JPS592004A - Optical rotator - Google Patents

Abstract

PURPOSE:To prevent a shift in the angle of optical rotation due to a shift in wavelength without increasing the size of an optical system by placing a wavelength plate in which the primary differential value of the angle of optical rotation with respect to wavelength is made zero between the 1st and the 2nd wavelength plates for optical rotation. CONSTITUTION:Light of wavelength lambda passed through a linear polarizer 1 is rotated by the 1st and the 2nd wavelength plates 5a, 5b of an optical rotator 5 having different thicknesses and principal axes in accordance with the angle theta of optical rotation. A wavelength plate 5c in which the primary differential value (dtheta/dlambda) of the angle of optical rotation with respect to wavelength is made zero is present between the plates 5a, 5b, so a shift in the angle of optical rotation due to a shift in wavelength is well corrected using a small-sized optical system requiring no optical rotator made of quartz crystal.

Description

Detailed Description of the Invention (1) 0 Technical Field of the Invention The present invention relates to an optical rotator used in optical devices for optical communications, and more specifically, an optical rotator that rotates the plane of polarization by a desired angle when linearly polarized light passes through it. Regarding.

+21. Background of the Technology Optical rotators used in optical devices for optical communication and the like have wavelength dependence. For example, in an optical isolator,
When linearly polarized light passes through a 45° Faraday rotator, a plane of polarization is obtained that is rotated 45° around the direction of passage, but this only applies to light of a predetermined wavelength; if there is a shift in wavelength, the polarized light The optical rotation angle of the surface also deviates, which deteriorates the isolation of the optical isolator. Therefore, there is a need for an optical rotator without wavelength dependence.

(3) Problems with the Prior Art FIG. 1 illustrates a conventional optical isolator equipped with an optical rotator with an optical rotation angle compensation function. Faraday rotator, 3
is an analyzer placed after the Faraday rotator 2),
A crystal polarizer 4 for compensating the optical rotation angle is arranged between the analyzer 3 and the Faraday rotator 2, and this crystal polarizer 4 compensates for the optical rotation angle deviation of the polarization plane caused by the wavelength deviation. I was under pressure.

However, although the crystal optical rotator 4 combined with the conventional Faraday rotator 2 as described above can correct the shift in the angle of optical rotation due to the wavelength shift, the dimension in the optical axis direction is 1105 I or more. Therefore, either the optical rotator becomes large and the optical device itself becomes large in size, or the optical rotator alone cannot produce a wavelength-independent polarizer.

(4) Purpose of the Invention The present invention solves the above-mentioned conventional problems, and combines three wavelength plates, which by themselves have no wavelength dependence of the angle of rotation, or can be ignored even if there is, The object of this invention is to provide an optical rotator that is designed to miniaturize an optical rotator and an optical device using the same.

(5)0 Structure of the Invention In order to achieve this object, the optical rotator of the present invention rotates the plane of polarization by a desired angle when linearly polarized light of a desired wavelength passes therethrough. First, the main axis is different. A second wave plate and a third wave plate disposed between the two are combined so that the first derivative of the optical rotation angle with respect to the wavelength is zero.

(6) Example of 1 invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an example in which the optical rotator according to the present invention is applied to an optical isolator. As in the case of FIG.
and analyzer 3 are arranged, and this linear polarizer 1 and analyzer 3
In between, there is an optical rotator 5 that rotates the polarization plane of the linearly polarized light by a desired angle θ.
is arranged, and this optical rotator 5 is the first. It is composed of second and third wave plates 5a+5b+5a.

The first to third wave plates have birefringence and are made of materials with different principal axes and thicknesses, and the linear polarizer 1
First wave plate 5a from the side.

Arranged in the order of third wave plate 5C0 second wave plate 5b,
The MU polarized light passes through each of the wavelength plates 5 & *5 c * 5 b in order, so that the first differential part of the optical rotation angle θ with respect to the wavelength λ is set to 0, and so-called wavelength-independent optical rotation is performed.

The polarization state of the optical rotator 5 will be further explained in detail using the Poincaré sphere shown in FIG.

In the Poincaré sphere shown in Figure 3, if light from point A on the equator of the sphere is moved to point B, the plane of polarization of linearly polarized light is changed to an angle θ
(2θ on the spherical surface).In this case, first, the light at point A is transferred to the first wavelength plate 5atl-
Using the third wave plate 5C, move the spherical surface by an angle δ along the line 11 with the main axis S1 as the center in the direction of the arrow, By passing through the second wave plate 5b, the light is rotated by an angle δ on the spherical surface along the line 11 around the principal axis S2, and is transferred to the exit polarization state point B. Here, the first, second... Third wave plate 5
& e 5 b # 5 Since e has wavelength dependence, the input polarization state point Human light has a width at point A as shown by the x mark, and similarly the output polarization state point B (Light has a width at point B.) If we use the wavelength dependence of such a wave plate to transfer the light from point ^ to point B'', which goes up to the third wave plate 5c, The second wavelength plate 5b is at point B.
is transferred to the output polarization state point B. In other words, the state point A of the incident polarized light is moved on the equator of the spherical surface by the first to third wavelength plates 56 to 5C, without being affected by the wavelength shift, and the optical rotation angle is 0.
K is shifted by an angle twice as large as K and converted to the output polarization state point B. Also, since this state point B is on the equator of the Poincaré sphere, the plane of polarization at that point becomes linearly polarized light rotated by the optical rotation angle θ relative to point A.

In addition, the above 1. Second. The angle δ1 of the third wave plates 5a to 5C. δ2. δ is set according to the thickness of each plate υ, and the first to third wavelength plates 58 to 5C are set to the third wavelength plate 58 to 5C.
It goes without saying that the form of polarized light displayed on the Poincaré sphere shown in the figure is not limited to that, but also the form displayed on the sphere depending on the wavelength and angle of rotation of the optically rotated light.

7) Effect of the invention As described above, according to the present invention, by combining three wavelengths so that the first derivative of the angle of rotation θ with respect to the wavelength λ is 0, the wavelength dependence of the angle of rotation is reduced. This has the effect that the total optical rotator alone can be made small or large, and that the optical rotator and the optical device using the same can be made smaller.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional optical isolator, FIG. 2 is an explanatory diagram of an optical isolator having an optical rotator according to the present invention, and FIG. 3 is an explanatory diagram of the display state of polarized light by the Poincaré sphere of the optical rotator in the present invention. It is a diagram. In the drawings, 1 is a linear polarizer, 3 is an analyzer, 5 is an optical rotator, 5& is a first wave plate, 5b is a second wave plate, and 5e is a third wave plate. Patent applicant: Fujitsu Limited 1.

Claims (1)

[Claims] In an optical rotator that rotates the polarization plane by a desired angle when linearly polarized light of a desired wavelength passes therethrough, the first... The second wave plate and the third wave plate disposed between the two are arranged so that the first derivative of the optical rotation angle with respect to the wavelength is 0.
A rotator characterized by being combined so that.