Subgigahertz channel filtering by optical heterodyne detection using a single axial mode from an injection-locked passively mode-locked semiconductor laser

We report experimental results of fine (subgigahertz) channel filtering via optical heterodyne detection based on an optical injection locking technique. A passively mode-locked semiconductor laser injection locked to a master oscillator forms a comb of discrete frequency probes, and a single axial mode is used as a local oscillator (LO). The injection-locked LO carrier showed 42-dB phase noise suppression at 100-kHz offset. One of two analog radio frequency signals detuned by only 200 MHz showed a signal-to-noise ratio over 65 dB/Hz through demultiplexing with a commercially available microwave bandpass filter. The single sideband noise of the heterodyne beat tone at 13.160 GHz was measured to be -123 dBc/Hz at 100 kHz offset from the carrier under injection-locked state.