Compact semiconductor lasers

摘要

As the field of optoelectronics advances, OEICs (Opto Electronic Integrated Circuits) become smaller and more complex. To allow for large-scale integration in photonic circuits, the overall "footprint" of the lasers integral to these devices must be greatly reduced. Short cavity in-plane semiconductor lasers (or microlayers) offer an attractive solution, as they are well suited to monolithic integration and posses low power consumption. The aim of this project was to design and fabricate extremely compact, low threshold current edge-emitting laser diodes, emitting in 980 nm range wavelength. To account for the reduced cavity length, HR (high-reflectivity) microstructure mirrors were formed at each end of the cavity. The HR microstructure mirrors take the form of a DBR (Distributed Bragg Reflectors) grating with deeply etched air slots. This periodic and high refractive index contrast (-3.5:1) structure can also be viewed as a 1-D photonic crystal. Theoretically, these structures can produce reflectivity values as high as 99+% over a broad wavelength range and with good tolerance to imperfections in fabrication. Microstructure mirrors were defined utilising electron-beam lithography and the RIE (Reactive Ion Etching) facilities within the department. In addition, compact semiconductor lasers featuring an oxide confined current aperture - for the purpose of current confinement above the active core, were produced, assessed and demonstrated to further reduce operational threshold current as low as 1.7 mA (compared to 3.2 mA, for a similar standard compact laser, without oxide-confinement) for 44 mum cavity-length lasers. Further improvement of mirror design allowed optimum threshold currents to be reduced to just below 1 mA for 24mum-long compact lasers. Estimates for effective reflectivity values from microstructure mirrors produced approach 87% and 97%, for 3-period and 10-period structures respectively. 2-D FDTD computer simulation also indicates reflectivity values from such mirrors to saturate at approximately 98% for any more that 3-periods in the mirror structures.