@article{4271,
  author = {Mamoru Endo and Tyko Shoji and Thomas Schibli},
  title = {High-sensitivity optical to microwave comparison with dual-output Mach-Zehnder modulators},
  abstract = {<p>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\textquoterights 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.</p>},
  year = {2018},
  journal = {Scientific Reports},
  month = {2018-03},
  url = {https://www.nature.com/articles/s41598-018-22621-1$\#$Abs1},
  doi = {10.1038/s41598-018-22621-1},
}