CN101608946A - Fiber laser hydrophone signal demodulating system - Google Patents

Abstract

Fiber laser hydrophone signal demodulating system, the laser of fiber laser hydrophone output transfers to the b end of optical fiber 3 * 3 coupling mechanisms (3) by single-mode fiber (2) from input end (1), laser is divided into three tunnel outputs by 3 * 3 coupling mechanisms, wherein the e end is vacant, laser is divided into two-way by d end and f end, laser signal behind the two-way laser interference is by a end and the output of c end of 3 * 3 coupling mechanisms, and the laser signal of a end and c end is received by photodetector (8), two road V of two photodetector outputs ₁(t), V ₂(t) signal transfers to the size that demodulation arithmetic processing system (10) draws acoustic pressure through signal transmssion line (9).Fiber laser hydrophone signal demodulating system of the present invention, based on the non-equilibrium fibre optic interferometer of Michelson (Michelson), demodulate to high resolving power, high stability sound pressure signal, and eliminate in the general single mode fiber interferometer polarization state random variation interfering the influence of restituted signal.

Description

Fiber laser hydrophone signal demodulating system

Technical field

The invention belongs to the modulating and demodulating signal system, more particularly it is a kind of fiber laser hydrophone signal demodulating system.It is mainly used in the fiber laser hydrophone signal demodulating based on non-equilibrium fibre optic interferometer.

Background technology

Fiber laser hydrophone is the underwater sound sensing technology that latest developments are got up, because its advantage tiny, highly sensitive and anti-electromagnetic interference (EMI) just is being subjected to paying close attention to widely.The sensing element of fiber laser hydrophone is a fiber laser, be subjected in the water acoustic pressure to do the time spent, the outgoing wavelength of laser instrument produces and is proportional to moving of extraneous acoustic pressure size, as long as the displacement that detects wavelength just can draw the size of extraneous sound pressure variations, therefore the Wavelength demodulation technology has directly limited the accuracy of detection of total system, and it is most important that rational design wavelength moves demodulation scheme.

Interferometry is a sensitiveest present wavelength detection technique, adopt non-equilibrium fibre optic interferometer, with the displacement conversion of fiber laser outgoing wavelength is the variation of interferometric phase, obtain carrying the interference strength output of phase change information by photodetector, because interferometer is output as cosine signal, therefore, how from nonlinear cosine output, to demodulate the phase information that is proportional to sound pressure amplitudes, need design demodulating algorithm and corresponding interferometer structure.

Developing the symmetrical demodulation scheme based on 3 * 3 coupling mechanisms that does not at present need carrier modulation and Filtering Processing, and the simple relatively and dynamic range of demodulator circuit is not subjected to the restriction of wave filter and modulating frequency.See interference type optical fiber hydrophone modulation project studies such as Shen Liang, 2001, semiconductor optoelectronic, Vol.22 (2).Laser transfers to a end of optical fiber 2 * 2 coupling mechanisms 17 by single-mode fiber 2 from input end 1, the b end is vacant, laser holds a end and the generation of c end that are transmitted through the fiber to 3 * 3 coupling mechanisms 3 to interfere through 2 * 2 coupling mechanism c end and d, wherein the b end is vacant, laser after the interference is divided into three tunnel outputs by 3 * 3 coupling mechanisms, directly received by photodetector 8, the output signal of three photodetectors transfers to the size (as shown in Figure 3) that demodulation arithmetic processing system 10 draws acoustic pressure through signal transmssion line 9.

Yet, because little curved, the distortion of optical fiber and the variation of environment temperature may cause the variation of the polarization state of the two-beam that participates in interfering, make output signal be hidden state at random, especially when the polarization state quadrature of light wave in interferometer two arms, the output visibility of interferometer is zero, and the information of extraneous parameter will be lost fully.And the splitting ratio of 3 * 3 coupling mechanisms can not keep strict symmetry, and asymmetrical three road signals will make external environment change demodulated output signal is produced effect of nonlinear.

Summary of the invention

The present invention proposes a kind of fiber laser hydrophone signal demodulating system, based on the non-equilibrium fibre optic interferometer of Michelson (Michelson), demodulate to high resolving power, high stability sound pressure signal, and eliminate in the general single mode fiber interferometer polarization state random variation interfering the influence of restituted signal.

The objective of the invention is to reach: fiber laser hydrophone signal demodulating system by following measure, it is characterized in that the laser of fiber laser hydrophone output transfers to the b end of optical fiber 3 * 3 coupling mechanisms by single-mode fiber from input end, laser is divided into three tunnel outputs by 3 * 3 coupling mechanisms, wherein the e end is vacant, laser is divided into two-way by d end and f end, wherein one road laser is back to the d end of 3 * 3 coupling mechanisms along original route by first via faraday rotator mirror reflection back behind the lag line of single-mode fiber coiled, the single-mode fiber circle of another road laser through being wound in the piezoelectric ceramics cylinder held along the f that original route is back to 3 * 3 coupling mechanisms by the second road faraday rotator mirror reflection back after introducing high frequency modulated, laser signal behind the two-way laser interference is by a end and the output of c end of 3 * 3 coupling mechanisms, the laser signal of a end and c end is received by photodetector, two road V of two photodetector outputs ₁(t), V ₂(t) signal transfers to the size that the demodulation arithmetic processing system draws acoustic pressure through signal transmssion line.

In technique scheme, described demodulation arithmetic processing system uses the two-way input signal of photodetector to demodulate the acoustic pressure size that acts on fiber laser hydrophone, V ₁(t) signal through first via direct current eliminate handle V ' ₁(t), V ₂(t) through the second road direct current eliminate handle V ' ₂(t), V ' ₂(t) amplitude is adjusted to and V ' ₁(t) amplitude equates that the two paths of signals addition gets voltage U then ₊(t), subtract each other voltage U _-(t), U ₊(t) behind differential processor differential with U _-(t) multiply each other U _-(t) behind differential processor differential with U ₊(t) multiply each other, draw the voltage N that is directly proportional with the differential of acoustic pressure size, U after the two paths of signals that the differential that intersects multiplies each other subtracts each other ₊(t) handle back and U through gain adjustment _-(t) respectively by square multiplier, addition obtains the AGC voltage relevant with relevant visibility with laser power, and N and AGC voltage are divided by and draw the not signal of Stimulated Light power influences, obtains the voltage output that harmony is pressed into direct ratio behind Integral Processing device integration.

The fibre optic interferometer that the present invention adopts is the Michelson interferometer based on 3 * 3 coupling mechanisms, and introduces high frequency modulated in interferometer, and the two-way output visibility of interferometer is stable, the signal attenuation that does not have polarization to cause.The demodulating algorithm that native system adopts need not complicated coefficient adjustment process can obtain stable output under the not exclusively symmetrical situation of 3 * 3 coupling mechanism splitting ratios, have good practical values.

Description of drawings

Fig. 1 is the non-equilibrium optical fibre Michelson interferometer structural representation of fiber laser hydrophone signal demodulating device.

Fig. 2 is that the fiber laser hydrophone signal demodulating device is interfered demodulation calculation process scheme block diagram.

Fig. 3 is the symmetrical demodulation scheme non-equilibrium optical fiber Mach-Zehnder interferometer structure synoptic diagram of fiber laser hydrophone based on 3 * 3 coupling mechanisms.

1. laser input ends among the figure, 2. single-mode fiber, 3.3 * 3 coupling mechanisms, 4. be wound in the single-mode fiber circle of piezoelectric ceramics cylinder, 5. piezoelectric ceramics cylinder driving circuit, 6. first via faraday rotator mirror, 7. the second road faraday rotator mirror, 8. photodetector, 9. signal transmssion line, 10. demodulation arithmetic processing system, 11. first via direct currents are eliminated and are handled, 12. eliminating, handles the second road direct current, 13. the differential processor, 14. gain adjustment are handled 15. squares of multipliers, 16. the Integral Processing device, 17.2 * 2 coupling mechanisms.

Embodiment

Describe performance of the present invention in detail below in conjunction with accompanying drawing, but they do not constitute limitation of the invention, only do for example.Simultaneously by illustrating that advantage of the present invention will become clear more and understanding easily.

Consult accompanying drawing as can be known: fiber laser hydrophone signal demodulating system of the present invention, the laser of fiber laser hydrophone output transfers to the b end of optical fiber 3 * 3 coupling mechanisms 3 by single-mode fiber 2 from input end 1, laser is divided into three tunnel outputs by 3 * 3 coupling mechanisms, wherein the e end is vacant, laser is divided into two-way by d end and f end, wherein one road laser is back to the d end of 3 * 3 coupling mechanisms 3 along original route by first via faraday rotator mirror 6 reflection backs behind the lag line of single-mode fiber 2 coileds, the single-mode fiber circle 4 of another road laser through being wound in the piezoelectric ceramics cylinder held along the f that original route is back to 3 * 3 coupling mechanisms 3 by the second road faraday rotator mirror, 7 reflection backs after introducing high frequency modulated, laser signal behind the two-way laser interference is by a end and the output of c end of 3 * 3 coupling mechanisms, the laser signal of a end and c end is received by photodetector 8, two road V of two photodetector outputs ₁(t), V ₂(t) signal transfers to the size (as shown in Figure 1) that demodulation arithmetic processing system 10 draws acoustic pressure through signal transmssion line 9.

Demodulation arithmetic processing system 10 uses the two-way input signal of photodetector (8) to demodulate the acoustic pressure size that acts on fiber laser hydrophone, V ₁(t) signal is eliminated processing (11) through first via direct current and is got V ' ₁(t), V ₂(t) eliminate processing (12) through the second road direct current and get V ' ₂(t), V ' ₂(t) amplitude is adjusted to and V ' ₁(t) amplitude equates that the two paths of signals addition gets voltage U then ₊(t), subtract each other voltage U _-(t), U ₊(t) behind differential processor (13) differential with U _-(t) multiply each other U _-(t) behind differential processor (13) differential with U ₊(t) multiply each other, draw the voltage N that is directly proportional with the differential of acoustic pressure size, U after the two paths of signals that the differential that intersects multiplies each other subtracts each other ₊(t) handle (14) back and U through gain adjustment _-(t) respectively by square multiplier (15), addition obtains the AGC voltage relevant with relevant visibility with laser power, N and AGC voltage are divided by and draw the not signal of Stimulated Light power influences, obtain the voltage output (as shown in Figure 2) that harmony is pressed into direct ratio behind Integral Processing device (16) integration.

The laser telegram in reply field vector of supposing to transfer to 3 * 3 coupling mechanisms (3) b end is E _In, according to coupled mode theory, the electric field (E of three output terminals of 3 * 3 fiber couplers _{O, 1}, E _{O, 2}And E _{O, 3}) be:

$\left[\begin{array}{c}{E}_{O,1}\\ E_{O,2}\\ E_{O,3}\end{array}\right]=\left[\begin{array}{ccc}f& c& c\\ c& f& c\\ c& c& f\end{array}\right]\left[\begin{array}{c}{E}_{i,1}\\ E_{i,2}\\ E_{i,3}\end{array}\right]$

E in the formula _{I, 1}, E _{I, 2}And E _{I, 3}Be laser telegram in reply field vector, the wherein E of three input ends of 3 * 3 coupling mechanisms (3) _{I, 1}, E _{I, 3}Be zero vector, E _{I, 2}=E _In, f=[exp (i2k _cL)+2exp (ik _cL)]/3, c=[exp (i2k _cL)-2exp (ik _cL)]/3, k _cWith L be respectively the coupling coefficient and the coupling length of 3 * 3 coupling mechanisms.Suppose that coupling mechanism is unreflected and reciprocity, consider added losses, then the Jones matrix of 3 * 3 coupling mechanisms is:

$N_{\mathrm{ad}}=N_{\mathrm{da}}=N_{\mathrm{be}}=N_{\mathrm{eb}}=N_{\mathrm{cf}}=N_{\mathrm{fe}}={\mathrm{<figure-callout\; id="0"\; label="t\; N\; f"\; filenames="A2009100628340014H3.png"\; state="\{\{state\}\}">t</figure-callout>}}_N\left[\begin{array}{c}f\end{array}\right]\left[\begin{array}{cc}& 0\\ 0& f\end{array}\right]$

$N_{\mathrm{ae}}=N_{\mathrm{ea}}=N_{\mathrm{af}}=N_{\mathrm{fa}}=N_{\mathrm{bd}}=N_{\mathrm{db}}$

$=N_{\mathrm{bf}}=N_{\mathrm{fb}}=N_{\mathrm{cd}}=N_{\mathrm{dc}}=N_{\mathrm{ce}}=N_{\mathrm{ec}}={\mathrm{<figure-callout\; id="0"\; label="t\; N\; c"\; filenames="A2009100628340014H3.png"\; state="\{\{state\}\}">t</figure-callout>}}_N\left[\begin{array}{c}c\end{array}\right]\left[\begin{array}{cc}& 0\\ 0& c\end{array}\right]$

T in the formula _NBe the transmission coefficient of 3 * 3 coupling mechanisms, N _Mn(m, n=a～f) represent laser from the input of m port, the Jones matrix when the n port is exported.

When the laser one way is passed through faraday rotation mirror, 45 ° of its polarization principal axis rotations, when laser beam is reflected, folded light beam is rotated 45 ° once more, thereby with the incident beam quadrature, the polarization of noticing laser develops and changed symbol in the x direction when returning, and then laser along optical fiber through the transmission matrix that Faraday rotating mirror and Michelson catoptron return optical fiber again is:

$T=t_T\left[\begin{array}{cc}0& -1\\ -1& 0\end{array}\right],$

T in the formula _TIt is the optical power attenuation factor.

Birefringence in the optical fiber can be simulated with the oval retardation plate of a broad sense, and when laser beam was passed through optical fiber, the Jones matrix of fl transmission can be expressed as:

$\stackrel{\&RightArrow;}{S}=\frac{{\mathrm{\&alpha;}}_s}{d_s}\left[\begin{array}{cc}{a}_s& -b_s^{*}\\ b_s& a_s^{*}\end{array}\right]$

In the formula ^*The expression conjugation, α _sBe the loss of optical fiber, ${\mathrm{<figure-callout\; id="2"\; label="d\; s"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">d</figure-callout>}}_s^{}=a_s{a}_s^{*}+b_s{b}_s^{*},$ Parameter a _sAnd b _sRelevant with the birefringent characteristic of optical fiber.If laser beam is returned, then the back to the Jones matrix of transmission is:

$\stackrel{\&LeftArrow;}{S}=\frac{{\mathrm{\&alpha;}}_s}{d_s}\left[\begin{array}{cc}{a}_s& -b_s\\ b_s^{*}& a_s^{*}\end{array}\right]$

The work of interferometer can be described with the product of each several part matrix, the Optical Fiber Transmission matrix of interferometer one arm respectively by

With The expression, the transmission matrix of another arm optical fiber respectively by With

Expression.The phase change of supposing laser one-way transmission in two arm optical fiber is φ _s/ 2, φ _L/ 2, loss is α _s, α _L, then the telegram in reply field vector of 3 * 3 coupling mechanisms, three tunnel output laser is:

$E_1=N_{\mathrm{da}}\&CenterDot;\stackrel{\&LeftArrow;}{S}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{S}\&CenterDot;N_{\mathrm{bd}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_s\right)$

$+N_{\mathrm{fa}}\&CenterDot;\stackrel{\&LeftArrow;}{L}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{L}\&CenterDot;N_{\mathrm{bf}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_L\right)$

$=-c{t}_N^2{t}_T[{\mathrm{\&alpha;}}_s^2\mathrm{fexp}\left(j{\mathrm{\&phi;}}_s\right)+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\mathrm{cexp}\left(j{\mathrm{\&phi;}}_L\right)]\&times;\left[\begin{array}{cc}0& 1\\ 1& 0\end{array}\right]E_{\mathrm{in}}$

${\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">E</figure-callout>}}_2=N_{\mathrm{db}}\&CenterDot;\stackrel{\&LeftArrow;}{S}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{S}\&CenterDot;N_{\mathrm{bd}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_s\right)$

$+N_{\mathrm{fb}}\&CenterDot;\stackrel{\&LeftArrow;}{L}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{L}\&CenterDot;N_{\mathrm{bf}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_L\right)$

$=-c{t}_N^2{t}_T[{\mathrm{\&alpha;}}_s^2\exp \left(j{\mathrm{\&phi;}}_s\right)+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\exp \left(j{\mathrm{\&phi;}}_L\right)]\&times;\left[\begin{array}{cc}0& 1\\ 1& 0\end{array}\right]E_{\mathrm{in}}$

${\mathrm{<figure-callout\; id="3"\; label="E"\; filenames="A2009100628340014H1.png,A2009100628340014H3.png"\; state="\{\{state\}\}">E</figure-callout>}}_3=N_{\mathrm{dc}}\&CenterDot;\stackrel{\&LeftArrow;}{S}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{S}\&CenterDot;N_{\mathrm{bd}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_s\right)$

$+N_{\mathrm{fc}}\&CenterDot;\stackrel{\&LeftArrow;}{L}\&CenterDot;T\&CenterDot;\stackrel{\&RightArrow;}{L}\&CenterDot;N_{\mathrm{bf}}\&CenterDot;E_{\mathrm{in}}\&CenterDot;\exp \left(j{\mathrm{\&phi;}}_L\right)$

$=-c{t}_N^2{t}_T[{\mathrm{\&alpha;}}_s^2\mathrm{cexp}\left(j{\mathrm{\&phi;}}_s\right)+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\mathrm{fexp}\left(j{\mathrm{\&phi;}}_L\right)]\&times;\left[\begin{array}{cc}0& 1\\ 1& 0\end{array}\right]E_{\mathrm{in}}$

The polarization state of three road interference signals is always identical with input beam as can be seen from top equation.Therefore the interferometer of the present invention signal attenuation that do not have polarization to cause.

For splitting ratio is 1: 1: 1 ideal 3 * 3 coupling mechanisms, cos (3k _cL)=-1/2, ${\left|c\right|}^2={\left|f\right|}^2=\frac{1}{3},$ Can derive the intensity of three tunnel interference output signals:

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">P</figure-callout>}}_2={\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">E</figure-callout>}}_2\&CenterDot;{\mathrm{<figure-callout\; id="2"\; label="E"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">E</figure-callout>}}_2^{*}=\frac{t_T^2{t}_N^4{\left|c\right|}^2}{3}[{\mathrm{\&alpha;}}_s^4+{\mathrm{\&alpha;}}_L^4+2{\mathrm{\&alpha;}}_s^2{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="A2009100628340014H1.png,A2009100628340014H2.png"\; state="\{\{state\}\}">L</figure-callout>}}^2\cos ({\mathrm{\&phi;}}_s-{\mathrm{\&phi;}}_L)]P_{\mathrm{in}}$

In the formula $P_{\mathrm{in}}=E_{\mathrm{in}}\&CenterDot;E_{\mathrm{in}}^{*}$ Expression input laser intensity.Phase differential between the two-way output interference strength is 120 ° arbitrarily as can be seen from the above equation.

From top to commentary of the present invention as can be seen the phase differential between any two-way of optical fibre Michelson interferometer 3 * 3 coupling mechanisms output interference strength be 120 °, and three tunnel output visibilitys of optical fibre Michelson interferometer are stable, the signal attenuation that does not have polarization to cause.Follow-up demodulation computing is exactly to utilize the two paths of signals of 120 ° of phase phasic differences to demodulate and be proportional to the phase information of sound pressure amplitudes, and demodulation scheme as shown in Figure 2.

The splitting ratio not exclusively phase differential between the output of 3 * 3 coupling mechanisms of symmetry will depart from 120 °, and the direct current amplitude is with to exchange amplitude also inconsistent, the voltage signal V of the two-way laser signal after the interference after photodetector detects ₁(t), V ₂(t) brief note is:

V ₁(t)＝A ₁(t)+B ₁(t)cos[Ф(t)+Ccos(ω ₀t)]

V ₂(t)＝A ₂(t)+B ₂(t)cos[Ф(t)+Ccos(ω ₀t)-120°-δ]

In the formula

The interferometer phase low frequency wonder that causes for external environment,

For wavelength moves the phase change that causes, phase change is proportional to the size of extraneous underwater sound pressure, and d is the length in the non-equilibrium path of interferometer, Ccos (ω ₀T) be the phase modulation (PM) that the single-mode fiber on the piezoelectric ceramics cylinder produces, C is a modulation amplitude, ω ₀Be the high frequency modulated frequency away from the underwater sound signal frequency, A ₁(t), A ₂(t) for the DC terms of detector output, relevant with laser intensity, optical path loss and coupling mechanism splitting ratio.B ₁(t), B ₂(t) for exchanging the amplitude of item, because the application of faraday rotator mirror, these two variations with polarization state are irrelevant, only relevant with laser intensity, optical path loss, coupling mechanism splitting ratio and laser coherence length, δ is that phase differential departs from 120 ° low-angle between the two-way output, can be assumed to constant.A ₁(t), A ₂(t), B ₁(t) and B ₂(t) influence of Stimulated Light intensity is gradual variations per hour.

Because two that are not positioned at same straight line are waited mould vector addition sum and the difference quadrature that subtracts each other, can be with V ₁(t), V ₂(t) addition after two cancellation DC component, subtract each other, use the differential multiplication cross draw with

Proportional signal.The specific algorithm of demodulation as shown in Figure 2.

In order to obtain V ₁(t), V ₂(t) DC terms with exchange amplitude, make modulation amplitude C 〉=π rad, then regardless of the value of Ф (t), V ₁, V ₂Interchange Xiang Zaiyi can both reach maximal value and minimum value in the modulation period, can obtain

A ₁(t′)＝(V _1max+V _1min)/2

B ₁(t′)＝V _1max-V _1min

In like manner can get A ₂(t ') and B ₂(t ') in signal processing, according to the size of sample frequency and modulation period, obtains the sampling number N of a modulation period, and N was ordered before the data of each sampled point were used maximal value and minimum value are calculated, and the starting stage that not enough N is ordered Uses Defaults, A ₁(t), A ₂(t), B ₁(t) and B ₂(t) be gradual amount, because A ₁(t), A ₂(t), B ₁(t) and B ₂(t) be gradual variations per hour.Adopt high frequency modulated, can suppose that the direct current in previous cycle, interchange amplitude equate with the direct current of back one-period, the amplitude that exchanges.V ₁(t) cancellation DC terms, V ₂The cancellation DC terms and multiply by gain coefficient after the brief note be

V′ ₁(t)＝B ₁(t)cos[Ф(t)+C?cos(ω ₀t)]

V′ ₂(t)＝B ₁(t)cos[Ф(t)+Ccos(ω ₀t)-120°-δ]

Make ψ (t)=Ф (t)+Ccos (ω ₀T) two additions, subtract each other

U ₊(t)＝B ₁(t){(1+cos(120°+δ))·cos(ψ(t))+sin(120°+δ)·sin(ψ(t))}

U _-(t)＝B ₁(t){(1-cos(120°+δ))·cos(ψ(t))-sin(120°+δ)·sin(ψ(t))}

The differential that intersects multiplies each other and subtracts each other:

In order to eliminate B ₁ ²(t) influence that changes of amplitude can utilize the U of quadrature ₊(t) and U _-(t), summed square draws B ₁ ²(t) value.

U ₊(t) adjust handling (14) by gain multiply by coefficient and makes its amplitude and U _-(t) equate U ₊(t) and U _-(t) amplitude can obtain by maximal value in the modulation period and minimum value equally.U ₊(t) gain coefficient is:

Consider that δ is a low-angle, gain coefficient also can directly be made as

U behind the adjustment amplitude ₊(t) and U _-(t) summed square gets:

N gets divided by this:

Integration must be exported:

Through bandpass filter, the filtering low frequency wonder

With high-frequency modulation signal Ccos (ω ₀T), obtain the phase information that is directly proportional with acoustic pressure

The demodulating algorithm that native system adopts is under the not exclusively symmetrical situation of 3 * 3 coupling mechanism splitting ratios, need not complicated coefficient adjustment process can obtain stable output, the high-frequency modulation signal of introducing can pass through the low-pass filtering filtering, can not influence the dynamic range of sensor-based system, but the frequency span of meeting restriction system, in the underwater sound sensing practical application of selected signal Processing frequency span, suitably select modulating frequency, this demodulating algorithm can be eliminated many influences that the incomplete symmetry of 3 * 3 coupling mechanism splitting ratios is brought, obtain the stable output of signal in the whole frequency band, have practical value.

Claims (2)

1, fiber laser hydrophone signal demodulating system, it is characterized in that the laser of fiber laser hydrophone output transfers to the b end of optical fiber 3 * 3 coupling mechanisms (3) by single-mode fiber (2) from input end (1), laser is divided into three tunnel outputs by 3 * 3 coupling mechanisms, wherein the e end is vacant, laser is divided into two-way by d end and f end, wherein one road laser is back to the d end of 3 * 3 coupling mechanisms (3) along original route by first via faraday rotator mirror (6) reflection back behind the lag line of single-mode fiber (2) coiled, the single-mode fiber circle (4) of another road laser through being wound in the piezoelectric ceramics cylinder held along the f that original route is back to 3 * 3 coupling mechanisms (3) by the second road faraday rotator mirror (7) reflection back after introducing high frequency modulated, laser signal behind the two-way laser interference is by a end and the output of c end of 3 * 3 coupling mechanisms, the laser signal of a end and c end is received by photodetector (8), two road V of two photodetector outputs ₁(t), V ₂(t) signal transfers to the size that demodulation arithmetic processing system (10) draws acoustic pressure through signal transmssion line (9).

2, fiber laser hydrophone signal demodulating system according to claim 1 is characterized in that demodulation arithmetic processing system (10) uses the two-way input signal of photodetector (8) to demodulate the acoustic pressure size that acts on fiber laser hydrophone, V ₁(t) signal is eliminated processing (11) through first via direct current and is got V ' ₁(t), V ₂(t) eliminate processing (12) through the second road direct current and get V ' ₂(t), V ' ₂(t) amplitude is adjusted to and V ' ₁(t) amplitude equates that the two paths of signals addition gets voltage U then ₊(t), subtract each other voltage U _-(t), U ₊(t) behind differential processor (13) differential with U _-(t) multiply each other U _-(t) behind differential processor (13) differential with U ₊(t) multiply each other, draw the voltage N that is directly proportional with the differential of acoustic pressure size, U after the two paths of signals that the differential that intersects multiplies each other subtracts each other ₊(t) handle (14) back and U through gain adjustment _-(t) respectively by square multiplier (15), addition obtains the AGC voltage relevant with relevant visibility with laser power, N and AGC voltage are divided by and draw the not signal of Stimulated Light power influences, obtain the voltage output that harmony is pressed into direct ratio behind Integral Processing device (16) integration.

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