JPH026236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for stabilizing the frequency by matching the oscillation frequency of a laser to the center of an absorption or transmission spectrum serving as a frequency reference.

When using a laser as a light source for heterodyne and homodyne optical communications, or as a light source for measurement devices that utilize light interference, such as optical interferometric length measurement devices, it is required that the oscillation frequency be stabilized. be done.

The method for stabilizing the oscillation frequency of this type of laser is generally to use either the absorption spectrum of the molecule or the transmission spectrum of a Fabry-Perot interferometer as a reference, and to calculate the difference between the center frequency of this spectrum and the laser oscillation frequency ( It is known to detect an error signal (hereinafter referred to as an error signal) and control the laser oscillation frequency so that the error signal becomes zero. Conventionally, in this type of laser frequency stabilization device, in order to detect the error signal, the laser beam is reflected on a mechanically vibrated mirror and the frequency is modulated by the Doppler effect, or a Fabry-Perot interferometer is used. A method of mechanically vibrating one mirror to fluctuate its transmission spectrum is employed. However, these methods have problems with durability and robustness because they have a mechanical vibrating part, and furthermore, because the vibration frequency is limited to several tens of kHz, the response speed of the frequency stabilization control device is slow. There is.

The present invention was proposed in order to eliminate all the problems of the conventional laser oscillation frequency stabilizing device described above, and its purpose is to use an acousto-optic frequency modulator for frequency modulation of laser light. The objective is to stabilize the laser oscillation frequency by using the modulation signal, detecting an error signal using this modulation signal as a reference signal, and controlling the oscillation frequency of the laser oscillator based on the detected error signal.

Next, embodiments of the laser frequency stabilizing device according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block circuit diagram showing the basic configuration of the device of the present invention. That is, in Figure 1, 1
is a laser oscillator, 2 is a beam splitter, 3 is an acousto-optic frequency modulator, 4 is a device having an absorption or transmission spectrum as a frequency reference, 5 is a photoelectric conversion element, 6 is a reference signal generator, and 7 is a voltage control 8 represents an oscillator, 8 represents a phase detector, and 9 represents an integrator.

Next, the operation of the circuit shown in FIG. 1 will be explained.

First, the laser beam 1 emitted from the laser oscillator 1
0 is reflected by the beam splitter 2 and enters the acousto-optic frequency modulator 3. This acousto-optic frequency modulator 3 gives the incident light 11 a frequency shift equal to the frequency of the output signal of the voltage controlled oscillator 7 controlled by the reference signal generated by the reference signal generator 6 to obtain output light. . Therefore,
Now, if the frequency of the reference signal generated by the reference signal oscillator 6 is r, and the center frequency of the voltage controlled oscillator 7 controlled by this signal is v, then the output signal of the voltage controlled oscillator 7 has a center frequency of v. The modulation frequency becomes a frequency modulated wave of r. Therefore,
The frequency of the incident light of the acousto-optic frequency modulator 3 is
If o, the output light from the acousto-optic frequency modulator 3 becomes frequency modulated light with a center frequency o±v and a modulation frequency r. Note that in this case, the sign or minus of the deviation of the center frequency is determined by the configuration of the acousto-optic frequency modulator 3.

Next, the output light of the acousto-optic frequency modulator 3 obtained in this way is input to a device 4 having an absorption or transmission spectrum serving as a frequency reference, and the obtained transmitted light is converted into an electric signal by a photoelectric conversion element 5. is converted to The electrical signal thus obtained is subjected to phase detection by the phase detector 8 with reference to the reference signal of frequency r generated by the reference signal generator 6 described above. Therefore, let us now assume that the device 4, which has an absorption or transmission spectrum that serves as a frequency reference, has an absorption or transmission spectrum that has a center frequency s as shown in FIG. It is assumed that an integrator 9 is provided which has a time constant that can sufficiently eliminate the noise. In this case, the output signal of the integrator 9 has a center frequency o±v of the output light of the acousto-optic frequency modulator 3, as shown in FIG.
When it matches s, it becomes zero, and before and after that, the sign becomes opposite. Therefore, by the output signal of the integrator 9,
By controlling the frequency o of the laser oscillator 1, the frequency o±v of the emitted light from the acousto-optic frequency modulator 3 can be adjusted.
can always be made to coincide with the center frequency s of the absorption or transmission spectrum of the device 4 serving as a frequency reference. That is, this means that the oscillation frequency o of the laser oscillator 1 is stabilized to match the stable frequency s±v.

In the laser frequency stabilization device mentioned above,
The higher the frequency r of the reference signal, the smaller the time constant of the integrator 9 required to remove that frequency component, and as a result, the response speed of this type of device can be increased. Furthermore, by using the acousto-optic frequency modulator 3, it is easy to increase the frequency r of the reference signal to several MHz, and it is possible to improve the performance and reliability of this type of device.

As is clear from the embodiments described above, according to the present invention, frequency stabilization of the laser can be easily achieved without providing a mechanical vibrating section unlike conventional devices. Therefore, the device of the present invention has superior characteristics in terms of durability, robustness, and response speed compared to conventional devices.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of a laser frequency stabilizing device according to the present invention, FIG. 2 is a frequency characteristic curve diagram of absorption or transmission spectrum of the device serving as a frequency reference shown in FIG. Figure 3 is the first
FIG. 3 is a frequency characteristic curve diagram of the output signal of the integrator shown in the figure. 1... Laser oscillator, 2... Beam splitter, 3
... Acousto-optic frequency modulator, 4... Frequency reference device, 5... Photoelectric conversion element, 6... Reference signal generator, 7... Voltage controlled oscillator, 8... Phase detector, 9...
Integrator.

Claims (1)

[Claims] 1. A laser oscillator whose oscillation frequency can be controlled, an acousto-optic frequency modulator, a device having an absorption or transmission spectrum serving as a frequency reference, and a center frequency of the spectrum serving as a frequency reference and laser oscillation. and a means for controlling the oscillation frequency of the laser oscillator so that the difference approaches zero by detecting the difference between the two frequencies, and means for applying frequency modulation to a part of the laser beam by the acousto-optic frequency modulator, thereby causing the laser oscillation. A laser frequency stabilizing device characterized by being configured to detect a difference between a frequency and a center frequency of a spectrum serving as a frequency reference. 2. In the frequency stabilizing device according to claim 1, the acousto-optic frequency modulator generates a frequency modulation signal having a predetermined center frequency by being controlled by a reference signal of a predetermined frequency generated from a reference signal generator. A frequency stabilizing device for a laser, which is configured to give incident light a frequency shift equal to the frequency of an output signal of the oscillator by a generated voltage controlled oscillator. 3. In the frequency stabilizing device according to claim 1, the means for controlling the oscillation frequency of the laser oscillator by detecting the difference between the center frequency of the spectrum serving as the frequency reference and the laser oscillation frequency serves as the frequency reference. A photoelectric conversion element that converts light emitted from the device into an electrical signal, a phase detector that detects the phase of the electrical signal by referring to a reference signal having a predetermined frequency generated by a reference signal generator, and the reference signal. A laser frequency stabilizing device comprising an integrator having a time constant that can sufficiently remove a predetermined frequency component.