Digital System for Keeping Optical Frequency Comb in Long- Term Stable Operation

0436829 - ÚPT 2015 RIV US eng C - Konferenční příspěvek (zahraniční konf.)
Čížek, Martin - Šmíd, Radek - Hucl, Václav - Lazar, Josef - Číp, Ondřej
Digital System for Keeping Optical Frequency Comb in Long- Term Stable Operation.
28th European Frequency and Time Forum (EFTF 2014). Piscataway: IEEE, 2014, s. 193-195. ISBN 978-1-4799-5252-6.
[EFTF 2014. European Frequency and Time Forum /28./. Neuchatel (CH), 23.07.2014-26.07.2014]
Grant CEP: GA ČR GAP102/10/1813; GA MŠMT(CZ) LO1212; GA MŠMT ED0017/01/01; GA MŠMT EE2.4.31.0016
Institucionální podpora: RVO:68081731
Klíčová slova: optical frequency comb * long-term operation * stabilization * digital signal processing
Obor OECD: Optics (including laser optics and quantum optics)

A passive optical resonator is a special sensor used for measurement of lengths on the nanometer and sub-nanometer scale. A stabilized optical frequency comb can provide an ultimate reference for measuring the wavelength of a tunable laser locked to the optical resonator. If we lock the repetition and offset frequencies of the comb to a high-grade radiofrequency (RF) oscillator its relative frequency stability is transferred from the RF to the optical frequency domain. Experiments in the field of precise length metrology of low-expansion materials are usually of long-term nature so it is required that the optical frequency comb stays in operation for an extended period of time. The optoelectronic closed-loop systems used for stabilization of combs are usually based on conventional analog electronic circuits processing signals from photodetectors. From an experimental point of view, these setups are very complicated and sensitive to ambient conditions and disturbances, especially in the optical part, therefore maintaining long-time operation is not easy. The presented work deals with a novel approach based on digital signal processing and software-defined radio algorithms. We are using a twostage stabilization scheme. A frequency-locked loop (FLL) pre-stabilizes the offset frequency and steers it into the capture range of a phase-locked loop (PLL) that consequently takes control. Such combination of FLL and PLL together with additional control logics is also able to handle situations when the PLL unexpectedly goes out of lock and so it is capable of keeping the optical frequency comb in a long-time stable operation. The stability of the resulting system was investigated. Allan deviations from data measured during 8 days of operation were computed. The resulting long-term stability of the setup is better than 1.6 x 10−11.
Trvalý link: http://hdl.handle.net/11104/0240484