On-chip Kerr frequency combs have attracted significant attention because of their compact footprint and numerous applications. While many integrated material systems are being investigated for generating the on-chip Kerr frequency combs, so far only silica devices have achieved quality factors above 100 million, which is important for decreasing the threshold and power consumption of the system. However, as an intrinsic property of silica, the hydroxyl groups present on the surface of the devices will attract water molecules in the air, which decreases the quality factor of the devices. To maintain the performance of the frequency combs, methods like putting the devices in nitrogen purged boxes or building covers for the system are proposed, which would largely increase the complexity of the system. Here we studied another material system, silicon oxynitride microtoroids, whose quality factors can achieve and stay constant at more than 100 million because of the lack of the hydroxyl groups on the surface. Kerr frequency combs are generated from the SiOxNy microtoroids with normal dispersion with avoided mode crossing. Thresholds as low as 280 μW are achieved as a result of the high quality factor. The comb spectrum remains the same for the same pump power over the nine day period after fabrication, which indicates that the performance of the frequency combs remains constant despite the silicon oxynitride devices being stored in ambient atmosphere without any special treatment the whole time.
A novel method of preparing magnetic ink belonging to the class of ferrofluids which contains magnetic particles with a polar surface-active agent is disclosed. The magnetic material belongs to the group known as magnetite (Fe3O4), typically to those with γ-Fe2O3 and their likes. Ni-Zn ferrite and Mn ferrite inks were prepared using this method. The inks have a PH value and total dissolved solute of about 6.3, 3.78 mS and 5.9, 4.2 mS respectively, and a viscosity of about 7 cPa, 7.4 cPa respectively. The saturation magnetization of Mn ferrite ink at 300K was 62 emu/cm3. This lower value of the saturation magnetization of Mn ferrite compared to the bulk is because of the shell-core structure of the surfactant coated ferrite particles. The inks were used to prepare various thicknesses ranging from 0.5um to 20um of both Ni-Zn ferrite and Mn ferrite thin films. The surface morphology of the thin film was observed using Atomic Force Microscopy (AFM), showing a compact, dense and relatively smooth film. The microstrip transmission line permeameter approach was used to extract the permittivity and permeability of the thin film samples within the frequency range of 10MHz-1GHz. A relative permeability of 2 was measured. The developed ink and thin film are promising for future magneto-optical applications.
Recent advances in optical materials have enabled the development of a wide range of integrated photonic devices from high speed modulators to frequency combs. With low optical loss over a wide wavelength range and environmental stability in ambient environments for several weeks, silicon oxynitride (SiOxNy) shows potential in many of these applications. However, unlike many classic optical materials, the thermo-optic response (dn/dT) in both the visible and near-IR is poorly characterized, limiting researcher’s ability to accurately model device performance. Here, we leverage the intrinsic thermal response of resonant cavities to measure the dn/dT of SiOxNy with a 12.7:1 and 4:1 oxygen to nitrogen ratio based on EDX measurements. The thermo-optic coefficient is measured in the visible and near-IR and compared with SiO2. The refractive indices of the silicon oxynitride films were also measured using spectroscopic ellipsometry. Based on an analysis of the O:N ratio and a comparison with both SiO2 and Si3N4, an expression for the dependence of the dn/dT on the stoichiometric ratio is developed.
We present a new structure with nitrogen incorporation in barrier and new material with antimony for developing post-annealed long wavelength material. This new structure and new material result in a shift of the post-annealed luminescence out to 1.6 um. The new structure, nitrogen in barrier, reduces the blue-shift of the emission spectrum by suppressing nitrogen out-diffusion from the quantum wells (QWs) and decreasing carrier confinement between barriers and QWs. GaNAs or GaNAsSb barriers can also reduce the overall strain of the active region because the high indium mole fraction QWs are compressively strained and the barriers with nitrogen are tensely strained. By adding small amount of antimony, we were able to incorporate up to 46% indium. We will present results of high efficiency long wavelength multiple QW GaInNAs ridge-waveguide laser diodes using GaNAs barriers. We will also show GaInNAsSb QWs with GaNAsSb barriers ridge waveguide laser emitting at 1.465 um. We have observed photoluminescence up to 1.6 um with different indium and antimony concentrations. Our GaInNAs and GaInNAsSb ridge waveguide laser diodes have broad emission spectra covering 1.27 um to 1.465 um with pulsed operation up to 90 degree(s)C. The maximum output power at room temperature, under pulsed operation was 350 mW with a differential efficiency of 0.67 W/A.
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