JPH0279035A - Optical frequency shifter - Google Patents

Abstract

PURPOSE:To shift an optical frequency continuously over a wide range by making one of two focuses of an elliptic mirror correspond to an operation point where light incident on an acoustooptic element from a light input means is put under acoustooptic effect and the other correspond to the incidence end of a light output means. CONSTITUTION:The acoustooptic element 1, the elliptic mirror 10, and an optical fiber 11 for output are arranged so that the operation point 12 where the incident light 7 is Bragg-diffracted with a surface acoustic wave 6 and the input end 13 of the optical fiber 11 for output correspond to the two focuses of the elliptic mirror 10. The diffracted light 9 is reflected by the elliptic mirror 10 to go to a light beam 14, which is entered into the optical fiber 11 for output. A lens 15 for input is so arranged that the light beam is focused on the input end 13. The band of the shift quantity of the optical frequency is limited to only the numerical aperture of the optical fiber for output. Consequently, the optical frequency can be varied continuously over a wide range.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical frequency shifter that changes optical frequency, and particularly relates to an optical frequency shifter that uses an acousto-optic element.

[Conventional technology]

As is well known, the acousto-optic effect is the common name for the Bragg diffraction or Raman-Nass diffraction phenomenon of a light beam caused by surface acoustic waves. Focusing only on the first-order diffracted light, acousto-optic elements using this phenomenon include the following: It has certain characteristics.

λ・f θ= −(1) ■ f, = f, ±f (2) Here, θ:: Angle of diffraction from passing light (deflection angle) λ: Wavelength of light from two people fI Frequency of light emitted from two people fo: Output Emitted light (diffracted light) frequency f: Frequency of surface acoustic waves (optical frequency shifter) (2): Speed of surface acoustic waves in acousto-optical medium FIG. 2 shows a conventional optical frequency shifter. The acousto-optic element 1 is composed of a sound optical medium 2, a transducer 3, and a sound absorbing material 4. When an ultrasonic wave is applied to the transducer 3 from the oscillator 5, a surface acoustic wave 6 propagates toward the sound absorbing material 4. When the incident light 7 enters the acousto-optic element 1 in this state,
Due to the Bragg diffraction phenomenon of the incident light 7 caused by the surface acoustic wave 6, transmitted light 8 and diffracted light 9 appear. Diffraction light 9 is output lens 19
is introduced into the output optical fiber 11 through the. In this way, the conventional optical frequency shifter introduces the output light of the acousto-optic element 1 into the optical fiber 11 using the output lens 19, and connects the acousto-optic element, the output lens, and the output light to obtain the output light 16. fiber was placed.

[Problem to be solved by the invention]

As shown in the above characteristic equation, when the wavelength of the incident light is constant, there is a one-to-one correspondence between the frequency of the surface acoustic wave, that is, the amount of frequency shift, and the deflection angle. Therefore, in the prior art, only the emitted light having a specific deflection angle is introduced into the output optical fiber, and the light other than the specific deflection angle is not introduced into the output optical fiber. Therefore, the center frequency of the optical frequency shift amount is fixed and limited to an ultra-narrow band, and there is a drawback that the optical frequency shift amount cannot be changed continuously. The present invention
It is an object of the present invention to provide an optical frequency shifter capable of eliminating the above-mentioned conventional drawbacks and continuously shifting optical frequencies over a wide band.

[Means to solve the problem]

In order to achieve such an object, the present invention comprises a light input means, an acousto-optic element, an elliptical mirror, and a light output means, and one of the two focal points of the elliptical mirror is connected from the light input means to the acousto-optic device. It is characterized in that the light incident on the element corresponds to the point of action where the light receives the acousto-optic effect, and the other corresponds to the input end of the light output means.

Furthermore, the present invention comprises a light input means, an acousto-optic element, an elliptical mirror, a light output means, a diffraction grating mirror and a lens provided between the elliptical mirror and the light output means, One of the focal points corresponds to the point of action where the light incident on the acousto-optic element from the light input means receives an acousto-optic effect, and the other focal point is
It is characterized in that it corresponds to the reflection point of the diffraction grating mirror.

[For production]

Wood invention uses an elliptical mirror.

Due to the nature of an ellipse, a ray that passes through one of the two focal points is reflected by the elliptical mirror surface and always passes through the other focal point, and the distance from one focal point to the other focal point after being reflected by the elliptical mirror surface depends on the direction of the ray. are equal. Therefore, the incident light that has passed through the point of action of the acousto-optic effect is reflected by the elliptical mirror surface and reaches the input end of the optical fiber or the reflection point of the diffraction grating mirror. Unlike a lens, an elliptical mirror has no aberrations, so it is possible to condense light rays that pass through one focal point and spread over a wide range onto the other focal point. Therefore, the band of the optical frequency shift amount is limited only by the numerical aperture of the output optical fiber, making it possible to continuously change the optical frequency over a wide band.

〔Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention.

The acousto-optic element 1 is composed of an acousto-optic effect 2, a transducer 3, and a sound absorbing material 4, as in the conventional example. When ultrasonic waves (frequency f1 to f2) are input from the oscillator 5 to the transducer 3, surface acoustic waves 6 travel toward the sound absorbing material 4. When the incident light 7 is incident on the acousto-optic element l while the ultrasonic wave fI is manually applied to the transducer 3 from the oscillator 5, the transmitted light 8 and the diffracted light 9 are separated by the Bragg diffraction phenomenon of the incident light 7 due to the surface acoustic wave 6. appear. Here, the frequency and diffraction angle of the diffracted light 9 are expressed by the aforementioned equations (2) and (1), respectively. Further, the intensity of the diffracted light 9 depends on the 'π force of the ultrasonic wave inputted from the oscillator 5 to the transducer 3. Sound #IF optical element 1.
The elliptical mirror 1O and the output optical fiber 11 have a point of action 12 where the incident light 7 is Bragg diffracted by the surface acoustic wave 6,
The input end 13 of the output optical fiber 11 is connected to the elliptical mirror lO2.
They are arranged to correspond to each focal point. The diffracted light 9 is reflected by the elliptical mirror lO and becomes a light beam 14,
It is dedicated to the output optical fiber 11. Human power lens 15
are arranged so that the light beam is focused at the input end 13. It is also possible to use a manual optical fiber instead of a manual lens. In that case, its output end is arranged sufficiently close to the point of application 12. The optical frequency of the output light 16 is (
2) It is shifted by fl as shown in the equation. Furthermore, when the frequency of the ultrasonic wave is changed to fl, the incident light 7 is similarly Bragg-diffracted into a light ray J7 by the surface acoustic wave 6, and the diffracted light 17 is reflected by the elliptical mirror 10 to become a light ray 18, which is output. is introduced into the optical fiber 11 for use. At this time, the optical frequency of the output light 16 is shifted by fl as shown in equation (2). The speed at which the optical frequency shift amount changes from fl to fl is the speed at which the surface acoustic wave 6 changes from fl to acousto-optic medium 2.
depends on the speed at which it progresses.

Due to the nature of an ellipse, a ray that passes through one of the two focal points is reflected by the elliptical mirror surface and always passes through the other focal point, and the distance from one focal point to the other focal point after being reflected by the elliptical mirror surface depends on the direction of the ray. are equal. Therefore, the incident light that has passed through the point of application of the acousto-optic effect is reflected by the elliptical mirror surface and reaches the input end of the optical fiber. Furthermore, unlike lenses, elliptical mirrors do not have aberrations, so it is possible to condense light rays that pass through one focal point and spread out over a wide range onto the other focal point. therefore,
The band of the optical frequency shift amount is limited only by the numerical aperture of the output optical fiber, and it is possible to continuously change the optical frequency over a wide band.

FIG. 2 is a schematic diagram illustrating another embodiment of the present invention.

In this embodiment, an elliptical mirror lO and an output optical fiber 1 are used.
1, a diffraction grating mirror 22 and an output lens 19 are provided. As the diffraction grating mirror 22, it is preferable to use one having an inverse dispersion characteristic that compensates for the dispersion of the light emitted from the acousto-optic element. Similar to the embodiment shown in FIG. 1, an ultrasonic wave (frequency f.

~f2) is manually applied to the transducer 3, the surface acoustic wave 6 advances toward the sound absorbing material 4. When the ultrasonic wave f from the oscillator 5 is manually applied to the transducer 3, the input optical fiber 20 transmits the incident light 7 to the acousto-optic element 1.
When the incident light 7 is incident on the surface acoustic wave 6, a transmitted light 8 and a diffracted light 9 appear due to the Bragg diffraction phenomenon of the incident light 7. The human power optical fiber fiber 20 is arranged such that its output end 21 is sufficiently close to the point of action 12 where the incident light 7 is Bragg diffracted by the surface acoustic wave 6 . Acousto-optic element 1. The elliptical mirror IO and the diffraction grating mirror 22 are arranged so that the point of action 12 and the reflection point 23 of the diffraction grating mirror 22 correspond to the two focal points of the elliptical mirror 10, respectively. The diffracted light 9 is reflected by the elliptical mirror 10 and the diffraction grating mirror 14 to become light beams 14.24, which are introduced into the output optical fiber 11 by the output lens 19. At this time, the optical frequency of the output light 16 is shifted by f. Furthermore, when the frequency of the ultrasonic wave is changed to fl, the incident light 7 is similarly Bragg-diffracted by the surface acoustic wave 6, and the diffracted light 17 is reflected by the elliptical mirror 1O and the diffraction grating mirror 22, and the light beam 18.24 Then,
It is introduced into the output optical fiber 11 through the output lens 19 . At this time, the optical frequency of the output light 20 is shifted by f2.

In the wooden embodiment, the incident light that has passed through the point of action of the acousto-optic effect is reflected by the elliptical mirror surface and reaches the reflection point of the diffraction grating mirror. Since this diffraction grating mirror has an inverse dispersion characteristic that compensates for the dispersion of the output light of the acousto-optic element reflected by the elliptical mirror, the light rays reflected by the diffraction grating mirror match regardless of the amount of optical frequency shift. Furthermore, as mentioned earlier, unlike a lens, an elliptical mirror has no aberrations, so it is possible to condense a ray of light that passes through one focal point and spreads over a wide range onto the other focal point. Therefore, it is possible to continuously change the optical frequency over a wide band.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to continuously change the optical frequency over a wide frequency range6.For example, gas lasers and solid-state lasers, which have better frequency stability than semiconductor lasers, It cannot sweep over a wide range, and its single stroke speed is extremely slow. The present invention is effective as a technique for rapidly changing the frequency of such a light source.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams explaining the present invention in detail, and FIG. 3 is a schematic diagram explaining a conventional optical frequency shifter. 1... Acousto-optic element, 2... Acousto-optic medium, 3... Transducer, 4... Sound absorbing material, 5... Oscillator, 6... Surface acoustic wave, 7, 8.9 .14,1647,18.24...ray,
DESCRIPTION OF SYMBOLS 10... Elliptical mirror, 11... Output fiber, 12... Point of action, 13... Input end, 15... Input lens, 19... Output lens, 20... Human power Optical fiber for use, 22... Diffraction grating mirror, 23... Reflection point.

Claims (1)

[Claims] 1) comprising a light input means, an acousto-optic element, an elliptical mirror, and a light output means, one of the two focal points of the elliptical mirror;
An optical frequency shifter characterized in that the light inputting means corresponds to a point of action where light incident on the acousto-optic element receives an acousto-optic effect, and the other corresponds to an input end of the light outputting means. 2) comprising a light input means, an acousto-optic element, an elliptical mirror, a light output means, a diffraction grating mirror and a lens provided between the elliptical mirror and the light output means; One of the two focal points corresponds to a point of action where light entering the acousto-optic element from the light input means receives an acousto-optic effect, and the other one corresponds to a reflection point of the diffraction grating mirror. optical frequency shifter.