CN103337776A - All-optical fiber type self-mixing distance measuring system of laser - Google Patents

Abstract

The invention discloses an all-optical fiber type self-mixing distance measuring system of laser, which is characterized in that a tunable laser and an output end of a coupled system send a laser signal with an initial wavelength of lambada, a tuning frequency of nu m, and a tuning range of delta lambada to a to-be-measured object through light collection, and receives a feedback signal comes from a scattering face of the to-be-measured object to form a self-mixing signal of the laser; an optoelectronic signal conversion unit receives the self-mixing signal of the laser and switches the self-mixing signal of the laser to an electrical signal; a signal processing unit utilizes the vibration frequency delta nu L of the self-mixing signal of the laser to obtain the distance between the scattering face of the to-be-measured object and an output end of the tunable laser. The system has high measuring accuracy, stable performance, and wide application occasions, and is particularly suitable for distant measurement.

Description

A kind of full fiber type laser is from the mixed ranging system

Technical field

The present invention relates to the optical detection system of object absolute distance, particularly a kind of from the hybrid laser ranging system.

Background technology

The optical detection of object absolute distance can be widely used in numerous areas such as coal mine excavation, electric power, water conservancy, communication, environment, building, agricultural, forestry.In the prior art, lower based on the flight time distance-finding method relative accuracy of pulse laser, sensitivity is lower; Heterodyne type phase type laser ranging instrument system includes reference arm and gage beam, and structure is comparatively complicated; Have compact conformation, in light weight, advantages such as volume is little, reliability is high, suitable in-site measurement based on the semiconductor laser that injects electric current tuning from the mixed ranging technology, be used widely gradually.

Laser from the mixed ranging principle as shown in Figure 4, interference system is made up of tunable laser and external reflection object.When existing, feedback light can cause the laser medium refractive index to change and then frequency and the intensity of modulated laser itself by changing carrier density in the laser chamber, the formation self-mixed interference.

Making the length between laser front facet 17 and the laser rear end face 18 is L ₀, the reflection coefficient of front end face and rear end face is respectively r ₁And r ₂, front end face is L to the external cavity length between the target object scattering end face 19 _Ext, the exocoel reflection coefficient is r ₃, the refractive index of laser medium is n, initial light field is E ₀, the light field behind the self-mixed interference is E (t), then has:

$E\left(t\right)=r_1{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00003333907900011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2\exp \{-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA00003333907900011.png"\; state="\{\{state\}\}">j</figure-callout>}4\mathrm{\&pi;v}\frac{{\mathrm{nL}}_0}{c}+(g-\mathrm{\&gamma;})L_0\}{E}_0+$ (2)

$r_1(1-{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="HDA00003333907900011.png"\; state="\{\{state\}\}">r</figure-callout>}}_2^2)\exp \{-\mathrm{<figure-callout\; id="4"\; label="j"\; filenames="HDA00003333907900011.png"\; state="\{\{state\}\}">j</figure-callout>}4\mathrm{\&pi;v}\frac{{\mathrm{nL}}_0+L_{\mathrm{ext}}}{c}+(g-\mathrm{\&gamma;})L_0\}{E}_0$

G is the linear gain that unit length causes in the laser cavity in the formula (2), and γ is the loss of unit length in the laser cavity, and ν is the frequency of oscillation of laser.Because the laser threshold gain is fed light modulation, the laser output power ratio gains in laser threshold, and therefore, output power of laser is fed light modulation, and the luminous power of output is expressed suc as formula (3):

I=I ₀[1+mcos(2πντ _L)] (3)

In the formula (3), index of modulation m is that ratio is in the constant of feedback intensity regularly at operating current one.

For laser is propagated time of delay in a week, I at interior exocoel ₀Laser intensity when not having the exocoel feedback for laser.

In formula (3), the output intensity of laser is relevant with the variation of laser external cavity length displacement relevant and the feedback thing, supposes that institute adds modulation and causes that the fluctuation of laser optical frequency is:

I(t)=I ₀+ΔI(t) (4)

ν(t)=ν ₀+Δν(t) (5)

In formula (4) and the formula (5), I ₀, ν ₀Representative does not have feedback and does not have modulation laser light intensity and frequency of light wave down, and I (t), ν (t) represent laser output laser intensity and frequency of light wave under modulation respectively, and laser intensity and frequency of light wave can be by light power meter and frequency spectrograph mensuration.Δ ν (t) is frequency variable quantity in time under the tuned cell effect, and defining its amplitude of variation is Δ ν.Δ I (t) wherein, Δ ν (t) is determined by the modulating characteristic of laser.

I(t)=[I ₀+ΔI(t)]{1+mcos[2πν(t)τ _L]} （6）

Therefore the distance of object scattering surface and laser emitting end face is shown in the formula (1):

By formula (1) as can be known object scattering surface and laser emitting end face distance and from the vibration frequency Δ ν of mixed signal _LLinear, and the laser certainty of measurement is influenced by tuning range delta lambda mainly.

This output wavelength by injection electric current tuning semiconductor laser, and then realize that mainly there is following problem in the range finding purpose:

1, be subject to semi-conductive injection current work scope because semiconductor laser injects the amplitude of electric current, thereby limited the tuning range of its output wavelength, the tuning range of typical current-injecting F-P type semiconductor laser is generally about 10nm.According to range measurement principle, λ is less for the tuning range Δ, causes certainty of measurement to descend, and can't realize precision distance measurement;

2, the current-injecting semiconductor laser carries out when tuning, the laser works unstable properties, and output-power fluctuation is serious, causes output from the mixed signal instability, influence range finding effect;

3, semiconductor laser typical case live width scope is 2nm, be generally the work of many longitudinal modes, cause the monochromaticjty of laser beam and coherence poor, influenced its transmission and sensing characteristics, and the angle of divergence is bigger during telecommute, and directly limit laser is from mixed ranging The Application of Technology occasion and operating distance.

Summary of the invention

The present invention is for avoiding above-mentioned existing in prior technology deficiency, provides that a kind of certainty of measurement is higher, service behaviour is more stable, and the application scenario is extensive, and particularly the full fiber type laser of telemeasurement is from the mixed ranging system.

The present invention adopts following technical scheme for the technical solution problem:

Full fiber type laser of the present invention from the characteristics of mixed ranging system is: adopt a tunable optical fiber laser, the light that is equipped with photosignal converting unit, the signal processing unit with photodetector and the front end that is positioned at described tunable optical fiber laser with described tunable optical fiber laser is collected and coupled system; Described tunable laser is collected by light and the output of coupled system is that λ, tuned frequency are ν to the initial wavelength of testee outgoing _m, tuning amplitude is the laser signal of Δ λ, and collect the light signal fed back that output with coupled system receives from the scattering surface of testee by light and form laser from mixed signal; Described photosignal converting unit is to be received in the laser that forms in the described tunable laser from mixed signal and to be converted to the signal of telecommunication with photodetector; Described signal processing unit receives and handles the signal of telecommunication from described photosignal converting unit, utilizes laser from the vibration frequency Δ ν of mixed signal _L, obtained the distance L between the output end face of the scattering surface of testee and tunable optical fiber laser by formula (1) _Ext:

$L_{\mathrm{ext}}=\frac{{\mathrm{\&Delta;v}}_L{\mathrm{\&lambda;}}^2}{4v_m\mathrm{\&Delta;\&lambda;}}---\left(1\right).$

Full fiber type laser of the present invention also is from the design feature of mixed ranging system:

The version that described tunable optical fiber laser is set is: adopt the resonant cavity of linear cavity structure, described resonant cavity is made up of the narrowband reflection mirror of the front end face position that is arranged on tunable optical fiber laser and the broadband mirrors of rear end face position; By the pump light access resonant cavity of wavelength division multiplex device with pump unit output, excite the active gain medium in the resonant cavity in described resonant cavity, to produce laser with described pump light; The output of described wavelength division multiplex device connects the input of coupler; Connect described light with first output of described coupler and collect and coupled system, connect described photosignal converting unit with second output of described coupler; It is the tuber function device that tuned cell is set, and it is ν from first output output tuned frequency of described coupler that the tunning effect by described tuned cell makes described tunable optical fiber laser _m, tuning amplitude is the laser signal of Δ λ.

Described broadband mirrors is set to fiber loop mirror speculum or deielectric-coating fiber reflector, and described narrowband reflection mirror is set to have the fiber grating of frequency-selecting function.

Full fiber type laser of the present invention also is from the design feature of mixed ranging system:

The version that described tunable optical fiber laser is set is: the resonant cavity that adopts ring cavity structure, inserted in the resonant cavity of ring cavity structure by the pump light of wavelength division multiplex device with pump unit output, excite active gain medium in the resonant cavity with described pump light, and in described resonant cavity, produce laser through the narrowband reflection mirror; The input of coupler is connected with the resonant cavity of described ring cavity structure, and first output of coupler connects the narrowband reflection mirror, and tuned cell connects described light to be collected and coupled system, and second output of coupler connects described photosignal converting unit; It is the tuber function device that tuned cell is set, and it is ν from described narrowband reflection mirror output output tuned frequency that the tunning effect by described tuned cell makes described tunable optical fiber laser _m, tuning amplitude is the laser signal of Δ λ.

Described narrowband reflection mirror is set to have the fiber grating of frequency-selecting function, adds an isolator between Active Optical Fiber and coupler, isolates the one-way transmission of feedback light control laser in described resonant cavity by described isolator.

Described light is collected with coupled system and is set to lens or set of lenses, is used for regulating the output intensity of described tunable optical fiber laser and from the light signal fed back light intensity of described testee.

Compared with the prior art, beneficial effect of the present invention is embodied in:

The moving range of the tuning wavelength of tunable optical fiber laser that 1, the present invention adopts can reach 100nm even higher, and the semiconductor laser that injects electric current tuning relatively has bigger tuning range.Therefore system accuracy of the present invention is higher relatively.

2, fiber laser wide-band tuning characteristic can guarantee that high gain characteristics and power output that fiber laser tuning process broadband is smooth are stable, can guarantee that therefore full fiber type laser of the present invention is from the stability of mixed ranging system and range finding effect.

3, fiber laser output laser linewidth of the present invention can reach 0.02nm; with respect to semiconductor laser; be single longitudinal mode or few longitudinal mode output; good coherence, mode characteristic and less beam divergence angle can fully be applied to remote recording and measure; and all optical fibre structure coupled modes are simple, compact conformation, can satisfy the application demand that particular distance is measured occasion.

Description of drawings

Fig. 1 is structural representation of the present invention;

Fig. 2 is linear cavity configuration tunable optical fiber laser structural representation among the present invention;

Fig. 3 is ring cavity structure tunable optical fiber laser structural representation among the present invention;

Fig. 4 is the self-mixed interference system schematic;

Number in the figure: 1 tunable optical fiber laser, 2 photosignal converting units, 3 signal processing units, 4 light collections and coupled system, 5 testees, 6 pump unit, 7 tuned cells, 8 broadband mirrors, 9 narrowband reflection mirrors, 10 wavelength division multiplex devices, 11 active gain media, 12 couplers; 13 first outputs; 14 second outputs, 15 isolators, 16 laser output mouths, 17 laser front facet, 18 laser rear end faces, 19 target object scattering end faces.

Embodiment

Referring to Fig. 1, full fiber type laser is to adopt a tunable optical fiber laser 1 from the mixed ranging system in the present embodiment, and the light that is equipped with photosignal converting unit 2, the signal processing unit 3 with photodetector and the front end that is positioned at tunable optical fiber laser 1 with tunable optical fiber laser 1 is collected and coupled system 4; Tunable laser 1 is collected by light and the output of coupled system 4 is that λ, tuned frequency are ν to the initial wavelength of testee 5 outgoing _m, tuning amplitude is the laser signal of Δ λ, and collect the light signal fed back that output with coupled system 4 receives from the scattering surface of testee 5 by light and form laser from mixed signal; Photosignal converting unit 2 is to be received in the tunable laser 1 laser that forms from mixed signal and to be converted to the signal of telecommunication with photodetector; Signal processing unit 3 receives and handles the signal of telecommunication from photosignal converting unit 2, utilizes laser from the vibration frequency Δ ν of mixed signal _L, obtained the distance L between the output end face of the scattering surface of testee 5 and tunable optical fiber laser 1 by formula (1) _Ext:

$L_{\mathrm{ext}}=\frac{{\mathrm{\&Delta;v}}_L{\mathrm{\&lambda;}}^2}{4v_m\mathrm{\&Delta;\&lambda;}}---\left(1\right)$

In concrete the enforcement, signal processing unit 3 routines are provided with amplification, filtering and demodulation part; Light is collected with coupled system 4 and is set to lens or set of lenses, is used for regulating the output intensity of tunable optical fiber laser 1 and from the light signal fed back light intensity of testee 5.

As shown in Figure 2, the version that tunable optical fiber laser 1 is set is: adopt the resonant cavity of linear cavity structure, resonant cavity is made up of the narrowband reflection mirror 9 of the front end face position that is arranged on tunable optical fiber laser 1 and the broadband mirrors 8 of rear end face position; By the pump light access resonant cavity of wavelength division multiplex device 10 with pump unit 6 outputs, excite the active gain medium 11 in the resonant cavity in resonant cavity, to produce laser with pump light; The output of wavelength division multiplex device 10 connects the input of coupler 12; First output 13 with coupler 12 connects light collection and coupled system 4, with second output, the 14 connection photosignal converting units 2 of coupler 12; Tuned cell 7 is set is the tuber function device, as piezoelectric ceramic etc., it is ν from first output, the 13 output tuned frequencies of coupler 12 that the tunning effect by tuned cell 7 makes tunable optical fiber laser 1 _m, tuning amplitude is the laser signal of Δ λ.

In this technical scheme, broadband mirrors 8 can be set to fiber loop mirror speculum or deielectric-coating fiber reflector, and narrowband reflection mirror 9 is set to have the fiber grating of frequency-selecting function.

As shown in Figure 3, the version that tunable optical fiber laser 1 is set is: the resonant cavity that adopts ring cavity structure, inserted in the resonant cavity of ring cavity structure by the pump light of wavelength division multiplex device 10 with pump unit 6 outputs, excite active gain medium 11 in the resonant cavity with pump light, and in resonant cavity, produce laser through narrowband reflection mirror 9; The input of coupler 12 is connected with the resonant cavity of ring cavity structure, and first output 13 of coupler 12 connects narrowband reflection mirror 9, and tuned cell 7 connects light to be collected and coupled system 4, and second output 14 of coupler 12 connects photosignal converting unit 2; Tuned cell 7 is set is the tuber function device, as piezoelectric ceramic etc., it is ν from narrowband reflection mirror 9 outputs 16 output tuned frequencies that the tunning effect by tuned cell 7 makes tunable optical fiber laser 1 _m, tuning amplitude is the laser signal of Δ λ.

Narrowband reflection mirror 9 is set to have the fiber grating of frequency-selecting function, adds an isolator 15 between Active Optical Fiber 11 and coupler 12, isolates the one-way transmission of feedback light control laser in resonant cavity by isolator 15.

In concrete the enforcement, fiber grating is wrapped on the piezoelectric ceramic that is subjected to the cyclical signal driving, piezoelectric ceramic causes fiber grating to produce stretching or shrinks, thereby the variation of grating constant generating period realizes the cyclic variation of tunable laser output optical maser wavelength.Can add Polarization Controller in laser resonant cavity, the polarization state of control laser guarantees the output laser stabilization to eliminate the influence that fiber birefringence brings.

Cyclical signal such as triangular signal act on piezoelectric ceramic, fiber grating generation strain under the piezoelectric ceramic effect, according to:

$\frac{{\mathrm{\&Delta;\&lambda;}}_{\mathrm{FBG}}}{{\mathrm{\&lambda;}}_{\mathrm{FBG}}}=(1-P)\mathrm{\&Delta;\&epsiv;}---\left(8\right)$

In the formula (8), λ _FBGBe optical grating reflection centre wavelength, Δ λ _FBGBe optical grating reflection centre wavelength change amount, P is effective elasto-optical coefficient, and Δ ε is the change amount of axial strain.When the power of applying was pulling force, grating constant increased, and optical grating reflection centre wavelength moves toward the long wave direction; Otherwise, move towards the shortwave direction, thus the output of realization tunable wave length.

Claims (6)

1. a full fiber type laser is from the mixed ranging system, it is characterized in that adopting a tunable optical fiber laser (1), the light that is equipped with photosignal converting unit (2), the signal processing unit (3) with photodetector and the front end that is positioned at described tunable optical fiber laser (1) with described tunable optical fiber laser (1) is collected and coupled system (4); Described tunable laser (1) is collected by light and the output of coupled system (4) is that λ, tuned frequency are ν to the initial wavelength of testee (5) outgoing _m, tuning amplitude is the laser signal of Δ λ, and collect the light signal fed back that output with coupled system (4) receives from the scattering surface of testee (5) by light and form laser from mixed signal; Described photosignal converting unit (2) is to be received in the middle laser that forms of described tunable laser (1) from mixed signal and to be converted to the signal of telecommunication with photodetector; Described signal processing unit (3) receives and handles the signal of telecommunication from described photosignal converting unit (2), utilizes laser from the vibration frequency Δ ν of mixed signal _L, obtained the distance L between the output end face of the scattering surface of testee (5) and tunable optical fiber laser (1) by formula (1) _Ext:

$L_{\mathrm{ext}}=\frac{{\mathrm{\&Delta;v}}_L{\mathrm{\&lambda;}}^2}{{4v}_m\mathrm{\&Delta;\&lambda;}}---\left(1\right).$

2. full fiber type laser according to claim 1 is from the mixed ranging system, it is characterized in that: the version that described tunable optical fiber laser (1) is set is: adopt the resonant cavity of linear cavity structure, described resonant cavity is made up of the narrowband reflection mirror (9) of the front end face position that is arranged on tunable optical fiber laser (1) and the broadband mirrors (8) of rear end face position; By the pump light access resonant cavity of wavelength division multiplex device (10) with pump unit (6) output, excite the active gain medium (11) in the resonant cavity in described resonant cavity, to produce laser with described pump light; The output of described wavelength division multiplex device (10) connects the input of coupler (12); First output (13) with described coupler (12) connects described light collection and coupled system (4), with second output (14) the connection described photosignal converting unit (2) of described coupler (12); It is the tuber function device that tuned cell (7) is set, and it is ν from first output (13) the output tuned frequency of described coupler (12) that the tunning effect by described tuned cell (7) makes described tunable optical fiber laser (1) _m, tuning amplitude is the laser signal of Δ λ.

3. full fiber type laser according to claim 2 is from the mixed ranging system, it is characterized in that: described broadband mirrors (8) is set to fiber loop mirror speculum or deielectric-coating fiber reflector, the fiber grating that described narrowband reflection mirror (9) is set to have the frequency-selecting function.

4. full fiber type laser according to claim 1 is from the mixed ranging system, it is characterized in that: the version that described tunable optical fiber laser (1) is set is: the resonant cavity that adopts ring cavity structure, inserted in the resonant cavity of ring cavity structure by the pump light of wavelength division multiplex device (10) with pump unit (6) output, excite active gain medium (11) in the resonant cavity with described pump light, and in described resonant cavity, produce laser through narrowband reflection mirror (9); The input of coupler (12) is connected with the resonant cavity of described ring cavity structure, first output (13) of coupler (12) connects narrowband reflection mirror (9), tuned cell (7) connects described light to be collected and coupled system (4), and second output (14) of coupler (12) connects described photosignal converting unit (2); It is the tuber function device that tuned cell (7) is set, and it is ν from described narrowband reflection mirror (9) output (16) output tuned frequency that the tunning effect by described tuned cell (7) makes described tunable optical fiber laser (1) _m, tuning amplitude is the laser signal of Δ λ.

5. full fiber type laser according to claim 4 is from the mixed ranging system, it is characterized in that: the fiber grating that described narrowband reflection mirror (9) is set to have the frequency-selecting function, between Active Optical Fiber (11) and coupler (12), add an isolator (15), isolate the one-way transmission of feedback light control laser in described resonant cavity by described isolator (15).

6. full fiber type laser according to claim 1 is from the mixed ranging system, it is characterized in that described light is collected with coupled system (4) is set to lens or set of lenses, is used for regulating the output intensity of described tunable optical fiber laser (1) and from the light signal fed back light intensity of described testee (5).

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