CN102401666A - Method and device for demodulating reflection wavelength of fiber Bragg grating - Google Patents

Abstract

A method for demodulating reflection wavelength of fiber Bragg grating includes inputting reflection light wave from the fiber Bragg grating into asymmetrical M-Z type waveguide modulator, dividing the reflection light wave into two beams of light wave in the asymmetrical M-Z type waveguide modulator, respectively inputting the two beams of light wave into a waveguide upper arm and a waveguide lower arm unequal to each other in arm length, impacting two parallel waveguides under electric fields of the same magnitude and opposite directions, interfering phase modulation light waves outputted from the waveguide upper arm and the waveguide lower arm respectively at a junction to generate strength modulation light wave so as to output interfering light wave, and measuring light intensity change of the interfering light wave outputted by the asymmetrical M-Z type waveguide modulator to obtain wavelength change of the reflection light wave of the fiber Bragg grating. The method and the device have the advantages of high measuring precision, small demodulator size and low demodulation cost.

Description

A kind of demodulation method of fiber grating reflection wavelength and device

Technical field

The present invention relates to the fiber-optic grating sensor technical field, more specifically, relate to a kind of demodulation method and device of fiber grating reflection wavelength.

Background technology

Fiber-optic grating sensor belongs to a kind of of Fibre Optical Sensor.The sensing process of fiber grating is through the influence of extraneous parameter sensing to the reflecting light wavelength of fiber grating, just can be learnt the variable quantity of extraneous parameter sensing by the reflecting light wavelength change amount of fiber grating.The output signal of fiber grating is a reflecting light; Therefore to expect that the variation of extraneous parameter at first need obtain the reflecting light wavelength information to the reflecting light demodulation; Obtain reflecting light wavelength change information by a plurality of reflecting light wavelength information then, obtain the external sense parameter by reflecting light wavelength change information more at last.

Wavelength demodulation method commonly used is to adopt spectroanalysis instrument, but the method can only provide the curve of spectrum, can't directly obtain the variation of external parameter, and the price of spectrometer is higher.If want to obtain the variation of external parameter, at first need convert the reflecting light wavelength signals of fiber grating into light intensity signal, light intensity signal is received by photodetector change electric signal into then.Satisfy particular kind of relationship between the variation of electric signal and the variation of grating wavelength, according to this relation, electric signal is carried out promptly can obtaining the reflecting light wavelength variation information after the data processing, this is Wavelength demodulation.Further, obtain the change information of external parameter according to the relation between external parameter and the reflection wave optical wavelength.

The fiber grating reflecting light Wavelength demodulation method of research has multiple both at home and abroad at present; Like edge filter method, fiber optic loop interferometric method, chirped fiber grating demodulation method, coupling raster method and tunable laser scanning method etc., the demodulation method that is based on tunable F-P cavity filter of comparative maturity.Former kinds of demodulation methods all have the problem of the not high or poor stability of movable member, demodulation accuracy, and the cost of F-P cavity filter demodulation method is higher, and the (FBG) demodulator volume is bigger.

To sum up, fiber grating reflection wavelength demodulation method of the prior art exists that measuring accuracy is low to be demodulated to this high problem greatly with the (FBG) demodulator volume.

Summary of the invention

The embodiment of the invention proposes a kind of demodulation method of fiber grating reflection wavelength, has the measuring accuracy height, the (FBG) demodulator volume is little and is demodulated to this low advantage.

The embodiment of the invention also proposes a kind of demodulating equipment of fiber grating reflection wavelength, has the measuring accuracy height, the (FBG) demodulator volume is little and is demodulated to this low advantage.

A kind of demodulation method of fiber grating reflection wavelength, this method comprises:

To import asymmetric M-Z type waveguide modulator from the reflecting light of fiber grating;

In asymmetric M-Z type waveguide modulator, said reflecting light is divided into other input waveguide upper arm of two-beam wavelength-division and waveguide underarm, being uneven in length of said waveguide upper arm in the length of said waveguide underarm;

Interfere at the meet of said waveguide upper arm and said waveguide underarm with the light wave of exporting from said waveguide underarm from the light wave of said waveguide upper arm output, export said interference light wave;

Measure the light intensity of the said interference light wave of asymmetric M-Z type waveguide modulator output, obtain the reflecting light wavelength of said fiber grating by the light intensity of said interference light wave.

Said two-beam ripple equates by minute luminous power or unequally carries out beam split.

When asymmetric M-Z type waveguide modulator list polarization is worked; Said will the input from the reflecting light of fiber grating further comprises before the asymmetric M-Z type waveguide modulator; Adjust the polarization direction of said fiber grating reflection wave, be the polarization direction of asymmetric M-Z type waveguide modulator work.

The reflecting light wavelength that said light intensity by said interference light wave obtains said fiber grating comprises; Convert said light intensity into analog electrical signal; Convert said analog electrical signal into digital signal, obtain the reflecting light wavelength of said fiber grating according to said digital signal.

Said reflecting light from fiber grating is to import said fiber grating by the light wave that wideband light source sends through coupling mechanism, the light wave that is reflected by said fiber grating again.

A kind of demodulating equipment of fiber grating reflection wavelength; This device comprises: reflecting light device, asymmetric M-Z type waveguide modulator and reflection wave light intensity-wavelength detection computations device, and reflecting light device, asymmetric M-Z type waveguide modulator and reflection wave light intensity-wavelength detection computations device sequence are connected;

The reflecting light device produces the asymmetric M-Z type of the reflecting light incident waveguide modulator of fiber grating; Comprise on the crystal substrates of said asymmetric M-Z type waveguide modulator, two waveguide upper arm and waveguide underarms that brachium does not wait, and be arranged on the electrode between waveguide, the residing electric field level equal direction of residing electric field of waveguide upper arm and waveguide underarm is opposite; Reflecting light is the two-beam ripple in the y-branch punishment of waveguide upper arm and waveguide underarm; Import said waveguide upper arm and said waveguide underarm respectively; And in the Y type meet generation interference of light of waveguide upper arm and waveguide underarm, output intensity is with the interference light wave of reflecting light wavelength change; Reflection wave light intensity-wavelength detection computations device detects and calculates the wavelength of reflecting light to the interference light intensity of wave of asymmetric M-Z type waveguide modulator output.

Also be connected with Polarization Controller between said reflecting light device and the asymmetric M-Z type waveguide modulator, the reflecting light of the fiber grating of said reflecting light device output adjusted to the polarization direction of the asymmetric M-Z type waveguide modulator of single polarization work.

The said electrode that is arranged between waveguide comprises, be arranged on waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the waveguide upper arm and the waveguide underarm between electrode;

The polarization direction of said asymmetric M-Z type waveguide modulator is the polarization direction that is parallel to plane of crystal, and said Polarization Controller is adjusted said reflecting light by horizontal polarization direction;

The action direction of the electrooptical effect of said crystal substrates is parallel to plane of crystal.

The said electrode that is arranged between waveguide comprises, be arranged on electrode, the waveguide underarm top on electrode, the waveguide upper arm upper strata of electrode, the waveguide upper arm below of waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the electrode on waveguide underarm upper strata;

The polarization direction of said asymmetric M-Z type waveguide modulator is perpendicular to the polarization direction of plane of crystal, and said Polarization Controller is adjusted said reflecting light by vertical polarization;

The action direction of the electrooptical effect of said crystal substrates is perpendicular to plane of crystal.

Said reflecting light device comprises wideband light source, isolator, coupling mechanism and the fiber-optic grating sensor that is linked in sequence; Wideband light source output broadband light wave; Behind isolator, through coupling mechanism input optical fibre grating sensor, fiber-optic grating sensor is exported said reflecting light.

Said reflection wave light intensity-wavelength detection computations device comprises PIN photodiode, current-voltage I-U converting unit, mould/number A/D converting unit, single-chip microcomputer and the computing machine that is linked in sequence; PIN photodiode detects the light intensity signal of said interference wave; And be converted into current signal and import said current-voltage I-U converting unit; With convert digital voltage signal into through mould/number A/D converting unit; After by single-chip microcomputer said digital voltage signal being carried out data acquisition, reflected light wavelength signals and handles, send the parameter sensing of the said fiber-optic grating sensor of COMPUTER CALCULATION.

From technique scheme, can find out, in embodiments of the present invention, through importing asymmetric M-Z type waveguide modulator from the reflecting light of fiber grating; In asymmetric M-Z type waveguide modulator, said reflecting light is divided into other input waveguide upper arm of two-beam wavelength-division and waveguide underarm, the brachium of said waveguide upper arm is not equal to the brachium of said waveguide underarm; From the light wave and the meet generation interference of light of the light wave of exporting from said waveguide underarm of said waveguide upper arm output, export said interference light wave at said waveguide upper arm and said waveguide underarm; Measure asymmetric M-Z type waveguide modulator and export the light intensity variation of said interference light wave, obtain the reflecting light wavelength change of said fiber grating by the light intensity variation of said interference light wave.Fiber grating reflecting light wavelength changes, and what reflected is the variation that the light intensity of the interference light wave corresponding with fiber grating reflecting light wavelength takes place, and is therefore changed just to obtain fiber grating reflecting light wavelength change by the light intensity of interfering light wave.Utilize the variation of principle of interference measuring optical fiber optical grating reflection optical wavelength, measuring accuracy is high, good stability.And the asymmetric M-Z type waveguide modulator that the present invention adopted is on the basis of symmetrical M-Z type waveguide modulator, to change, and has solved the long-pending high problem of big cost of the (FBG) demodulator body that exists in the prior art.

Description of drawings

Fig. 1 is symmetrical M-Z type waveguide modulator structural representation among the present invention;

Fig. 2 is asymmetric M-Z type waveguide modulator structural representation among the present invention;

Fig. 3 is another asymmetric M-Z type waveguide modulator structural representation among the present invention;

Fig. 4 utilizes the Wavelength demodulation apparatus structure synoptic diagram of asymmetric M-Z type waveguide modulator for the embodiment of the invention;

Fig. 5 equals 0 o'clock asymmetric M-Z type waveguide modulator output intensity with the wavelength change synoptic diagram for arm length difference in the embodiment of the invention;

Asymmetric M-Z type waveguide modulator output intensity was with the wavelength change synoptic diagram when Fig. 6 equaled 0.1mm for arm length difference in the embodiment of the invention;

Asymmetric M-Z type waveguide modulator output intensity was with the wavelength change synoptic diagram when Fig. 7 equaled 0.5mm for arm length difference in the embodiment of the invention.

Embodiment

For making the object of the invention, technical scheme and advantage express clearlyer, the present invention is remake further detailed explanation below in conjunction with accompanying drawing and specific embodiment.

Core of the present invention is, adopts asymmetrical Mach-Ze De (M-Z) type waveguide modulator to realize converting the reflecting light wavelength change of fiber grating into the light intensity variation, thereby changes the reflecting light wavelength change that obtains fiber grating by the light intensity that is prone to measure.

In embodiments of the present invention; Through testing fiber grating reflection light wave being divided into the two-beam ripple and importing different waveguide upper arm of length and waveguide underarm respectively; Interfere at meet from the two-beam ripple of waveguide upper arm and the output of waveguide underarm; The interference light glistening light of waves to outgoing is measured by force, obtains the light intensity of the interference light wave corresponding with the reflecting light wavelength of fiber grating.In other words; It is reflecting light wavelength change with fiber grating; Convert corresponding with it interference light ripple intensity variations to; Just can confirm the reflecting light wavelength change of fiber grating through measuring interference light ripple intensity variations, thereby further confirm the variation of the measured external parameter of fiber grating.Adopt interferometric method that the light intensity of the reflecting light wavelength of fiber grating is measured, measuring accuracy is high; Only existing symmetrical M-Z type waveguide modulator is transformed, cost is low, the surveying instrument volume is little and stable height.

Referring to accompanying drawing 1 is symmetrical M-Z type waveguide modulator structural representation.Whole symmetrical M-Z type waveguide modulator is the crystal substrates material that is parallel to plane of crystal by the action direction of electrooptical effect.Light wave is divided into the two-way light wave from the single interface input of Y type waveguide by the waveguide of Y type, imports two parallel waveguide upper arm and waveguide underarms respectively, and the length L 1 of waveguide upper arm equates with the length L 2 of waveguide underarm.L1 is to the distance the Y type point of waveguide upper arm and waveguide underarm from symmetrical M-Z type waveguide modulator y-branch; Accordingly, L2 is to the distance the Y type point of waveguide upper arm and waveguide underarm from symmetrical M-Z type waveguide modulator y-branch.Above the waveguide upper arm, between waveguide upper arm and the waveguide underarm and the waveguide underarm below all be symmetrically arranged with the electrode that length is l.The polarity of the electrode below the electrode above the waveguide upper arm and waveguide underarm is identical; But it is opposite with the polarity of the electrode between upper and lower arm; Because all parallel plane of crystal of direction of an electric field in the last underarm and opposite, the change amount that therefore goes up the underarm optical index also is opposite.Voltage through regulating between the electrode is controlled last underarm refractive index, thus the intensity of adjustment outgoing light wave.Existing M-Z type waveguide modulator is mainly used in can producing in batches in speed fiber optic communication systems, optical fiber cable TV (CATV) system, is the device of a comparative maturity.

The present invention changes symmetrical M-Z type waveguide modulator of the prior art, forms asymmetric M-Z type waveguide modulator, is used for the reflecting light of fiber grating is carried out demodulation.Referring to accompanying drawing 2 are asymmetric M-Z type waveguide modulator structural representations.Only be with the difference of symmetrical M-Z type waveguide modulator: the waveguide upper arm of asymmetric M-Z type waveguide adjuster and the length of waveguide underarm are unequal.Reflecting light from the fiber grating of single interface incident of Y type waveguide is divided into other input waveguide upper arm of two-beam wavelength-division and waveguide underarm.Because the brachium of waveguide upper arm and waveguide underarm is unequal, the light wave from waveguide upper arm and the output of waveguide underarm interferes respectively.Owing to adopt the device in the accompanying drawing 2, need Polarization Controller that the reflecting light of the fiber grating of reflecting light device output is adjusted to horizontal polarization direction accordingly, so that go up the refractive index of underarm electric field modulated light wave.

Referring to accompanying drawing 3 are another asymmetric M-Z type waveguide modulator structural representations.The position of number and electrode that is electrode with the difference of asymmetric M-Z type waveguide modulator in the accompanying drawing 2 is different.Electrode in the accompanying drawing 3 comprises, be arranged on electrode, the waveguide underarm top on electrode, the waveguide upper arm upper strata of electrode, the waveguide upper arm below of waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the electrode on waveguide underarm upper strata.The polarity of the electrode below the electrode above the waveguide upper arm and waveguide upper arm is identical, but opposite with the polarity of electrode on waveguide upper arm upper strata, so the direction of an electric field in the upper arm is vertical crystal substrates surface.Similarly, the direction of an electric field of underarm also is vertical crystal substrates surface.But the direction of an electric field in the last underarm is opposite, and the change amount that therefore goes up the underarm optical index also is opposite.In the device of accompanying drawing 3; Because the direction of an electric field of last underarm is all perpendicular to crystal substrate; Therefore need Polarization Controller that the reflecting light of the fiber grating of reflecting light device output is adjusted to vertical polarization; So that the refractive index of last underarm electric field modulated light wave is selected the crystal substrates of the action direction of electrooptical effect perpendicular to plane of crystal accordingly for use.

Referring to accompanying drawing 4 are the Wavelength demodulation device synoptic diagram that adopt asymmetric M-Z type waveguide modulator.This device comprises reflecting light device, asymmetric M-Z type waveguide modulator and reflection wave light intensity-wavelength detection computations device.

The reflecting light device comprises; The wideband light source 401 that is linked in sequence, isolator 402, coupling mechanism 404 and fiber-optic grating sensor 404; Wideband light source 401 output broadband light waves; Behind isolator 402, through coupling mechanism 404 input optical fibre grating sensors 404, fiber-optic grating sensor 404 output reflection light waves to asymmetric M-Z type waveguide modulator.The effect of isolator is to stop that the reflecting light by fiber-optic grating sensor 404 outputs gets into wideband light source.When asymmetric M-Z type waveguide modulator is single polarization work; Between reflecting light device and asymmetric M-Z type waveguide modulator, also be connected with Polarization Controller 405, the reflecting light of the fiber grating of reflecting light device output adjusted to the polarization direction of the asymmetric M-Z type waveguide modulator 406 of single polarization work.If like the device in the accompanying drawing 2, then Polarization Controller is adjusted to the polarization direction polarization direction that is parallel to plane of crystal; If like the device in the accompanying drawing 3, then Polarization Controller is adjusted to the polarization direction perpendicular to plane of crystal with the polarization direction.

Asymmetric M-Z type waveguide modulator 406 comprises; Two waveguide upper arm and waveguide underarms that brachium does not wait; And be arranged on waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the waveguide upper arm and the waveguide underarm between electrode, isopolarity is opposite mutually for the voltage of the polarity of waveguide upper arm electrode and waveguide underarm electrode; Reflecting light is at the y-branch place of waveguide upper arm and waveguide underarm; Be divided into the two-beam ripple by equal branch luminous power or unequal minute luminous power; Import said waveguide upper arm and said waveguide underarm respectively; And in the Y type meet generation interference of light of waveguide upper arm and waveguide underarm, output intensity is with the interference light wave of reflecting light wavelength change.

Reflection wave light intensity-wavelength detection computations device comprises, PIN photodiode 407, current-voltage I-U converting unit 408, mould/number A/D converting unit 409, single-chip microcomputer 410 and computing machine 411; PIN photodiode 407 detects the light intensity signal of interference wave; And be converted into current signal input current-voltage I-U converting unit 408; With convert digital voltage signal into through mould/number A/D converting unit 409; After carrying out data acquisition, reflected light wavelength signals and handle by 410 pairs of digital voltage signals of single-chip microcomputer, send computing machine 411 to calculate the parameter sensing of said fiber-optic grating sensor.

Through said apparatus the reflecting light wavelength of the fiber grating measuring parameter sensing and change is carried out demodulation once more, can obtain another one interference wave light intensity.Thereby can obtain the interference wave intensity variations by the reflecting light wavelength change of fiber grating.Computing machine is handled and is analyzed data again according to the relation between wavelength and light intensity, parameter sensing and the wavelength, thereby obtains changing with the fiber grating reflection wavelength variation of corresponding external sense parameter by fiber grating reflecting light wavelength change.Light intensity by interference wave changes the variation that obtains the external sense parameter corresponding with fiber grating reflecting light wavelength, and its data handling procedure is a prior art, and this paper repeats no more.

Key component among the present invention is to adopt asymmetry M-Z type waveguide modulator and its application in the reflection wavelength demodulation method.Through importing asymmetric M-Z type waveguide modulator from the reflecting light of fiber grating; In asymmetric M-Z type waveguide modulator, the reflecting light wavelength of fiber grating of input is carried out demodulation; Be about to that said reflecting light is divided into the other input waveguide upper arm of two-beam wavelength-division and the waveguide underarm carries out independent transmission, when waveguide upper arm brachium is not equal to waveguide underarm brachium, just can interfere at meet from the light wave of waveguide upper arm and the outgoing of waveguide underarm; The residing electric field of waveguide upper arm equates with the residing electric field level of waveguide underarm but direction is opposite; It is phase-modulation wave that impressed voltage on modulator is modulated to the different light wave of phase place with waveguide upper arm and light wave in the waveguide underarm, and the effect of phase-modulation wave is the working point position of adjustment output intensity with wavelength change.Interfere at the meet of waveguide upper arm and waveguide underarm with the light wave of exporting from the waveguide underarm from the light wave of waveguide upper arm output, the light intensity of exporting said interference light wave is the accent high-amplitude wave.Interfere the light intensity of light wave to change through measuring asymmetric M-Z type waveguide modulator output, change by the light intensity of interfering light wave, through calculating the reflecting light wavelength change that just can obtain said fiber grating.

Embodiment one

Below to be divided into the light wave E that two beam intensities equate at the y-branch place ₁And E ₂, E ₁And E ₂The situation that gets into waveguide upper arm and waveguide bottom is respectively analyzed:

At Y type Waveguide branching place, because E ₁Equal E ₂So the light field in two arms is

$E=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos \mathrm{\&omega;t}---\left(1\right)$

Wherein, E ₀Be the amplitude of light field, ω is the angular frequency of light, and t is the time.

At the point of y-branch, be respectively through the light field in phase-adjusted two arms

${\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_1=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+{\mathrm{\&phi;}}_1),$ $E_2=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+{\mathrm{\&phi;}}_2)---\left(2\right)$

E then ₁And E ₂Synthetic light field

$E^{\&prime;}=\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+{\mathrm{\&phi;}}_1)+\frac{1}{2}{\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+{\mathrm{\&phi;}}_2)={\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+\frac{{\mathrm{\&phi;}}_1+{\mathrm{\&phi;}}_2}{2})\cos \left(\frac{{\mathrm{\&phi;}}_1-{\mathrm{\&phi;}}_2}{2}\right)$

$={\mathrm{<figure-callout\; id="0"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_0\cos (\mathrm{\&omega;t}+\frac{{\mathrm{\&phi;}}_1+{\mathrm{\&phi;}}_2}{2})\cos \left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)---\left(3\right)$

φ wherein ₁, φ ₂Be the phase change of light wave through two waveguide arms, Δ φ is their phase differential.The average intensity of output does

$I_{\mathrm{out}}=\frac{\mathrm{\&omega;}}{2\mathrm{\&pi;}}{\&Integral;}_0^{\frac{2\mathrm{\&pi;}}{\mathrm{\&omega;}}}\sqrt{\frac{{\mathrm{\&epsiv;}}_0}{{\mathrm{\&mu;}}_0}}{\left|E_y\right|}^2\mathrm{dt}=I_{\mathrm{in}}{\cos }^2\left(\frac{\mathrm{\&Delta;\&phi;}}{2}\right)---\left(4\right)$

ε ₀And μ ₀Be respectively specific inductive capacity and the magnetic permeability in the vacuum, I _InIt is the incident intensity of asymmetry M-Z type waveguide modulator.

Phase difference φ does

$\mathrm{\&Delta;\&phi;}=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}[n(L_1-L_2)+2\mathrm{\&Delta;nl}]=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}(\mathrm{nL}+2\mathrm{\&Delta;nl})---\left(5\right)$

λ ₀It is the wavelength in the vacuum; N is a waveguide index; L is an arm length difference, and l is an electrode length; Δ n is under the impressed voltage effect, the variations in refractive index that produces owing to electrooptical effect.Because of the alive polarity of institute on the two waveguide arm electrodes is opposite, so the change of refractive opposite in sign.

Phase difference φ in (5) is brought in (4) formula, obtain

$I_{\mathrm{out}}=\frac{\mathrm{\&omega;}}{2\mathrm{\&pi;}}{\&Integral;}_0^{\frac{2\mathrm{\&pi;}}{\mathrm{\&omega;}}}\sqrt{\frac{{\mathrm{\&epsiv;}}_0}{{\mathrm{\&mu;}}_0}}{\left|E_y\right|}^2\mathrm{dt}=I_{\mathrm{in}}{\cos }^2\left\{\frac{\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}(\mathrm{nL}+2\mathrm{\&Delta;nl})\right\}---\left(6\right)$

Can know that from formula (6) at voltage one regularly, output intensity will be with wavelength change.If but arm length difference L is 0, this variation is then very little.

For example, if adopt lithium niobate (LiNbO ₃) crystalline material making modulator, according to the electro-optical characteristic of lithium niobate material, the change amount of refractive index can be expressed as

$\mathrm{\&Delta;n}=-\frac{1}{2}{n}_e^3\mathrm{\&gamma;}\frac{V}{d}\mathrm{\&Gamma;}---\left(7\right)$

N wherein _eBe LiNbO ₃The very optical index of material; γ is an electrooptical coefficient; D is an electrode separation; V is an impressed voltage; Γ is the interaction factor of electric field and light field, generally is taken as 0.8.Accompanying drawing 5 to accompanying drawing 6 represented this lithium niobate modulator under different arm length difference output intensity with wavelength change.Wherein the L of Fig. 5, Fig. 6, Fig. 7 be respectively 0,0.1mm, 0.5mm.Can find out that L is big more, the cycle of light intensity curve is more little.Because light intensity is periodic with wavelength change, its usable range is a section between minimum point and the peak, i.e. 1/2 cycle, so the cycle is more little, the demodulation scope of wavelength is also more little, but sensitivity is high more.So L is the key parameter of system's demodulation accuracy and scope.

In addition, the impressed voltage on the modulator does not influence the cycle of light intensity curve, and just therefore the phase place of influence curve can adjust its position, working point through adding appropriate bias voltage to modulator.

Embodiment two

Below to be divided into the light wave E that two beam intensities do not wait at the y-branch place ₁And E ₂, E ₁And E ₂The situation that gets into waveguide upper arm and waveguide underarm is respectively analyzed:

At Y type Waveguide branching place, the light field in two arms is respectively

E ₁＝E ₁₀cosωt，E ₂＝E ₂₀cosωt (8)

Wherein, E ₁₀And E ₂₀Be E ₁And E ₂Amplitude, ω is the angular frequency of light, t is the time.

Point in branch, the light field in two arms is respectively

E ₁＝E ₁₀cos(ωt+φ ₁)，E ₂＝E ₂₀cos(ωt+φ ₂) (9)

φ wherein ₁, φ ₂Be the phase change of light wave through two arms.

Synthetic light field can be written as

E＝E ₁+E ₂＝E ₀cos(ωt+φ) (10)

Wherein

φ is the phase place of synthetic light field, E ₀Amplitude for synthetic light field.The vibration intensity be proportional to amplitude square.Observed in the reality is in a long time mean intensity, sometime at interval in the τ average intensity of (τ＞＞light vibration cycle T).

$I=\frac{1}{\mathrm{\&tau;}}{\&Integral;}_0^{\mathrm{\&tau;}}\sqrt{\frac{{\mathrm{\&epsiv;}}_0}{{\mathrm{\&mu;}}_0}}[{\mathrm{<figure-callout\; id="1"\; label="E"\; filenames="HSA00000266252100031.png,HSA00000266252100033.png"\; state="\{\{state\}\}">E</figure-callout>}}_1^2+E_2^2+2E_1{E}_2\cos ({\mathrm{\&phi;}}_2-{\mathrm{\&phi;}}_1)]{\cos }^2(\mathrm{\&omega;t}+\mathrm{\&phi;})\mathrm{d\&tau;}---\left(12\right)$

$=I_1+I_2+2\sqrt{I_1{I}_2}\left[\frac{1}{\mathrm{\&tau;}}{\&Integral;}_0^{\mathrm{\&tau;}}\cos ({\mathrm{\&phi;}}_2-{\mathrm{\&phi;}}_1)\mathrm{d\&tau;}\right]$

I ₁And I ₂It is respectively the light intensity in two waveguide arms.The average intensity I of point depends on integral.Because of phase differential (φ ₂-φ ₁) do not change in time, therefore (12) formula is written as

$I=I_1+I_2+2\sqrt{I_1{I}_2}\cos ({\mathrm{\&phi;}}_2-{\mathrm{\&phi;}}_1)]=I_1+I_2+2\sqrt{I_1{I}_2}\cos \mathrm{\&Delta;\&phi;}---\left(13\right)$

Δ φ is the phase differential of two arms, for

$\mathrm{\&Delta;\&phi;}=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}[n(L_1-L_2)+2\mathrm{\&Delta;nl}]=\frac{2\mathrm{\&pi;}}{{\mathrm{\&lambda;}}_0}(\mathrm{nL}+2\mathrm{\&Delta;nl})---\left(14\right)$

Can find out that from (12) formula and (13) formula when the light intensity in two branch support arms is unequal, as long as L is not 0, and satisfy at voltage one regularly, the interference light output intensity will also can be realized Wavelength demodulation with the reflection wave wavelength change.

Can know by (12) formula, Δ φ=0 o'clock, I has maximal value During Δ φ=π, I has minimum value

If E ₁≠ E ₂Be I ₁≠ I ₂, I _MinCan not be zero, thereby the demodulation sensitivity of system is reduced.I ₁With I ₂Difference big more, just big more to the influence of demodulation sensitivity.

Can know that by embodiment one and embodiment two the reflection wave beam split at Y type Waveguide branching place with fiber grating is that luminous power is respectively E ₁And E ₂The two-beam ripple, E ₁And E ₂Whether equate not influence the enforcement of technical scheme of the present invention.But in actual application, E ₁And E ₂Light intensity difference influence demodulation sensitivity, optimum implementation is E ₁And E ₂Light intensity equate.In beam split place, exist the light wave of the waveguide arm of arm length difference to have phase differential through upper and lower two respectively, at meet, the two-way light wave interferes, and interferes the output power of light wave relevant with reflected light wavelength and arm length difference.When confirming arm length difference, just can be according to the output power of interfering light wave, promptly the interference light wave intensity obtains the reflecting light wavelength.

The above is merely preferred embodiment of the present invention, is not to be used to limit protection scope of the present invention.All within spirit of the present invention and principle, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (11)

1. the demodulation method of a fiber grating reflection wavelength is characterized in that, this method comprises:

To import asymmetric M-Z type waveguide modulator from the reflecting light of fiber grating;

In asymmetric M-Z type waveguide modulator, said reflecting light is divided into other input waveguide upper arm of two-beam wavelength-division and waveguide underarm, being uneven in length of said waveguide upper arm in the length of said waveguide underarm;

Interfere at the meet of said waveguide upper arm and said waveguide underarm with the light wave of exporting from said waveguide underarm from the light wave of said waveguide upper arm output, export said interference light wave;

Measure the light intensity of the said interference light wave of asymmetric M-Z type waveguide modulator output, obtain the reflecting light wavelength of said fiber grating by the light intensity of said interference light wave.

2. according to the demodulation method of the said fiber grating reflection wavelength of claim 1, it is characterized in that said two-beam ripple equates by minute luminous power or unequally carries out beam split.

3. according to the demodulation method of claim 1 or 2 said fiber grating reflection wavelengths; It is characterized in that; When asymmetric M-Z type waveguide modulator list polarization is worked; Said will the input from the reflecting light of fiber grating further comprises before the asymmetric M-Z type waveguide modulator, adjusts the polarization direction of said fiber grating reflection wave, is the polarization direction of asymmetric M-Z type waveguide modulator work.

4. according to the demodulation method of claim 1 or 2 said fiber grating reflection wavelengths; It is characterized in that; The reflecting light wavelength that said light intensity by said interference light wave obtains said fiber grating comprises; Convert said light intensity into analog electrical signal, convert said analog electrical signal into digital signal, obtain the reflecting light wavelength of said fiber grating according to said digital signal.

5. according to the demodulation method of claim 1 or 2 said fiber grating reflection wavelengths; It is characterized in that; Said reflecting light from fiber grating is to import said fiber grating by the light wave that wideband light source sends through coupling mechanism, the light wave that is reflected by said fiber grating again.

6. the demodulating equipment of a fiber grating reflection wavelength; It is characterized in that; This device comprises: reflecting light device, asymmetric M-Z type waveguide modulator and reflection wave light intensity-wavelength detection computations device, and reflecting light device, asymmetric M-Z type waveguide modulator and reflection wave light intensity-wavelength detection computations device sequence are connected;

The reflecting light device produces the asymmetric M-Z type of the reflecting light incident waveguide modulator of fiber grating; Comprise on the crystal substrates of said asymmetric M-Z type waveguide modulator, two waveguide upper arm and waveguide underarms that brachium does not wait, and be arranged on the electrode between waveguide, the residing electric field level equal direction of residing electric field of waveguide upper arm and waveguide underarm is opposite; Reflecting light is the two-beam ripple in the y-branch punishment of waveguide upper arm and waveguide underarm; Import said waveguide upper arm and said waveguide underarm respectively; And in the Y type meet generation interference of light of waveguide upper arm and waveguide underarm, output intensity is with the interference light wave of reflecting light wavelength change; Reflection wave light intensity-wavelength detection computations device detects and calculates the wavelength of reflecting light to the interference light intensity of wave of asymmetric M-Z type waveguide modulator output.

7. according to the demodulating equipment of the said fiber grating reflection wavelength of claim 6; It is characterized in that; Also be connected with Polarization Controller between said reflecting light device and the asymmetric M-Z type waveguide modulator, the reflecting light of the fiber grating of said reflecting light device output adjusted to the polarization direction of the asymmetric M-Z type waveguide modulator of single polarization work.

8. according to the demodulating equipment of the said fiber grating reflection wavelength of claim 7; It is characterized in that; The said electrode that is arranged between waveguide comprises, be arranged on waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the waveguide upper arm and the waveguide underarm between electrode;

The polarization direction of said asymmetric M-Z type waveguide modulator is the polarization direction that is parallel to plane of crystal, and said Polarization Controller is adjusted said reflecting light by horizontal polarization direction;

The action direction of the electrooptical effect of said crystal substrates is parallel to plane of crystal.

9. according to the demodulating equipment of the said fiber grating reflection wavelength of claim 7; It is characterized in that; The said electrode that is arranged between waveguide comprises, be arranged on electrode, the waveguide underarm top on electrode, the waveguide upper arm upper strata of electrode, the waveguide upper arm below of waveguide upper arm top electrode, waveguide underarm below electrode and be arranged on the electrode on waveguide underarm upper strata;

The polarization direction of said asymmetric M-Z type waveguide modulator is perpendicular to the polarization direction of plane of crystal, and said Polarization Controller is adjusted said reflecting light by vertical polarization;

The action direction of the electrooptical effect of said crystal substrates is perpendicular to plane of crystal.

10. according to the demodulating equipment of the said fiber grating reflection wavelength of the arbitrary claim of claim 6 to 9; It is characterized in that; Said reflecting light device comprises wideband light source, isolator, coupling mechanism and the fiber-optic grating sensor that is linked in sequence, and wideband light source output broadband light wave is behind isolator; Through coupling mechanism input optical fibre grating sensor, fiber-optic grating sensor is exported said reflecting light.

11. demodulating equipment according to the said fiber grating reflection wavelength of claim 10; It is characterized in that said reflection wave light intensity-wavelength detection computations device comprises PIN photodiode, current-voltage I-U converting unit, mould/number A/D converting unit, single-chip microcomputer and the computing machine that is linked in sequence; PIN photodiode detects the light intensity signal of said interference wave; And be converted into current signal and import said current-voltage I-U converting unit; With convert digital voltage signal into through mould/number A/D converting unit; After by single-chip microcomputer said digital voltage signal being carried out data acquisition, reflected light wavelength signals and handles, send the parameter sensing of the said fiber-optic grating sensor of COMPUTER CALCULATION.

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