Optical waveguides – Planar optical waveguide
Reexamination Certificate
2001-03-29
2003-10-07
Healy, Brian (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S130000, C385S131000, C385S132000, C385S042000, C385S014000
Reexamination Certificate
active
06631236
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photonic crystal waveguide, and a directional coupler using the same and more particularly to a photonic crystal waveguide in a form of a photonic crystal micro optical circuit for optical communications.
It has been known in the art that the photonic crystal waveguide is used as an optical filter for selecting transmittable optical wavelength, an optical multiplexer/demultiplexer, and an optical dispersion-compensating device in the various fields of optical communication systems, optical switching systems and optical measuring systems. The directional coupler uses the photonic crystal waveguide.
In recent years, a photonic crystal has received a great deal of attention as a three-dimensional periodic structure having a refractive index in the same order as the optical wavelength. This photonic crystal has a potential capability of a remarkable size reduction of the optical circuit by three digits or more. For this reason, it has been on the great expectation to apply the photonic crystal to the micro-optical circuit. Various structures of the optical waveguide in the form of the micro-optical circuit formed in the photonic crystal have been proposed.
FIG. 1
is a fragmentary schematic perspective view illustrative of a first conventional optical waveguide in the photonic crystal. The optical waveguide comprises a line defect introduced in the photonic crystal which has a complete photonic band gap to a wavelength of the optical wave to be propagated through the optical waveguide. Namely, the line defect in the photonic crystal is used as the optical waveguide. This line defect optical waveguide has a high optical confinement function, for which reason the line defect optical waveguide is responsible to a abrupt or tight curve. Thus, the line defect optical waveguide provides a large freedom in pattern of the optical circuit and also allows a remarkable size reduction of the optical circuit.
The photonic crystal has a three dimensional periodical structure which comprises lamination structures of a bottom cladding layer
11
of a first material having a low refractive index, a core layer
12
of a second material having a high refractive index and a top cladding layer
13
of the first material, wherein the core layer
12
is sandwiched between the top and bottom cladding layers
11
and
13
. The core layer
12
has a high refractive index, whilst the top and bottom cladding layers
11
and
13
have a low refractive index. The core layer
12
may be made of silicon. Each of the top and bottom cladding layers
11
and
13
may be made of silicon dioxide. The three dimensional periodical structure has a photonic band gap defined by forbidden bands against the propagation of a light having a specific wavelength. If a light is generated in the photonic crystal having the photonic band gap, then the light is confined in the photonic crystal, wherein the propagation of the light is inhibited. The complete photonic band gap inhibits the three dimensional propagation of light. If the line defect is introduced into the photonic crystal having the complete photonic band gap, the line defect permits the propagation of light along the line defect in the photonic crystal. The line defect serves as the waveguide in the photonic crystal. In
FIG. 1
, hexagons represent lattice structures of the crystal. The photonic crystal has lattice defects aligned in a direction along arrow marks, wherein the lattice defects are represented by the absences of the hexagons. The incident light
10
represented by the arrow mark is propagated through the line defect in the photonic crystal.
Japanese laid-open patent publication No. 11-218627 discloses the following second conventional technique for stabilizing properties of the photonic crystal waveguide and reducing the manufacturing cost. The second conventional photonic crystal waveguide has a dielectric slab waveguide over a surface of a silicon substrate, wherein the dielectric slab waveguide has a matrix array of a lattice array of refractive index varying regions which are different in refractive index from a core layer of the dielectric slab waveguide. The refractive index varying regions are made of the same material as the core layer, and have been subjected to a refractive index varying treatment due to an optical induced effect. The dielectric slab waveguide comprises laminations of a bottom cladding layer, the core layer and a top cladding layer. Those lamination structure may be formed over the substrate by a metal organic chemical vapor deposition method or a liquid phase epitaxy to complete the slab waveguide over the substrate. Subsequently, the core layer is subjected to a selective irradiation through the top cladding layer with any one of an electron beam, a synchrotron orbital radiation light, a ultraviolet ray, and an infrared ray in order to cause a variation in refractive index, due to the optical induced effect, of the irradiated parts of the core layer of the slab waveguide, whereby the refractive index varying regions are formed, which are different in refractive index from the remaining non-irradiated parts of a core layer of the dielectric slab waveguide.
The above first and second conventional photonic crystal waveguides have the following disadvantages. A sectioned area of the line defect waveguide is extremely small and it is difficult to obtain a sufficient optical coupling with any external optical system. The actually available method of forming the line defect waveguide has not yet been established.
In the above circumstances, it had been required to develop a novel photonic crystal waveguide free from the above problem.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel photonic crystal waveguide free from the above problems.
It is a further object of the present invention to provide a novel photonic crystal waveguide having a high optical coupling coefficient in coupling the photonic crystal waveguide to an external optical system.
It is a still further object of the present invention to provide a novel photonic crystal waveguide which is suitable for manufacturing the same.
It is yet a further object of the present invention to provide a novel directional coupler utilizing the novel photonic crystal waveguide free from the above problems.
It is a further object of the present invention to provide a novel directional coupler utilizing the novel photonic crystal waveguide having a high optical coupling coefficient in coupling the photonic crystal waveguide to an external optical system.
It is a still further object of the present invention to provide a novel directional coupler utilizing the novel photonic crystal waveguide which is suitable for manufacturing the same.
It is yet a further object of the present invention to provide a novel directional coupler utilizing the novel directional coupler utilizing the novel photonic crystal waveguide.
It is another object of the present invention to provide a novel method of use of a novel photonic crystal waveguide free from the above problems.
It is a further object of the present invention to provide a novel method of use of a novel photonic crystal waveguide having a high optical coupling coefficient in coupling the photonic crystal waveguide to an external optical system.
It is a still further object of the present invention to provide a novel method of use of a novel photonic crystal waveguide which is suitable for manufacturing the same.
It is another object of the present invention to provide a novel method of forming a novel photonic crystal waveguide free from the above problems.
It is a further object of the present invention to provide a novel method of forming a novel photonic crystal waveguide having a high optical coupling coefficient in coupling the photonic crystal waveguide to an external optical system.
It is a still further object of the present invention to provide a novel method of forming a novel photonic crystal waveguide which is suitable fo
Healy Brian
NEC Corporation
Young & Thompson
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