In any type of optical communication system there is the need for interconnecting different discrete components. These components can include such devices as lasers, detectors, fibers modulators, switches, to name a few. Polymers can offer a viable way of interconnecting these components, and can offer a potentially inexpensive interconnection scheme.
Mode transformation waveguides
When coupling between different components, there
is the problem of mode mismatches between the devices. For example
as seen in Figure 1, the mismatch between several single mode
components is illustrated. A fiber has a mode diameter of about
9 um, and is radially symmetric. A laser, on the other hand, has
dimensions of about 2x0.2 um with an asymmetric mode field diameters
of about 3x1 um. A waveguide generally has dimensions somewhere
between those of a fiber and a laser.
In order to reduce the coupling losses, several approaches have been used including the use of lensed fibers, microlenses, as well as tapered waveguides. Most emphasis on tapered waveguides has been focused on incorporating a monolithic taper in devices such as lasers and SOAs, to increase the coupling into a fiber. Our approach has been to use tapered polymer waveguides in order to perform a mode transformation to increase coupling efficiencies.
As an example, we can look at coupling between a single mode laser and an optical fiber, as illustrated in Figure 2. A tapered waveguide is used which has 2 guiding layers in order to be able to change the mode in the vertical as well as the lateral directions. Computer simulation analysis was performed to find the peak coupling efficiency in addition to finding the sensitivity of the waveguide to misalignments.
References
"Tapered polymer single mode waveguides for mode transformation",
Regis S. Fan, D. J. Goodwill and R. Brian Hooker, submitted to the
Journal of Lightwave Technology, July 1997.
"Polymer tapered waveguides and flip-chip solder bonding as
compatible technologies for efficient OEIC coupling",
Regis S. Fan, D. J. Goodwill, R. Brian Hooker, Y-C Lee, B. K.
McComas, Alan R. Mickelson, N. D. Morozova and Darja Tomic, 47th
ECTC Proceedings, pp. 788-796. May, 1997
"Optical coupling with tapered polymer waveguides",
R. Brian Hooker, Regis S. Fan, Dominic Goodwill and Brian McComas,
ASME INTERpack-97, Kohala Coast, Hawaii, June 17, 1997.
"Single mode tapered polymer waveguides for mode conversion",
Regis S. Fan, D. Goodwill and R. B. Hooker, IEEE/LEOS '96 Conference
Proceedings, Vol.2, pp.38-39. Nov, 1996.
"Laser-array to single-mode-fiber coupling module with
increased tolerance budget using polymer waveguide tapers",
D. J. Goodwill, Regis S. Fan, D. Tomic, N. Morozova, R. B. Hooker,
A. R. Mickelson and Y. C. Lee, SPIE Proceedings Vol. 2844,
Aug. ,1996.
SOA Optical switch
Another example of how polymer waveguides can be
used as interconnects can be seen in Figure 3. This is an
example of an SOA (semiconductor optical amplifier) switch, where
SOAs are used in order to gate the signals. The passive polymer
waveguides serve a dual purpose. The first is to route the optical
signal between the fibers and the SOAs and back to the output
fibers. The second is to perform mode transformations to increase
coupling between the different elements in the switch.
References
"Hybrid Optical Switch Using Polymer Waveguides and Semiconductor
Optical Amplifiers (SOAs)", Regis Fan and R. Brian Hooker,
48th ECTC Proceedings, May, 1998.
Embossed waveguides
One of the applications where waveguides can be useful
is in that of out of plane coupling, as is illustrated in Figure
4. Several of the approaches used to create a mirrored facet in
a waveguide include laser ablation, RIE, and dicing at an angle.
We are studying the use of passive polymer waveguides for making out of plane interconnects. In particular, we are looking into the use of embossed waveguides. Embossed waveguides are made by pressing a master structure into a layer of polymer in order to define the channel. Figure 5 shows an embossed structure. Two pictures were taken of the different planes present on the the embossed structure. As can be seen from the pictures in Figure 5, the embossed structure is very well replicated as seen from the sharp edges.
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