CN101603857A - Phase Carrier Demodulation Method in Fabry-Perot Interferometric Fiber Optic Hydrophone - Google Patents

Abstract

The invention provides a phase carrier demodulation method in a Fabry-Perot interference fiber optic hydrophone, which is characterized in that: the incident light is divided into two beams according to the light intensity ratio of 1:4, and the light directly detected by one path is The intensity is I ₀ , and the other path is injected into the optical fiber FP cavity through the cascaded 3dB coupler. After forming multi-beam interference, the reflected light intensity I _R is measured, so that I ₀ and I _R pass through the subtractor, divider hardware or The software algorithm realizes that the system output is 1/T=I ₀ /(I ₀ -I _R ), and then performs PGC demodulation to obtain the phase output. The invention adopts a new optical path design through the reciprocal calculation of the transmittance of the FP cavity, and proposes a method of using the PGC demodulation technology in the FP multi-beam interference system. Widen the application range of PGC demodulation. All F-P interferometers that need to use phase detection can use this method to realize signal demodulation.

Description

Phase carrier demodulation method in the Fabry-Perot interference type fibre optic hydrophone

(1) technical field

What invention related to is a kind of system's output detecting method of Fabry-Perot interference type fibre optic hydrophone, specifically adopts the inventive method can realize the utilization of phase modulation and demodulation of interferometric in Fabry-Perot interference type fibre optic hydrophone.

(2) background technology

Fibre optic hydrophone is highly sensitive, small and light, be not subjected to electromagnetic interference (EMI); Vector hydrophone has good low audio frequency and infra-acoustic frequency performance, itself does not produce tangible sound field distortion, can be considered as a receiver, so its directive property is good, and performance parameter is stable, can be used for accurately measuring or long-time the measurement.Both advantages are combined, will will produce significant effects the future development of underwater sound Detection Techniques.Current emphasis is the optical fiber vector hydrophone unit in the development towing line array sonar, utilizes high sensitivity and low noise optical fiber sound pressure nautical receiving set and optical fiber acceleration transducer to realize.This not only can fundamentally solve the problem that the port and starboard target is differentiated, and can improve the spatial gain of dragging linear array, help surveying long-range weak target, so fibre optic hydrophone will become one of optimal acoustical signal receiving device in the following marine technology.

In F-P interference type optical fiber hydrophone scheme, because of multiple-beam interference, phse sensitivity is higher.Because the sensing transmission is all finished on an optical fiber, light channel structure is simple, does not have double light path inherent defects such as polarization interference.But also owing to multiple-beam interference, ripe PGC detection technique can't be directly used in F-P and interfere.

(3) summary of the invention

The object of the present invention is to provide the phase carrier demodulation method in a kind of Fabry-Perot interference type fibre optic hydrophone that in the phase detection technique of the position of Fabry-Perot interference type fibre optic hydrophone, can use PGC modulation and demodulation technology.

The object of the present invention is achieved like this:

Incident light is divided into two bundles by beam intensity ratio at 1: 4, and the light intensity of one road direct sunshine electro-detection is I ₀, fiber F-P cavity is injected through the three-dB coupler of cascade in another road, behind the formation multiple-beam interference, measures reflective light intensity I _R, make I ₀, I _RBe output as by subtracter, divider hardware or software algorithm realization system $\frac{1}{T}=\frac{I_0}{I_0-I_R},$ Next carry out the PGC demodulation, output mutually must put in place.

Or:

Incident light through three-dB coupler with light intensity I ₀Inject fiber F-P cavity and interfere, carry the transmitted light I of measured signal _TThrough opto-electronic conversion, by being transformed to the inverse output of transmissivity behind divider hardware or the computer software algorithm $\frac{1}{T}=\frac{I_0}{I_T},$ Next carry out the PGC demodulation, output mutually must put in place.

The present invention has proposed a kind of method that can use the PGC demodulation techniques in the F-P interference type optical fiber hydrophone on the basis of original double light path PGC detection technique.Expanded conventional P GC The Application of Technology scope.

1, F-P interferes the mathematical expression form of output intensity

As Fig. 1, incident light is injected the fiber F-P cavity that fineness is F by three-dB coupler, and order treats that location is mutually

, the reflective light intensity in F-P chamber is I _R, reflection coefficient is R, then

2, PGC technology

In the input treatment technology of interference type optical fiber hydrophone, generally adopt the disposal route of PGC, can adopt software algorithm to realize, algorithm is reliable and stable and to be convenient to digitizing integrated.As Fig. 2, the phase modulation (PM) frequency of establishing light source or PZT generation is ω _c, the output signal of typical two-beam interference is

Links such as the expansion of process Bessel's function, mixing, low-pass filtering, differentiate multiplication cross are subtracted each other, integration, high-pass filtering obtain measured signal Linearity output.Because F-P is a multiple-beam interference, output intensity (1) formula does not satisfy the mathematical expression form of typical two-beam interference---(2) formula, thereby ripe PGC technology can't adopt.

Make the phase modulation (PM) frequencies omega _c, F-P chamber transmissivity $T=\frac{I_0-I_R}{I_0}=1-R,$ Can get by formula (1) conversion

As seen, if measure

Order $A=1+\frac{F}{2},$ $B=-\frac{F}{2},$ Then (3) formula is identical with (2) formula in form, and the technology of PGC just can realize in F-P interferes.

Method of the present invention has solved the intensity of light source and has risen and fallen to the influence of fibre optic hydrophone PGC demodulation, has promptly solved the parastic modulation problem.

Conventional P GC demodulation is to realize the phase carrier modulation by modulation PZT or light source injection current.The modulated light source injection current will unavoidably exert an influence to light source output power, i.e. parastic modulation.In (2) formula, A, B are the functions of incident intensity, and this just makes conventional P GC technology face this influence.And by (3) formula, A=1+F/2, B=-F/2 and incident intensity are irrelevant, only are the functions of F-P chamber fineness F, thereby follow-uply carry out the influence that the PGC demodulation is not risen and fallen by the intensity of light source.

Method of the present invention can extend to all phase-detection that adopt the various systems of Fabry-Perot interference formation.

It is typical multiple-beam interference that F-P interferes, and the phse sensitivity height is all finished in an optical fiber owing to interfere with transmission course, thereby the influence that not disturbed by asymmetry.Constitute the interfere type Fibre Optical Sensor with it and have distinct advantages.But carry out because conventional P GC demodulation is interfered at typical double light path, can't be directly used in F-P and interfere.The present invention takes new light path design by the computing reciprocal to F-P chamber transmissivity, has proposed the method for utilization PGC demodulation techniques in F-P multiple-beam interference system.Widened the range of application of PGC demodulation.All need utilize the F-P interferometer of phase-detection all can use this method to realize the signal demodulation.

(4) description of drawings

The theory diagram that Fig. 1 F-P interferes;

Fig. 2 PGC theory diagram;

The PGC demodulation principle block diagram of the F-P interference type optical fiber hydrophone of the reflective detection of Fig. 3;

The PGC demodulation principle block diagram of the F-P interference type optical fiber hydrophone that Fig. 4 transmission-type detects;

F-P interference type optical fiber hydrophone unit outward appearance and experimental system that Fig. 5 transmission-type detects;

The sound pressure sensitivity measured curve of Fig. 6 F-P interference type optical fiber hydrophone;

Fig. 7 F-P interference type optical fiber hydrophone acceleration sensitivity measured curve.

(5) embodiment

For example the present invention is done description in more detail below in conjunction with accompanying drawing:

In conjunction with Fig. 3, first kind of embodiment of the present invention is: incident light is divided into two bundles by beam intensity ratio at 1: 4, and one tunnel direct photoelectricity is converted to output intensity I ₀, fiber F-P cavity is injected through the three-dB coupler of cascade in another road, and behind the formation multiple-beam interference, the reflected light that carries measured signal detects reflective light intensity I through opto-electronic conversion _RMake I ₀, I _RBe output as by subtracter, divider hardware or software algorithm realization system $\frac{1}{T}=\frac{I_0}{I_0-I_R},$ Next carry out the PGC demodulation, output mutually must put in place.

Method of the present invention can also take to detect the method for F-P chamber transmitted light intensity except that the method for the detection F-P cavity reflection light intensity of taking above-mentioned embodiment, realize the PGC demodulation of Fabry-Perot interference type fibre optic hydrophone.In conjunction with Fig. 4, second kind of embodiment of the present invention is: incident light through three-dB coupler with light intensity I ₀Inject fiber F-P cavity and interfere, carry the transmitted light I of measured signal _TThrough opto-electronic conversion, by being transformed to the inverse output of transmissivity behind divider hardware or the computer software algorithm $\frac{1}{T}=\frac{I_0}{I_T},$ Next carry out the PGC demodulation, output mutually must put in place.

With F-P interference type optical fiber hydrophone example effect of the present invention is made aid illustration below in conjunction with accompanying drawing.F-P interference type optical fiber hydrophone with Fig. 3 light path formation, its basic mechanical structure is to twine the fiber F-P resonator cavity on elasticity post shell, acoustic pressure makes post shell generation deformation drive the long variation in F-P chamber in the water, produce the variation of phasic difference, through the present invention---the PGC method of F-P realizes the sound pressure signal demodulation.Nautical receiving set physical dimension is seen Fig. 5 much smaller than the wavelength of measured sound wave.

F-P interference type optical fiber hydrophone sensitivity measure carries out in national defence underwater sound metering first order station.In calibrating device, carry out during 63Hz～2kHz, press GB4310-84 " low frequency hydrophone calibration method " and implement; In anechoic tank,, carry out during 2kHz～5kHz, press GB7965-87 " acoustics-underwater acoustic transducer is measured " and implement.The sensitivity index of three nautical receiving sets of actual measurement: the range of sensitivity-130dB～-115dB (the corresponding 1V/ μ of 0dB Pa).During working band 20Hz～2kHz, rise and fall in the band less than ± 5dB; When working band was 2kHz～5kHz, rising and falling in the band was not more than ± 3dB.Acceleration sensitivity is measured frequency range 20Hz～200Hz, carries out the acceleration during according to the confirmed test of experiment situation, the acceleration sensitivity when converting out 1g: 26-30dB (the corresponding 1V/g of 0dB) on shaking table.

Claims (2)

1, a phase carrier demodulation method in the Fabry-Perot interference type optical fiber hydrophone, it is characterized in that: incident light is divided into two beams by light intensity ratio 1: 4, and the light intensity of direct photoelectric detection all the way is 1 ₀ , the other path is injected into the optical fiber FP cavity through the cascaded 3dB coupler, and after forming multi-beam interference, the reflected light intensity I _R is measured, so that I ₀ and I _R can realize the system output through the subtractor, divider hardware or software algorithm for $\frac{1}{T}=\frac{I_0}{I_0-I_R},$ Next, PGC demodulation is performed to obtain the phase output. 2, a kind of phase-carrier demodulation method in the Fabry-Perot interference type fiber optic hydrophone, it is characterized in that: incident light is injected into the optical fiber FP cavity interference with light intensity I ₀ through 3dB coupler, carries measured signal The transmitted light I _T is photoelectrically converted, and then transformed into the reciprocal output of the transmittance through the divider hardware or computer software algorithm $\frac{1}{T}=\frac{I_0}{I_T},$ Next, PGC demodulation is performed to obtain the phase output.

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