The fields of precision timekeeping and spectroscopy increasingly rely on
optical frequency comb interferometry. However, comb-based measurements are not
described by existing quantum theory because they exhibit both large mode
mismatch and finite strength local oscillators. To establish this quantum
theory, we derive measurement operators for homodyne with arbitrary mode
overlap. These operators are a combination of quadrature and intensity-like
measurements, which inform a filter that maximizes the quadrature measurement
signal-to-noise ratio. Furthermore, these operators establish a foundation to
extend frequency-comb interferometry to a wide range of scenarios, including
metrology with nonclassical states of light.Comment: 5 pages plus appendice