Vladimir I. Denisov

Hybrid highly nonlinear fiber for spectral supercontinuum generation in mobile femtosecond clockwork

We have proposed and tested a novel design of a short-length dispersion-managed hybrid highly nonlinear fiber (HNLF), which is intended for low-noise spectral supercontinuum generation with controlled intensity distribution over the range 1?2??m. It is shown experimentally that such a HNLF facilitates development of a mobile femtosecond optical clockwork, which is based on a fiber-optic femtosecond laser system and an original fiber-coupled Nd?:?YAG/I2 optical frequency standard with a long-term instability lowered to 3???10?15.

Optical trigger based on a fiber-coupled liquid crystal

Triggering capability of a laser radiation transmission through a fiber-coupled nematic liquid crystal (NLC) was experimentally investigated. This capability arises from light-induced reorientation of NLC molecules that enables self-focusing and self-confinement of propagating laser radiation. It was shown, that triggered optical coupling of two single-mode optical fibers terminated coaxially in NLC can be achieved through a self-induced light guide. It allows implementation of a miniature all-fiber devise, which can act as a precision power-sensitive optical trigger.

Precise modulation of laser radiation by an acousto-optic modulator for stabilisation of the Nd : YAG laser on optical resonances in molecular iodine

A system of precise frequency modulation of laser radiation by an acousto-optic modulator, which makes it possible to stabilise the radiation power and simultaneously suppress the residual amplitude modulation to a level of 10-8 of the total laser power at the third harmonic of modulation frequency (~500 Hz), is presented. The use of this system for the Nd : YAG/I2 optical frequency standard and application of digital signal synthesis and processing methods provided a level of frequency standard instability as small as ~10-15 for ~6 × 104 s.

Femtosecond combs for precision metrology

A new stage of development of optical clocks and synthesizers is possible with the use of highly stable femtosecond lasers. Using femtosecond lasers and special optical fibres, a highly stable frequency comb covering the frequency interval up to several hundreds of THz with a spacing from 100 MHz to 1 GHz has been developed. Experimental schemes for the femtosecond optical clock based on the He-Ne/CH4 and Nd:YAG/I2 frequency standards are presented. The possibility of using tapered fibres for optical clocks and synthesizers is investigated. It is shown that, depending on their influence on the frequency characteristics of the spectral components of the transmitted radiation, tapered fibres can be used in femtosecond optical clocks and synthesizers.

Stabilisation of a fibre frequency synthesiser using acousto-optical and electro-optical modulators

A fibre-optic frequency synthesiser is developed that is stabilised to the optical frequency standard based on molecular iodine . The possibility of transferring stability of the optical frequency standard to other optical frequencies in the IR range and to the RF range by using synthesiser phase-locked loops (PLLs) with acousto-optical and electro-optical modulators is experimentally demonstrated. The additive instability introduced into the optical frequency comb of the synthesiser (which arises due to PLL residual random errors) is several orders less than the intrinsic instability of the reference optical frequency standard employed (i.e., is noticeably less than for and for ).

Femtosecond optical clock with the use of a frequency comb

The principles of precision measurement of frequency intervals in optical range with the help of femtosecond lasers are described. An experimental scheme of femtosecond optical clock is described. The characteristics of the basic elements and units of the setup are presented. The results of a broadened spectrum researches with the help of tapered fibers are reported.

Fiber-based femtosecond optical frequency comb stabilized to iodine frequency standard

A fiber-based femtosecond optical frequency comb spanning wavelengths from 1 to 2 μm was stabilized precisely to an iodine frequency standard by means of heterodyne optical phase-locked loops. It enables transfer of frequency stability across electromagnetic spectrum and implementation of compact optical clocks with ~10-15 long-term instability.

Universal femtosecond fiber-optic clockwork

We report on development of a universal optical clockwork based on a fiber-optic femtosecond frequency comb generator with an advanced stabilization system. The comb generator employs a highly-stable mode-locked erbium-fiber laser and an original hybrid highly-nonlinear fiber. The implemented concept of frequency stabilization provides universality of the clockwork and allows frequency stability transfer from different types of optical standards to the generated radio and optical frequencies. The clockwork can ensure ultra-low relative instability (less than 10-17) of generated frequencies provided that a proper optical frequency standard is applied. The clockwork is approved for operation with molecular (I2), and single-ion (Yb+) optical standards.

Features of measurements of small surface displacements by femtosecond lasers

In our work the theoretical and experimental investigations of the measurement of small harmonic surface oscillations using a femtosecond laser are presented. It is shown that the large number of laser radiation modes allows a considerable increase in the signal-to-noise ratio.

Nonlinear noise and femtosecond frequency comb broadening in tapered fiber

We present a theoretical study of broadened femtosecond frequency comb, affected by nonlinear fiber noises, by use of semi-qualitative numerical model based on the noise statistics and pulse propagation in fiber problem.