Application of WGM Resonances to the Measurement of the Temperature Increment of Ho and Ho-Yb Doped Optical Fibers Pumped at 1125 and 975 nm.

Optical fiber characterization using whispering gallery mode resonances of the fiber itself has been demonstrated to be a powerful technique. In this work, we exploit the thermal sensitivity of whispering gallery mode resonances to characterize the pump-induced temperature increment in holmium doped and holmium-ytterbium codoped optical fibers. The technique relies on the measurement of the resonances' wavelength shift due to temperature variation as a function of the pump power. Holmium doped fibers were pumped to the second excited level 5I6 of the Ho3+ ion using a laser diode at 1125 nm and ytterbium-holmium codoped fibers to the 2F5/2 level of the Yb3+ ion by a laser diode at 975 nm. Our results demonstrate that pumping ytterbium-holmium codoped fibers at 975 nm results in dramatic thermal effects, producing a temperature increment two orders higher than that observed in holmium doped fibers pumped with a 1125 nm laser diode.

Ytterbium-doped fiber laser as pulsed source of narrowband amplified spontaneous emission.

We report random noise pulsed regime of an ytterbium-doped fiber laser arranged in common Fabry-Perot configuration. We show that the laser output obeys the photon statistics inherent to narrowband amplified spontaneous emission and that the noise pulsing is properly addressed in terms of probability density and autocorrelation functions. Our novel approach reveals, in particular, that the regime's coherence time dramatically shortens, from few ns to tens ps, with increasing laser power.

ASE narrow-band noise pulsing in erbium-doped fiber amplifier and its effect on self-phase modulation.

In this paper, we report a study of the features of polarized and unpolarized narrow-band amplified spontaneous emission (ASE) in a low-doped erbium fiber at 976-nm pumping. We demonstrate that ASE noise can be treated as a train of Gaussian-like pulses with random magnitudes, widths, and inter-pulse intervals. ASE noise can also provide a statistical analysis of these three parameters. We also present the data that reveal ASE noise's role in optical spectrum broadening through self-phase modulation of light propagating in a communication fiber. In particular, the data show that the ASE noise derivative defines the broadening's spectral shape.

Polarimetric parameters associated to special microstructured fibers.

The Mueller matrices associated to six homemade special index-guiding microstructured fibers are determined at a transmission wavelength of 1550 nm. Diattenuation, polarizance, and polarization-dependent loss, among other polarimetric parameters, are determined from the Mueller matrix associated to a 2 m length of each fiber studied here. Results show that the fiber fabrication parameters have a clear effect on the output degree of polarization (DoP), providing an inverse relationship between the DoP output and the relative hole diameter, the d/Λ value.

Determination of the Mueller matrix of UV-inscribed long-period fiber grating.

An explicit method for determination of the Mueller matrix elements of a commercial long-period fiber grating inscribed with ultraviolet CW laser irradiation (UV-LPFG) is presented. From the Mueller matrix obtained for such UV-LPFG, the full polarimetric response of the grating was found. Our polarimetric analysis was focused mainly on the polarization-dependent loss and other polarimetric properties, such as the polarizance, the depolarization index, and the diattenuation parameters. The full polarimetric analysis allows us to obtain more complete information than the usually reported ones, in which only two orthogonal linear polarizations are considered; for example, with our analysis, we prove that a small depolarization effect is inherent in UV-LPFG and that attenuation depends on the polarization state. This additional polarimetric information could be useful to control the output LPFG signal, for instance, for the realization of wavelength switchable or Q-switched fiber lasers, among other applications.

Smart Q-switching for single-pulse generation in an erbium-doped fiber laser.

In this paper, we report an active Q-switching of an erbium-doped fiber laser with special modulation functions and novel laser geometry. We experimentally demonstrate that using such a smart Q-switch approach, Q-switch ripple-free pulses with Gaussian-like shape and 17.3 ns width can be easily obtained. The idea behind the smart Q-switch is to suppress one of two laser waves contra-propagating along the fiber cavity, which arises after Q-cell opening, and to eliminate the minor sub-pulses.

Electrically tunable photonic true-time-delay line.

We present a new application of the acousto-optic superlattice modulation of a fiber Bragg grating based on the dynamic phase and group delay properties of this fiber-optic component. We demonstrate a tunable photonic true-time-delay line based on the group delay change of the light reflected from the grating sidebands. The delay is electrically tuned by adjusting the voltage applied to a piezoelectric transducer that generates the acoustic wave propagating along the grating. In our experiments, a true-time delay of 400 ps is continuously adjusted (300 ps within the 3 dB amplitude range of the first sideband), using a 12 cm long uniform grating.

Experimental characterization of hopping dynamics in a multistable fiber laser.

We demonstrate experimental evidence of noise-induced attractor hopping in a multistable fiber laser. Multistate hopping dynamics displays complex statistical properties characterized by nontrivial scalings. When hopping is encountered between two states, the dynamics of the system is characterized by the -32 power law for the probability distribution of periodic windows versus their length, just as in the case of two-state on-off intermittency. A surprising noise saturation effect is found: average output noise in the hopping regime is almost independent of input noise. Such robustness of the system against external noise may be beneficial for some applications: for example, for communications with multistable systems or for designing noise-insensitive detectors.

Cooperative luminescence and absorption in Ytterbium-doped silica fiber and the fiber nonlinear transmission coefficient at lambda=980 nm with a regard to the Ytterbium ion-pairs' effect.

An experimental and theoretical investigation of the nonlinear transmission coefficient in a set of Ytterbium-doped silica fibers (YFs) with various concentrations of Yb(3+) ions at continuous-wave 980-nm pumping is reported. An analysis of the obtained experimental data shows that YF transmission coefficient is notably affected by the presence of Yb(3+) - Yb(3+) ion-pairs in the fibers, especially in heavily-doped ones. The last fact is confirmed by the study of the cooperative luminescence and absorption effects in the fibers, where a detailed inspection of their dependence on Yb3+ concentration is presented. The pairs' effect is shown to seriously modify both the nonlinear character of YF transmission coefficient at lambda = 980 nm and Yb(3+) excited-state relaxation. A modeling of the experimental data is performed, which allows to find the coefficients addressing the pairs' effect in each of YFs under study and, as a result, to fit the experimentally measured dependences of YF transmission coefficient on pump power, fiber length, and Yb(3+) concentration.

Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings.

In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.

Cooperative luminescence and absorption in Ytterbium-doped silica fiber and the fiber nonlinear transmission coefficient at lambda = 980 nm with a regard to the Ytterbium ion-pairs' effect: Reply.

We reply to the comment [R. Paschotta and A.C. Tropper, Opt. Express, to be published (2006)] on our recent work reporting a study of the cooperative absorption and emission in heavily-doped Ytterbium silica fibers and mechanisms of the fiber nonlinear transmission coefficient reduction due to the Ytterbium ion-pairs' effect [A.V. Kir'yanov et al., Opt. Express, 14 (9), 3981 (2006)]. We provide some additional evidences for that our work hypotheses and conclusions.