JPH0814647B2 - Optical demultiplexer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In order to prevent the demultiplexed light from being deformed into an elliptical shape when demultiplexing light with a diffraction grating and detecting it, 90 ° is set to the grating groove of the diffraction grating. By arranging the prisms at an angle of 45 degrees, it is possible to prevent the demultiplexed light from being deformed by one diffraction grating.

[Industrial applications]

Diffraction gratings are used to demultiplex incoming signals in WDM communications over optical fibers. The present invention relates to a device that enables demultiplexing with a simpler optical system with less crosstalk when demultiplexing using a diffraction grating as described above.

[Conventional technology]

FIG. 4 is a plan view for explaining the optical demultiplexing effect of the diffraction grating. Reference numeral 1 is an output optical fiber, which outputs light of various frequencies. Then, the emitted light reaches the diffraction grating 3 via the collimator lens 2, is demultiplexed for each wavelength, and then passes through the collimator lens 2 again, and the optical fibers 4a, 4b for receiving light arranged for each wavelength. Enter in ...

By the way, the light diffracted by the diffraction grating 3 does not become a perfect circle due to manufacturing errors of the diffraction grating, but becomes an ellipse. FIG. 5 shows how the demultiplexed light is received by the light-receiving optical fibers 4a, 4b ...
As seen from the front. The diffracted light 5 which is diffracted by the diffraction grating 3 and has an elliptical shape also enters the other adjacent light receiving optical fibers 4a and 4c and causes crosstalk.

Therefore, as shown in FIG. 6, it has been proposed to use two diffraction gratings, 3a and 3b, and arrange them in a state of being rotated by 90 degrees so that the grating grooves are orthogonal to each other. The collimating lens is omitted in the illustration. In this device, the light emitted from the optical fiber 1 and diffracted by the first diffraction grating 3a becomes an elliptic shape as in 5, but is diffracted by the next diffraction grating 3b with the grating groove inclined by 90 degrees. Then, as shown by 6,
The elliptical light 5 is expanded in the minor axis direction to form a perfect circle. Therefore, when the light is received by the optical fibers 4a, 4b, ..., The light is not dispersed in the direction of the adjacent optical fibers 4a, 4c to cause crosstalk.

[Problems to be solved by the invention]

However, with this configuration, the two diffraction gratings 3a and 3b must be spatially separated and accurately arranged, and the device is large and requires very high accuracy. A technical problem of the present invention is to solve such a problem in the conventional optical demultiplexer and to prevent the demultiplexed light from being deformed by one diffraction grating.

[Means for solving problems]

FIG. 1 is a plan view illustrating the basic principle of the optical demultiplexer according to the present invention. 1 is the position of the output light, 7 is a 90 degree prism,
Reference numeral 4 denotes a light receiving position, which faces the diffraction grating 3 via the collimator lens 2. Ie output position 1
The light emitted from passes through the collimator lens 2, is once diffracted by the diffraction grating 3, then passes through the collimator lens 2, is reflected twice by the 90-degree prism 7, passes through the collimator lens 2 again, and is diffracted again. After being diffracted by the grating 3, the light passes through the collimator lens 2 and is received by the light receiving position 4. The 90-degree prism 7 has its symmetry axis direction 7c inclined by 45 degrees with respect to the direction of the grating groove of the diffraction grating 3,
Moreover, the light incident on the 90-degree prism 7 from the incident light position through the diffraction grating 3 is arranged so as to be reflected toward the diffraction grating 3 again.

[Action]

Once emitted from the emission position 1 and once diffracted by the diffraction grating 3, the diffracted light becomes a laterally oblong elliptical light similar to the elliptical light 5. However, since the 90-degree prism 7 is tilted 45 degrees with respect to the direction of the grating groove of the diffraction grating 3, the ellipse light is rotated 90 degrees by being reflected twice in the 90-degree prism 7,
Longitudinal direction becomes vertical. And in a state that is long in the vertical direction,
It is diffracted again by the diffraction grating 3. That is, when the light is diffracted by the diffraction grating 3 for the second time, it is rotated by 90 degrees with respect to the diffraction grating 3. In FIG. 6, the second diffraction grating 3b is rotated 90 degrees, whereas in the present invention, the demultiplexed light is rotated 90 degrees. As a result, the light diffracted twice by the diffraction grating 3 becomes a perfect circle.

〔Example〕

Next, practical examples of how the optical demultiplexer according to the present invention is embodied will be described. FIG. 2 shows an embodiment of the optical demultiplexer according to the present invention, and is shown in a perspective view for easy understanding of the pattern of reflection by the 90-degree prism 7. Further, a plurality of light receiving optical fibers 4a, 4b ... Are arranged so that the demultiplexed light can be detected for each wavelength. The demultiplexed light that has now emerged from the optical fiber 1 for emergence and is first diffracted by the diffraction grating 3 has the symmetry axis azimuth 7c at the beginning of the 90-degree prism 7 whose inclination is 45 degrees with respect to the grating groove direction of the diffraction grating 3. By being reflected by the reflecting surface 7a by 90 degrees and by being reflected by the next reflecting surface 7b by 90 degrees, the direction of the demultiplexed light is rotated by 90 degrees before and after being incident on the 90-degree prism 7. Instead of arranging two diffraction gratings 3a and 3b with the direction of the grating groove changed by 90 degrees as shown in FIG. 6, when the light is incident on the diffraction grating 3 for the second time, the demultiplexed light is 90 degrees. Since it is in a rotated state, it is possible to restore the demultiplexed light into a perfect circular state with only one diffraction grating 3.

In the illustrated example, the light emitted from the optical fiber 1 is collimated lens 2 → diffraction grating 3 → collimated lens 2 →
The 90-degree prism 7 → collimator lens 2 → diffraction grating 3 → collimator lens 2 → light-receiving optical fibers 4a, 4b ... Can pass through the path but do not pass through the collimator lens between the diffraction grating 3 and 90-degree prism 7. Is.

FIG. 3 is a perspective view showing a pattern in which the image is rotated 90 degrees by the 90-degree prism 7, and is a state in which the 90-degree prism 7 is viewed from the front. It is now assumed that the azimuth of the symmetry axis 7c of the 90-degree prism 7 is vertical and the incident image is inclined 45 degrees like 51. Then, when the light beam is once reflected by the first reflecting surface 7a of the 90-degree prism 7 and reaches the second reflecting surface 7b, the upper left point 5a on the reflecting surface 7a becomes the upper right point on the reflecting surface 7b.
The lower right point 5b of 7a is the lower left of the reflecting surface 7b. As a result, the image 54 reflected by the reflecting surface 7b is rotated by 90 degrees with respect to the image 51 before entering the 90 degree prism 7. It can be seen that by tilting the symmetry axis azimuth 7c of the 90-degree prism 7 by 45 degrees with respect to the incident image, the image reflected and emitted twice is rotated by 90 degrees.

〔The invention's effect〕

As described above, according to the present invention, the 90 ° prism 7 is arranged so that the symmetry axis azimuth 7c is inclined by 45 ° with respect to the direction of the grating groove of the diffraction grating 3, and the light is emitted from the emitting position. When the light is diffracted twice by the diffraction grating 3,
In the mode, the incident direction on the diffraction grating 3 is rotated by 90 degrees. Therefore, even though only one diffraction grating is used, the deformation of the demultiplexed light is prevented, as in the case of using two diffraction gratings in which the direction of the grating groove is rotated by 90 degrees.
Crosstalk is eliminated.

[Brief description of drawings]

1 is a plan view illustrating the basic principle of the optical demultiplexer according to the present invention, FIG. 2 is a perspective view showing an embodiment of the optical demultiplexer according to the present invention, and FIG. 3 is a front view of a 90-degree prism. FIG. 4 is a plan view for explaining the optical demultiplexing action by the diffraction grating, FIG. 5 is a front view showing a light receiving state of the demultiplexed light, and FIG. 6 is a demultiplexed light using two diffraction gratings. It is a perspective view showing a deformation prevention device. In the figure, 1 is an emission position (emission optical fiber), 2 is a collimating lens, 3 3a and 3b are diffraction gratings, 4 is a light receiving position, 4a, 4b ... are light receiving optical fibers, 7 is a 90-degree prism,
7c shows the symmetry axis directions, respectively.

Claims (1)

[Claims] 1. Input / output light positions (1) (4) of an optical fiber or the like
By providing a diffraction grating (3) facing each other with the lens (2) interposed therebetween, in a device that performs demultiplexing, on the opposite side of the diffraction grating (3) and the lens (2),
The 90-degree prism (7) that totally reflects twice and returns the light has a symmetry axis direction (7c) and the direction of the grating groove of the diffraction grating (3).
It is arranged so that light incident on the 90-degree prism (7) from the incident light position through the diffraction grating (3) at an angle of 45 degrees is reflected again toward the diffraction grating (3). The optical demultiplexer is characterized by