Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2000-08-25
2002-09-10
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S041000, C385S008000, C385S010000, C385S024000, C359S199200, C359S199200
Reexamination Certificate
active
06449411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical wavelength tunable filter and more particularly to the optical wavelength tunable filter which can be suitably used for an optical wavelength multiplexing transmission system.
2. Description of the Related Art
In recent years, a transmission capacity of one communication line increases as types of information communications are diversified. To meet a need for such increased transmission capacity of the communication line, a variety of technologies have been developed. Among them, a dense wavelength division multiplexing (DWDM) transmission technology capable of transmitting a plurality of lightwave signals by only one optical fiber and/or an optical cross-connect (OXC) technology in particular have received widespread attention.
FIG. 5
is a schematic block diagram showing configurations of a conventional communication system employing the DWDM transmission technology. In this communication system, sending lightwave signals
10
1
to
10
N
each having a different wavelength component &lgr;
1
to &lgr;
N
input on a sender side are multiplexed by an optical multiplexing section
11
. The optical multiplexing section
11
is made up of an array-waveguide grating (AWG) serving as a planar lightwave circuit (PLC). A lightwave signal multiplexed by the optical multiplexing section
11
is amplified by an optical amplifier
12
and is sent out to an optical fiber
13
. On a receiver side, the lightwave signal received through the optical fiber
13
is amplified by an optical amplifier
14
and is then input to an optical demultiplexing section
15
. The optical demultiplexing section
15
is made up of the AWG as in the optical multiplexing section
11
. Generally, by inverting the AWG from its input side to its output side or vice versa, it can be used not only as an optical multiplexer but also as an optical demultiplexer. An amplified lightwave signal input into the optical demultiplexing section
15
is output as received lightwave signals
16
1
to
16
N
each having a different wavelength component &lgr;
1
to &lgr;
N
. Though the AWG used on the receiver side in the communication system employing the DWDM transmission technology is able to extract light having a specified wavelength component with high accuracy, it is expensive. Moreover, the AWG has a problem in that an easy changing of the wavelength component to be extracted is impossible. To solve this problem, in some cases, an optical wavelength tunable filter capable of extracting light having a specified wavelength from a plurality of rays of light branched by an optical branching device is used as the optical demultiplexer, instead of the AWG. Various types of optical wavelength tunable filters are proposed and one of them is disclosed in Japanese Patent Application Laid-open No. Hei4-168416 under “An optical wavelength tunable filter”.
FIG. 6
is a perspective view showing configurations of the optical wavelength tunable filter employed in the technology disclosed in Japanese Patent Application Laid-open No. Hei4-168416. In the optical wavelength tunable filter disclosed above, an optical waveguide
21
is formed on a substrate
20
having an electro-optic effect. Electrode
22
and electrode
23
are formed by evaporation on both sides of the optical waveguide
21
on an upper face of the substrate
20
. The electrode
22
is connected to a terminal of a supply power voltage V. The electrode
23
is grounded. On each of end faces of the optical waveguide
21
are mounted reflecting film
26
and reflecting film
27
. The optical wavelength tunable filter having configurations as described above has a Fabry-Perot resonance characteristic upon which a specified wavelength component causing a relative transmittance to be “1” is periodically dependent in a state where the reflecting film
26
and reflecting film
27
are mounted at both end face
24
and end face
25
of the optical waveguide
21
and when a voltage is applied between the electrode
22
and electrode
23
. Therefore, when a plurality rays of light
28
each having a different wavelength component out of &lgr;
1
to &lgr;
N
, branched by the optical branching device mounted in the optical demultiplexing section
15
shown in
FIG. 5
, are input from the end face
24
of the optical wavelength tunable filter shown in
FIG. 6
, only lightwave signal having the wavelength component conforming to the specified wavelength component that causes the relative transmittance to be “1” is output from the end face
25
as output light
29
. Moreover, by changing the voltage V to be applied between the electrode
22
and electrode
23
, a refractive index of the optical waveguide is changed by the electro-optic effect. The wavelength component of the output light
29
to be emitted can be changed as well.
Thus, by using the optical wavelength tunable filter described as above for a plurality rays of light each having a different wavelength component out of &lgr;
1
to &lgr;
N
, branched by the optical branching device mounted in the optical demultiplexing section
15
, only lightwave signal having a desired wavelength component can be extracted at low costs.
However, the conventional optical wavelength tunable filter has a problem in that it requires a substrate having electro-optic effects as a special material, thus making it costly when compared with one fabricated using a silica based material with properties being equivalent to optical fiber. Moreover, another problem is that the conventional optical wavelength tunable filter can be made less integrated when compared with one fabricated using the silica based material.
Thus, a demand is increasing for the optical wavelength tunable filter which can be formed on a substrate made of the silica based material allowing low-cost production and high integration.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide an optical wavelength tunable filter which can be highly integrated and fabricated at low costs.
According to a first aspect of the present invention, there is provided an optical wavelength tunable filter including:
an optical waveguide having a first branched optical waveguide and a second branched optical waveguide merging into one piece of the optical waveguide through which optical wavelength multiplexed signals each having a different wavelength component being incident from an end face of the first branched optical waveguide are propagated;
one comb-type electrode or a plurality of comb-type electrodes each corresponding to each of the different wavelength components, mounted vertically to a propagating direction of the optical wavelength multiplexed signals leaving a specified space apart from the optical waveguide formed by the merger of the first branched optical waveguide with the second branched optical waveguide; and
a voltage applying circuit to apply a predetermined voltage to each of the comb-type electrodes.
By configuring as above, since a refractive index of the optical waveguide is changed by an electric field produced by the voltage applied to the comb-type electrode and since only light having a diffraction wavelength contained in the optical wavelength multiplexed light can be reflected, the light having any wavelength component can be extracted by simplified configurations of the optical wavelength tunable filter as provided by the present invention.
According to a second aspect of the present invention, there is provided an optical wavelength tunable filter including:
an optical waveguide formed in parallel to an upper face of a substrate made-of a silica based material having a first branched optical waveguide and second optical branched waveguide merging into one, through which optical wavelength multiplexed signals each having a different wavelength component being incident from the first branched optical waveguide are propagated;
one comb-type electrode or a plurality of comb-type electrodes each corresponding to each of the different
Healy Brian
McGinn & Gibb PLLC
NEC Corporation
Wood Kevin S
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