JPS5850512A - Optical isolator - Google Patents

Abstract

PURPOSE:To withdraw restrictions regarding the selection of crystals and to apply even a double refracting crystal to an optical isolator, by dissolving the double refracting influence by disposing orthogonally two pieces of double reftacting crystals. CONSTITUTION:Magnetic and optical crystals 5, 6 have double refracting properties and their optical axis C are disposed orthogonally to each other in the constitution in which a 45 deg. revolving optical rotatory plate 4 and the magnetic and optical crystals 5, 6 are disposed between polarizers 2, 3. When a C axis of the crystal having the thickness (t) and a vertical axis (a) are made to easily magnetized axes and linearly polarized light is made incident to this axis direction, exit light becomes an oval polarized wave. A lengthwise direction of this oval polarization surface corresponds to the linearly polarized surface made incident and the plate thickness (t) of each of magnetic optical crystals 5 and 6 is finished by abrading so that the rotatory angle theta by Faraby rotation at this time becomes 45 deg., and the optical rotatory plate 4 is disposed behind these crystals 5, 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-performance optical isolator that prevents the oscillation of a laser light source from becoming unstable due to its own reflected light.

The configuration of a conventional optical isolator is shown in FIG.

The function of the optical isolator operates and explodes as described below. The linearly polarized light propagating in the magnetization direction of the magneto-optical material L rotates clockwise due to Faraday rotation, roughly 4! It is rotated as0 clockwise by the j0 rotation optical rotation plate and passes through the polarizer 3 on the output side. Therefore, the planes of polarization of polarizer 3 and polarizer 3 are arranged so as to be perpendicular to each other.

On the contrary, the light incident from the polarizer 3 is rotated clockwise by the 4IS0 rotating optical rotation plate and rotated by S0, and is rotated counterclockwise by as0 by the magneto-optic material 1, so the plane of polarization that reaches the incident side polarizer is not rotated. There is the same effect as □′□, and the light from the incident side polarizer becomes extinct.

Here, when the linearly polarized light rotates once by 7 degrees, the linear polarization property must be maintained. If it is glass or a magneto-optical material without cubic crystal anisotropy, linear polarization is maintained.

However, if the magneto-optical material l is a crystal with birefringence, such as orthoferrite or hexagonal ferrite, the axis of easy magnetization does not coincide with the optical axis, so the birefringence affects the Faraday rotation, resulting in linear polarization. , is no longer maintained and becomes elliptically polarized. This leads to a deterioration of the extinction ratio of the optical isolator, resulting in the loss of its function as an optical isolator.

Therefore, even if a crystal with a high figure of merit or a crystal with extremely low optical loss at the required wavelength exists, it cannot be applied as an optical isolator in the case of a Faraday rotation having birefringence. In order to solve the above-mentioned problems, this method is characterized by eliminating the influence of birefringence by orthogonally arranging a single birefringent crystal.

The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, in which C and J are polarizers, q is a rotary polarizing plate, j and O are magneto-optical crystals, and 7 is an arrow indicating the direction of easy magnetization. .

be. Magneto-optic crystal with birefringence! The optical axes of and B (in the figure, the a-axis) are orthogonal to each other. The structure of the present invention will be explained by taking a rhombohedral crystal represented by FeF3 or FeBO3 as an example.

In this crystal system, the optical axis coincides with the 3-fold symmetry axis C', but the axis of easy magnetization is perpendicular to the a axis. The axis is the axis of easy magnetization, and when linearly polarized light is incident in the direction of this axis, the emitted light becomes elliptically polarized due to birefringence. The long axis direction of this elliptically polarized wave surface corresponds to the incident linearly polarized wave surface, and the rotation angle θ due to Faraday rotation at that time is given by the following equation.

B = −T−(no −no)t
(2) 'Here, F is the Faraday rotation coefficient (d
eg/cm ), λ is the wavelength of light, no is the refractive index of the ordinary ray, no is the refractive index of the extraordinary ray, and B is the phase delay angle due to birefringence.

As seen from equation (1), even if F is large, B and 5
Because of the iin term, θ becomes extremely small compared to the case where there is no birefringence.

Therefore, as shown in FIG. 2, the optical axis of two birefringent magneto-optic crystals j, ie. If the axes are arranged so that they are orthogonal to each other, then B becomes B = - ((no-no)tl + (no-no)tg)
(s)λ. Here, since tl w tg w t, B=
0〇 Therefore, in equation (1), if B −+ o, #−
, 2Ft (4) is obtained.

Equation (4) is exactly the same as the equation for one revolution of 7 Alade in a cubic crystal system or an isotropic magneto-optical material such as glass that does not exhibit normal birefringence.

゛ When using the present invention as an optical isolator,
Each magneto-optical crystal is expressed as 0w4I3'! , after polishing the plate thickness t, one magneto-optical crystal j
, After pasting them together so that the a-axes of B are perpendicular to each other,
As shown in FIG. 2, a magneto-optic crystal j+4 and a 130-rotational polarization plate bonded together are inserted between two polarizers whose polarization planes are perpendicular to each other. For example, the Faraday rotation coefficient of FeF, which is transparent in the visible light range, is λ=0.7 and y-100deg/cm, so t-co...
It becomes 2S-.

As explained above, since the optical isolator of the present invention can be constructed using a birefringent crystal, there are no restrictions on the selection of the crystal. Even crystals like
It has the advantage of being able to be applied to optical isolators, and since the apparent reduction in the 7 Alladay effect due to birefringence is eliminated, the thickness of the crystal can be made smaller and the loss of optical isolators can be reduced. .

[Brief explanation of drawings]

Claims (1)

[Claims] L In a magneto-optic crystal that has a birefringence and whose easy axis of magnetization does not coincide with the optical axis, one magneto-optic crystal having the same thickness along the easy axis of magnetization is placed so that its optical axes are orthogonal to each other. and the total thickness of the two magneto-optic crystals is in such a range that the plane of polarization of light of the desired wavelength rotates llj' along the axis of easy magnetization, The magneto-optic crystals have polarization planes of 900 to each other.
1. An optical isolator, characterized in that the optical isolator is set between two polarizers or polarizing plates, and an ls0 rotation optical rotation plate is installed after the magneto-optic crystal.