JPS63202726A - Optical frequency shifter - Google Patents

Abstract

PURPOSE:To generate a desired beat frequency by polarizing a 1st laser light of laser light which is emitted by a common laser light source and split into two by an acoustooptical modulating element and imposing frequency modulation, converting it to an optical path parallel to the optical axis by a concave mirror, and mixing the light with the other laser light by an optical mixing means to cause interference. CONSTITUTION:The laser light from the laser light source 10 is split into two by a polarization beam splitter 12 to obtain a P polarized light Lp parallel to an incidence surface and an S polarized light Ls perpendicular to the incidence surface. Then the angle of polarization of, for example, a 2nd acoustooptic modulating element 24 is made constant, the set value in a setter 71 is varied, and the frequency of the P polarized light Lp of a 1st acoustooptic modulating element 24 and an angle of deflection are varied. Then the P polarized light Lp is reflected by a parabolic mirror 30 and converted into a deviation parallel to the optical axis K to generate a deviation parallel to the optical path of the S polarized light Ls. Then, this deviation is detected by a photosensor 46 and the optical axes of the P polarized light Lp and S polarized light Ls are aligned with each other to obtain the desired beat frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an improvement in an optical frequency shifter that generates a beat frequency significantly lower than two different frequencies of light by mixing them.

BACKGROUND ART It is generally considered difficult to detect such changes in the frequency of light because it is necessary to use a highly responsive optical sensor to detect changes in the frequency of light. For this reason, it is desirable to generate light with a low beat frequency whose frequency change can be detected by an ordinary optical sensor.

In contrast, a transverse Zeeman type laser device has been considered. This applies a magnetic field in the axial direction of the laser tube, and generates two types of laser beams with two frequencies 1.8 MHz apart from each other on the same axis based on the Zeeman effect, thereby preventing interference between the two types of laser beams. This outputs a laser beam having a beat frequency according to the following.

It has also been considered that by utilizing the slight deviation in the frequency of light deflected by an acousto-optic modulator, a laser beam having a beat frequency can be generated by interference of the lights that have passed through a pair of acousto-optic modulators. There is. For example, as shown in FIG. 4, the laser light output from the laser light source 100 is split into two by the polarizing beam splitter 102 into P polarized light and S polarized light, and the P polarized light is transmitted to the acousto-optic modulator 1.
04, the S-polarized light is deflected by the acousto-optic modulator 105 via the mirror 103, and undergoes a frequency shift according to the deflection angle.

The P-polarized light that has undergone a frequency shift in this way is mirrored at mirror 1.
06 and passes through the polarizing beam splitter 108, and the S-polarized light is reflected by the polarizing beam splitter 108. Then, in the polarization beam splitter 10B, the P
The polarized light and the S-polarized light are superimposed and synthesized, and a laser beam having a beat frequency due to the interference of the P-polarized light and the S-polarized light is output.

Problems to be Solved by the Invention However, with such conventional optical frequency shifters, it is difficult to continuously change the beat frequency. In other words, in the transverse Zeeman type laser device, the frequency difference between the two types of laser beams generated by the Zeeman effect is a fixed value of 8 MHz, so the beat frequency obtained is only a constant 1° 8 MHz. There wasn't. Furthermore, in the optical frequency shifter using the acousto-optic modulation element, when the deflection angle is changed in the acousto-optic modulation element,
Since the coaxial relationship between the P-polarized light and the S-polarized light breaks down and an angle is formed between their optical axes, it becomes more difficult to superimpose the P-polarized light and the S-polarized light on each other as the distance from the acousto-optic modulator increases. . Therefore, since the deflection angle in the acousto-optic modulator is fixed, only light with a constant beat frequency can be obtained.

Means for Solving the Problems The present invention has been made against the background of the above circumstances.
Its gist is that it is an optical frequency shifter for changing the low beat frequency corresponding to the frequency difference between two types of laser beams by mixing them; a beam subrifter that divides the laser beam into two, a first laser beam and a second laser beam, and (b) has a focal point on the optical axis and converts the optical path of the light passing through the focal point into an optical path parallel to the leading axis. (C) an acousto-optic modulator that deflects the first laser beam around the focal point and continuously changes the frequency of the deflected light; and (d) the acousto-optic modulator. and a light mixing means for generating a composite light having a beat frequency caused by the mutual interference by aligning the optical paths of the first laser beam and the second laser beam deflected by the laser beam and causing mutual interference. It is in.

Operation and Effect of the Invention By doing this, one of the first laser beams split into two from a common laser light source is deflected and frequency-modulated by the acousto-optic modulation element, and the laser beam thus deflected is The optical path is converted by a concave mirror into an optical path parallel to its optical axis. Then, the optical mixing means causes the optical path of the first laser beam and the optical path of the other second laser beam, which is divided into two from the common laser light source, to overlap each other, so that the first laser beam and the second laser beam A beat frequency is generated by mutual interference by mixing with light. Therefore, by changing the frequency of the first laser beam using the acousto-optic modulator, the beat frequency can be changed to obtain a desired beat frequency.

Here, the beam splitter is preferably a polarizing beam splitter that splits the laser beam into P-polarized light and S-polarized light.

In addition, the acousto-optic modulator includes, for example, a transparent substrate having an acousto-optic effect, a surface acoustic wave applied to the transparent substrate, and a period of refractive index formed in the transparent substrate corresponding to the surface acoustic wave. It is equipped with an ultrasonic transducer that diffracts light based on a diffraction grating formed by dense and dense parts, and the frequency of the diffracted light is adjusted as the frequency of the surface acoustic wave applied from the ultrasonic transducer changes. Along with shifting,
The diffraction (deflection) angle is also changed by changing the lattice constant. Usually, the first-order diffracted light of Bragg diffraction is used as the polarized light by the acousto-optic modulation element.

Further, the light mixing means preferably includes a polarizing beam splitter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splitter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splitter or a half mirror for outputting the first laser beam and the second laser beam in the same direction. and a positioning mechanism for aligning the output optical axes of the second laser light.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

In FIG. 1, laser light emitted from a laser light source 10 is split into two by a polarization beam splitter 12 into P-polarized light parallel to the plane of incidence and S-polarized light perpendicular to the plane of incidence. This plane of incidence is a plane that includes the incident ray, the surface normal of the point of incidence, the reflected ray, or the refracted ray. The P-polarized light transmitted through the polarization beam splitter 12 is made incident on the first acousto-optic modulation element 14 . The first acousto-optic modulator 14 includes a transparent substrate 16 having an acousto-optic effect, a surface acoustic wave applied to the transparent substrate 16, and a refractive index formed in the transparent substrate 16 in response to the surface acoustic wave. It includes an ultrasonic transducer 18 that diffracts light based on a diffraction grating made up of periodic dense and dense parts. Frequency controller 7
0 changes the oscillation frequency of the oscillator 72 for supplying a high-frequency drive signal to the ultrasonic transducer 18 in response to the setting value of the setting device 71, and generates a surface acoustic wave applied from the ultrasonic transducer 18. By changing the frequency of P-polarized light LP, the frequency of P-polarized light LP is shifted, and by changing the diffraction grating constant,
It also changes the diffraction (deflection) angle of the polarized light.

The S-polarized light L1 reflected by the polarization beam splitter 12 is made incident on the second acousto-optic modulation element 24.

The second acousto-optic modulation element 24 is the first acousto-optic modulation element 1
4, a transparent substrate 26 having an acousto-optic effect, a surface acoustic wave applied to this transparent substrate 26, and a periodic irregularity of refractive index formed in the transparent substrate 26 in response to the surface acoustic wave. It includes an ultrasonic transducer 28 that diffracts light based on a diffraction grating made up of sections. The frequency controller 74 changes the oscillation frequency of an oscillator 76 for supplying a high-frequency drive signal to the ultrasonic transducer 28 in response to the setting value of the setting device 75, and changes the oscillation frequency of an oscillator 76 for supplying a high-frequency drive signal to the ultrasonic transducer 28. S-polarization by changing the frequency of elastic waves,
As well as shifting the frequency of the S-polarized light, the diffraction (deflection) angle of the S-polarized light can also be changed by changing the diffraction grating constant.

In this embodiment, the first acousto-optic modulator 14 is arranged such that the emission point S of the first acousto-optic modulator 14 coincides with the focal point above the optical axis of the parabolic mirror 30 functioning as a concave mirror in this embodiment. The relative positions of the modulation element 14 and the parabolic mirror 30 have been determined. The parabolic mirror 30 includes the first acousto-optic modulator 1
P-polarized light incident through the emission point S1 of No. 4 is converted into an optical path parallel to the optical axis K, regardless of its deflection angle. Above P
Polarization is the first-order diffracted light of the first acousto-optic modulator 14 selected by a mask (not shown).

The P-polarized light, which is converted into an optical path parallel to the optical axis K by the parabolic mirror 30, enters the beam splitter 38 from the X direction, where it is transmitted, goes straight, and is outputted to the outside in a direction perpendicular to the beam. The reflected beam is split into a beam that is received by optical sensor 44.

Further, the S-polarized light that has passed through the second acousto-optic modulator 24 is incident on the beam splitter 38 from the y direction, reflected at the beam splitter 38, and outputted to the outside along the X direction, and the beam splitter 3B. and a beam that is transmitted through and received by the optical sensor 44.

Then, the beam splitter 38 and the optical sensor 44
is a Y table 5 that is moved in the Y direction by a Y direction drive motor 50 so that their relative positions do not change.
It is fixed on 2. Here, the beam splitter 38 is known as a so-called half mirror, and
Approximately half the amount of light of the incident light is reflected, and the remaining amount of light is transmitted.

As shown in FIG. 2, the optical sensor 44, which receives the P-polarized light and the S-polarized light from the beam splinter 38 as described above, detects the deviation in the X direction of the incident P-polarized light L2 and S-polarized light. A pair of detection units 54 and 56 for detection
is provided.

The signals output from the detection units 54 and 56 are differentially amplified by the differential amplifier 62, and the motor drive circuit 64 generates a drive signal for moving the Y table 52 in the direction in which the signal from the differential amplifier 62 becomes smaller. It is supplied to the Y direction drive motor 50.

In this embodiment, a beam splitter 38 is installed at the center of the optical sensor 44 so that the S-polarized light L8 from the second acousto-optic modulator 24 can be received regardless of the moving position of the Y table 52.
and an optical sensor 44, and the motor drive circuit 64 detects the P-polarized light received by the optical sensor 44, as shown in FIG.

The moving position of the Y table 52 is adjusted so that the S-polarized light coincides with the S-polarized light. As a result, the optical paths of the P-polarized light and the S-polarized light L1 emitted from the beam splinter 38 to the outside along the X direction are suitably matched, and a composite light with a beat frequency corresponding to the frequency difference between the two is output. be done. That is, in this embodiment, the beam splinter 38.
Optical sensor 44, Y table 52. Differential amplifier 62. and the Y-direction drive motor 64 constitute a light mixing means. In FIGS. 2 and 3, circles drawn with solid lines indicate beam spots of S-polarized light L8, and circles drawn with broken lines indicate beam spots of P-polarized light, respectively.

The operation of this embodiment will be explained below.

In order to obtain a desired beat frequency, for example, the deflection angle of the S-polarized light in the second acousto-optic modulation element 24 is kept constant, while the setting value in the setting device 71 is changed according to manual or automatic operation, so that the oscillator 72 When the oscillation frequency of the first acousto-optic modulator 14 is changed,
The frequency of the P-polarized light is changed, and the deflection angle thereof is also changed, resulting in an optical path shown by the broken line in FIG. When the optical path of the P-polarized light is reflected by the parabolic mirror 30, the deviation in the deflection angle is converted to a deviation parallel to the optical axis, so the optical path of the S-polarized light is changed to a deviation parallel to the optical axis. is formed. When the P-polarized light is shifted from the S-polarized light in this way, the P-polarized light is received by the optical sensor 44 in a state that is shifted from the S-polarized light, as shown in FIG. It will be done. Therefore, the spot of P-polarized light is located at the center of the optical sensor 44, in other words, the spot of P-polarized light coincides with the spot of S-polarized light located at the center of the optical sensor 44. The Y table 52 is automatically moved in the y direction so as to do so.

As a result, as shown in FIG.
1, the beam splinter 38
The optical paths of the P-polarized light and the S-polarized light output from L3 to the outside are made to fail, and light having a beat frequency corresponding to the frequency difference between the P-polarized light and the S-polarized light L3 is output.

Therefore, by changing the vibration frequency of the ultrasonic transducer 18 in the first acoustic modulation element 14, the P-polarized light is
When the frequency of L3 is changed, the beat frequency between the P-polarized light and the S-polarized light L3 can be changed to a desired value.

Although one embodiment of the present invention has been described above in detail based on the drawings, the present invention can also be applied to other aspects.

For example, in the embodiment shown in FIG. 1 described above, the deflection angle of the P-polarized light LP in the first acousto-optic modulator 14 is constant, and the frequency and deflection angle of the S-polarized light in the second acousto-optic modulator 24 are set by the setting device. Even if changed by 75,
The beat frequency between P polarization and S polarization 1 can be changed to a desired value. In this case, a parabolic mirror is provided so that the focal point is at the output point of the second acousto-optic modulator 24, and an X table movable in the X direction is prepared in place of the Y table 52. X table
By automatically moving the P-polarized light and the S-polarized light L output from the beam splinter 38 to the outside,
1 optical axes are made to coincide.

In addition, another parabolic mirror is newly provided opposite to the parabolic mirror 30, and the output point of the second acousto-optic modulator 24 is made to coincide with the focal point of this new parabolic mirror, thereby changing the beat frequency. In order to change it to a desired value, the deflection angle of the P-polarized light LP in the first acousto-optic modulation element 14 and the deflection angle of the S-polarized light L5 in the second acousto-optic modulation element 24 may be changed simultaneously. be.

Further, in the above-mentioned embodiment, the polarizing beam splitter 12 is used to split the laser beam output from the laser light source 10 into two, but the polarizing beam splitter 12 may be configured by a so-called half mirror or the like. .

Furthermore, although the parabolic mirror 30 was used in the above embodiment, a spherical mirror may also be used. In short, any concave mirror is sufficient as long as the reflected light of the light incident through the focal point is parallel to the optical axis.

Furthermore, in the embodiments described above, the optical path may be changed as necessary, and other optical elements may be provided as appropriate.

Note that the above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the configuration of an embodiment of the present invention. FIGS. 2 and 3 are diagrams for explaining the configuration and light receiving state of the detection section in the optical sensor shown in FIG. 1, respectively. FIG. 4 is a diagram illustrating a conventional optical frequency shifter. 10: Laser light source 30: Parabolic mirror (concave mirror) 12
:i Optical beam splitter (beam splitter) 14: First acousto-optic modulator (acousto-optic modulator) 24: Second acousto-optic modulator (acousto-optic modulator) Applicant: Brother Industries, Ltd. Figure 1 Figure 2 3rIfJ

Claims (1)

[Claims] An optical frequency shifter for changing a low beat frequency corresponding to a frequency difference between two types of laser beams by mixing two types of laser beams, the method comprising: a beam splitter that splits the laser beam into two; a concave mirror that has a focal point on the optical axis and converts the optical path of the light passing through the focal point into an optical path parallel to the optical axis; and the first laser. an acousto-optic modulator that deflects light around the focal point and continuously changes the frequency of the deflected light; An optical frequency shifter comprising: a light mixing means for generating combined light having a beat frequency resulting from the mutual interference by aligning optical paths and causing mutual interference;