JPS6030734Y2 - High reverse loss compact optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical isolator in the light wave region, and particularly to a compact optical isolator with high reverse loss suitable for optical fiber communication.

Recently, the practical application of optical fiber communication is progressing in various places.
Various optical circuits are needed to improve the performance and expand the functionality of optical fiber communication systems.

An optical isolator is one such optical circuit. For example, when a light beam emitted from a laser oscillator returns due to reflection, it prevents it from entering the original oscillator, thereby improving the stability and stability of the oscillator. Used to improve reliability.

A conventional optical isolator has a Faraday rotator that provides a 45-angle decoration to a light beam between two polarizing elements whose azimuth angles are 45 angles to each other.

Although various optical isolators have been reported so far, there have been very few small ones in the 0.8 μm band, which is the oscillation wavelength range of gallium aluminum arsenide (GaAIAs) semiconductor lasers.

The main factor that determines the dimensions of an optical isolator is the magnet that applies the magnetic field to the Faraday rotator, so if the magnet can be made smaller, a smaller optical isolator can be realized.

However, if the magnet of the optical isolator is simply made smaller, the magnetic field applied to the Faraday rotator will be insufficient, and the illumination angle of the light beam passing through it will become smaller than 45 degrees, resulting in increased forward loss and converse This had the disadvantage of having the undesirable result of reduced directional loss.

An object of the present invention is to provide an optical isolator that is small and has high reverse loss.

According to the present invention, there is provided a first polarizing element, which is disposed next to the first polarizing element, and is arranged at a angle of 45 degrees thicker than 0 degrees to the passing light beam.
a Faraday rotator that provides decorative illumination with an angle smaller than degrees;
Next to the Faraday rotator, a second polarizing element is arranged such that the azimuth angle is substantially complementary to the above angle with respect to the azimuth angle of the first polarizing element; A small optical isolator with a high reverse direction loss is obtained, comprising a magnetic field generating means for applying a magnetic field necessary to provide the decorative light at the angle described above to the Faraday rotator.

Note that a polarizing element is a general term for an optical element that has the function of extracting a linearly polarized component from any incident light, and includes a polarizing plate and an optical element whose internal optical axis and optical axis form an angle other than 0 degrees or 90 degrees. These include birefringent crystals, polarizing prisms (such as a mirror prism), and polarizing beam splitters using dielectric multilayer deposits.

In the present invention, the decoration angle of the light beam passing through the Faraday rotator is set to an angle of less than 45 degrees, unlike the passing optical isolator, so the magnet that applies the magnetic field to the Faraday rotator can also be smaller. It turns out.

For example, the size of the magnet when the decorative light angle is set to 35 degrees can be reduced by about 20% compared to the normal case where the decorative light angle is set to 45 degrees.

Now, if the decorative light angle given to the light beam exiting the Faraday rotator is angle θ, then the azimuth angle of the second polarizing element changes by the complementary angle of angle θ, that is, by (90-θ) degrees, the first polarizing element Since the angle is rotated from the azimuth of the element, the azimuth of the second polarizing element and the polarization direction of the light beam incident thereon are deviated by (90-20) degrees. The resulting increase in forward loss is small.

For example, when the decoration angle θ is 35 degrees, the increase in forward loss is
It is about 0.5 dB.

Now, when a light beam enters the optical isolator of the present invention from the opposite direction (the side of the second polarizing element), only the linearly polarized light extracted by the second polarizing element passes through the Faraday rotator. However, the polarization direction at that time is that the initial azimuth angle of the linearly polarized light is (90-θ) degrees, and the Faraday rotator applies the light to the first polarizing element. is 90 degrees to the azimuth of, and in the normal case (
This results in an optical circuit with high reverse direction loss, similar to that in the case where the decorative light angle at the Faraday rotator is 45 degrees).

The smaller the decoration angle θ is, the smaller the magnet is, but the forward loss increases accordingly, so the dimensions of the magnet are determined based on the allowable forward loss.

Next, the present invention will be explained in detail using the drawings.

The figure is a sectional view of one embodiment of the present invention.

This example has a wavelength of 0.8 μm, which is difficult to miniaturize.
It is a band optical isolator.

The first lens acting element 4, the first polarizing element 1, the Faraday rotator 2, the second polarizing element 3, and the second lens acting element 5 are attached to each other in this order with an optical adhesive as shown in FIG. It is fixed with adhesive.

The magnet 6 is a rectangular rare earth permanent magnet having a through hole in which the Faraday rotator 3 is disposed, and is magnetized in the direction of the through hole.

The first and second lens acting elements 4 and 5 are rod lenses obtained by cutting a converging light transmitter into a length of about 1 pitch, and the light spreading from a point on one end surface is transmitted from the other end surface to approximately 1 pitch. It has the function of emitting as a parallel light beam (note that 1
(Pitch is the meandering period of a light beam traveling through a focusing light transmitter).

An antireflection film 41 is formed on the entrance surface of the first lens effecting element 4 in order to reduce reflection of the optical isolator itself.

The Faraday rotator 2 is made of paramagnetic glass containing rare earth ions, and has two slightly oblique surfaces on both sides.
, a second reflective film 23.24, and the light beam incident perpendicularly from the first surface 21 passes through the first and second reflective films 23.2.
4 and is reflected a total of four times and exits from the second surface 22 perpendicularly.

The first and second polarizing elements 1.3 are Rochon prisms made of calcite.

The above configuration is almost the same as the optical isolator using one permanent magnet by Seki and Ueki described in Utility Model Application No. 76885/1985, so please refer to that for details.

However, the difference is that in this embodiment, the difference in azimuth between the first polarizing element 1 and the second polarizing element 3 is not 45 degrees, but approximately 35 degrees, which is only 10 degrees smaller. and the number of reflections of the light beam is two more.

The size of the magnet 6 is such that the decorative light angle at the Faraday rotator 2 is 3
By setting the angle to 5 degrees, the decoration angle is approximately 20% smaller than the usual case of 45 degrees.

Note that if the decorative light angle is further reduced, the size of the magnet 6 can be further reduced.

In this example, the illuminating angle of the light beam at the Faraday rotator 2 is 35 degrees, and the azimuth angle of the second polarizing element is 5 degrees.
Since the angle is 5 degrees, transmission loss occurs due to either of these angles, but the amount is only about 0.5 dB.

On the other hand, for the light beam incident from the opposite direction, only linearly polarized light with a polarization direction of 55 degrees is extracted by the second polarizing element 3, and is given a destination of approximately 35 degrees by the Faraday rotator 2, so that the first polarized light is When the light beam is incident on the forward incident light beam, the linearly polarizing element 1 polarizes the light in a direction approximately 90 degrees with respect to its azimuth angle, and the light beam is almost completely emitted at an angle different from that of the forward incident light beam.

In addition to the embodiments described above, various modifications can be made to the high reverse loss small optical isolator of the present invention.

In this example, the illumination angle at the Faraday rotator 2 is set to 35
degrees, but the present invention is not limited to this, and any other angle smaller than 45 degrees may be used, and the angle can be determined based on the allowable forward loss value.

In this example, the optical components (polarizing element, Faraday rotator, etc.) were adhesively fixed to each other with optical adhesive.
Needless to say, the present invention is not limited to this, and can also be applied to optical isolators having a conventional classical configuration.

Further, the first and second polarizing elements 1 and 3 may be optical elements other than the a-joon prism.

Furthermore, the concept of the present invention can be applied no matter how many times the light beam passes through the Faraday rotator 2.

Further, although the magnet 6 is used to apply the necessary magnetic field to the Faraday rotator 2, other shapes of permanent magnets or electromagnets may be used.

In addition, from this embodiment, the first and second lens action elements 4,
5 can be removed to create a compact optical isolator for emitting a parallel light beam.

[Brief explanation of the drawing]

The figure is a sectional view of one embodiment of the present invention. In the figure, 1 and 3 are polarizing elements, 2 is a Faraday rotator, 21 and 22 are surfaces, 23 and 24 are reflective films, 4 and 5 are lens acting elements, 41 is an antireflection film, and 6 is a magnet.

Claims (1)

[Scope of utility model registration request] a first polarizing element, a Faraday rotator disposed next to the first polarizing element and providing illumination with an angle larger than 0 degrees and smaller than 45 degrees to the passing light beam; a second polarizing element disposed such that its azimuth is substantially complementary to the angle described above with respect to the azimuth angle of the first polarizing element; and magnetic field generating means for applying a magnetic field necessary to provide the Faraday rotator with a high reverse direction loss.