Gray Lin

Single-mode monolithic quantum-dot VCSEL in 1.3 /spl mu/m with sidemode suppression ratio over 30 dB

We present monolithic quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs) operating in the 1.3-/spl mu/m optical communication wavelength. The QD VCSELs have adapted fully doped structure on GaAs substrate. The output power is /spl sim/330 /spl mu/W with slope efficiency of 0.18 W/A at room temperature. Single-mode operation was obtained with a sidemode suppression ratio of >30 dB. The modulation bandwidth and eye diagram in 2.5 Gb/s was also presented.

Vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

Molecular beam epitaxy-grown 0.98-mum vertical-cavity surface-emitting lasers (VCSELs) with a three-stack submonolayer (SML) InGaAs quantum-dot (QD) active region and fully doped AlxGa 1-xAs-GaAs DBRs was studied. Large-aperture VCSELs demonstrated internal optical losses less than 0.1% per one pass. Single-mode operation throughout the whole current range was observed for SML QD VCSELs with the tapered oxide apertures diameter less than 2 mum. Devices with 3-mum tapered-aperture showed high single-mode output power of 4 mW and external quantum efficiency of 68% at room temperature

Extremely small vertical far-field angle of InGaAs-AlGaAs quantum-well lasers with specially designed cladding structure

We report on a very small vertical far-field angle achieved by lasers with a specially designed structure. For an InGaAs-AlGaAs quantum-well laser with a 2.5-/spl mu/m-wide ridge waveguide, the far-field pattern has a vertical far-field angle of 13/spl deg/ and a lateral far-field angle of 8/spl deg/. Meanwhile, the threshold current remains acceptably low (/spl ap/36 mA for a 500-/spl mu/m-long cavity). The slope efficiency of the L-I characteristic is high (>0.9 W/A) compared to that of the conventional laser.

Engineering laser gain spectrum using electronic vertically coupled InAs-GaAs quantum dots

Continuous large-broad laser gain spectra near 1.3 /spl mu/m are obtained using an active region of electronic vertically coupled (EVC) InAs-GaAs quantum dots (QDs). A wide continuous electroluminescence spectrum, unlike that from conventional uncoupled InAs QD lasers, was obtained around 230 nm (below threshold) with a narrow lasing spectrum. An internal differential quantum efficiency as high as 90%, a maximum measured external differential efficiency of 73% for a stripe-length of L=1 mm, and a threshold current density for zero total optical loss as low as 7 A/cm/sup 2/ per QD layer were achieved.

Comparison of 1300 nm quantum well lasers using different material systems

The band structure and material gain are calculated for 1300-nm band quantum well lasers of GaInNAs, AlGaInAs and GaInAsP material systems. The material compositions for each system are carefully chosen for comparison. The calculated results show that the peak gain is around the same in spite of the difference in band structures for the three systems.

Low threshold current and widely tunable external cavity lasers with chirped multilayer InAs/InGaAs/GaAs quantum-dot structure.

Low threshold and widely tunable InAs/GaAs quantum-dot lasers are implemented with grating-coupled external-cavity arrangement. Throughout the tuning range of 130 nm, from 1160 to 1290 nm, the threshold current density is not more than 0.9 kA/cm2 and no noticeable threshold jump is observed. For a shorter-cavity device, the injection current is kept at a record low value of 90 mA but the tuning range is further extended to 150 nm, from 1143 to 1293 nm. The effect of cavity length on the tuning characteristics is discussed and the strategy for design and optimization of multilayer quantum-dot structure is also proposed.

Characteristics of InGaAs Submonolayer Quantum-Dot and InAs Quantum-Dot Photonic-Crystal Vertical-Cavity Surface-Emitting Lasers

We have made InGaAs submonolayer (SML) quantum-dot (QD) and InAs QD photonic-crystal vertical-cavity surface-emitting lasers (PhC-VCSELs) for fiber-optic communications in the 990 and 1300 nm ranges, respectively. The active region of the InGaAs SML QD PhC-VCSEL contains three InGaAs SML QD layers, with each of the SML QD layer formed by alternating depositions of InAs and GaAs. The active region of the InAs QD PhC-VCSEL contains 17 undoped InAs-InGaAs QD layers. Both types of QD PhC-VCSELs exhibit single-mode characteristics throughout the current range, with side-mode suppression ratio (SMSR) larger than 35 dB. A maximum output power of 5.7 mW has been achieved for the InGaAs SML QD PhC-VCSEL. The near-field image study of the QD PhC-VCSELs indicates that the laser beam is well confined by the photonic-crystal structure of the device.

Low-Threshold Short-Wavelength Infrared InGaAs/GaAsSb ‘W’-Type QW Laser on InP Substrate

The electrically driven short-wavelength infrared semiconductor laser using InP-based InGaAs/GaAsSb W-type quantum wells (QWs) is investigated. Using Sb-free separate confined layer and engineered QWs, the laser lasing at 2.35 μm exhibits a low-threshold current density at infinite cavity length of 83 A/cm² per QW under pulsed operation at room temperature. The internal loss α_i and internal quantum efficiency η_i of the laser are 17.5 cm^-1 and 15%, respectively.

Polarization Characteristics of Quantum-Dot Vertical-Cavity Surface-Emitting Laser With Light Injection

This investigation explores experimentally the optical characteristics of long-wavelength quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs). The InAs QD VCSEL, fabricated on a GaAs substrate, is grown by molecular beam epitaxy with fully doped distributed Bragg reflectors. The optical characteristics of QD VCSEL without and with light injection are studied in detail. The QD VCSEL has the potential to be used in all-optical signal processing systems.

Experiments and Simulation of Spectrally-Resolved Static and Dynamic Properties in Quantum Dot Two-State Lasing

We investigated the spectrally-resolved static and dynamic properties of quantum-dot lasers. The ground-state quenching and abnormal turn-on delay in quantum-dot two-state lasing behaviors are systematically studied. We found that the more saturated ground-state gain would quench ground-state emission more easily and result in the abnormal turn-on delay. Using a rate-equation model, we have successfully simulated such phenomena by considering the current heating effect.