CN113078552B - Frequency stabilizing device of single-frequency laser based on intracavity self-reference - Google Patents

Abstract

The utility model provides a single frequency laser instrument frequency stabilising arrangement based on intracavity is from referencing, includes frequency control module, single frequency laser instrument, semi-transparent semi-reflecting mirror, photoelectric detector and frequency phase discriminator, single frequency laser instrument inside have two non-degenerate laser modes, and the frequency difference of two non-degenerate laser modes corresponds with the laser frequency of two laser modes respectively. According to the invention, two nondegenerate modes are introduced into a laser cavity of the laser, the correlation between the beat frequency signal of the nondegenerate mode and the laser frequency is utilized, the beat frequency signal is taken as the frequency reference to obtain the central frequency drift amount of the laser, and finally, the stability of the central frequency of the single-frequency laser is realized through feedback control, so that the frequency stability is improved. The invention has the advantages of no need of third-party frequency reference, simple and compact device, high frequency stability and capability of realizing the frequency stability of any central wavelength, and can effectively promote the application of the single-frequency laser in many fields such as coherent laser communication and the like.

Description

Single-frequency laser frequency stabilization device based on intracavity self-reference

technical field

The invention relates to a single-frequency laser, in particular to a single-frequency laser frequency stabilization device based on intra-cavity self-reference and an adjustment method thereof. The device can be applied to laser atomic cooling, high-resolution laser spectroscopy, cold atomic clocks, laser radar, coherent Laser communication and other cutting-edge basic science and high-tech fields.

Background technique

In recent years, single-frequency laser technology has developed rapidly, the performance of single-frequency laser has been continuously improved, and its application has become more and more extensive. Due to its narrow linewidth and low noise, single-frequency lasers are widely used in many fields such as laser atomic cooling, high-resolution laser spectroscopy, and cold atomic clocks. These application fields have high requirements on the linewidth and frequency stability of the laser, and the output frequency of free-running single-frequency lasers (such as semiconductor lasers, fiber lasers, etc.) is very sensitive to the pump intensity and operating temperature, even in single longitudinal The spectral line width is also relatively wide, so that its central wavelength fluctuates in a considerable range, and the frequency stability is very poor. This is a problem that must be solved for applications such as laser atomic cooling and high-resolution laser spectroscopy. Further active frequency stabilization measures need to be taken to meet the requirements of single-frequency lasers in the field of scientific research. Therefore, it is of great academic significance and application value to study the frequency stabilization technology of single-frequency lasers and solve the key physical problems involved, and has received extensive attention.

The frequency stabilization technology of single-frequency lasers usually locks the center frequency of the output laser to a frequency reference with high frequency stability, such as the absorption lines of atoms and molecules, Fabry-Perot etalons, etc. Among them, the laser frequency stabilization technology based on atomic absorption lines is the most widely used. Its main principle is that the frequency of the output light of the laser is compared with the frequency at the atomic absorption peak, and the error signal is obtained and fed back to the frequency tuning mechanism of the laser to complete the closed-loop control, so that the center frequency of the laser is locked to the corresponding reference frequency. to complete frequency stabilization. For example, the absorption lines of rubidium (Rb) atoms can be used for frequency stabilization of semiconductor lasers in the 780nm band; the absorption lines of cesium (Cs) atoms can be used for frequency stabilization of semiconductor lasers in the 852nm band. In this regard, Motoichi Ohtsu proposed a semiconductor laser modulation frequency stabilization technology for atomic absorption lines (see Prior Art [1]: "Linewidth reduction of a semiconductor laser by electrical feedback", IEEE JOURNAL OF QUANTUM ELECTRONICS, Vol.QE-21, No.12, December 1985). The basic principle is to modulate the laser frequency, and then compare it with the reference atomic absorption spectrum to obtain the AC error signal, and generate a closed-loop control to stabilize the frequency. However, the frequency stabilization technology based on atomic absorption lines will cause a series of problems:

1. The central wavelength of frequency stabilization depends on the position of the absorption line of atoms or molecules, which is very limited and cannot achieve laser frequency stabilization of any wavelength.

2. In order to generate strong absorption lines, long atomic or molecular absorption cell devices are often required, which greatly increases the volume of the entire single-frequency laser frequency stabilization device.

In order to overcome the problem of the first point above, Timothy Day proposed a single-frequency laser frequency stabilization technique using the transmission peak of the Fabry-Perot etalon as a frequency reference (see prior art [2]: "Sub-Hertzrelativefrequency stabilization" of two diode laser-pumped Nd:YAG lasers locked toaFabry-Perot Interferometer", IEEE JOURNAL OF QUANTUM ELECTRONICS,Vol.28,No.4,1992), its main principle is the frequency of laser output light and Fabry-Perot Interferometer The frequency at the transmission peak of the etalon is compared, and the error signal is obtained and fed back to the frequency tuning mechanism of the laser to complete the closed-loop control, so that the center frequency of the laser is locked to the corresponding transmission peak of the Fabry-Perot etalon. At the reference frequency, frequency stabilization is completed. The advantage is that the Fabry-Perot etalon has multiple transmission peaks, which in principle can achieve frequency stabilization at any center wavelength. But there are still the following disadvantages:

1. The center frequency of the transmission peak of the Fabry-Perot etalon itself is easily affected by ambient temperature and vibration, and its frequency stability is not as good as that of atomic or molecular absorption spectra, which directly affects the accuracy of laser frequency stability.

2. The volume of the Fabry-Perot etalon itself is relatively large, which increases the volume of the entire single-frequency laser frequency stabilization device.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art, and to provide a single-frequency laser frequency stabilization device based on intra-cavity self-reference and an adjustment method thereof. The relationship between the beat frequency signal of the non-degenerate mode in the laser cavity of the frequency laser and the absolute frequency of the laser, the frequency reference is constructed in the laser oscillation cavity, and the laser frequency self-reference effect of the single-frequency laser is formed, and then the center frequency drift of the laser can be accurately obtained. Finally, the stability of the center frequency of the single-frequency laser is realized through feedback control, which can effectively suppress the fluctuation of the center frequency of the free-running single-frequency laser and improve the frequency stability.

The technical solution of the present invention is as follows:

A single-frequency laser frequency stabilization device based on intra-cavity self-reference, comprising a frequency control module, a single-frequency laser, a half mirror, a photodetector, and a frequency phase detector, which is characterized in that the single-frequency laser There are two non-degenerate laser modes inside, and the frequency difference of the two non-degenerate laser modes corresponds to the laser frequencies of the two non-degenerate laser modes respectively;

The photodetector is used to detect beat signals of two non-degenerate laser modes, and the frequency of the beat signals is equal to the frequency difference of the two non-degenerate laser modes;

The frequency phase detector is used to detect the frequency fluctuation of the beat frequency signal detected by the photodetector, and convert it into a DC voltage signal and input it to the frequency control module;

The frequency control module is used to receive the DC voltage signal output by the frequency phase detector, and output the corresponding frequency control signal to the single-frequency laser to control the output frequency of the single-frequency laser;

The laser output from the single-frequency laser is divided into reflected light and transmitted light by the half mirror, and the reflected light is incident on the photodetector for laser frequency stabilization.

Along the said transmitted light direction, an optical filter is also provided for filtering out one laser mode among the two non-degenerate laser modes, and the remaining one laser mode is used as the output of the whole device.

Compared with the prior art, the present invention has the following advantages and positive effects:

1. Compared with the prior art [1], the single-frequency laser frequency stabilization device based on the intra-cavity self-reference of the present invention adopts the beat frequency signals of two non-degenerate modes in the single-frequency laser laser cavity as the self-reference of the laser frequency The signal is not limited by the frequency position of atomic or molecular absorption lines, and can achieve frequency stabilization at any central wavelength.

2. Compared with the prior art [2], the single-frequency laser frequency stabilization device based on intra-cavity self-reference uses the beat frequency signals of two non-degenerate modes in the single-frequency laser laser cavity as the self-reference signal of the laser frequency, avoiding The problem that the center frequency of the transmission peak of the third-party frequency reference, such as the Fabry-Perot etalon, is easily affected by the ambient temperature and vibration, which can effectively improve the frequency stability accuracy.

3. Compared with the prior art [1] and the prior art [2], the present invention is based on the intra-cavity self-reference single-frequency laser frequency stabilization device, and adopts the beat frequencies of two non-degenerate modes in the single-frequency laser laser cavity. As the self-reference signal of the laser frequency, the signal does not need frequency reference such as an external atomic/molecular absorption cell or a Fabry-Perot etalon, which effectively simplifies the whole device, reduces the volume and reduces the cost.

Description of drawings

FIG. 1 is a structural block diagram of a single-frequency laser frequency stabilization device based on intracavity self-reference according to the present invention.

Detailed ways

The present invention will be further described below with reference to examples and accompanying drawings, but the protection scope of the present invention should not be limited by this.

Please refer to FIG. 1 first. FIG. 1 is a structural block diagram of a frequency stabilization device for a single-frequency laser based on intra-cavity self-reference according to the present invention. As can be seen from the figure, the single-frequency laser frequency stabilization device based on intra-cavity self-reference includes a single-frequency laser 2 with a frequency control module 1, a half mirror 3, a photodetector 4, an optical filter 5, and a frequency phase discrimination. device 6.

There are two non-degenerate laser modes inside the single-frequency laser 2, and there is a one-to-one correspondence between the frequency difference of the two laser modes and the absolute laser frequencies of the two modes.

The photodetector 4 is used to detect the beat signal of two non-degenerate laser modes, and the frequency of the beat signal is equal to the frequency difference of the two non-degenerate laser modes.

The frequency phase detector 6 is used to obtain the frequency fluctuation of the beat frequency signal detected by the photodetector, and convert it into a DC voltage signal and input it to the frequency control module. Since there is a one-to-one correspondence between the frequency fluctuation of the beat signal and the absolute frequency of the laser, the DC voltage signal output by the frequency phase detector directly represents the frequency fluctuation of the laser output by the laser.

The frequency control module 1 receives the DC voltage signal output by the frequency phase detector 6 , and outputs a corresponding frequency control signal to the single-frequency laser to control the output frequency of the single-frequency laser 2 .

The half mirror 3 is used to split the output laser into two beams, the reflected light 3a is used for laser frequency stabilization, and the transmitted light 3b passes through the optical filter 5 to filter out two non-degenerate laser modes. one of the modes, and the remaining one laser mode is used as the output of the whole device.

The concrete operation steps of the present invention are as follows:

1. Roughly adjust the working wavelength of the single-frequency laser through the frequency control module, and roughly adjust the wavelength of the single-frequency laser to the vicinity of the required working wavelength.

2. Adjust the overall optical path, and input the light reflected by the half mirror into the photodetector, so that the photodetector detects the beat frequency signals of two non-degenerate laser modes.

3. Input the beat frequency signal into the frequency phase detector, and convert the frequency fluctuation of the beat frequency signal into a DC voltage signal. The DC voltage signal at this time directly represents the frequency fluctuation of the single-frequency laser.

4. Input the obtained DC voltage signal directly into the frequency control module to stabilize the output wavelength of the single-frequency laser.

The present invention is based on an intra-cavity self-reference single-frequency laser frequency stabilization device, uses the non-degenerate mode beat frequency signal in the laser cavity as the laser frequency reference signal, and has the advantages of no need for third-party frequency reference, simple and compact device, high frequency stability, The advantage of frequency stability at any center wavelength can be achieved. The invention can effectively promote the application of the single-frequency laser in microwave photonics, laser radar, coherent laser communication and many other fields.

Claims (2)

1. A frequency stabilizing device of a single-frequency laser based on intracavity self-reference comprises a frequency control module (1), a single-frequency laser (2), a semi-transparent semi-reflecting mirror (3), a photoelectric detector (4) and a frequency phase discriminator (6), and is characterized in that two non-degenerate laser modes exist inside the single-frequency laser (2), and the frequency difference of the two non-degenerate laser modes and the respective absolute laser frequencies of the two modes have a one-to-one correspondence relationship;

the photoelectric detector (4) is used for detecting beat frequency signals of two nondegenerate laser modes, and the frequency of the beat frequency signals is equal to the frequency difference of the two nondegenerate laser modes;

the photoelectric detector 4 is used for detecting beat frequency signals of two nondegenerate laser modes, the frequency of the beat frequency signals is equal to the frequency difference of the two nondegenerate laser modes, and the frequency fluctuation of the beat frequency signals and the absolute frequency of laser have a one-to-one correspondence relationship;

the frequency phase discriminator (6) is used for detecting the frequency fluctuation of the beat frequency signal detected by the photoelectric detector, converting the beat frequency signal into a direct current voltage signal and inputting the direct current voltage signal into the frequency control module (1);

the frequency control module (1) is used for receiving the direct-current voltage signal output by the frequency phase discriminator (6), outputting a corresponding frequency control signal to the single-frequency laser (2), and controlling the output frequency of the single-frequency laser (2);

the laser output by the single-frequency laser (2) is divided into reflected light (3a) and transmitted light (3b) through the half-transmitting and half-reflecting mirror (3), and the reflected light (3a) is incident to the photoelectric detector (4) and is used for stabilizing the laser frequency.

2. An intracavity self-reference based single frequency laser frequency stabilization device as claimed in claim 1 wherein an optical filter (5) is further provided along said transmitted light (3b) direction for filtering out one of two non-degenerate laser modes.

Images