High-sensitivity optical to microwave comparison with dual-output Mach-Zehnder modulators.

ABSTRACT: We demonstrate the use of two dual-output Mach-Zehnder modulators (DO-MZMs) in a direct comparison between a femtosecond (fs) pulse train and a microwave signal. Through balanced detection, the amplitude-to-phase modulation (AM-PM) conversion effect is suppressed by more than 40?dB. A cross-spectrum technique enables us to achieve a high-sensitivity phase noise measurement (-186 dBc/Hz above 10-kHz offset), which corresponds to the thermal noise of a +9?dBm carrier. This method is applied to compare a 1-GHz fs monolithic laser to a 1-GHz microwave signal generated from photodetection of a free-running 500?MHz mode-locked laser. The measured phase noise is -160 dBc/Hz at 4-kHz, -167 dBc/Hz at 10-kHz, and -180 dBc/Hz at offset frequencies above 100-kHz. The measurement is limited by the free-running 500-MHz laser's noise, the flicker noise of the modified uni-traveling carrier photodiode and the thermal noise floor, not by the method itself. This method also has the potential to achieve a similar noise floor even at higher carrier frequencies.

SUBMITTER: Endo M 

PROVIDER: S-EPMC5847530 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature