JPS62136618A - Optical device - Google Patents

Abstract

PURPOSE:To eliminate polarization dependency by arranging a birefringence plate in an optical path and also arranging a 1/4-wavelength plate right behind it. CONSTITUTION:A light wave 3 entering an optical device is incident on the incidence surface of the birefringence plate 1 at a 0 deg. angle of incidence, and the polarized component S wave perpendicular to the incidence surface ravels straight (3A) and is transmitted through the 1/4-wavelength plate 2 to travel while coinciding with the axis of the light wave 3. The polarized component P wave of the light wave 3 which is parallel to the incidence surface is refracted abnormally (3B) and passes through the birefringence plate 1, and the light is refracted by a projection surface in parallel to the axis of the light wave 3 and passed through the 1/4-wavelength plate 2 to travel in parallel to the axis of the light wave 3. The P and S waves shift in phase by a quarter as much as the wavelength when passing through the 1/4-wavelength plate 2, so the light projected from the 1/4-wavelength plate 2 is circularly polarized light. This is therefore equivalent to random polarized light apparatently and characteristic variation (polarization dependency) of the degree of optical coupling, transmission loss, and transmission waveform, etc., is eliminated, thereby facilitating the design of an optical device.

Description

DETAILED DESCRIPTION OF THE INVENTION (Summary) In an optical device in which optical components for transmitting and receiving light waves are arranged, a birefringent plate and a
By inserting a four-wavelength plate, the polarization dependence of the optical device is eliminated.

[Industrial application field]

The present invention relates to an optical device having functions such as optical coupling, optical branching, optical demultiplexing, and optical multiplexing.

In optical communication equipment and the like, optical devices having functions such as optical coupling, optical branching/demultiplexing, and optical multiplexing are widely used.

The light emitted by a semiconductor laser used for optical communication is polarized light that is almost linearly polarized. The polarization conditions of such polarized light vary due to environmental conditions such as temperature changes, bending of an optical transmission path (for example, an optical fiber), lateral pressure, and the passage of time.

Due to this, when an optical device with functions such as optical coupling, optical branching, optical demultiplexing, and optical multiplexing is installed in such an optical path, problems such as coupling degree, transmission loss, transmission waveform, etc. Characteristics vary. That is, optical devices have so-called polarization dependence.

Therefore, an optical device with less polarization dependence is desired.

[Conventional technology]

FIG. 3 is an optical path diagram of a conventional optical device with little polarization dependence, and the light emitted by the semiconductor laser 5 is transmitted through the optical transmission path (
The signal is transmitted to the optical device 20 via an optical fiber (optical fiber) 6.

Note that the polarized light incident on the optical transmission path 6 includes S waves (the component in which the electric field of the incident light is perpendicular to the plane of incidence, and is shown in the figure as light that oscillates within a plane perpendicular to the plane of the paper), and P waves. Waves (refers to the components of the electric field of incident light parallel to the plane of incidence, and are shown in the figure as light that oscillates in a plane parallel to the plane of the paper).

The illustrated optical device 20 is an optical splitter, and the output side terminal of the optical transmission line 6 is fixed to the side wall (not shown) of the housing, and is further equipped with a lens 7 that makes the output light parallel. It is.

An optical transmission line (optical fiber) 11, which is one output path, is fixed to opposing side walls on the extension line of the axis of the optical transmission line 6.
A lens 8 is mounted just in front of the end face of the optical transmission line 11.

Reference numeral 10 denotes an optical film plate having a function of, for example, a half mirror, which is formed by forming dielectric films in multiple layers as desired on the surface of a thin glass plate.

The optical film plate 10 is located approximately midway between the lenses 7 and 8,
It is fixed to the bottom plate of the housing so that the incident angle α with respect to the optical transmission line 6 is 15 degrees or less.

Further, a lens 9 and an optical transmission path (optical fiber) 12, which is another output path, are attached to the side wall on the path of the light emitted from the optical transmission path 6 and reflected by the optical film plate 10.

It is well known that when the optical film plate 10 is arranged so that the incident angle is within 15 degrees as described above, the power transmittance and power reflectance of P waves and S waves become almost equal. .

Therefore, approximately half of the optical power emitted from the optical transmission path 6 of the optical device 20 passes through the optical film plate 10 and enters the optical transmission path 11, and the remaining half is reflected by the optical film plate 10. The light enters the optical transmission line 12.

That is, the optical device 20 reacts equally to P waves and S waves, and polarization dependence is largely eliminated.

The optical film plate is designed to respond equally to S waves and P waves, and the optical film plate is arranged so that the incident angle is 45 degrees, that is, the output path on the reflected light side is There are also optical devices that have little polarization dependence even if they are arranged in a direction perpendicular to the incident path.

[Problem that the invention seeks to solve]

However, in the above-mentioned conventional illustrated optical device, the arrangement of the optical transmission path on the incident side and the optical transmission path on the reflected light side is at an angle of 30 degrees or less, reducing the degree of freedom in optical path design. There is a problem in that the casing of the optical device must be made larger in order to fix the optical device.

On the other hand, for optical devices whose membranes are designed to respond equally to S waves and P waves, not only is the membrane design complicated and difficult, but it is also difficult to form a desired multilayer membrane, resulting in high costs. There is a problem.

[Means for solving problems]

In order to solve the above-mentioned conventional problems, the present invention, as shown in the principle diagram of FIG. A 174-wavelength plate 2 is disposed immediately after the refracting plate 1, and the light wave passing through the 174-wavelength plate 2 is made into circularly polarized light.

[Effect]

According to the means of the present invention, the optical path of the optical device is provided with a birefringent plate 1 whose crystal axis is parallel to the plane of paper and whose light-receiving surface is perpendicular to the plane of paper, and further, immediately after the birefringent plate 1, Birefringent plate 1
A 1/4 wavelength plate 2 is arranged parallel to the .

Therefore, the light wave 3 that has entered the optical device passes through the birefringent plate l.
The polarized light component perpendicular to the incident plane of the light wave 3, that is, the S wave, which is incident on the incident plane at an incident angle of 0 degrees, enters the birefringent plate 1 as ordinary light. Therefore, the S wave travels straight (indicated by light wave 38), enters the 174-wave plate 2, passes through the quarter-wave plate 2, and travels in the direction of the axis of the light wave 3.

On the other hand, the polarization component parallel to the plane of incidence of light wave 3, that is, the P wave, is
The light enters the birefringent plate 1 as extraordinary light. Therefore, the P wave is refracted by the extraordinary refractive index (indicated by light wave 3B), passes through the birefringent plate 1, is refracted roughly parallel to the axis of the light wave 3 at the exit surface, and enters the 174-wave plate 2. incident. The light then passes through a 1/4 wavelength plate 2 and travels parallel to the axis of the light wave 3.

These P waves and S waves have a phase of 1 when passing through the 174-wave plate 2.
Since the wavelength is shifted by /4 wavelength, the light emitted from the 1/4 wavelength plate 2 is circularly polarized light. Therefore, the appearance is equivalent to randomly polarized light, and there is no polarization dependence.

〔Example〕

The present invention will be specifically explained below with reference to illustrated examples. Note that the same reference numerals indicate the same objects throughout the figures.

FIG. 2 is an optical path diagram of one embodiment of the present invention, in which light emitted from a semiconductor laser passes through an optical transmission line 6 and then passes through an optical device 3.
Transmitted to 0.

In the optical device 30, the output end of the optical transmission path 6 is fixed to the side wall of the housing, and a lens 7 is further attached.

An optical transmission line 11, which is one output path, is fixed to opposing side walls on an extension of the axis of the optical transmission line 6, and a lens 8 is mounted just in front of the end surface of the optical transmission line 11.

Then, the optical film plate 10 is fixed to the bottom plate of the housing approximately halfway between the lenses 7 and 8 so that the angle of incidence with respect to the optical transmission path 6 is 45 degrees.

In addition, a lens 9 and other output paths are provided along the course of the light waves emitted from the optical transmission path 6 and reflected by the optical film plate 10, that is, in a direction perpendicular to the optical axes of the optical transmission path 6 and the optical transmission path 11. A certain optical transmission line 12 is attached.

A birefringent plate 1 whose crystal axis is parallel to the plane of the paper and whose light-receiving surface is perpendicular to the plane of the paper is arranged between the lens 7 and the optical film plate 10. 174 wavelength plates 2 are arranged in parallel.

In the optical device 30 configured as described above, the light incident from the optical transmission line 6 is incident on the light receiving surface of the birefringent plate 1 at an incident angle of 0 degrees, and the S wave is incident on the birefringent plate 1 as ordinary light. The light then travels straight (indicated by light wave 3A), enters the 174-wave plate 2, passes through the 174-wave plate 2, and enters the optical film plate 10.

In addition, the P wave is refracted with an extraordinary refractive index (shown as light wave 3B),
The light passes through the birefringent plate 1, is further refracted at the exit side surface so as to be parallel to the axis of the light wave 3, and enters the 174-wavelength plate 2.

The light then passes through the 174-wavelength plate 2 and proceeds parallel to the axis of the light wave 3 and enters the optical film plate 10 .

Since the light passing through the quarter-wave plate 2 is circularly polarized, half of the optical power goes straight through the optical film plate 10 and enters the optical transmission path 11, and the other half is reflected by the optical film plate 10. optical transmission line 1
2.

As described above, in the optical device 30, not only polarization dependence is eliminated, but also the arrangement of the optical transmission path on the reflected light side can be set at any angle with respect to the incident path.

In addition, there is a large degree of freedom in optical path design, which not only facilitates design, but also facilitates miniaturization.Furthermore, membrane design is easy and costs are low.

By separating the light into S waves and P waves using a birefringent plate, as a means of preventing a decrease in the degree of coupling, the birefringent plate is made thinner to reduce the translational shift d, and even if parallel to each other, it is , to eliminate angular shake.

Note that the present invention is effective when applied not only to the illustrated optical splitter but also to optical devices having functions such as optical demultiplexing and optical multiplexing.

〔Effect of the invention〕

As explained above, the present invention is an optical device that eliminates the polarization dependence of the optical device by inserting a birefringent plate and a quarter-wave plate in the optical path on the incident side of the optical device, and It has excellent practical effects such as less erosion, more freedom in optical path design, easier design, miniaturization, easier membrane design, and lower cost.

[Brief explanation of drawings]

Figure 1 is a diagram of the principle of the present invention. FIG. 2 is an optical path diagram of one embodiment of the present invention, FIG. 3 is an optical path diagram of a conventional optical device. In the figure, l is a birefringent plate, 2 is a 174 wavelength plate, 5 is a semiconductor laser; 6, 11.12 is an optical transmission line, 10 indicates an optical film plate.

Claims (1)

[Claims] In an optical path within an optical device in which optical components for transmitting and receiving light waves (3) are arranged, a birefringent plate (1) and a quarter-wavelength filter immediately after the birefringent plate (1) are provided. An optical device characterized in that a plate (2) is arranged.