for receiving the signal according to->Calculating a time decay constant tau to finish the measurement of the to-be-detected quantity;
where L represents the loop length in the FLRD sensor, Ω represents the angular modulation frequency, v represents the speed of light in the fiber, Δt represents the additional propagation time compared to the propagation time in the fiber, and n represents the number of turns the signal light has propagated along the FLRD sensor.
2. The FLRD sensor system according to claim 1, wherein the signal light generating means comprises: a light source, a signal generator, a modulator and a first coupler;
the light source is used for generating an original light beam;
the signal generator is used for generating a modulation signal;
the modulator is arranged on the output light path of the light source, connected with the signal generator and used for modulating the original light beam into sine light according to the modulating signal;
the first coupler is arranged on the output light path of the modulator and is used for dividing the sine light output by the modulator into two parts, wherein the sine light of a larger part is used as the signal light, and the sine light of a smaller part is used as the reference light.
3. The FLRD sensor system according to claim 1 or 2, wherein the signal light detection module and the reference light detection module are the same type of photo detector.
4. The FLRD sensor system according to claim 1 or 2, wherein the FLRD sensor comprises: the second coupler, the third coupler and the sensing unit; the second coupler and the third coupler are both 1×2 couplers;
the 1 port of the second coupler is connected with the 1 port of the third coupler, and the high coupling ratio end of the second coupler and the high coupling ratio end of the third coupler are respectively connected with the two ends of the sensing unit;
the low coupling ratio end of the second coupler is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler is used as the output end of the FLRD sensor.
5. A phase drift based FLRD sensing device, comprising: the device comprises a light source, a signal generator, a modulator, a first coupler, an FLRD sensor, a signal light detection module, a reference light detection module and a phase difference calculation module;
the light source is used for generating an original light beam;
the signal generator is used for generating a modulation signal;
the modulator is arranged on the output light path of the light source, connected with the signal generator and used for modulating the original light beam into sine light according to the modulating signal;
the first coupler is arranged on the output light path of the modulator and is used for dividing the sine light output by the modulator into two parts, wherein the sine light of a larger part is used as the signal light, and the sine light of a smaller part is used as the reference light;
the FLRD sensor is arranged on the propagation light path of the signal light and is used for sensing the quantity to be detected, so that the signal light carries the information of the quantity to be detected;
the signal light detection module is arranged on an output light path of the FLRD sensor and is used for detecting information signal light carrying the to-be-detected quantity and converting the information signal light into an electric signal, and recording the electric signal as a first electric signal;
the reference light detection module is arranged on a transmission light path of the reference light and is used for detecting the reference light and converting the reference light into an electric signal, and the electric signal is recorded as a second electric signal;
the phase difference calculation module is connected with the signal light detection module and the reference light detection module and is used for respectively extracting the phases of the first electric signal and the second electric signal and calculating the phase difference
6. The phase drift based FLRD sensing device of claim 5, wherein the signal light detection module and the reference light detection module are the same type of photo detector.
7. The phase drift based FLRD sensing device of claim 5 or 6, wherein the phase difference calculation module is a lock-in amplifier.
8. The phase-drift based FLRD sensing device of claim 5 or 6, wherein the FLRD sensor comprises: the second coupler, the third coupler and the sensing unit; the second coupler and the third coupler are both 1×2 couplers;
the 1 port of the second coupler is connected with the 1 port of the third coupler, and the high coupling ratio end of the second coupler and the high coupling ratio end of the third coupler are respectively connected with the two ends of the sensing unit;
the low coupling ratio end of the second coupler is used as the input end of the FLRD sensor, and the low coupling ratio end of the third coupler is used as the output end of the FLRD sensor.
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