A dual-channel GaAs waveguide modulator of the type shown in Fig. 9.5,
with waveguides of 5 μm × 5 μm cross-section, is used to modulate light of
wavelength (in air) λ0 = 1.06 μm. It has a coupling coefficient κ = 1 cm−1 for
the coupling of optical energy from one channel to the other when the voltage
applied to the field plates is zero. (Assume absorption loss is negligible).
(a) What length L must the device have to completely couple the light from
channel 0 to channel 1? (Assume lossless propagation of the lowest order
mode only).
(b) What is the minimum voltage V1 which must be applied to cause the light
output from channel 1 to go to zero if V0 = 0 and if the effective electrooptic coefficient for the geometry shown is r = 1 × 10−12 m/V. Assume
that the substrate conductivity is so large that all of the electric field is
confined to the waveguide channel.