Optimizing the generation of polarization squeezed light in nonlinear optical fibers driven by femtosecond pulses.

Bright squeezed light can be generated in optical fibers utilizing the Kerr effect for ultrashort laser pulses. However, pulse propagation in a fiber is subject to nonconservative effects that deteriorate the squeezing. Here, we analyze two-mode polarization squeezing, which is SU(2)-invariant, robust against technical perturbations, and can be generated in a polarization-maintaining fiber. We perform a rigorous numerical optimization of the process and the pulse parameters using our advanced model of quantum pulse evolution in the fiber that includes various nonconservative effects and real fiber data. Numerical results are consistent with experimental results.

Coherent amplification of high-power laser radiation in multicore fibers from a rectangular array of cores.

The coherent propagation and amplification of high-power laser radiation in a multicore fiber consisting of a square array of weakly bound cores are studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams in such fibers. The analytical results are confirmed by direct numerical simulation of the wave equation. The stability conditions of the out-of-phase mode in the active medium are found.

Coherent propagation and amplification of intense laser pulses in hexagonal multicore fibers.

Propagation and amplification of intense coherent laser pulses in a multicore fiber of 24 weakly coupled cores arranged in the form of seven close-packed hexagons were studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams and temporal soliton solutions in such fibers. Their stability is demonstrated. The analytical results are confirmed by the direct numerical simulation of the wave equation.

Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 µm and 2.3 µm.

Ultrabroadband amplification and two-color CW lasing simultaneously near 1.9 µm and 2.3 µm in a Tm3+-doped tellurite fiber were demonstrated experimentally, for the first time to the best of our knowledge. A low-loss Tm3+-doped core fiber from TeO2-ZnO-La2O3-Na2O glasses stable against crystallization was produced by a special technique, providing a low concentration of hydroxyl groups. Supercontinuum from a highly GeO2 doped silica fiber pumped by an Er fiber laser system was used as a seed for an amplifier. A maximum gain of 30 dB and 7 dB was measured at 1.9 µm and 2.3 µm, respectively. We report detailed experimental and theoretical studies, which are in a very good agreement, of laser amplification and generation in the manufactured fiber with carefully measured and calculated parameters. A quantitatively verified numerical model was used to predict power scalability at 2.3 µm in schemes with optimized parameters at increased pump power. The presented results show that a high-quality tellurite fiber is a promising candidate for developing lasers in the 2.3 µm atmospheric window which are particularly relevant for applications in gas sensing, eye-safe laser radars, breath analysis, remote sensing and stand-off trace gas detection.

Toward a mid-infrared femtosecond laser system with suspended-core tungstate-tellurite glass fibers.

A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 µm range is discussed. This design incorporates conventional fs near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 µm and of DW generation beyond 5 µm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

Widely tunable mid-infrared fiber laser source based on soliton self-frequency shift in microstructured tellurite fiber.

A turnkey fiber laser source generating high-quality pulses with a spectral sech shape and Fourier transform-limited duration of order 100 fs widely tunable in the 1.6-2.65 µm range is presented. It is based on Raman soliton self-frequency shifting in the suspended-core microstructured TeO2-WO3-La2O3 glass fiber pumped by a hybrid Er/Tm fiber system. Detailed experimental and theoretical studies, which are in a very good agreement, of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters are reported. A quantitatively verified numerical model is used to show Raman soliton shift in the range well beyond 3 µm for increased pump energy.

Generating femtosecond optical pulses tunable from 2 to 3 µm with a silica-based all-fiber laser system.

Femtosecond pulses with broad tunability in the range of 2-3 µm are generated in a germanate-glass core silica-glass cladding fiber with a driving pulse at 2 µm produced by an all-fiber laser system consisting of an Er:fiber source at 1.6 µm, a Raman fiber shifter, and a Tm:fiber amplifier. We demonstrate optical pulses with a duration of the order of 100 fs that are the shortest ones reported in the 2.5-3 µm range obtained by fiber laser systems.

Two-color optically synchronized ultrashort pulses from a Tm/Yb-co-doped fiber amplifier.

A method of producing high quality, optically synchronized two-color ultrashort pulses in an active thulium-doped fiber is proposed. We show that sech-shaped femtosecond pulses with essentially different wavelengths can be generated directly from a Tm/Yb-co-doped amplifier: one pulse at about 2 µm and the second pulse with a tunable wavelength up to 2.3 µm, which covers the pump and gain regions of Cr:ZnSe and Cr:ZnS amplifiers. The shortest pulses with durations of 145 fs at 2.25 µm and 125 fs at 2 µm were measured by the FROG (frequency-resolved optical gating) technique.

Generating tunable optical pulses over the ultrabroad range of 1.6-2.5 µm in GeO2-doped silica fibers with an Er:fiber laser source.

We report generation of femtosecond optical pulses tunable in the 1.6-2.5 µm range using GeO2-doped core silica-cladding fibers. Optical solitons with a duration of 80-160 fs have been measured by the FROG technique in the 2-2.3 µm range. To the best of our knowledge, these are the longest wavelength temporally characterized solitons generated in silica-based fibers. We have also demonstrated more than octave-spanning femtosecond supercontinuum generation in the 1.0-2.6 µm range.

All-fiber design of erbium-doped laser system for tunable two-cycle pulse generation.

We report a simple all-fiber design of an Er-doped laser system that is capable of generating widely tunable two-cycle pulses. In particular, 13-fs pulses at a wavelength of 1.7 µm are produced. The mechanism of pulse shortening is identical to the higher-order soliton compression and is supported by modeling based on the slowly evolving wave approximation, which is well suited for down to single-cycle pulse propagation in nonlinear dispersion-shifted fibers.