Showing papers by "Vitalii Sichkovskyi published in 2016"

Temperature-Insensitive High-Speed Directly Modulated 1.55- $\mu \text{m}$ Quantum Dot Lasers

Abstract: Modulation properties and temperature stability of short cavity ridge waveguide lasers based on high-quality InAs quantum dots exhibiting a total modal gain of ~90 cm -1 are reported. The 338-μm-long lasers show a threshold current of 20 mA at room temperature and an output powers of up to 36 mW. A maximum small signal modulation bandwidth of 15 GHz was obtained at 14 °C, which degrades to 13 GHz at 60 °C and 8 GHz at 80 °C. Digital modulation at 25 Gb/s between 15 °C and 50 °C was obtained with clear open eyes under constant drive conditions (dc and ac). The maximum data rates of 32 and 35 Gb/s were obtained for 338- and 230-μm-long lasers, respectively, at 14 °C.

1.5μm quantum dot laser material with high temperature stability of threshold current density and external differential efficiency

Abstract: Self-organized InAs quantum dot (QD) lasers based on InP substrate were grown by means of solid source molecular beam epitaxy (SSMBE). Six InAs QD layers with high dot density and highly uniform dot sizes were used as active medium. Broad area (BA) and ridge waveguide (RWG) lasers with different cavity lengths were processed and characterized. Also the influence of a post-growth rapid thermal annealing (RTA) process on the laser characteristics was investigated. The lasers showed a high modal gain of 12 - 14.5 cm-1 per dot layer and a threshold current density for infinite cavity length of 120 A/cm2 per dot layer. In pulsed operation, as-cleaved BA lasers with a cavity length of 292 μm can be operated up to 120 °C. High characteristic temperature values were obtained with T0 = 125 K (20 °C to 45 °C) and T0 = 100 K up to 120 °C. The slope efficiency of about 0.28 W/A can be kept constant over a wide operating temperature range of up to 100 °C. Mounted RWG lasers with 388 μm cavity length and operated in pulsed mode showed a maximum output power of 120 mW a slope efficiency of 0.42 W/A at 15 °C. The lasers can be operated at 150 °C with 25 mW output power. These results demonstrate very well the temperature insensitive lasing performance expected in nearly ideal QD lasers due to the high density of states localized at the transition energy, which allow a very robust ground state lasing.

High-speed directly modulated 1.5μm quantum dot lasers

Abstract: Due to the discrete density of states distribution and spatial localization of carriers in quantum dot (QD) material, the dynamics should be strongly enhanced in comparison to quantum well material. Based on improved 1.5 μm InAs/InGaAlAs/InP QD gain material short cavity ridge waveguide lasers were fabricated. Devices with cavity, lengths of 230 to 338 μm with high reflection coatings on the backside exhibit record value for any QD laser in small and large signal modulation performance with up to 15 GHz and 36 GBit/s, respectively, obtained at 14 °C. Due to the high temperature stability of threshold current and external differential efficiency, the lasers exhibit also nearly constant modulation bandwidth between 14-60 °C.

Narrow-linewidth 1.5μm quantum dot distributed feedback lasers

Abstract: The ever-growing need for higher data rates is a driving force for the implementation of higher order coherent communication formats. A key element in coherent detection is the local oscillator (LO) of the decoding unit. This device has to provide coherent light with a narrow linewidth in order to distinguish between different phase and amplitude states of the incoming signal. As predicted by theory, a drastic linewidth reduction is expected from quantum dot (QD) laser materials by the quasi zero-dimensional nature of the gain function. The impact of different gain materials consisting of different numbers of QD layers on the linewidth of distributed feedback (DFB) lasers was investigated and shows an unambiguous dependence on the layer design. Intrinsic linewidths as low as 110 kHz could be determined.

Monolithically integrated widely tunable narrow-linewidth light source for the C+ band based on quantum dot laser material

Abstract: A monolithically integrated narrow-linewidth (≈ 200 kHz) light source was realized on InP-based quantum dot laser material, which can be tuned over the whole C+ communication band and utilizes the low linewidth enhancement factor as well as the broad gain bandwidth of quasi-zero dimensional gain material.