High Performance Quantum Dot Laser WDM Arrays for Optical Interconnects (original) (raw)
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QD lasers: physics and applications
Semiconductor and Organic Optoelectronic Materials and Devices, 2005
Quantum dot (QDs) heterostructures structurally represent tiny 3D insertions of a narrow bandgap material, coherently embedded in a wide-bandgap single-crystalline matrix. The QDs are produced by conventional epitaxial techniques applying self-organized growth and behave electronically as artificial atoms. Strain-induced attraction of QDs in different rows enables vertically-coupled structures for polarization, lifetime and wavelength control. Overgrowth with ternary or quaternary alloy materials allows controllable increase in the QD volume via the island-activated alloy phase separation. Repulsive forces during overgrowth of QDs by a matrix material enable selective capping of coherent QDs, keeping the defect regions uncapped for their subsequent selective evaporation. Low-threshold injection lasing is achieved up to 1350 nm wavelength at 300K using InAs-GaAs QDs. 8 mW VCSELs at 1.3 µm with doped DBRs are realized. Edge-emitters demonstrate 10 GHz bandwidth up to 70 o C without current adjustment. VCSELs show ~4 GHz relaxation oscillation frequency. QD lasers demonstrate above 3000 h of CW operation at 1.5 W at 45 o C heat sink temperature without degradation. The defect reduction technique (DRT) applied to thick layers enables realization of defect-free structures on top of dislocated templates. Using of DRT metamorphic buffer layers allowed 7W GaAs-based QD lasers at 1500 nm.
Quantum dot lasers: breakthrough in optoelectronics
Thin Solid Films, 2000
Semiconductor heterostructures with self-organized quantum dots (QDs) have experimentally exhibited properties expected for zerodimensional systems. When used as active layer in the injection lasers, these advantages help to strongly increase material gain and differential gain, to improve temperature stability of the threshold current, and to provide improved dynamic properties. Molecular beam epitaxy (MBE) represents a developed technology well suited for fabrication of self-organized QDs. Optimization of deposition parameters can ensure that the self-organized islands are small (,10 nm), have a similar size and shape and form dense arrays. Saturation material gain is as high as 150000 cm 21 compared with QW values of about 3000 cm 21. Maximum differential gain reported for QD lasers approaches 10 212 cm 2 and exceeds the QW laser values by about three orders of magnitude. Direct observation of relaxation oscillations reveals present cutoff frequencies close to 10 GHz. High internal (.96%) and differential (70%) ef®ciencies at 300 K are realized. Using the novel concept of electronically-coupled QDs and oxide-de®ned 10 mm apertures, CW lasing with J th 180 A/cm 2 , is realized in surface-emitting QD lasers (300 K). Wall-plug ef®ciencies are up to 16%. Total currents as low as 68 mA are measured for 1mm apertures. GaAs-based lasers for the 1.3 mm range with low J th (65 A/cm 2) at room temperature (RT) are realized using InAs/InGaAs/GaAs QDs obtained by activated spinodal decomposition. In stripes the lasing occurs via the QD ground state (J th 90 A/cm 2) for cavity lengths L. 1 mm (uncoated). Differential ef®ciency is 55% and internal losses are 1.5 cm 21. A characteristic temperature near RT is 160 K. 3W CW operation at RT is achieved. The recent progress in lasers based on self-organized MBE QDs already made it possible to fabricate devices with dramatically improved characteristics as compared to recent QW devices for the most important commercial applications.
QD lasers: physics and applications
Storage and Retrieval for Image and Video Databases, 2005
Quantum dot (QDs) heterostructures structurally represent tiny 3D insertions of a narrow bandgap material, coherently embedded in a wide-bandgap single-crystalline matrix. The QDs are produced by conventional epitaxial techniques applying self-organized growth and behave electronically as artificial atoms. Strain-induced attraction of QDs in different rows enables vertically-coupled structures for polarization, lifetime and wavelength control. Overgrowth with ternary or quaternary alloy
External cavity InAs∕InP quantum dot laser with a tuning range of 166 nm
Applied Physics Letters, 2006
We have studied the tuning behavior of an external cavity laser in Littrow configuration using antireflection/high-reflection coated InAs/ InGaAsP/ InP quantum dot laser diodes as the amplifying element. Adding the coatings improves the performance of the setup, and the tunability of the external cavity laser output has been increased up to 166 nm. Detailed investigations have revealed that laser diode length and width influence the magnitude of the tuning range. Furthermore, the external differential quantum efficiency is systematically increasing as the external cavity laser wavelength is decreasing. These characteristics are discussed in terms of energy levels available in the inhomogeneous broadening of the self-assembled quantum dots.
Novel In-Plane Semiconductor Lasers V, 2006
We have performed a systematic study of structural and optical properties of Quantum dot (QDs) lasers based on InAs/InGaAs quantum dots grown on GaAs substrates emitting in the 1.3 -1.5 µm range. 1.3 µm range QD lasers are grown using GaAs as matrix material. It is shown that the lasers, grown with large number of QD stacks are metamorphic, with plastic relaxation occurring through the formation of misfit dislocations. Thus, 1.3 µm QD lasers with large number of stacks grown without strain compensation are metamorphic. Another type of defects is related to local dislocated clusters, which are the most dangerous. When proper optimization of the growth conditions is carried out, including a selective thermal etching off of statistically formed dislocated clusters through the defect-reduction technique (DRT), no significant impact of misfit dislocations on the degradation robustness is observed. In uncoated devices a high cw single mode power of ~700 mW is realized limited by thermal roll-over, which is not affected by 500 h ageing at room temperature. At elevated temperatures the main degradation mechanism revealed is catastrophic optical mirror damage (COMD). When the facet are passivated, the devices show the extrapolated operation lifetime in excess of 10 6 h at 40 o C at ~100 mW cw single mode output power. Longer wavelength (1.4 -1.5 µm) devices are grown on metamorphic (In,Ga,Al)As layers deposited on GaAs substrates. In this case, the plastic relaxation occurs through formation of both misfit and threading dislocations. The latter kill the device performance. Using DRT in this case enables blocking of threading dislocation with growth of QDs in defect-free upper layers. DRT is realized by selective capping of the defect-free areas and high-temperature etching of nano-holes at the non-capped regions near the dislocation. The procedure results in etching of holes and is followed by fast lateral overgrowth with merger of the growth fronts. If the defect does not propagate into the upper layer when the hole is capped, the upper layers become defect-free. Lasers based on this approach exhibited emission wavelength in the 1.4 -1.5 µm range with a differential quantum efficiency of about ~50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm -2 without degradation. A maximum continuous-wave output power of 220 mW limited by thermal roll-over is obtained. No beam filamentation was observed up to the highest pumping levels. Narrow stripe devices with as-cleaved facets are tested for 60 o C (800 h) and 70 o C (200 h) on-chip temperature. No noticeable degradation has been observed at 50 mW cw single mode output power. This shows the possibility of degradation-robust devices on foreign substrates. The technology opens a way for integration of various III-V materials and may target degradation-free lasers on silicon for further convergence of computing and communications.
Enhanced Dynamic Performance of Quantum Dot Semiconductor Lasers Operating on the Excited State
IEEE Journal of Quantum Electronics, 2014
The modulation dynamics and the linewidth enhancement factor of excited-state (ES) lasing quantum dot (QD) semiconductor lasers are investigated through a set of improved rate equation model, in which the contribution of off-resonant states to the refractive index change is taken into account. The ES laser exhibits a broader modulation response associated with a much lower chirp-to-power ratio in comparison with the ground-state (GS) lasing laser. In addition, it is found that the laser emission in ES reduces the linewidth enhancement factor of QD lasers by about 40% than that in GS. These properties make the ES lasing devices, especially InAs/InP ones emitting at 1.55 µm, more attractive for direct modulation in high-speed optical communication systems.