FREE STANDING PHOTONIC CRYSTAL CAVITIES FOR DIAMOND COLOR CENTERS

Abstract

The sub-wavelength optical confinement of low optical loss photonics intensely increases the probability of light-matter interaction up to a single quantum level. The chip based photonics provide a scalable platform from which to study many effects that are crucial in many applications ranging from chemical sensing and nonlinear optics, to quantum information processing and cavity optomechanics. This work addresses the use of photonic devices in quantum optics, including device design, fabrication and characterization, and optical coupling. We present a scalable "semicircular holes" design for 1D photonic crystal cavities that combines an ultrahigh Q=V value and high transmission. In high refractive index materials such as gallium phosphide (GaP), our design ideally possesses Q=V > 107 and transmission over 90%. We also address the fabrication of GaP-based photonic devices using different methods despite the challenges due to mainly the lack of the necessary tools and equipment. Besides the design and fabrication, we propose a new scheme for coupling photons strongly to a single photon emitter, namely germanium vacancy (GeV) center in diamond, based on cavity QED. Our analysis reveals a strong coupling regime can be achieved for the first time using a solid-state single photon emitter. Next, we shift to silicon nitride (Si3N4) material that is cheap and easy to grow, fabricate, and measure. We again design silicon nitride nanobeam cavities based on the quadratic tapering method with and without semicircular holes. The designed devices feature large optical quality factors, in excess of 105. We also study cavity QED for a single GeV center that is strongly coupled to the cavity field. The fabrication of Si3N4 nanobeam cavities is discussed together with the optimization needed mostly for electron-beam lithography (EBL) process. We demonstrate engineered nanobeam cavities for Si3N4 grown by plasma-enhanced chemical vapor deposition (PECVD) films as well as low pressure chemical vapor deposition (LPCVD) films. The devices grown by the latter method possess relatively large optical quality factors, approaches 104, around the zero-phonon line (ZPL) of GeV center. Lastly, we present a method for fiber-waveguide coupling that allows efficient power transfer from an optical fiber into a waveguide and vice versa. We study the design and fabrication method in details for both structures, and optimize the coupling using finite difference time domain (FDTD). Our method uses conical tapered optical fibers (with a tapering angle of ~ 4 degrees) that are coupled over ~ 11 um to a Si3N4 waveguide taper (with a tapering angle of ~ 1 degree). We demonstrate using a deterministic approach single-mode fiber-waveguide coupling efficiency as high as 96%.