Fabrication of gratings in planar waveguide devices

Details Fabrication of gratings in planar waveguide devices Fabrication of gratings in planar waveguide devices

2001-08-29

2002-08-06

McPherson, John A. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making named article

C430S290000

Reexamination Certificate

active

06428944

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application claims the benefit of European Application No. 00402451.9, filed Sep. 6, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method of fabricating an optical grating or multiple gratings in a planar waveguide device.
2. Description of the Related Art
Periodic grating elements have numerous applications in planar optical waveguides: for example, as Bragg reflectors they can be used for spectral filtering, add/drop multiplexing or dispersion compensation elements. They also have applications as beam deflectors, waveguide lenses, mode converters and input/output couplers.
In particular, Bragg reflectors can be used in a zero-order phasar component. For example, in the commonly owned and co-pending PCT application no. WO 99/36817, a monolithic planar waveguide device is described. In this device, multiple grating elements are placed over the parallel paths of a phasar region (also referred to as an arrayed waveguide grating (“AWG”) region) in which each grating respectively reflects one specific wavelength and therefore the device can act as a drop-multiplexer.
For example,
FIG. 1
represents a schematic layout of a device described in WO 99/36817. Optical device
10
includes an M×N evanescent coupler
30
and N×O coupler
70
, e.g., free space N×N couplers having a planar arrangement of two linear waveguide arrays separated by a free space region. M×N evanescent coupler
30
has M exterior ports
20
and N interior ports
40
. Exterior ports
20
are used to access the exterior of the device
10
. Interior ports
40
are individually connected to N optical paths
110
to
11
N. The optical paths
110
to
11
N are connected at the other end to the N interior ports
60
of N×O evanescent coupler
70
. N×O coupler
70
also includes exterior ports
80
, which access the exterior of device
10
. Wavelength selecting elements
50
to
5
M-
1
are disposed on the N optical paths
110
to
11
N. Wavelength selecting element
52
, e.g., a Bragg reflector, is tuned to &lgr;
1
, element
52
is tuned to &lgr;
2
, and element
5
M-
1
is tuned to the M−1
th
wavelength supported by device
10
. Thus, light having wavelengths &lgr;
M−1
enters exterior port
20
M and is equally divided.
In such a device, if Bragg reflectors are used as wavelength selecting elements, sub-micron positioning precision of the Bragg reflectors (
50
,
52
, et seq.) within the phase array is needed in order to achieve the desired optical functionality of the device.
In addition to the required positioning precision, it is also desirable to utilize a Bragg reflector having a high reflectivity. For example, consider that Bragg reflectors utilized in a device such as optical device
10
are required to reflect 99.9% of the incident light power at the design wavelength to ensure a maximum crosstalk of −30 dB. From the coupled-wave theory of Bragg reflectors the reflectivity is given by:
|
r
(&ohgr;)|
2
=|tanh(&kgr;
L
)|
2
The reflectivity specification of 99.9% implies that
&kgr;
L
>4.15
where &kgr; is the grating contra-directional mode coupling coefficient and L is the grating length. Thus, in order to achieve a &kgr;·L value of 4.15, either the grating length needs to be large, or the mode coupling coefficient needs to be large.
SUMMARY OF THE INVENTION
Thus, what is needed is a straightforward method of fabricating a grating in a planar waveguide device in a high precision manner. Also, what is needed is a straightforward method of fabricating a grating in a planar waveguide device to increase the coupling coefficient &kgr; thereby allowing for a reduced grating length. In view of the foregoing, according to an embodiment of the present invention, a method of fabricating a grating in a planar waveguide device comprises providing a substrate material that includes a substrate layer, a first core layer, a second core layer, and a first photoresist layer. An exposure of a grating and a plurality of alignment marks is formed onto the substrate material. The second core layer is etched to form the grating in the second core layer. A second photoresist layer is deposited on the substrate material that remains after the first etching. An exposure of a waveguide pattern is formed in the first core layer. The first core layer is etched to define a first waveguide in the first core layer, where the first waveguide includes a first portion having the surface grating.
According to another embodiment of the present invention, a method of fabricating a grating in a planar waveguide device comprises providing a substrate material that includes a substrate layer, a core layer, and a first photoresist layer. A first photo-mask that includes a plurality of alignment marks is disposed between the first photoresist and a light source. An exposure of the first photo-mask is performed and the alignment marks are etched into the core layer. A grating is written into the core layer by a photosensitive effect. A second photoresist layer is deposited on the substrate material and an exposure of a waveguide pattern is formed in the core layer. The core layer is etched to define a first waveguide in the core layer, where the first waveguide includes a first portion having the surface grating.
Further features of the invention form the subject matter of the claims and will be explained in more detail, in conjunction with further advantages of the invention, with reference to exemplary embodiments.


REFERENCES:
patent: 5178978 (1993-01-01), Zanoni et al.
patent: 5371817 (1994-12-01), Revelli, Jr. et al.
patent: 5471552 (1995-11-01), Wuu et al.
patent: 5550088 (1996-08-01), Dautartas et al.
patent: 5915051 (1999-06-01), Damask et al.
patent: 6-027338 (1994-02-01), None
patent: WO 00/43817 (2000-07-01), None

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