CN103809166A - Resonant frequency locking device and method for Michelson interference type spectrum filter - Google Patents

Abstract

The invention discloses a resonant frequency locking device and a resonant frequency locking method for a Michelson interference type spectrum filter. The device comprises a laser beam splitting system, a Michelson interference type spectrum filter system and a photoelectric detection system; the laser beam splitting system comprises a laser device, a collimation and beam expander, a first spectroscope, a first reflector, a second reflector, a second spectroscope and a third reflector; the Michelson interference type spectrum filter system comprises a cubic beam splitter prism, a fourth reflector and a fifth reflector; and the photoelectric detection system comprises a lens, a first photomultiplier, a second photomultiplier, a third photomultiplier, a differential amplifier and an oscilloscope. The method comprises the following specific steps: firstly, calculating the incident angles of the two probe light beams; secondly, adjusting the incident angles of the two probe light beams; and thirdly, examining the oscilloscope to judge a frequency locking state. The method and the device can be realized simply, and the complicate requirements of a traditional frequency locking method on circuits and light paths can be prevented, so that the device has stronger system stability and robustness.

Description

A kind of Michelson interference type spectral filter resonance frequency locking device and method

Technical field

The invention belongs to laser radar technique field, particularly relate to a kind of Michelson (Michelson) interference type spectral filter resonance frequency locking device and method.

Background technology

High spectral resolution lidar is owing to having adopted spectral filtering technology, and having solved traditional back scattering laser radar needs many a priori assumptions just can be finally inversed by the deficiency of atmospheric parameter, thereby has improved the precision of atmospheric remote sensing.In high spectral resolution lidar, the use of spectral filter is a very crucial technology.By the high spectral resolution ability of spectral filter, can will in atmospheric backscatter spectrum, come by the composition of atmospheric aerosol scattering with by the component separating of atmospheric molecule scattering, so just can obtain the more details of atmospheric backscatter spectrum.Can be finally inversed by more accurately the atmospheric optics such as atmospheric backscatter coefficient, extinction coefficient attribute in conjunction with relevant Remote Sensing Principles.

At present, iodine molecule absorption filter is because of the high filtration rate to atmospheric aerosol scattering signal, the high stability of spectral absorption characteristics and do not rely on the advantages such as the mechanical alignment with incident light and be used in a lot of high spectral resolution lidars.But because the absorption peak (absorption harmonic peak) of this type of wave filter is to be determined by the natural absorption mechanism of molecule, can not change arbitrarily it and use wave band, expand therefore limited the spectrum of laser radar.In order to solve this shortcoming, Michelson interference type spectral wave filter more and more receives publicity and is progressively applied in laser radar.Owing to having adopted interference of light principle, the resonance frequency of Michelson interference type spectral wave filter can be arranged on any interested optical maser wavelength, has widened greatly the spectrum of use field of laser radar.

But it is stable like that the resonance frequency of Michelson interference type spectral wave filter but can not show a candle to iodine molecule absorption filter.Temperature, external stress etc. all can cause the drift of resonance frequency.How Michelson interference type spectral filter resonance frequency being locked in to the laser center frequency needing is its key technical problem for high spectral resolution lidar.In the document having been reported, all adopt the technology of frequency modulation (PFM) frequency locking.This technology is by after the modulation by electrooptic modulator or acousto-optic modulator of the laser beam of frequency locking, producing the sideband frequency signal that is symmetrically distributed in original laser frequency both sides by being used for.This sideband signals and former laser signal, by after interference type spectral wave filter to be locked, can obtain the voltage signal of amplitude modulation(PAM) on photodetector.Finally need one to carry out this am signals of demodulation with the voltage signal of the signal synchronised of driven modulator, thus the error signal while obtaining frequency losing lock.By this error signal being fed back to the frequency harmony equipment of interference type spectral wave filter, as piezoelectric sensor (PZT), just can be transferred to used laser frequency by again humorous the wave filter that loses locking.Although this technology is widely used, weak point is that needed equipment is very complicated.For example at least need two electric light frequency modulators to reach reasonable modulation effect; In order to keep synchronizeing of restituted signal and modulator driving signal, often need phase-locked loop circuit; Because modulating frequency is conventionally all in MHz magnitude, therefore detector needs very high frequency response just can detect the photosignal needing.These have all increased the complexity of circuit and the optical device of this technology.

Summary of the invention

The object of the invention is in order to overcome above-mentioned the deficiencies in the prior art, reduce the device complicacy of Michelson interference type spectral filter resonance frequency locking, proposed a kind of Michelson interference type spectral filter resonance frequency locking means.

The present invention has utilized the dependence of the incident angle of Michelson interference type spectral filter resonance frequency and incident laser cleverly, the probe beam matching by two bundle incident angles carries out real-time detection to Michelson interference filter resonance frequency, once exist frequency losing lock fixed, the frequency harmony equipment that can produce error signal and feed back to wave filter is with by its humorous Frequency Locking state of being transferred to again.Owing to not needing high frequency modulated and synchronous demodulation, therefore greatly reduced the complexity of circuit, light path.

A kind of Michelson interference type spectral filter resonance frequency locking device, comprises laser instrument divided beam system, Michelson interfere type filter system and Photodetection system;

Laser instrument divided beam system comprises laser instrument, collimator and extender device, the first spectroscope, the first catoptron, the second catoptron, the second spectroscope, the 3rd catoptron; Michelson interfere type filter system comprises a cube Amici prism, the 4th catoptron, the 5th catoptron, and wherein the 5th catoptron is connected and realizes resonance frequency adjustment with frequency harmony plant machinery; Photodetection system comprises lens, the first photomultiplier, the second photomultiplier, the 3rd photomultiplier, differential amplifier, oscillograph;

The laser beam of laser instrument transmitting is expanded as angle pencil of ray directional light through collimator and extender device; Angle pencil of ray directional light is divided into two-way through the first spectroscope, and wherein the Michelson interference filter system for the treatment of frequency locking is directly injected as monitoring light beam in a road after the first spectroscope transmission; Another road successively after the first catoptron, the second catoptron, then is divided into two-way through the second spectroscope, and wherein the first via, after the second spectroscope transmission, then reflects with angle θ through the 3rd catoptron ₂enter the Michelson interference filter system for the treatment of frequency locking as probe beam; The second tunnel after the second spectroscope reflection directly with angle θ ₁enter the Michelson interference filter system for the treatment of frequency locking as probe beam; Two-way probe beam and monitoring light beam are through in the time of the Michelson of frequency locking interference filter system, two-way probe beam is divided into two-way with monitoring light beam by intrasystem cube of Amici prism of Michelson interference filter, one tunnel is reflected back a cube Amici prism by the 4th catoptron again after cube Amici prism transmission, and enters lens through a cube Amici prism reflection; Another road is reflected back a cube Amici prism by the 5th catoptron again after cube Amici prism reflection, and enters lens through a cube Amici prism transmission; Several roads light beam is also interfered respectively at its focal plane diverse location by lens focus, and interference signal is received and convert to electric signal by the first photomultiplier, the second photomultiplier, the 3rd photomultiplier respectively; By the electric signal input difference amplifier of the first photomultiplier, the second photomultiplier output, the output signal of differential amplifier feeds back to frequency harmony equipment; And the output electrical signals of the 3rd photomultiplier input oscillograph is as frequency locking status monitoring signal.

A kind of Michelson interference type spectral filter resonance frequency locking means, comprises the steps:

Step 1. is calculated the incident angle of two bundle probe beams;

Step 2. regulates the incident angle of two bundle probe beams;

Step 3. is checked oscillograph, judges frequency locking state;

The incident angle of the two-way probe beam described in step 1 comprises θ ₁and θ ₂; θ ₁and θ ₂needing to meet following coupling requires:

θ ₁the difference Δ OPD (θ that chooses the optical path difference need to make the optical path difference of the probe beam of Michelson interference filter to this angle incident and 0 degree angle incident time ₁) be (n ₁+ 1/4) λ ₀,

ΔOPD(θ ₁)＝(n ₁+1/4)λ ₀ (1)

Wherein, λ ₀laser instrument centre wavelength, n ₁be one and treat selected integer (recommendation is 0～10); Δ OPD (θ ₁) computing method relevant with the structural parameters of Michelson interference filter used; If Michelson interference filter two interferes the length of arm to be respectively d ₁and d ₂, refractive index is respectively ρ ₁and ρ ₂, Δ OPD (θ ₁) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_1\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(2a\right)$

OPD(0)＝2·abs(ρ ₁d ₁-ρ ₂d ₂) (2b)

ΔOPD(θ ₁)＝abs[OPD(θ ₁)-OPD(0)] (2c)

Wherein, abs () represents to take absolute value, OPD (θ ₁) represent with angle θ ₁the optical path difference of Michelson interference filter when incident, the optical path difference of Michelson interference filter when OPD (0) represents light normal incidence; As long as selected Integer n ₁after, simultaneous formula (1), (2) can solve θ ₁;

Want and θ ₁match, incidence angle θ ₂variation between optical path difference must meet the optical path difference of Michelson interference filter to this probe beam and normal incidence time:

ΔOPD(θ ₂)＝(n ₂-1/4)λ ₀ (3)

In formula (3), n ₂treating selected integer for another, is 0～50 and than selected n ₁greatly, in like manner, Δ OPD (θ ₂) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_2\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(4a\right)$

ΔOPD(θ ₂)＝abs[OPD(θ ₂)-OPD(0)] (4b)

Wherein OPD (θ ₂) represent with angle θ ₂the optical path difference of Michelson interference filter when incident.As long as selected Integer n ₂after, simultaneous formula (3), (4) can solve θ ₂;

The incident angle of the adjusting probe beam described in step 2, specific as follows:

2-1., before two-way probe beam regulates, is manually adjusted to 0 by the output of the 3rd photomultiplier by frequency harmony equipment, allows the initialization of Michelson interferometer filter in Frequency Locking state;

2-2. regulates the second spectroscope and the 3rd catoptron, makes the incidence angle θ of probe beam ₁and θ ₂angle and the incidence angle θ that calculates of step 1 ₁and θ ₂consistent;

Concrete consistent determination methods is as follows:

In the time of actual optical path adjusting, first disconnect differential amplifier and receive the feedback end of frequency harmony equipment, first the incident angle of a branch of probe beam is wherein adjusted to θ with accurate mobile turntable ₁, then the angle of another bundle probe beam is determined to the θ calculating in theory ₂near, then finely tune the mobile turntable of precision of the second bundle probe beam, until the output of differential amplifier reaches 0; After the angular adjustment of two probe beams completes, then by the frequency harmony equipment of the feedback end access Michelson interference filter of differential amplifier;

Described in step 3, check oscillograph, judge frequency locking state, specific as follows:

If Michelson interference filter is just locked in laser instrument centre frequency, oscillographic output signal is 0; If the impact of external environmental factor causes Michelson interferometer frequency losing lock fixed, differential amplifier can output error signal and is fed back to the frequency harmony equipment of Michelson interference filter, frequency harmony equipment is automatically adjusted the resonance frequency of interferometer under the driving of this error signal, until lock onto required laser center frequency; In this process, also convergence 0 progressively of oscillographic output signal.

The first described spectroscope is the spectroscope that reflectivity is greater than transmissivity; The second spectroscope is the spectroscope of 50%:50% splitting ratio.

First described spectroscopical reflectivity is as follows with transmissivity ratio: T:R=10%:90%.

Beneficial effect of the present invention is as follows:

The present invention is suitable for the resonance frequency locking of various Michelson interference type spectral wave filters, realizes simply, can avoid the complicated requirement of traditional locks frequency method to circuit and light path, thereby have stronger system stability and robustness.

Accompanying drawing explanation

Fig. 1 is the index path of apparatus of the present invention;

Fig. 2 is an example of Michelson interference type spectral wave filter optical path difference variation and incident angle relation in the present invention;

Fig. 3 is the present invention while locking Michelson interference type spectral wave filter, error signal and the quantitative relation curve of frequency losing lock of differential amplifier output.

In figure, laser instrument 1, collimator and extender device 2, the first spectroscope 3, the first catoptron 4, the second catoptron 5, the second spectroscope 6, the 3rd catoptron 7, cube Amici prism 8, the 4th catoptron 9, the 5th catoptron 10, lens 11, the first photomultiplier (PMT) 12, the second photomultiplier 13, the 3rd photomultiplier 14, differential amplifier 15, frequency harmony equipment 16, oscillograph 17.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described.

As shown in Figure 1, a kind of Michelson interference type spectral filter resonance frequency locking device, comprises laser instrument divided beam system a, Michelson interfere type filter system b and Photodetection system c;

Laser instrument divided beam system a comprises laser instrument 1, collimator and extender device 2, the first spectroscope 3, the first catoptron 4, the second catoptron 5, the second spectroscope 6, the 3rd catoptron 7; Michelson interfere type filter system b comprises cube Amici prism 8, the 4th catoptron 9, the 5th catoptron 10.Wherein the 5th catoptron 10 and frequency harmony equipment 16 mechanical connections are realized resonance frequency adjustment; Photodetection system c comprises lens 11, the first photomultiplier (PMT) 12, the second photomultiplier 13, the 3rd photomultiplier 14, differential amplifier 15, oscillograph 17.

The laser beam that laser instrument 1 is launched is expanded as angle pencil of ray directional light through collimator and extender device 2; Angle pencil of ray directional light is divided into two-way through the first spectroscope 3, and wherein the Michelson interference filter system b that treats frequency locking is directly injected as monitoring light beam in a road after the first spectroscope 3 transmissions; Another road successively after the first catoptron 4, the second catoptron 5, then is divided into two-way through the second spectroscope 6, and wherein the first via, after the second spectroscope 6 transmissions, then reflects with angle θ through the 3rd catoptron 7 ₂enter the Michelson interference filter system b that treats frequency locking as probe beam; The second tunnel after the second spectroscope 6 reflection directly with angle θ ₁enter the Michelson interference filter system b that treats frequency locking as probe beam.Two-way probe beam and monitoring light beam are through in the time of the Michelson of frequency locking interference filter system b, two-way probe beam is divided into two-way with monitoring light beam by cube Amici prism 8 in Michelson interference filter system b, one tunnel is reflected back cube Amici prism 8 by the 4th catoptron 9 again after 8 transmissions of cube Amici prism, and enters lens 11 through 8 reflections of cube Amici prism; Another road is reflected back cube Amici prism 8 by the 5th catoptron 10 again after 8 reflections of cube Amici prism, and enters lens 11 through 8 transmissions of cube Amici prism; Several roads light beam is focused on its focal plane diverse location and interferes respectively by lens 11, and interference signal is received and convert to electric signal by the first photomultiplier 12, the second photomultiplier 13, the 3rd photomultiplier 14 respectively.The electric signal input difference amplifier 15 that the first photomultiplier 12, the second photomultiplier 13 are exported, the output signal of differential amplifier 15 feeds back to frequency harmony equipment 16; And the output electrical signals of the 3rd photomultiplier 14 input oscillograph 17 is as frequency locking status monitoring signal.

A kind of Michelson interference type spectral filter resonance frequency locking means, specifically comprises the steps:

Step 1. is built Michelson interference type spectral filter resonance frequency locking device;

Step 2. is calculated the incident angle of two bundle probe beams;

Step 3. regulates the incident angle of two bundle probe beams;

Step 4. is checked oscillograph, judges frequency locking state.

Michelson interference type spectral filter resonance frequency locking device described in step 1 is the device shown in Fig. 1;

The incident angle of the two-way probe beam described in step 2 comprises θ ₁and θ ₂; θ ₁and θ ₂need meet certain coupling requirement, specific as follows definite:

θ ₁the difference Δ OPD (θ that chooses the optical path difference need to make the optical path difference of the probe beam of Michelson interference filter to this angle incident and 0 degree angle incident time ₁) be (n ₁+ 1/4) λ ₀,

ΔOPD(θ ₁)＝(n ₁+1/4)λ ₀ (1)

Wherein, λ ₀laser instrument centre wavelength, n ₁be one and treat selected integer (recommendation is 0～10); Δ OPD (θ ₁) computing method relevant with the structural parameters of Michelson interference filter used; If Michelson interference filter two interferes the length of arm to be respectively d ₁and d ₂, refractive index is respectively ρ ₁and ρ ₂, Δ OPD (θ ₁) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_1\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(2a\right)$

OPD(0)＝2·abs(ρ ₁d ₁-ρ ₂d ₂) (2b)

ΔOPD(θ ₁)＝abs[OPD(θ ₁)-OPD(0)] (2c)

Wherein, abs () represents to take absolute value, OPD (θ ₁) represent with angle θ ₁the optical path difference of Michelson interference filter when incident, the optical path difference of Michelson interference filter when OPD (0) represents light normal incidence; As long as selected Integer n ₁after, simultaneous formula (1), (2) can solve θ ₁;

Want and θ ₁match, incidence angle θ ₂variation between optical path difference must meet the optical path difference of Michelson interference filter to this probe beam and normal incidence time:

ΔOPD(θ ₂)＝(n ₂-1/4)λ ₀ (3)

In formula (3), n ₂treating selected integer for another, is 0～50 and than selected n ₁greatly, in like manner, Δ OPD (θ ₂) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_2\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="HDA0000459308710000011.png,HDA0000459308710000021.png"\; state="\{\{state\}\}">sin</figure-callout>}}^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(4a\right)$

ΔOPD(θ ₂)＝abs[OPD(θ ₂)-OPD(0)] (4b)

Wherein OPD (θ ₂) represent with angle θ ₂the optical path difference of Michelson interference filter when incident.As long as selected Integer n ₂after, simultaneous formula (3), (4) can solve θ ₂.

The incident angle of the adjusting probe beam described in step 3, specific as follows:

3-1., before two-way probe beam regulates, is manually adjusted to 0 by the output of the 3rd photomultiplier 14 by frequency harmony equipment, allows the initialization of Michelson interferometer filter in Frequency Locking state;

3-2. regulates the second spectroscope 6 and the 3rd catoptron 7, makes the incidence angle θ of probe beam ₁and θ ₂angle and the incidence angle θ that calculates of step 2 ₁and θ ₂consistent.

Concrete consistent determination methods is as follows: in the time of actual optical path adjusting, first disconnect differential amplifier 15 and receive the feedback end of frequency harmony equipment 16, first the incident angle of a branch of probe beam is wherein adjusted to θ with accurate mobile turntable ₁, then the angle of another bundle probe beam is determined to the θ calculating in theory ₂near, then finely tune the mobile turntable of precision of the second bundle probe beam, until the output of differential amplifier 15 reaches 0; After the angular adjustment of two probe beams completes, then by the frequency harmony equipment 16 of the feedback end access Michelson interference filter of differential amplifier.

Described in step 4, check oscillograph, judge frequency locking state, specific as follows:

If Michelson interference filter is just locked in laser instrument centre frequency, the output signal of oscillograph 17 is 0; If the impact of the factors such as external environment condition causes Michelson interferometer frequency losing lock fixed, differential amplifier can output error signal and is fed back to the frequency harmony equipment of Michelson interference filter, frequency harmony equipment is automatically adjusted the resonance frequency of interferometer under the driving of this error signal, until lock onto required laser center frequency.In this process, also convergence 0 progressively of the output signal of oscillograph 17.

The first described spectroscope 3 is reflectivity spectroscopes much larger than transmissivity, as T:R=10%:90%; The second spectroscope 6 is the spectroscopes that have 50%:50% splitting ratio.In order to facilitate angular setting, the second spectroscope 6 and the 3rd catoptron 7 can be placed on precise rotation platform.

Embodiment

In Fig. 1, laser instrument 1 and laser radar transmitter share by the mode of light splitting, and its frequency is exactly the reference frequency that needs locking;

Above-mentioned collimator and extender device 2 can adopt common beam expander, the GCO-141602 model beam expanding lens of for example Beijing company of Daheng, and 6 times expand;

Above-mentioned the first spectroscope 3 adopts the spectroscope of T:R=10%:90%, as the GCC-411215 of Beijing company of Daheng; The spectroscope of the common T:R=50%:50% of the second spectroscope 6 use, as the GCC-411102 of Beijing company of Daheng;

Above-mentioned: the first catoptron 4, the second catoptron 5, the 3rd catoptron 7 adopt normal mirror, for example GCC-101102 of Beijing company of Daheng, diameter 25.4mm;

Lens 11 are long-focus lenss, for example Beijing GCL-010214 of company of Daheng, burnt long 400mm;

The first photomultiplier (PMT) 12, the second photomultiplier 13, the 3rd photomultiplier 14 can use the R6358 model photomultiplier of Japanese Bin Song company;

The chip I NA126 that differential amplifier 15 can select Texas Instruments (TI) to produce;

Oscillograph 17 adopts common oscillograph, as YB4320/20A/40.

Michelson interference filter can be homemade can be also buy integrating device.If homemade, the general piezoelectric sensor PZT that uses of its frequency harmony device 16, as the PZ150E of PI company, cube common cube of Amici prism that Amici prism 8 is 50%:50%, as Beijing GCC-401012 of company of Daheng, the 4th catoptron 9, the 5th catoptron 10 are normal mirror, for example GCC-101102 of Beijing company of Daheng; If the integrated products of buying can be accompanied with frequency harmony device.

Further describe the method for its Frequency Locking below in conjunction with concrete Michelson interference filter parameter.

First put up device by the light path shown in Fig. 1, then calculate the incident angle of two probe beams by the method described in step 2.

It is d that the Michelson interference filter two of supposing to treat frequency locking is interfered the length of arm and refractive index ₁=87.578mm, d ₂=59.318mm, ρ ₁=1.4765, ρ ₂=1.00027.In order to be determined by formula (1-4) incidence angle θ of two probe beams ₁and θ ₂, also need selected two Integer n wherein arbitrarily ₁and n ₂.Conventionally this n, ₁can choose arbitrarily, recommendation is 0～10, can guarantee that like this incident angle calculating is unlikely to too little, also can guarantee that the OPD variation of the probe beam of Michelson interference filter to this angle incident is unlikely to too greatly.Same, n ₂choose and should guarantee the θ that calculates ₁and θ ₂differ unlikely too little, also will guarantee that Michelson interference filter changes as far as possible in wavelength magnitude the OPD of this probe beam, recommendation is 0～50 and is less than selected n ₁.

A kind of auxiliary n that chooses ₁and n ₂method be make according to formula (2) or formula (4) that this Michelson interference filter incident angle changes with OPD be related to schematic diagram, as shown in Figure 2.As seen from Figure 2, that this Michelson interference filter OPD changes with incident angle and not obvious, therefore can choose less n ₁and n ₂.For example, can choose n ₁=0, n ₂=1, substitution formula (1-4) can solve θ ₁=4.024 °, θ ₂=5.086 °.

After having calculated the incident angle of two probe beams, then regulate the incident angle of two probe beams by step 3.Be can be observed the state of resonance frequency locking by step 4.

For the feasibility of the party's case can be described, Fig. 3 has provided the relation curve of error signal with frequency losing lock situation.Can see, this technical scheme can detect the direction that frequency losing lock is fixed: in the time that the resonance frequency of Michelson interference filter is greater than laser instrument centre frequency, differential amplifier is exported positive error signal, and in the time that the resonance frequency of Michelson interference filter is less than laser instrument centre frequency, differential amplifier is exported negative error signal.System can be moved towards correct direction with driving Michelson interferometer frequency harmony equipment according to the symbol of the fixed direction of frequency losing lock and big or small alignment error signal automatically and size, thereby makes interferometer come back to Frequency Locking state.And error signal variations is precipitous, show to have very high frequency locking sensitivity.

Claims (4)

1. Michelson relates to a type spectral filter resonance frequency locking device, it is characterized in that comprising laser instrument divided beam system, Michelson interfere type filter system and Photodetection system;

Laser instrument divided beam system comprises laser instrument, collimator and extender device, the first spectroscope, the first catoptron, the second catoptron, the second spectroscope, the 3rd catoptron; Michelson interfere type filter system comprises a cube Amici prism, the 4th catoptron, the 5th catoptron, and wherein the 5th catoptron is connected and realizes resonance frequency adjustment with frequency harmony plant machinery; Photodetection system comprises lens, the first photomultiplier, the second photomultiplier, the 3rd photomultiplier, differential amplifier, oscillograph;

The laser beam of laser instrument transmitting is expanded as angle pencil of ray directional light through collimating and beam expanding system; Angle pencil of ray directional light is divided into two-way through the first spectroscope, and wherein the Michelson interference filter system for the treatment of frequency locking is directly injected as monitoring light beam in a road after the first spectroscope transmission; Another road successively after the first catoptron, the second catoptron, then is divided into two-way through the second spectroscope, and wherein the first via, after the second spectroscope transmission, then reflects with angle θ through the 3rd catoptron ₂enter the Michelson interference filter system for the treatment of frequency locking as probe beam; The second tunnel after the second spectroscope reflection directly with angle θ ₁enter the Michelson interference filter system for the treatment of frequency locking as probe beam; Two-way probe beam and monitoring light beam are through in the time of the Michelson of frequency locking interference filter system, two-way probe beam is divided into two-way with monitoring light beam by intrasystem cube of Amici prism of Michelson interference filter, one tunnel is reflected back a cube Amici prism by the 4th catoptron again after cube Amici prism transmission, and enters lens through a cube Amici prism reflection; Another road is reflected back a cube Amici prism by the 5th catoptron again after cube Amici prism reflection, and enters lens through a cube Amici prism transmission; Several roads light beam is also interfered respectively at its focal plane diverse location by lens focus, and interference signal is received and convert to electric signal by the first photomultiplier, the second photomultiplier, the 3rd photomultiplier respectively; By the electric signal input difference amplifier of the first photomultiplier, the second photomultiplier output, the output signal of differential amplifier feeds back to frequency harmony equipment; And the output electrical signals of the 3rd photomultiplier input oscillograph is as frequency locking status monitoring signal.

2. the method that uses a kind of Michelson interference type spectral filter resonance frequency locking device as claimed in claim 1, is characterized in that comprising the steps:

Step 1. is calculated the incident angle of two bundle probe beams;

Step 2. regulates the incident angle of two bundle probe beams;

Step 3. is checked oscillograph, judges frequency locking state;

The incident angle of the two-way probe beam described in step 1 comprises θ ₁and θ ₂; θ ₁and θ ₂needing to meet following coupling requires:

θ ₁the difference Δ OPD (θ that chooses the optical path difference need to make the optical path difference of the probe beam of Michelson interference filter to this angle incident and 0 degree angle incident time ₁) be (n ₁+ 1/4) λ ₀,

ΔOPD(θ ₁)＝(n ₁+1/4)λ ₀ (1)

Wherein, λ ₀laser instrument centre wavelength, n ₁be one and treat selected integer (recommendation is 0～10); Δ OPD (θ ₁) computing method relevant with the structural parameters of Michelson interference filter used; If Michelson interference filter two interferes the length of arm to be respectively d ₁and d ₂, refractive index is respectively ρ ₁and ρ ₂, Δ OPD (θ ₁) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_1\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\sin }^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\sin }^2{\mathrm{\&theta;}}_1}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(2a\right)$

OPD(0)＝2·abs(ρ ₁d ₁-ρ ₂d ₂) (2b)

ΔOPD(θ ₁)＝abs[OPD(θ ₁)-OPD(0)] (2c)

Wherein, abs () represents to take absolute value, OPD (θ ₁) represent with angle θ ₁the optical path difference of Michelson interference filter when incident, the optical path difference of Michelson interference filter when OPD (0) represents light normal incidence; As long as selected Integer n ₁after, simultaneous formula (1), (2) can solve θ ₁;

Want and θ ₁match, incidence angle θ ₂variation between optical path difference must meet the optical path difference of Michelson interference filter to this probe beam and normal incidence time:

ΔOPD(θ ₂)＝(n ₂-1/4)λ ₀ (3)

In formula (3), n ₂treating selected integer for another, is 0～50 and than selected n ₁greatly, in like manner, Δ OPD (θ ₂) can calculate by following several formulas

$\mathrm{OPD}\left({\mathrm{\&theta;}}_2\right)=2\&CenterDot;\mathrm{abs}[{\mathrm{\&rho;}}_1{d}_1{(1-\frac{{\sin }^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_1}^2})}^{1/2}-{\mathrm{\&rho;}}_2{d}_2{(1-\frac{{\sin }^2{\mathrm{\&theta;}}_2}{{{\mathrm{\&rho;}}_2}^2})}^{1/2}]---\left(4a\right)$

ΔOPD(θ ₂)＝abs[OPD(θ ₂)-OPD(0)] (4b)

Wherein OPD (θ ₂) represent with angle θ ₂the optical path difference of Michelson interference filter when incident.As long as selected Integer n ₂after, simultaneous formula (3), (4) can solve θ ₂.

The incident angle of the adjusting probe beam described in step 2, specific as follows:

2-1., before two-way probe beam regulates, is manually adjusted to 0 by the output of the 3rd photomultiplier by frequency harmony equipment, allows the initialization of Michelson interferometer filter in Frequency Locking state;

2-2. regulates the second spectroscope and the 3rd catoptron, makes the incidence angle θ of probe beam ₁and θ ₂angle and the incidence angle θ that calculates of step 1 ₁and θ ₂consistent;

Concrete consistent determination methods is as follows:

In the time of actual optical path adjusting, first disconnect differential amplifier and receive the feedback end of frequency harmony equipment, first the incident angle of a branch of probe beam is wherein adjusted to θ with accurate mobile turntable ₁, then the angle of another bundle probe beam is determined to the θ calculating in theory ₂near, then finely tune the mobile turntable of precision of the second bundle probe beam, until the output of differential amplifier reaches 0; After the angular adjustment of two probe beams completes, then by the frequency harmony equipment of the feedback end access Michelson interference filter of differential amplifier;

Described in step 3, check oscillograph, judge frequency locking state, specific as follows:

If Michelson interference filter is just locked in laser instrument centre frequency, oscillographic output signal is 0; If the impact of external environmental factor causes Michelson interferometer frequency losing lock fixed, differential amplifier can output error signal and is fed back to the frequency harmony equipment of Michelson interference filter, frequency harmony equipment is automatically adjusted the resonance frequency of interferometer under the driving of this error signal, until lock onto required laser center frequency; In this process, also convergence 0 progressively of oscillographic output signal.

3. the method for a kind of Michelson interference type spectral filter resonance frequency locking as claimed in claim 1 or 2, is characterized in that the first described spectroscope is the spectroscope that reflectivity is greater than transmissivity; The second spectroscope is the spectroscope of 50%:50% splitting ratio.

4. the method for a kind of Michelson interference type spectral filter resonance frequency locking as claimed in claim 3, is characterized in that first described spectroscopical reflectivity is as follows with transmissivity ratio: T:R=10%:90%.

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