JPS5921379Y2 - optical shutter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an optical shutter device using a crystal having an electro-optic effect as an optical shutter element.

As a method of optical shuttering, a method using a crystal having an electro-optic effect (in this specification, such a crystal is referred to as an electro-optic crystal) is well known.

Here, we will explain the principle of optical shutter using Tung as a modulating element.
sten-Bronze type 5rXBa□-XNb206
(abbreviated as SBN in this specification) will be explained as an example.

SBN crystal belongs to a crystal group that has a tetragonal system and a point group symmetry of 4 mm at a temperature below the Curie point, and has C
It is a uniaxial crystal whose axis is the optical axis.

Now, the orthogonal coordinate system x is parallel to the a-axis, b-axis, and c-axis of the crystal, respectively.7. Considering z, the refractive index of a solid can be written as follows.

Here n.

, no are refractive indexes for ordinary rays and extraordinary rays, respectively.

Next, when an external electric field E2 is applied in the Z-axis direction, the refractive index of the solid in equation (1) changes as follows.

Here r13. r33 is a first-order electro-optic effect.

As is clear from equation (2), it can be seen that the refractive index and the principal axis of the solid do not change before and after the application of E2.

In equation (2), no′γ13EZ<<1. ne
When expanded using the relationship ``γ33E2 〈1,'' it becomes.

Here, a one-type optical shutter will be described in which an electric field is applied in the Z-axis direction of the SBN and light is transmitted from the y-axis direction.

As shown in FIG. 1, the shape of the crystal (optical shutter element) is cut out along the X-axis, y-axis, and Z-axis, and is elongated in the X-axis direction.

In FIG. 1, 1 is incident light, 2 is an electrode, and 3 is an electro-optic crystal.

Considering an optical system in which the crystal 3 and the quarter-wave plate 4 are inserted between the polarizer 2 and the analyzer 5 as shown in Fig. 2, when no electric field is applied, π/4 (rad) The phase difference caused by the propagation of linearly polarized light in the X-axis direction of the crystal is: where λ is the wavelength of the light and l is the length of the crystal in the X-axis direction.

Note that F(0) is a phase difference caused by the natural birefringence of the crystal.

The phase difference that occurs when electric field E2 is applied in the Z-axis direction is:
The phase difference of (0) is the phase difference F(0) shown in equation (5).
It will be added to.

If the azimuth angles of the polarizer, quarter-wave plate, and analyzer of the above optical system are respectively α, ε, and σ (based on the Z-axis of the crystal),
Intensity I of light incident on the crystal.

The ratio of the intensity of light emitted from the detected photon (2) is as follows.

Here α σ = (3/4π The formula is yr /4 (rad), t = yr /4 (
rad) and F(0)/2)(rad) becomes the default (7).

That is, an optical shutter can be realized by turning on and off a voltage (half-wavelength voltage) at which F(E) is π (rad).

The conventional optical shutter described above is intended to turn on and off a single light beam.

When turning on and off multiple light beams coming from different directions, multiple light shutters must be used.

This poses a cost problem, and when it is incorporated into a laser application system, it is clear that it is disadvantageous in terms of installation space and the like.

The present invention was made to overcome the above-mentioned problems, and uses a Tungsten-Bronze type electro-optic crystal such as SBN (7) belonging to a point group of 4 mm as an optical shutter element to emit multiple light beams. The purpose of the present invention is to provide an optical shutter that can be turned on and off simultaneously and independently.

Hereinafter, a case where an SBN crystal is used as an optical shutter element will be explained as an example.

As is clear from equations (1) and (4), the refractive indices nx and ny in the X-axis direction and y-axis direction when no electric field is applied are respectively, and when an electric field is applied in the Z@force direction, X@force direction y @The refractive indexes nx and ny in the force direction are respectively.

That is, although the magnitude of the refractive index changes before and after applying the electric field, the refractive index in the X-axis direction and the refractive index in the y-axis direction remain equal (nx-n7.uXl-nyl).

Uniaxiality is maintained even when an electric field is applied in the Z-axis direction.

Therefore, even if light is incident in any direction perpendicular to the Z-axis, the same phase difference will be given if the lengths of the crystal in the direction of spreading are equal.

Next, the shape of the optical shutter element will be explained using FIGS. 3a and 3l). FIG. 3a is a plan view, and FIG. 3b is a front view.

1 is a 4m school of fish like SBH as an optical shutter element.
Electro-optic crystals 2-1 and 2-2 belonging to m are incident light beams, 3 is an electrode, and 4 is a lead wire for applying an external electric field.

The optical shutter element 1 has two sides parallel to the plane of the paper,
Cut the sides so that both sides are square.

Although the axial direction of the crystal is shown in Figure 3 (the [stock] mark is positive upwards with respect to the paper surface, and the * mark is negative downwards with respect to the paper surface), the X-axis and y-axis are taken as follows. Any direction on the Z plane may be used.

In the following explanation, the polarity of the applied electric field is assumed to be the polarity shown in FIG. 3.

Now, assuming that 2-1 and 2-2 are linearly polarized lights with a 45° azimuth, the phase difference can be changed by applying an electric field in the Z-axis direction.
Together, the two light beams 2-1 and 2-2 can be modulated in the same way.

Next, the operating principle of the optical shutter of the present invention will be explained with reference to FIG.

FIG. 4 is a plan view of two cascaded optical shutter elements shown in FIG. 3.

1-1.1-2 is the optical shutter element shown in FIG.
is the incident light beam, 3 is the polarizer (azimuth angle 45°), 4 is 1
/2 wavelength plate (azimuth angle 45°), 5 is analyzer (azimuth angle -4
5°).

The above azimuth angles are based on the Z axis of the crystal (optical shutter element).

With this configuration, the phase difference F(0) caused by the natural birefringence shown in Equation 11 is compensated and becomes zero.

Now, with polarity ■ in 1-1, F(E)π shown in equation (11)
/2 (rad) (1/4 half wavelength voltage)
Vλ/4 is constantly applied.

When a voltage Vλ/4 with polarity ○ is applied to 1-2, p(E) is canceled out by the two optical shutter elements and becomes zero.

That is, the intensity of the light emitted from the analyzer becomes minimum (ideally zero), and the analyzer is in an off state.

When voltage Vλ/4 is applied to 1-2 with polarity ■, μ) becomes π(
rad), and the intensity of the light emitted from the analyzer becomes maximum.

Optical shutter operation can be realized by changing the polarity of the voltage applied to 1-2.

The content of the present invention will be explained below with reference to Examples.

In the present invention, as shown in FIG. 5, the optical shutter elements shown in FIG. 3 are arranged vertically and horizontally, two each.

Optical shutter element 1 1, 1 2.1 shown in Figure 3
3. '+4゜ Monochromatic incident light beam 2-1 such as laser
．． 2-2.2-3゜2-4. Polarizer 3- with an azimuth angle of 45°
1.3-2. 1/2 wavelength plate with azimuth angle of 45° 4-1.4-
2.4-3.4-4. Polarization plane rotator 5, azimuth -45°
It consists of analyzers 6-1 and 6-2.

The above azimuth angle is taken with the Z axis of the optical shutter element as a reference, as in FIG. 4.

In addition, in 5, the plane of polarization rotates 90° when an external force is applied,
Elements that do not rotate the plane of polarization when no voltage is applied include electro-optical elements, Faraday elements, photorotation electric elements whose optical rotation power changes when voltage is applied, and half-wave plates whose orientation can be changed mechanically. can.

First, let us consider the case where the light beams 2-1.2-2.2-3.2-4 pass through, that is, the case where the optical shutter is turned on for all the light beams.

In this case, voltages 1-1.1-2.1-3.1-4 with 1 polarity and 2 λ C voltages may be applied, and no external force may be applied to 5.

Focusing on the light beam 2-1, 45
The linearly polarized light in the azimuth is π (rad
) is given, and the plane of polarization is rotated by 90°.

Since the analyzer is set at an azimuth of -45°, the light is emitted from the analyzer with maximum intensity.

Regarding light beam 2-3.2-4, similarly to 2-1,
It is emitted from the analyzer at maximum intensity.

Considering the light beam 2-2, the linearly polarized light at 45° azimuth emitted from the polarizer becomes π(
rad), and the plane of polarization is rotated by 90°.

Since no external force is applied to 5, it enters the analyzer as it is.

Since the analyzer is set at an azimuth of -45°, the light is emitted from the analyzer with maximum intensity.

Next, consider the case where the optical shutter is turned on for the light beams 2-1, 2-2, and 2-3, and turned off for the light beam 2-4.

In this case, apply a voltage of ■λ/4 with ■polarity to 1-1, 1-2, and 1-4, apply a voltage of ■λ/4 with ■polarity to 1-3, and 5 by applying an external force.

Focusing on the light beam 2-1, the 45° beam emitted from the polarizer
Directional linear polarization is π (rad) by 1-1.1-4
The plane of polarization is rotated by 90°.

Since the analyzer is set at an azimuth of -45°, the light is emitted from the analyzer with maximum intensity.

Similarly, the light beam 2-3 is emitted from the analyzer at maximum intensity.

Considering light beam 2-4, the linearly polarized light at 45° azimuth emitted from the polarizer becomes -π/2 (r
ad), and 1-4 gives π/2(r
ad) (7) Since the phase difference is given, 1-3.1-4
When passing through, the phase difference is canceled out and becomes zero.

Therefore, the plane of polarization does not rotate.

Since the analyzer is set at an azimuth of -45°, the intensity of the light beam emitted from the analyzer is minimum (zero).

For light beam 2-2, similarly to 2-4, 12.1
-3, the phase difference is canceled out and becomes zero.

However, since the external light is applied to 5, the plane of polarization is rotated by 90 degrees, and the light is emitted from the analyzer with maximum intensity.

In this way, the optical shutter operation can be performed independently for each of the four light beams.

Table 1 shows the on/off state of each light beam and the corresponding state of voltage application to the optical shutter element.

In Table ■, the ○ mark in the light beam section indicates that light passes through it.
That is, the optical shutter is on, and the X mark is off.

And ■ in the term of optical shutter element is depolar and ■λ
/4 voltage is applied. ○ is unipolar and also Vλ/4
This means applying a voltage of .

Further, On in 5 indicates that an external force is applied to rotate the polarization plane by 90 degrees, and Off indicates that no external force is applied.

Although Table 1 shows the case where the voltage (2) is always applied to the optical shutter element 1-1, the same operation can be performed when the voltage (e) is always applied.

In this case, the polarities of 1-2, 1-3, and 1-4 shown in Table 1 may be reversed.

Although the case where optical shutter elements are arranged in two rows and columns has been described above, the invention can generally be extended to a case in which a plurality of optical shutter elements are arranged in rows and columns.

As mentioned above, the present invention has the following advantages: (1) A single optical shutter device can simultaneously turn on and off multiple light beams that are perpendicular to each other, and each beam can be turned on and off independently. A wide range of uses can be considered as circuit elements.

(2) Due to the reason in (1), costs can be reduced.

(3) High-speed optical shutter operation is possible because the electro-optic effect is used.

(4) Since the structure is such that the natural birefringence of the crystal can be compensated for each light beam, movement of the operating point can be compensated for and stable operation is possible.

[Brief explanation of the drawing]

Figure 1 shows tungsten-bronze (Tu) with SBN.
Figure 2 is a diagram for explaining the shape, axial direction, etc. of an optical shutter element using an electro-optic crystal (Ngsten-Bronze) type electro-optic crystal. FIG. 3 is a diagram explaining the shape axis direction of the optical shutter element of the present invention, FIG. 4 is a diagram explaining the operation of the optical shutter of the present invention, and FIG. This is an example diagram. 2-1 to 2-4: Light beam, 1-1 to 1-4: Optical shutter element, 3-1.3-2: Polarizer, 4-1 to 4-4:
1/2 wavelength plate, 5: polarization plane rotator, 6-1.6-2: analyzer.

Claims (1)

[Scope of utility model registration request] The 0-face of an electro-optic crystal has a symmetry that gives the same electro-optic effect to light beams that are perpendicular to the 0-face and perpendicularly incident on two mutually orthogonal faces. A plurality of optical shutter elements with processed side surfaces are arranged on a plane parallel to the 0 plane so that they are an even number in both the vertical and horizontal directions, and one half-wave plate is inserted between each adjacent optical shutter element, Polarizers are installed parallel to the outer side surfaces of which the optical shutter elements are arranged in even numbers both vertically and horizontally, and furthermore, the azimuths of the two opposing polarizers are arranged to be orthogonal to each other, and further, the optical shutter elements A polarizing element whose polarization plane can be rotated by applying an external force is inserted between one of the polarizers and one of the polarizers, and among the plurality of light beams that are incident on each of the two planes orthogonal to the zero plane, Depending on the combination of light beams to be emitted, a quarter of a different polarity is placed in the C-axis direction of each of the light shutter elements.
An optical shutter device characterized in that it is provided with means for applying a wavelength voltage and controlling the application of an external force to the polarizing element.