
INTERFERENCE 201
from a stationary target at f will produce a signal in the detector at exactly f
o
, and any target
will produce a signal at
|
f
o
+f
d
|
. If we choose the offset frequency f
o
larger than any expected
value of
|
f
d
|
, then we can always determine the Doppler velocity unambiguously.
7.3.2 Optical Quadrature
Knowing that the ambiguities in interferometry arise because of the cosine in Equation 7.24,
we may ask whether it is possible to obtain a similar measurement with a sine. Having both
the cosine and the sine terms would be equivalent to having the complex value of I
mix
. Optical
quadrature detection implements the optical equivalent of an electronic ...