Davide Grassani

Characterization and modeling of microstructured chalcogenide fibers for efficient mid-infrared wavelength conversion

We experimentally demonstrate wavelength conversion in the 2 µm region by four-wave mixing in an AsSe and a GeAsSe chalcogenide photonic crystal fibers. A maximum conversion efficiency of -25.4 dB is measured for 112 mW of coupled continuous wave pump in a 27 cm long fiber. We estimate the dispersion parameters and the nonlinear refractive indexes of the chalcogenide PCFs, establishing a good agreement with the values expected from simulations. The different fiber geometries and glass compositions are compared in terms of performance, showing that GeAsSe is a more suited candidate for nonlinear optics at 2 µm. Building from the fitted parameters we then propose a new tapered GeAsSe PCF geometry to tailor the waveguide dispersion and lower the zero dispersion wavelength (ZDW) closer to the 2 µm pump wavelength. Numerical simulations shows that the new design allows both an increased conversion efficiency and bandwidth, and the generation of idler waves further in the mid-IR regions, by tuning the pump wavelength in the vicinity of the fiber ZDW.

Mid-infrared frequency comb via coherent dispersive wave generation in silicon nitride nanophotonic waveguides

Clemens Herkommer, 2, ∗ Adrien Billat, ∗ Hairun Guo, ∗ Davide Grassani, Chuankun Zhang, 4 Martin H. P. Pfeiffer, Camille-Sophie Brès, † and Tobias J. Kippenberg ‡ École Polytechnique Fédérale de Lausanne (EPFL), LPQM, CH-1015 Lausanne, Switzerland Technische Universität München (TUM), Physik-Department, D-80333 München, Germany École Polytechnique Fédérale de Lausanne (EPFL), PHOSL, CH-1015 Lausanne, Switzerland Tsinghua University, Beijing 100084, China

A chip-based silicon nitride platform for mid-infrared nonlinear photonics

We developed a chip-based silicon nitride platform with thick waveguides (> 2 μm) that overcomes the usual fabrication limitation. We demonstrate both microresonator frequency comb generation at 2.5 μm and supercontinuum generation extending beyond 4.0 μm in this platform.

Recent advances on nonlinear optics in Silicon Nitride waveguides

Nonlinear phenomena based on the material 2nd or 3rd order nonlinear susceptibility tensor χ(2) and χ(3), respectively, offer potential in a wide variety of applications by exploiting wave-mixing capabilities. The integration of these nonlinear effects at the chip scale represents the best path towards portable, compact and low power optical signal processing devices. A significant body of work has been done recently in this direction, in particular focusing on CMOS-compatible platforms. While many nonlinear effects have been demonstrated in Silicon, Silicon Nitride has recently sparked significant interest. Owing to a larger band gap, wide transparency window and low loss, the potential of SiN waveguides for linear and nonlinear optics is now well established. In this paper, we report recent results on nonlinear processes in SiN waveguides. In particular we will cover generation of an extremely broad supercontinuum extending 400 THz from the visible to 3.6 µm pumped by a turnkey telecom wavelength pulsed source. We will also report on a tunable pulse source based on dispersive wave generation in an engineered thick waveguide. Finally, we will show that SiN offers some interesting potential for χ(2) based nonlinear effects, an important step towards integrating second order nonlinearity on chip.

All-optically induced quasi phase matching in SiN waveguides for second harmonic generation enhancement

We report more than 30dB second harmonic generation enhancement in SiN waveguide by all-optical writing of a persistent χ(2) grating. Phase matching peaks are observed for different writing wavelengths.

Large second harmonic generation enhancement in Si 3 N 4 waveguides by all-optically induced quasi-phase-matching

Efficient second harmonic generation in integrated platforms is usually achieved by resonant structures, intermodal phase-matching or quasi-phase matching by periodically poling ferroelectric waveguides. However, in all these structures, it is impossible to reconfigure the phase-matching condition in an all-optical way. Here, we demonstrate that a Watt-level laser causes a periodic modification of the second-order susceptibility in a silicon nitride waveguide, allowing for quasi-phase-matching between the pump and second harmonic modes for arbitrary wavelengths inside the erbium band. The grating is long-term inscribed, and leads to a second harmonic generation enhancement of more than 30 dB. We estimate a χ(2) on the order of 0.3 pm/V, with a maximum conversion efficiency of 0.05% W−1. We explain the observed phenomenon with the coherent photogalvanic effect model, which correctly agrees with the retrieved experimental parameters.Phase-matching and quasi-phase-matching in periodically poled ferroelectrics ensure efficient harmonic generation, but only statically. Here, Billat et al. demonstrate all-optically reconfigurable second harmonic generation by inscribing a stable grating in CMOS-compatible nonlinear waveguides.

Generation of high-brightness spectrally flat supercontinuum in 1900-2450 nm range inside a small core thulium-doped fiber amplifier

We demonstrate the generation of high-brightness supercontinuum inside thulium-doped fiber amplifier in 1950-2450nm spectral range with 1.7W output power and 32% slope efficiency, seeded by tunable 2000nm mode-locked laser and assisted by 3H4-3H5/3F4-3H6 thulium transitions