High-efficiency second-harmonic generation in doubly-resonant χ(²) microring resonators.

By directly simulating Maxwell's equations via the finite-difference time-domain (FDTD) method, we numerically demonstrate the possibility of achieving high-efficiency second harmonic generation (SHG) in a structure consisting of a microscale doubly-resonant ring resonator side-coupled to two adjacent waveguides. We find that ≳ 94% conversion efficiency can be attained at telecom wavelengths, for incident powers in the milliwatts, and for reasonably large bandwidths (Q ∼ 1000s). We demonstrate that in this high efficiency regime, the system also exhibits limit-cycle or bistable behavior for light incident above a threshold power. Our numerical results agree to within a few percent with the predictions of a simple but rigorous coupled-mode theory framework.

Optical waveguides in TiO2 formed by He ion implantation.

We report on the formation and the optical properties of the planar and ridge optical waveguides in rutile TiO2 crystal by He+ ion implantation combined with micro-fabrication technologies. Planar optical waveguides in TiO2 are fabricated by high-energy (2.8 MeV) He+-ion implantation with a dose of 3 × 10¹6 ions/cm² and triple low energies (450, 500, 550) keV He+-ion implantation with all fluences of 2 × 10¹6 ions/cm² at room temperature. The guided modes were measured by a modal 2010 prism coupler at wavelength of 1539 nm. There are damage profiles in ion-implanted waveguides by Rutherford backscattering (RBS)/channeling measurements. The refractive-index profile of the 2.8 MeV He+-implanted waveguide was analyzed based on RCM (Reflected Calculation Method). Also ridge waveguides were fabricated by femtosecond laser ablation on 2.8 MeV ion implanted planar waveguide and Ar ion beam etching on the basis of triple keV ion implanted planar waveguide, separately. The loss of the ridge waveguide was estimated. The measured near-field intensity distributions of the planar and ridge modes are all shown.