We demonstrate a GaAs based Quantum Dot (QD) optoelectronic integration platform with results for surface grating couplers (SGC) and edge emitting lasers. SGCs usually perform poorly in systems without a large refractive index contrast and here we utilize thin oxidized Al0.98Ga0.02As layers to overcome this issue. The results show an increase from 10% to 30% in surface grating coupling efficiency, for the unoxidized compared to oxidized, and substrate-loss decrease from 70% to 20%. Electrically pumped edge-emitting lasers on the same platform exhibit comparable performance to more standard 1300nm QD designs. We describe the design, fabrication and characterization of these devices.
1-port and 2-port multi-mode interference reflectors (MMIR) are excellent components for Photonic Integrated Circuits, being highly reflective and easy to fabricate. We demonstrate InAs-Quantum-Dot MMIR lasers, where the high reflectivity is particularly advantageous, with lower threshold current than Fabry-Perot ridge lasers with the same cavity length e.g. 6mA compared to 46-mA. The threshold current density of the 1-mm MMIR laser is equivalent to the Fabry-Perot laser with a 3-mm cavity length. MMIRs have a higher optical slope efficiency, indicating mirror reflectivity above 85%.
We demonstrate high-gain InAs QDs targeting C-band and L-band using a five QD-layer structure grown via MOCVD, with a photoluminescence broadening of ~55 meV. Lasers were fabricated with cavity lengths from 2000-µm down to 333-µm, with cleaved un-coated facets. Threshold current density increases monotonically with temperature over a range of 300 K to 380 K for all cavity lengths with a factor of 3.0 and 3.4 increase for the longest and shortest cavities, respectively. Measurements of lasing spectrum reveal that even the shortest cavity maintains a stable increase in wavelength up to 390 K with no observable transition to the excited state.
We report on the epi-design and characterisation of VCSELs for atomic sensors, including miniaturised clocks and magnetometers. To understand how epi-design impacts device performance and separate this from effects of growth and fabrication, we employ techniques to study the interplay between optically-active gain medium and the cavity-resonance. We experimentally determine the net modal-gain spectrum of VCSEL material using a single-pass stripe-length method covering the range of pumping and hence gain requirements of VCSELs. This is compared to photovoltage spectroscopic measurements, which are used to determine the quantum well transition energies and cavity resonance, aiding further optimisation of device design.
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