JPS63202724A - 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 layer 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 a convex lens, 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 acoustooptica modulating element 24 and an angle of deflection are varied. Then the P polarized light Lp is passed through a convex lens 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 the frequencies of two types of light by mixing two types of light with different frequencies. .

Prior Art Since it is necessary to use an optical sensor with extremely high responsiveness to detect changes in the frequency of light, it is generally considered difficult to directly detect such 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. 7, the laser beam 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 108, 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 change the beat frequency to a desired value. That is, in the transverse Zeeman type laser device, the frequency difference between the laser beams of two different frequencies generated by the Zeeman effect is a fixed value of 1.13 MHz, so the beat frequency obtained is only a constant 1.8 MHz. 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 is significantly disrupted, and an angle is formed between their optical axes, it becomes difficult to superimpose the P-polarized light and the S-polarized light on each other as the distance from the acousto-optic modulator increases. becomes. 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 beat frequency lower than the frequency of the laser beams obtained by mixing two types of laser beams; A beam splitter that splits the laser beam into two, a first laser beam and a second laser beam, and a) a beam splitter 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. Convex lens and (C)
(d) a first laser beam deflected by the acousto-optic modulation element; The present invention further includes 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 second laser light and causing mutual interference.

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 convex lens into an optical path parallel to its optical axis. Then, by the light mixing means, the optical path of the first laser beam and the optical path of the other second laser beam divided into two from the common laser light source are made to coincide with each other.
The laser beam and the second laser beam are suitably mixed to generate a beat frequency due to mutual interference. therefore,
By changing the frequency of the first laser beam using the acousto-optic modulation means, 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 splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter or a half mirror for outputting the first laser beam and the second laser beam in the same direction, and a polarizing beam splinter 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 beam.

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 L9 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 Lp 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 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.
A surface acoustic wave is applied to this transparent substrate 26, and light is emitted 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 portions of refractive index. It is equipped with an ultrasonic transducer 28 that causes diffraction. 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 the oscillator 76 for supplying a high frequency drive signal to the ultrasonic transducer 28, S by changing the frequency of elastic waves
The frequency of the polarized light L1 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 and are respectively at the focal point of the convex lens 30. In order to match, the first acousto-optic modulation element 14
And the relative position of the second acousto-optic modulator 24 with respect to the convex lens 30 is determined. The convex lens 30 is connected to the masks 32 and 34 from the emission point S1 of the first acousto-optic modulation element 14 and the emission point S2 of the second acousto-optic modulation element 24.
P-polarized light Ll incident through, and S-polarized light Ll.

into an optical path parallel to the optical axis K, regardless of their deflection angle. The masks 32 and 34 are for selectively passing the first-order diffracted light from 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 LP is reflected by the mirror 36 and enters the beam splinter 38 from the y direction, where it is transmitted, goes straight, is reflected in a direction perpendicular to the beam that enters the next beam splinter 40, and is output to the outside along the X direction. The beam is divided into two beams. 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 the mirror 42 and r43 and enters the beam splinter 38 from the X direction. This S-polarized light is also split by the beam splitter 38 into a beam that travels straight and is output to the outside along the X direction, and a beam that is reflected in the right angle direction and enters the next beam splitter 4o from the X direction. Ru.

As described above, the P polarized light LP and S polarized light incident on the beam splitter 4o are split into the X direction and the , S-polarized light L8 passes through the polarizer 45 and reaches the optical sensor 44, where it is detected. Both the P-polarized light and the S-polarized light L8 emitted from the beam splitter 40 in the X direction are detected by the optical sensor 46. The beam splitter 38.40, polarizer 45, and optical sensor 44.46 are moved in the X direction by the X direction drive motor 48 and moved in the X direction by the Y direction drive motor 5o so that their relative positions do not change. It is fixed on an X-Y table 52 that can be moved in the direction. 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. 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 S-polarized light in the X direction. ing.

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 shifts as shown in FIG. 4 for some reason, the x-Y table 52 is automatically moved in the X direction, as shown in FIG. As shown in FIG.
It is always located in between. This causes the center of the S polarization 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 automatically changes. is moved in the X direction, so that the center of the P-polarized light Ll 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 paths of the S-polarized light L8 and the P-polarized light L8 outputted from the beam splitter 38 to the outside through the mask 68 are matched and mixed, so that the optical paths of the S-polarized light L8 and the P-polarized light Lp output from the beam splitter 38 to the outside are matched and mixed. Light having a beat frequency is output. In this embodiment, a beam splitter 38.40, an optical sensor 44.46, an X-direction drive motor 4
8. Y-direction drive motor 50, X-Y table 52, differential amplifiers 62, 66, motor drive circuit 64, etc. function as light mixing means for mixing two types of laser light, S-polarized light L1 and P-polarized light. do. In addition, in Fig. 2, Fig. 3, Fig. 4, and Fig. 5, the circle drawn with a solid line is S.
The beam spot of polarized light is indicated by a circle drawn with a dashed line P.
The beam spots of polarized light 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 deviation in the deflection angle to a deviation parallel to the optical axis by passing through the convex lens 3o, so that a deviation parallel to the optical path of the S-polarized light L3 is formed. In this way, P polarized light, S polarized light L
When a deviation from s is formed, for example, as shown in FIG. 5, P polarization occurs.

is received by the optical sensor 46 in a state shifted from the S polarization direction. Therefore, the spot of P-polarized light is on the optical sensor 4.
In other words, the spot of the P-polarized light LP coincides with the spot of the S-polarized light L3 located at the center of the optical sensor 46.
2 is automatically moved in the X direction. As a result, the optical axes of the P-polarized light and the S-polarized light output from the beam splitter 38 to the outside are matched, and they are suitably mixed to correspond to the frequency difference between the P-polarized light LP and the S-polarized light Ls. Light having a desired beat frequency is output.

As described above, according to this embodiment, the common laser light source 1
Of the P-polarized light LP and S-polarized light divided into two from 0, P
The polarized light is deflected by the first acousto-optic modulator 14 and its frequency is changed, and the P-polarized light is finally converted into an optical path parallel to the S-polarized light L3 by the convex lens 30.

In other words, the optical paths of the P-polarized light and the S-polarized light do not form an angle with each other (they maintain a parallel relationship, so after the beam splitter 38, the P-polarized light and the S-polarized light L3 are suitably mixed and mutually By changing the vibration frequency of the vibrator 18 in the first acoustic modulation element 14, a beat frequency is generated due to the interference of P.
When the frequency of the polarized light Lp is changed, the beat frequency between the P polarized light LP and the S polarized light L8 is continuously changed to a desired value. Furthermore, by discontinuously changing the set value of the setter 71, the beat frequency can be discontinuously changed.

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 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 L2 and S polarized light emitted from the beam splitter 38 in the Y direction are , 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 The moving position of the X table 80 is adjusted so that the P-polarized light received by the optical sensor 46 coincides with the S-polarized light, as shown in FIG.

Thereby, the P-polarized light 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.

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. Even if changed by 75,
The beat frequency between the P-polarized light and the S-polarized light 51 can be changed continuously. In this case, by automatically moving the X-Y table 52 in the y direction, the P-polarized light L output from the beam splitter 38 to the outside.
The optical axes of the P and S polarized lights L8 are made to coincide.

Furthermore, in order to continuously change the beat frequency, 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 in the second acousto-optic modulation element 24 are simultaneously changed. It is also good.

Further, in the above-mentioned embodiment, the polarizing beam splitter 2 is used to divide the laser beam output from the laser light source 10 into two, but it may also be constituted by a so-called half mirror. be.

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

It should be noted that the above-mentioned example is just 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. FIG. 6 is a diagram corresponding to FIG. 1 in another embodiment of the present invention. FIG. 7 is a diagram illustrating a conventional optical frequency shifter. 10: Laser light source 12: Polarized beam splitter (beam splitter) 14
: First acousto-optic modulator (acousto-optic modulator) 24; Second acousto-optic modulator (acousto-optic modulator) 30: Convex lens Applicant: Brother Industries, Ltd. 1st t! 1 Figure 2 Figure 3

Claims (1)

[Claims] An optical frequency shifter for changing a beat frequency lower than the frequency of laser light obtained by mixing two types of laser light, the optical frequency shifter changing the beat frequency lower than the frequency of the laser light obtained by mixing two types of laser light, a beam splitter that splits the laser beam into two; a convex lens 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 beam. an acousto-optic modulator that deflects light around the focal point and continuously changes the frequency of the deflected light; and an optical path of the first laser beam and the second laser beam that are deflected by the acousto-optic modulator. 1. An optical frequency shifter comprising: an optical mixing means that generates synthesized light having a beat frequency caused by the mutual interference by matching and mutually interfering with each other;