The above-threshold operation of a Fabry-Perot laser with a nonlinear PT (parity time) mirror is investigated. For the first time, the analysis accounts for gain saturation of an active medium as well as gain and loss saturation effects in the PT mirror. The obtained laser output intensity characteristics have been demonstrated as a function of various PT mirror parameters such as: the ratio of the PT structure period to laser operating wavelength, number of PT mirror primitive cells, and gain and loss saturation intensities of the PT mirror gain and loss layers. Two functional configurations of the laser have been considered: laser operating as a discrete device, and as a component of an integrated circuit. It has been shown that, in general, the laser operation depends on the PT mirror orientation with respect to the active medium of the laser. Moreover, when the laser radiation is outcoupled through the PT mirror to the free space, bistable operation is possible, when losses of the mirror’s loss layer saturate faster than gain of the gain layer. Furthermore, for a given saturation intensity of the mirror loss layers, the increase of the saturation intensity of the mirror gain layers causes increasing output intensity, i.e., the PT mirror additionally amplifies the laser output signal.

We have numerically studied different designs of technologically feasible microstructured fibers with a germanium-doped core in order to obtain normal dispersion reaching possibly far in the mid infrared. Hexagonal, Kagome and the combination of both geometries were numerically examined with respect to different constructional parameters like pitch distance, filling factor of air holes, number of layers surrounding the core, and level of germanium doping in the core. Our analysis showed that the broadest range of normal dispersion reaching 2.81 μm, while keeping an effective mode area smaller than 30 μm², was achieved for a hexagonal lattice and a 40 mol% GeO₂ doped core. The proposed fibers designs can be used in generation of a normal dispersion supercontinuum reaching the mid-IR region.

All normal dispersion (ANDi) and highly nonlinear chalcogenide glass photonic crystal fiber (PCF) is proposed and numerically investigated for a broad, coherent and ultra-flat mid-infrared supercontinuum generation. The proposed PCF consists of a solid core made of Ga₈Sb₃₂S₆₀ glass surrounded by seven rings of air holes arranged in a triangular lattice. We show by employing the finite difference frequency domain (FDFD) method that the Ga₈Sb₃₂S₆₀ PCF dispersion properties can be engineered by carefully adjusting the air holes diameter in the cladding region and ANDi regime is achieved over the entire range of wavelengths with a zero chromatic dispersion around 4.5 μm. Moreover, we demonstrate that injecting 50 fs width and 20 kW peak power laser pulses (corresponding to a pulse energy of 1.06 nJ) at a pump wavelength of 4.5 μm into a 1 cm long ANDi Ga₈Sb₃₂S₆₀ PCF generates a broad, flat-top and perfectly coherent SC spectrum extending from 1.65 μm to 9.24 μm at the 20 dB spectral flatness. These results make the proposed Ga₈Sb₃₂S₆₀ PCF an excellent candidate for various important mid-infrared region applications including mid-infrared spectroscopy, medical imaging, optical coherence tomography and materials characterization.

Jerzy Kołodziejczak, who died on August 1st, 2022 at the age of 87, was a distinguished Polish physicist and a visionary science manager. He graduated at the Physics Faculty of Warsaw University in 1958, received PhD in 1961, habilitation in 1963, and became Professor in 1968. From the beginning of his brilliant and rapid scientific career he worked at the newly created Polish Academy of Sciences Institute of Physics in Warsaw, of which he became director in 1970 (for 12 years) and then the creator of the new institute site and its structure of today. His major theoretical and experimental contributions to science of semiconductors followed the observation that understanding of galvanomagnetic and optical phenomena of medium and narrow-gap semiconductors cannot be done without proper account of the nonparabolicity of their bands. He then formulated general theory of these properties, what brought him not only international acclaim, but also several highest recognitions in Poland (first Maria Skłodowska-Curie Scientific Prize of the Polish Academy of Sciences (PAS) in 1967, the State Award of the first class 1978, Polonia Restituta Commander Order with the Star 2005) and membership to the Polish Academy of Sciences (Corresponding Member 1973 and Ordinary Member in 1991). He served several highest offices in the Academy up to the Academy Presidency in 2002. In 1983 was elected a Fellow of the Warsaw scientific Society. He published well over 100 scientific papers and was a Ph Thesis advisor of his 15 associates.