Study On A New Two-dimensional Photonic Crystal Ring Resonator And Its Application

Optical ring resonators, owing to their high spectral selectivity and large free spectral range (FSR), have attracted growing attention in a wide range of applications like optical filters, sensors, modulators, switches as well as nonlinear devices for the cavity quantum electrodynamics. To date, ring resonators have been successfully demonstrated in a variety of materials including optical fibers, low index contrast dielectric materials (with material index contrast An< 2, e.g., polymer), and high index contrast semiconductor materials (Δn≥2, e.g., SOI). Typically, systems based on traditional optical fiber ring technology are bulky and incompatible with photonic integration. One of the most promising designs is planar-waveguide-based integrated micro-ring resonator, also called whispering-gallery-mode (WGM) micro-resonator. However, for WGM ring resonators, limited by total internal reflection (TIR) confinement principle, their propagation losses increase exponentially with the reduction of ring radii. This presents a problem or "roadblock" to scaling, which in practice sets a lower limit on the ring radius of a few micrometers (e.g.3 m). Additionally, the performance of WGM ring resonators is also highly sensitive to the surface roughness and the nano-gap between the ring resonator and the bus waveguide, which creates another challenge in manufacturing. On the other hand, photonic crystals (PCs) offer great promise in ultra-compact photonic components mainly due to their unique properties in controlling the flow of light at optical wavelength scale, which will lead to a significant reduction in the size and power consumption.In this thesis, we proposed a new 45°photonic crystal ring resonator (PCRR) by considering the effect of self collimation and band gap of photonic crystals. The characteristics of proposed configurations were numerically analyzed by using plane-wave expansion method and finite-difference time-domain technique. Then, a new two-dimensional photonic crystal micro-ring add/drop filters (ADFs) and logic gates were demonstrated according to the theory of beam interference. The major research achievements have been summarized as follows:1. A new 2D PCRR based ADF has been introduced by combing the merits of photonic crystal band gap and its self collimation. It is not necessary to consider the mode conversion during the whole design process, which make the structure relatively simple and compactable.2. A new PCRR was provided by removing the line defect along theΓМdirection instead of traditionalΓХdirection. We compared the performance of new PCRR and traditional one including transmission intensity, dropped efficiency and quality factor etc. The spectral information affected by physical parameters was numerically analyzed. More than 830 spectral quality factor and 90% dropped efficiency at 1550-nm channel can be obtained with less than 2.2-μm ring radius. This can potentially overcome the challenge of traditional micro-ring resonators.3. New all-optical NOT and NOR logic gates based on a single ultra-compact PCRR have been proposed. The PCRR was formed by removing the line defect along aforementioned FM direction in a square-pattern cylindrical silicon-rod photonic crystal structure. The behavior of proposed logic gates affected by physical parameters like the initial phase of probing signal is first qualitatively analyzed with the theory of beam interference and then numerically investigated. The definition of logic'0'and'1'are also introduced. No nonlinear material is required. The wavelengths of input signal and probing signal are the same. For the operating wavelength of 1550 nm, this new device provides potential applications for all-optical logic circuits and ultra-compact high density photonic integrationThe key contributions of this work are summarized. Firstly, we applied the effect of photonic crystal band gap and its self collimation to offer a new PCRR; Secondly, we provided a 45°PCRR by removing the line defect along theГМdirection. It makes the configuration much smaller and high spectral selectivity which offers potential applications for ultra-compact high density photonic integration; Finally, we proposed a new all-opticl logic gates by combining PCRR and Y branch. By comparing with reported works, this new structure only require a single ring, single operating wavelength and no additional non-linear materials introduced, which make it relatively easy, simple and compact.