Rim Cherif

Highly nonlinear As 2 Se 3 -based chalcogenide photonic crystal fiber for midinfrared supercontinuum generation

We propose a real, highly nonlinear, As 2 Se 3 -based chalcogenide photonic crystal fiber in which a supercontinuum (SC) spanning more than 2 octaves is generated at =2.8 µm in the femtosecond regime. The designed PCF is characterized for ultrabroadband mid-infrared SC generation in only few millimetres of fiber length. A full modal analysis of the optical properties of the fiber is presented in terms of the effective area, the nonlinearity coefficient, and the chromatic dispersion. A second-order Sellmeier approximation is proposed to estimate the variation of the refractive index of the As 2 Se 3 material as a function of wavelength. The numerical study shows that a SC spanning from 1.9 to 4 µm can be generated in the chalcogenide PCF with an air-hole diameter of 1.26 µm and a pitch of 1.77 µm. We examine the interplay of the nonlinear effects that lead to the construction of the SC as a function of the input power and the fiber length. We find that the dynamics behind the SC generation is mainly ruled by the effects of self phase modulation and stimulated Raman scattering. The intrinsic properties of the chalcogenide glasses and the microstructure provide enhanced optical properties and offer numerous applications in the infrared field.

Soliton-self compression in highly nonlinear chalcogenide photonic nanowires with ultralow pulse energy.

We design As2Se3 and As2S3 chalcogenide photonic nanowires to optimize the soliton self-compression with short distances and ultralow input pulse energy. We numerically demonstrate the generation of single optical cycle in an As2S3 photonic nanowire: a 5.07 fs compressed pulse is obtained starting from 250 fs input pulse with 50 pJ in 0.84 mm-long As2S3 nanowire. Taking into account the high two photon absorption (TPA) coefficient in the As2Se3 glass, accurate modeling shows the compression of 250 fs down to 25.4 fs in 2.1 mm-long nanowire and with 10 pJ input pulse energy.

Full modal analysis of the Brillouin gain spectrum of an optical fiber

We present a numerical study of stimulated Brillouin scattering in optical fibers based on a full modal analysis of the acoustic and optical properties. The computation of each acoustic mode supported by the fiber structure allows us a deep and detailed investigation of the characteristics of the Brillouin gain spectrum. We focus our attention on optical fibers acting as acoustic antiwaveguides where the biggest contribution to the Brillouin response often comes from very high-order modes but it is sometimes overlooked because of computational issues. Our analysis clearly highlights their role and their dependence on the physical and geometrical structure of the fiber.

Design and analysis of equiangular spiral photonic crystal fiber for mid-infrared supercontinuum generation

A design of equiangular spiral photonic crystal fiber (PCF) in As2Se3 chalcogenide glass is reported for mid-infrared supercontinuum generation. Supercontinuum covering the 1.2–15 μm molecular fingerprint region is achieved using only 8 mm long designed PCF pumped with 50 fs laser pulses of 500 W peak power. The structural parameters have been tailored for all-normal dispersion characteristic. Proposed structure has high nonlinearity (γ = 12474 W−1 km−1) at 3.5 μm with very low and flat dispersion −2.9 [ps/(nm × km)]. Supercontinuum with such broadening and high coherence degree is applicable for mid-infrared spectroscopy, gas sensing, early cancer diagnostics and free space communication.

Impact of small geometrical imperfections on chromatic dispersion and birefringence in photonic crystal fibers

Slight geometrical imperfections that can occur during the fabrication process, in the lattice of index-guiding photonic crystal fibers (PCF), are evaluated to determine the sensitivity of the chromatic dispersion and the birefringence to these defects. Furthermore, the impact of fluctuations in the lattice profile of a real photonic crystal fiber on its propagation characteristics is pointed out. Numerical and experimental analyses show that chromatic dispersion of a large core PCF is more robust to the geometrical imperfections, while its birefringence reveals more sensitivity to these defects. This analysis is performed using the finite element method, which assures high solution accuracy.

Super-flat coherent supercontinuum source in As 38.8 Se 61.2 chalcogenide photonic crystal fiber with all-normal dispersion engineering at a very low input energy

We numerically report super-flat coherent mid-infrared supercontinuum (MIR-SC) generation in a chalcogenide As38.8Se61.2 photonic crystal fiber (PCF). The dispersion and nonlinear parameters of As38.8Se61.2 chalcogenide PCFs by varying the diameter of the air holes are engineered to obtain all-normal dispersion (ANDi) with high nonlinearities. We show that launching low-energy 50 fs optical pulses with 0.88 kW peak power (corresponding to pulse energy of 0.05 nJ) at a central wavelength of 3.7 μm into a 5 cm long ANDi-PCF generates a flat-top coherent MIR-SC spanning from 2900 to 4575 nm with a high spectral flatness of 3 dB. This ultra-wide and flattened spectrum has excellent stability and coherence properties that can be used for MIR applications such as medical diagnosis of diseases, atmospheric pollution monitoring, and drug detection.

Rigorous Optical Modeling of Elliptical Photonic Nanowires

We analyze the optical properties including chromatic dispersion, birefringence, and nonlinear coefficient dependence on the ellipticity of photonic nanowires. We propose a linear approximation to determine the equivalent-circular photonic nanowire exhibiting similar optical characteristics with the elliptical nanowire. We find strong birefringence up to the order of 10-2 in elliptical photonic nanowires that could be very attractive for optical fiber sensors and stable combs. We also investigate the effect of the ellipticity on the supercontinuum generation which is found to be detrimental to the spectral broadening.

Stimulated Brillouin Scattering of Higher-Order Acoustic Modes in Four-Core Tellurite Microstructured Optical Fiber

In this paper, we present a new way of enhancing the Stimulated Brillouin scattering (SBS) of higher-order acoustic modes in the four-core tellurite (TZLB) microstructured optical fiber (MOF). The Brillouin gain spectrum (BGS) in the MOF is calculated based on a full model analysis of the optical and acoustic properties. In contradict to the single-core tellurite MOF, BGS of the four-core tellurite MOF has three peaks, which are contributed by the fundamental and higher-order acoustic modes. The higher-order acoustic modes can enhance the interaction with the optical mode and provide a strong contribution to the Brillouin response.

Low-energy single-optical-cycle soliton self-compression in air-silica nanowires

We investigated and optimized the process of soliton self-compression in few millimeters-long air-silica nanowires. A 100 fs prechirped input pulse was compressed to a 1.4 fs pulse by pumping at very low energy of 2.5 nJ an air-silica nanowire. More than one octave spanning coherent broadband supercontinuum extending from 260 to 1800 nm was

Maximizing the bandwidth of coherent, mid-IR supercontinuum using highly nonlinear aperiodic nanofibers

We describe in detail a new procedure of maximizing the bandwidth of mid-infrared (mid-IR) supercontinuum (SC) in highly nonlinear microstructured As2Se3 and tellurite aperiodic nanofibers. By introducing aperiodic rings of first and secondary air holes into the cross-sections of our microstructured fiber designs, we achieve flattened and all-normal dispersion profiles over much broader bandwidths than would be possible with simple periodic designs. These fiber designs are optimized for efficient, broadband, and coherent SC generation in the mid-IR spectral region. Numerical simulations show that these designs enable the generation of a SC spanning over 2290 nm extending from 1140 to 3430 nm in 8 cm length of tellurite nanofiber with input energy of E = 200 pJ and a SC bandwidth of over 4700 nm extending from 1795 to 6525 nm generated in only 8 mm-length of As2Se3-based nanofiber with input energy as low as E = 100 pJ. This work provides a new type of broadband mid-IR SC source with flat spectral shape as well as excellent coherence and temporal properties by using aperiodic nanofibers with all-normal dispersion suitable for applications in ultrafast science, metrology, coherent control, non-destructive testing, spectroscopy, and optical coherence tomography in the mid-IR region.