JPS6159485B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam polarization selection device that can change the polarization state of a light beam at high speed by using an acousto-optic element.

Conventional optical beam polarization selection devices include devices that mechanically rotate using a polarizing plate or Glan-Thompson prism, and devices that change polarization by changing the phase of light using a stress modulator or electro-optic material. be. However, the former is inferior in selection speed, and the latter has disadvantages of high dependence on temperature changes and high driving voltage.

The present invention aims to eliminate these drawbacks and provide a device that can select the polarization state of a light beam at high speed and with low power consumption.

As an embodiment of the present invention, an acousto-optic filter element utilizing the anisotropic Bragg diffraction phenomenon of tellurium dioxide (TeO ₂ ) single crystal will be used as an acousto-optic element.

This acousto-optic filter element using tellurium dioxide single crystal has a structure as shown in FIG. Therefore, it is converted into a transverse ultrasound wave. When a white light source or a laser light source 3 is used as the incident light 4, monochromatic light is selected from the white light corresponding to the ultrasonic frequency and comes out as diffracted lights 5a and 5b. Alternatively, when an ultrasonic frequency corresponding to the wavelength of the laser beam is applied, diffracted lights 5a and 5b emerge. In these cases, the diffracted lights 5a and 5b differ from the polarization state of the incident light 4.
The wavelengths on both sides of the undiffracted light 6 which are not selected and travel straight are slightly different, and the polarization planes thereof are different by 90 degrees. 5a' and 5b' are diffracted lights 5a,
The polarization states of 5b are shown perpendicular and horizontal to the plane of the paper, respectively. The polarization state of the diffracted lights 5a and 5b is such that the traveling direction of the light beam incident on the tellurium dioxide single crystal 26 constituting the acousto-optic filter element 2 is set to the optical axis of the tellurium dioxide single crystal 2b (<001 The polarized light changes from circularly polarized light to elliptically polarized light to right angle polarized light depending on the angle of inclination from the optical axis), but in the acousto-optic filter element 2, the traveling direction of light is generally inclined by 10 degrees or more from the optical axis within the crystal. , the angle is
In the case of an 18.6-degree element, the polarization state of the diffracted light has an ellipticity of about 1%, making it almost completely linearly polarized light. Therefore, 90
The number of polarized light components with different planes of polarization is 1% or less. 7
is a λ/4 plate for converting into a circularly polarizing plate, which is unnecessary in the case of a white light source. 8 is a slit for removing the undiffracted light 6.

On the other hand, the oscillation frequency from the high-frequency oscillator and the wavelength of selectively diffracted light are as shown in FIG. 2 for each polarization component. In Figure 2, λ is the wavelength of the diffracted light, is the driving frequency, A and B are the relationship between the wavelength λ and frequency when the polarization state of the diffracted light is vertical or horizontal, and 5a' and 5b' in Figure 1. Compatible. Here, the vertically polarized component refers to the diffracted light that has a polarization component perpendicular to the plane of the paper, as shown in Figure 1, and the horizontally polarized component refers to the diffracted light that has a polarization plane within the plane of the paper. There is. As can be seen from Fig. 2, for example, for light of 6000 Å, the diffracted light yields a vertically polarized wave at 53.5 MHz and a horizontally polarized wave at 57 MHz. Conversely, at 53.5MHz, the vertically polarized wave is
The wavelength of the light is 6000 Å, and the horizontally polarized light is 6300 Å.

Hereinafter, the present invention will be explained with reference to FIGS. 3 to 6 showing respective embodiments, with the same numbers assigned to the same parts as above.

First, in the first embodiment shown in FIG. 3, a 6328 Å He-Ne laser with a linearly polarized light output is used as the light source 3, which is converted into a circularly polarized light wave by a λ/4 plate 7, and an acousto-optic filter element. 2. As a driver for the acousto-optic filter element 2, ₁ =
Two high-frequency oscillators 11a and 11b having oscillation frequencies of 50.4 MHz and ₂ = 53.3 MHz are used, and the oscillation frequency is selected by a changeover switch 10 controlled externally or internally. This selected frequency has an output of approximately
The power is amplified to about 200 mW and applied to the acousto-optic filter element 2. 12 is a switching signal.

In this case, the diffracted light is
50.4MHz becomes a vertically polarized component and 53.3MHz becomes a horizontally polarized component, and by using each independently, a light beam with a polarization state different by 90 degrees can be obtained. The intensity of the diffracted light at this time is approximately the intensity of the incident light as each component light depending on the high frequency output.
You can get up to about 45%.

A second embodiment is shown in FIG. 4, in which AM modulators 13a and 13b are provided between the oscillation section and the amplification section of the first embodiment, and modulation signals 14a and 14b are introduced from the outside, respectively. This is a device that can change the intensity of each polarized light component by changing the intensity of each polarized light component. This device reflects two diffracted lights using a mirror 15.
A, 15b, etc. can be easily synthesized, and a polarization control device can be easily obtained.

A third embodiment is shown in FIG. 5, in which one voltage-controlled high-frequency oscillator 16 whose oscillation frequency is changed by voltage control is used as the high-frequency oscillators 11a and 11b of the first embodiment. For example, when the external DC voltage is 0V, it is 50.4MHz, and when it is 1V, it is 50.4MHz.
When the voltage controlled oscillator 16 is adjusted to have an oscillation frequency of 53.3MHz, the external control signal 17 is
0V by applying 0V and 1V pulse signals
A vertically polarized wave is obtained when the voltage is 1V, and a horizontally polarized wave is obtained when the voltage is 1V. In this case, a changeover switch becomes unnecessary.

The embodiment of FIG. 4 is shown in FIG.
It uses In this case, the polarization state of the output light from the lamp is random, and contains 50% each of horizontally and vertically polarized waves. As the oscillator, a voltage-controlled high-frequency oscillator 16 is used as in the third embodiment, and the control voltage is controlled to have the frequency characteristics of the light wavelength as shown in FIG. 2 in accordance with the emission spectrum of the light source. The voltage is controlled by a computer or the like. 19 is an optical system for obtaining a parallel light beam consisting of a lens and a slit, 20 is a voltage signal generator, and 21 is a computer.

The following effects can be obtained in the above-described embodiments of the present invention.

(b) High-speed polarization selection is possible.

The selective response speed is determined by the diameter of the incident light beam, and for example, a response of about 100 KHz is possible with a beam diameter of 5 mmφ.

(b) Good temperature characteristics.

There is no temperature dependence on the polarization state of the acousto-optic filter element.

(c) Good linear polarization.

For example, the excess linearly polarized light component is 1% or less.

(d) The drive system is simple.

An output of about 100 mW is sufficient for the drive system of the acousto-optic filter element of this device, and a voltage output of about 2.5 V is sufficient, so the power amplifier can be made small and easily.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the operating principle of an acousto-optic filter element using tellurium dioxide single crystal, Fig. 2 is a characteristic diagram showing an example of the relationship between the wavelength of diffracted light and the driving frequency of the acousto-optic filter element, and Figs. FIG. 6 is a principle diagram showing each embodiment of the light beam polarization selection device according to the present invention. 1, 18... light source, 2... acousto-optic element, 9...
... wideband amplifier, 11a, 11b, 16... high frequency oscillator.

Claims (1)

[Claims] 1. A light source containing monochromatic or multispectral light;
It consists of an optical system that shapes a light beam, an acousto-optic element, one or two high-frequency oscillators, and a broadband amplifier, and by switching the oscillation frequency of the one or two high-frequency oscillators, A light beam polarization selection device characterized in that the polarization plane of light diffracted by a beam is switched between horizontal and vertical polarization.