Low-threshold Vertical-cavity Surface-emitting Laser Research Articles

High-yield flip-chip bonding and packaging of low-threshold VCSEL arrays on sapphire substrates

Oxide-confined top-emitting 850 nm and bottom-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) 8/spl times/8 arrays were designed and fabricated for applications of optical interconnects. The arrays were flip-chip bonded onto sapphire substrates that contain complimentary metal-oxide-semiconductor (CMOS) driver and fan-out circuitries. The off-sited bonding contacts and minimized bonding force produced very high yield of the hybridization process without causing damage to the VCSEL mesas. The hybridized devices were further mounted either on printed circuit board (PCB) or in 68-pin pin-grid-array (PGA) packages. The transparent sapphire substrate allowed optical outputs from the top-emitting VCSEL arrays to transmit directly through without additional substrate removal procedure. Lasing thresholds below 250 /spl mu/A for 850 nm VCSELs and 800 /spl mu/A for 980 nm VCSEL were found at room temperature. The oxide confinement apertures of VCSELs were measured to be around 6 /spl mu/m in diameter. High-speed data transmission demonstrated a bandwidth of up to 1 Gbits/s per channel for these hybridized VCSEL transmitters.

Monolithically integrated low-power phototransceivers for optoelectronic parallel sensing and processing applications

A low-power GaAs-based monolithically integrated phototransceiver, consisting of a high-gain heterojunction phototransistor (WPT) and a microcavity light-emitting diode (MCLED) or a low-threshold vertical-cavity surface-emitting laser (VCSEL), is demonstrated. The HPT and MCLED/VCSEL are grown by molecular-beam epitaxy in a single step. The phototransistor exhibits a responsivity of 60 A/W at an input power of 1 /spl mu/W. The input and output wavelengths are 850 and 980 nm, respectively. The MCLED-based phototransceiver exhibits an optical gain of 7 dB and power dissipation of 400 /spl mu/W for an input power of 1.5 /spl mu/W. The small signal modulation bandwidth is 80 MHz. On the other hand, the VCSEL-based phototransceiver exhibits an optical gain of 10 dB and power dissipation of 760 /spl mu/W for an input power of 2.5 /spl mu/W.

Ultralow-threshold cryogenic vertical-cavity surface-emitting laser

Data are presented characterizing a low-threshold vertical-cavity surface-emitting laser designed for cryogenic operation. A threshold current of 12 /spl mu/A and current density of 25 A/cm/sup 2/ are obtained at 77 K with the low-loss cavity design. From 77 K to 160 K, the threshold increases linearly with temperature, but only approximately tracks the detuning of the cavity resonance from the minimum energy transition of the quantum well. At 77 K, we estimate that the 25-A/cm/sup 2/ threshold current density is about twice that required for transparency.

Intracavity contacts for low-threshold oxide-confined vertical-cavity surface-emitting lasers

Very low threshold vertical-cavity surface-emitting lasers are demonstrated using intracavity contacts, an upper dielectric Bragg reflector, and an undoped lower AlAs-GaAs Bragg reflector. The undoped lower mirror allows the demonstration of the highest differential efficiency yet achieved for sub-100-μA threshold, which is 60% for a 67-μA threshold. Devices with smaller output coupling show threshold current densities as low 98 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and a minimum threshold current of 23 μA for a small aperture.

Low-threshold vertical-cavity surface-emitting lasers based on oxide-confinement and high contrast distributed Bragg reflectors

The interest in low-threshold vertical-cavity surface-emitting lasers (VCSEL's) is increased by the demonstration of the small size, low loss optical mode due to oxide-confinement in the Fabry-Perot microcavity laser. Intense recent work in this area has resulted in numerous record breaking demonstrations of low-threshold current, high wall-plug efficiency, and high speed. In this paper, we discuss the impact of the dielectric cavity design to enhance control of the optical mode. We argue that high contrast dielectric mirrors can become an important design approach, especially for small apertures limited by diffraction loss. Experimental results are compared for different types of mirror and aperture designs.

Low threshold vertical-cavity surface-emitting lasers based on high contrast distributed Bragg reflectors

Data are presented on vertical-cavity surface-emitting lasers that use high contrast distributed Bragg reflectors on both sides of the cavity. The upper reflector consists of a six pair ZnSe/MgF quarter-wave stack, while the lower reflector consists of an eleven pair AlxOy/GaAs stack fabricated using selective oxidation. Strain due to the lower reflector is reduced by using AlxOy layers of less than a quarter-wave thickness. Device sizes ranging from 1 to 7 μm diameters are characterized, with a minimum threshold current of 53 μA.

ON MICROCAVITY EFFECT IN VERTICAL CAVITY SURFACE EMITTING QUANTUM WELL LASER WITH MULTILAYER HETEROSTRUCTURE REFLECTORS

Effects of the multilayer heterostructures as the feedback end facets and quantum well structure as the active medium on the lasing behavior in the vertical cavity surface emitting laser (VCSEL) have been analyzed theoretically and systematically. It is shown that the degree of phase matching and the effective length of the distributed reflector have prominent effects on the laser characteristics, and the available low threshold VCSEL may not be due to the microcavity effect. The possible ways to improve the design and the device characteristics have been proposed, both for low threshold and simplified device technology, and for satisfying the condition of microcavity effect in VCSEL.

Fabrication processes for low threshold InGaAs vertical-cavity surface-emitting lasers

In order to realize a low threshold vertical-cavity surface-emitting laser (VCSEL), we have fabricated a micro-cavity structure by a native oxidation technique. The strong optical and electrical confinements enabled to achieve low thresholds. For further threshold reduction, we have demonstrated an n-type modulation doped quantum well (QW) laser and a 30% reduction of threshold in n-type doped QW laser compared with undoped QW lasers is observed. These are the first experiments for InGaAs/AlGaAs materials.

780 nm oxidised vertical-cavity surface-emittinglasers with Al 0.11 Ga 0.89 As quantum wells

Low threshold vertical-cavity surface-emitting lasers with Al0.11Ga0.89As four quantum wells for 780 nm wavelength emission are fabricated using aluminum oxide apertures. The fabrication process requires only single step mask alignment. The 3.4 µm square laser exhibits a low threshold current of 200 µA, which is more than an order of magnitude smaller than the previous values obtained at 780 nm. Singlemode peak output power is 1.1 mW. This 3.4 µm laser is found to operate in the fundamental transverse mode over the complete operating current range. The 7.6 µm square laser shows peak output power of 2.7 mW.

Low-threshold vertical cavity surface-emitting lasers with metallic reflectors

Continuous-wave room-temperature operation is reported for the first time of vertical cavity current injection semiconductor lasers with a metallic reflector. The GaAs/(AlGa)As lasers have low-threshold currents of 8 mA for 8-μm-diam contacts and threshold current densities of 9.5 kA/cm2. Single longitudinal mode and bimodal operation are obtained for short and long Fabry–Perot étalons, respectively. The spectral width of the single-mode laser line is 0.1 Å. The laser structures have a very small series resistance which results in a voltage drop of 1.8 V along the diodes at lasing threshold.