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

Abstract

The dual-longitudinal-mode thermoelectric cooling bias frequency locking method and device based on iodine frequency stabilization reference belong to the field of laser application technology; the invention uses the iodine frequency stabilization laser center frequency with a relative frequency accuracy of ^10-11 as the reference frequency, The frequency of the output laser of the longitudinal mode laser is frequency-locked, so that multiple lasers and the reference frequency are kept at a fixed difference, and the relative frequency accuracy of the dual longitudinal mode laser can be improved from 10 ^-7 to 10 ^-8 to 10 ^-9 , the frequency consistency of multiple dual longitudinal mode lasers is increased from 10 ^-7 to 10 ^-9 , and at the same time, the symmetrical thermal structure of the thermoelectric cooler is used to preheat and adjust the cavity length for frequency stabilization, which eliminates the uneven heating of the laser tubes. The influence of radial distortion of the laser tube on the stability of the output frequency enhances the ability to adapt to the environment, shortens the warm-up time and improves the life of the laser tube.

Description

Dual longitudinal mode thermoelectric cooling bias frequency locking method and device based on iodine frequency stabilization reference

technical field

The invention belongs to the technical field of laser applications, in particular to a dual longitudinal mode thermoelectric cooling bias frequency locking method and device based on an iodine frequency stabilization reference.

Background technique

Laser interferometry technology is widely used in ultra-precision processing and measurement equipment industry due to its characteristics of non-contact, high precision, large measuring range, traceability, and multi-channel spectroscopic measurement. The accuracy of laser vacuum wavelength (laser frequency stability) determines It has become one of the core issues of fast ultra-precision laser interferometry technology to achieve the highest relative measurement uncertainty that the interferometry system can achieve. Under the impetus of the development of national defense equipment and microelectronics manufacturing industry for ultra-precision processing, laser The relative measurement accuracy requirement of interferometry technology is about to exceed 10 ^-8 , and correspondingly, the frequency accuracy of the interference light source is required to be 10 ^-8 ~ 10 ^-9 , especially in ultra-precision processing equipment, it is often necessary to perform multi-dimensional Synchronous measurement, this multi-dimensional measurement requirement will cause the total laser power consumption of the interferometry system to increase to more than 5mW, which requires the use of more than 3 frequency-stabilized lasers for combined measurement at the same time. However, even for frequency-stabilized lasers of the same model and batch from the same manufacturer, the consistency of the output light frequency can only reach 1×10 ^-7 . This will inevitably bring about the problems of wavelength reference, wavelength drift and inconsistent spatial coordinates, which will affect the comprehensive measurement accuracy of the entire multi-dimensional laser interferometry system. Therefore, it is an urgent problem to be solved in the field of laser application technology to improve the frequency stabilization accuracy, anti-interference ability, output optical power and wavelength consistency of multiple frequency-stabilized lasers of a single frequency-stabilized laser.

At present, the light sources used in laser interferometers mainly include longitudinal Zeeman frequency-stabilized lasers, dual-longitudinal-mode frequency-stabilized lasers, and iodine-stabilized lasers. The laser frequency stabilization methods can be divided into piezoelectric ceramic stabilized lasers according to the difference in cavity length adjustment actuators. Frequency method, heating wire frequency stabilization method, discharge current frequency stabilization method and air cooling frequency stabilization method, etc.

The relative accuracy of the center frequency of the output light of the iodine frequency-stabilized laser is as high as 10 ^-11 to 10 ^-12 , and the center frequency consistency of multiple similar lasers can reach 10 ^-11 . However, the output light of the iodine frequency-stabilized laser modulated in the cavity is For frequency modulated lasers, the modulation depth of the light wave frequency is several MHz, so the overall relative frequency accuracy of the laser is 10 ^-8 . In addition, the output power of this type of iodine-stabilized laser is only tens of μW, and the piezoelectric ceramic is used as the cavity length adjustment device. Vibration performance is poor.

In order to overcome the shortcomings of iodine-stabilized He-Ne laser output laser frequency modulation and low optical power, RRDonaldson et al. of Lawrence Livemore Laboratory in the United States developed a bias-locked 633nm He-Ne laser (RRDonaldson, SRPaterson.Design and Construction of aLarge , Vertical-axis Diamond Turning Machine. Proc. Of SPIE. 1983, (433): 62-67). The feature of this laser is that a free-running laser tracks another iodine frequency-stabilized laser with high precision, and deviates from a fixed frequency value of the iodine-stabilized laser, thus maintaining the relatively high accuracy of the center frequency of the iodine-stabilized laser The advantage is that it can output a high-power laser with no frequency modulation, its relative frequency accuracy reaches 10 ^-9 , and its output power reaches 15mW. However, this type of laser adopts an external cavity resonator structure and piezoelectric ceramic adjustment elements. In addition to the shortcomings of long warm-up time and poor anti-vibration characteristics, the entire laser device is very bulky. At present, this type of laser is only used in individual dedicated large-scale ultra-precision processing equipment, and additional anti-vibration measures are required.

Other main light sources used in laser interferometers are Zeeman-type frequency-stabilized lasers and dual-longitudinal-mode lasers. Zeeman-type dual-frequency lasers have good frequency stabilization characteristics and reliability, but the acquisition of dual-frequency lasers requires additional magnetic fields. Manufacturing The process is complex, the cost is high, and its frequency difference is less than 3MHz, so its measurement speed is limited and cannot adapt to the current high-speed measurement occasions. The dual longitudinal mode thermal frequency stabilization method is low in cost, and the frequency stabilization device is simple. Mann-type frequency-stabilized lasers have the same level of frequency-stabilized accuracy, so they have been widely used.

For the frequency stabilization of dual longitudinal mode lasers, Balhorn et al proposed a frequency stabilization method for dual longitudinal mode lasers (R.Balhorn, H.Kunzmann, F.Lebowsky.Frequency Stabilization of Internal- Mirror Helium-Neon Lasers. Applied Optics, 1972, 11(4): 742-746). This method has the advantages of small thermal inertia and high adjustment efficiency, but the center frequency of the laser gain curve is easily changed by the change of the discharge current, and its relative frequency accuracy is not more than 10 ^-7 .

In order to improve the relative frequency stability of dual-longitudinal-mode lasers, the British Renishaw company proposed a method of thermally stabilizing dual-longitudinal-mode lasers based on electric heating wires (International Patent WO8801798: Pre-heat Control System for a Laser; International Patent WO8801799: Frequency Stabilized Laser andControl System Therefore), this method uses the difference between the optical power of the two orthogonally polarized lights output by the dual longitudinal mode laser as the feedback signal of the frequency stabilization control, and changes the work of the heating wire wound on the outer wall of the laser tube according to the frequency stabilization control algorithm Current, adjust the temperature and cavity length of the laser tube, so as to stabilize the output laser frequency of the laser tube. Domestically, Sichuan University and Harbin Institute of Technology have respectively proposed a frequency stabilization method for dual longitudinal mode lasers based on electromagnetic induction heating in recent years (Chinese patent CN100367579: Frequency stabilization device and method for electromagnetic induction heating of dual longitudinal mode lasers). However, Since the electrothermal device is used to adjust the cavity length to stabilize the frequency, the preheating target temperature is generally higher than the natural preheating equilibrium temperature of the laser tube, so the preheating time varies greatly under different ambient temperatures, and the higher preheating temperature brings The drift of the performance parameters of photoelectric conversion devices and other devices leads to the instability of the frequency stabilization control circuit system, and the higher operating temperature reduces the working life of the laser tube.

In order to solve the above-mentioned shortcomings of the electrothermal device adjustment cavity length stabilization method, Harbin Institute of Technology proposed a dual longitudinal mode laser frequency stabilization method based on a thermoelectric cooler (Chinese patent CN100382398: Dual longitudinal mode laser stabilization based on a thermoelectric cooler frequency method and apparatus). This method applies a reverse current to the thermoelectric cooler to preheat the laser tube to its natural operating thermal equilibrium temperature, and then controls the laser output dual longitudinal mode optical power by controlling the magnitude and direction of the current of the thermoelectric cooler and changing the cavity length of the laser resonator The difference is zero to achieve the purpose of frequency stabilization. It avoids the disadvantages of the existing frequency stabilization device that the preheating time becomes longer with different ambient temperatures, the preheating effect is unsatisfactory, and it is easily affected by changes in the external ambient temperature and air velocity. However, in its designed heat transfer structure, the thermoelectric cooler is installed on the same side of the laser tube, resulting in uneven heating or cooling of the outer wall of the laser tube, and a temperature gradient, which in turn leads to radial distortion of the laser tube and affects the stability of the output laser frequency. sex. In addition, this type of dual longitudinal mode frequency-stabilized laser still uses the center frequency of the laser gain curve as the frequency reference point for frequency stabilization control, but this center frequency is easily changed by factors such as temperature and air pressure, and the relative frequency accuracy of the laser is difficult to exceed 10. ^-8 .

Umeda of Shizuoka University in Japan proposed a method to adjust the length of the resonant cavity by using the air-cooling effect (N. Umeda, M. Tsukiji, H. Takasaki. Stabilized 3He-20Ne Transverse Zeeman Laser. Applied Optics. 1980, 19: 442-450. ). The basic principle of this adjustment method is: the laser tube resonant cavity is placed in the circulating air to achieve approximate thermal balance, and the fan is used to adjust the speed of the circulating air. Since the ambient temperature is lower than the temperature of the laser tube resonant cavity, increasing the fan speed can reduce the laser tube resonance. The temperature of the cavity, and reducing the fan speed can increase the temperature of the laser tube resonant cavity, so as to achieve the purpose of adjusting the cavity length. Umeda et al. used the air-cooling effect to adjust the resonator length of the transverse Zeeman laser, and obtained a short-term frequency stability of 10 ^-10 . This cavity length adjustment method has been applied in the frequency-stabilized laser products of Teletrac Company. However, due to the influence of ambient air humidity and temperature changes, the parameters of the frequency stabilization model change greatly, so that the frequency stabilization laser that uses the air-cooling effect to adjust the resonator length has low adaptability to industrial field environmental factors, and cannot effectively achieve high-precision stabilization. frequency.

In order to further improve the relative frequency accuracy of the dual-longitudinal-mode frequency-stabilized laser, Japanese scholar FumioMurakami et al. applied the iodine absorption frequency-stabilized technology to the dual-longitudinal-mode frequency-stabilized laser, and improved the relative frequency accuracy of the dual-longitudinal-mode frequency-stabilized laser to 10 ^{- 9} (Fumio Murakami, et al. Frequency Stabilization of 633-nm He-Ne Laser by Using Frequency Modulation Spectroscopy of ¹²⁷ I ₂ Enhanced by an External Optical Cavity. Electronics and Communications in Japan. 2000, Part 2, Vol.83, No.3: 1-9). In this method, the dual longitudinal mode frequency-stabilized laser is an internal cavity structure, and an auxiliary optical cavity is added outside to increase the external intensity of the laser, so as to meet the laser power requirement of ¹²⁷ I ₂ molecular saturation absorption. However, the introduction of the auxiliary optical cavity leads to a complex structure of the entire device, and the piezoelectric ceramic element is used in the auxiliary optical cavity, which reduces the anti-vibration capability of the device.

In summary, the iodine frequency-stabilized laser based on piezoelectric ceramics and locked on ^{the 127} I ₂ hyperfine absorption line, although its center frequency has a relative accuracy of 10 ^-11 or better, and multiple iodine-stabilized lasers The consistency of the center frequency reaches 10 ^-11 , but due to the shortcomings of low output power, poor anti-vibration performance, and high requirements for the working environment, it cannot be directly applied to industrial field measurements; the dual longitudinal mode frequency-stabilized laser based on electrothermal devices has a simple structure, However, the preheating time varies greatly under different ambient temperatures. At the same time, the higher preheating temperature brings the drift of the performance parameters of photoelectric conversion devices and other devices and the reduction of the life of the laser tube. The thermoelectric cooling stability proposed by Harbin Institute of Technology Although the frequency method solves the shortcomings of the above-mentioned electrothermal device frequency stabilization method, its heat transfer structure has defects, and it cannot uniformly heat or cool the laser tube, which affects the frequency stability of the laser. The relative frequency accuracy is difficult to break through 10 ^-8 , and at the same time The frequency consistency between multiple dual-longitudinal-mode frequency-stabilized lasers can only reach 10 ^-6 □10 ^-7 , which will bring wavelength reference, wavelength drift and The problem of inconsistency in spatial coordinates affects the comprehensive measurement accuracy of the interferometric system; the frequency relative accuracy of the bias-locked He-Ne laser based on piezoelectric ceramics and the dual-longitudinal-mode frequency-stabilized laser using iodine absorption frequency-stabilized technology reaches 10 ^-9 , However, the structure is complex and the anti-vibration ability is poor, and the applicable occasions are strictly limited. It can be seen that the existing frequency-stabilized laser technology will be difficult to meet the requirements of the development of a new generation of ultra-precision processing and measurement technology.

Contents of the invention

Aiming at the deficiencies of existing laser frequency stabilization technology, the present invention proposes a dual longitudinal mode thermoelectric cooling bias locking method and device based on iodine frequency stabilization reference, the purpose of which is to integrate iodine frequency stabilization laser and dual longitudinal mode thermoelectric cooling The advantages of frequency-stabilized lasers provide a new type of laser light source with higher precision and can be directly applied to industrial sites for the rapidly developing ultra-precision processing and measurement technology.

The object of the present invention is achieved through the following technical solutions:

A dual longitudinal mode thermoelectric cooling bias frequency locking method based on iodine frequency stabilization reference comprises the following steps:

(1) Turn on the power of the iodine frequency-stabilized laser. After preheating and frequency stabilization, the working frequency of the iodine-stabilized laser is locked on the ultrafine absorption line of the ¹²⁷ I ₂ molecule located in the 633nm band, and its output laser is frequency-modulated linearly polarized light , _the center frequency of the light wave is recorded as v _ro , the instantaneous frequency is recorded as v _r , and the modulation _period is recorded as T _{m .} , whose center frequency v _ro serves as the frequency reference for the bias frequency locking of the dual longitudinal mode laser;

(2) Turn on the power supply of the dual longitudinal mode lasers L ₁ , L ₂ ,...,L _n , all dual longitudinal mode lasers enter the preheating process at the same time, measure the current ambient temperature T _e , and determine according to the current ambient temperature to preheat the target The temperature value T _set , and T _e < T _set , the laser tubes of the dual longitudinal mode lasers L ₁ , L ₂ ,..., L _n are preheated by the thermoelectric cooler, and preheated according to the current temperature T _real and The difference between the target temperature T _set continuously adjusts the reverse current value of the thermoelectric cooler, so that the temperature of the laser tube gradually tends to the preset temperature value T _set and reaches a thermal equilibrium state. At this time, the output laser light of each laser tube includes polarization Two longitudinal mode lights with directions orthogonal to each other, using a polarization splitter to separate one of the longitudinal mode lights as the output light of the dual longitudinal mode lasers L ₁ , L ₂ ,...,L _n , denoted as beams Y ₁ , Y ₂ ,..., Y _n , the corresponding light wave frequencies are denoted as v ₁ , v ₂ ,..., v _n ;

(3) The dual longitudinal mode lasers L ₁ , L ₂ , ..., L _n enter the frequency-locking control process after the preheating process ends, and the beams X ₁ , X ₂ , ..., X _n are respectively connected to the beam Y ₁ , Y ₂ ,..., Y _n carry out optical mixing and form n-way beat-frequency optical signals, and use high-frequency photodetectors to convert n-way beat-frequency optical signals into n-way electrical signals, wherein the i-th electrical signal The frequency of is |v _i -v _r |(i=1, 2,..., n);

(4) After the signal conditioning of the n-channel electrical signal, its frequency value is measured by the frequency measurement module. If the sampling time τ≥200T _m is taken, the average value of the electrical signal frequency within the time τ is measured, that is, the beam X ₁ , X ₂ , ..., X _n center frequency v _ro and light wave frequency difference of light beam Y ₁ , Y ₂ , ..., Y _n , denoted as Δv ₁ , Δv ₂ , ..., Δv _n , where Δv _i =| v _i -v _ro |(i=1,2,...,n);

(5) Dual longitudinal mode frequency-stabilized lasers L ₁ , L ₂ ,...,L _n achieve laser frequency locking in the same monotonic interval where the respective light wave frequency differences Δv ₁ , Δv ₂ ,..., Δv _n change , and the pre-set frequency reference value Δv _set of all lasers is the same, the measured light wave frequency difference Δv ₁ , Δv ₂ ,..., Δv _n is used as the feedback signal of the frequency-locked closed-loop control, and the preset Calculate the difference of the bias frequency reference value Δv _set , and adjust the thermoelectric cooler to apply according to the positive, negative and magnitude of the difference obtained from the difference between the light wave frequency difference Δv ₁ , Δv ₂ ,..., Δv _n and the bias frequency reference value Δv _set The forward, reverse and magnitude of the current, so as to control the cooling and heating of the laser tube, and then change the temperature of the laser tube, the length of the resonant cavity and the frequency of the longitudinal mode of the laser, so that Δv ₁ , Δv ₂ ,..., Δv _n tend to at Δv _set ;

(6) When Δv ₁ =Δv ₂ =...=Δv _n =Δv _set , the frequency-locking control process of the dual longitudinal mode lasers L ₁ , L ₂ ,...,L _n is completed, and all the dual longitudinal mode lasers The frequency of the output laser is locked on the same frequency value, that is, v ₁ =v ₂ =...=v _n =v _ro +Δv _set (or v ₁ =v ₂ =...=v _n =v _ro -Δv _set );

(7) Adjust the preset bias frequency reference value to Δv′ _set , repeat steps (4), (5) and (6), the output laser of the dual longitudinal mode laser L ₁ , L ₂ ,..., L _n The frequency is locked on the reset frequency value v _ro +Δv′ _set (or v _ro -Δv′ _set ), and the frequency v _ro +Δv′ _set (or v _ro -Δv′ _set ) is the same as the frequency v _ro +Δv′ _set (or v _ro -Δv _set ) correspond to different gain values on the laser gain curve, so that the output laser power values of the dual longitudinal mode lasers L ₁ , L ₂ , . . . , L _n are also adjusted.

A dual-longitudinal-mode thermoelectric cooling bias frequency locking device based on an iodine frequency-stabilized reference, including an iodine-stabilized laser power supply, an iodine-stabilized laser, a first status indicator light, and an optical fiber beam splitter, and the device also includes n≥1 Dual longitudinal mode lasers L ₁ , L ₂ , ..., L _n with the same structure and in parallel relationship, wherein the assembly structure of each dual longitudinal mode laser L is: the power supply of the dual longitudinal mode laser is connected to the laser tube, the first The polarization beam splitter is placed in front of the main output end of the laser tube, the second polarization beam splitter is placed between the secondary output end of the laser tube and one input end of the fiber beam combiner, and the other input end of the fiber beam combiner is connected to the fiber beam splitter Connected to one of the output ends of the fiber optic combiner, the polarizer is placed between the output end of the fiber combiner and the high-speed photodetector, the high-speed photodetector, the high-speed frequency divider, the preamplifier, the postamplifier, the high-speed comparator, the frequency The measurement module, microprocessor, D/A converter, thermoelectric cooler driver, thermoelectric cooler and its heat transfer structure are connected in sequence, and the heat transfer structure is equipped with a thermally conductive adhesive layer from the inside to the outside of the laser tube. a. Copper tube heat conduction layer, heat conduction adhesive layer b, thermoelectric cooler, heat conduction adhesive layer c, radiator, and heat insulation layer, and each has two thermoelectric coolers and radiators placed symmetrically on both sides of the outer wall of the laser tube , the laser tube temperature sensor is located in the heat-conducting adhesive layer a inside the heat-conducting layer of the copper tube, the ambient temperature sensor is placed in the air, its output terminal is connected to the microprocessor, and the second status indicator communicates with the microprocessor.

The detection bandwidth of the high-speed photodetector is greater than 500MHz.

The present invention has following characteristics and good effect:

(1) The dual-longitudinal-mode frequency-stabilized laser in the present invention adopts an inner cavity structure, and a thermoelectric cooler is used as the actuator for adjusting the length of the resonant cavity. At the same time, a symmetrical heat transfer structure design of the thermoelectric cooler is adopted to eliminate the uneven heating of the laser tube The resulting radial distortion of the laser tube affects the stability of the output frequency; compared with the electrothermal device as the actuator for adjusting the length of the resonator, it reduces the temperature of the laser tube during frequency stabilization, enhances the ability to adapt to the environment, and shortens the warm-up It reduces the influence of temperature drift of photoelectric conversion devices and other device performance parameters on the frequency stabilization effect, and improves the life of the laser tube. This is one of the innovations different from the existing technology.

(2) The present invention adopts the center frequency of the iodine frequency-stabilized laser with a relative frequency accuracy of ^10-11 as the frequency reference of the frequency locking of the dual longitudinal mode lasers, and performs parallel frequency locking on a plurality of dual longitudinal mode lasers, and all the dual longitudinal mode lasers are stabilized The output laser of the frequency laser has a uniform frequency value, which overcomes the disadvantage of poor frequency consistency of multiple frequency-stabilized lasers in ordinary power-balanced dual-longitudinal-mode frequency-stabilized lasers due to inconsistent frequency references. The frequency consistency is improved from 10 ^-7 to 10 ^-9 , which is the second innovation point different from the prior art.

(3) By setting the bias frequency reference value _Δvset value, when the output laser frequency of the dual longitudinal mode frequency stabilized laser in the present invention is located near the center frequency of the laser gain curve, its output optical power can reach the dual longitudinal mode of ordinary power balance The frequency mode laser is more than 1.5 times, which is the third innovation point different from the existing technology.

Description of drawings

Fig. 1 is the principle schematic diagram of device of the present invention

Figure 2 is a schematic diagram of the structure of the dual longitudinal mode thermoelectric cooling bias frequency locking device based on iodine frequency stabilization reference

FIG. 3 is a cross-sectional view along A-A in FIG. 2 , that is, a schematic diagram of a heat transfer structure.

Fig. 4 is a graph showing the relationship between the preheating equilibrium temperature of the dual longitudinal mode laser and the ambient temperature.

Fig. 5 is a schematic diagram of the closed-loop control system of the preheating process of the dual longitudinal mode frequency-stabilized laser in the device of the present invention

Figure 6 is a schematic diagram of the control system for the frequency stabilization process of a common power-balanced dual-longitudinal-mode frequency-stabilized laser

Fig. 7 is a schematic diagram of the closed-loop control system of the frequency locking process of the dual longitudinal mode frequency-stabilized laser in the device of the present invention

Figure 8 is a schematic diagram of the relative position between the frequency locking position of the dual longitudinal mode frequency stabilized laser and the reference frequency in the present invention

(a) and (b) in Fig. 9 are the relationship diagrams between the operating frequency and the laser gain coefficient of the ordinary power balanced dual longitudinal mode frequency stabilized laser and the dual longitudinal mode frequency stabilized laser in the present invention

Figure 10 is a schematic diagram of the relationship between the current direction and the heat exchange direction of the thermoelectric cooler in the present invention

Fig. 11 is the preheating temperature curve diagram of the embodiment of the present invention under different initial environments

Curves a, b and c in Fig. 12 are the short-term relative frequency drift simulation curves of the output laser of the iodine frequency-stabilized helium-neon laser, the ordinary power balanced dual longitudinal mode laser and the dual longitudinal mode frequency stabilized laser of the present invention respectively

Curves a, b and c in Fig. 13 are the long-term relative frequency drift simulation curves of the output lasers of the iodine frequency-stabilized helium-neon laser, the ordinary power balanced dual longitudinal mode laser and the dual longitudinal mode frequency stabilized laser of the present invention respectively

In the figure, 1 iodine frequency stabilized laser power supply, 2 iodine frequency stabilized laser, 3 first status indicator light, 4 fiber optic beam splitter, 5 dual longitudinal mode laser power supply, 6 microprocessor, 7 ambient temperature sensor, 8 laser tube temperature Sensor, 9 laser tube, 10 D/A converter, 11 thermoelectric cooler driver, 12 thermoelectric cooler, 13 second polarization beam splitter, 14 first polarization beam splitter, 15 fiber beam combiner, 16 analyzer , 17 high-speed photodetector, 18 high-speed frequency divider, 19 preamplifier, 20 signal amplifier, 21 high-speed comparator, 22 frequency measurement module, 23 second status indicator light, 24 heat conduction adhesive layer a, 25 copper pipe heat conduction layer , 26 thermally conductive adhesive layer b, 27 thermally conductive adhesive layer c, 28 radiator, 29 heat insulating layer.

Detailed ways

The implementation examples of the present invention will be described in detail below in conjunction with the accompanying drawings.

The dual longitudinal mode laser bias frequency locking device based on thermoelectric cooler includes: iodine frequency stabilized laser power supply 1, iodine frequency stabilized laser 2, first status indicator light 3, optical fiber beam splitter 4, the device also includes n≥1 Dual longitudinal mode lasers L ₁ , L ₂ , ..., L _n with the same structure and in parallel relationship, the assembly structure of each dual longitudinal mode laser L is shown in Figure 2: the dual longitudinal mode laser power supply 5 and the laser The tube 9 is connected, the first polarization beam splitter 14 is placed before the main output end of the laser tube 9, and the second polarization beam splitter 13 is placed between the secondary output end of the laser tube 9 and an input end of the fiber combiner 15, and the optical fibers are bundled The other input end of the device 15 is connected with one of the output ends of the optical fiber beam splitter 4, and the polarizer 16 is placed between the output end of the optical fiber beam combiner 15 and the high-speed photodetector 17, the high-speed photodetector 17, the high-speed photodetector Frequency divider 18, preamplifier 19, postamplifier 20, high-speed comparator 21, frequency measurement module 22, microprocessor 6, D/A converter 10, thermoelectric cooler driver 11, thermoelectric cooler 12 and The heat transfer structure is connected in sequence, and its heat transfer structure is shown in Figure 3: starting from the laser tube 9, it is equipped with a thermally conductive adhesive layer a 24, a copper tube thermally conductive layer 25, a thermally conductive adhesive layer b 26, and a thermoelectric sensor. Cooler 12, thermal conductive adhesive layer c 27, radiator 28, heat insulation layer 29, and each has two thermoelectric coolers 12 and radiator 28 placed symmetrically on both sides of the outer wall of laser tube 9, laser tube temperature sensor 8 places Inside the heat-conducting adhesive layer a24 of the copper pipe heat-conducting layer 25 , the ambient temperature sensor 7 is placed in the air, its output terminal is connected to the microprocessor 6 , and the second status indicator light 23 communicates with the microprocessor 6 .

The high speed photodetector 17 used in the device of the present invention has a bandwidth greater than 500 MHz.

In view of the fact that the device includes multiple dual-longitudinal-mode frequency-stabilized lasers L ₁ , L ₂ , ..., L _n , and the control process of preheating and frequency locking of all dual-longitudinal-mode frequency-stabilized lasers is exactly the same, the following is only for dual longitudinal mode Mode-stabilized laser L ₁ is used to describe the process, and these descriptions are also applicable to any other dual-longitudinal-mode-stabilized lasers in the device.

When the device embodiment starts to work, the iodine frequency-stabilized laser power supply 1 is turned on, and the iodine-frequency-stabilized laser 2 enters the preheating and frequency-stabilization process. In a stable working state, the output light of laser 2 is frequency-modulated laser at this time, and its instantaneous frequency can be expressed as:

v _r (t)＝v _ro +Δv _m cos(2πf _m t)

In the formula, v _ro , Δv _m , and f _m are laser center frequency, frequency modulation amplitude, and frequency modulation signal frequency respectively, Δv _m =3MHz, f _m =2KHz. The output laser light from the laser 2 is coupled into the fiber beam splitter 4 and split into n channels of frequency reference beams, denoted as beams X ₁ , X ₂ , . . . , X _n .

When the status of the first status indicator light 3 is enabled, turn on the dual longitudinal mode frequency stabilized laser power supply 5, and the dual longitudinal mode frequency stabilized laser enters the preheating process. Figure 4 shows the dual longitudinal mode laser ambient temperature and preheating thermal equilibrium temperature curve As shown in the figure, the preheating heat equilibrium temperature is different under different ambient temperatures, but the heat exchange energy between the laser tube and the external environment temperature is the same in each heat equilibrium state, and the heat exchange energy is related to the temperature difference, that is, there is a fixed temperature difference between the temperature and the ambient temperature. The preheating heat balance temperature T _set is determined according to the preheating temperature curve. Fig. 5 is a schematic diagram of a closed-loop control system for the preheating process of a dual longitudinal mode laser. The microprocessor 6 sets the thermal equilibrium temperature T _set for preheating according to the ambient temperature measured by the ambient temperature sensor 7 , and uses T _set as a reference input for the preheating closed-loop control system, and at the same time measures the temperature of the laser tube with the laser tube temperature sensor 8 . The temperature t _real of 9 is used as a feedback signal, and the microprocessor 6 calculates the difference between the two, and outputs a digital control signal according to the MPC control algorithm, which is converted into an analog signal by the D/A converter 10, and the analog signal is passed through the thermoelectric The cooler driver 11 performs amplification to control the working current of the thermoelectric cooler 12 to heat the laser tube 9 .

After the laser tube 9 reaches the thermal equilibrium temperature T _set , the microprocessor 6 switches the dual longitudinal mode frequency-stabilized laser L ₁ to enter the frequency locking control process. Figure 7 illustrates the closed-loop control process of the frequency locking of the dual longitudinal mode frequency-stabilized laser. Both the main and auxiliary output ends of the laser tube 9 output two longitudinal mode lights whose polarization directions are orthogonal to each other, and the first polarization beam splitter 14 and the second polarization beam splitter 13 are used to separate the two longitudinal mode lights at the main and auxiliary output ends respectively, The horizontally polarized longitudinal-mode light at the secondary output end is used for frequency-locking control, denoted as beam Y ₁ , and its frequency is denoted as v ₁ , and the horizontally polarized longitudinal-mode light at the main output end is used as the output light of the dual longitudinal-mode frequency-stabilized laser L ₁ . The light beam _Y1 is coupled into the fiber beam combiner 15, combined with the reference beam _X1 into one beam, passes through the analyzer 16 to form a beat-frequency optical signal, and is converted into a voltage signal by the high-speed photodetector 17, and the voltage signal passes through the high-speed The frequency divider 18, the preamplifier 19, the postamplifier 20, and the high-speed comparator 21 become square wave signals, which are sent to the frequency measurement module 22 for frequency measurement. The instantaneous frequency of a square wave signal can be expressed as:

f(t)=f _c +Δfcos(2πf _m t)

In the formula, f _c =|v ₁ -v _ro |/M, Δf=Δv _m /M, and M is the frequency division number of the frequency divider. When measuring the frequency, take the sampling time τ=(N+ε)T _m , T _m =1/f _m , N and ε are the integer and fractional periods of the time τ including T _m respectively, then the light beam within the time τ can be measured The average value of optical frequency difference between _X1 and beam _Y1 :

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; m</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}_{\mathrm{<span\; class="notranslate">\; 0</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}$

$<span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; ro</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="v\; m"\; filenames="A2009100725230019H3.png,A2009100725230020H1.png"\; state="\{\{state\}\}">v</figure-callout></span><figure-callout\; id="2"\; label="v\; m"\; filenames="A2009100725230019H3.png,A2009100725230020H1.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span>}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;f\&epsiv;</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span>$

The derivation of the above formula assumes that v ₁ is a constant within the sampling time τ, which is in line with the actual situation. In the state of thermal equilibrium or near thermal equilibrium, v ₁ is a slow variable, which can be approximated as a constant within the sampling time τ. The first item in the above formula can be regarded as the true value of the frequency measurement, and its value is tens to hundreds of MHz, and the second item can be regarded as the error item of the frequency measurement. In this example, N=200, then the value of the error item Not greater than Δv _m /[2π(N+ε)]≈2.4KHz. The influence of the frequency measurement error on the precision of the offset frequency locking is in the order of 10 ^-11 , so the frequency measurement accuracy has met the requirement of relative accuracy of 10 ^-9 for the offset frequency locking.

According to the measured frequency value Δv ₁ , the microprocessor 6 locks the laser frequency in the same monotonic interval of its change. FIG. 8 is a schematic diagram of the relative position between the frequency locked position of the dual longitudinal mode frequency stabilized laser and the reference frequency in the present invention. In the figure, the bandwidth of the high-speed photodetector 17 is Δv _detect , and the frequency Δv ₁ measured by the frequency measurement module 22 is the absolute value of the difference between the center frequency v _ro of the beam X ₁ and the frequency v ₁ of the beam Y ₁ , according to v ₁ and the laser tube The relationship between cavity length v ₁ =qc/2ηl, where c is the speed of light, q is the sequence number of the longitudinal mode, η is the refractive index in the resonant cavity, and l is the length of the laser tube cavity. The temperature of the dual longitudinal mode laser approaches thermal equilibrium in the preheating stage, the temperature rises at a slow rate, and the length l of the laser cavity increases. For the longitudinal mode of each horizontal polarization direction that the dual longitudinal mode laser can form, the oscillation The frequency v ₁ changes from large to small, and Δv ₁ =|v ₁ -v _ro | (Figure 8 shows the variation law of Δv ₁ with v ₁ ) from the detection bandwidth Δv _detect of the high-speed photodetector 17 to zero, Then change linearly from zero to Δv _detect , including two monotonous intervals: the monotonous falling interval and the monotonous rising interval. Therefore, in the case of the set Δv _set , the Δv ₁ corresponding to the longitudinal mode of a certain horizontal polarization direction is: Two frequency locking intervals, in order to make the output lasers of the dual longitudinal mode frequency stabilized lasers L ₁ , L ₂ ,...,L _n have a uniform frequency value, it is necessary to lock all the dual longitudinal mode frequency stabilized lasers to v _ro On the same side, that is, in the same monotonic interval of its change, the laser frequency is locked, so the microprocessor 6 judges the monotonic interval it is in according to the transformation trend of Δv ₁ , and will be within the set monotonic interval during the change process. The direction longitudinal mode is locked, and when the Δv ₁ measured by the measurement module 22 is included in the range of Δv _set set by the control algorithm, the frequency stabilization stage is entered. In this example, the monotone descending interval is selected as the locking interval.

In the frequency stabilization stage, the microprocessor 6 uses the Δv ₁ value measured by the frequency measurement module 22 as the feedback signal of the frequency locking closed-loop control system, and simultaneously uses the preset offset frequency reference value Δv _set (this example takes Δv _set =120MHz) as The reference input of the control system, the microprocessor 6 calculates the difference between the two, and adjusts the output digital control signal according to the positive, negative and size of the obtained difference according to the MPC control algorithm, and is converted into analog by D/A converter 10 signal, this analog signal is amplified by the thermoelectric cooler driver 11, and is used to adjust the forward, reverse and magnitude of the current applied by the hot spot cooler 12, thereby controlling its cooling and heating of the laser tube, thereby changing the temperature of the laser tube , resonator length and laser longitudinal mode frequency, so that Δv ₁ , Δv ₂ ,..., Δv _n tend to Δv _set , when Δv ₁ ≈ Δv _set , the frequency locking process of the dual longitudinal mode laser L ₁ is completed, enabling the first Two status indicator lights 23 indicate that the dual longitudinal mode laser L ₁ has entered a stable working state, and at this time v ₁ =v _ro +Δv _set .

Adjusting the preset bias frequency reference value to Δv′ _set and repeating the above frequency locking process, the output laser frequency of the dual longitudinal mode laser L ₁ is adjusted to v _ro +Δv′ _set . Since the frequency v _ro +Δv′ _set and the frequency v _ro +Δv _set have different gain values on the laser gain curve, the output laser power of the dual longitudinal mode laser L ₁ is also adjusted, so select an appropriate preset bias frequency reference The value of Δv _set can realize the maximization of the output optical power of the dual longitudinal mode laser _L1 , and its value can reach more than 1.5 times of the ordinary power balanced dual longitudinal mode frequency-stabilized laser, which is illustrated in conjunction with Figure 7.

(a) in FIG. 9 is a schematic diagram of the relationship between the operating frequency and the gain coefficient of a common power balanced dual longitudinal mode frequency stabilized laser. After frequency stabilization, the optical frequencies v _L and v _R of the two longitudinal modes of the laser are symmetrical about the center v _o of the laser gain curve, and the frequency interval between the two longitudinal modes can be expressed as

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; q</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="c"\; filenames="A2009100725230019H3.png,A2009100725230020H1.png"\; state="\{\{state\}\}">c</figure-callout></span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&eta;l</span>}}$

(b) in Fig. 9 is a schematic diagram of the relationship between the operating frequency and the gain coefficient of the dual longitudinal mode frequency stabilized laser in the present invention, taking the dual longitudinal mode frequency stabilized laser _L1 as an example, the locked position of the output laser frequency is v _ro +Δv _set (Due to the difference in laser tube parameters, the frequency reference v _ro does not coincide with the center frequency v _o of the laser gain curve, and the value of v _ro can be greater or less than v _o . The figure is the case of v _ro ≤ v _o ). If the bias frequency reference value Δv _set ≈v _o -v _ro is selected, then the frequency value of the output laser is v ₁ ≈v _o , so as to obtain the maximum laser gain value.

Fig. 10 illustrates the relationship between the current direction and the thermal energy direction of the thermoelectric cooler 12 in the embodiment.

In the embodiment, the thermoelectric cooler 12 is a semiconductor component designed and manufactured using the remarkable Peltier effect of semiconductor materials and other related thermoelectric effects. It has the advantages of small size, long life, no noise, vibration and no pollution. The principle is : When an N-type semiconductor material and a P-type semiconductor material are connected into a galvanic pair, after a DC current is connected in this circuit, energy transfer can occur: the current flows from the N-type element to the P-type element, and the joint absorbs heat , become the cold end; the current flows from the P-type element to the N-type element, and the joint releases heat. become the hot end. The direction of heat energy is determined by the direction of the current, and the amount of heat absorbed and released is determined by the magnitude of the current.

When the current is input to the positive electrode terminal of the thermoelectric cooler 12 in the embodiment, the heat energy is output from the laser tube 9, and then passes through the thermally conductive adhesive layer a24, the copper tube thermally conductive layer 25, the thermally conductive adhesive layer b26, the thermoelectric cooler 12, and the thermally conductive adhesive Layer c27 reaches the radiator 28, and the radiator 28 has a large area, so heat is easy to disperse in the air by air convection and radiation; when the negative electrode terminal of the thermoelectric cooler 12 in the embodiment inputs current, the radiator 28 absorbs heat energy from the air in the form of air convection and radiation, and then passes through the thermally conductive adhesive layer c27, the thermoelectric cooler 12, the thermally conductive adhesive layer b26, the copper tube thermally conductive layer 25, and the thermally conductive adhesive layer a24 to reach the laser tube 9.

Figure 11 shows the preheating temperature curves of the device embodiment of the present invention under different initial environments. From the curve change trend, it can be concluded that under different initial temperature environments, the laser preheating curve change trend is basically the same, at about 15 minutes The temperature rises to within 0.1°C from the target temperature, and the temperature change rate is very small, basically reaching thermal equilibrium. It shows that in different industrial sites, the device can obtain heat balance and provide better frequency stabilization conditions after preheating with basically the same time.

Figure 6 is a schematic diagram of the control system for the frequency stabilization process of a common power-balanced dual-longitudinal-mode frequency-stabilized laser. Compared with Figure 5, it can be seen that in a common frequency-stabilized control system, since the laser frequency cannot be directly measured, indirect quantities such as optical power difference are used for this purpose. As a feedback control signal, it is essentially a semi-closed-loop control system; in this method, since the center frequency of the high-precision iodine frequency-stabilized laser is used for frequency mixing, the laser frequency value of the dual longitudinal mode laser can be collected with high precision As a control feedback, it is essentially a fully closed-loop control system. Based on the large difference in control performance between semi-closed-loop and full-closed-loop control systems, the effect of frequency stabilization control will be described in conjunction with Figure 10 and Figure 11.

Curve a in Fig. 12 is the short-term relative frequency drift simulation curve of the iodine-stabilized laser output laser, and its ordinate is the relative frequency drift, which is defined as (v _r -v _ro )/v _ro . It can be seen from curve a that the output frequency of the iodine-stabilized laser has a modulation depth of about 6MHz, and the modulation angular frequency is 2KHz, so the overall short-term relative frequency drift is 10 ^-8 , but the short-term relative frequency drift of the central frequency is much larger than this The values are more than 3 orders of magnitude higher.

Curve b in Fig. 12 is the short-term simulation curve of the output laser frequency drift of ordinary power balanced dual longitudinal mode frequency stabilized laser, and its relative drift on the vertical axis is defined as (Δv-Δv _ave )/v _ro , where Δv=|vv _ro |, v is the output laser frequency of ordinary power balanced dual longitudinal mode frequency stabilized laser, v _ro is the center frequency of iodine frequency stabilized laser output laser, Δv _ave is the arithmetic mean value of Δv. It can be seen from the curve b that the short-term relative frequency drift of the output laser of the ordinary power balanced dual longitudinal mode frequency-stabilized laser is 10 ^-8 , and its center frequency has no obvious drift in the short term.

Curve c in Fig. 12 is the simulation curve of the short-term drift of the output laser frequency of the dual longitudinal mode frequency stabilized laser in the present invention, and the definition of relative frequency drift on the vertical axis is the same as that of curve b. It can be seen from the curve c that the short-term relative drift of the output laser of the dual longitudinal mode frequency-stabilized laser in the present invention can reach 10 ^-9 , and the center frequency has no obvious drift in the short term.

Curves a, b, and c in Fig. 13 are the simulation curves of the long-term relative frequency drift of the output laser of the iodine frequency-stabilized laser, the ordinary power balanced dual-longitudinal-mode frequency-stabilized laser, and the dual-longitudinal-mode frequency-stabilized laser in the present invention, wherein the iodine-frequency stabilized laser The long-term relative frequency drift is similar to its short-term frequency drift curve; the center frequency of the output laser of the ordinary power balance dual longitudinal mode frequency stabilized laser has a large long-term drift, and its long-term relative frequency drift reaches 10 ^-7 ; There is no obvious long-term drift of the central frequency of the output laser of the mode-stabilized laser, and its long-term relative frequency drift is still 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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