<P>PROBLEM TO BE SOLVED: To provide an electrooptical delay line frequency discriminator which is little influenced by a laser RIN. <P>SOLUTION: The electrooptical delay line frequency discriminator is equipped with optical signal sources generating 1st and 2nd optical signals to be sent along 1st and 2nd paths of the discriminator. On each path, an electrooptical converter for converting the 1st or 2nd optical signal into a 1st or 2nd corresponding optical signal corresponding to an electric input signal, an optical delay line for delaying the 1st or 2nd corresponding optical signal, and an optoelectric converter for converting the 1st or 2nd corresponding optical signal into a 1st or 2nd corresponding electric signal are provided. The electrooptical converter amplitude-modulates the optical signal passing through it and the optoelectric converter is an amplitude demodulator. The electric output signal is sent out from the electrooptical delay line discriminator by a phase detector responding to the 1st or 2nd corresponding electric signal. <P>COPYRIGHT: (C)2006,JPO&NCIPI 
ELECTROOPTICAL DELAY LINE FREQUENCY DISCRIMINATOR