I. Bugar

Linear and nonlinear properties of multicomponent glass photonic crystal fibers

Processes resulting in supercontinuum generation in multicomponent glass photonic crystal fibers are reviewed in this paper. Multicomponent glass photonic crystal fibers are shown to have a broad transmission range, extending up to 4.5 μm in selected cases. Pumping with a 1240-nm femtosecond pulse at very low sub-nJ energies resulted in soliton formation and dispersive wave generation in a multicomponent PCF sample having a double-core square-lattice structure. These processes were described using a phase-matching model derived from the simulated dispersive properties of the fiber. Third-harmonic generation was observed in the radiation modes of a different cobweb sample with the simultaneous formation of a soliton in the NIR.

Nonlinear microstructured fibers for supercontinuum generation

Microstructured fibers with small core are successfully used as a medium for supercontinuum generation. Since light can be confined in a small core a high density of energy in the fiber is obtained and stimulate nonlinear effects. Use of lead multicomponent glass allows increasing nonlinear refractive index in the fiber and shape dispersion properties of the fiber. In this case effective broadening of the spectrum can be obtained with less then 1 m of the fiber. In this paper we present properties of photonic crystal fibers optimized for supercontinuum generation.

Soliton-based ultrafast multi-wavelength nonlinear switching in dual-core photonic crystal fibre

Systematic experimental study of ultrafast multi-wavelength all-optical switching performance in a dual-core photonic crystal fibre is presented. The focus is on nonlinearly induced switching between the two output ports at non-excitation wavelengths, which are generated during nonlinear propagation of femtosecond pulses in the anomalous dispersion region of a dual-core photonic crystal fibre made of multicomponent glass. Spatial and spectral characteristics of the fibre output radiation were measured separately for both fibre cores under various polarization and intensity conditions upon selective, individual excitation of each fibre core. Polarization-controlled nonlinear switching performance at multiple non-excitation wavelengths was demonstrated in the long-wavelength optical communication bands and beyond. Depending on the input pulse polarization, narrowband switching operation at 1560 nm and 1730 nm takes place with double core extinction ratio contrasts of 9 dB and 14.5 dB, respectively. Moreover, our approach allows switching with simultaneous wavelength shift from 1650 to 1775 nm with extinction ratio contrast larger than 18 dB. In addition, non-reciprocal behaviour of the soliton fission process under different fibre core excitations was observed and its effect on the multi-wavelength nonlinear switching performance was explained, taking into account the slight dual-core structure asymmetry. The obtained results represent ultrafast all-optical switching with an extended dimension of wavelength shift, controllable with both the input radiation intensity and the polarization by simple propagation along a 14 mm long fibre.

Nonlinear performance of asymmetric coupler based on dual-core photonic crystal fiber: Towards sub-nanojoule solitonic ultrafast all-optical switching

We demonstrate ultrafast soliton-based nonlinear balancing of dual-core asymmetry in highly nonlinear photonic crystal fiber at sub-nanojoule pulse energy level. The effect of fiber asymmetry was studied experimentally by selective excitation and monitoring of individual fiber cores at different wavelengths between 1500 nm and 1800 nm. Higher energy transfer rate to non-excited core was observed in the case of fast core excitation due to nonlinear asymmetry balancing of temporal solitons, which was confirmed by the dedicated numerical simulations based on the coupled generalized nonlinear Schrodinger equations. Moreover, the simulation results correspond qualitatively with the experimentally acquired dependences of the output dual-core extinction Ratio on excitation energy and wavelength. In the case of 1800 nm fast core excitation, narrow band spectral intensity switching between the output channels was registered with contrast of 23 dB. The switching was achieved by the change of the excitation pulse energy in sub-nanojoule region. The performed detailed analysis of the nonlinear balancing of dual-core asymmetry in solitonic propagation regime opens new perspectives for the development of ultrafast nonlinear all-optical switching devices.

Higher-order mode investigations by intermodal interference in a dual-core photonic crystal fiber

This article presents an investigation of the linear optical properties of a dual-core photonic crystal fiber with a square lattice made of a multicomponent glass in a second communication window. An experimental method based on intermodal interference was used to determine the effective refractive indices of higher-order modes, with knowledge of the fundamental mode dispersion. The effective refractive indices were also determined by an FDTD-based simulation and the obtained values provided a good agreement in comparison to the experimental results. The obtained results help to clarify the nonlinear spectral transformation processes observed in the same fiber at propagation in the higher-order modes.

Ultrafast multi-wavelength switch based on dynamics of spectrally-shifted solitons in a dual‑core photonic crystal fiber.

Nonlinear propagation of ultrafast near infrared pulses in anomalous dispersion region of dual-core photonic crystal fiber was studied. Polarization tunable soliton-based nonlinear switching at multiple non-excitation wavelengths was demonstrated experimentally for fiber excitation by 100 fs pulses at 1650 nm. The highest-contrast switching was obtained with the fiber length of just 14 mm, which is significantly shorter compared to the conventional non-solitonic in-fiber switching based on nonlinear optical loop mirror. Advanced numerical simulations show good agreement with the experimental results, suggesting that the underlying dual-core soliton fission process supports nonlinear optical switching and simultaneous pulse compression to few-cycle durations at the level of 20 fs.

Dual-core microstructure optical fiber as a potential polarization splitter

Polarization splitting performance of a special multi-component glass made dual – core microstructure optical fiber (DC MOF) was investigated in the near infrared region. The output dual-core intensity ratio changes were analyzed behind a rotating polarizer both in spectrally resolved and integrated manner under broadband femtosecond pulse excitation of the fiber in the C-band. The polarization angle dependence of the dual-core intensity ratio exhibited similar non-symmetrical character in the case of both camera and spectrometer registration method. The 70 nm broad femtosecond radiation allowed to set an optimal wavelength, at which the extinction ratio difference between the extreme cases was maximized with significantly higher value than by the spectrally integrated method. Non-proper polarization splitting performance was observed with angle distance different than 90° between the extreme cases for the both orthogonal input polarization directions. Afterwards, optimizing the input polarization angle the angle distance became the proper right-angle, which behavior is interpreted in terms of inhomogenously polarized fundamental supermodes supported also by numerical mode analysis of the investigated DC MOF.

Towards ultrafast sub-nanojoule solitonic nonlinear directional coupler based on soft glass dual-core photonics crystal fibers

We demonstrate narrow band spectral intensity switching in dual-core photonic crystal fibers made of highly nonlinear glass under femtosecond excitation. The fibers expressed dual-core asymmetry, thus the slow and fast fiber cores were unambiguously distinguished according to their dispersion profiles. The asymmetry effect on the dual-core propagation in anomalous dispersion region was studied both experimentally and numerically. The experimental study was carried out using femtosecond laser amplifier system providing tunable pulses in range of 1500 nm - 1800 nm. The obtained results unveiled, that it is possible to improve nonlinearly the coupling between the two waveguides by excitation of the fast fiber core. The results were obtained in regime of high-order soliton propagation and were verified numerically by the coupled generalized nonlinear Schrödinger equations model. The spectral analysis of the radiation transferred to the non-excited core revealed the role of effects such as third order dispersion, soliton compression and spectral dependence of the coupling efficiency. The simulation results provide reasonable agreement with the experimentally observed spectral evolutions in the both fiber cores. Under 1800 nm excitation, narrow band spectral intensity switching was registered with contrast of 23 dB at 10 mm fiber length by changing the excitation pulse energy in sub-nanojoule range.

Diode-pumped mode-locked holmium fiber laser at 2.138 μm

Mode-locked fiber lasers emitting in the wavelength range beyond 2 μm [1] are promising for a number of applications including environmental sensing, material processing, medicine etc. Mode-locked holmium fiber lasers tend to operate below 2.1 μm wavelength. For some applications it is important to shift the laser wavelength further to the infrared. Previous demonstration of a 2107-nm mode-locked Ho-fiber laser used Tm-fiber laser pumping and graphene-based saturable absorber. Here we report the longest-wavelength operation of a mode-locked holmium fiber laser, realized in a compact diode-pumped setup.

Compact Diode-pumped Dispersion-managed SESAM-mode-locked Ho:fiber Laser

We demonstrate for the first time a compact mode-locked holmium fiber laser diode-pumped at 1150 nm. The laser was operated in the dispersion-managed dissipative-soliton regime and provided 3.7 nJ pulse energy at 7.8 MHz PRF