Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-12-05
2004-02-10
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Input/output coupler
C398S117000
Reexamination Certificate
active
06690861
ABSTRACT:
BACKGROUND OF THE INVENTION
This application claims benefit of Japanese Patent Application No. 2000-371434 filed on Dec. 6, 2000, the contents of which are incorporated by the reference.
The present invention relates to arrayed waveguide grating, arrayed waveguide grating module, arrayed waveguide grating module waveguide compensation method, optical communication device and optical communication system and, more particularly, to the arrayed waveguide grating, which permits ready selection of wavelength to be used, the arrayed waveguide grating module using such arrayed waveguide grating, the arrayed waveguide grating module wavelength compensation method of compensating in the arrayed waveguide grating module and the optical communication unit and the optical communication system.
In optical fiber communication systems, further transfer capacity increase has been called for together with transmission data capacity increase. In DWDM (Dense Wavelength Division Multiplexing), the importance of the optical wavelength filter as multiplexing/demultliplexing device for multiplexing and demultiplexing wavelengths has been increasing.
Optical wavelength filters are of various types. Among the optical wavelength filters, the arrayed waveguide gratings have narrow wavelength characteristic and high extinguishing ratio, and they further have features as multiple-input multiple-output filter device. Thus, the optical wavelength filters capable of demultilexing the multiplexed signals and performing inverse operation, and thus it can readily constitute a multiplexing/demultiplexing device. By using quarts waveguide for the arrayed waveguide grating, it is possible to obtain excellent coupling to optical fiber and realize low insertion loss operation with an insertion loss of several dB (decibels). The arrayed waveguide grating has attracting attention as particularly important device among the optical wavelength filters, and its extensive home and abroad researches and investigations are in force.
FIG. 18
shows the overall construction of a prior art arrayed waveguide grating. The arrayed waveguide grating
10
as shown comprises, formed on a substrate
11
, one or more input waveguides
12
, a plurality of output waveguides
13
, a channel waveguide array
14
curved in a predetermined direction with different radii of curvature, an input side slab-waveguide
15
inter-connecting the input waveguides
12
and the channel waveguide array
14
, and an output side slab-waveguide
16
inter-connecting the channel waveguide art
14
and the output waveguides
13
. A multiplexed light signal inputted from the input waveguide or waveguides
12
to the input side slab-waveguide
15
is expanded as it passes therethrough and then inputted to the channel waveguide array
14
.
The channel waveguide array
14
includes a plurality of arrayed waveguides with lengths progressively increasing or decreasing by a predetermined waveguide length difference. The light signals passing through the these arrayed waveguides reach the output side slab-waveguide
16
one after another by a predetermined phase difference internal. Actually, however, wavelength dispersion is present, and the in-phase plane is tilted independence on the wavelength. Consequently, the light signals are focused (i.e., converged) on different positions on the interface between the output side slab-waveguide
16
and the output waveguides
13
. With the output waveguides
13
disposed at the positions corresponding to the respective wavelengths, it is possible to take out a desired wavelength component from the output waveguides
13
.
In the meantime, in such arrayed waveguide grating
10
, the wavelength selection should be performed in conformity to the grid of the ITU (International Telecommunication Union). The wavelength of the arrayed waveguide grating
10
, by the way, is very susceptible to the refractive index changes of the waveguide material. This means that the center wavelength as selected wavelength is subject to variations due to fluctuations in a film formation process as manufacturing process. Therefore, it is frequently impossible to obtain a value as desired. Also, the selected wavelength variation poses a problem that the optical loss with the wavelength in use is increased. Accordingly, it has been in practice to do wavelength compensation to a proper value by some means after completion of the arrayed waveguide grating.
For example, according to Japanese Patent Laid-Open No. 9-49936 an input/output waveguides for wavelength compensation are provided in addition to the normal input/output waveguides based on AWG arrayed waveguide, and are changed according to the wavelength compensation amount.
Denoting the demultiplication direction angle difference with respect to the wavelength difference by &dgr;&lgr;, in the arrayed waveguide grating it is possible to compensate for the center wavelength &lgr;
in
by an amount given by the following equation (1) by changing the positions of the output waveguides
12
, i.e., the slab incidence angle &thgr;
in
.
&dgr;&lgr;
in
=(&dgr;&lgr;/&dgr;&thgr;)·&thgr;
in
(1)
The input/output waveguides, however, are disposed discretely. Therefore, the wavelength compensation amount is also discrete, and it is possible to obtain wavelength compensation as desired. In order to obtain the wavelength compensation amount as desired, it is necessary to set the slab incidence angle &thgr;
in
as desired.
According to Japanese Patent Laid-Open No. 2000-162453, the selected wavelength center is shifted by irradiating an AWG array part with infrared rays and thus changing the refractive index of the irradiated art. According to P. C. Clemens et al, IEEE Photon. Tech. Lett., Vol. 7, No. 10, pp. 1040-1041, 1955 and Transactions of Institute of Electronics and Data Communication Engineers of Japan, C-3-76, 2000, the selected wavelength compensation is performed by changing the position of light incidence on an input side slab-waveguide.
FIG. 19
shows the construction of an arrayed waveguide grating, which does selected wavelength compensation by changing the position of incidence of light on an input side slab-waveguide. In the proposal in the above P. C. Clemens et al, IEEE, Photon, Tech. LETT., Vol. 7, No. 10, pp. 1040-1041, 1995, the AWG wafer
21
of the substrate is severed at an input side slab-incidence part
22
. The slab-incidence part
22
is reinforced with glass, and an input fiber
24
which is also reinforced with glass is bonded (i.e., secured by adhesive) to the slab-incidence part
22
. At the time of the bonding, the centering is performed directly, and the position of the input fiber
24
is changed as desired in correspondence to the wavelength compensation amount.
FIG. 20
shows what is proposed in the Transactions of Institute of Electronics and Data Communication Engineers of Japan, C-3-76, 2000. This proposal is different from the above structure described in connection with
FIG. 19
, in which the input fiber
24
is bonded to the slab-incidence part
22
. As shown in
FIG. 20
, an input fiber
31
is connected via a slab-introduction optical waveguide
32
to the input side slab-waveguide
33
. The input and output side slab-waveguides
33
and
34
are formed on an AWG element wafer
35
, and a channel waveguide array
36
is connected between these slab-waveguides. Output waveguides
38
are connected between the output side slab-waveguide
34
and a fiber array
37
.
In addition to the above proposals, it is in practice to change the temperature of mainly the channel waveguide array part (see channel waveguide array
14
shown in
FIG. 18
) of the arrayed waveguide grating and change the wavelength by adjusting the refractive index width a thermo-optical effect thus obtained. To this end, a temperature controller such as a Velch element or a heater is used.
When carrying out such arrayed wavelength grating wavelength compensation as to match the ITU grid by the above various proposals or method, such high accuracy compensation with an error of several p
McGinn & Gibb PLLC
NEC Corporation
Ullah Akm Enayet
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