Optical: systems and elements – Optical modulator – Having particular chemical composition or structure
Reexamination Certificate
2002-09-13
2004-03-16
Spector, David N. (Department: 2873)
Optical: systems and elements
Optical modulator
Having particular chemical composition or structure
C359S322000, C385S039000, C385S050000
Reexamination Certificate
active
06707597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical device used for optical communication.
2. Description of the Related Art
FIG. 19
shows an example of an optical coupler using a Y-separation waveguide, which is a conventional optical device. A conventional optical coupler
206
has a configuration in which a Y-shaped core
203
is formed on a substrate
204
. A first ingoing optical fiber
201
and a second ingoing optical fiber
202
are placed on one end face of the optical coupler
206
, and an outgoing optical fiber
205
is placed on the other end face thereof. The first and second ingoing optical fibers
201
and
202
and the outgoing optical fiber
205
respectively are placed in the vicinity of the end faces of the Y-shaped core
203
.
Light is incident upon the optical coupler
206
via the first and second ingoing optical fibers
201
and
202
. The respective light beams propagate through the core
203
and are coupled to be output so as to propagate through the outgoing optical fiber
205
. The light beams to be coupled need to be in the same phase.
On the other hand, if the ingoing side and the outgoing side of the above-mentioned optical coupler are used in a reverse manner, the optical coupler functions as an optical separator. That is, if incident light is allowed to propagate through the outgoing optical fiber
205
, the light is separated to be incident upon the first and second ingoing optical fibers
201
and
202
, respectively.
In an optical device such as the above-mentioned optical coupler
206
, in order to couple light among the core
203
, the first and second ingoing optical fibers
201
and
202
, and the outgoing optical fiber
205
, it is required to conduct the alignment of optical axes and matching in a mode shape with high precision. Therefore, skilled labor is required for assembling the device. In addition, a coupling angle of the optical coupler
206
is small, so that the device cannot be miniaturized.
Furthermore, in a conventional optical device, a light transmitting/receiving module for WDM (wavelength division multiplexing) that couples a plurality of light beams or separates light is constituted by using an optical waveguide, a multi-layer filter, and the like. This increases the number of components, making it difficult to achieve a low cost.
In order to solve the above-mentioned problems, recently, producing an optical fiber by using a photonic crystal has drawn attention. For example, JP 11(1999)-271541 A discloses a wavelength separating circuit using a photonic crystal of a two-dimensional triangular lattice.
In the present specification, the term “photonic crystal” refers to an artificial multi-dimensional periodic structure substantially having a period of a light wavelength. It is known that light with a predetermined frequency, which propagates through a photonic crystal, is deflected. More specifically, a photonic crystal has wavelength dispersion characteristics with a strong deflection that is not found in general optical crystal. Due to the characteristics, a photonic crystal is used for an optical device such as a device for WDM.
The wavelength separating circuit using a photonic crystal disclosed in JP 11(1999)-271541 A allows light to be incident thereupon by placing a light incident surface to a photonic crystal in a non-vertical direction to a lattice vector or by tilting the light incident surface with respect to an incident surface perpendicular to the lattice vector direction. This is because the above-mentioned wavelength separating circuit uses a photonic crystal with a high symmetry such as a tetragonal lattice and a triangular lattice. This configuration requires a higher processing precision of an incident angle of an optical system in the course of production of a photonic crystal, making modularization difficult.
Furthermore, in a conventional optical device using a photonic crystal, such as an optical fiber, only two kinds of wavelengths are used, and in an optical device for power separation, only one kind of wavelength is used.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide an optical device, such as an optical filter for WDM and an ADD-DROP apparatus for separating at least three kinds of wavelengths, a separator for WDM for power-separating at least two wavelengths, and an optical coupler, which can be produced easily and miniaturized, and a method for producing a photonic crystal.
An optical device of the present invention includes: a complex photonic crystal in which a plurality of materials with different refractive indices are placed periodically, whereby a plurality of photonic crystals with a periodic refractive index distribution are arranged in a column in a direction of a common primitive lattice vector; an ingoing optical waveguide for allowing light to be incident upon the complex photonic crystal; and an outgoing optical waveguide for receiving light output from the complex photonic crystal. Because of this, an optical device used for optical communication can be produced easily.
Furthermore, in each of the photonic crystals, at least one of a refractive index of the plurality of materials and a periodic structure of a refractive index thereof may be varied on the photonic crystal basis.
Furthermore, each of the photonic crystals may be a two-dimensional photonic crystal.
Furthermore, preferably, two primitive lattice vectors of each of the photonic crystals are parallel to each other, and either one of the two primitive lattice vectors is matched with an optical axis. Because of this, light (selection light) is deflected in a photonic crystal and can be controlled.
Furthermore, the photonic crystal may be interposed between a first cladding and a second cladding.
Furthermore, preferably, a refractive index of at least one of the first cladding and the second cladding is 1. Because of this, the cladding can be made of air, which reduces the number of components.
Furthermore, preferably, the above-mentioned optical device includes a groove for positioning the ingoing optical waveguide and the outgoing optical waveguide that are optical fibers. Because of this, it is possible to position an optical fiber easily without alignment of optical axes and matching in a mode shape with high precision.
Furthermore, the groove may be integrated with each of the photonic crystals directly or indirectly.
Furthermore, preferably, the complex photonic crystal is covered with an air-tight case completely, and an inside of the air-tight case is filled with a gas or evacuated. Because of this, the refractive index of the columnar materials that are made of a gas is not varied by a change in an external environment. This allows an optical device with good stability to realized.
Furthermore, preferably, each of the photonic crystals has a refractive index period determined by a specific wavelength of light that is deflected in each of the photonic crystals, and the specific wavelength is varied depending upon each of the photonic crystals. Because of this, light with a plurality of wavelengths can be dealt with.
Furthermore, an order in a column of each of the photonic crystals may be determined based on the specific wavelength of each of the photonic crystals.
Furthermore, preferably, each of the photonic crystals has a two-dimensional lattice structure in which a first material and columnar materials having different refractive indices are provided, and the columnar materials are arranged periodically in the first material so that axes of the columnar materials are parallel to each other, an acute angle between two primitive lattice vectors of the photonic crystal is larger than 60° and smaller than 90°, the photonic crystals are arranged in a column in a direction of a first primitive lattice vector that is one of the two primitive lattice vectors to form the complex photonic crystal. The ingoing optical waveguide includes a first ingoing optical waveguide that is placed on a photonic cryst
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Spector David N.
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