JPS645283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical element with substantially constant Faraday rotation ability over a wide temperature range.

Magneto-optical elements that utilize Faraday rotation ability are
Widely used as optical isolators for optical communications. Note that the Faraday rotation ability is the Faraday rotation angle in a saturated magnetization state.

Generally, an optical isolator is composed of polarizing prisms 1 and 2, a magneto-optical element 3, and a permanent magnet 4, as shown in FIG.
It is a kind of rare earth iron garnet.
Y ₃ Fe ₅ O ₁₂ is often used. The magneto-optical element 3 is kept in a state of saturation magnetization by the permanent magnet 4, the rotation angle of the deflection surface based on the Faraday effect of the magneto-optical element 3 is defined to, for example, 45 degrees, and the polarizing prism 1,
2 are arranged so that their deflection directions differ by 45 degrees.
As a result, the light 5 traveling in the forward direction is selected to have a single polarization by the polarizing prism 1, and after rotating the polarization plane by 45 degrees by passing through the magneto-optical element 3,
It can pass through the polarizing prism 2. However, the light 6 traveling in the opposite direction is selected as a single polarized light by the polarizing prism 2, and by passing through the magneto-optic element 3, the polarization plane is rotated by 45 degrees, the same as in the case of the forward direction. The polarization direction after passing through the element 3 and the polarization direction of the polarizing prism 1 are orthogonal. Therefore, the light 6 traveling in the opposite direction cannot pass through the polarizing prism 1, so that the passing characteristic can be given directionality.

However, since the Faraday rotation ability of the magneto-optical element 3 has a temperature dependence, as shown in FIG. Change. Therefore, there was a drawback that sufficient directionality could not be obtained unless the operating temperature of the optical isolator was kept constant.

The present invention has a Faraday rotation ability that can be adjusted over a wide range of temperatures by mixing Y ₃ Fe ₅ O ₁₂ , which has a positive temperature coefficient, and rare earth iron garnet Gd ₃ Fe ₅ O ₁₂ , which has a negative temperature coefficient, in a specific ratio. It is an object of the present invention to provide a magneto-optical element whose Faraday rotation ability is substantially constant over a range.

The present invention will be explained below using the drawings.

As shown in FIG. 2, the Faraday rotation ability of the magneto-optical material Y ₃ Fe ₅ O ₁₂ decreases as the temperature rises above -75°. The general tendency of rare earth iron garnets is that the Faraday rotation ability decreases as the temperature increases, but some
Some have opposite temperature coefficients, such as Gd ₃ Fe ₅ O ₁₂ .

Therefore, in the mixed crystal _of Y ₃ Fe ₅ O ₁₂ and Gd ₃ Fe ₅ O _{12 ( Y 1-X Gd} It is possible to bring it close to zero. Furthermore, (Y _1-X Gd _X )
₃ Fe ₅ O ₁₂ can be obtained by mixing Y ₃ Fe ₅ O ₁₂ and Gd ₃ Fe ₅ O ₁₂ by a well-known method.

FIG. 4 shows the range of change in Faraday rotational performance when the value of X is adjusted from 0 to 0.7 and the temperature is varied from -50°C to +100°C in the above example. As is clear from this, the mixed crystal ratio X=
The temperature coefficient of Faraday rotation ability reaches a minimum value around 0.3, and as shown in Figure 4, for liquid crystals with 0.1≦X≦0.45, the temperature coefficient of Faraday rotation ability is approximately 2.7% or less over a wide range of -50℃ to +100℃. In practical terms, the change in Faraday rotational ability due to temperature can be ignored.

Furthermore, while the saturation magnetization of Y ₃ Fe ₅ O ₁₂ is 1200 Oe, the saturation magnetization of (Y _0.7 Gd _0.3 ) ₃ Fe ₅ O ₁₂ is
Since it is 900 Oe, it has the advantage that the permanent magnet can be made smaller when used in an optical isolator as shown in FIG.

As explained above, the present invention can virtually eliminate the temperature-related change in Faraday rotation ability during saturation magnetization, which was essentially unavoidable in the past. An optical isolator that can ensure stable operation without the need for a constant temperature device, even under changing environments.
Light switches and the like can be easily provided, and its practicality is great.

[Brief explanation of drawings]

Figure 1 shows the configuration of an optical isolator using a magneto-optical element, Figure 2 shows the temperature dependence of the Faraday rotation ability of Y ₃ Fe ₅ O ₁₂ , and Figure 3 shows the structure of an optical isolator using a magneto-optical element.
A diagram showing the temperature dependence of Faraday rotation ability of Gd ₃ Fe ₅ O ₁₂ , Figure 4 shows the temperature range of (Y _1-X Gd _X ) ₃ Fe ₅ O ₁₂ -
Figure 5 shows the rate of change in Faraday rotational power due to mixed crystallization at 50°C to + ₁₀₀ ° _C , _which is _an example of _the present invention. It is a diagram showing dependence. 1, 2...Polarizing prism, 3...Magneto-optical element, 4...Permanent magnet, 5...Light traveling in the forward direction, 6
...Light traveling in the opposite direction.

Claims (1)

[Claims] 1 In the optical path between the first and second polarizing prisms, the general formula (Y _1-x Gd _x ) ₃ Fe ₅ O ₁₂ is expressed, and x is 0.1≦x
≦0.45 rare earth garnet mixed crystal is arranged, a magnet is installed around the mixed crystal, the mixed crystal is magnetically saturated by the magnet, and the light traveling along the optical path is subjected to Faraday rotation by the mixed crystal. A magneto-optical element featuring: