Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
2001-04-18
2004-03-02
Chang, Audrey (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S014000, C385S033000, C385S129000
Reexamination Certificate
active
06701043
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an arrayed waveguide grating having a reflective input, and particularly a reflective input that permits variable coupling to adjust the center wavelength.
BACKGROUND OF THE INVENTION
An arrayed waveguide grating (AWG) is a dispersive optical device used for multiplexing or demultiplexing a set of optical telecommunications channels having different wavelengths. An example of an AWG is shown in FIG.
1
. The AWG
100
is an integrated optics device formed on a substrate. The AWG has at least one input waveguide
10
for launching a multiplexed signal comprising a plurality of wavelength channels, &lgr;
1
to &lgr;n, into a free-space slab such as a star coupler
12
. The star coupler
12
distributes a wavefront of the signal evenly to a plurality of waveguides that form the grating
14
. Each of the plurality of waveguides has a different optical length, the optical lengths of adjacent waveguides differing by a constant value and increasing geometrically from one side of the grating to the other. Interference caused by the relative phase differences introduced by the grating
14
occurs in a second free-space slab such as a star coupler
16
. The dispersion of the grating
14
physically separates the different wavelengths and focuses the dispersed light on an output plane
17
of the second star coupler, where separated wavelengths are coupled into a plurality of output waveguides
18
. A center wavelength of a selected channel is located at a selected output waveguide
18
for optimized coupling. The center wavelength and the spacing of the individual wavelength channels are determined by the geometry of the AWG layout and by the effective refractive index of the waveguides of the grating. The output waveguides
18
determine the bandwidth of the individual channels by their width. Operated in a reverse direction, multiple signals of different wavelengths are launched from the plurality of waveguides
18
and pass through the grating
14
to interfere in the star coupler
12
, and be combined as a multiplexed signal into a single waveguide
10
.
The position of the input waveguide
10
at the input plane
20
of the star coupler
12
, from which a multiplexed signal is launched, affects the location of the focused output signals. Input waveguides have been included as a part of the integrated device. However, manufacturing tolerances are not tight enough to accurately set the center wavelength in manufacture for narrow channel spacing. The index accuracy achieved with the many deposition techniques used to make AWGs is not sufficient to set the central wavelength within the required tolerances.
In U.S. Pat. No. 5,732,171, assigned to Siemens Aktiengesellschaft, Michel et al. disclose placing the input plane of the star coupler at the edge of the substrate in which the device is formed to permit coupling a waveguide at a selected location after manufacture. Tuning may be performed to align the center wavelength of the channels of the multiplexed signal with their respective output ports to optimize coupling.
Tuning by affixing a fiber pigtail is subject to alignment error over 5 degrees of freedom. With reference to
FIG. 1
, X-Y-Z coordinates are shown. The X axis indicates lateral movement along the input plane
13
of the star coupler
12
, which affects the center wavelength alignment. The Y axis indicates vertical movement with the planar slab, which is generally single mode in the vertical direction. Consequently fine alignment is necessary to reduce coupling losses. The Z axis indicates movement in and out from the input plane
13
of the star coupler
12
. Alignment in this axis affects the pitch, or separation of the focused channel outputs on the output plane
17
of the second star coupler
16
. In addition &thgr;X and &thgr;Y indicate rotational tilt about the X and Y axes, which will further affect tuning of the center wavelength and insertion loss.
A different approach to setting the center wavelength of an arrayed waveguide grating is disclosed in U.S. Pat. No. 5,290,663, assigned to Lucent Technologies Inc., by Dragone. This patent teaches deformation of the grating in order to control either of its ambient temperature dependence or its transmission characteristics. The deformation is designed to stretch or compress the optical lengths of the grating arms. Such changes give rise to birefringence effects that produce different propagation constants for the TE and TM waveguide modes. For temperature compensation the deformation of the grating serves to maintain the difference in successive arms of the grating in the same relative proportions despite changes in the ambient temperature. Such deformation also provides some tuning of the transmission characteristics of the router to correct for departures from the design characteristics or manufacturing aberrations. However, the birefringent effects increase polarization dependent loss and polarization mode dispersion.
It is desired to provide an improved coupling into an arrayed waveguide grating which would simplify the assembly and permit variable tuning to adjust the center wavelength.
It is further desired to provide an arrayed waveguide having an integrated variable input waveguides to provide tuning flexibility.
SUMMARY OF THE INVENTION
The present invention has found that by providing an arrayed waveguide grating having one or more precisely positioned input waveguides coupled through a reflective lens assembly, for providing a lateral offset to a signal propagating from the input waveguide to the planar waveguide, and for focusing a reflected input signal at a selected input point of the input planar waveguide, alignment and tuning of an input and assembly can be improved and simplified.
Accordingly, the present invention provides an arrayed waveguide grating comprising:
a substrate for supporting an integrated arrayed waveguide grating formed therein including:
an input planar waveguide, having an input plane at an edge of the substrate and an output plane, for propagating a wavefront from an input point on the input plane to an output plane;
a grating comprising an array of waveguides optically coupled to the output plane of the input planar waveguide for receiving the wavefront, an optical length of the waveguides differing by a substantially equal amount from a first waveguide to an nth waveguide; and,
an output planar waveguide for focusing separated wavelength signals on an output plane of the output planar waveguide for coupling to output waveguides; and
an input assembly for launching a signal into the integrated arrayed waveguide grating including:
at least one input waveguide disposed on a plane substantially parallel to the input planar waveguide having a waveguide end for launching a signal into the input planar waveguide;
a lens assembly including a lens means symmetrically disposed between the coupled input point and the waveguide end of a selected one of the at least one waveguide, and a reflective element optically coupled to the lens, the lens assembly for providing a lateral offset to a signal propagating from the input waveguide to the planar waveguide, and for focusing a reflected input signal at the input point of the input planar waveguide.
Advantageously, variable coupling parameters can be incorporated into the reflective coupling including input position, waveguide taper and planar waveguide length increment to provide relatively simple tuning in an integrated device.
REFERENCES:
patent: 5732171 (1998-03-01), Michel et al.
patent: 5905824 (1999-05-01), Delisle et al.
patent: 5920663 (1999-07-01), Dragone
patent: 6011885 (2000-01-01), Dempewolf et al.
patent: 6069990 (2000-05-01), Okawa et al.
patent: 6243514 (2001-06-01), Thompson
patent: 2001/0033714 (2001-10-01), Delisle et al.
patent: 11326975 (1999-11-01), None
patent: 2000098148 (2000-07-01), None
“Optical Phased Array Filter Module with Passively Compensated Temperature Dependence” Heise et al., ECOC, Sep. 1998, Madrid, Spain pp. 319-320.
Delisle Vincent
Hnatiw Alan J. P.
Oliver Steven David
Allen Denise S.
Chang Audrey
JDS Uniphase Inc.
MacLean Doug
Teitelbaum Neil
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