Integrated Optics - Applied Optics Fundamentals and Device Applications - page 282

Four 12-wide leads with MT Cabinet

Optical
flex-
board

Four 12-wide leads with MT

FIGURE 5.46
Optical configuration board.

5.12.4 Configuration of a Curved Transition Waveguide

Intersecting waveguides may be joined either abruptly or smoothly. Abrupt
joining is easier from a fabrication standpoint but provides undesirable dis-
continuities to the traveling waves. The ideal coupling is a curved section,
joined tangentially to the end of each individual waveguide. To fabricate
such a section, one needs to specify the radius of curvature of this section
and one needs to know the location of the center of this curvature relative to
some well-established reference point.
Figure 5.47 shows the intersection of waveguides at the Double-Y out-
put. In this case, a single waveguide is split abruptly at point D, into two
waveguides which separate at an angle β. This abrupt separation is used so
that the angle where the split occurs remains finite. It is desirable to keep
this angle small to permit good coupling between the guides. On the other
hand, one also desires a larger spread between the guides, in a reasonable
distance, than would be attainable with the angle β. So the angle is further
increased by the angle γ to a total of α. The following derivation yields the
necessary values to locate a curved section of waveguide between points A
and B.
The problem can be specified in terms of the angles α and β and the dis-
tances a and R . The segment DE is the distance a between the intersections
of the individual guides with the straight output guide (inclined at 0 ° ), and R
is the radius of curvature of the connecting section measured from point C .
Other angles in the figure are related as follows:

γ α β = − (5.32)