CN102288387A - Method for measuring modulation depth of semiconductor laser sinusoidal phase modulation interferometer - Google Patents

Abstract

The invention provides a method for measuring a modulation depth of a semiconductor laser sinusoidal phase modulation interferometer. The interferometer structurally comprises a light source, an isolator, an optical fiber coupler, a collimator, a photoelectric detector and a signal processor. The photoelectric detector converts a received interference signal into an electric signal and inputs the electric signal and a voltage signal of a light source driving power supply into the signal processor together for data processing, so that the sinusoidal phase modulation depth is obtained. In the measuring method disclosed by the invention, the influence of the light intensity modulation of the light source is considered and the sinusoidal phase modulation depth can be determined in real time under the condition that an initial optical path difference of the interferometer and a wavelength modulation coefficient of the light source are unknown.

Description

The measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation

Technical field

The present invention relates to the semiconductor laser interference instrument, particularly a kind of measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation.

Background technology

Infotech and microelectromechanical systems (MEMS) technology rapid development has proposed more and more higher requirement to the displacement detection technique.Interferometry because have high precision, high resolving power, advantage such as untouchable is widely studied.The sinusoidal phase modulation interference technique is a kind of interfere measurement technique of international forward position, has precision height, convenient, the advantages of simple structure and simple of modulation, is subjected to researchist's attention in recent years, has obtained very great development in the displacement measurement field.

In sinusoidal phase-modulation displacement measurement interferometer, the sinusoidal phase modulation degree of depth is the key parameter of finding the solution displacement to be measured, and its measuring accuracy will directly influence the precision of displacement to be measured.

O.Sasaki etc. have proposed a kind of full optical fiber sinusoidal phase modulation interferometer (technology [1] formerly: " Sinusoidal phase modulating interferometer using optical fibers for displacement measurement ", Appl.Opt.27,4139-4142,1988).This interferometer utilizes in the interference signal ratio of three order components and first order spectrum component to determine the sinusoidal phase modulation degree of depth, because in measuring process, utilize approximate interference signal expression formula that data are handled, do not consider the influence of intensity modulation, thereby introduced certain systematic error, and then reduced the measuring accuracy of displacement.

Wang Xuefeng etc. have proposed a kind of full optical fiber sinusoidal phase modulation interferometer of eliminating intensity modulation influence (technology [2] formerly: " A sinusoidal phase-modulating fiber-optic interferometer insensitive to the intensity charge ofthe light source ", Opt.Laser Technol.35,219-222,2003).This interferometer is determined on the basis of the sinusoidal phase modulation degree of depth in the method for priority of use technology [1], eliminated the measuring error that the light source intensity modulation brings by the output intensity of synchronous acquisition interference signal and light source, but this interferometer need use extra photodetector probe source output intensity.

Li Zhongliang etc. have proposed a kind of displacement measure interferometer of eliminating intensity modulation influence (technology [3] formerly: " Sinusoidal phase-modulating laser diode interferometer insensitive to the intensity modulation ofthe light source ", Optik.120,799-803,2009).The method is utilized formula before displacement measurement

The offset of sinusoidal phase modulation (PM) degree of depth is calculated, and utilizes this method to determine that depth of modulation need not to relate to interference signal, but need know the initial light path difference 2D of interferometer ₀Wavelength-modulated factor beta with light source _λExact value Deng running parameter.

Summary of the invention

The objective of the invention is to overcome the deficiency of above-mentioned technology formerly, a kind of measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation is provided.Measuring method of the present invention can be determined the sinusoidal phase modulation degree of depth in real time under the condition of interferometer initial light path difference and the unknown of the optical source wavelength index of modulation.

Technical solution of the present invention is as follows:

A kind of measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation, described semiconductor laser sinusoidal phase modulation interferometer structure comprises the light source that has temperature controller that is driven by driving power, isolator, fiber coupler, collimating apparatus, testee, photodetector, signal processor, described driving power provides DC current and Sine Modulated electric current for light source, light beam by light emitted passes through by isolator, shine on the testee behind fiber coupler and the collimating device collimation, by the light of testee surface reflection and by the light of collimating apparatus outgoing end face reflection by after the collimating apparatus, incide in the photodetector via fiber coupler, signal processor comprises two input ports: the first input end and second input port, the first input end mouth links to each other with the output terminal of photodetector, and second input port links to each other with driving power.

The structure of described signal processor is that the first input end mouth links to each other with second multiplier with first multiplier, insert in the single-chip microcomputer after wherein first multiplier is connected with first low-pass filter and first analog to digital converter, second multiplier is connected with second low-pass filter and second analog to digital converter in the back access single-chip microcomputer, second input port of signal processor links to each other with second multiplier with frequency multiplier, and wherein frequency multiplier links to each other with first multiplier.

Said single-chip microcomputer has the program of finding the solution ordered series of numbers maximal value, minimum value.

Said light source is a semiconductor laser, uses as measurement light source.

The temperature of said temperature controller control light source only changes the temperature of light source in ± 0.01 ℃ scope.

The measuring method of the sinusoidal phase modulation degree of depth of said semiconductor laser sinusoidal phase modulation interferometer, its concrete measuring process is as follows:

1. gather sinusoidal phase modulation interference signal S (t):

Open light source, the injection current direct current biasing that light source is set is I ₀, utilize driving power to produce sinusoidal signal I _m(t)=acos ω t modulated light source, and by photodetector detection sinusoidal phase modulation interference signal, the interference signal of this moment is:

S(t)＝g(t){S ₀+S ₁cos[zcosωt+α(t)]}

＝β _i[I ₀+I _m(t)]{S ₀+S ₁cos[zcosωt+α(t)]}，

＝S(1+βcosωt){S ₀+S ₁cos[zcosωt+α(t)]}

Wherein, g (t)=β _i[I ₀+ I _m(t)]=S (1+ β cos ω t) is the output intensity of light source; S=β _iI ₀It is the direct current component of light source output intensity; β=a/I ₀Be injection current alternating component I _m(t) amplitude a and flip-flop I ₀Ratio; S ₀And S ₁Be respectively flip-flop and the alternating component of interference signal item S (t) when not considering intensity modulation;

Be the sinusoidal phase modulation degree of depth; α (t)=α ₀+ α _d(t), α ₀=(4 π/λ ₀) l ₀Be the initial phase of optical path difference decision, α _d(t)=(4 π/λ ₀) d (t) is the phase place of ohject displacement d (t) decision;

2. utilize signal processor offset of sinusoidal phase modulation (PM) interference signal S (t) to carry out Filtering Processing:

The sinusoidal phase modulation interference signal S (t) that photodetector detects is inputed in the signal processor by the first input end mouth of signal processor, multiply each other by second multiplier with the modulation signal cos ω t after the normalization of second input port of signal processor input, and through obtaining signal P after the second low-pass filter filtering ₁(t):

$P_1\left(t\right)=\mathrm{LPF}[S\left(t\right)\·\cos \mathrm{\ωt}]$

$=\frac{1}{2}\mathrm{\&beta;}\{\mathrm{<figure-callout\; id="0"\; label="S\; S"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">S</figure-callout>}{S}_{}{}_0+S{S}_1[J_0\left(z\right)-J_2\left(z\right)\left]\cos \mathrm{\&alpha;}\left(t\right)\right\}-S{S}_1{J}_1\left(z\right)\sin \mathrm{\&alpha;}{\left(t\right)}^{,}$

Modulation signal cos ω t after the normalization of second input port input of signal processor generates two frequency-doubled signal cos2 ω t by frequency multiplier, the interference signal S (t) of signal cos2 ω t and the input of first input end mouth multiplies each other by first multiplier, and through obtaining signal P after the first low-pass filter filtering ₂(t):

$P_2\left(t\right)=\mathrm{LPF}[S\left(t\right)\&CenterDot;\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&omega;t}]$

$=-\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_1[J_1\left(z\right)-J_3\left(z\right)]\sin \mathrm{\&alpha;}\left(t\right)-S{S}_1{J}_2\left(z\right)\sin \mathrm{\&alpha;}{\left(t\right)}^{,}$

With the signal P that obtains after the filtering ₁(t) and P ₂(t) converting digital signal to by second analog to digital converter and first analog to digital converter respectively sends in the single-chip microcomputer;

3. utilize signal processor to extract P ₁(t) and P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2min, and calculate (P _1max-P _1min)/(P _2max-P _2min) value:

In 2., P ₁(t) and P ₂(t) parameter in is carried out conversion and is obtained

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\frac{1}{2}\mathrm{\&beta;}[J_0\left(z\right)-J_2\left(z\right)]\\ {\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=-J_1\left(z\right)\\ {\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3=-J_2\left(z\right)\\ {\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4=-\frac{1}{2}\mathrm{\&beta;}[J_1\left(z\right)-J_3\left(z\right)]\end{array}\right.,$

P then ₁(t) and P ₂(t) be rewritten as:

$P_1\left(t\right)=\frac{1}{2}\mathrm{\&beta;}{\mathrm{<figure-callout\; id="0"\; label="SS"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">SS</figure-callout>}}_0+{\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}\sin [\mathrm{\&alpha;}\left(t\right)+\mathrm{\&phi;}],$

Wherein, φ=arctan (K ₁/ K ₂),

P ₁(t) and P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2minCan be expressed as

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\max }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{<figure-callout\; id="0"\; label="SS"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">SS</figure-callout>}}_0+{\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}$

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\min }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_0{-\mathrm{SS}}_1{\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}}^{,}$

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_{2\max }={\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}$

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_{2\min }=-{\mathrm{SS}}_1{\sqrt{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}}^{,}$

Utilize single-chip microcomputer to extract P ₁(t) and P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2min, and by calculating:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\max }-{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\mathrm{<figure-callout\; id="2"\; label="min\; P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">min</figure-callout>}}}{P_{}}=\sqrt{\frac{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}};$

K as can be known ₁, K ₂, K ₃And K ₄Be the parameter relevant, then with z and β

Can regard as sinusoidal phase modulation depth z and beta function F (z, β);

4. utilize formula β=a/I ₀Calculate β, and will

Be defined as the function R (z) of sinusoidal phase modulation depth z, and R (z) is single-valued function in z ∈ (0,3.5) interval, utilize described single-chip microcomputer to determine to satisfy condition

The sinusoidal phase modulation depth z.

The present invention compares with technology formerly, has the following advantages and good effect:

1, compare with technology [1] formerly, the measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation of the present invention has been considered the influence of light source intensity modulation when the definite sinusoidal phase modulation degree of depth, improved the measuring accuracy of the sinusoidal phase modulation degree of depth.

2, compare with technology [2] formerly, the semiconductor laser interference instrument that measuring method adopted of semiconductor laser sinusoidal phase modulation interferometer depth of modulation of the present invention is simple in structure, does not need extra optical element.

3, compare with technology [3] formerly, the measuring method of semiconductor laser sinusoidal phase modulation interferometer depth of modulation of the present invention, the interference signal offset of sinusoidal phase modulation (PM) degree of depth of utilizing displacement to be measured to produce is calculated, can under the condition of interferometer initial light path difference and the unknown of the optical source wavelength index of modulation, determine the sinusoidal phase modulation degree of depth in real time.

Description of drawings

Fig. 1 is the structural representation of semiconductor laser sinusoidal phase modulation interferometer of the present invention.

Fig. 2 is the circuit diagram of signal processor of the present invention.

Fig. 3 is the process flow diagram of semiconductor laser sinusoidal phase modulation interferometer depth of modulation measuring method of the present invention.

Fig. 4 is that the light intensity alternating current-direct current is 0.1 o'clock than β, the curve of function R (z).

Embodiment

Below in conjunction with example and accompanying drawing the present invention is further specified, but should not limit protection scope of the present invention with this.

Semiconductor laser sinusoidal phase modulation interferometer structure synoptic diagram of the present invention as shown in Figure 1.As seen from the figure, semiconductor laser sinusoidal phase modulation interferometer structure comprises the light source that has temperature controller 13 that is driven by driving power 2, isolator 4, fiber coupler 5, collimating apparatus 6, testee 7, photodetector 8, signal processor 9, described driving power 2 provides DC current and Sine Modulated electric current for light source 3, pass through by isolator 4 by light source 3 emitted light beams, shine on the testee 7 behind fiber coupler 5 and collimating apparatus 6 collimations, by the light of testee 7 surface reflections and by the light of collimating apparatus 6 outgoing end face reflections by after the collimating apparatus 6, incide in the photodetector 8 via fiber coupler 5, signal processor 9 comprises two input ports: the first input end 9a and the second input port 9b, first input end mouth 9a links to each other with the output terminal of photodetector 8, and the second input port 9b links to each other with driving power 2

As shown in Figure 2, the structure of signal processor 9 is: first input end mouth 9a links to each other with second multiplier 903 with first multiplier 902, insert in the single-chip microcomputer 908 after wherein first multiplier 902 is connected with first low-pass filter 904 and first analog to digital converter 906, second multiplier 903 is connected with second low-pass filter 905 and second analog to digital converter 907 in the back access single-chip microcomputer 908, the second input port 9b of signal processor 9b links to each other with second multiplier 903 with frequency multiplier 901, and wherein frequency multiplier 901 links to each other with first multiplier 902.

The temperature of temperature controller 1 control light source 3 only changes the temperature of light source 3 in ± 0.01 ℃ scope.

Driving power 2 provides direct current and simple alternating current modulating current for light source 3, the outgoing light wavelength of light source 3 and intensity by Sine Modulated after through behind the isolator 4 successively by fiber coupler 5 and collimating apparatus 6, the end face reflection that part light has a common boundary at collimating apparatus 6 and air, another part light process collimating apparatus 6 backs are with parallel light emergence, after object under test 7 surface reflections, enter optical fiber through collimating apparatus 6 again.The thing light of reference light that collimated device 6 end face reflections go back and body surface reflection is interfered, and the interference signal of generation is detected by photodetector 8.Send into together by the output AC signal of photodetector 8 detected signals and driving power 2 and to obtain the sinusoidal phase modulation degree of depth after signal processor 9 is handled.

Fig. 3 is the process flow diagram of semiconductor laser sinusoidal phase modulation interferometer depth of modulation measuring method of the present invention.Comprise four steps:

1. open light source 3, the described signal processor 9 of sinusoidal phase modulation interference signal S (t) input that described photodetector 8 is gathered:

2. described signal processor 9 offset of sinusoidal phase modulation (PM) interference signal S (t) carry out Filtering Processing and obtain digital signal P ₁(t) and digital signal P ₂(t), and with P ₁(t) and P ₂(t) and send in the described single-chip microcomputer 908;

3. described single-chip microcomputer 908 extracts digital signal P ₁(t) and digital signal P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2min, and calculate (P _1max-P _1min)/(P _2max-P _2min) value:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\max }-{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\mathrm{<figure-callout\; id="2"\; label="min\; P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">min</figure-callout>}}}{P_{}}=\sqrt{\frac{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}}=F(z,\mathrm{\&beta;});$

4. utilize formula β=a/I ₀Calculate β, and (z β) is defined as the function R (z) of sinusoidal phase modulation depth z, utilizes described single-chip microcomputer 908 to determine the sinusoidal phase modulation depth z with F.

Its principle of work and process are as follows:

Open light source 3, behind light source 3 injection currents, wavelength X of light source 3 (t) and strength g (t) are expressed as respectively:

λ(t)＝λ ₀+β _λI _m(t)， (1)

g(t)＝β _i[I ₀+I _m(t)]， (2)

Wherein: λ ₀Be the centre wavelength of light source 3, β _λ, light source 3 wavelength with the variation factor of drive current, β _iBe the light intensity of light source 3 variation factor with drive current.I ₀Be the dc bias current that driving power 2 provides, I _m(t) simple sinusoidal alternating current that provides for driving power 2, it can be expressed as:

I _m(t)＝acosωt， (3)

Wherein: ω is the Sine Modulated angular frequency of light source 3, the amplitude of the simple sinusoidal alternating current that a provides for driving power 2.

Photodetector 8 detected interference signals can be expressed as:

S(t)＝g(t){S ₀+S ₁cos[zcosωt+α(t)]}

＝β _i[I ₀+I _m(t)]{S ₀+S ₁cos[zcosωt+α(t)]}， (4)

＝S(1+βcosωt){S ₀+S ₁cos[zcosωt+α(t)]}

Wherein, g (t)=β _i[I ₀+ I _m(t)]=S (1+ β cos ω t) is the output intensity of light source; S=β _iI ₀It is the direct current component of light source output intensity; β=a/I ₀Be injection current alternating component I _m(t) amplitude a and flip-flop I ₀Ratio; S ₀And S ₁Be respectively flip-flop and the alternating component of interference signal item S (t) when not considering intensity modulation;

Be the sinusoidal phase modulation degree of depth; α (t)=α ₀+ α _d(t), α ₀=(4 π/λ ₀) l ₀Be the initial phase of optical path difference decision, α _d(t)=(4 π/λ ₀) d (t) is the phase place of ohject displacement d (t) decision.

As shown in Figure 2, the output signal of driving power 2 is input to signal processor 9, enters second multiplier 903 and first frequency multiplier 901, and the signal of being exported by first frequency multiplier 901 enters first multiplier 902 again.The output signal of photodetector 8 is input to signal processor 9, enter first multiplier 902 and second multiplier 903, the output signal of the output signal of first multiplier 902 and second multiplier 903 through behind first low-pass filter 904 and second low-pass filter 905, enters first digital to analog converter 906 and second digital to analog converter 907 respectively.

The output signal of first digital to analog converter 906 and second digital to analog converter 907 is respectively the modulation signal cos ω t after interference signal S (t) and driving power 2 normalization and two frequency multiplication component cos2 ω t multiply each other and the low pass pass filter after signal, they can be expressed as:

$P_1\left(t\right)=\frac{1}{2}\mathrm{\&beta;}\{{\mathrm{<figure-callout\; id="0"\; label="SS"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">SS</figure-callout>}}_0+{\mathrm{SS}}_1[J_0\left(z\right)-J_2\left(z\right)\left]\cos \mathrm{\&alpha;}\left(t\right)\right\}-{\mathrm{SS}}_1{J}_1\left(z\right)\sin \mathrm{\&alpha;}\left(t\right)---\left(5\right)$

$P_2\left(t\right)=-\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_1[J_1\left(z\right)-J_3\left(z\right)]\sin \mathrm{\&alpha;}\left(t\right)-{\mathrm{SS}}_1{J}_2\left(z\right)\cos \mathrm{\&alpha;}\left(t\right)---\left(6\right)$

Parameter in (5) formula and (6) formula is carried out conversion, order

$\left\{\begin{array}{c}{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\frac{1}{2}\mathrm{\&beta;}[J_0\left(z\right)-J_2\left(z\right)]\\ {\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=-J_1\left(z\right)\\ {\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3=-J_2\left(z\right)\\ {\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4=-\frac{1}{2}\mathrm{\&beta;}[J_1\left(z\right)-J_3\left(z\right)]\end{array}\right.---\left(7\right)$

(5) formula and (6) formula can be rewritten as:

$P_1\left(t\right)=\frac{1}{2}\mathrm{\&beta;}{\mathrm{<figure-callout\; id="0"\; label="SS"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">SS</figure-callout>}}_0+{\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}\sin [\mathrm{\&alpha;}\left(t\right)+\mathrm{\&phi;}]---\left(8\right)$

Can calculate the maximal value and the minimum value of (8) formula and (9) formula by single-chip microcomputer 908, they can be expressed as respectively:

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\max }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{<figure-callout\; id="0"\; label="SS"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">SS</figure-callout>}}_0+{\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}$ (10)

${\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\min }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_0{-\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}$

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_{2\max }={\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}$ (11)

${\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">P</figure-callout>}}_{2\min }={-\mathrm{SS}}_1\sqrt{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}$

By (10) formula and (11) Shi Kede:

$\frac{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\max }-{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">P</figure-callout>}}_{1\mathrm{<figure-callout\; id="2"\; label="min\; P"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">min</figure-callout>}}}{P_{}}=\sqrt{\frac{{{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_1}^2+{{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000021.png"\; state="\{\{state\}\}">K</figure-callout>}}_2}^2}{{{\mathrm{<figure-callout\; id="3"\; label="K"\; filenames="HSA00000481955000011.png,HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_3}^2+{{\mathrm{<figure-callout\; id="4"\; label="K"\; filenames="HSA00000481955000022.png"\; state="\{\{state\}\}">K</figure-callout>}}_4}^2}}---\left(12\right)$

By (7) formula parameter K in (12) formula as can be known ₁, K ₂, K ₃, K ₄Be the parameter relevant with β, then following formula equal sign the right with the sinusoidal phase modulation depth z

(z, β), wherein β can pass through formula β=a/I can to regard function F about sinusoidal phase modulation depth z and β as ₀Calculate, then (z β) can be defined as the function R (z) of sinusoidal phase modulation depth z to F, Fig. 4 has provided the light intensity alternating current-direct current than β=0.1 o'clock, and the curve of function R (z) is as shown in Figure 4 at z ∈ (0,3.5) interval in be single-valued function, then determine to satisfy condition by single-chip microcomputer 908

Z, be the sinusoidal phase modulation degree of depth of being asked.

Semiconductor laser interference instrument as shown in Figure 1, the angular frequency of driving power sinusoidal phase modulation electric current is ω=5000Hz, and light source 3 is the semiconductor laser of 1310nm for wavelength, and peak power output is 10mW.The cutoff frequency of simulation low-pass filter is 1000Hz.During measurement, utilize photodetector 8 to survey the sinusoidal phase modulation interference signal that produces by ohject displacement, and send into signal processor 9 with the Sine Modulated electric current of driving power 2 output and carry out signal Processing, the sinusoidal phase modulation depth z just can be recorded in the storer of the built-in single-chip microcomputer 908 of signal processor 9 in real time.

Owing in signal processing, considered the influence of light source 3 intensity modulation, the measuring accuracy of the sinusoidal phase modulation degree of depth is improved, measuring error is less than 1%, and interferometer structure is simple, do not need extra optical element, can under the condition of interferometer initial light path difference and the unknown of the optical source wavelength index of modulation, determine the sinusoidal phase modulation degree of depth in real time.

Claims (2)

1. the measuring method of a semiconductor laser sinusoidal phase modulation interferometer depth of modulation, the semiconductor laser sinusoidal phase modulation interferometer structure that this method is measured comprises the light source that has temperature controller (1) (3) that is driven by driving power (2), isolator (4), fiber coupler (5), collimating apparatus (6), testee (7), photodetector (8), signal processor (9), described driving power (2) provides DC current and Sine Modulated electric current for light source (3), pass through by isolator (4) by light source (3) emitted light beams, shine on the testee (7) behind fiber coupler (5) and collimating apparatus (6) collimation, by the light of testee (7) surface reflection and by the light of collimating apparatus (6) outgoing end face reflection by after the collimating apparatus (6), sinusoidal phase modulation interference signal S (t) via fiber coupler (5) output is surveyed by photodetector (8), described signal processor (9) comprises two input ports: first input end (9a) and second input port (9b), first input end mouth (9a) links to each other with the output terminal of described photodetector (8), second input port (9b) links to each other with described driving power (2), the inner structure of said signal processor (9) is: first input end mouth (9a) links to each other with second multiplier (903) with first multiplier (902), described first multiplier (902) is connected with first low-pass filter (904) and first analog to digital converter (906) in the back access single-chip microcomputer (908), second multiplier (903) is connected with second low-pass filter (905) and second analog to digital converter (907) in the back access single-chip microcomputer (908), second input port (9b) links to each other with second multiplier (903) with frequency multiplier (901), the output terminal of described frequency multiplier (901) links to each other with first multiplier (902), it is characterized in that the concrete measuring process of this method is as follows:

1. the sinusoidal phase modulation interference signal S (t) that described photodetector (8) is gathered imports described signal processor (9):

Open light source (3), the injection current direct current biasing that light source (3) is set is I ₀, utilize driving power (2) to produce sinusoidal signal I _m(t)=and acos ω t modulates described light source (3), and the sinusoidal phase modulation interference signal that photodetector (8) is surveyed is:

S(t)＝g(t){S ₀+S ₁cos[zcosωt+α(t)]}

＝β _i[I ₀+I _m(t)]{S ₀+S ₁cos[zcosωt+α(t)]}，

＝S(1+βcosωt){S ₀+S ₁cos[zcosωt+α(t)]}

Wherein, g (t)=β _i[I ₀+ I _m(t)]=S (1+ β cos ω t) is the output intensity of light source (3); S=β _iI ₀It is the direct current component of light source (3) output intensity; β=a/I ₀Be injection current alternating component I _m(t) amplitude a and flip-flop I ₀Ratio; S ₀And S ₁Be respectively flip-flop and the alternating component of interference signal item S (t) when not considering intensity modulation;

Be the sinusoidal phase modulation degree of depth; α (t)=α ₀+ α _d(t), α ₀=(4 π/λ ₀) l ₀Be the initial phase of optical path difference decision, α _d(t)=(4 π/λ ₀) d (t) is the phase place of testee (7) displacement d (t) decision;

2. described signal processor (9) offset of sinusoidal phase modulation (PM) interference signal S (t) carries out Filtering Processing:

The sinusoidal phase modulation interference signal S (t) that photodetector (8) detects is by first input end mouth (9a) input of signal processor (9), the normalized modulation signal cos ω t that imports with second input port (9b) of signal processor (9) multiplies each other by second multiplier (903), and through obtaining signal P after second low-pass filter (905) filtering ₂(t):

$P_2\left(t\right)=\mathrm{LPF}[S\left(t\right)\&CenterDot;\cos 2\mathrm{\&omega;t}]$

$=-\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_1[J_1\left(z\right)-J_3\left(z\right)]\sin \mathrm{\&alpha;}\left(t\right)-S{S}_1{J}_2\left(z\right)\sin \mathrm{\&alpha;}{\left(t\right)}^{,}$

Generate two frequency-doubled signal cos2 ω t by the modulation signal cos ω t after the normalization of second input port (9b) input by described frequency multiplier (901), the sinusoidal phase modulation interference signal S (t) of this two frequency-doubled signal cos2 ω t and first input end mouth (9a) input multiplies each other by first multiplier (902), and through obtaining signal P after first low-pass filter (904) filtering ₁(t):

$P_1\left(t\right)=\mathrm{LPF}[S\left(t\right)\&CenterDot;\cos \mathrm{\&omega;t}]$

$=\frac{1}{2}\mathrm{\&beta;}\{S{S}_0+S{S}_1[J_0\left(z\right)-J_2\left(z\right)\left]\cos \mathrm{\&alpha;}\left(t\right)\right\}-S{S}_1{J}_1\left(z\right)\sin \mathrm{\&alpha;}\left(t\right)$

With described signal P ₁(t) and signal P ₂(t) convert digital signal P to by first analog to digital converter (906) and second analog to digital converter (907) respectively ₁(t) and digital signal P ₂(t) and send in the described single-chip microcomputer (908);

3. described single-chip microcomputer (908) extracts digital signal P ₁(t) and digital signal P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2min, and calculate (P _1max-P _1min)/(P _2max-P _2min) value:

Described single-chip microcomputer (908) is to described digital signal P ₁(t) and digital signal P ₂(t) parameter in is descended rank transformation:

$\left\{\begin{array}{c}{K}_1=\frac{1}{2}\mathrm{\&beta;}[J_0\left(z\right)-J_2\left(z\right)]\\ K_2=-J_1\left(z\right)\\ K_3=-J_2\left(z\right)\\ K_4=-\frac{1}{2}\mathrm{\&beta;}[J_1\left(z\right)-J_3\left(z\right)]\end{array}\right.,$

Then described digital signal P ₁(t) and digital signal P ₂(t) be rewritten as:

$P_1\left(t\right)=\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_0+{\mathrm{SS}}_1\sqrt{{K_1}^2+{K_2}^2}\sin [\mathrm{\&alpha;}\left(t\right)+\mathrm{\&phi;}],$

Wherein, φ=arctan (K ₁/ K ₂),

P ₁(t) and P ₂(t) maximal value and minimum value P _1max, P _1min, P _2maxAnd P _2minBe expressed as respectively:

$P_{1\max }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_0+{\mathrm{SS}}_1\sqrt{{K_1}^2+{K_2}^2}$

$P_{1\min }=\frac{1}{2}\mathrm{\&beta;}{\mathrm{SS}}_0{-\mathrm{SS}}_1{\sqrt{{K_1}^2+{K_2}^2}}^{,}$

$P_{2\max }={\mathrm{SS}}_1\sqrt{{K_3}^2+{K_4}^2}$

$P_{2\min }=-{\mathrm{SS}}_1{\sqrt{{K_3}^2+{K_4}^2}}^{,}$

Described single-chip microcomputer (908) calculates through following:

$\frac{P_{1\max }-P_{1\min }}{P_{2\max }-P_{2\min }}=\sqrt{\frac{{K_1}^2+{K_2}^2}{{K_3}^2+{K_4}^2}}=F(z,\mathrm{\&beta;});$

4. utilize formula β=a/I ₀Calculate β, and will

Be defined as the function R (z) of sinusoidal phase modulation depth z, utilize described single-chip microcomputer (908) to determine to satisfy condition

The sinusoidal phase modulation depth z.

2. the measuring method of the described semiconductor laser sinusoidal phase modulation of claim 1 interferometer depth of modulation is characterized in that said single-chip microcomputer (908) has the program of finding the solution ordered series of numbers maximal value, minimum value.

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