Matthew G. Peters

Band-gap engineered digital alloy interfaces for lower resistance vertical-cavity surface-emitting lasers

We report on a technique of grading the heterobarrier interfaces of a p‐type distributed Bragg reflector mirror to reduce the operating voltages of vertical‐cavity surface‐emitting lasers (VCSELs). We report VCSELs with lower operating voltages (2–3 V) and record continuous‐wave room‐temperature power‐conversion efficiencies (17.3%). We experimentally demonstrate that by using a parabolic grading and modulating the doping correctly, a flat valence band is generated that provides low voltage hole transport. The low resistance mirrors are achieved using low Be doping, digital‐alloy grading and 600u2009°C growth temperatures.

Monolithic integration of refractive lenses with vertical-cavity lasers and detectors for optical interconnections

We present a technique for monolithic integration of vertical cavity lasers and detectors with refractive microlenses etched on the back side of the semiconductor substrate in a wafer-scale process. This integration provides collimated or focused laser beam sources for applications in free-space interconnections or for coupling to optical fibers, and it improves the collection efficiency of detectors.

Reliability and performance of InGaAs broad-area lasers emitting between 910 and 980 nm

High power InGaAs multi-mode broad area semiconductor lasers emitting between 190 nm and 980 nm are required as optical pumps for Er+ and Yb+ doped double clad fiber lasers and amplifiers. In this paper, we present performance and reliability of two generations of 100 micrometer aperture broad area devices emitting at 920 nm and 970 nm. The first generation devices have been deployed in the field with up to 2.5 W ex-facet optical power. More than 500,000 device-hrs of actual multi-cell lifetest data, and nearly 100 million accelerated device-hrs have been accumulated with 91FIT at 1.2W and 25 degrees Celsius or 1.9 million hrs MTBF at 2W and 25 degrees Celsius. A next-generation design further reduces thermal resistance, optical loss, and far-field divergence resulting in up to 4W ex-facet CW output power with superb reliability. Multi-mode fiber coupled modules demonstrate high coupling efficiency due to the reduced divergence angles of the new design. Lifetest of the new generation devices demonstrate the reliability of 167 FIT at 2W and 25 degrees Celsius or 499,000 hrs MTBF at 4W and 25 degrees Celsius.

Analysis of VCSEL degradation modes

VCSELs have recently made a great deal of progress both in improved performance with threshold currents now < 100 (mu) A, as well as in their commercialization. Parallel communication links based on VCSEL arrays are now commercially available. However, little information has been published to date on VCSEL reliability or on what causes VCSEL failures. In this presentation, we will describe the VCSEL degradation processes observed in the wide variety of structures we have tested. These include GaAs- and InGaAs-QW VCSELs; top- and bottom-emitting structures; and proton-implanted and etched-pillar VCSELs. We will discuss the novel observation that in most VCSELs we have examined, defects in the upper mirror (a p-type Distributed Bragg Reflector) can be associated with VCSEL degradation. Laser spectra show a luminescence peak from these mirrors, indicating the presence of minority carriers in the low-bandgap layers of the mirrors. These minority carriers are thought to be at the origin of the defect formation in the p-mirrors. We will discuss the possible sources of this minority carrier injection, and present spectra which shed light on the cause of this phenomenon. We will also discuss how fabrication and packaging stresses for some structures significantly accelerate the degradation process. The failure modes observed for various designs will be shown, and possible design improvements suggested.

High wall-plug efficiency temperature-insensitive vertical-cavity surface-emitting lasers with low-barrier p-type mirrors

Vertical-cavity surface-emitting lasers (VCSELs) are promising candidates as efficient sources for optical fiber communication due to their high efficiency coupling to fibers, single longitudinal mode operation, and ability to be integrated as arrays on a single chip. The best overall measurement of practical device performance is the wall-plug efficiency, defined as total optical power out divided by total electrical power in. The theoretical mechanisms that effect the wall-plug efficiency of VCSELs will be analyzed and discussed, especially the trade- off between differential efficiency and threshold current. Experimentally, modifications of the growth structure which improve wall-plug efficiency have been implemented. The drive voltage has been reduced and the optical loss is also decreased by using lower barrier p-type Al0.67Ga0.33As/GaAs mirrors with special interface gradings. Also, by offsetting the quantum- well gain peak from the cavity mode, the gain overlap is optimized at the true active-region operating temperature (above room-temperature). These effects combine to yield a peak CW room- temperature wall-plug efficiency of 17.3%.

Vertical-cavity surface-emitting laser technology

The technology of vertical cavity surface emitting lasers (VCSELs) has grown dramatically in recent years. We have processed and packaged VCSELs, for various applications. The thermal, output coupling, and spectral characteristics for different devices and packages are shown. Practical single device and array packages, and the results of their coupling to optical fibers are presented.

Low-power high-speed vertical cavity lasers for dense array applications

Vertical-cavity lasers have demonstrated the ability to produce mW level output powers in a low divergence circular beam. This has made them attractive sources for high density applications such as free space interconnects and optical computing. Moving from device demonstration to practical applications, however, poses additional demands. High density arrays require very low power consumption for thermal management while the interconnect lines must not introduce excessive stray capacitance. We have developed vertical cavity lasers with intra-cavity contacts on semi-insulating substrates which provide solutions to these practical problems. The intra-cavity design allows the use of ring contacts on the same surface with either top or bottom emission. The lasers can thus be connected in a raster interconnect pattern or any other contacting configuration without impairing the high speed performance. On chip resistors can be incorporated into the circuit so that simple voltage drives can be used. Using a current constriction to provide electrical and optical confinement has removed the limitations of surface recombination, allowing the development of high external efficiency, sub-milliamp threshold vertical cavity lasers. The 7 micrometers diameter lasers have output powers of 1 mW at a bias current of 3 mA with modulation bandwidths above 8 GHz while consuming only 10 mW of power. The lasers can therefore be driven with full on/off current modulation to transmit data at rates exceeding 1 Gbit/s, simplifying the driver electronics considerably. The structure and fabrication sequence is discussed along with bit error rate measurements including on/off modulation conditions.

High power, high brightness diode lasers for kW lasers systems

Laser diodes with high power and brightness are critical for pumping kW-class fiber lasers and direct diode laser systems. We present performance data of current generation broad area chips and new chips as well as multi-emitter fiber-coupled modules. Improved lateral beam quality at high power allows new designs to reach 15W power with lateral beam parameter product (BPP) <;4 mm-mrad. A fiber-coupled module that spatially and polarization combines multiple emitters shows a brightness of 3.4 W/(mm-mrad)2 at 185 W of power, which represents a 30% improvement over the present generation.

Advances in high-power 9XXnm laser diodes for pumping fiber lasers

A multi-mode 9XXnm-wavelength laser diode was developed to optimize the divergence angle and reliable ex-facet power. Lasers diodes were assembled into a multi-emitter pump package that is fiber coupled via spatial and polarization multiplexing. The pump package has a 135μm diameter output fiber that leverages the same optical train and mechanical design qualified previously. Up to ~ 270W CW power at 22A is achieved at a case temperature ~ 30ºC. Power conversion efficiency is 60% (peak) that drops to 53% at 22A with little thermal roll over. Greater than 90% of the light is collected at < 0.12NA at 16A drive current that produces 3.0W/(mm-mr)2 radiance from the output fiber.

High-efficiency, high power laser diodes

Laser diodes and bars with high efficiency and power are used for a wide variety of applications including direct material processing and pumping fiber and solid state lasers. Efficient electro-optical. conversion is critical to achieve high output power as it allows to reduce dissipated heat and cooling load. This work presents progress achieved by JDSU in the DARPA Super High Efficiency Diode Sources (SHEDS) program. A highly efficient laser diode in the form of a single 100um wide emitter (910nm-980nm wavelength range) reaches 16.5W of CW power and more than 30W of pulsed power. Implementation of radically asymmetric waveguide structure, extensive optimization in doping, composition profiles resulted in more than 70% power conversion efficiency at a power of 80W from bars mounted and tested by different bar manufactures. The best bar power conversion efficiency achieved approaches 73% at 80W and 22°C cooling water.Laser diodes and bars with high efficiency and power are used for a wide variety of applications including direct material processing and pumping fiber and solid state lasers. Efficient electro-optical. conversion is critical to achieve high output power as it allows to reduce dissipated heat and cooling load. This work presents progress achieved by JDSU in the DARPA Super High Efficiency Diode Sources (SHEDS) program. A highly efficient laser diode in the form of a single 100um wide emitter (910nm-980nm wavelength range) reaches 16.5W of CW power and more than 30W of pulsed power. Implementation of radically asymmetric waveguide structure, extensive optimization in doping, composition profiles resulted in more than 70% power conversion efficiency at a power of 80W from bars mounted and tested by different bar manufactures. The best bar power conversion efficiency achieved approaches 73% at 80W and 22°C cooling water.