By judicious engineering of grating parameters such as tooth shape, duty cycle
and phase offset, the grating strengths and effective indices of the polarization
modes of a grated waveguide are adjusted over a wide range of values to achieve
a desired level of polarization sensitivity, or insensitivity. In the typical example,
the physical geometry of the grating teeth is adjusted so that degenerate behavior
(nTE=nTM and TE=TM) is
obtained for two polarization modes; the effective refractive indices and grating
strengths are matched for the TE and TM polarization modes. In the current embodiment
the sidewall gratings are used in which the tooth profile is selected in order
to equalize the grating strength for each polarization mode.
