Pavel Honzatko

Long-period fiber grating as wavelength selective element in double-clad Yb-doped fiber-ring lasers

Cladding-pumped ytterbium-doped fiber lasers belong presently among the most attractive high-power laser sources for wavelengths around 1060 nm. While the most typical configuration of the fiber laser cavity is linear Fabry-Perot arrangement with fiber Bragg gratings (FBGs), for some applications the ring cavity is preferable as it offers higher stability when unidirectional operation is enforced with fiber optic isolator [1]. Indeed, Yb doped fiber lasers are prone to the so-called sustained self pulsing that in the case of highly Yb-doped fiber (YDF) may lead to relatively stable self-Q-switched operation [2]. Occurrence of this phenomenon complicates investigation of laser configurations that use other Q-switching mechanism possibly allowing for more stable operation, other repetition rate and peak power, etc

Twin-core fiber design and preparation for easy splicing

Several methods of preparing twin-core fibers (TCFs) that can be easily spliced to standard single-core single-mode fiber are proposed. Unlike the conventional TCF preparation methods that are used to fabricate a TCF with both cores placed symmetrically with respect to the fiber axis, these methods result in twin-core fibers that have one core in the fiber center. Experimental results obtained with the TCF fabricated by using one of the designs are presented.

All-fiber Ho-doped mode-locked oscillator based on a graphene saturable absorber

In this Letter, we demonstrate a graphene mode-locked, all-fiber Ho-doped fiber laser generating 1.3 nJ energy pulses directly from the oscillator. The graphene used as a saturable absorber was obtained via chemical vapor deposition on copper substrate and immersed in a poly(methyl methacrylate) support. The laser generated ultrashort soliton pulses at 2080 nm with bandwidth up to 6.1 nm. The influence of the output coupling ratio and the SA modulation depth on the mode-locking performance was also investigated.

Effects of polarization dependent gain and dynamic birefringence of the SOA on the performance of the ultrafast nonlinear interferometer gate.

The model of ultrafast nonlinear interferometer gate accounting for the polarization dependent gain and dynamic birefringence has been developed. It is shown that these effects can lead to appearance of the satellite pulses and limit the achievable extinction ratio. The effect of dynamic birefringence can be completely eliminated by proper adjustment of SOA axes but it can strongly impair the performance of the gate when the axes are misaligned. The switching window should not be set to half of a bit-period to avoid interference of the satellites of neighbor pulses.

Generation of high-repetition-rate pulse trains in a fiber laser through a twin-core fiber

We demonstrate the application of a twin-core fiber comb filter to the generation of high repetition rate pulse trains in fiber lasers. We have found experimentally that passive mode locking of the fiber laser can be established due to concurrent effects of a nearly periodic transmission function of the twin-core fiber filter and of the modulational instability. The period of the generated pulse train is determined by the intermodal dispersion of the twin-core fiber inserted into the fiber laser cavity. A repetition rate as high as 206 GHz was achieved. The width of the generated pulses was 2.7 ps.

Coherently combined power of 20 W at 2000 nm from a pair of thulium-doped fiber lasers

We experimentally demonstrated coherent beam combining of a pair of thulium-doped fiber lasers using an all-fiber Fox‐Smith resonator. We built two thulium-doped fiber lasers from PM fibers and pumped them at 793 nm. Each laser provided a power of more than 10 W at a wavelength of 2000 nm with a slope efficiency of more than 0.5. Then a compound Fox‐Smith resonator was created using the PM coupler. The obtained laser power was more than 20 W due to a constructive interference at the output of the laser, while the slope efficiency decreased to a value of 0.35. A stable CW output signal was achieved despite the fact that the individually operated lasers had the tendency to self-pulsate. (Some figures may appear in colour only in the online journal)

Channel addition-removal response in all-optical gain-clamped lumped Raman fiber amplifier

Application of all-optical gain-clamped (AOGC) lumped Raman fiber amplifier (RFA) for protection of surviving channels in multiwavelength networks is investigated experimentally and theoretically. Channel addition-removal was simulated by transmitting signals of two lasers through a counterdirectionally pumped RFA consisting of 16 km of dispersion compensating fiber. Light of one of the lasers was square-wave modulated at 500 Hz; power fluctuations of the other laser caused by cross-gain modulation of the RFA were monitored at the output of the amplifier with a digital oscilloscope. An all-optical feedback loop was implemented in the form of a ring laser. Theoretical analysis of the AOGC lumped RFA is based on numerical solution of coupled propagation equations for forward and backward-propagating pumps, signals, and spectral components of amplified spontaneous emission powers.

Self-swept holmium fiber laser near 2100 nm

Self-sweeping of laser wavelength corresponding to holmium emission near 2100 nm is reported. The sweeping occurred in ~4 nm interval with rate ~0.7 nm/s from longer towards shorter wavelengths. Origins of the selection of the sweeping direction are discussed. The laser wavelength drift with time was registered by Fourier transform infrared spectrometer. To our knowledge it is the first observation of self-swept fiber laser beyond 2000 nm.

Enhanced pump absorption efficiency in coiled and twisted double-clad thulium-doped fibers.

Results of the first experimental demonstration of the recently proposed technique for improvement of the pump absorption in double-clad fibers by their simultaneous coiling and twisting are reported. The peak absorption (14 dB) of 3-m long hexagonal thulium-doped fiber was increased by 8 dB by its simultaneous coiling and twisting. Explanation of the effect is given by numerical modelling of the pump absorption in hexagonal and panda-type double-clad fibers. Improvement of fiber laser performance was also proved. The slope efficiency increased from 19.6% of the straight fiber to 23.9% of the coiled only fiber and 29.4% of the simultaneously coiled and twisted fiber.

10 Gb/s and 40 Gb/s Multi-Wavelength Conversion Based on Nonlinear Effects in HNLF

We present experimental results and numerical simulations of multi-wavelength conversion of 10 Gb/s NRZ signals based on 2-pumps four-wave mixing, 10 Gb/s and 40 Gb/s RZ signals derived from supercontinuum (SC) generated in highly nonlinear fibre (HNLF). High quality SC with bandwidth exceeding 50 nm was generated when the HNLF was pumped with 25 dBm average power. Sliced SC can be used as a source for all-optical multicasting