Detuning the signal-recycling cavity length from a cavity resonance significantly improves the quantum noise beyond the standard quantum limit, while there is no km-scale gravitational-wave detector successfully implemented the technique. The detuning technique is known to introduce great excess noise, and such noise can be reduced by a laser modulation system with two Mach-Zehnder interferometers in series. This modulation system, termed Mach-Zehnder Modulator (MZM), also makes the control of the gravitational-wave detector more robust by introducing the third modulation field which is non-resonant in any part of the main interferometer. On the other hand, mirror displacements of the Mach-Zehnder interferometers arise a new kind of noise source coupled to the gravitational-wave signal port. In this paper, the displacement noise requirement of the MZM is derived, and also results of our proof-of-principle experiment is reported.
@article{arxiv.1908.05914,
title = {Design and experimental demonstration of a laser modulation system for future gravitational-wave detectors},
author = {Kohei Yamamoto and Keiko Kokeyama and Yuta Michimura and Yutaro Enomoto and Masayuki Nakano and Gui-Guo Ge and Tomoyuki Uehara and Kentaro Somiya and Kiwamu Izumi and Osamu Miyakawa and Takahiro Yamamoto and Takaaki Yokozawa and Yuta Fujikawa and Nobuyuki Fujii and Takaaki Kajita},
journal= {arXiv preprint arXiv:1908.05914},
year = {2019}
}