JPS6014330B2 - Optical frequency stabilizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stabilizing device for stabilizing optical frequencies absolutely or relatively.

For example, as shown in FIG. 1, in a laser oscillator in which reflecting mirrors 12 and 13 are arranged on both sides of a laser medium 11 and emitted light 14 is obtained from the center hole of one of the reflecting mirrors 13, the frequency of the emitted light is In order to stabilize the output light, conventionally
4 is incident on the half mirror 15, and the reference light 16 is also incident on this half mirror 15, and from the half mirror 15,
The two lights 14 and 16 are combined and supplied to a photodetector 17.

An electrical signal of the frequency difference between the two lights 14 and 16 incident on the photodetector 17 is obtained, and the electrical signal is compared with a reference frequency in the control signal generation circuit 18, and an electrical signal corresponding to the difference is generated. , the piezoelectric solid object 19 holding the reflecting mirror 12 is controlled by the electric signal. Through this control, the position of the reflecting mirror 12 was adjusted, and the frequency of the emitted light 14 was kept constant with respect to the frequency of the reference light 16. The position adjustment of the reflecting mirror 12 has been performed not only using piezoelectricity but also mechanically. As described above, since the conventional device uses a method of changing the position of the reflecting mirror 12, the operating speed is slow.

That is, when the frequency of the emitted light 14 fluctuates from the reference frequency, it takes a long time to compensate for this fluctuation and return to the predetermined reference frequency again. Furthermore, when mechanical vibrations are applied to the laser oscillator from the outside, the reflecting mirror 12 itself that performs the stabilizing operation vibrates, so there is also the disadvantage that sufficient frequency stabilization cannot be performed against such mechanical vibrations. there were. An object of the present invention is to provide a frequency stabilizing device that stabilizes the difference frequency between two laser beams, which has a long operating speed and operates stably against external vibrations.

According to this invention, a variable frequency converter is provided which can control the frequency of incident light to output light using an electrical control signal, and the output light of the first laser oscillator is connected to the variable frequency converter. is incident.

The output light of the variable frequency converter and the output light of the second laser oscillator are input to a control signal generating means, the difference frequency between these two lights is detected, and the fluctuation of this difference frequency with respect to the reference frequency is detected as an electrical signal. is detected, and the electrical signal is used to generate an electrical control signal for suppressing the fluctuation, thereby controlling the variable frequency converter. As a result, the frequency difference between the output lights of the first and second laser oscillators is kept constant. Second
The figure shows an example of an optical frequency stabilization device according to the present invention.

Output light 14 from first laser oscillator 20 is incident on variable frequency converter 21 . This variable frequency converter 21 converts the frequency of incident light using an electrical control signal and outputs the frequency.
A known method that utilizes electric or magneto-optical effects can be used. The variable frequency converter 21 is controlled by a control signal 23 from a drive circuit 22.

As a result, the frequency of the incident light 14 is changed to the frequency converter 21.
After passing through, the output light 24 has a frequency of 10 Δ.
Output light 24 is supplied to control signal generating means 25 . Within the control signal generating means 25, a portion of the output light 24 is reflected by a half mirror 34, further reflected by a half mirror 35, and is incident on a photodetector 29. On the other hand, the output light 16 of the second laser oscillator 33 is supplied to the half mirror 35 of the control signal generating means 25, and is incident on the photodetector 29 at the same time as the output light 24 from the half mirror 34. In this case, the frequency of the output light 24 is 10△ and the frequency of the output light 16 is. A heterodyne beat signal having a difference frequency Δf is generated, and this beat signal is supplied to the control signal generation circuit 31. When the difference frequency Δf varies from a predetermined reference frequency Δ, the control signal generation circuit 31 generates a control signal to compensate for the variation. The control signal generation circuit 31 uses the difference frequency △f and the reference frequency △
Compare fo and find that △f is larger (or smaller) than △ et al.
In this case, a control signal 26 is generated to increase (or decrease) the conversion frequency Δ, and this control signal 26 is supplied to the drive circuit 22 to generate the control signal 23.

As a result, the frequency of the output light 24 of the frequency converter 21 is 10Δ and the frequency of the output light 16 of the second laser oscillator 33 is different. The difference frequency △f is kept as stable as △fo. Since the control signal generation circuit 31 can be easily realized using existing technology, a detailed explanation thereof will be omitted. A component indicated by 32 in the output light of the frequency converter 21 is a component that is not frequency converted, and although it is small, it generally occurs. By using the conventional frequency stabilizing device shown in FIG. 1 together with the device of the present invention, it is also possible to realize more advanced stabilization or stabilization of a laser with large frequency fluctuations. As explained above, in the optical frequency stabilizing device according to the present invention, frequency stabilization is achieved only by electrical signal processing without requiring mechanical displacement such as moving a reflector in the conventional technology. Therefore, it is possible to realize stabilization of the optical frequency with a fast operation response speed and unaffected by mechanical vibration.

To further stabilize the conversion frequency △ 10 z
It is also possible to set the frequency band below, and in this case, it is extremely easy to generate this frequency △ for a long time with a stability of 10-8 or higher even with existing technology, and therefore it is possible to It is possible to achieve an extremely high degree of stabilization of frequencies of 10-15 or more.

Furthermore, since there is no need to move the reflecting mirror, it is easy to downsize and extend the life of the laser oscillator, and it is possible to create a laser oscillator that is immune to the effects of atmospheric pressure fluctuations and temperature fluctuations in the outside world.

In the case of a configuration in which a frequency converter is installed outside the laser oscillator, the frequency converter functions as an optical isolator, so it is possible to stabilize the frequency and prevent reflected light from returning to the laser oscillator. . A frequency stabilized light source to which the device of the present invention is applied can be used in various devices or systems that require a light source with high frequency stability.

It is particularly useful as a light source on the transmitting side or a local light source on the receiving side in a heterodyne communication system. For example, the frequency is △
By transmitting two output lights 16 and 24 that differ by f by an optical fiber from the transmitting side and obtaining the beat signal on the receiving side, this is equivalent to the conventional transmission method in which spatial transmission was performed using microwaves with a frequency of △f. It is possible to transmit signals using optical fiber, and it is possible to perform long-distance, non-repeater, and highly reliable transmission.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing the subordinate optical frequency stabilization device, Figure 2
The figure is a configuration diagram showing an embodiment of an optical frequency stabilizing device according to the present invention. 14... Incident light, 25... Control signal generation means, 21... Variable frequency converter, 22... Drive circuit, 24... Output light, 20, 33... Laser oscillator, 31... Control signal Generation circuit, 34, 35...half mirror. Figure 1 Soup Figure 2

Claims (1)

[Claims] 1. A variable frequency converter into which the output light from the first laser oscillator is incident, the frequency of the incident light is converted by an electrical control signal, and the frequency conversion amount outputs light according to the electrical control signal. The difference frequency between the output light of the variable frequency converter and the output light from the second laser oscillator is detected, and the variation of the difference frequency with respect to the reference frequency is detected as an electrical signal, and the variation is detected by this electrical signal. and control signal generating means for supplying the electrical control signal to the variable frequency converter to suppress the frequency.