Optical frequency sweeper using an optical ring circuit with a tunable injection-locking filter

We report an optical-frequency sweeper based on an optical ring circuit containing an optical-frequency shifter and a delay-line fiber. High signal-to-noise ratio (30 dB) is achieved by introducing a tunable injection-locking filter (TILF), The TILF utilizes a tunable laser (distributed Bragg reflector (DBR) laser), which is injection locked to an input signal light. We have achieved a total sweep frequency of 141 GHz by switching the longitudinal modes of the DBR laser.