JPH01281402A - Polarizing beam splitter and optical isolator - Google Patents

Abstract

PURPOSE:To raise the extinction ratio and to eliminate a need of adjustment of angles of inclination of polarizing films by arranging two polarizing films at 45 deg. to the incident light in the same direction or opposite directions in a glass body. CONSTITUTION:Two polarizing films 2a and 2b inclined at 45 deg. to the incident light are arranged in parallel in a square prism-shaped glass body 1, thereby constituting a polarizing beam splitter. Two polarizing films 2a and 2b may be arranged at 45 deg. to the incident light in opposite directions. With respect to formation of polarizing films 2a and 2b in the glass body 1, a high-refractive index film and a low-refractive index film consisting of a non-absorption transparent material are alternately laminated on two slopes of parts, namely, two triangular prisms and one parallelogrammic prism of the glass body 1, which is divided along slopes inclined at 45 deg. where polarizing films should be formed, by vapor deposition, and thereafter, respective parts of the glass body are adhered into a square prism. Thus, the extinction ratio is raised and the adjustment between two polarizing films 2a and 2b is unnecessary.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention provides a polarizing beam splitter that can separate light into transmitted light and reflected light with a high extinction ratio, and a polarizing beam splitter that uses the polarizing beam splitter. The present invention relates to an optical isolator that is compatible with wavelength division multiplexing communication systems.

"Prior Art" When combining laser signals or monitoring laser power, a polarizing beam splitter is used to separate laser beams. A polarizing beam splitter is constructed by depositing an extremely thin metal film on a glass body, and separates incident light into transmitted light and reflected light. A polarizing beam splitter is desired to have a high extinction ratio in order to effectively separate light. However, since one polarizing beam splitter cannot provide an extinction ratio higher than I, two polarizing beam splitters are generally arranged in series.

Since the present invention uses the polarizing beam splitter as an optical isolator, the optical isolator will be explained here.

When the light generated by a semiconductor laser is propagated through an optical fiber, if the reflected light returns to the semiconductor laser, its operation becomes unstable, so 1 reflected light t: In 11:
Optical isolators are used to In recent optical communications, a multi-wavelength communication system has been adopted as one of the systems for high-density communication, and corresponding optical isometry is required. Generally, the wavelengths used for optical communication are l,
3m band and 1.55μ.

In order to enable optical communication to operate in both wavelength bands simultaneously, it has recently been proposed to use two optical isolators operating in the respective wavelength bands connected in series. In this case, between a pair of Faraday rotators,
The analyzer and the polarizer are arranged in series.

"Problem to be Solved by the Invention" Conventionally, in order to configure a polarizing beam splitter with a high extinction ratio of 41, two pieces are arranged in succession.
When using a series of polarizing beam splitters, the inclination angles of the respective polarizing films must be made to match in order to ensure separation into transmitted light and reflected light, which is difficult to adjust.

Furthermore, when two optical isolators are used to operate optical communications in two wavelength bands, it is necessary to match the planes of polarization of two adjacent polarizers. However, the adjustment for matching was difficult as described above.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a polarizing beam splitter which has a high extinction ratio and does not require adjusting the tilt angle of the polarizing film to 7JJ.

Still another object is to provide an optical isolator that uses the polarizing beam splitter and eliminates the need to adjust the plane of polarization of a polarizer.

"Means for Solving the Problem" The first invention includes two polarizing films on a glass body, each tilted at 45° in the same direction with respect to the incident light, or 45°ψ in the opposite direction. There is a polarizing beam splitter characterized in that the polarizing beam splitter is arranged as follows.

A second invention is the polarized beam sprit of the above invention.

This optical isolator uses a Faraday rotator as a polarizer, and has a configuration in which two polarizers and analyzers are placed on both sides of a Faraday rotator.
The polarizer and analyzer located between two Faraday rotators are replaced with a polarizing beam splitter having two polarizing films.When using a polarizing beam splitter as a polarizer, the reflected light In order to prevent Form 1 from occurring, the surface parallel to the direction in which light travels on the peripheral surface of the glass body is formed to be a rough surface.

"Operation" Since the one-stage polarizing beam splitter has two polarizing films, it can obtain a high extinction ratio similar to the case where two conventional polarizers are arranged in series.

Furthermore, since the two polarizing films are fixed at a predetermined inclination angle within one glass body, there is no need to adjust the inclination deviation of the two polarizing films.

These effects are the same in the case of an optical isolator incorporating a polarization beam splitter as polarization f, and the optical isolator can be easily assembled without the need for polarizer deviation '7JA1!5. In this case, the polarizing beam splitter is
Since it only transmits light of one plane of polarization, it is used as a polarizer.

"Example" A polarizing beam splitter of the present invention will be explained with reference to FIG. 1.2.

For example, a polarizing beam splitter is constructed by arranging two polarizing films 2a and 2b, which are tilted at 45 degrees with respect to the incident light (the lower surface of the glass body), in parallel in a square columnar glass body 1. Instead of arranging the two polarizing films 2a and 2h in parallel, they may be arranged at an angle of 45 degrees in the opposite direction to the bud as shown in FIG. are not limited to those shown in FIGS. 1 and 2, and may be arranged at intervals in the longitudinal direction of the glass body l than in the illustrated state.

When forming polarizing films 2a and 2b on the glass body l.

Prepare a glass body part (two triangular prisms and one parallelogram) divided by a 45° inclined plane on which a polarizing film is arranged, and
A high refractive index film and a low refractive index film made of a non-absorbing transparent material are alternately formed in multiple layers on one inclined surface by vapor deposition, and then each glass body portion is bonded in a prismatic shape. Note that each inclined surface of the glass body must be formed at an accurate angle of inclination of 45° to prevent deviation of the plane of polarization.

Next, a two-stage coupled optical isolator using the polarizing beam splitter will be explained with reference to FIG. In addition, since the polarizing beam spree used in the optical isolator acts as a polarizer, the surface parallel to the direction of light propagation on the circumferential surface of the glass body is formed as tlI, so that the shape of the reflected light is I've lost it.

The optical isolator of the present invention is a combination of, for example, an optical isolator that operates in a 1.3 gm wavelength band and an optical isolator that operates in a 1.55 μm wavelength band. In the drawing, the left half is the former, and the right half is the former. The minute is the latter.

The optical isolator for the 1.3Bm band is composed of a polarizer P1, a Faraday rotator FRI placed at the center of a hollow magnet magnetized in the direction of propagation of light, and the left half of a polarizing beam splitter 3. , the light is made to enter the polarizer P1 via the lens 4, and the optical heavy isolator for the 1.55 gm band is configured by the right half of the polarizing beam splitter 3, the Faraday rotator FR2, and the analyzer P2. The analyzer P2 is configured such that the analyzer P2 first emits light through the lens 5.

When light enters through the lens 4, the polarizer P1
selectively passes only polarized light 1, e.g., vertically polarized light, in a certain direction from the incident light, and further, the direction of polarization is rotated by 4b by the Faraday rotator FRI, and the light with that polarized plane is directly transmitted to the polarization beano splitter 3. It passes through polarizing films 2δ and 2b. The polarization direction of the passed light is rotated by 45° by the Faraday rotator FR2, and then output via the analyzer P2.

On the other hand, the reflected light generated in the optical fiber or the like is rotated by 45° in the same direction as the previous time by the Faraday rotator FR2, so that it is prevented from passing through the polarizing film 2b of the polarizing beam splitter. Furthermore, the reflected light that has passed through the polarizing film 2a of the polarizing beam splitter is also reflected by the Faraday rotator FR.
The polarizer P is rotated by 45° in the same direction as before by I.
1 is prevented from passing.

"Effects of the Invention" The polarizing beam splitter of the present invention has two polarizing beam splitters in one glass body.
Since it has two polarizing films, the extinction ratio is large, and since the two polarizing films are fixed at a predetermined angle of inclination, there is no need to adjust the deviation between them when incorporating them into optical communication.

The optical isolator using the polarizing beam splitter has one polarizer in the position where two polarizers would conventionally be placed in series.
Since it is sufficient to provide one polarizing beam splitter, it is not necessary to adjust the polarization plane by W12m, and moreover, it functions as a polarizer with a large extinction ratio.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of different embodiments of the polarizing beam splitter of the present invention, and FIG. 3 is a configuration diagram of an optical isolator using a polarizing beam splitter as a polarizer.

Claims (2)

[Claims] (1) In a polarizing beam splitter that separates light into transmitted light and reflected light, two polarizing films are tilted at 45° in the same direction relative to the incident light, or 45° in opposite directions to each other on the glass body. A polarizing beam splitter characterized by the following: (2) Consisting of two connected basic components consisting of a Faraday rotator placed in the center of a hollow magnet magnetized in the direction of propagation of light, a polarizer and an analyzer placed on both sides of the Faraday rotator. In an optical isolator, a polarizer and an analyzer are arranged between a pair of Faraday rotators, and two polarizing films are placed on one glass body at 45 degrees in the same direction relative to the incident light, or at 45 degrees in opposite directions to each other. An optical isolator characterized in that it is formed by being arranged at an angle.