Methods and apparatus for dither control of a micromirror using a servo
control loop in an optical switching apparatus, an optical switching
apparatus and optical network are disclosed. A servo control loop may use
dither tone having two or more frequency components to dither an output
driver that controls the position of a micromirror in an optical switch.
The two components may be demodulated from an optical signal deflected by
the micromirror. The optical signal may be fed into two band-pass
filters. Each band-pass filter may have a pass band centered on a
different one of the two frequency components. The envelope detector may
compare the envelopes of the band-pass filter outputs. If the envelopes
differ by more than a set threshold the output of the envelope detector
may be forced to zero. Otherwise, the output of the envelope detector may
be the sum of the two band-pass filter outputs.