JPS63202725A - 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 acoustooptic modulating element and imposing frequency modulation, converting it to an optical path parallel to the optical axis through an optical path converting element, 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 passed through a convex lens 30 as the optical path converting element 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 optical frequency chic, which 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 laser beams with two frequencies 1.8 MHz apart from each other on the same axis based on the Zeeman effect.
This outputs a laser beam having a beat frequency due to the interference of different types of laser beams.

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. 8, 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 and S-polarized light are split by the acousto-optic modulator 104 and Mirror 1 for S polarized light
03, and are each deflected by the acousto-optic modulation element 105 and subjected to a frequency shift according to the deflection angle. The P-polarized light that has undergone the frequency shift in this manner is reflected by the mirror 106 and passes through the polarizing beam splitter 108, and the S-polarized light is reflected by the polarizing beam splitter 108. Then, in the polarizing beam splitter 108, the P-polarized light and the S-polarized light, which have undergone different frequency shifts, 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 switching, it is difficult to change the beat frequency to a desired value. That is, in the transverse Zeeman type laser device, the frequency difference force between the laser beams of two types of frequencies generated by the Zeeman effect is a fixed value of 8 MHz, so the beat frequency obtained is only a constant 1.8 Mtlz. Ta. Furthermore, in the optical frequency shifter using the acousto-optic modulator, when the deflection angle is changed in the acousto-optic modulator,
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. . For this reason, the deflection angle in the acousto-optic modulator is fixed, and 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 thickening method for changing the low beat frequency corresponding to the frequency difference between two types of laser beams obtained by mixing two types of laser beams. (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 optical axis; fc) an acousto-optic modulation element that deflects the first laser beam around the focal point and continuously changes the frequency of the deflected light; and (d) the acousto-optic modulation element. and a light mixing means for generating a composite light having a beat frequency due to the mutual interference by mutually interfering the first laser light and the second laser light deflected by the laser beam.

Operation and Effect of the Invention In this way, one of the first laser beams split into two from a common laser light source is deflected and frequency-modulated by the acousto-optic modulator, and the optical path of the deflected first laser beam is is converted into an optical path parallel to the optical axis of the optical path conversion element. As a result, the optical paths of the first laser beam and the other second laser beam divided into two from the common laser light source are maintained in a parallel relationship without forming an angle with each other. The laser beam and the second laser beam can be suitably mixed, and a beat frequency is generated due to mutual interference. Therefore, the acousto-optic modulator allows the first
By changing the frequency of the laser beam, a desired beat frequency can be obtained.

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

Moreover, a convex lens, a parabolic mirror, two spherical mirrors, etc. are preferably used for the optical path conversion element.

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.

The light mixing means preferably includes a polarizing beam splitter, a half mirror, etc., which converts two laser beams into one laser beam by substantially aligning them with a common optical axis.

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

In FIG. 1, a laser beam emitted from a laser light source 10 is split into two by a polarization beam splitter 12 into P-polarized light Lp parallel to the plane of incidence and S-polarized light Ls 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 or 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. The frequency of P-polarized light L9 is shifted by changing the frequency of P-polarized light L9, and the P-polarized light L9 is shifted by changing the
It also changes the diffraction (deflection) angle of the polarized light.

The S-polarized light reflected by the polarization beam splitter 12 is reflected by mirrors 20, 21 and 22, and is made incident on the second acousto-optic modulator 24. Like the first acousto-optic modulator 14, the second acousto-optic modulator 24 includes a transparent substrate 26 having an acousto-optic effect.
Then, a surface acoustic wave is applied to this transparent substrate 26, and light is diffracted based on a diffraction grating formed in the transparent substrate 26 corresponding to the surface acoustic wave, which is made up of periodic dense and dense parts of the refractive index. The ultrasonic transducer 28 is equipped with an ultrasonic transducer 28 for causing 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
By changing the frequency of the surface acoustic wave applied from 8, the frequency of the S-polarized light is shifted, and the diffraction (deflection) angle of the S-polarized light is also changed by changing the diffraction grating constant.

In this embodiment, the emission point S of the first acousto-optic modulation element 14 and the emission point S2 of the second acousto-optic modulation element 24 are located above the optical axis of the convex lens 30 functioning as the optical path conversion element of this embodiment. The relative positions of the first acousto-optic modulation element 14 and the second acousto-optic modulation element 24 are determined with respect to the convex lens 30 so that the first acousto-optic modulation element 14 and the second acousto-optic modulation element 24 are located at the focal point of the convex lens 30 . The convex lens 30 is located at the exit point S of the first acousto-optic modulator 14 and the second acousto-optic modulator 24.
P-polarized light and S-polarized light incident from the emission point S2 through the masks 32 and 34 are converted into optical paths parallel to the optical axis K, regardless of their polarization angles. The above mask 32
and 34 are for selectively passing the first-order diffracted light of the first acousto-optic modulator 14 and the second acousto-optic modulator 24, respectively.

P converted into an optical path parallel to the optical axis K by the convex lens 30
The polarized light is reflected by the mirror 36 and enters the beam splitter 38 from the X direction, where it is transmitted, goes straight, is reflected in a direction perpendicular to the beam that enters the next beam splitter 40, and goes outside along the X direction. The output beam is split into two. Further, the S-polarized light, which is converted into an optical path parallel to the optical axis K by the convex lens 30, is reflected by mirrors 42 and 43 and enters the beam splinter 38 from the X direction. This S-polarized light is also reflected in a direction perpendicular to the beam that travels straight through the beam splitter 38 and is output to the outside along the X direction, and is reflected to the next beam splitter 4.
0 and a beam incident from the X direction.

As described above, the P-polarized light and the S-polarized light L3 incident on the beam splitter 40 are split into the X direction and the Only the S-polarized light Ls passes through the polarizer 45 and reaches the optical sensor 44, where it is detected. P-polarized light and S-polarized light emitted from the beam splinter 40 in the X direction.

Both are detected by the optical sensor 46. Then, the beam splitter 38, 40, polarizer 45, optical sensor 44
．． 46 is an X-Y motor which is moved in the X direction by an X direction drive motor 48 and moved in the X direction by a Y direction drive motor 50 so that their relative positions do not change.
It is fixed on the table 52. Here, the beam splitters 38 and 40 are known as so-called half mirrors, and reflect approximately half the amount of light of the incident light while transmitting the remaining amount of light.

As shown in FIG. 2, the light-receiving surface of the optical sensor 44 for detecting the S-polarized light that has passed through the polarizer 45 has a pair of sensors for detecting the deviation of the incident S-polarized light in the X direction. Detectors 54 and 56 are provided separated by a predetermined distance 1ifI. Further, as shown in FIG. 3, the light receiving surface of the optical sensor 46 is also provided with a pair of detection sections 58 and 60 for detecting the deviation of the incident P-polarized light and the S-polarized light L8 in the X direction. There is.

The signals output from the detection units 54 and 56 in the optical sensor 44 are differentially amplified by the differential amplifier 62, and the motor drive circuit 64 moves the X-Y table 52 in the direction where the signal from the differential amplifier 62 becomes smaller. A drive signal for movement is supplied to the Y-direction drive motor 50. Therefore, if the center of the S-polarized light L3 shifts for some reason as shown in FIG. 4, the X-Y table 52 is automatically moved in the , the center of the S-polarized light L1 is the center of the optical sensor 44, that is, its detection parts 54 and 56.
It is always located in between. This causes the center of the S-polarized light to pass through the center of beam splitters 38 and 40 and to be received at the center of optical sensor 46, as shown in FIGS. 3 and 5.

Further, the signals output from the detection units 58 and 60 in the optical sensor 46 are differentially amplified by the differential amplifier 66, and the motor drive circuit 64 moves the X-Y table 52 in the direction in which the signal from the differential amplifier 66 becomes smaller. A drive signal for moving the is supplied to the X-direction drive motor 48. As a result, when the frequency of the P-polarized light is changed in the first acousto-optic modulator 14 and the light receiving position in the optical sensor 46 changes as shown in FIG. 5, the X-Y table 52 is automatically moved. is moved in the X direction so that the center of the P-polarized light is located at the center of the optical sensor 46, that is, between its detection portions 58 and 60, as shown in FIG. As a result, the optical axes of the S-polarized light L3 and the P-polarized light Lp output from the beam splinter 3 to the outside through the mask 68 are matched and mixed, so the frequency difference between the S-polarized light and the P-polarized light L9 is accommodated. Light having a beat frequency is output. In this embodiment, the beam splitter 3
8 is S-polarized light, which is two types of laser light.

and P-polarized light. In addition, in FIGS. 2, 3, 4, and 5, the circles drawn with solid lines represent S-polarized light.

The circle drawn with a broken line indicates the beam spot of P-polarized light,
The beam spots are shown 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. The optical path of the P-polarized light is converted from a deflection angle deviation to a deviation parallel to the optical axis by passing through the convex lens 30, so that a deviation parallel to the optical path of the S-polarized light is formed. . When the P-polarized light L2 is shifted from the S-polarized light in this way, the P-polarized light becomes P-polarized as shown in FIG. 5, for example.

The light is S-polarized and is received by the optical sensor 46 in a state shifted from the S-polarized light. Therefore, the spot of the P-polarized light LI is located at the center of the optical sensor 46, in other words, the spot of the P-polarized light L2 is located at the center of the optical sensor 46.
The X-Y table 52 is automatically moved in the X direction so as to match the spot of the polarized light L8. This results in
P-polarized light L9 output from the beam splitter 38 to the outside
The optical paths of the P-polarized light and the S-polarized light are matched, and they are suitably mixed to output light having a beat frequency corresponding to the frequency difference between the P-polarized light and the S-polarized light.

As described above, according to this embodiment, the common laser light source 1
Of the P polarized light divided into two from 0, and the S polarized light L8,
The P-polarized light is deflected and frequency-modulated by the first acousto-optic modulator 14, and this P-polarized light is
0, the light is finally S-polarized and converted into an optical path parallel to the S-polarized light. As a result, the optical paths of the P-polarized light LP and the S-polarized light L8 are maintained in a parallel relationship without forming an angle with each other.
After the beam splitter 38, P polarized light LP and S
The polarized lights are suitably mixed to generate a beat frequency due to mutual interference. That is, the first acoustic modulation element 1
When the frequency of P-polarized light is changed by changing the vibration frequency of the vibrator 18 in 4, P-polarized light and S-polarized light are generated.

The beat frequency in between can be continuously changed to a desired value. Furthermore, by setting the set value of the setter 71 to a discontinuous value, the beat frequency can be changed discontinuously.

Next, another embodiment of the present invention will be described. Note that in the following embodiments, parts common to those in the above-described embodiments are designated by the same reference numerals, and explanations thereof will be omitted.

In FIG. 6, the S-polarized light reflected by the polarizing beam splitter 12 passes through mirrors 20, 21 and 43, and is incident on the beam splitter 38 from the X direction without passing through the acousto-optic modulator. The beam splitter 38 and the optical sensor 46 are attached to the X table 80 which is driven only in the X direction by the X direction drive motor 48, and the P polarized light Lp and the S polarized light L3 emitted from the beam splitter 38 in the y direction. is received by the optical sensor 46. Normally, the beam splitter 38 and the optical sensor 46 are arranged in the center of the optical sensor 46 so as to receive S-polarized light regardless of the moving position of the X table 80, and the motor drive circuit 64 is connected to the As shown in , the P polarized light LP received by the optical sensor 46 becomes the S polarized light
Adjust the moving position of the X table 80 so that it matches 3.

As a result, the P-polarized light LP and the S-polarized light emitted from the beam splitter 38 to the outside along the X direction are suitably mixed, and a beat frequency corresponding to the frequency difference between the two is obtained. Therefore, as described above, by changing the frequency of the P-polarized light in the first acousto-optic modulation element 14 by the setter 71, the beat frequency is continuously changed.

Furthermore, as shown in FIG. 7, a parabolic mirror 90 may be used as the optical path conversion element. That is, the P polarized light Lp and the S polarized light L divided into two by the polarizing beam splitter 12
1 is made incident on the first acousto-optic modulation element 14 and the second acousto-optic modulation element 24, respectively. The emission point S1 of the first acousto-optic modulator 14 is located at the focal point of the parabolic mirror 90, and the P-polarized light deflected by the first acousto-optic modulator 14 is radiated regardless of its deflection angle. The light is converted into an optical path parallel to the optical axis of the object mirror 90, and is incident on the beam splitter 38 from the X direction. The P-polarized light Ll incident on the beam splitter 38 in this manner is transmitted through it and emitted to the outside along the X direction, and is reflected in the y direction and received by the optical sensor 44. It is divided into two beams. On the other hand, the second
The S-polarized light emitted from the acousto-optic modulator 24 is y
The beam enters the beam splinter 38 from this direction, and is divided into two beams: a beam that is reflected in the X direction and emitted to the outside, and a beam that is transmitted in the Y direction and received by the optical sensor 44.

Y driven only in the X direction by the Y direction drive motor 50
The beam splitter 38 and the optical sensor 44 are attached to the table 92, and the beam splitter 38 and the optical sensor 44 are attached to the table 92.
P polarized light LP and S polarized light L8 emitted from 8 in the X direction
is received by the optical sensor 44. Usually, the optical sensor 44
A beam splitter 38 and an optical sensor 44 are arranged at the center of the Y-table 92 so as to receive S-polarized light regardless of the moving position of the Y-table 92, and the motor drive circuit 64 operates as shown in FIG. The moving position of the Y table 92 is adjusted so that the P-polarized light received by the optical sensor 44 coincides with the S-polarized light. As a result, beam splinter 3
P-polarized light and S-polarized light emitted from 8 to the outside along the X direction are suitably mixed, and a beat frequency corresponding to the frequency difference between the two is obtained. Therefore, in this embodiment as well, the beat frequency is continuously changed by changing the frequency of the P-polarized light L9 in the first acousto-optic modulation element 14 by the setter 71, as described above.

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, 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 L8 in the second acousto-optic modulator 24 are set by the setter 75. Even if changed by
The beat frequency between the P polarized light Lp and the S polarized light L8 can be changed continuously. In this case, by automatically moving the X-Y table 52 in the X direction, the optical axes of the P-polarized light and the S-polarized light output from the beam splitter 38 to the outside are made to coincide.

Furthermore, in order to continuously change the beat frequency, the deflection angle of the P-polarized light L2 in the first acousto-optic modulation element 14 and the deflection angle of the S-polarized light L1 in the second acousto-optic modulation element 24 may be changed simultaneously. It's good.

In the embodiment shown in FIG. 7, the P-polarized light emitted from the second acousto-optic modulator 24 is directed to the optical axis K by another parabolic mirror newly provided opposite the parabolic mirror 30. It is also possible to convert the light into a parallel optical path and then make it incident on the beam splitter 38. Further, the second acousto-optic modulator 24 may be removed. Furthermore, a spherical mirror or the like may be used instead of the parabolic mirror 30.

Furthermore, in the embodiment described above, the beam splitter 38 is
Y table 52, X table 80. It is attached to the Y table 92 and is configured so that the optical axes of the P-polarized light and the S-polarized light L8 outputted from the beam splitter 38 to the outside are completely aligned. If the change in the deflection angle of the P-polarized light in the acousto-optic modulator 14 is slight, a continuously changing beat frequency can be obtained even if the beam splitter 38 is provided in a fixed position.

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, 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. FIG. 2, FIG. 3, FIG. 4, and FIG. 5 are diagrams each illustrating the configuration and light receiving state of the detection section in the optical sensor of FIG. 1. 6 and 7 are diagrams corresponding to FIG. 1 in other embodiments of the present invention, respectively. FIG. 8 is a diagram illustrating a conventional optical frequency shifter. 10: Laser light source 12: Polarizing beam splitter (beam splitter) 14
: First acousto-optic modulator (acousto-optic modulator) 24: Second acousto-optic modulator (acousto-optic modulator) 30: Convex lens (optical path conversion element) 38: Beam splitter (light mixing means) 90: Parabolic mirror (Optical path conversion element) Fig. 1 Fig. 2 Fig. 38 Fig. 4 S Fig. 6 Fn

Claims (1)

[Claims] An optical frequency shifter for changing a low beat frequency corresponding to a frequency difference between two types of laser beams obtained by mixing two types of laser beams, the laser beam output from a laser light source. 2 to the first laser beam and the second laser beam
a beam splitter that has a focal point on the optical axis and converts an optical path of light passing through the focal point into an optical path parallel to the optical axis; and a beam splitter that deflects the first laser beam around the focal point. an acousto-optic modulator that simultaneously changes the frequency of the deflected light; and a first laser beam deflected by the acousto-optic modulator and the second laser beam that mutually interfere with each other. An optical frequency shifter comprising: an optical mixing means for generating a composite light having a beat frequency due to mutual interference; and an optical frequency shifter.