Interferometric signal processing apparatus

This invention relates to an interferometric signal processing apparatus. An interferometric signal processing apparatus () producing an output signal from a first input signal () and a second input signal (), the input signals () having substantially equal carrier frequencies, comprising a bridge () having a first arm () and a second arm (), each arm having a first end () and a second end (), the first and second input signals () being input to the first end () of the first and second arms (), respectively; a device-under-test () provided the first arm (); a carrier suppressor () connected to the second ends () of the first and second arms () to produce a carrier-suppressed signal at its output (A); an amplifier () arranged to amplify said carrier-suppressed signal; and a mixer () responsive to the amplified carrier-suppressed signal and a carrier-dominated signal to produce the output signal; wherein the differential group delay between: the first end () of the first arm () and the output (A) of the carrier suppressor (); and the first end () of the second arm () and the output (A) of the carrier suppressor () is less than or equal to 1000/fseconds, where fis the time-averaged mean value of the carrier frequencies of the input signals ().