JPH01131517A - Optical isolator - Google Patents

Abstract

PURPOSE:To facilitate handling of an optical isolator by paralleling the light incident face of a Faraday rotor with the light incident face of a box body and inclining the respective light incident faces of a polarizer and analyzer symmetrically at the same angle to each other with respect to the light incident face of the Faraday rotor. CONSTITUTION:The Faraday rotor is disposed in the boxy body 1 in such a manner that the polarization directions of the polarizer 2 and the analyzer 3 vary by 45 deg. from each other. The Faraday rotor 4 and a permanent magnet 5 which saturates the magnetization of the Faraday rotor 4 are disposed between said polarizer 2 and the analyzer 3. The light incident face of the Faraday rotor 4 is paralleled with the light incident face of the box body 1 and the respective light incident faces of the polarizer 2 and the analyzer 3 are inclined symmetrically at the same angle to each other with respect to the incident face of the Faraday rotor 4. The reflected light is, therefore, prevented from returning to the light source and the light incident face of the box body 1 is positioned perpendicular to the incident light. In addition, the incident optical axis and the exit optical axis are aligned. Mounting of the optical isolator, i.e., handling of the optical isolator is thereby extremely facilitated.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical isolator.

More specifically, the present invention relates to a device for preventing reflected light from optical fibers, lens systems, and nectar facets in optical communications, writable video discs, etc. that use semiconductor lasers as light sources.

The basic configuration of conventional optical isolators is that the polarization directions are 45° to each other.
! 45° between the polarizer and analyzer arranged so that
In this configuration, a magneto-optic crystal having a thickness that provides a Faraday rotation angle of is placed as a Faraday rotator, and a permanent magnet t ta for applying an external saturation magnetic field to the magneto-optic crystal is placed around the magneto-optic crystal.

The principle of optical isolator t - Figure 4 shows the state of the polarization plane of light incident in the forward direction. Polarizer 11
Of the light 12a incident on the light 12a, the amount of light that passes through the polarizer 11:
The line Uii1 light 12b undergoes a rotation of 45° with a Faraday rotation angle 13. The fc linearly polarized light 12c rotated by 45 degrees passes through the analyzer 14, which is arranged 45 degrees apart from the polarizer 11, and is emitted. Among the incident light 15a showing the polarization plane of the light incident in the opposite direction, the direct M polarized light 15b that has passed through the analyzer 14 is 'Due to the non-reciprocity of Faraday rotation, Since the direction of Faraday rotation is determined only by the direction 16 of the magnetic field, regardless of the direction of incidence of the light, when the light passes through the Faraday rotator 13, an additional 4
It is subjected to a 5° Faraday rotation, is perpendicular to the polarization direction of the polarizer 11, and cannot pass through. An optical isolator allows light to pass in only one direction.

The configuration of a conventional optical isolator will be explained based on FIG. 3. In FIG. 3, 21 is a case, on one end of which is a polarizer 22, on the other end a analyzer 23, and at an intermediate position is a Faraday rotator 24 and this Faraday rotator 2.
4's circumference 'lr: A covering cylindrical permanent magnet 25 is arranged respectively. And these polarizer 22, analyzer 2
3 and each light incident surface 22a of the Faraday rotator 24,
23a and 24a are parallel to each other and the case 21
The incident optical axis C is parallel to the light incident surface 21a of the case 21, and the incident optical axis C is parallel to the light incident surface 21a of the case 21 in order to prevent the reflected light from each of the light incident surfaces 22a, 23a, and 24a from returning to the light source (for example, a semiconductor laser). In other words, the incident light 26 is not incident perpendicularly to the light incident surface 21a, but is incident at an angle at an appropriate angle to the light incident surface 21a.

Problems to be Solved by the Invention According to the above-mentioned conventional configuration, the output optical axis d is shifted by a predetermined amount δ with respect to the input optical axis C, and the incident light 26 is transferred to the optical isolator, that is, the light incident surface 21a of the case 21. The problem is that the beam must be incident at an appropriate angle and is difficult to handle.

Therefore, an object of the present invention is to provide an optical isolator 41 that can solve the above problems.

Means for Solving the Problems In order to solve the above problems, the optical isolator of the present invention has a polarizer and an analyzer arranged in a box so that their polarization directions differ by 45 degrees from each other, and
A Faraday rotator and a permanent magnet that saturates the magnetization of the Faraday rotator are arranged between the photons and the analyzer, and the light incident surface of the Faraday rotator is made parallel to the light incident surface of the box, and the polarized light is The light incident surfaces of the rotator and the analyzer are symmetrically inclined at the same angle with respect to the light incident surface of the Faraday rotator.

Effect In the above configuration, the light entrance surface of the Faraday rotator is made parallel to the light entrance surface of the box, and the light entrance surfaces of the polarizer and analyzer are set at the same angle with respect to the light entrance surface of the Faraday rotator. Since they are tilted symmetrically, even if incident light is perpendicularly incident on the box, the reflected light will not return to the light source, and the incident optical axis and output optical axis can be aligned. Therefore, handling of the optical isolator becomes easy.

Example An embodiment of the present invention will be described below with reference to FIG.

In Fig. 1, 1 is a case (box), inside of which a polarizer 2 is arranged at one end, and an analyzer 3 at the other end.
A Faraday rotator 4 is arranged at an intermediate position between the polarizer 2 and the analyzer 3, and a permanent magnet 5 that saturates the magnetization of the Faraday rotator 4 is placed around the Faraday rotator 4. It is located. That is,
This permanent magnet 5 is connected to the light input/output surface 4 of the Faraday rotator 4.
a.

It has a cylindrical shape with 4bt-a and its surroundings covered. The light entrance surface 4a of the Faraday rotator 4 is parallel to the light entrance surface of the case (for example, a window member), and the light entrance surface 2a of the polarizer 2 and analyzer 3 is
, 3a are tilted at the same angle (therefore symmetrically) with respect to the light incidence surface 4a of the Faraday rotator 4, that is, with respect to the light incidence surface 1a of the case 1.Of course, the light incidence surface of the polarizer 2 2a and the light exit surface The light entrance surface 3a and the light exit surface 3b of the analyzer 3 are parallel to each other, and the light entrance surface 4a and the light exit surface 4b of the Faraday rotator 4 are parallel to each other. The above-mentioned inclination angle (θ) is set to such an angle that the reflected light from each of the light incident surfaces 2a and 3a does not return to the light source.

In the above 114 configuration, from the light source to the light incidence surface 1 of the case 1
The incident light 6 that is incident perpendicularly to a is changed in direction by an angle (θ) by the polarizer 2, is emitted parallel to the incident optical axis a and deviated by an amount Kh, and passes straight through the Faraday rotator 4. After that, it enters the analyzer 3, and the angle (-) is opposite to the polarizer 2.
The light beam is emitted from the same position and in the same direction as the incident light beam 1a by changing its direction by θ). Therefore, the optical axis a of incidence on the optical isolator and the optical axis of output from the optical isolator coincide.

Therefore, although the incident light 6 from the light source is perpendicularly incident on the optical isolator, the light input/exit surfaces 2a, 2b of the polarizer 2, analyzer 3, and Faraday rotator 4 are
, 3a, 3b, 4a, 4b does not return to the light source.

Note that, as shown in FIG. 2, the same effect can be obtained even if the direction of inclination of the polarizer 2 and analyzer 3 is reversed from that in FIG.

Effects of the Invention According to the above configuration of the present invention, the light entrance surface of the Faraday rotator is made parallel to the light entrance surface of the box, and each light entrance surface of the polarizer and analyzer is parallel to the light entrance surface of the Faraday rotator. By tilting the box symmetrically at the same angle to prevent the reflected light from returning to the light source, the light input/exit surface of the box can be made perpendicular to the incident light, and the incident optical axis and output light can be aligned. The optical isolator can be aligned with the optical isolator axis, which makes installation of the optical isolator, that is, handling of the optical isolator extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a side view of an optical isolator according to an embodiment of the present invention, FIG. 2 is a side view of an optical isolator according to another embodiment of the invention, FIG. 3 is a side view of a conventional optical isolator, and FIG. Figures (at and (bl) are perspective views explaining the principle of the optical isolator. 1... Case frame, 2... Polarizer, 3... Analyzer, 4... Faraday rotator, la, 2a,
3a, 4a...Light reflecting surface, 5...Water filled magnet. Agent Yoshihiro Shikamoto is placed in Figure 4- Faraday 15 car! 2 [1',',',:l *LMIQ Figure 3

Claims (1)

[Claims] 1. A polarizer and an analyzer are arranged in the box so that their polarization directions differ by 45 degrees from each other, and a Faraday rotator is provided between the polarizer and the analyzer, and the magnetization of the Faraday rotator is saturated. A permanent magnet is arranged so that the light incidence surface of the Faraday rotator is parallel to the light incidence surface of the box, and each light incidence surface of the polarizer and analyzer is parallel to the light incidence surface of the Faraday rotator. Optical isolators tilted symmetrically at the same angle.