VECSEL Chip Research Articles

High average output power from a backside-cooled 2-µm InGaSb VECSEL with full gain characterization.

We compare the gain and continuous wave lasing properties of two InGaSb-based vertical external cavity surface emitting lasers (InGaSb VECSEL) with different heat management approaches operating at a center wavelength of around 2μ m. To date, intracavity heatspreaders have been required for good average output power, which have many trade-offs, especially for passive modelocking. Here we demonstrate a record high average output power of 810 mW without an intracavity heatspreader using a backside-cooled non-resonant VECSEL chip optimized for modelocking. In addition, we introduce and demonstrate an optical characterization for a wavelength range of 1.9 to 3μ m to precisely measure wavelength-dependent gain saturation and spectral gain. Gain characteristics are measured as a function of wavelength, fluence, pump power and temperature. Small signal gain of more than 5%, small saturation fluences and broad gain bandwidths of more than 90 nm are demonstrated. In comparison to a commercial VECSEL chip with an intracavity heatspreader, we have obtained similar average output power even though our VECSEL chip is designed for antiresonance.

Comparison of AlGaInP-VECSEL gain structures

We present a comparison of epitaxial designs for barrier pumped vertical external-cavity surface-emitting lasers in the red spectral range. The VECSEL chips are grown by metal-organic vapor-phase epitaxy as GaInP/AlGaInP multi-quantum well structures with 20 and 21 compressively strained quantum wells, respectively. The QWs are placed in various packages in a separate confinement heterostructure with quaternary AlGaInP-barrier and cladding layers. Beneath the active region there is a distributed Bragg reflector consisting of 55 λ/4 pairs of Al0.5Ga0.5As/AlAs. We compare three different QW distributions: one design includes 20 QWs arranged in 10 pairs, the second one contains 20 QWs arranged in 10 pairs with tensile strained barriers to compensate the compressive strain of the QWs, the third one has an exponential distribution of the QWs in tensile strained barriers. Laser parameters such as wavelength, differential efficiency, optical output power and absorption of the pump laser were measured for the different designs. By using the exponential distribution of QWs we could improve the differential efficiency by 42% and the output power by 20% compared to the not strain compensated 10×2 QW design. Furthermore we could improve the absorption efficiency by 60% at nearly the same laser wavelength.

Strain compensation techniques for red AlGaInP-VECSELs: Performance comparison of epitaxial designs

We present a strain-compensation design for non-resonantly pumped vertical external cavity surface-emitting lasers for emission in the red spectral range around 665nm. Here, the VECSEL chip is based on a metal-organic vapor-phase epitaxy grown (GaxIn1−x)0.5P0.5/[(AlxGa1−x)yIn 1−y]0.5P0.5 multi-quantum-well structure with 20 compressively strained quantum wells. By introducing tensile strained quaternary barriers and cladding layers in a 5×4 QW design, we could compensate for the compressive strain introduced by the quantum wells. Photoluminenscence measurements of structures with different numbers of quantum well packages reveal a more homogenous quantum well growth due to the strain-compensation technique. Furthermore, with the strain compensation technique, the output power could be increased over 30% compared to our conventional structures.

Cost-Effective Thermally-Managed 1.55-$\mu{\rm m}$ VECSEL With Hybrid Mirror on Copper Substrate

An electroplated copper substrate was evaluated for heat dissipation in 1.55-μ.m optically pumped vertical extended cavity surface emitting lasers (OP-VECSELs). It is a cost-effective and flexible solution compared with the previously proposed chemical vapor deposition diamond substrate assembled by metallic bonding. Continuous-wave (CW) lasing operation was demonstrated from a device (with copper electroplated substrate) under optical pumping with pump spot diameter of 100 μm and a maximum output power of 260 mW at 0°C; heatsink temperature was achieved. Room-temperature CW operation with an output power of 75 mW and an external quantum efficiency of 35% was achieved in an optimized plane-concave cavity. The thermal resistance and the maximum output power of VECSEL chips assembled with bonded bulk copper and electroplated copper substrates were measured and compared. A value of ~50 K/W was estimated for both devices, and a similar rollover point was observed, which indicates that the electroplated copper solution leads to similar thermal properties as a bonded bulk copper substrate.

Highly efficient InGaAs QW vertical external cavity surface emitting lasers emitting at 1060 nm

We report on the high-power operation of an optically pumped VECSEL emitting at 1060 nm. The VECSEL structure, grown by MOVPE, consists of resonant periodic gains and 35 pairs of AlAs/AlGaAs DBR. A single In 0.28GaAs quantum well is positioned at each antinode of the optical standing wave. The VECSEL chip is water-bonded by capillarity to a diamond heatspreader. 10 W continuous wave operation is achieved with an optical-to-optical conversion efficiency of 44% at room temperature. High efficiency and good thermal stability are mainly due to the optimization of epitaxial quality and the high conductivity of the diamond heatspreader. We have found that the increase of the round trip caused by the heat spreader is about 1%.

98/01411 Numerical prediction of InGaAs/GaAs MQW solar cell characteristics under concentrated sunlight: Ohtsuka, H. et al. Solar Energy Materials and Solar Cells, 1998, 50, (1–4), 251–257

We present a comparison of epitaxial designs for barrier pumped vertical external-cavity surface-emitting lasers in the red spectral range. The VECSEL chips are grown by metal-organic vapor-phase epitaxy as GaInP/AlGaInP multi-quantum well structures with 20 and 21 compressively strained quantum wells, respectively. The QWs are placed in various packages in a separate confinement heterostructure with quaternary AlGaInP-barrier and cladding layers. Beneath the active region there is a distributed Bragg reflector consisting of 55 λ/4 pairs of Al0.5Ga0.5As/AlAs. We compare three different QW distributions: one design includes 20 QWs arranged in 10 pairs, the second one contains 20 QWs arranged in 10 pairs with tensile strained barriers to compensate the compressive strain of the QWs, the third one has an exponential distribution of the QWs in tensile strained barriers. Laser parameters such as wavelength, differential efficiency, optical output power and absorption of the pump laser were measured for the different designs. By using the exponential distribution of QWs we could improve the differential efficiency by 42% and the output power by 20% compared to the not strain compensated 10×2 QW design. Furthermore we could improve the absorption efficiency by 60% at nearly the same laser wavelength.