PROBLEM TO BE SOLVED: To provide an optical heterodyne detection system allowing high polarization independency (non-dependency) or intensity noise suppression. SOLUTION: One example of this optical spectrum analyzing system comprises a depolarization element 307 having an input for receiving a sweep partial oscillator signal and an output for outputting a depolarization sweep partial oscillator signal, an optical coupler 310 having a first input for receiving an input signal, a second input optically connected to the depolarization element to receive the depolarization sweep partial oscillator signal, and an output for outputting a coupling signal including the input signal and the depolarization sweep local oscillator signal, and a heterodyne receiver 312 having an input for receiving the coupled optical signal from the optical coupler and an output for outputting an electric signal showing the coupled light signal.
OPTICAL SPECTRUM ANALYZING METHOD AND OPTICAL SPECTRUM ANALYZING SYSTEM