CN101615759A - Double longitudinal-mode thermoelectric cooling frequency-offset-lock method and device based on iodine frequency stabilization reference - Google Patents

Abstract

Double longitudinal-mode thermoelectric cooling frequency-offset-lock method and device based on iodine frequency stabilization reference belong to the laser application technique field; The present invention reaches 10 with the relative frequency accuracy ^-11Iodine Frequency Stabilized Lasers centre frequency as reference frequency, the frequency of many double-longitudinal-mode lasers output laser is carried out frequency locking, make multi-station laser and this reference frequency remain a fixing difference, can be with the relative frequency accuracy of double-longitudinal-mode laser from 10 ^-7～10 ^-8Bring up to 10 ^-9, the frequency invariance of many double-longitudinal-mode lasers is from 10 ^-7Bring up to 10 ^-9And long adjusting the in chamber of adopting thermoelectric cooling module symmetry heat structure to carry out preheating and frequency stabilization simultaneously eliminated laser tube and has been heated the inhomogeneous laser tube radial distortion that causes to the influence of output frequency stability, strengthened adaptive capacity to environment, shorten warm-up time, improved the life-span of laser tube.

Description

Double longitudinal-mode thermoelectric cooling frequency-offset-lock method and device based on iodine frequency stabilization reference

Technical field

The invention belongs to the laser application technique field, particularly a kind of double longitudinal-mode thermoelectric cooling frequency-offset-lock method and device based on iodine frequency stabilization reference.

Background technology

But characteristics such as noncontact, precision height, range are big, the multichannel spectroscopic measurements of can tracing to the source that the laser interferometry technology is because of having, be widely used in ultraprecise processing, measure in the equipment industry, vacuum laser wavelength accuracy (laser frequency stability) has determined the highest relative measurement uncertainty that interferometer measuration system can reach, become one of key problem of quick ultraprecise laser interferometry technology, under defence equipment, the impetus of microelectronics development of manufacturing to the ultraprecise process requirements, laser interferometry technology relative measurement accuracy demand is about to break through 10 ^-8, correspondingly the frequency accuracy of interfering light source has been proposed 10 ^-8～10 ^-9Requirement, in the ultraprecise process unit, often need especially a plurality of spatial degrees of freedom are carried out the multidimensional synchro measure, this multidimensional measure demand will cause total laser power consumption of interferometer measuration system to be increased to more than the 5mW, adopt the frequency stabilized carbon dioxide laser more than 3 to carry out measurement in a closed series when this will seek common ground.Even yet for the frequency stabilized carbon dioxide laser of the same model of same producer batch, consistency of its output light frequency also only can reach 1 * 10 ^-7This wavelength standard that will bring, wave length shift and the inconsistent problem of space coordinates, thus the integrated measurement accuracy of whole multi-dimension laser interference system influenced.Therefore needing the consistent wavelength of precision frequency stabilization, antijamming capability, Output optical power and a plurality of frequency stabilized carbon dioxide lasers of the single frequency stabilized carbon dioxide laser of raising is the problem that the laser application technique field presses for solution.

Adopt light source to mainly contain vertical zeeman frequency stabilization laser at present in the laser interferometer, dual vertical mode stable frequency laser, iodine stabilizd laser, its laser frequency stabiliz ation method mainly can be divided into piezoelectric ceramic frequency stabilizing method, heating wire frequency stabilizing method, discharging current frequency stabilizing method and air-cooled frequency stabilizing method etc. according to the long difference of regulating actuator in chamber.

The relative accuracy of iodine stabilizd laser output light center frequency is up to 10 ^-11～10 ^-12, and many similar laser centre frequency consistency can reach 10 ^-11Yet,, the iodine stabilizd laser output light of chamber internal modulation is laser of frequency modulation, and the modulation depth of its frequency of light wave is several MHz, and therefore laser relative frequency accuracy is 10 generally ^-8In addition, the power output of such iodine stabilizd laser has only tens μ W, adopts piezoelectric ceramic as the long trim in chamber, and the process structure complexity costs an arm and a leg, and the piezoelectric creep is big and life cycle short, and warm-up time is long, resistance to shock is relatively poor.

Have modulation, luminous power shortcoming less than normal in order to overcome iodine frequency stabilized He-Ne laser output laser frequency, the breadboard R.R.Donaldson of U.S. Lawrence Livemore etc. has developed the 633nm helium neon laser (R.R.Donaldson of rrequency-offset-lock, S.R.Paterson.Design and Construction of aLarge, Vertical-axis Diamond Turning Machine.Proc.Of SPIE.1983, (433): 62～67).The characteristics of this laser are another iodine stabilizd lasers of laser high precision tracking that is freely turned round, and depart from the fixing frequency values of iodine stabilizd laser one, thereby both kept the high advantage of iodine stabilizd laser centre frequency relative accuracy, again can the unmodulated high power laser of output frequency, its relative frequency accuracy reaches 10 ^-9, power output reaches 15mW.Yet such laser adopts external cavity type cavity resonator structure and piezoelectric ceramic regulating element, removes outside the deficiency of length warm-up time, antivibration characteristic difference, and whole laser device volume is very huge.At present, such laser only is used for indivedual special-purpose large-scale ultraprecise process equipments, and need take extra vibration protection.

The main light source of other that adopt in the laser interferometer is Zeeman frequency stabilized carbon dioxide laser and double-longitudinal-mode laser, the Zeeman two-frequency laser has wen-frequency characteristics and reliability preferably, but the acquisition of double-frequency laser needs complementary field, the manufacturing process complexity, cost is higher, its frequency difference is less than 3MHz in addition, so its measuring speed is restricted, can not adapt to the occasion that present high speed is measured, the hot frequency-stabilizing method cost of two longitudinal modes is low, frequency regulator is simple, can reach the precision frequency stabilization with the same magnitude of traditional Zeeman frequency stabilized carbon dioxide laser again, thereby has obtained using widely.

At the stabilizing double-longitudinal mold laser frequency problem, Balhorn etc. have proposed to control the stabilizing double-longitudinal mold laser frequency method (R.Balhorn of cavity length by adjusting the laser tube discharging current, H.Kunzmann, F.Lebowsky.Frequency Stabilization of Internal-Mirror Helium-Neon Lasers.Applied Optics, 1972,11 (4): 742～746).This method have thermal inertia little, regulate the high advantage of efficient, but the centre frequency of laser gain curve is subjected to the influence that discharging current changes easily and changes, its relative frequency accuracy is no more than 10 ^-7

In order to improve the relative frequency stability of double-longitudinal-mode laser, Britain Renishaw company is in hot frequency stabilization double-longitudinal-mode laser method (the international monopoly WO8801798:Pre-heat ControlSystem for a Laser that has proposed based on heating wire; International monopoly WO8801799:Frequency Stabilized Laser andControl System Therefor), the feedback signal that this method is controlled as frequency stabilization with the difference of the luminous power of two kinds of crossed polarized lights of double-longitudinal-mode laser output, according to the frequency stabilization control algolithm, change the operating current that is wrapped in heating wire on the laser tube outer wall, temperature and the chamber of adjusting laser tube are long, thus the frequency of stabilized lasers pipe output laser.Domestic aspect, Sichuan University and Harbin Institute of Technology in proposed respectively in recent years based on electromagnetic induction heating stabilizing double-longitudinal mold laser frequency method (Chinese patent CN100367579: the frequency regulator of double-longitudinal-mode laser electromagnetic induction heating and frequency-stabilizing method thereof) still, regulate chamber progress row frequency stabilization owing to adopt electrothermal device, the preheating target temperature generally exceeds laser tube natural preheating equilibrium temperature, therefore differ greatly following warm-up time in different ambient temperatures, the drift that higher preheat temperature of while has been brought the performance parameter of electrooptical device and other devices, the instability that has caused the frequency stabilization control circuit system, and higher working temperature has reduced the laser tube working life.

Regulate the above-mentioned shortcoming of the long frequency-stabilizing method in chamber in order to solve electrothermal device, Harbin Institute of Technology has proposed a kind of stabilizing double-longitudinal mold laser frequency method based on thermoelectric cooling module (Chinese patent CN100382398: based on the stabilizing double-longitudinal mold laser frequency method and apparatus of thermoelectric cooling module).This method adds reverse current to thermoelectric cooling module laser tube is preheated to its heat balance temperature that turns round naturally, size and Orientation by control thermoelectric cooling module electric current changes laser resonant cavity chamber length to control the difference of the two longitudinal mode luminous powers of laser output is zero again, reaches the purpose of frequency stabilization.Lengthening warm-up time of having avoided existing frequency regulator to occur along with ambient temperature is different, pre-heat effect is undesirable, is subject to the shortcoming of ambient temperature, air velocity variable effect.But in the heat transfer structure of its design, thermoelectric refrigerating unit is installed in the same side of laser tube, causes the laser tube outer wall to be heated or freezes inhomogeneously, has temperature gradient, and then causes the radial distortion of laser tube, the stability of influence output laser frequency.This class dual vertical mode stable frequency laser is still with the centre frequency of the laser gain curve frequency reference point as frequency stabilization control in addition, and this centre frequency is subjected to the influence of factors such as temperature, air pressure easily and change, and laser relative frequency accuracy is difficult to surpass 10 ^-8

Propositions such as the Umeda of Japan Government utilize air-cooled effect to regulate the long method (N.Umeda of resonant cavity, M.Tsukiji, H.Takasaki.Stabilized 3He-20Ne Transverse Zeeman Laser.Applied Optics.1980,19:442～450.).The basic principle of this regulative mode is: laser-tube cavity places ventilating air to reach approximate thermal equilibrium, utilize fan to regulate the speed of ventilating air, because ambient temperature is lower than the laser-tube cavity temperature, the rotating speed that increases fan can reduce the temperature of laser-tube cavity, and the rotating speed that reduces fan can make the temperature of laser-tube cavity increase, and regulates the long purpose in chamber thereby reach.It is long that Umeda etc. utilize air-cooled effect to regulate the transverse zeeman laser resonant cavity, obtained 10 ^-10Short-term frequency stability.The long regulative mode in this chamber once was applied in the frequency stabilized carbon dioxide laser product of Teletrac company.Yet, being subjected to surrounding air humidity, influence of temperature variation, the frequency stabilization model parameter changes greatly, makes to adopt the long frequency stabilized carbon dioxide laser of air-cooled effect adjusting resonant cavity lower to industry spot environmental factor adaptive faculty, can not realize the high accuracy frequency stabilization effectively.

In order further to improve the relative frequency accuracy of dual vertical mode stable frequency laser, Japanese scholar FumioMurakami etc. absorbs Frequency Stabilization Technique with iodine and is applied in the dual vertical mode stable frequency laser, and dual vertical mode stable frequency laser relative frequency accuracy has been brought up to 10 ^-9(Fumio Murakami, et al.FrequencyStabilization of 633-nm He-Ne Laser by Using Frequency ModulationSpectroscopy of ¹²⁷I ₂Enhanced by an External Optical Cavity.Electronics andCommunications in Japan.2000, Part 2, Vol.83, No.3:1-9).Dual vertical mode stable frequency laser is the intracavity structure in this method, and its auxiliary optical chamber of outside increase is used to improve the external intensity of laser, thereby satisfies ¹²⁷I ₂The laser power requirement of molecule saturated absorption.Yet, introduce the auxiliary optical chamber and cause whole apparatus structure complicated, and the auxiliary optical chamber adopted piezo ceramic element, reduced the antivibration ability of device.

In sum, regulate and be locked in based on piezoelectric ceramic ¹²⁷I ₂Iodine stabilizd laser on the hyperfine absorption line is though its centre frequency relative accuracy reaches or is better than 10 ^-11, and the consistency of many iodine stabilizd laser centre frequencies reaches 10 ^-11, but because power output is little, resistance to shock is poor, operational environment is had relatively high expectations etc. shortcoming, can't directly apply to during industry spot measures; The ambient temperatures simple in structure but different based on the dual vertical mode stable frequency laser of electrothermal device differ greatly following warm-up time, the drift and the reduction in laser tube life-span that higher preheat temperature of while has been brought the performance parameter of electrooptical device and other devices, though the thermoelectric cooling frequency-stabilizing method that Harbin Institute of Technology proposes has solved the shortcoming of above-mentioned electrothermal device frequency-stabilizing method, but there is defective in its heat transfer structure, can not evenly heat or freeze laser tube, influence the frequency stability of laser, the relative frequency accuracy is difficult to break through 10 ^-8, the frequency invariance between while many dual vertical mode stable frequency lasers only can reach 10 ^-610 ^-7, adopting multi-station laser to cooperate at needs and carry out the occasion of various dimensions synchro measure, this will bring the inconsistent problem of wavelength standard, wave length shift and space coordinates, thereby influence the integrated measurement accuracy of interferometer measuration system; Rrequency-offset-lock helium neon laser based on piezoelectric ceramic reaches 10 with the dual vertical mode stable frequency laser frequency relative accuracy that uses iodine to absorb Frequency Stabilization Technique ^-9, but complex structure, antivibration ability, applicable situation is subjected to strict restriction.As seen, existing frequency stabilized carbon dioxide laser technology will be difficult to satisfy the requirement of ultraprecise processing of new generation and measuring technique development.

Summary of the invention

Deficiency at existing laser frequency stabilization technology, the present invention proposes double longitudinal-mode thermoelectric cooling frequency-offset-lock method and device based on iodine frequency stabilization reference, its objective is the advantage that merges iodine stabilizd laser and dual vertical mode stable frequency thermoelectric cooling frequency stabilized carbon dioxide laser, for ultraprecise processing and the measuring technique that develops rapidly provides a kind of more high-precision, new pattern laser light source that can directly apply to industry spot.

Purpose of the present invention is achieved through the following technical solutions:

A kind of double longitudinal-mode thermoelectric cooling frequency-offset-lock method based on iodine frequency stabilization reference may further comprise the steps:

(1) open the iodine stabilizd laser power supply, after preheating and frequency stabilization process, the iodine stabilizd laser operating frequency is locked in ¹²⁷I ₂Molecule is positioned on the hyperfine absorption line of 633nm wave band, and its output laser is the frequency modulation linearly polarized light, and the light wave centre frequency is designated as v _Ro, instantaneous frequency is designated as v _r, be designated as T modulation period _m, this linearly polarized light is separated into the n road by light-splitting device, is designated as light beam X ₁, X ₂..., X _n, its centre frequency v _RoFrequency reference as double-longitudinal-mode laser frequency-offset-lock;

(2) open double-longitudinal-mode laser L ₁, L ₂..., L _nPower supply, all double-longitudinal-mode lasers enter warm simultaneously, measure current environmental temperature T _e, and definite according to current environmental temperature, preheating target temperature value T _Set, and T _e＜T _Set, by thermoelectric cooling module to double-longitudinal-mode laser L ₁, L ₂..., L _nLaser tube carry out preheating, and according to Current Temperatures T _RealWith preheating target temperature T _SetDifference constantly adjust thermoelectric cooling module reverse current value size, make the temperature of laser tube be tending towards predefined temperature value T gradually _Set, and reaching thermal equilibrium state, this moment, each laser tube output laser included two mutually orthogonal longitudinal mode light of polarization direction, utilized polarized light splitting device to isolate one of them longitudinal mode light as double-longitudinal-mode laser L ₁, L ₂..., L _nOutput light, be designated as light beam Y ₁, Y ₂..., Y _n, corresponding frequency of light wave is designated as v ₁, v ₂..., v _n

(3) double-longitudinal-mode laser L ₁, L ₂..., L _nAfter finishing, its warm enters the frequency locking control procedure, with light beam X ₁, X ₂..., X _nRespectively with light beam Y ₁, Y ₂..., Y _nCarry out optical frequency mixing and form n road beat frequency light signal, utilize the high frequency light electric explorer that n road beat frequency light signal is converted to the n road signal of telecommunication, wherein the frequency of the i road signal of telecommunication is | v _i-v _r| (i=1,2 ..., n);

(4) the n road signal of telecommunication is behind signal condition, and its frequency values is measured by the frequency measurement module, gets sampling time τ 〉=200T _m, then measure the mean value of signal of telecommunication frequency in the time τ, i.e. light beam X ₁, X ₂..., X _nCentre frequency v _RoWith light beam Y ₁, Y ₂..., Y _nThe frequency of light wave difference, be designated as Δ v ₁, Δ v ₂..., Δ v _n, Δ v wherein _i=| v _i-v _Ro| (i=1,2 ..., n);

(5) dual vertical mode stable frequency laser L ₁, L ₂..., L _nAt frequency of light wave difference DELTA v separately ₁, Δ v ₂..., Δ v _nThe same monotony interval that value changes is realized the locking of laser frequency, and the predefined offset frequency reference value of all lasers Δ v _SetIdentical, with the frequency of light wave difference DELTA v that measures ₁, Δ v ₂..., Δ v _nAs the feedback signal of frequency locking closed-loop control, with predefined offset frequency reference value Δ v _SetAsk poor, according to frequency of light wave difference DELTA v ₁, Δ v ₂..., Δ v _nWith offset frequency reference value Δ v _SetAsk the positive and negative and big or small adjustment thermoelectric cooling module of poor gained difference to apply the forward and reverse and big or small of electric current, thereby control it, and then change temperature, cavity length and the laser longitudinal module frequency of laser tube, make Δ v laser tube refrigeration and heating ₁, Δ v ₂..., Δ v _nBe tending towards Δ v _Set

(6) as Δ v ₁=Δ v ₂=...=Δ v _n=Δ v _SetThe time, double-longitudinal-mode laser L ₁, L ₂..., L _nThe frequency locking control procedure is finished, the frequency lock of all double-longitudinal-mode lasers output this moment laser on same frequency values, i.e. v ₁=v ₂=...=v _n=v _Ro+ Δ v _Set(or v ₁=v ₂=...=v _n=v _Ro-Δ v _Set);

(7) default offset frequency reference value is adjusted into Δ v ' _Set, repeating step (4), (5) and (6), double-longitudinal-mode laser L ₁, L ₂..., L _nThe frequency values v that the frequency lock of output laser is being reset _Ro+ Δ v ' _Set(or v _Ro-Δ v ' _Set) on, frequency v _Ro+ Δ v ' _Set(or v _Ro-Δ v ' _Set) and frequency v _Ro+ Δ v _Set(or v _Ro-Δ v _Set) gain values of correspondence is inequality on the laser gain curve, thereby double-longitudinal-mode laser L ₁, L ₂..., L _nThe performance number of output laser also obtains adjusting.

A kind of double longitudinal-mode thermoelectric cooling rrequency-offset-lock device based on iodine frequency stabilization reference, comprise iodine stabilizd laser power supply, iodine stabilizd laser, first status indicator lamp, fiber optic splitter, comprise also in the device that n 〉=1 structure is identical and be the double-longitudinal-mode laser L that concerns in parallel ₁, L ₂..., L _nWherein the assembly structure of each double-longitudinal-mode laser L is: the double-longitudinal-mode laser power supply is connected with laser tube, before first polarizing beam splitter is placed on laser tube master output, second polarizing beam splitter is placed between the input of secondary output of laser tube and optical-fiber bundling device, another input of optical-fiber bundling device is connected with one of output of fiber optic splitter, analyzer is placed between the output and high-speed photodetector of optical-fiber bundling device, high-speed photodetector, high-speed frequency divider, preamplifier, post amplifier, high-speed comparator, the frequency measurement module, microprocessor, D/A converter, the thermoelectric cooling module driver, thermoelectric cooling module and heat transfer structure thereof connect successively, its heat transfer structure is to begin equipped successively from inside to outside heat conduction glue-line a from laser tube, the copper pipe heat-conducting layer, heat conduction glue-line b, thermoelectric cooling module, heat conduction glue-line c, radiator, thermal insulation layer constitutes, and respectively having two thermoelectric cooling modules and radiator to be symmetrical in laser tube outer wall both sides places, the laser tube temperature transducer is in the inboard heat conduction glue-line of the copper pipe heat-conducting layer a, environment temperature sensor is placed in the air, its output termination microprocessor, second status indicator lamp is communicated with microprocessor.

Its detective bandwidth of described high-speed photodetector is greater than 500MHz.

The present invention has following characteristics and good result:

(1) dual vertical mode stable frequency laser adopts the intracavity structure among the present invention, and adjust executive component as cavity length with thermoelectric cooling module, adopt the design of thermoelectric refrigerating unit symmetry heat transfer structure simultaneously, eliminated the laser tube influence of the inhomogeneous laser tube radial distortion that causes of being heated output frequency stability; Compare as the executive component of cavity length adjustment with electrothermal device, temperature when having reduced laser tube frequency stabilization work, strengthened adaptive capacity to environment, shortened warm-up time, the temperature that has reduced electrooptical device and other device performance parameters is floated the influence to the frequency stabilization effect, improved the life-span of laser tube, this is one of innovative point that is different from prior art.

(2) the present invention adopts the relative frequency accuracy to reach 10 ^-11Iodine Frequency Stabilized Lasers centre frequency as the frequency reference of double-longitudinal-mode laser frequency locking, and a plurality of double-longitudinal-mode lasers are carried out frequency lock in parallel, all dual vertical mode stable frequency laser output laser have unified frequency values, overcome in the common power balanced type dual vertical mode stable frequency laser and to have caused many shortcomings that the frequency stabilized carbon dioxide laser frequency invariance is relatively poor owing to frequency reference is inconsistent, can be with the frequency invariance of many frequency stabilized carbon dioxide lasers from 10 ^-7Bring up to 10 ^-9, this be different from prior art innovative point two.

(3) by offset frequency reference value Δ v is set _SetValue, when making the frequency of the output of dual vertical mode stable frequency laser among the present invention laser be positioned near the laser gain center of curve frequency, its Output optical power can reach the two vertical frequency stabilization mode laser of common power balanced type more than 1.5 times, this be different from prior art innovative point three.

Description of drawings

Fig. 1 is the principle schematic of apparatus of the present invention

Fig. 2 is the double longitudinal-mode thermoelectric cooling rrequency-offset-lock apparatus structure schematic diagram based on iodine frequency stabilization reference

Fig. 3 be among Fig. 2 A-A to cutaway view, i.e. heat transfer structure schematic diagram.

Fig. 4 is pre-thermal equilibrium temperature of double-longitudinal-mode laser and ambient temperature graph of relation.

Fig. 5 is the closed-loop control system schematic diagram of dual vertical mode stable frequency laser warm in apparatus of the present invention

Fig. 6 is the control system schematic diagram of common power balanced type dual vertical mode stable frequency laser frequency stabilization process

Fig. 7 is the closed-loop control system schematic diagram of dual vertical mode stable frequency laser frequency lock process in apparatus of the present invention

Fig. 8 is the relative position schematic diagram of dual vertical mode stable frequency laser frequency lock position among the present invention and reference frequency

(a) and (b) are respectively dual vertical mode stable frequency laser operating frequency and laser gain coefficient graph of a relation among common power balanced type dual vertical mode stable frequency laser, the present invention among Fig. 9

Figure 10 is the correlation schematic diagram of the thermoelectric cooling module sense of current among the present invention and heat exchange direction

Figure 11 is the preheat temperature curve chart of the embodiment of the invention under different initial environment

Curve a, b and c are respectively dual vertical mode stable frequency laser output laser short-term relative frequency drift simulation curve among iodine frequency stabilized He-Ne laser, common power balanced type double-longitudinal-mode laser and the present invention among Figure 12

Curve a, b and c are respectively dual vertical mode stable frequency laser output laser long-run relative frequency drift simulation curve among iodine frequency stabilized He-Ne laser, common power balanced type double-longitudinal-mode laser and the present invention among Figure 13

Among the figure, 1 iodine stabilizd laser power supply, 2 iodine stabilizd lasers, 3 first status indicator lamps, 4 fiber optic splitters, 5 double-longitudinal-mode laser power supplys, 6 microprocessors, 7 environment temperature sensors, 8 laser tube temperature transducers, 9 laser tubes, 10 D/A converters, 11 thermoelectric cooling module drivers, 12 thermoelectric cooling modules, 13 second polarizing beam splitters, 14 first polarizing beam splitters, 15 optical-fiber bundling devices, 16 analyzers, 17 high-speed photodetectors, 18 high-speed frequency dividers, 19 preamplifiers, 20 signal amplifiers, 21 high-speed comparators, 22 frequency measurement modules, 23 second status indicator lamps, 24 heat conduction glue-line a, 25 copper pipe heat-conducting layers, 26 heat conduction glue-line b, 27 heat conduction glue-line c, 28 radiators, 29 thermal insulation layers.

Embodiment

Below in conjunction with accompanying drawing embodiment of the present invention is described in detail.

Double-longitudinal-mode laser frequency-offset-lock device based on thermoelectric cooling module comprises: iodine stabilizd laser power supply 1, iodine stabilizd laser 2, first status indicator lamp 3, fiber optic splitter 4 comprise also in the device that n 〉=1 structure is identical and are the double-longitudinal-mode laser L that concerns in parallel ₁, L ₂..., L _nWherein the assembly structure of each double-longitudinal-mode laser L as shown in Figure 2: double-longitudinal-mode laser power supply 5 is connected with laser tube 9, before first polarizing beam splitter 14 is placed on laser tube 9 main outputs, second polarizing beam splitter 13 is placed between the input of laser tube 9 secondary outputs and optical-fiber bundling device 15, another input of optical-fiber bundling device 15 is connected with one of output of fiber optic splitter 4, analyzer 16 is placed between the output and high-speed photodetector 17 of optical-fiber bundling device 15, high-speed photodetector 17, high-speed frequency divider 18, preamplifier 19, post amplifier 20, high-speed comparator 21, frequency measurement module 22, microprocessor 6, D/A converter 10, thermoelectric cooling module driver 11, thermoelectric cooling module 12 and heat transfer structure thereof connect successively, its heat transfer structure is as shown in Figure 3: be from the equipped successively from inside to outside heat conduction glue-line a 24 of laser tube 9 beginnings, copper pipe heat-conducting layer 25, heat conduction glue-line b 26, thermoelectric cooling module 12, heat conduction glue-line c 27, radiator 28, thermal insulation layer 29 constitutes, and respectively having two thermoelectric cooling modules 12 and radiator 28 to be symmetrical in laser tube 9 outer wall both sides places, laser tube temperature transducer 8 is in the copper pipe heat-conducting layer 25 inboard heat conduction glue-line a24, environment temperature sensor 7 is placed in the air, its output termination microprocessor 6, the second status indicator lamps 23 are communicated with microprocessor 6.

High-speed photodetector 17 bandwidth of using in the device of the present invention are greater than 500MHz.

In view of comprising a plurality of dual vertical mode stable frequency laser L in the device ₁, L ₂..., L _n, and the control procedure of the preheating of all dual vertical mode stable frequency lasers and frequency lock is in full accord, below only to dual vertical mode stable frequency laser L ₁Make process prescription, these descriptive texts are equally applicable to arbitrary other dual vertical mode stable frequency laser in the device.

When device embodiment starts working, open iodine stabilizd laser power supply 1, iodine stabilizd laser 2 enters preheating and frequency stabilization process, when said process is finished, enable first status indicator lamp 3, expression iodine stabilizd laser 2 enters steady-working state, and this moment, laser 2 output light were laser of frequency modulation, and its instantaneous frequency can be expressed as:

v _r(t)＝v _ro+Δv _mcos(2πf _mt)

V in the formula _Ro, Δ v _m, f _mBe respectively laser center frequency, frequency modulation(FM) amplitude, FM signal frequency, Δ v _m=3MHz, f _m=2KHz.Laser 2 output laser coupled enter fiber optic splitter 4, are separated into n road frequency reference light beam, are designated as light beam X ₁, X ₂..., X _n

In the situation of first status indicator lamp 3 when enabling, open dual vertical mode stable frequency laser power supply 5, dual vertical mode stable frequency laser enters warm, Fig. 4 is double-longitudinal-mode laser ambient temperature and preheating heat equilibrium temperature curve chart, its preheating heat equilibrium temperature difference under the varying environment temperature, but laser tube is identical with the heat-exchange power of ambient temperature under each thermal equilibrium state, and heat-exchange power is relevant with the temperature difference, and promptly temperature and ambient temperature all have the fixing temperature difference.Determine preheating heat equilibrium temperature T according to the preheat temperature curve _SetFig. 5 is the closed-loop control system schematic diagram of double-longitudinal-mode laser warm.The ambient temperature that microprocessor 6 measures according to environment temperature sensor 7 is set the thermal equilibrium temperature T of preheating _Set, and with T _SetAs the reference input of preheating closed-loop control system, measure the temperature t of laser tube 9 simultaneously with laser tube temperature transducer 8 _RealAs feedback signal, microprocessor 6 calculates the difference of the two, and according to the MPC control algolithm, the output digital controlled signal, by D/A converter 10 digital-to-analogue conversions is analog signal, this analog signal is amplified through thermoelectric cooling module driver 11, is used to control the operating current of thermoelectric cooling module 12, and laser tube 9 is heated.

Reach thermal equilibrium temperature T at laser tube 9 _SetAfter, microprocessor 6 switch dual vertical mode stable frequency laser L ₁Enter the frequency lock control procedure.Fig. 7 has illustrated the closed-loop control process of dual vertical mode stable frequency laser frequency lock.Laser tube 9 major and minor outputs are all exported two mutually orthogonal longitudinal mode light of polarization direction, utilize first polarizing beam splitter 14 and second polarizing beam splitter 13 to separate two longitudinal mode light of major and minor output respectively, the longitudinal mode light of wherein secondary output horizontal polarization is used for frequency locking control, is designated as light beam Y ₁, its frequency is designated as v ₁, the longitudinal mode light of main output horizontal polarization is as dual vertical mode stable frequency laser L ₁Output light.Light beam Y ₁Be coupled into optical-fiber bundling device 15, with reference beam X ₁Be combined into a branch of, form the beat frequency light signal by analyzer 16, and be converted to voltage signal by high-speed photodetector 17, this voltage signal is successively by high-speed frequency divider 18, preamplifier 19, post amplifier 20, high-speed comparator 21, become square-wave signal, send into frequency measurement module 22 and carry out frequency measurement.The instantaneous frequency of square-wave signal can be expressed as:

f(t)＝f _c+Δfcos(2πf _mt)

F in the formula _c=| v ₁-v _Ro|/M, Δ f=Δ v _m/ M, M are the frequency divider divider ratio.During frequency measurement, get sampling time τ=(N+ ε) T _m, T _m=1/f _m, N and ε are respectively time τ and comprise T _mInteger, decimal periodicity, then can measure time τ inner light beam X ₁With light beam Y ₁The mean value of optical frequency difference:

$\mathrm{\Δ}{v}_1=\frac{M}{(N+\mathrm{\ϵ})T_m}{\∫}_0^{(N+\mathrm{\ϵ})T_m}f\left(t\right)\mathrm{dt}$

$=|v_1-v_{\mathrm{ro}}|+\frac{\mathrm{\&Delta;}{v}_{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="A2009100725230019H3.png,A2009100725230020H1.png"\; state="\{\{state\}\}">m</figure-callout>}}}{2\mathrm{\&pi;}(N+\mathrm{\&epsiv;})}\sin \left(2\mathrm{\&pi;f\&epsiv;}{T}_m\right)$

V in the sampling time τ has been supposed in the derivation of following formula ₁Be constant, this is realistic situation, under heat balance or near-thermal poised state, and v ₁Be gradual amount, can be approximately constant in the sampling time τ.First actual value that can be considered frequency measurement in the following formula, its numerical value are tens to hundreds of MHz, and second error term that can be considered frequency measurement is got N=200 in this example, and then the numerical value of error term is not more than Δ v _m/ [2 π (N+ ε)] ≈ 2.4KHz.The frequency measurement error influences 10 for the rrequency-offset-lock precision ^-11Magnitude, so frequency-measurement accuracy has satisfied rrequency-offset-lock relative accuracy 10 ^-9Requirement.

Microprocessor 6 is according to the frequency values Δ v that measures ₁, realize that at the same monotony interval of its variation the locking of laser frequency, Fig. 8 are the relative position schematic diagrames of dual vertical mode stable frequency laser frequency lock position and reference frequency among the present invention.The bandwidth of figure high speed photodetector 17 is Δ v _Detect, the frequency Δ v that frequency measurement module 22 measures ₁Be light beam X ₁Centre frequency v _RoWith light beam Y ₁Frequency v ₁The absolute value of difference, according to v ₁The v that concerns with laser tube chamber length ₁=qc/2 η l, in the formula, c is the light velocity, and q is the longitudinal mode ordinal number, and η is the refractive index in the resonant cavity, and l is long for the laser tube chamber.Double-longitudinal-mode laser levels off to heat balance in the warm-up phase temperature, and temperature rises with speed slowly, and the long l of laser tube chamber increases, and can form the longitudinal mode of each horizontal polarization direction of vibrating, its frequency of oscillation v for double-longitudinal-mode laser ₁Change from big to small, and Δ v ₁=| v ₁-v _Ro| (Fig. 8 has shown Δ v ₁With v ₁Changing Pattern) from the detective bandwidth Δ v of high-speed photodetector 17 _DetectTo zero, again from zero to Δ v _DetectCarry out linear change, comprise two monotony intervals: the interval and dull interval that rises, therefore the Δ v of setting fall in dullness _SetUnder the situation, the resulting Δ v of the longitudinal mode of corresponding certain level polarization direction ₁, two frequency lock intervals are arranged, in order to make dual vertical mode stable frequency laser L ₁, L ₂..., L _nOutput laser has unified frequency values, all dual vertical mode stable frequency laser unifications need be locked onto v _RoThe same side, promptly realize the locking of laser frequency, so microprocessor 6 is according to Δ v at the same monotony interval of its variation ₁Conversion trend judge its residing monotony interval, and lock, as the Δ v that measures by measurement module 22 being in the horizontal direction longitudinal mode that sets in the monotony interval in the change procedure ₁Be included in the Δ v that control algolithm sets _SetEnter the frequency stabilization stage in the time of in the scope.This example is chosen dullness and is fallen interval between the lock room.

The Δ v of gained measured frequency measurement module 22 by frequency stabilization stage microprocessor 6 ₁Value is as the feedback signal of frequency lock closed-loop control system, simultaneously with predefined offset frequency reference value Δ v _Set(this example is got Δ v _Set=120MHz) as the reference input of control system, microprocessor 6 calculates the difference of the two, positive and negative and big or small adjustment output digital controlled signal according to MPC control algolithm and gained difference, by D/A converter 10 digital-to-analogue conversions is analog signal, this analog signal is amplified through thermoelectric cooling module driver 11, be used to regulate thermo-electric cooler 12 and apply the forward and reverse and big or small of electric current, thereby control it to laser tube refrigeration and heating, and then temperature, cavity length and the laser longitudinal module frequency of change laser tube, make Δ v ₁, Δ v ₂..., Δ v _nBe tending towards Δ v _Set, as Δ v ₁≈ Δ v _SetThe time, double-longitudinal-mode laser L ₁The frequency lock process is finished, and enables second status indicator lamp 23, expression double-longitudinal-mode laser L ₁Enter steady-working state, at this moment v ₁=v _Ro+ Δ v _Set

Default offset frequency reference value is adjusted into Δ v ' _Set, repeat above-mentioned frequency lock process, then double-longitudinal-mode laser L ₁The frequency of output laser is adjusted into v _Ro+ Δ v ' _SetBecause frequency v _Ro+ Δ v ' _SetWith frequency v _Ro+ Δ v _SetGain values corresponding on the laser gain curve is inequality, double-longitudinal-mode laser L ₁The power of output laser also obtains adjusting, and therefore selects suitable default offset frequency reference value Δ v _SetValue can realize double-longitudinal-mode laser L ₁The maximization of Output optical power, its numerical value can reach the dual vertical mode stable frequency laser of common power balanced type more than 1.5 times, in conjunction with Fig. 7 this point are described.

(a) is the schematic diagram that concerns of common power balanced type dual vertical mode stable frequency laser operating frequency and gain coefficient among Fig. 9.After the frequency stabilization, two longitudinal mode light frequency v of laser _L, v _RAbout laser gain center of curve v _oSymmetry, the frequency interval of two longitudinal modes can be expressed as

$\mathrm{\&Delta;}{v}_q=v_R-v_L=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="A2009100725230019H3.png,A2009100725230020H1.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\mathrm{\&eta;l}}$

Among Fig. 9 (b) be among the present invention dual vertical mode stable frequency laser operating frequency and gain coefficient concern schematic diagram, with dual vertical mode stable frequency laser L ₁Be example, the latched position of its output laser frequency is v _Ro+ Δ v _Set(since the difference of laser tube parameter, frequency reference v _RoWith laser gain center of curve frequency v _oDo not overlap v _RoNumerical value can be greater than or less than v _o, be v among the figure _Ro≤ v _oSituation).If choose offset frequency reference value Δ v _Set≈ v _o-v _Ro, then export the frequency values v of laser ₁≈ v _oThereby, obtain maximum laser gain numerical value.

Figure 10 has illustrated thermoelectric cooling module 12 senses of current and heat energy direction correlation among the embodiment.

Thermoelectric cooling module 12 is to use the relevant thermoelectric effect with other of the significant peltier effect of semi-conducting material and the semiconductor subassembly that manufactures and designs among the embodiment, according to there being volume little, life-span is long, noiseless vibration and do not have advantage such as any pollution, principle is: when a N type semiconductor material and P type semiconductor material be unified into galvanic couple to the time, in this circuit, connect direct current after, the transfer of energy just can take place: electric current flows to P type element by N type element, joint absorbs heat, becomes cold junction; Electric current flows to N type element, joint release heat by P type element.Become the hot junction.The heat energy direction is determined by sense of current, absorbs heat and exothermic size and is determined by size of current.

When the positive electricity end input current of thermoelectric cooling module among the embodiment 12, heat energy is from laser tube 9 outputs, successively through heat conduction glue-line a24, copper pipe heat-conducting layer 25, heat conduction glue-line b26, thermoelectric cooling module 12, heat conduction glue-line c27, arrive radiator 28, radiator 28 has than large tracts of land, so heat is easy to loose in air by the form of cross-ventilation and radiation; When the extreme input current of negative electricity of thermoelectric cooling module among the embodiment 12, radiator 28 absorbs heat energy by the form of cross-ventilation and radiation from air, successively through heat conduction glue-line c27, thermoelectric cooling module 12, heat conduction glue-line b26, copper pipe heat-conducting layer 25, heat conduction glue-line a24 arrives laser tube 9.

Figure 11 has provided the preheat temperature curve chart of apparatus of the present invention embodiment under different initial environment, can draw under different initial temperature environment from plots changes, laser warm-up curve variation tendency basically identical, rise within 0.1 ℃ of the target temperature in temperature about 15 minutes, and rate of temperature change is very little, reaches heat balance substantially.Device is described in different industry spot, the preheating of elapsed time basically identical can both obtain heat balance, and frequency stabilization condition preferably is provided.

Fig. 6 is the control system schematic diagram of common power balanced type dual vertical mode stable frequency laser frequency stabilization process, with Fig. 5 as seen, in the common frequency stabilization control system, because laser frequency can't directly be measured, adopt optical power difference etc. amount is as feedback control signal indirectly for this reason, so it is a kind of half-closed loop control system in essence; In this method owing to adopt high-precision iodine stabilizd laser centre frequency to carry out mixing, thereby laser frequency value that can high-precision collection double-longitudinal-mode laser as Control and Feedback, so it is a kind of closed-loop control system in essence.On control performance, have than big-difference based on semiclosed loop and closed-loop control system, its frequency stabilization control effect is described in conjunction with Figure 10 and Figure 11.

Curve a is an iodine stabilizd laser output laser short-term relative frequency drift simulation curve among Figure 12, and its ordinate is a relative frequency drift, is defined as (v _r-v _Ro)/v _RoFrom curve a as can be seen, the output frequency of iodine stabilizd laser has the modulation depth of about 6MHz, and the modulation angular frequency is 2KHz, so the short-term relative frequency drift is 10 generally ^-8, but its centre frequency short-term relative frequency drift will exceed 3 more than the order of magnitude than this numerical value.

Curve b is a common power balanced type dual vertical mode stable frequency laser output laser frequency short term drift simulation curve among Figure 12, and its longitudinal axis drift relatively is defined as (Δ v-Δ v _Ave)/v _Ro, Δ v=|v-v wherein _Ro|, v is the frequency of common power balanced type dual vertical mode stable frequency laser output laser, v _RoBe the centre frequency of iodine stabilizd laser output laser, Δ v _AveArithmetic mean for Δ v.From curve b as can be seen, the short-term relative frequency drift of common power balanced type dual vertical mode stable frequency laser output laser is 10 ^-8, not significantly drift of its centre frequency in a short time.

Curve c is dual vertical mode stable frequency laser output laser frequency short term drift simulation curve among the present invention among Figure 12, and its longitudinal axis relative frequency drift definition is identical with curve b.From curve c as can be seen, the relative drift of short-term frequency of dual vertical mode stable frequency laser output laser can reach 10 among the present invention ^-9, not significantly drift of its centre frequency in a short time.

Curve a, b and c are respectively dual vertical mode stable frequency laser output laser long-run relative frequency drift simulation curve among iodine stabilizd laser, common power balanced type dual vertical mode stable frequency laser and the present invention among Figure 13, and wherein the drift of the long-run relative frequency of iodine stabilizd laser and its short-term frequency drift class of a curve are seemingly; There is bigger long term drift in the centre frequency of common power balanced type dual vertical mode stable frequency laser output laser, and its long-run relative frequency drift reaches 10 ^-7The centre frequency of dual vertical mode stable frequency laser output laser does not have the obvious long drift in apparatus of the present invention, and its long-run relative frequency drift still is 10 ^-9

Claims (3)

1, a kind of double longitudinal-mode thermoelectric cooling frequency-offset-lock method based on iodine frequency stabilization reference is characterized in that this method may further comprise the steps:

(1) open the iodine stabilizd laser power supply, after preheating and frequency stabilization process, the iodine stabilizd laser operating frequency is locked in ¹²⁷I ₂Molecule is positioned on the hyperfine absorption line of 633nm wave band, and its output laser is the frequency modulation linearly polarized light, and the light wave centre frequency is designated as v _Ro, instantaneous frequency is designated as v _r, be designated as T modulation period _m, this linearly polarized light is separated into the n road by light-splitting device, is designated as light beam X ₁, X ₂..., X _n, its centre frequency v _RoFrequency reference as double-longitudinal-mode laser frequency-offset-lock;

(2) open double-longitudinal-mode laser L ₁, L ₂..., L _nPower supply, all double-longitudinal-mode lasers enter warm simultaneously, measure current environmental temperature T _e, and definite according to current environmental temperature, preheating target temperature value T _Set, and T _e＜T _Set, by thermoelectric cooling module to double-longitudinal-mode laser L ₁, L ₂..., L _nLaser tube carry out preheating, and according to Current Temperatures T _RealWith preheating target temperature T _SetDifference constantly adjust thermoelectric cooling module reverse current value size, make the temperature of laser tube be tending towards predefined temperature value T gradually _Set, and reaching thermal equilibrium state, this moment, each laser tube output laser included two mutually orthogonal longitudinal mode light of polarization direction, utilized polarized light splitting device to isolate one of them longitudinal mode light as double-longitudinal-mode laser L ₁, L ₂..., L _nOutput light, be designated as light beam Y ₁, Y ₂..., Y _n, corresponding frequency of light wave is designated as v ₁, v ₂..., v _n

(3) double-longitudinal-mode laser L ₁, L ₂..., L _nAfter finishing, its warm enters the frequency locking control procedure, with light beam X ₁, X ₂..., X _nRespectively with light beam Y ₁, Y ₂..., Y _nCarry out optical frequency mixing and form n road beat frequency light signal, utilize the high frequency light electric explorer that n road beat frequency light signal is converted to the n road signal of telecommunication, wherein the frequency of the i road signal of telecommunication is | v _i-v _r| (i=1,2 ..., n);

(4) the n road signal of telecommunication is behind signal condition, and its frequency values is measured by the frequency measurement module, gets sampling time τ 〉=200T _m, then measure the mean value of signal of telecommunication frequency in the time τ, i.e. light beam X ₁, X ₂..., X _nCentre frequency v _RoWith light beam Y ₁, Y ₂..., Y _nThe frequency of light wave difference, be designated as Δ v ₁, Δ v ₂..., Δ v _n, Δ v wherein _i=| v _i-v _Ro| (i=1,2 ..., n);

(5) dual vertical mode stable frequency laser L ₁, L ₂..., L _nAt frequency of light wave difference DELTA v separately ₁, Δ v ₂..., Δ v _nThe same monotony interval that value changes is realized the locking of laser frequency, and the predefined offset frequency reference value of all lasers Δ v _SetIdentical, with the frequency of light wave difference DELTA v that measures ₁, Δ v ₂..., Δ v _nAs the feedback signal of frequency locking closed-loop control, with predefined offset frequency reference value Δ v _SetAsk poor, according to frequency of light wave difference DELTA v ₁, Δ v ₂..., Δ v _nWith offset frequency reference value Δ v _SetAsk the positive and negative and big or small adjustment thermoelectric cooling module of poor gained difference to apply the forward and reverse and big or small of electric current, thereby control it, and then change temperature, cavity length and the laser longitudinal module frequency of laser tube, make Δ v laser tube refrigeration and heating ₁, Δ v ₂..., Δ v _nBe tending towards Δ v _Set

(6) as Δ v ₁=Δ v ₂=...=Δ v _n=Δ v _SetThe time, double-longitudinal-mode laser L ₁, L ₂..., L _nThe frequency locking control procedure is finished, the frequency lock of all double-longitudinal-mode lasers output this moment laser on same frequency values, i.e. v ₁=v ₂=...=v _n=v _Ro+ Δ v _Set(or v ₁=v ₂=...=v _n=v _Ro-Δ v _Set);

(7) default offset frequency reference value is adjusted into Δ v ' _Set, repeating step (4), (5) and (6), double-longitudinal-mode laser L ₁, L ₂..., L _nThe frequency values v that the frequency lock of output laser is being reset _Ro+ Δ v ' _Set(or v _Ro-Δ v ' _Set) on, frequency v _Ro+ Δ v ' _Set(or v _Ro-Δ v ' _Set) and frequency v _Ro+ Δ v _Set(or v _Ro-Δ v _Set) gain values of correspondence is inequality on the laser gain curve, thereby double-longitudinal-mode laser L ₁, L ₂..., L _nThe performance number of output laser also obtains adjusting.

2, a kind of double longitudinal-mode thermoelectric cooling rrequency-offset-lock device based on iodine frequency stabilization reference, comprise iodine stabilizd laser power supply (1), iodine stabilizd laser (2), first status indicator lamp (3), fiber optic splitter (4), it is characterized in that also comprising in the device that n 〉=1 structure is identical and be the double-longitudinal-mode laser L that concerns in parallel ₁, L ₂..., L _nWherein the assembly structure of each double-longitudinal-mode laser L is: double-longitudinal-mode laser power supply (5) is connected with laser tube (9), before first polarizing beam splitter (14) is placed on the main output of laser tube (9), second polarizing beam splitter (13) is placed between the input of secondary output of laser tube (9) and optical-fiber bundling device (15), one of output of another input of optical-fiber bundling device (15) and fiber optic splitter (4) is connected, analyzer (16) is placed between the output and high-speed photodetector (17) of optical-fiber bundling device (15), high-speed photodetector (17), high-speed frequency divider (18), preamplifier (19), post amplifier (20), high-speed comparator (21), frequency measurement module (22), microprocessor (6), D/A converter (10), thermoelectric cooling module driver (11), thermoelectric cooling module (12) and heat transfer structure thereof connect successively, its heat transfer structure is from the equipped successively from inside to outside heat conduction glue-line a (24) of laser tube (9) beginning, copper pipe heat-conducting layer (25), heat conduction glue-line b (26), thermoelectric cooling module (12), heat conduction glue-line c (27), radiator (28), thermal insulation layer (29) constitutes, and respectively having two thermoelectric cooling modules (12) and radiator (28) to be symmetrical in laser tube (9) outer wall both sides places, laser tube temperature transducer (8) is in copper pipe heat-conducting layer (25) the inboard heat conduction glue-line a (24), environment temperature sensor (7) is placed in the air, it exports termination microprocessor (6), and second status indicator lamp (23) is communicated with microprocessor (6).

3, the double longitudinal-mode thermoelectric cooling rrequency-offset-lock device based on iodine frequency stabilization reference according to claim 2, it is characterized in that: high-speed photodetector (17) detective bandwidth is greater than 500MHz.

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