Zhongliang Qiao

Design and Analysis of 2-μm InGaSb/GaSb Quantum Well Lasers Integrated Onto Silicon-on-Insulator (SOI) Waveguide Circuits Through an Al 2 O 3 Bonding Layer

GaSb-based quantum well (QW) laser diode, with emission wavelength ~2 μm, integrated onto a silicon-on-insulator (SOI) waveguide circuit through a high-thermal-conductivity Al2O3 bonding layer has been designed and analyzed. Prior to bonding, the fabricated Fabry-Perot GaSb QW laser worked under continuous wave operation at room temperature, with a low threshold current of 37 mA at the emission wavelength of 2019 nm, demonstrating high material quality. A tapered structure has been used for evanescent coupling of light from the GaSb laser to the underlying Si waveguide. Instead of using SiO2 for direct bonding or Benzocyclobutene for adhesive bonding, the use of Al2O3 to directly bond GaSb lasers onto SOI wafers is proposed. The optical mode distribution simulations by a beam propagation method software show that light can be coupled efficiently to the underlying Si waveguide through the tapered structure without compromise in optical coupling efficiency. Furthermore, there is a significant reduction (~70%) in the total thermal resistance compared with the same structure using a SiO2 bonding layer. Our results suggest that the Al2O3 bonding layer could be a promising candidate for III-V lasers integrated on SOI circuits, where thermal dissipation is very critical.

Temperature- and current-dependent spontaneous emission study on 2 µm InGaSb/AlGaAsSb quantum well lasers

Spontaneous emission measurements, as a function of injection current and temperature, were carried out from the sidewall of a working 2 ?m InGaSb/AlGaAsSb quantum well laser. The local Z power parameter was extracted to investigate the carrier recombination behaviors. A model involving the activation energy is presented to interpret the carrier loss mechanisms. Our findings show that the majority of the injected carriers recombine radiatively at low injection currents, and that Auger nonradiative recombination increases significantly with injection current. More importantly, no obvious temperature dependence of Z is observed from 20 to 80 ?C.

Investigation of regime switching from mode locking to Q-switching in a 2 µm InGaSb/AlGaAsSb quantum well laser

A two-section InGaSb/AlGaAsSb single quantum well (SQW) laser emitting at 2 μm is presented. By varying the absorber bias voltage with a fixed gain current at 130 mA, passive mode locking at ~18.40 GHz, Q-switched mode locking, and passive Q-switching are observed in this laser. In the Q-switched mode locking regimes, the Q-switched RF signal and mode locked RF signal coexist, and the Q-switched lasing and mode-locked lasing happen at different wavelengths. This is the first observation of these three pulsed working regimes in a GaSb-based diode laser. An analysis of the regime switching mechanism is given based on the interplay between the gain saturation and the saturable absorption.

Characteristic temperature of a 2 µm InGaSb/AlGaAsSb mode-locked quantum well laser

Mode locking is achieved in a 2 μm GaSb-based laser up to 60 °C. The laser has a T0 of ~82 K at room temperature, and the absorber bias voltage has little effect on T0.

Monolithic Fabrication of InGaAs/GaAs/AlGaAs Multiple Wavelength Quantum Well Laser Diodes via Impurity-Free Vacancy Disordering Quantum Well Intermixing

InGaAs/GaAs/AlGaAs multiple wavelength quantum well (QW) semiconductor laser diodes (LDs) have been fabricated by impurity-free vacancy disordering (IFVD) QW intermixing (QWI) method. The IFVD-QWI process was carried out by sputtering-depositing SiO2 mask layers on top of the complete InGaAs/GaAs/AlGaAs QW laser structure, emitting at 980 nm wavelength, and followed by a rapid thermal annealing at 880 °C for 60 s. The lasing wavelength of the devices fabricated from the intermixed wafer was blue-shifted with the increase of the mask layer thickness. The maximum emission wavelength blue shift of a processed as-cleaved laser reached 112 nm with the output-power more than 1000 mW. By using such an IFVD-QWI technique, multi-wavelength integrated LDs have also been successfully fabricated from a single chip.

Modal gain characteristics of a 2 μm InGaSb/AlGaAsSb passively mode-locked quantum well laser

Passive mode locking with a fundamental repetition rate at ∼18.46 GHz is demonstrated in a two-section InGaSb/AlGaAsSb quantum well laser emitting at 2 μm. Modal gain characteristics of the laser are investigated by performing the Hakki-Paoli method to gain better insight into the impact of the absorber bias voltage (Va) on the light output. The lasing action moves to longer wavelengths markedly with increasing negative Va. The light output contains more longitudinal modes in the mode locking regime if the gain bandwidth is larger at a certain Va. Our findings provide guidelines for output characteristics of the mode-locked laser.

Optimization of semiconductor ridge waveguide lasers for improved temperature characteristics

Summary form only given. Semiconductor ridge waveguide (RWG) laser fabrication process has been optimized. RWG lasers with different ridge height of 0.39 μm, 0.80 μm, 1.23 μm, 1.55 μm and 1.77 μm were fabricated. All the RWG lasers have the same contact ridge width of 50 μm and cavity length of 1100 μm. The dependence of the ridge height on the temperature performance of these lasers has been systematically investigated. It was found that the optimum ridge height is 1.23 μm, corresponding to an etching depth where all the p-doped layers above the active region were removed. The RWG laser with this ridge height worked up to 100 °C successfully, and also showed the highest characteristic temperature (T0) among all the five group lasers. The T0 became worse when the ridge height extends below the active region. Our study suggests the significance of the optimization of the ridge waveguide to the laser diode performance.

Two-state lasing in GaAs-based InAs/InGaAs quantum dot mode-locked laser

Summary form only given. GaAs-based InAs/InGaAs quantum dot (QD) mode-locked lasers (MLLs) have been fabricated and characterized. The fundamental mode locking at 17.08 GHz was obtained, with the second harmonic mode locking at 34.165 GHz. When keeping the QD MLL gain section bias current (Igain) constant at 200 mA, two-state lasing was observed by changing the reverse bias at saturable absorber (SA) section (VSA) of QD MLL. The two lasing states at 1277 nm region and 1170 nm region are attributed to ground state (GS) and excited state (ES) transitions, respectively. For the first time, spontaneous emission (SE) measurement at the sidewall of the QD MLL gain section has been performed to investigate the two state transitions. The significant carrier recombination competition has been observed at the GS and ES transitions from SE measurement. Our study suggests the significance of the carrier competition in QD mode-locked laser performance and characteristics.