Page 325 - Introduction to Information Optics

no 6. Interconnection with Optics

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Fig. 6.9. Microscope pictures of waveguide structure components, (a) A splitter, (b) The end
portion of a waveguide, (c), Tapered waveguide, (d) Curved waveguide.

6.2.3. WAVEGUIDE LOSS MEASUREMENT
Waveguide losses are important parameters in determining total insertion
loss for transmitters and receivers. Low-loss waveguides significantly ease
optoelectronic packaging. However, there is no simple technique available to
measure waveguide propagation loss with reasonable accuracy for integrated
optical waveguides that are fabricated on substrates. So far the most widely
used method is the sliding-prism measurement. In this technique, the optical
coupling prism is slid along the streak in the waveguide and the ratio of light
coupled in and out of the waveguide is measured as a function of the
propagation length. A second technique employs a moving fiber probe, in
which the optical fiber is traced along the streak and the light scattered out of
the waveguide is coupled into the fiber probe. These methods, however, suffer
from lack of accuracy and reproducibility because of the mechanical nature of
the measurement technique. The sliding-prism technique will also damage the
waveguide.
This section describes a semiautomatic method for quickly measuring
optical loss using a video camera combined with a laser beam analyzer. This
method does not require any mechanical alignment, leading to accurate and
reproducible measurements, and can be used with all kinds of waveguides
employed in this research. This technique is routinely employed in our
laboratories to characterize the propagation properties of polymer-based