AM-to-PM conversion in a resonant microwave optical rectification detector

A LiNbO3-loaded microwave cavity pumped with weakly AM-modulated 30 fs optical pulses was used as a platform to investigate AM-to-PM conversion in the optical rectification process. Theoretical treatment of AM-to-PM conversion (i.e., peak-induced electrical phase deviation beta(i) due to optical power modulation with index m) suggests that the dominant mechanism is self-group-velocity modulation due to. chi((3)) and cascaded. chi((2)) processes with a value of delta = beta(i)/m = -151 dB, linearly dependent on the optical power at intensities of 6 x 10(10) W/m(2) in a 40 mm long LiNbO3 crystal. This is in stark contrast to p-i-n photodiodes which can exhibit an AM-to-PM conversion gain delta > 0 dB. In this experiment, we measured values of d for a resonant optical rectification detector using typical mode-locked Ti: sapphire laser pulses (100 MHz, 30 fs, P-avg approximate to 100 mW) and found an instrumentation-limited lower bound of d approximate to -43.5 dB, independent of the optical power. (C) 2017 Optical Society of America