Optical waveguides – With optical coupler – Plural
Reexamination Certificate
2002-05-30
2004-10-12
Fureman, Jared J. (Department: 2876)
Optical waveguides
With optical coupler
Plural
C385S027000, C398S048000
Reexamination Certificate
active
06804430
ABSTRACT:
BACKGROUND OF THE INVENTION
Very recently, traffics in the Internet are rapidly increased. Under such circumstances, expansions of communication network capacities are strongly required. In connection with these strong demands, wavelength division multiplexing (WDM) transmission techniques have been positively developed and popularized. Since the wavelength division multiplexing transmission techniques correspond to techniques capable of multiplexing a plurality of optical signals having different wavelengths with each other to transmit the multiplexed-optical signal to a single optical fiber, a transmission capacity can be expanded by a total number of multiplexed wavelengths.
To realize a wavelength division multiplexing transmission system, an optical device such as an optical multiplexer/demultiplexer is required. An optical multiplexer/demultiplexer corresponds to such an apparatus for multiplexing, for example, lights having a plurality of wavelengths, and for demultiplexing (separating) multiplexed light to a plurality of light having various wavelengths.
For instance, in such a wavelength division multiplexing transmission system, an optical multiplexer/demultiplexer provided for executing the multiplexing operation multiplexes lights having plural wavelengths with each other. The wavelength-multiplexed light which is formed by the multiplexing operation is transmitted to an optical fiber. Also, for instance, such an optical multiplexer/demultiplexer provided for the demultiplexing operation demultiplexes the wavelength-multiplexed light transmitted via the optical fiber. The demultiplexed light every wavelength is derived.
As one example of such an optical multiplexer/demultiplexer, an optical waveguide type optical multiplexer/demultiplexer may be employed. This optical waveguide type optical multiplexer/demultiplexer is manufactured by that an optical waveguide circuit is formed on a substrate. Since high-precision pattern techniques which have been developed in semiconductor fields may be applied to such an optical waveguide type optical multiplexer/demultiplexer, superior designing characteristics thereof may be obtained.
As this optical waveguide type optical multiplexer/demultiplexer, for example, a Mach-Zehnder interferometer (MZI) type optical multiplexer/demultiplexer has been practically utilized.
FIG. 9
indicates a structural example of a circuit (namely, optical multiplexing/demultiplexing circuit) which constitutes such a Mach-Zehnder interferometer type optical multiplexer/demultiplexer.
The optical multiplexing/demultiplexing circuit
8
shown in
FIG. 9
includes a first optical waveguide
3
, and a second optical waveguide
4
arranged side by side with respect to the first optical waveguide
3
. Also, this optical multiplexing/demultiplexing circuit
8
owns a first directional coupling portion
1
formed in such a manner that the first optical waveguide
3
is provided in proximity to the second optical waveguide
4
. Also, the optical multiplexing/demultiplexing circuit
8
owns a second directional coupling portion
2
formed in such a manner that the first optical waveguide
3
is provided in proximity to the second optical waveguide
4
at a position via an interval with respect to the first directional coupling portion
1
along a longitudinal direction of the first and second optical waveguides. Both the first optical waveguide
3
and the second optical waveguide
4
, which are sandwiched between the adjoining (adjacent) directional coupling portions
1
and
2
, own different lengths from each other.
The optical multiplexing/demultiplexing circuit
8
shown in
FIG. 9
corresponds to such an optical multiplexing/demultiplexing circuit which may multiplex lights and/or demultiplex light having different wavelengths by properly setting a product (n×&Dgr;L), while this product is defined by multiplying a difference “&Dgr;L” between the length of the first optical waveguide
3
and the length of the second optical waveguide
4
, which are sandwiched between both the first directional coupling portion
1
and the second directional coupling portion
2
, by diffractive indexes “n” of both the first and second optical waveguides
3
and
4
.
It should be noted that in the Mach-Zehnder interferometer type optical multiplexing/demultiplexing circuit
8
, generally speaking, the below-mentioned path of light is called as a “through transmission path.” In other words, such a through transmission path corresponds to a path of light which is entered from a light incident side
13
of the first optical waveguide
3
and then is outputted from a light projection side
23
of this first optical waveguide
3
, or another path of light which is entered from a light incident side
14
of the second optical waveguide
4
and then is outputted from a light projection side
24
of this second optical waveguide
4
. In this specification, a wavelength of such a light designed in such a manner that this light is transmitted via this through transmission path will be referred to as a “through transmission wavelength.” In
FIG. 9
, a wavelength “&lgr;1” corresponds to this through transmission wavelength.
Also, in the Mach-Zehnder interferometer type optical multiplexing/demultiplexing circuit
8
, generally speaking, the below-mentioned path of light is called as a “cross transmission path.” In other word, such a cross transmission path corresponds to a path of light which is entered from the light incident side
13
of the first optical waveguide
3
and then is outputted from the light projection side
24
of the second optical waveguide
4
, or another path of light which is entered from the light incident side
14
of the second optical waveguide
4
and then is outputted from the light projection side
23
of the first optical waveguide
3
. In this specification, a wavelength of such a light designed in such a manner that the light is transmitted via this cross transmission path will be referred to as a “cross transmission wavelength.” In
FIG. 9
, a wavelength “&lgr;2” corresponds to this cross transmission wavelength.
Also, for example, as shown in
FIG. 10
, such an optical multiplexer/demultiplexer has been proposed which is formed by connecting Mach-Zehnder interferometer type optical multiplexing/demultiplexing circuits
8
(
8
A to
8
G) to each other in a tree shape. This optical multiplexer/demultiplexer contains plural stages of optical multiplexing/demultiplexing circuit
8
, while plural stages (three stages in this example) are defined from a first stage up to an M-th stage (symbol “M” being integer larger than, or equal to 2, namely, 3 is selected in this example). That is, the plural stages of the optical multiplexing/demultiplexing circuits
8
are formed by arranging one, or plural sets of optical multiplexing/demultiplexing circuits
8
(
8
A to
8
G) side by side.
In the optical multiplexer/demultiplexer shown in
FIG. 10
, for instance, a first stage of plural optical multiplexing/demultiplexing circuits
8
(
8
A,
8
B,
8
C,
8
D) multiplex light entered from a corresponding first optical waveguide
3
and light entered from a corresponding second optical waveguide
4
respectively, and then, output the multiplexed light from either the first optical waveguide
3
or the second optical waveguide
4
respectively. A second stage of an optical multiplexing/demultiplexing circuit
8
(
8
E) furthermore multiplexes the optical outputs from the first stage of one pair of optical multiplexing/demultiplexing circuits
8
(
8
A,
8
B). The second stage of this optical multiplexing/demultiplexing circuit
8
(
8
F) furthermore multiplexes the optical outputs from the first stage of one pair of optical multiplexing/demultiplexing circuits
8
(
8
C,
8
D).
Furthermore, a third stage of optical multiplexing/demultiplexing circuit
8
(
8
G) multiplexes the optical outputs from the second stage of one pair of optical multiplexing/demultiplexing circuits
8
(
8
E,
8
F). As previously explained, in the optical multiplexer/demultiplexer shown
Kashihara Kazuhisa
Komatsu Takuya
Koshi Hiroyuki
Ooyama Isao
Fureman Jared J.
The Furukawa Electric Co., LTD
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