Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1998-05-21
2002-01-01
Schuberg, Darren (Department: 2872)
Optical waveguides
With optical coupler
Particular coupling structure
C385S032000, C385S040000, C385S041000, C385S044000, C385S045000
Reexamination Certificate
active
06335994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a waveguide element, a waveguide branch or coupler element and a waveguide integrated circuit. More specifically, the invention relates to a waveguide discontinuity, an extremely high frequency wave integrated circuit, an optical integrated circuit, a quantum electronic device or so forth using the waveguide discontinuity.
2. Description of the Related Art
Associating with increasing optical elements or increasing of kinds of the optical elements to be employed in an optical communication system, cost and mounting load for overall system is becoming significant. In such circumstance, necessity for optical integrated circuit [PIC (Photonic Integrated Circuit)], on which a plurality of optical elements are integrated on a single substrate in monolithic manner, for realizing a specific finction, has been put forward.
On the other hand, for the purpose of extreme enhancement of electronic circuit element, development and research has been started for a quantum electronic device seeking for new possibility of quantum effect as a wave of electron (de Broglie wave) employing a nanometer class fine fabricating technology.
In such element, function of a branch or coupler for coupling between respective functional elements becomes more important, as well as enhancement of performance of respective of individual functional elements. Particularly, for realizing higher two-dimensional package density, acute waveguide discontinuous element, such as a right angle bending (L-shaped bending) or a branching (T-shaped branching) is inherent for enhancing freedom in layout of respective functional elements to be comparable with an electrical integrated circuit.
However, in order to strictly analyze behavior of electron or so forth in a fine structure of extremely high frequency wave, a submillimeter wave and further nanometer class, it is necessary to handle these as a wave. Naturally, it is inevitable to cause reflection and radiation to be a primary cause of bending of the waveguide or loss in discontinuity.
As a known technology for restricting excessive loss in acute waveguide discontinuity, a tapered structure gradually deforng cross-sectional shape of the waveguide over a sufficiently long region in comparison with a wavelength, has been widely employed. However, this inherently increases the overall length of the waveguide integrated circuit. As a result, various problems to overcome, in constrainint layout freedom of respective elements, lowering of yield percenteedegration degree, increasing of absorption loss, have been encountered.
In order to arbitrarily bend propagating direction of a light beam, it is a typical method to employ a mirror (reflection mirror). A typical waveguide bending element widely studied for the purpose of application to optical integrated circuit or so forth, is a corner reflector.
In the foregoing conventional optical integrated circuit, the acute waveguide discontinuous element, such as right angle bending (L-shaped bend)or branching (T-shaped branch) is inherent for enhancing freedom in layout of respective functional elements to be comparable with an electrical integrated circuit.
While the reflection mirror is employed for bending propagating direction of the light beam at an arbitrary angle, the mirror functions as an ideal reflecting plane only when it is sufficiently larger than the wavelength of a beam form wave propagating in a multi-mode space. In other words, the mirror of the size substantially equal to the wavelength or smaller merely serves as scattering body arranged on a path, for the wave.
The corner reflector as the waveguide bending element does not effectively achieve function as a pure reflection mirror as long as it is mounted in a single mode waveguide. The reason why the corner reflector appears to behave for being the path of the light is that the single mode waveguide on the output side picking up a diffracted wave generated by scattering by the cornering reflector barely encloses the diffracted wave in lateral direction (direction perpendicular to a propagation axis).
As set forth above, as the structure for realizing acute waveguide discontinuity in the optical integrated circuit, the structure which is applicable for practical use, is not present.
SUMMARY OF THE INVENTION
The present invention has been worked out for solving the problems set forth above. Therefore, it is an object of the present invention to provide a waveguide element, a waveguide branch or coupler element and a waveguide integrated circuit, which can realize acute waveguide discontinuity, such as a right angle bending (L-shaped bending) or branching (T-shaped branching).
According to the first aspect of the present invention, a waveguide element having a waveguide discontinuity including at least one of bending and intersection of straight waveguide propagating a wave, comprises:
first and second straight waveguides forming at least one of bending and intersection; and
a leaky wave propagation region establishing a leaky wave coupling of the wave propagating through said first and second straight waveguides at substantially equal rate.
According to the second aspect of the present invention, a waveguide branch or coupler element having a waveguide discontinuity including at least one of bending and intersection of straight waveguides propagating a wave for branch or couplersaid wave, comprises:
first, second and third straight waveguide forming at least one of said bending and intersection;
a first leaky wave propagation region establishing a leaky wave coupling of said wave propagating through respective of said first and second straight waveguides at substantially the same rate; and
a second leaky wave propagation region establishing a leaky wave coupling of said wave propagating through respective of said first and third straight waveguides at substantially the same rate.
According to the third aspect of the present invention, a waveguide integrated circuit, in which a waveguide element having a waveguide discontinuity including at least one of a bending and an intersection of straight waveguide propagating a wave, is integrated on a substrate, comprises:
first and second straight waveguides forming at least one of bending and intersection; and
a leaky wave propagation region establishing a leaky wave coupling of the wave propagating through said first and second straight waveguides at substantially equal rate.
An object of the present invention is to realize an acute waveguide discontinuity by restricting an excessive loss caused by reflection or radiation of wave in the waveguide bending or intersecting the straight waveguides propagating a general wave including an electromagnetic wave, such as an extremely high frequency wave, a light and the like or a de Broglie wave of electron or the like.
The waveguide element includes two single mode waveguides have center axes extending in longitudinal directions and intersecting at an intersection angle &thgr; (0<&thgr;≦90°) and have effective propagation wavelength &lgr;G, and a leaky wave propagation region is a region of effective propagation wavelength &lgr;L having two edges located close to each other along the longitudinal direction of respective of two single mode waveguides so as to establish leaky wave coupling of the wave propagating through the single mode waveguides at substantially the same rate.
The two single mode waveguides and said leaky wave propagation region are single mode in the direction perpendicular to the plane including two single mode waveguides and in symmetric relationship with respect to a particular plane perpendicular to a plane including two single mode waveguides and including a straight line equally dividing a supplementary angle (&pgr;−&thgr;) of an intersecting angle &thgr; (0<&thgr;≦90°) of the two single mode waveguides.
A relationship expressed by:
cos(&thgr;/2)≈&lgr;L/&lgr;G
is substantially established to make various amounts of the effective prop
Boutsikaris Leo
NEC Corporation
Schuberg Darren
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