JPH0391715A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain an optical isolator which has no polarized wave dependency by dividing an analyzer and specifying its thickness in an optical isolator which uses parallel flat plate type birefringent materials for a polarizer and the analyz er. CONSTITUTION:The optical isolator is constituted of a lst analyzer 31 which is 2<1/2> times as thick as the polarizer by dividing the analyzer and a 2nd analyz er 32 which is as thick as the polarizer, a lst Faraday rotator 21 arranged between the polarizer 1 and the 1st analyzer 31, and a 2nd Fraday rotator 22 arranged between the lst analyzer 31 and the 2nd analyzer 32. Return light from an optical coupling position after being transmitted through the optical isolator in a forward direction is separated by the lst analyzer 31, the 2nd analyzer 32, and the polarizer 1 irrelevantly to its polarized component and does not return to a light incidence position, so that the device functions as the optical isolator.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator, and particularly to an optical isolator used in optical communication and optical information processing. [Prior Art] Conventionally, this type of optical isolator is composed of a polarizer 1, a Faraday rotator 2, an analyzer 3, and a permanent magnet 4, as shown in FIG. 3(a). It has the function of blocking the returning light from each reflection point. Conventionally, the insertion loss of an optical isolator has depended on the polarization of the incident light when a Rochon prism, polarizing beam splitter, or parallel plate birefringent material is used as a polarizer or analyzer. ), an optical isolator whose insertion loss does not depend on the incident polarization has been developed by using a wedge-shaped birefringent material.
103) [Problems to be Solved by the Invention] The above-mentioned conventional optical isolator that provides polarization-independent insertion loss has problems in processing because the polarizer and analyzer are made of wedge-shaped birefringent material. This method is difficult, and since the relative angles of the polarizer and analyzer must be adjusted and fixed for each optical isolator, there are drawbacks such as poor mass production and high cost.

[Means to solve the problem]

The present invention is an optical isolator consisting of a polarizer, a Faraday rotator, an analyzer, and a permanent magnet, and in which the polarizer and the analyzer are made of parallel plate birefringent material. A first analyzer having a thickness F7 times that of a polarizer, a second analyzer having a thickness equal to that of the polarizer, and a first Faraday rotator disposed between the polarizer and the first analyzer. and a second Faraday rotator disposed between the first analyzer and the second analyzer. [Embodiment] First, the operating principle of an optical isolator according to an embodiment of the present invention will be explained with reference to FIG. FIG. 2(a) is an exploded perspective view of each element according to this example, and FIG. 2(b) and (c)
FIG. 2 is an explanatory diagram showing the operation status of light when passing through each element in the forward direction and the reverse direction.

In the forward direction, the incident light with any polarization component has a thickness t
It is separated into ordinary light and extraordinary light by a parallel plate polarizer 1,
A certain portion of the extraordinary light is translated horizontally to the right by {(~O.it) and is incident on the first Faraday rotator 21 (point b). Each of the polarized lights separated into ordinary light and extraordinary light by the first Faraday rotator 21 has its polarization direction rotated by 45 degrees counterclockwise when viewed from the direction of the incident light, and then passes through the first analyzer 3.
1 (point C). The first analyzer 31 has a thickness of
The polarized light separated as extraordinary light by the polarizer 1 is moved in parallel to the lower left by F1, and is incident on the second Faraday rotator 22 (point d). The polarization direction of each polarized light is rotated by the second Faraday rotator 22 by 45 degrees counterclockwise when viewed from the direction of the incident light, and the polarized light is incident on the second analyzer 32 (point e>. The photon 32 is a parallel plate birefringent material with a thickness t, and it causes the polarized light separated as extraordinary light by the polarizer 1 to be translated upward by g (point f). The separated polarized lights are combined again after passing through the second analyzer 32, and their positions are the same as the positions where they entered the polarizer 1.

Next, in the reverse direction, the incident light with arbitrary polarization is separated by the second analyzer 32 into ordinary light and extraordinary light, and the extraordinary light component is translated downward by g when viewed from the forward direction. , enters the second Faraday rotator 22 (point e). It is rotated counterclockwise by 45 degrees when viewed from the forward direction by the second Faraday rotator 22, and enters the first analyzer 31 (point d).
. The light transmitted by the first analyzer 31 and the second analyzer 32 as ordinary light becomes a certain amount of extraordinary light, and when viewed from the forward direction, there is only F-1 in the upper right. Translated, the first Faraday rotator 2
1 (point C).The first Faraday rotator 21 rotates the light 45 degrees counterclockwise when viewed from the forward direction, and the light enters the polarizer 1 (point b). The light that has passed through the optical isolator in the forward direction becomes extraordinary light and moves in parallel by g horizontally to the left (point a). The returned light is separated by the first analyzer 31, second analyzer 32, and polarizer 1 regardless of its polarization, does not return to the light incident position, and operates as an optical isolator.

Next, the structure of this embodiment will be explained with reference to the drawings. FIG. 1 is a longitudinal sectional view showing this embodiment.

In this example, polarizer 1, L. P.
(GdBi)3I grown by E method (liquid phase growth method)
First and second Faraday rotators 21, 22 .
The first analyzer 31, 1 using rutile with a thickness of 100 mm
It has a second analyzer 32 made of thick rutile, and a plastic magnet is used as the permanent magnet 4.

When the optical isolator according to this embodiment is mounted in an LD module, the focal position of the polarized light after passing through the optical isolator shifts back and forth in the optical path direction due to the difference in refractive index of the birefringent material for ordinary light and extraordinary light. However, this amount of deviation is approximately O. The increase in coupling loss is only 2 dB, making it extremely effective as an optical isolator mounted in an LD module.

〔Effect of the invention〕

As explained above, the present invention is an optical isolator that uses a parallel plate birefringent material and has no polarization dependence, and can reduce the cost of the optical isolator. Also LD
When incorporating an optical isolator into a module, it was necessary to adjust the rotation of the optical isolator so that the insertion loss was minimized with respect to the polarization of the output light of the LD element. There is no need to make adjustments. The assembly man-hours can be significantly reduced. Furthermore, it is also possible to use this optical isolator as a big-tail type optical isolator module.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of one embodiment of the present invention, Fig. 2 (a) is an exploded perspective view of each element according to this embodiment, and Fig. 2 (b) and (C) are forward and reverse directions. An explanatory diagram showing the operation status of light when passing through each element in FIG. 3(a). (b) is a vertical cross-sectional view showing two examples of a conventional optical isolator. 1... Polarizer, 21... First Faraday rotator,
22... Second Faraday rotator, 31... First analyzer, 32... Second analyzer, 4... Permanent magnet,
2...Faraday rotator, 3...analyzer.

Claims (1)

[Claims] In an optical isolator consisting of a polarizer, a Faraday rotator, an analyzer, and a permanent magnet, and using a parallel plate birefringent material for the polarizer and the analyzer, the analyzer is divided and the thickness of the polarizer is a first analyzer with a thickness multiplied by √2, a second analyzer with a thickness equal to that of the polarizer, and a first Faraday rotator disposed between the polarizer and the first analyzer; An optical isolator comprising a second Faraday rotator disposed between the first analyzer and the second analyzer.