JPH0451804B2 - - Google Patents

Description

[Detailed description of the invention] [Summary] A dispersion splitting grating formed in a stepped manner with an apex angle of 60° is installed between the diffraction gratings on the optical path, and the transmission band width in each wavelength channel is wide. Introducing an optical wavelength multiplexer/demultiplexer.

[Industrial Application Field] The present invention relates to an optical wavelength multiplexer/demultiplexer constituting an optical communication system.

Wavelength multiplexing communication carries separate information for each wavelength of light (each wavelength channel) and combines them into one
A method is used in which the light is combined into two optical paths and transmitted through an optical fiber.

Therefore, on the receiving side, it is necessary to decompose the combined light into each wavelength channel and extract the information superimposed on each light.

In such a system, an optical wavelength multiplexer/demultiplexer is used to combine light of a plurality of wavelengths or to separate the combined light into wavelengths.

In the configuration of the wavelength division multiplexing optical communication system as described above, the narrow band problem caused by the wavelength dispersion of the diffraction grating in the optical wavelength multiplexer/demultiplexer is solved and the transmission bandwidth within each wavelength channel is widened. This is very important.

[Conventional technology]

FIG. 2 is a side sectional view of a conventional optical wavelength multiplexer/demultiplexer using a diffraction grating.

Here, for convenience of explanation, the case where the input/output relationship is split will be described.

In the figure, the light input from the input optical fiber 21 is turned into parallel light by the lens 24, and the diffraction grating 2
It is reflected by 2.

The light wavelength-dispersed by the diffraction grating 22 passes through the lens 24 and is focused onto each optical fiber of the output optical fiber array 23 provided for each wavelength, from which it is output. Ru.

[Problem that the invention seeks to solve]

The opening range of the output optical fibers provided for each wavelength is relatively narrow compared to the spacing between each optical fiber in the output optical fiber array, and the light entering the output optical fibers is in the same wavelength band. The disadvantage is that it produces light in a very narrow wavelength band.

[Means for solving problems]

FIG. 1 is a side sectional view of an optical wavelength multiplexer/demultiplexer using a diffraction grating and a dispersion splitting grating according to the present invention.

In the figure, 1 is an optical fiber, 2 is a first diffraction grating, 3 is a dispersion splitting grating, 4 is a second diffraction grating,
5 is an optical fiber array, and 6, 7, 8, and 9 are lenses.

The solution to the above problem is to convert the single optical fiber 1 into an optical fiber array 5 consisting of a plurality of optical fibers.
There are two diffraction gratings 2 and 4 on the optical path leading to
A dispersion splitting grating 3 having a step-shaped reflecting surface in which grooves each having a side cross section composed of isosceles triangles with an apex angle of 60° are arranged is installed between the diffraction gratings, and the incidence of light to the dispersion splitting grating 3 is This is achieved by an optical wavelength multiplexer/demultiplexer whose direction is parallel to one side of the slope constituting the grooves of the dispersion dividing grating, and whose output direction is parallel to the other side of the slope.

Furthermore, condensing lenses 7 and 8 are installed so as to condense the light onto the dispersion splitting grating 3, and the movement of the focusing point caused by the wavelength dispersion of the diffraction grating is caused by the surface forming the dispersion splitting grating 3. , that is, dispersion splitting grid 3
Adjust so that it is parallel to the straight line that intersects the plane containing the ridgeline of the plane and the plane perpendicular to the incident light.

[Effect]

In the following, in the present invention, as in the conventional example, for convenience of explanation, the input/output relationship will be explained in the case of demultiplexing.

FIG. 3 is a perspective view illustrating the shape and function of the dispersion dividing grid of the present invention.

In the figure, the dispersion dividing grid is y in Cartesian coordinates xyz
The grating is formed in the shape of steps with an apex angle of 60° carved into the surface, and light incident on the slope A of the groove parallel to the slope B of the groove is reflected twice and is reflected from the slope B of the groove into the groove. Slope A
It can be emitted parallel to.

Note that the directions of x′ and y′ are the direction of x′ (2 ^-1/2 , 2 ^-1/2 , 0) and the direction of y′ (−2 ^-1/2 , 2 ^-1/2 , 0 ), decide.

Now, let K ₁ be the incident light, L _M be the intermediate light between reflections, K _O be the outgoing light, and let θ be the angle between the x-axis and the direction of the groove, then the dispersion splitting grating satisfies the following limiting conditions. There is a need.

(1) The plane forming the lattice is the y-axis.

(2) It has many grooves with an apex angle of 60°.

(3) θ=Tan ^-1 (2 ^-1/2 )≒35.3°. (4) Direction of incident light K ₁ (2 ^-1/2 , -2 ^-1/2 , 0). (5) Direction of intermediate light K _M (0,0,1). (6) Direction of output light K _O (2 ^-1/2 , 2 ^-1/2 , 0). The expression equivalent to conditions (2) and (3) above is as follows.

The slopes A and B of the (2)′ and (3)′ grooves have the following orientations, respectively. That is, the direction of slope A (-2 ^-1 , 2 ^-1 , 2 ^-1/2 ), and the direction of slope B (2 ^-1 , 2 ^-1 , -2 ^-1/2 ). becomes.

Here, the orientation of each part is summarized as follows.

K ₁ : (2 ^-1/2 , −2 ^-1/2 , 0), K _M : (0, 0, 1), K _O : (2 ^-1/2 , 2 ^-1/2 , 0), A: (-2 ^-1 , 2 ^-1 , 2 ^-1/2 ), B: (2 ^-1 , 2 ^-1 , -2 ^-1/2 ). The above limiting conditions (1) to (6) are satisfied, and the following conditions are also applied.

(7) The dispersion direction of the incident side diffraction grating is the z direction.

(8) Focus the light onto the dispersive splitting grating.

Under these conditions, the action of the dispersion splitting grid can be summarized as follows.

(1) The dispersion direction on the output side is perpendicular to the z direction. That is, in the y′ direction.

(2) The angle of incidence is 45° for both reflections at the dispersion splitting grating.

(3) Since the z-direction polarized light upon incidence becomes P-polarized light on the A plane and S-polarized light on the B-plane, it becomes y′-direction polarized light upon exit.

(4) Similarly, x′-direction polarization at the time of incidence is polarized in the z′ direction at the time of exit.
It becomes directional polarized light.

(5) When the input position to this dispersion dividing grating moves in the -z direction as shown in the figure, the output position moves in the y' direction within the range where the light enters the same groove. When the incident position further moves in the -z direction and enters the next groove area, the output position changes discontinuously, and thereafter shows periodic movement in the same manner.

(6) Note that this dispersion dividing grating can be placed on the focal plane of the lens within an error range of about the depth of the groove.

FIGS. 4(1) to 4(4) are diagrams showing the positions of light at various parts within the optical wavelength multiplexer/demultiplexer according to the present invention.

If two diffraction gratings are configured to cancel wavelength dispersion within the same channel, one point at the time of incidence from the optical fiber (Fig. 4 (1)) will spread in one direction at the first diffraction grating ( (Fig. 4(2)), spread perpendicularly to the direction of Fig. 4(2) for each wavelength channel with a dispersion splitting grating (Fig. 4(3)), and spread 1 per wavelength channel with a second diffraction grating (Fig. 4(3)). It becomes a point (Figure 4 (4)).

In this way, wavelength dependence within the wavelength channel can be eliminated.

〔Example〕

An embodiment of the present invention will be described with reference to FIG.

Light input from the optical fiber 1 passes through the lens 6, becomes parallel light, enters the first diffraction grating 2, and is reflected there.

The light separated into wavelengths by reflection on the first diffraction grating 2 is transmitted through the lens 7 and focused onto the dispersion splitting grating 3.

The light focused on the dispersion splitting grating 3 becomes a line segment reflecting the wavelength dispersion of the diffraction grating 2, and this line segment is divided into line segments for each wavelength channel by the grating.

The light reflected by the dispersion splitting grating 3 passes through the lens 8, becomes parallel light, enters the second diffraction grating 4,
It is reflected here.

The second diffraction grating 4 is configured to have the same wavelength dispersion as the first diffraction grating 2, and to cancel them within the same channel.

Therefore, the light that passes through the lens 9 and is focused onto each optical fiber of the optical fiber array 5 provided for each wavelength band includes a wide band of light within the same wavelength band. Therefore, even if the wavelength changes, the optical signal can be output to each optical fiber of the optical fiber array 5.

FIGS. 5(1) and 5(2) are transmission characteristic diagrams showing the relationship between loss and wavelength of the optical wavelength multiplexer/demultiplexer according to the conventional example and the present invention, respectively.

In the figure, V- and U-shaped curves indicate each channel, and FIG. 5 (2) according to the present invention shows that the wavelength dependence of each channel is U-shaped, and the transmission bandwidth is widened. ing.

In this embodiment, a reflection type diffraction grating is used, but the same effect can be obtained by using a transmission type instead.

〔Effect of the invention〕

As described in detail above, according to the present invention, an optical wavelength multiplexer/demultiplexer with a wide transmission band width within a wavelength channel can be obtained.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an optical wavelength multiplexer/demultiplexer using a diffraction grating and dispersion splitting grating according to the present invention, and FIG. 2 is a side sectional view of an optical wavelength multiplexer/demultiplexer using a conventional diffraction grating. FIG. 3 is a perspective view illustrating the shape and function of the dispersion dividing grid of the present invention. Figures 4 (1) to (4) are diagrams showing the positions of light in each part of the optical wavelength multiplexer/demultiplexer according to the present invention, and Figures 5 (1) and (2) are diagrams showing the positions of light in each part of the optical wavelength multiplexer/demultiplexer according to the present invention, and Figures 5 (1) and (2) are diagrams showing the optical positions of the conventional example and the present invention, respectively. FIG. 2 is a transmission characteristic diagram showing the relationship between loss and wavelength of a wavelength multiplexer/demultiplexer. In the figure, 1 is an optical fiber, 2 is a first diffraction grating, 3 is a dispersion splitting grating, 4 is a second diffraction grating,
5 is an optical fiber array, and 6, 7, 8, and 9 are lenses.

Claims (1)

[Claims] 1. On the optical path from one optical fiber 1 to an optical fiber array 5 consisting of a plurality of optical fibers, there are two diffraction gratings 2 and 4, and a side wall between the two diffraction gratings. A dispersion splitting grating 3 having a step-shaped reflective surface in which grooves each having a cross section composed of an isosceles triangle with an apex angle of 60° are arranged is installed, and the direction of incidence of light to the dispersion splitting grating 3 is set according to the direction of the dispersion splitting grating 3. parallel to the slope on one side of the groove,
An optical wavelength multiplexer/demultiplexer characterized in that the output direction is parallel to the slope on the other side. 2. Two condensing lenses 7 and 8 are installed on the dispersion splitting grating 3 so as to focus the light on the surface forming the dispersion splitting grating, and the movement of the focusing point caused by the wavelength dispersion of the diffraction grating 2. The optical wavelength multiplexer/demultiplexer according to claim 1, wherein the wavelength multiplexer/demultiplexer is parallel to a straight line that intersects a plane forming the dispersion splitting grating and a plane perpendicular to the incident light.