Fabrication and characterization of high quality factor silicon nitride nanobeam cavities

Si3N4 is an excellent material for applications of nanophotonics at visible wavelengths due to its wide bandgap and moderately large refractive index (n $\approx$ 2.0). We present the fabrication and characterization of Si3N4 photonic crystal nanobeam cavities for coupling to diamond nanocrystals and Nitrogen-Vacancy centers in a cavity QED system. Confocal micro-photoluminescence analysis of the nanobeam cavities demonstrates quality factors up to Q ~ 55,000, which is limited by the resolution of our spectrometer. We also demonstrate coarse tuning of cavity resonances across the 600-700nm range by lithographically scaling the size of fabricated devices. This is an order of magnitude improvement over previous SiNx cavities at this important wavelength range

Photonic Crystal Nanobeam Cavity Strongly Coupled to the Feeding Waveguide

A deterministic design of an ultrahigh Q, wavelength scale mode volume photonic crystal nanobeam cavity is proposed and experimentally demonstrated. Using this approach, cavities with Q>10^6 and on-resonance transmission T>90% are designed. The devices fabricated in Si and capped with low-index polymer, have Q=80,000 and T=73%. This is, to the best of our knowledge, the highest transmission measured in deterministically designed, wavelength scale high Q cavities

Nanobeam Cavities for Reconfigurable Photonics

We investigate the design, fabrication, and experimental characterization of high quality factor photonic crystal nanobeam cavities, with theoretical quality factors of $1.4 × 10^7$ in silicon, operating at ~1550 nm. By detecting the cross-polarized resonantly scattered light from a normally incident laser beam, we measure a quality factor of nearly $7.5 × 10^5$. We show on-chip integration of the cavities using waveguides and an inverse taper geometry based mode size converters, and also demonstrate tuning of the optical resonance using thermo-optic effect. We also study coupled cavities and show that the single nanobeam cavity modes are coupled into even and odd superposition modes. Using electrostatic force and taking advantage of the highly dispersive nature of the even mode to the nanobeam separation, we demonstrate dynamically reconfigurable optical filters tunable continuously and reversibly over a 9.5 nm wavelength range. The electrostatic force, obtained by applying bias voltages directly to the nanobeams, is used to control the spacing between the nanobeams, which in turn results in tuning of the cavity resonance. The observed tuning trends were confirmed through simulations that modeled the electrostatic actuation as well as the optical resonances in our reconfigurable geometries. Finally we demonstrate reconfiguration of coupled cavities by using optical gradient force induced mechanical actuation. Propagating waveguide modes that exist over wide wavelength range are used to actuate the structures and in that way control the resonance of a localized cavity mode. Using this all-optical approach, more than 18 linewidths of tuning range is demonstrated. Using an on-chip temperature self-referencing method that we developed, we determined that 20% of the total tuning was due to optomechanical reconfiguration and the rest due to thermo-optic effects. By operating the device at frequencies higher than the thermal cut-off, we show high speed operation dominated by just optomechanical effects. Independent control of mechanical and optical resonances of our structures, by means of optical stiffening, is also demonstrated.Engineering and Applied Science

Fabrication of organic and inorganic nanoparticles using electrospray

A new fabrication process of organic and inorganic nanoparticles and cups by electrospraying blended polymer-sol-gel solutions followed by calcination has been investigated. Because of low viscosity and high surface tension of blended polymersol- gel solutions, an electrostatically extruded continuous liquid jet from the spray source became tiny droplets with diameter of less than 1µm in transit. They were collected as dried formats at the counter electrode. These are then calcinated to eliminate polymers as well as cross-link sol-gel material. Silica nanocups have been fabricated using the above technique and the probable methods to control their morphology by varying the ionic concentration have been investigated. Experiments with biodegradable polymers, like Poly Lactic Acid (PLA) and polyvinylpyrrolidine (PVP) to fabricate nanoparticles using the above technique, have also been carried out. The potential use of such biodegradable particles in drug delivery has been demonstrated. This method can encapsulate drug in the particles without the need of any stabilizer which can cause unwanted effect on the drug. The effect of solvents, polymer concentration and deposition distance on morphology and diameter of particles was also investigated on PLA particles. This process is a simple and efficient approach for producing nanocomposite cups that cannot be made by an aggregation method and also nano/micro particles which may find their use in drug delivery and filtration media. Finally, a new technique to sort the particles based on their dimensions is demonstrated. Because of interactions between charged droplets and a non-linear electrostatic field, nanoparticles with different dimensions are deposited at different locations. By using this principle, silica nanocups have been sorted into three groups with mean diameters of 0.31 µm, 0.7 µm and 1.1µm and a standard deviation of 20%