A multi-branch, fiber-based frequency comb with millihertz-level relative linewidths using an intra-cavity electro-optic modulator

• Published in: Optics express 2010-01, Vol.18 (2), p.1667-1676
• Main Authors: Nakajima, Yoshiaki, Inaba, Hajime, Hosaka, Kazumoto, Minoshima, Kaoru, Onae, Atsushi, Yasuda, Masami, Kohno, Takuya, Kawato, Sakae, Kobayashi, Takao, Katsuyama, Toshio, Hong, Feng-Lei
• Format: Article
• Language: English
• Subjects: Electronics - instrumentation; Equipment Design; Equipment Failure Analysis; Fiber Optic Technology - instrumentation; Filtration - instrumentation; Lasers; Microwaves; Optical Devices; Refractometry - instrumentation; Transducers
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.18.001667

We demonstrate that fiber-based frequency combs with multi-branch configurations can transfer both linewidth and frequency stability to another wavelength at the millihertz level. An intra-cavity electro-optic modulator is employed to obtain a broad servo bandwidth for repetition rate control. We investigate the relative linewidths between two combs using a stable continuous-wave laser as a common reference to stabilize the repetition rate frequencies in both combs. The achieved energy concentration to the carrier of the out-of-loop beat between the two combs was 99% and 30% at a bandwidth of 1 kHz and 7.6 mHz, respectively. The frequency instability of the comb was 3.7x10(-16) for a 1 s averaging time, improving to 5-8x10(-19) for 10000 s. We show that the frequency noise in the out-of-loop beat originates mainly from phase noise in branched optical fibers.