Here, we have presented the first design of a bottom to in-plane grating coupler with a high coupling efficiency and directionality. The grating coupler consists of a high contrast grating (HCG) and an etched silicon-on-insulator (SOI) grating device. The final coupling efficiency is 82.2% at 1.55µm, with a 57nm 3dB bandwidth, and the directionality is 14:1 (left to right ratio). This grating coupler can be further optimized with different low index materials. This grating coupler could work as the vertical to in-plane coupler for the label free silicon photonic bio-sensor.
Optical cavities are imperative in micro/nanophotonics for their ability to provide resonance feedback and radiation enhancement. In recent years, the interplay between gain and loss using parity-time (PT) symmetry has opened up a new degree of freedom for cavity mode and emission control. I will first discuss a PT micro-ring cavity with the unique features of thresholdless PT symmetry breaking and single-mode lasing. Next, I will reveal a novel PT optical cavity which can support lasing and coherent perfect absorption modes within a single device and enable strong modulation from coherent amplification to coherent absorption.
The concept of parity-time (PT) symmetry exploits the interplay between the material loss and gain to attain novel optical phenomena such as exceptional point and unidirectional light propagation. Here we experimentally demonstrate a PT symmetry breaking laser that allows unique control of the resonant modes. In contrast to conventional ring cavity lasers with multiple competing modes, our on-chip InGaAsP/InP based PT microring laser exhibits intrinsic single-mode lasing regardless of the gain spectral bandwidth. Thresholdless parity-time symmetry breaking due to the rotationally symmetric structure leads to stable single-mode operation at the specific whispering gallery mode order.
This paper reports the development of a low-cost inductively coupled passive wireless strain sensor which can be easily embedded within composite prepreg layers for structural health monitoring application. The sensor response shows great linearity, low hysteresis and drift, and sufficient sensing range for wireless interrogation. The sensor sensitivity is found to be relatively low, but with some modifications on the sensor pattern design approximately three-fold increase in sensitivity is obtained. The investigation on both sensor array and sensor directivity verifies its potential to be developed as wireless rosette strain sensor. In addition, mechanical tests are performed. Among the tested mechanical properties, the interlaminar shear strength of composite specimens degrades the most upon sensor embedment. Finally, an analytical model is developed. Its normalized resonant frequency shift due to strain change agrees well with the experimental result.
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