JPH02221912A - Optical isolator - Google Patents

Abstract

PURPOSE:To cut off return light completely even if the ambient temperature varies by providing two wedgelike magnetooptic elements in parallel to each other and fixing one end of one optical element to a member which is displaced with the temperature. CONSTITUTION:The two wedgelike magnetooptic elements 7 and 8 are arranged between a polarizer 4 and an analyzer 5 so that the incidence surface of the optical element 8 and the exiting surface of the optical element 7 are parallel to each other. The end part of the magnetooptic element 7 is fixed to the member 9 with is displaced with the ambient temperature. In this constitution, the angle of the polarization direction varies as the ambient temperature, but the optical element 7 is displaced at right angles to the optical axis as the member 9 is displaced and the thickness is so controlled that the angle of rotation of the polarization direction of light after the light passes through the magnetooptic element 7 is invariably 45 deg.. Consequently, the reflected return light is cut off completely even if the ambient temperature varies.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical isolator used for optical communication, optical measurement, optical recording, and the like.

Conventional technology When a semiconductor laser is used as a light source for an optical signal transmission system such as optical communication, a portion of the light emitted from the semiconductor laser is reflected at the transmission line or at each connection of the transmission optical components, causing oscillation of the semiconductor laser. This causes instability of characteristics and increase in noise. In order to prevent this reflected return light from returning to the semiconductor laser, an optical isolator is used in the negative role.

For example, as shown in FIG. 2, the optical isolator includes a polarizer 4. Magneto-optical element 3. It is equipped with an analyzer 5 and a magnet 6. The emitted light 1 from the semiconductor laser passes through a polarizer 4 and becomes linearly polarized light, and when it passes through the magneto-optical element 3, its polarization direction is rotated by 45 degrees, and passes through an analyzer 6 arranged at an angle of 46 degrees with the polarizer 4. do.

On the contrary, the reflected return light 2 passes through the analyzer 6 and becomes [f-ray scratched light, and when passing through the magneto-optical element 3, the polarization direction is further rotated by 46° due to the non-reciprocity of the Faraday effect, Linearly polarized light cannot pass through because it is orthogonal to the Based on the principle described above, it is possible to prevent the reflected return light 2 from returning to the semiconductor laser.

Problems to be Solved by the Invention However, magneto-optical elements have the property that the rotation angle of the polarization direction changes with changes in ambient temperature.

For this reason, even if the thickness of the magneto-optical element 3 is determined so that the rotation angle of the polarization direction is 46 degrees at a certain temperature, the rotation angle of the polarization direction will deviate from 45 degrees due to temperature changes and the reflection will return. A portion of the light 2 passes through the polarizer 4 and returns to the semiconductor laser.

Means for Solving the Problems In order to solve the problem, a plurality of magneto-optical elements are provided between the polarizer and the analyzer, and the thickness of the plurality of magneto-optical elements is relative to the optical axis. The wedge-shaped magneto-optical element is arranged so that one light incident surface and the light output surface of one of the wedge-shaped magneto-optical elements are parallel to each other. At least one end of the magneto-optical element is fixed to a member that is displaced by temperature.

Function According to the optical isolator of the present invention, the wedge-shaped magneto-optical element is displaced in the direction perpendicular to the optical axis as the ambient temperature changes. The thickness of the magneto-optical element can be controlled so that the rotation angle of the polarization direction of the light after passing through is always 46 degrees, and reflected return light can be completely blocked even if the ambient temperature changes. becomes. Further, by arranging two or more magneto-optical elements so that the light incident surface and the light exit surface are parallel to each other, it is possible to prevent the optical axis from shifting.

Example Figure M1 shows the configuration of the optical isolator of the present invention.

Note that the same parts as in FIG. 2 are given the same numbers.

The wedge-shaped magneto-optical elements 7 and 8 are placed inside a magnet 6 provided outside so that a saturation magnetic field is applied to the entire wedge-shaped magneto-optical elements 7 and 8. The light that has passed through the polarizer 4 becomes a circular circular beam, and when it passes through the wedge-shaped magneto-optical elements 8 and 7, its polarization direction is rotated by 46 degrees, and then passes through the analyzer 6, which is arranged at an angle of 45 degrees with the polarizer 4. do. On the contrary, the reflected return light passes through the analyzer 6 and becomes linearly polarized light, and when it passes through the wedge-shaped magneto-optical elements 7 and 8, the polarization direction is further changed to 4 due to the non-reciprocity of the Faraday effect.
It is rotated by 6 degrees and is perpendicular to the polarizer 4, so it cannot pass through the linear polarizer.

However, if the ambient temperature changes, the rotation of the polarization direction of the light that has passed through the wedge-shaped magneto-optical elements 8 and 7 will deviate from 46°, so the amount of transmitted light that passes through the analyzer 6 will decrease, and the reflected back light will be reduced. The amount of light passing through the polarizer 4 also increases, and the infraction ratio deteriorates.

On the other hand, the rotation angle θ of the magneto-optical element is expressed as θ = VHL V Niverde's constant H = magnetic field strength L: thickness of the magneto-optical element, so by changing the thickness of the magneto-optical element, the polarization direction can be rotated. The angle can be controlled. Therefore, when the ambient temperature changes, the wedge-shaped magneto-optical element 8
The rotation of the polarization direction of the light that has passed through and 7 deviates from 46 degrees, but - the member 9 whose one end is fixed to the fixed part 1o and whose a end is displaced by temperature is displaced, and the wedge-shaped magneto-optical element 7 is Displaced in the direction perpendicular to the optical axis, the thickness of the magneto-optical element in the optical path portion changes, and the deviation in rotation of the polarization direction is reduced by 46
It can be corrected to ゜. In this way, the optical isolator of the present invention provides a higher isolation ratio than conventional optical isolators.

Furthermore, a lens and an optical fiber may be added to the above-described embodiments of the optical isolator of the present invention to form a semiconductor laser module with an optical isolator.

Effects of the Invention As described above, according to the present invention, the wedge-shaped magneto-optical element is displaced in the direction perpendicular to the optical axis as the ambient temperature changes. The thickness of the magneto-optical element can be controlled so that the rotation angle in the dimming direction after passing is always 46 degrees, and the reflected return light can be completely blocked even if the ambient temperature changes. Become. In addition, multiple wedge-shaped magneto-optical elements are arranged so that the light entrance and exit surfaces are parallel to each other, which prevents misalignment of the optical axis and facilitates optical axis adjustment. .

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an optical isolator according to the present invention, and FIG. 2 is a sectional view showing the structure of a conventional optical isolator. 1... Outgoing light, 2... Reflected return light, 3
...Magneto-optical element, 4...Polarizer, 6
...Analyzer, 6...Magnet, 7...--
Wedge-shaped magneto-optical element installed on a member that is displaced by temperature, 8... Wedge-shaped magneto-optical element, 9...
・・Members that are displaced by temperature, 1o・・・Fixed parts.

Claims (1)

[Claims] A plurality of magneto-optical elements are provided between the polarizer and the analyzer, and magnets are provided outside of these magneto-optical elements, and the plurality of magneto-optical elements have a thickness that is perpendicular to the optical axis. The wedge-shaped element gradually changes, and the light incident surface of one wedge-shaped magneto-optical element is arranged so that the light exit surface of the other wedge-shaped magneto-optical element is parallel to each other, and at least one of these wedge-shaped An optical isolator in which one end of a magneto-optical element is fixed to a member that is displaced by temperature.