JPS60257411A - Optical multiplexer/demultiplexer - Google Patents

Abstract

PURPOSE:To obtain diffraction grating-type optical multiplexer/demultiplexer of wide band by providing a slab waveguide substrate with plural diffraction gratings and plural plane reflectors to focus an incident fiber image of no chromatic aberration on the end face of an exit fiber. CONSTITUTION:The incident light incident from an input fiber 10 is propagated as a diffused light in a slab waveguide and is led to a concave diffraction grating 13a and is converted to diffracted lights. The diffracted light whose wavelength range is lambda1-lambda2 out of these diffracted light is converged on the reflective face of a plane reflector 14a and is reflected and are propagated as a diffused light and is led to a concave diffraction grating 13b. The light diffracted again by the concave diffraction grating 13b is propagated in the slab waveguide again and is converged to an output fiber 11b. The light whose wavelength range is lambda3-lambda4 out of diffracted lights due to the concave diffraction grating 13a is propagated in the slab waveguide and is converged on the reflective face of a plane reflector 14b and is reflected and is diffracted again by a concave diffraction grating 13c and is converged to an output fiber 11c.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a diffraction grating type optical multiplexer/demultiplexer having a wide band and a simple structure.

[Background of the invention]

Conventionally, interference film type multiplexers and demultiplexers and angle dispersive type multiplexers and demultiplexers have been proposed as optical multiplexers and demultiplexers used in wavelength multiplexing optical fiber transmission systems. Angular dispersion type multiplexer/demultiplexer is capable of demultiplexing multiple wavelengths with one angle dispersion element, and has the advantage that the structure is simpler than interference film type multiplexer/demultiplexer when a large number of wavelengths are used. have. In order to take full advantage of this feature, a structure has been developed in which a slab waveguide and a concave diffraction grating are combined and the lens system is omitted, as shown in FIG.

In FIG. 2, a substrate 1, a core layer 2, and a cladding layer 3 are laminated, and the refractive index of the core layer 2 is set to the substrate 1 and the cladding layer 3.
A slab waveguide is formed by making the refractive index larger than the refractive index of the waveguide.

Note that 4 is an input fiber, 5 is an output fiber, and 6 is a four-sided diffraction grating.

The inverse linear dispersion of the diffraction grating 6 is γ, the core diameter of the input fiber 4 is Dl, and the core diameter of the output fiber 5 is R. , output fiber 5
If the core center spacing of 8 to 5d is C, then the passing wavelength bandwidth Δλ and the passing wavelength center spacing λ.

is given by the following equation.

Δλ=γ(Do−Di) (1) λ. =γ·C (2) By the way, the minimum core center spacing is equal to the flood diameter Dc when the output fibers 58 to 5d are adjacent to each other, l, and from Th, the fractional band Δλ/λ0 is given by the following equation.

For example, D(=]25/7mφ, DH=50mmφ, D0
= 507 mφ, Δλ, Δλ/λ. Both become zero.

Therefore, it is usually a beam. >Di is required. However, if Do approaches DC, the degree of separation deteriorates, so the following conditions are required to obtain a sufficient degree of separation.

・l' (oc-o,)≧o, (4-)D, , :12
5//IIIφ, if DH=:507zn+φ, Do
≦75//mφ, and in this case, Δλ/λ020.2 becomes the maximum specific band, which has the disadvantage that it is difficult to obtain a wide passing wavelength band.

[Purpose of the invention]

The present invention forms a chromatic aberration-free input fiber image on the output fiber end face by providing a plurality of diffraction gratings and a plurality of plane reflectors on a slab waveguide substrate, thereby creating a broadband diffraction grating type optical multiplexer/demultiplexer. The purpose is to obtain.

[Summary of the invention]

In order to achieve the second object, an optical multiplexer/demultiplexer 1j according to the present invention: a slab waveguide formed on a substrate, a plurality of diffraction gratings and input fibers provided on the end face of the slab waveguide, and a plurality of outputs. In an optical multiplexer/demultiplexer having a fiber, a plurality of plane reflectors are provided on the other end face of the slab waveguide, and a low land of the first diffraction grating guides the incident light from the input fiber through the slab waveguide. An input fiber end face and the plurality of plane reflectors are arranged on a circle, and the corresponding plane reflector and the output fiber end face are arranged on a circle to the Loran 1 of each diffraction grating that guides the reflected light from the plane reflector. By arranging these, a broadband optical multiplexer/demultiplexer is obtained.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of an optical multiplexer/demultiplexer according to the present invention. In FIG. 7 and the cladding layer 9 to form a slab waveguide. The slab waveguide is formed on the glass substrate 7 using a known electric field ion diffusion method, and the input fiber 1 is formed with a core layer 8 having a thickness of 50 μm and a relative refractive index difference of 1%.
0, the core diameter of the output fiber 11, and the relative refractive index difference, but the present invention is not limited to this example, and may be performed using known methods such as CV Drii, sputtering method, electron beam evaporation method, etc. technology can be applied. The input fiber 10 and the output fiber 11 are GI type fibers with a core diameter of 50 μm and an outer diameter of 25 Ijrn, and the cladding layer 9, core layer 8, and part of the substrate 7 are processed by reactive ion etching technology. Groove 1
2, and the end face of the core layer 8 exposed at the end of the fiber ID groove 12 and the core end face of the input and output cuff 7'' fibers 10.11 are coupled.

The concave diffraction grating 13 and the plane reflector 14 are formed by etching a part of the stacked layer consisting of the cladding layer 9, core layer 8, and substrate 7 using reactive ion etching technology in the same way as in "2 fiber installation grooves" 2. AD is formed by vapor deposition on the end face of the car core layer 8 exposed on the side wall of the recess. In this embodiment, concave diffraction gratings], 3a, 13b, and 13c have the same grating constant. The input end face of the input fiber 10 and the plane reflectors 14a, 14b are arranged on the Rowland circle of the concave diffraction grating 13a.

Similarly, the plane reflector 14a and the output fiber llb are arranged on the Rowland circle of the concave diffraction grating 13b, and the plane reflector 1
4b and the output fiber 1.1c are arranged on the Rowland circle of the concave diffraction grating 13c. Note that the two planar reflectors 14a and 1.4b have reflective surfaces that are larger than the input fiber real image over each passing wavelength band near the convergence position of the diffracted light.

The operating principle of the present invention will now be explained. Input fiber] 0 propagates in the slab waveguide as diffused light, and is guided to the concave diffraction grating 1.3a to become diffracted light. Among these diffracted lights, the wavelength range is λ1~2
．． The second diffracted light is converged and reflected within the reflective surface of the plane reflector 1.4a, propagates in the slab waveguide as diffused light, and is guided to the concave diffraction grating 13b. The light diffracted again by the second concave diffraction grating 13b propagates within the slab waveguide and converges on the output fiber 1b. Also, concave diffraction grating 1
Among the diffracted lights of 3a, the light with a wavelength range of λ3 to 2.4 propagates in the slab waveguide and is converged and reflected within the reflective surface of 4b, concave diffraction grating], 3c. Diffraction again and output fiber], 1. converges to c.

Light incident from the input fiber 10 at an angle α with respect to the normal to the concave diffraction grating 1.3a is diffracted and output at an angle β,
When reaching the plane reflector 14a, the following relational expression approximately holds true.

d (sj−n a□+sinβ1)2mλ. (5)
where d is the lattice constant, λ. is the center wavelength of the passband, m is the diffraction order, and in this embodiment, m is selected to be 1. The diffracted light incident at an angle O with respect to the normal line of the plane reflector is reflected at an angle -0 with respect to the normal line of the plane reflector, and is reflected by the concave diffraction grating 13.
The light enters at an angle α2 with respect to the normal line of b, becomes re-diffracted light, and exits at an angle β2, reaching the output fiber llb. Similarly to equation (1), the following relationship holds true for the re-diffracted light.

d (sin a2+sjnβ2)=mλo(6)
Here, if the normal direction of the plane reflector 1.4a is set so that it becomes 02-α1, then β, = βu from (1) and (2). The wavelength is λ. When the angle changes to ten δλ, the diffraction light emission angle of the concave diffraction grating 13a increases by δβ.

Along with this, the incident angle θ and reflection angle −〇 of the plane reflector are −
Since the concave diffraction grating 13 changes by δβ1 and 10δβ1,
The angle of incidence of b increases by δβ1. At this time, the change in the output angle δβ2 of the re-diffracted light by the concave diffraction grating 13b is (])
From equations (2) and (3), it is given by the following equation.

If you choose 1α1)≦10°, 1β, 1≦10°, δβ2≦
0.02δβ, so the inverse line fraction γ is more than 50 times that of a single diffraction grating, and the passing wavelength bandwidth as defined by the first equation becomes extremely large, but the effective passing wavelength bandwidth Δλ, passing wavelength center spacing λ. is a flat reflector 1.4a
The reflecting surface width W and the center distance S of the planar reflectors 14a and 14b
and the inverse line fraction of the concave diffraction grating 13a are approximately given by the following equation.

Δλ#-(W-Di) (9) λCdou-8(] 0) Here, R is the radius of curvature of the concave diffraction grating 1.3a, and Dl is the core diameter of the input fiber 0. Also (9), (10)
is 1α1≦10°, Iβ1≦10°, 11111≦10
This is an approximate expression under the limit of °. Since the condition (S-W)≧D1 is required to obtain a sufficient degree of separation, the maximum fractional band is given by the following equation.

In this example, DH=507/In, W=200
71m, S = 250Itm, d = = 57
1m, R:= ], Omm, so Δλ=7
5 nm, Δλ/λ. = 0.6, making it possible to achieve a duplexer with an extremely wide range and high ratio band compared to the conventional technology.

〔Effect of the invention〕

As described above, the optical multiplexer/demultiplexer according to the present invention includes a slab waveguide formed on a substrate, a plurality of diffraction gratings provided on the end face of the slab waveguide, a human power fiber, and a plurality of output fibers. In this step, a plurality of backside reflectors are provided on the other end face of the slab waveguide, and the incident light from the input fiber is guided to the Laurent 1-circle 2 of the second diffraction grating. A plurality of plane reflectors are arranged on the fiber end face and the output -2 eyeglass end face, and the corresponding plane reflector and the end face of the output eyeglass are arranged on the Rowland circle of each diffraction grating that guides the reflected light from the plane reflector. As a result, the light incident from the input fiber is guided to the output fiber through the diffraction grating again without using a lens system, so an input fiber image with no chromatic aberration is formed on the end face of the output fiber, which is superior to conventional technology. As a result, a demultiplexer with an extremely wide band and high ratio band can be obtained, and furthermore, since the demultiplexing characteristics are hardly restricted by the parameters of the input and output fibers, it has the advantage that it is also possible to configure a multiplexer. ing. Furthermore, since the entire multiplexer is constructed as a slab waveguide, it is possible to obtain a diffraction grating type optical multiplexer/demultiplexer that is suitable for mass production, has a stable connection to the fiber, and does not require adjustment during assembly.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of an optical multiplexer/demultiplexer according to the present invention, and FIG. 2 is an explanatory diagram showing a conventional diffraction grating type demultiplexer. 7... Substrate 8... Core layer 10... Input fiber Ilb, Ilc... Output fiber 13a, 13b, +3cm diffraction grating 14a, 14b... Planar reflector ゛Patent applicant Nippon Telegraph and Telephone Public Corporation representative patent attorney Junnosuke Nakamura 5jP1 Figure

Claims (2)

[Claims] (1) In an optical multiplexer/demultiplexer having a slab waveguide formed on a substrate, a plurality of diffraction gratings provided on the end face of the slab waveguide, an input fiber, and a plurality of output fibers, the other end face of the slab waveguide A plurality of plane reflectors are provided in the input fiber, and the input fiber end face and the plurality of plane reflectors are arranged on the Rowland circle of the first diffraction grating that guides the incident light from the input fiber through the slab waveguide, and the plane reflection An optical multiplexer/demultiplexer characterized in that a corresponding plane reflector and an end face of an output fiber are respectively arranged on the Rowland circle of each diffraction grating that guides reflected light from the device. (2) The diffraction grating and the plane reflector are formed by processing the surface of the substrate on which the slab waveguide is formed to provide a recess, and forming the surface of the slab waveguide exposed on the side wall of the recess. The optical multiplexer/demultiplexer as claimed in claim 1, wherein the optical multiplexer/demultiplexer is inserted into another recess formed in the substrate to couple each fiber end face with the slab waveguide end face of the recess. .