Experimental demonstration of time-delay interferometry with optical frequency comb

Heterodyne laser phase measurements in the Laser Interferometer Space Antenna (LISA) are degraded by the phase fluctuations of the onboard clocks, resulting in unacceptable sensitivity performance levels of the interferometric data. The current scheme for cancellation of the clock phase noise requires 1 GHz modulation of the ranging laser beams and additional interspacecraft clock recovery heterodyne phase measurements. Here, we report experimental results for an alternative approach to clock noise cancellation based on modified second generation time-delay interferometry (TDI) with optical frequency combs (OFCs). The use of OFCs in the LISA scheme allows simultaneous cancellation of both laser and clock noises, and would eliminate the need for 1 GHz laser modulations and associated demodulation detections. Two Mach-Zehnder interferometers with acousto-optic modulators were used to simulate two LISA arms with Doppler shifts and time delays. With a self-referenced OFC locked to the laser providing the clock signal, we achieve simultaneous suppression of laser and clock noises by 7 and 1.5 orders of magnitudes, respectively, down to the setup noise floor. Based on a numerical analysis, we further show that the noise suppression performance of the OFC-based TDI scheme can meet the LISA mission requirements with an ample margin.