Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-09-13
2004-09-07
Bruce, David V. (Department: 2882)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06788848
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an arrayed waveguide grating device, a process for producing the same, an arrayed waveguide module, and an optical communication system. More particularly, the invention relates to an arrayed waveguide grating device, which can correct the wavelength to be selected, a process for producing the same, and an arrayed waveguide module and an optical communication system using said arrayed waveguide grating device.
BACKGROUND OF THE INVENTION
An increase in capacity of data to be transmitted has led to a demand for further increased transmission capacity in an optical fiber communication system. For this reason, optical wavelength filters are becoming increasingly important as multiplexing/demultiplexing devices for dividing or multiplexing wavelengths by dense wavelength division multiplexing (DWDM).
There are various types of optical wavelength filters. Among others, arrayed waveguide gratings have a high extinction ratio in narrow band wavelength characteristics and can also function as a multi-input/multi-output filter device. Therefore, the separation of multiplexed signals and the multiplexing of separated signals are possible, and, thus, advantageously, a wavelength multiplexing/demultiplexing device can be easily constructed. Further, when an arrayed waveguide grating device is constructed by a quartz waveguide, the efficiency of coupling to optical fibers is high and low insertion loss operation with an insertion loss of about several dB (decibels) can be realized. By virtue of this, arrayed waveguide gratings have drawn attention as a particularly important device among the optical wavelength filters, and have been energetically studied in Japan and other countries.
FIG. 1
shows the whole construction of a conventional arrayed waveguide grating. An arrayed waveguide grating
11
comprises: a single or plurality of input waveguides
12
provided on a substrate (not shown); a plurality of output waveguides
13
; a channel waveguide array
14
of channel waveguides bent in a certain direction with respectively different curvatures; an input-side slab waveguide
15
for connecting the input waveguides
12
to the channel waveguide array
14
; and an output-side slab waveguide
16
for connecting the channel waveguide array
14
to the output waveguides
13
. The course of multiplexed signal lights introduced through the input waveguides
12
is widen by the input-side slab waveguide
15
, and the multiplexed signal lights are incident as equal phases on the channel waveguide array
14
. The incident light intensity varies depending upon incident positions of the input-side slab waveguide
15
. Specifically, the closer the incident position to the center portion, the higher the intensity The intensity distribution is substantially a Gaussian distribution.
In the channel waveguide array
14
, a certain optical path difference is provided among the arrayed waveguides constituting the channel waveguide array
14
. The optical path lengths are set so as to be successively increased or decreased. Therefore, a phase difference is provided at certain spacings in the lights guided through the arrayed waveguides, and, in this state, the lights reach the output-side slab waveguide
16
. In fact, due to wavelength dispersion, the equal phase face is inclined according to the wavelength. As a result, light image formation (focusing) take place at different positions at the interface of the output-side slab waveguide
16
and the output waveguides
13
according to wavelengths. Since the output waveguides
13
are disposed at positions corresponding respectively to the wavelengths, desired wavelength components can be taken out of the output waveguides
13
.
The center wavelength of this type of arrayed waveguide grating
11
is very sensitive to a change in refractive index of the waveguide material. Therefore, a variation in the film formation process as the production process leads to a change in the center wavelength, This in many cases makes it impossible to obtain values as designed. The change in center wavelength poses a problem that optical loss at the wavelength used is increased.
In order to overcome this problem, Japanese Patent Laid-Open No. 49936/1997 proposes the provision of I/O (input/output) waveguides for wavelength correction in addition to I/O waveguides of conventional AWGs (arrayed waveguides). In this case, the I/O waveguides are changed according to the correction level of the wavelength.
When the difference in the accuracy of the demultiplexing direction relative to the wavelength difference &dgr;&lgr; is &dgr;&thgr;, in the arrayed waveguide grating, the center wavelength &lgr;
in
can be corrected by a value represented by equation (1) by changing the position of the input waveguides
12
, that is, changing the angle &thgr;
in
of incidence on the slab.
δλ
in
=
δλ
δθ
·
θ
in
(
1
)
Since, however, the I/O waveguides for wavelength correction are discretely disposed, the degree of correction for the wavelengths is also discrete and, thus, the wavelength cannot be corrected as desired. To provide the degree of wavelength correction as desired, the angle &thgr;
in
of incidence on the slab should be arbitrary.
FIG. 2
shows the construction of an arrayed waveguide grating device for solving the above problem. For example, in this proposal described in “P. CPU. Clements et al., IEEE, Photon, Tech., Lett., Vol. 7, No. 10, pp. 1040-1041, 1995,” the substrate is cut at the section
22
of incidence on the slab on the input side of AWG (arrayed waveguides) wafer
21
. In the section
22
, of incidence on the slab, reinforced with a dolly (glass), an input fiber
24
, which is likewise sandwiched by the dolly
23
, is bonded (fixed). At the time of the bonding, aligning is directly carried out, and the position of the input fiber
24
is changed as desired according to the degree of wavelength correction.
In general, however, the production error of the input fiber
24
having a spot size is much larger than that of the optical waveguides having a spot size. Therefore, the adoption of this technique raises a problem that a large variation in spot size of the input fiber
24
is causative of a deterioration in characteristics of the arrayed waveguides.
FIG. 3
shows a proposal for solving the above problem. For example, in “THE 2000 IEICE (The Institute of Electronics, Information and Communication Engineers) GENERAL CONFERENCE, C-3-76,” as shown in
FIG. 3
, the input fiber
31
is connected to the input-side slab waveguide
33
through an optical waveguide
32
for introduction into the slab, rather than bonding of the input fiber
24
at the section
22
of incidence on the slab. Both the input-side slab waveguide
33
and the output-side slab waveguide
34
are provided on an AWG device wafer
35
, and a channel waveguides array
36
is provided between and connected to the input-side slab waveguide
33
and the output-side slab waveguide
34
. Further, output waveguides
38
are provided between and connected to the output-side slab waveguide
34
and the fiber array
37
.
In the case of the arrayed waveguide grating device shown in
FIG. 3
, the optical waveguide
32
for introduction into the slab is provided between the input fiber
31
and the input-side slab waveguide
33
. In this case, waveguides are connected to the input-side slab waveguide
33
, and, thus, the problem of a variation in spot size as described above is reduced. Since, however, the optical waveguide
32
for introduction into the slab should be separately provided, this may be an obstacle to mass production.
In the methods shown in
FIGS. 2 and 3
, the incident section of the slab is cut. Therefore, the generation of an error in the optical axis direction at the slab cut position causes a change in slab length which is causative of a deterioration in wavelength characteristics. Specifically, when the slab has been cut in a larger length than the necessary length, the length can be regulated,
Bruce David V.
McGinn & Gibb PLLC
NEC Corporation
Suchecki Krystyna
LandOfFree
Arrayed waveguide grating device, process for producing the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Arrayed waveguide grating device, process for producing the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Arrayed waveguide grating device, process for producing the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261457