JPH09105827A - Directional coupler type wdm filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized element whose directional coupler type WDM filter which is less in length than conventional one. SOLUTION: Light of wavelength λ1 shifts in power three times in a directional coupler which is twice as large as complete coupling length to light of wavelength λ2 and three times as large as the complete coupling length to the light of wavelength λ1 and is the outputted from an output port 10 when guided in the directional coupler from an input port 7, and the light of wavelength λ2 shifts in power twice in the directional coupler and is outputted from an output port 9 as well. Thus, the multiplexing and demultiplexing operation of the WDM is performed. This WDM filter can be made more small-sized than conventional WDM filter consisting of a directional coupler which has the complete coupling length to the light of wavelength λ2 and is twice as large as the complete coupling length to the light of wavelength λ1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a directional coupler type WDM (wavelength multiplex) filter using an optical waveguide. In recent years, a wavelength division multiplexing transmission technology for simultaneously transmitting optical signals of different wavelengths on an optical fiber has been studied in an optical communication network, and a WDM filter for inputting / outputting different wavelengths to an optical fiber as a transmission line is indispensable for realizing the technology. Is. Especially in recent years, as the research toward opticalization of the subscriber network progresses,
It is desired to reduce the size and loss of the WDM filter, and the importance of the optical waveguide type WDM filter formed on a substrate such as a silicon wafer is increasing.

[0002]

2. Description of the Related Art Conventionally, a wavelength λ1 and a wavelength λ2 longer than the wavelength λ1 have been used by using a directional coupler composed of an optical waveguide.
In order to form a WDM filter that demultiplexes and multiplexes the light of wavelength λ2, the directivity is such that it has a complete coupling length for the light of wavelength λ2 and twice the full coupling length for the light of wavelength λ1. Was manufacturing a combiner. This directional coupler has the wavelength λ
1. It is used that the power transfer of the wavelength λ2 in the directional coupler is once and twice respectively, and the two-input and one-output type multiplexing operation and the one-input and two-output type demultiplexing operation occur. Was obtained.

[0003]

When a directional coupler is manufactured so that the light having the wavelength λ2 has a perfect coupling length and the light having the wavelength λ1 has a double coupling length, There is a problem that the directional coupler type WDM filter becomes long.

An object of the present invention is to provide a small-sized element by making the length of the directional coupler type WDM filter shorter than the conventional one.

[0005]

In order to realize this problem, it is twice the full coupling length for the light of the wavelength λ2 and three times the full coupling length for the light of the wavelength λ1. A WDM filter is constructed using a directional coupler.

The directional coupler type WDM filter of the present invention has an optical waveguide for inputting and propagating light of wavelength λ1 and light of wavelength λ2 having a wavelength longer than wavelength λ1, and a perfect coupling length for light of wavelength λ2. It is characterized by comprising an optical waveguide type directional coupler which is twice as long as three times the complete coupling length with respect to the light of the wavelength λ1 and an optical waveguide which outputs the multiplexed / demultiplexed light.

(Operation) FIG. 3 shows the distance 5 (d) between the cores of the optical waveguide of the directional coupler and the directional coupler when the core width 4 of the optical waveguide and the relative refractive index difference are fixed. FIG. 6 is a characteristic diagram showing the relationship of the full bond length of 6 (L).

The principle of the present invention will be described with reference to FIG.

When the size of the core of the optical waveguide and the relative refractive index difference are fixed, the complete coupling lengths at wavelengths λ1 and λ2 are L1 and L2, respectively, and L1 is twice the length of L2 which is 1.5 times L2. Is L3 and L4, respectively, at the wavelengths λ1 and λ2. Since L3 is shorter than the length of L3, which is twice the length of L4, the directional coupler is made with twice the length of L2. However, the total length of the WDM filter becomes short.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a directional coupler section of a directional coupler type WDM filter formed by a silica optical waveguide according to the first embodiment.

FIG. 2 is a schematic diagram for explaining the operation of the directional coupler.

A first embodiment will be described with reference to FIGS. An optical waveguide is formed by embedding a core 3 made of GPSG (germanium, phosphorus-doped glass) in a silicon substrate 1 with a cladding 2 made of PSG (phosphorus-doped glass). Generally, it is made of a material having a different refractive index, and an optical waveguide can be obtained by making the core have a higher refractive index than the clad.

Directional coupler operation can be obtained by bringing the cores 3 of the two optical waveguides close to each other. The length 6 of the directional coupler when the light incident from the input port 7 of the optical waveguide is completely transferred to the output port 8 is defined as the complete coupling length.

When the width 4 of the core of the optical waveguide and the relative refractive index difference are fixed, the complete coupling lengths at wavelengths λ1 and λ2 are L respectively.
A WDM filter according to the present invention can be obtained by forming the directional coupler as L1, L2, and the inter-waveguide distance d1 where L1 is 1.5 times L2 and twice the length of L2.

When the directional coupler is manufactured as described above,
Wavelength λ1 from input port 7, wavelength λ2 from input port 8
Light is made incident on the optical waveguide and introduced into the directional coupler 6 which has twice the full coupling length for the light of the wavelength λ2 and three times the full coupling length for the light of the wavelength λ1. . At this time, the light of the wavelength λ1 is power-transferred three times in the directional coupler, and the light of the wavelength λ2 is power-transferred twice from the output port 10 and in the directional coupler. By doing so, the output is similarly output from the output port 10, and at this time, the WDM multiplexing operation is obtained.

Further, the light having the wavelengths λ1 and λ2 receives the input port 7
When incident on the directional coupler and introduced into the directional coupler, the light of the wavelength λ1 undergoes power transfer three times in the directional coupler, and the light of the wavelength λ2 is output from the output port 10. The same power is output twice from the output port 9 by transferring power twice in the directional coupler, and at this time, WD
A demultiplexing operation of M is obtained.

In the conventional filter, the complete coupling lengths at the wavelengths λ1 and λ2 are set to L3 and L4, respectively, and the directional coupler is formed at the length L3 with the inter-waveguide distance d2 where L3 is twice L4. Although the WDM filter has been obtained by the above method, since the length of L3 is larger than twice the length of L2, a small WDM filter can be obtained by the filter of the present invention.

FIG. 4 is a sectional view of the directional coupler section of the directional coupler type WDM filter formed by the silica type optical waveguide of the second embodiment of the present invention. The difference from the first embodiment is that the core is a ridge waveguide. As described above, the present invention can be applied not only to the buried waveguide but also to the ridge waveguide.

Although silicon is used for the substrate forming the waveguide in each of the first and second embodiments, glass, ceramics, organic materials, semiconductors, non-linear crystals, etc. other than silicon can also be used.

Although quartz is used as the material of the optical waveguide, as a material of the waveguide, a semiconductor using a III-V group material, lithium niobate, an organic material or the like which can constitute the optical waveguide is used. Widely applicable.

[0022]

By using the present invention, it is possible to obtain a WDM filter which is shorter and smaller than the conventional one.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a directional coupler section of a directional coupler type WDM filter formed of a silica optical waveguide according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating the operation of the directional coupler of the present invention.

FIG. 3 is a diagram for explaining the principle of the present invention, in which, when the core width 4 of the optical waveguide and the relative refractive index difference are fixed, the core-to-core distance 5 (d) of the optical waveguide of the directional coupler section is set with the wavelength as a parameter. )
It is a characteristic view which shows the relationship of the perfect coupling length 6 (L) of a directional coupler.

FIG. 4 is a cross-sectional view of a directional coupler section of a directional coupler type WDM filter formed by a silica optical waveguide according to a second embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 clad 3,3 'core 4,4' core width 5,5 'core-to-core distance 6 directional coupler length 7,8 input port 9,10 output port

Claims (1)

[Claims] 1. An optical waveguide in which light of wavelength λ1 and light of wavelength λ2 longer than the wavelength λ1 are input and propagated, and light of wavelength λ1 which is twice the complete coupling length with respect to light of wavelength λ2. And an optical waveguide type directional coupler that is three times the full coupling length,
A directional coupler-type WDM filter comprising an optical waveguide that outputs multiplexed / demultiplexed light.