JPS6380222A - Polarizing device - Google Patents

Abstract

PURPOSE:To always obtain a linearly polarized light having a constant intensity by providing a first polarizer for separating an incident light into light beams whose planes of polarization are different by 90 deg. and emitting them roughly in parallel, and a second polarizer which has been inclined by 45 deg. against those planes of polarization. CONSTITUTION:The titled device is provided with the first polarizer for separating an incident light into light beams whose planes of polarization are different by 90 deg. and emitting them roughly in parallel, and the second polarizer 12 which is installed by inclining it by 45 deg. against those planes of polarization. By the first polarizer 10, the incident light is separated into light beams P. S whose planes of polarization are different by 90 deg. and emitted roughly in parallel, and by the second polarizer 12, the respective separated light beams are further separated into light beams whose planes of polarization are different by 90 deg. and emitted. That is to say, by the second polarizer 12, light beams having an intensity of 1/2 of the respective incident light beams pass through and synthesized. Accordingly, even if a polarized state of the incident light to the first polarizer 10 is varied and a ratio of the intensity of both emitted light beams is varied, from the second polarizer 12, a linearly polarized light having an intensity of 1/2 of all the incident light beams can always be fetched in the end.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention combines two types of polarizers, and provides a polarizing device in which the intensity of the output light is always kept constant even if the polarization state of the incident light changes. It is related to.

[Prior Art] There are various optical devices such as optical isolators that require linearly polarized light. Generally PBS (Polarized Beam Splinter)
Linearly polarized light can be easily obtained by using a prism.

[Problems to be solved by the invention] There is not much of a problem when the incident light propagates through space, but there is a big problem when the incident light is transmitted through an optical fiber, especially when the light source is a semiconductor laser. This is because when emitting light close to linearly polarized light, even a slight movement of the optical fiber causes a significant change in the polarization state.

For example, in the case of a single mode optical fiber, the light intensity ratio k
(ratio of strength in the main axis direction and strength in the direction perpendicular to it)
does not change much, but the orientation θ of the principal axis changes significantly, and in the case of a multimode optical fiber, not only the orientation θ of the principal axis but also the ratio of light intensities changes.

In other words, even if the total amount of incident light is constant, when an optical fiber touches it or moves under its own weight, the polarization state changes, and the intensity of the emitted linearly polarized light changes significantly, greatly affecting the performance of various optical devices.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above,
It is an object of the present invention to provide a polarizing device that can always obtain linearly polarized light with a constant intensity even if the polarization state changes as long as the amount of incident light is constant.

[Means for Solving the Problems] The present invention, which can achieve the above objects, includes a first polarizer that separates incident light into lights whose polarization planes differ by 90 degrees and outputs the lights in substantially parallel directions. , is a polarizing device including a second polarizer installed at an angle of 45 degrees with respect to the plane of polarization.

What about the first polarizer? jl[It is most desirable to use an H-fold prism.

[Operation] The first polarizer separates the incident light into lights whose planes of polarization differ by 90 degrees, and the lights are emitted substantially in parallel. When a second polarizer is provided at an angle of 45 degrees with respect to these planes of polarization, the separated lights are further separated into lights whose planes of polarization differ by 90 degrees and are emitted. In other words, in each second polarizer, light having an intensity of 1/2 of the light incident thereon passes through and is combined.

Therefore, even if the polarization state of the light incident on the first polarizer changes and the ratio of the intensity of the Okayama incident light changes, the intensity of the light incident on the second polarizer will always be 1/2 of the total incident light. It is possible to extract linearly polarized light.

[Example] FIG. 1 is an explanatory diagram showing an example of a polarizing device according to the present invention. Here, a birefringent prism 10 made of a birefringent material such as rutile is used as the first polarizer, and a PBS prism 12 is used as the second polarizer.

The incident light is separated by the birefringent prism 10 into an S polarization component and a P polarization component. The S-polarized component has a light intensity represented by an arrow Pa, and the P-polarized component has a light intensity represented by an arrow pb. Here, a phase compensation plate 14 is placed in the optical path of S-polarized light.
is provided to match the phase difference of both polarized lights.

These lights enter the PBS prism 2 installed at an angle of 45 degrees with respect to their plane of polarization. Then, when passing through the PBS prism 12, each light beam has half (Pc,
(expressed in Pd).

Now, if the total intensity of the incident light is expressed by pi, the following relationship holds true, and the second PBS prism 12
In each case, since the plane of polarization is tilted by 45 degrees, the intensity becomes half, and therefore the total intensity Po of the emitted light is always constant.

It is most preferable to use a birefringent prism 10 as shown in FIG. 1 as the first polarizer because the structure is simple and two types of parallel linearly polarized light can be obtained.

However, in other embodiments, as shown in FIG.
The prism 16 and an ordinary triangular prism 16 may be combined to separate the incident light into lights whose polarization planes differ by 90 degrees and emit them almost in parallel.Other configurations are the same as in the case of FIG. Since they may be the same, corresponding members are given the same reference numerals and their explanations will be omitted.

When a phase compensation plate is provided, it is provided in either of the two optical paths between the first and second polarizers, or in either of the two optical paths on the output side of the second polarizer. If the thickness of the prism is processed with high precision so that the zero phase difference that can be inserted is sufficiently small, the phase compensation plate may be omitted, but it is actually easier to manufacture the prism using a phase compensation plate.

FIG. 3 is an explanatory diagram showing an example of an optical isolator using the polarization device 20 according to the present invention. Main polarizer 2 on the incident light side
The entire eight-piece polarizing device 20, which is an example in which a Faraday rotator 22, a polarizer 24, and a lens 26 are provided in the subsequent stage, performs the same function as a conventional polarizer.

With this configuration, it is possible to construct an optical isolator that always outputs the light with a constant intensity even if the polarization state of the incident light changes, and this provides good results, especially when an optical fiber is connected to the input side. can get.

FIG. 4 shows yet another example of application of the present invention. In this configuration, a phase compensator 28 and a 174-wave plate 30 are provided on the output side of the polarizing device 20, and a lens 32 is further provided. This makes it possible to manufacture an optical device that generates circularly polarized light with a constant intensity.

[Effects of the Invention] As described above, the present invention includes a first polarizer that separates incident light into lights whose polarization planes differ by 90 degrees and outputs the lights approximately parallel to each other; Since the polarizer is equipped with a second polarizer, linearly polarized light with a constant intensity can always be obtained even if the polarization state changes as long as the total amount of incident light is constant.

In particular, when light is guided through an optical fiber, the polarization state changes when it comes into contact with the optical fiber or moves under its own weight, which greatly affects the performance of various optical devices. However, incorporating the polarization device according to the present invention This makes it possible to prevent such harmful effects from occurring.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing one embodiment of a polarizing device according to the present invention, Fig. 2 is an explanatory diagram showing another embodiment of the invention, and Fig. 3 is an explanatory diagram showing an example of an optical isolator using the present invention. Explanatory diagram,
FIG. 4 is an explanatory diagram showing an example of a circularly polarized light producing device using the present invention. 10... Birefringent prism, 12... PBS prism, 14... Phase compensation plate, 16... PBS prism,
18...Triangular prism.

Claims (1)

[Claims] 1. A first polarizer that separates incident light into light beams with polarization planes different by 90 degrees and outputs the lights approximately in parallel, and a second polarizer that is installed at an angle of 45 degrees with respect to the polarization planes. A polarizing device equipped with a polarizer. 2. The polarizing device according to claim 1, wherein the first polarizer is a birefringent prism.