Page 323 - Introduction to Information Optics

308 6. Interconnection with Optics

6,2.2.2. Laser-Writing Technique
The laser-beam waveguide writing system has also been investigated for
fabricating high performance polymer-based channel waveguides. The laser-
beam writing system, shown in Fig. 6.2, consists of a dual-wavelength HeCd
laser (l l — 325 nm and 1 2 = 442 nm), beam-shaping optics, an electronic
shuttle, and a computer-controlled X-Y-Z translation stage with a stroke of
3
30 x 30 x 2.5 cm . The stage translation speed is continuously adjustable
below 1.0 cm/s. The positioning resolution is 0.5 /im and 0.01 /«n for the X-Y
axes and Z-axis, respectively. The Z-stage is employed to precisely control the
focused laser beam sizes. Figure 6.6 shows a polymeric waveguide H-tree
structure fabricated on a silicon wafer.
The laser-beam writing technique is a straightforward process with minimal
equipment and steps; uses dry, precoated and quality-controlled materials, and
is amenable to large area exposures, as opposed to etching, molding, or
embossing procedures. The ability to progressively laminate and bond success-
ive layers to build up polymeric waveguide structures provides a significant
and essential attribute for performance, applicability, and manufacturability.
Using pressure- and temperature-controlled laminators with precoated mater-
ials adjusted for adhesion properties, bubble-free high-quality multilayered
bonded structures can be created.

6.2.2.3. VLSI Lithography Technique
The most commonly used technique for research and development of
polymer waveguide circuits is based on conventional photolithography orig-

Fig. 6.6. Photograph of a polymeric waveguide H-tree fabricated on a silicon wafer.