Abstract:
Complex photonic systems for optical communications can benefit from monolithic integration of the key photonic devices with their interconnecting waveguides. Advantages include improved stability and environmental ruggedness, reduced size and reduced cost.
Although silicon photonics technology has demonstrated high performance optical modulators and detectors, efficient electrically pumped optical sources are key to delivering the required range of system functions.
This talk will review approaches to realising electrically pumped optical sources on silicon and will present new results on the first telecommunications wavelength quantum dot lasers monolithically integrated on silicon substrates, including initial measurements on operating lifetime which suggest that lifetimes in excess of 100,000 hours should be possible.
Quantum dot (QD) laser gain regions have proved to be less sensitive to defects than conventional bulk materials and quantum well structures, due to carrier localization and hence a reduced interaction with the defects [1,2]. In our work, we have combined QD gain regions with the use of superlattice defect filter layers to enable the direct epitaxial growth of telecommunications wavelength lasers on silicon substrates.
Broad area lasers were fabricated by optical lithography with as-cleaved facets. The measured room temperature threshold current density was 62.5 A cm-2, very similar to the best values for lasers grown on native substrates. Optical output powers of over 100 mW were measured for a current density of 650 A cm-2. Lasing was obtained for substrate temperatures as high as 120 °C [3]. An ageing test was carried out at 26 °C and 1.75 times threshold current for 3,100 hours, during which the output power reduced by 27.9% (26.4% in the first 500 hours) [4]. The extrapolated time to failure, defined as a doubling of threshold current, was over 100,000 hours.
In conclusion, we have demonstrated the first practical telecommunications wavelength quantum dot laser directly grown on a silicon substrate. The laser has performance comparable to lasers grown on native substrates and initial results suggest that long operating lifetime is possible. We expect such lasers to be key components in the realisation of low cost optical interconnects from silicon electronics.