JP2842968B2 - Waveguide directional coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide-type directional coupler having a waveguide portion made of silica glass, and more particularly to a waveguide-type directional coupler in which the core width of the coupling portion is asymmetric, and its introduction. The present invention relates to an integrated element of a waveguide directional coupler and a directional coupler module using the integrated element.

[0002]

2. Description of the Related Art In recent years, as a waveguide structure capable of broadening the branching ratio of a waveguide type directional coupler, as shown in FIG.
An asymmetric waveguide structure in which one core width of the coupling portion 13 formed by bringing the book cores 11 and 12 close to each other is made narrower than the other core width has been proposed (for example, literature: 1990 IEICE Autumn National Convention C). -179 "Broadband waveguide type 180 degree hybrid"), which is attracting attention as a basic structure for realizing a high-performance waveguide type directional coupler.

[0003]

However, the conventionally proposed directional coupler in which the core width of the coupling portion is asymmetrical is as follows.
Because of the structure in which the bent portion is formed on both the wider and narrower cores to form the joint, it takes time to design, and there are problems such as excessive loss due to the loss due to the bent portion. .

An object of the present invention is to make the structure of a directional coupler having a wider wavelength band simpler than that of a conventionally proposed structure, to reduce the design burden, and to maintain a constant branching ratio over an arbitrary wide wavelength band. It is an object of the present invention to realize a high-performance waveguide directional coupler.

[0005]

In order to achieve the above object, the present invention provides an asymmetric waveguide type directional coupling in which two cores having different widths and propagation constants are arranged in parallel in a cladding. In the container, the core and the clad are made of quartz glass, and one of the cores is formed narrower than the height,
The other core is formed equal in height and width,
To form a narrower core width linearly to form a bond portion is brought close to the intermediate portion narrower core width to form a wider core width curvilinear, narrower width Core of both
Narrow so that the ends are equal in size to the wider core
It gradually expands in a tapered shape from both sides of the part to both ends of the core.
One in which large it was.

[0006]

According to the directional coupler of the present invention having the above configuration, the propagation constant of the two cores can be made different by making the width of one core of the coupling portion different from the width of the other core. This slows down the change in the branching ratio with respect to the wavelength, and realizes a wider wavelength range of the branching ratio. There is bend to the core of who were wider, portion bent core better to narrow the width rather name than are linearly formed, it is easy to design, also reduces the loss caused by bending unit . And narrow
Both ends of the core are equal in size to the wider core
Tapered from both sides of the narrow part to both ends of the core
The connection with the optical fiber is facilitated because the shape is gradually enlarged .

[0007]

Next, an embodiment of the present invention will be described.

FIG. 1A is a plan view showing an embodiment of the directional coupler according to the present invention, and FIG. 1B is a sectional view taken along line aa of FIG. As shown in FIG. 1A, the directional coupler 2
The cores 2 and 3 are formed so as to traverse the substrate 1 in the longitudinal direction. One core 2 is linear, and the other core 3 has an intermediate portion only in parallel with the one core 2. The cores 2 and 3 are arranged close to each other to form a coupling portion 4 of a directional coupler at the center of the substrate 1. Core 2, 3
Is embedded in a clad 5 having a lower refractive index than the cores 2 and 3 formed on the substrate 1 as shown in FIG. The width of the straight core 2 is smaller than the width of the other core 3 at the joint 4. The core width at both ends of these cores 2 and 3 is
It is limited by the size that allows bonding with an optical fiber.
Therefore, the core width of the linear core 2 is gradually increased in a tapered manner from both sides of the narrow portion to both ends of the core so that both ends are equal to the size of the core 3. The substrate 1 is made of silicon, the cores 2 and 3 are made of SiO ₂ —TiO ₂ , and the clad 5 is made of SiO ₂ —B ₂ O ₅ —P ₂ O ₃ .

The height of the cores 2 and 3, the length of the coupling portion 4, the interval between the cores in the coupling portion 4 and the respective core widths, and the cores 2 and 3 in constructing the directional coupler. the refractive index of the refractive index of the cladding 5, the refractive index of the substrate 1, setting the value equal within conventional
It became easier than that. This is because the shapes of cores 2 and 3 are unpaired
The core 2, which is the narrower of the cores 2 and 3,
Due to being a line. Therefore, as shown in FIG. 1, the light Pin inserted into the incident port 7 of the core 2 is
From output port 9, certain branching ratio that is over a certain wide wavelength band pt: easily be output by pc
It became . For example, the height of the cores 2 and 3 is 8 μm,
Is 900 μm, the core interval at the joint 4 is 4 μm,
The width of the core 2 at the joint 4 is 6 μm, and the width of the core 3 is 8 μm.
m, the refractive indices of the cores 2 and 3 are 1.4624, and the cladding 11
When the refractive index of the substrate 1 was set to 1.458,
Almost P over a wide wavelength band of 3 μm to 1.55 μm
A branching ratio of t: Pc = 4: 1 was realized. FIGS. 5 and 6 show the evaluation results comparing the performance of the directional coupler according to the present invention with that of the conventional one. It can be seen that in all of the insertion loss pt, the coupling loss Pc, and the excess loss, the product of the present invention has lower loss than the conventional type. This is because, in the conventional type, the two cores 11 and 12 constituting the directional coupler are each formed with two bent portions at two locations (see FIG. 4), whereas in the product of the present invention, the width is changed. is only bent portions 14 and 15 are formed wider in the core 3 of whichever are Orazu, deer
From the narrow part of the narrow core 2 to both ends of the core
This is mainly due to the fact that the taper is gradually enlarged .

FIG. 2 shows an embodiment of an integrated device in which a number of the waveguide type directional couplers of FIG. 1 are arranged in parallel. The integrated element 16 can be manufactured by a general fine processing technique (photolithography, reactive ion etching, etc.) established as a manufacturing technique of a semiconductor integrated circuit. Since one of the two cores constituting each directional coupler 17 in the element 16 is formed in a straight line, the mask pattern design and the like at the time of element production are easy, and each directional coupler 1 is formed.
The loss due to the bent portion 7 is also small. Optical fibers 18 and 19 are connected to the input and output ports of the device 16 with a low loss through matching greases.

FIG. 3 shows an embodiment of a waveguide type directional coupler module constituted by using the integrated device of FIG. A waveguide package 21 accommodating the integrated element 16 is fixed via a spacer 22 in the center of the module casing 20. A V-groove block package 23 having a large number of V-grooves is mounted on both sides of the waveguide package 21, and a package introduced into the casing 20 from both ends thereof.
Each fiber strand 25 of the pre-fiber 24 is positioned by each V-groove of the V-groove block package 23 and connected to the input / output ports of the integrated device 16 with low loss. Reference numeral 26 denotes a bare fiber presser, 27 denotes a tape fiber presser, and 28 denotes a boot. As described above, the high-performance waveguide directional coupler integrated device 1 has a small coupling loss and excess loss of each directional coupler 17 and has a wide wavelength band of the branching ratio.
If the module 6 is modularized together with the tape fiber 24, various bidirectional optical transmission systems can be constructed easily and with high quality.

[0012]

In summary, the present invention has the following excellent effects.

(1) A narrow core of two cores constituting a directional coupler is formed in a straight line, and an intermediate portion of the wide core is brought close to the core to form a coupling part. With this simple structure, a low-loss broadband directional coupler that couples independently of wavelength can be realized.

(2) Since the narrower core is straight, the design can be simplified.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a waveguide type directional coupler according to the present invention, wherein FIG. 1 (a) is a plan view and FIG. 1 (b) is a sectional view taken along line aa of FIG. 1 (a).

FIG. 2 is a plan view showing one embodiment of a waveguide type directional coupler integrated device according to the present invention.

3A and 3B are views showing one embodiment of a waveguide type directional coupler module according to the present invention, wherein FIG. 3A is a plan view (with a casing lid removed), and FIG. It is a longitudinal cross-sectional view.

FIG. 4 is a plan view showing a conventional example.

FIG. 5 is a diagram comparing wavelength dependency of insertion loss and coupling loss between a conventional product and a product of the present invention.

FIG. 6 is a diagram comparing excess loss between a conventional product and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Core 3 Core 4 Coupling part 5 Cladding 16 Waveguide type directional coupler integrated element 17 Directional coupler 20 Module casing 24 Tape fiber

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hideaki Arai 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Opto-System Research Laboratories, Hitachi Cable Systems, Ltd. (72) Inventor Naoto Uezuka Hitachi City, Ibaraki Prefecture 5-1-1 Hidakacho Inside the Opto-System Laboratories, Hitachi, Ltd. (56) References JP-A-56-66819 (JP, A) JP-A-2-287408 (JP, A) Sho Akai 56-77815 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 6/12

Claims (3)

(57) [Claims] 1. An asymmetric waveguide directional coupler comprising two cores having different widths and different propagation constants arranged substantially in parallel in a cladding, wherein the core and the cladding are made of silica glass. The core is formed narrower than its height,
The other core is formed equal in height and width,
To form a narrower core width linearly to form a bond portion is brought close to the intermediate portion narrower core width to form a wider core width curvilinear, narrower width Core of both
Narrow so that the ends are equal in size to the wider core
It gradually expands in a tapered shape from both sides of the part to both ends of the core.
Waveguide directional coupler, characterized in that large it was. 2. A waveguide-type directional coupler integrated device comprising a plurality of the waveguide-type directional couplers according to claim 1 arranged in parallel. 3. A waveguide directional coupler module comprising an optical fiber connected to the waveguide directional coupler integrated device according to claim 2.