Silicon Nitride for Integrated Photonics CNF

We demonstrated micron scale silicon nitride photonic structures. We have measured lowest propagation losses (~ 0.1 dB/cm at 1550 nm) in highest confinement waveguides (900 × 750 nm) reported to date. We fabricated ring cavities with optical quality factor over 3,000,000 [1]. With a silicon oxide cladded cavity, we observed optical parametric oscillations (1243-2043 nm), a first for a fully integrated resonator [2]. We also observed generation of second and third harmonics from 1550 nm wavelength in our integrated devices (also not previously reported). In our air clad opto-mechanical cavities we induced a mechanical shift over 10 nm, purely from an optical force, another first for on chip devices. Summary of Research: Stoichiometric silicon nitride (Si3N4) is a dielectric commonly used in complimentary metal oxide semiconductor technology for insulating transistor gates. The high optical index contrast with silicon oxide and low absorption over the near ultraviolet to the near infrared makes SiN a versatile light guiding material for on chip integration. Low loss guiding has been demonstrated in low confinement waveguides in the telecom range [3] and high Q cavities have been shown in the visible spectrum [4]. We fabricated thick (750 nm) waveguides, with low sidewall roughness and low impurity content. We demonstrate highest confinement guiding and highest Q cavities (Figure 1) in the telecom range. These cavities support very high field intensities (over 100 TW/m2) without damage with only 1W of input laser power. Low pressure chemical vapor deposition of silicon nitride produces high quality films limited in thickness by intrinsic tensile stress (250 nm) [5]. We developed a process with high deposition temperature (800°C) and low pressure (0.02 mTorr) and thermal cycling to allow thick stoichiometric films (up to 750 nm) to be deposited. With further high temperature annealing, optimized resist (MaN 2403) reflow process, electron beam lithography and inductive coupled plasma etching, we were able to make waveguides with very smooth sidewalls and low oxygen and hydrogen impurities. This led to low absorption and low scattering losses in our nitride photonic devices, as well as strong field localization in the high index material. In order to accurately distinguish between scattering and absorption losses, we introduce carefully engineered defects in our photonic cavities and used Borselli’s method [6] to extract linear absorption and scattering Figure 1: Silicon nitride 36 μm diameter ring coupled to a waveguide on silicon dioxide.