| Narrow linewidth laser has high time coherence and low phase noise,so it has important applications in the fields of optical communication,optical sensing,spectroscopy,measurement and detection.The existing semiconductor lasers have the characteristics of low cost,low power consumption and small size.But its output linewidth is usually wide.Therefore,the development of semiconductor lasers with narrow linewidth is a research hotspot in the current academic circles.As an integrated photonic device,micro-ring resonator has the characteristics of enhanced resonance at specific frequencies,controllable optical transmission,high degree of freedom of design and easy integration.The semiconductor laser based on micro-ring resonator can effectively narrow the linewidth of laser by making use of the high quality factor and narrow-band optical feedback characteristics of micro-ring resonator.In this paper,the narrow linewidth laser based on micro-ring resonator was taken as the research object.From the aspects of theoretical simulation and process preparation,the micro-ring resonator used to reduce the linewidth of semiconductor laser was deeply studied.The main research contents are as follows:(1)Three kinds of light field coupling states of the micro-ring resonator were simulated by Matlab.The optical field resonance characteristics of micro-ring resonators with different parameters were simulated by changing the coupling coefficient,micro-ring radius,waveguide refractive index and waveguide loss.The light field feedback effect of the micro-ring resonator was analyzed,and the conditions for the reverse coupling transmission of the feedback light were obtained.(2)The critical coupling transmission characteristics of the micro-ring resonator to different wave bands were simulated by using the finite-difference time-domain method.Among them,the critical coupling condition of the aluminum nitride ring resonator with a radius of 30 μm satisfies that the coupling gap is larger than 200 nm in the band of 1.3-1.5μm.An end-face optical coupler which can be used to reduce the coupling loss of light field was designed and simulated.The simulation of the light field in the blue light band shows that when the width of the aluminum nitride tip is close to 100 nm and the cone length is more than 200 μm,the light field coupling efficiency is more than 90%.(3)Single crystal aluminum nitride thin films were epitaxially grown on sapphire substrate.The fabrication technology of micro-ring resonator and end-face optical coupler was studied.The electron beam lithography process was improved by depositing metal film on the chip and adjusting exposure dose and development parameters.Double-layer resist and silicon oxide film were used as etching mask.The parameters such as gas flow,electrode power and etching time of the inductively coupled plasma etching system were adjusted.The optimized etching of aluminum nitride and silicon nitride thin films was realized,and the fabrication of micro-ring resonator and end-face optical coupler was completed. |
