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 Al_0.67Ga_0.33As/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%.

A systematic and comparative study of the temperature dependence of the threshold current, threshold voltage, and output power of vertical-cavity surface-emitting lasers (VCSELs) is presented to discuss the factors that limit their temperature range for cw operation. To achieve high-performance for VCSELs, the position of the lasing mode must be in close proximity to (within +/- 5nm of) the gain peak under cw operation. In addition, by introducing continuously graded hetero-interfaces throughout the VCSEL structure, the effect of thermal self-heating is reduced. The combination of low thermal dissipation and alignment of the cavity mode to the gain peak resulted in VCSELs with excellent operating characteristics over a broad range of temperatures, including a thermally stable threshold voltage, and a very wide temperature range for both pulsed (100K to 540K) and cw (100K to 410K) operation.

Long lasting vertical-cavity surface-emitting lasers (VC-SELs) are reported for system applications. The 2700 hours of operation at 50 degree(s)C indicates approximately equals 0.5%/Khr degradation rate predicting mean time to failure of approximately equals 10⁵ hours. The substrate temperatures ranged from 20 degree(s)C to 65 degree(s)C.

The high frequency behavior of vertical-cavity surface-emitting lasers (VCSELs) has been investigated. The small-signal optical modulation response and the impedance characteristics of several different multiple-quantum-well (MQW) VCSEL device structures have been measured and modeled as a function of dc bias and frequency in the 0.13- to 20-GHz range. An equivalent circuit model describing the intrinsic and extrinsic response of the VCSEL was derived, and a good fit to the experimental impedance and modulation data has been achieved. The extrinsic model yields the VCSEL electrical transfer function from which the 3 dB corner frequency (attributed to RLC parasitics) can be evaluated. In some of the devices measured, the 3 dB cutoff frequency is higher than the 3 dB optical modulation bandwidth measured. It is demonstrated that the electrical circuit parasitics alone are not the limiting factor in obtaining the maximum modulation bandwidth from these devices. It is found that the output power roll-over effect due to thermal heating is also a significant limit in obtaining higher optical modulation frequencies. By fitting the model of the intrinsic modulation response to the measured data a maximum resonant relaxation frequency of over 22 GHz is obtained (for a device with an 11-micrometers -diameter active region). It is also found that the amplitude of the modulation in these MQW devices is significantly reduced as the current increases much above threshold, and that this attenuation of the amplitude is explained by the frequency roll-off of the electrical RC parasitics.

We have measured the active region size dependence of the high speed modulation characteristics of vertical cavity surface emitting lasers with lateral current injection. The moveout rate df₀d(root)P and K factor determined from a curve fit to the small signal modulation data were df₀d(root)P approximately equals 4.5-6.5 GHz/(root)mW and K approximately equals 0.68-0.85 ns for both 10 and 20 micron diameter devices. The maximum resonance frequency was limited by device heating, and a parasitic type of rolloff in the modulation response was observed, which we fit to a diffusion capacitance model.

We have fabricated wavelength tunable vertical-cavity laser diodes on n-GaAs substrates in 2D arrays by molecular beam epitaxy, proton implantation, and wet chemical etching. Record low threshold currents of 650 (mu) A for continuous wave and 600 (mu) A for pulsed operation are obtained for 8 micrometers active diameter devices. Output power is up to 170 (mu) W cw and 400 (mu) W pulsed. The Bragg reflectors consist of AlAs-GaAs stacks. The active region contains three strained In_0.2Ga_0.8As quantum wells. The emission wavelength is about 960 nm. Three terminals for each laser diode supply two separate currents for independent control of output power and emission wavelength of individual elements in the 2D array. A record wide continuous wavelength tuning range of 5.6 nm is achieved with tuning currents just below 1 mA. Highly efficient and alignment tolerant coupling to single-mode optical fibers is demonstrated with modified vertical-cavity laser diodes. Quasi planar devices providing two-sided light output have been fabricated with an inverted npn-doping profile. Direct contact butt coupling to flat cut single-mode optical fibers of 4.5 micrometers diameter core results in over 90% coupling efficiency. The lateral alignment tolerances defined by a -3 dB coupling efficiency decrease are as large as 5.6 micrometers . Maximum power in 9 micrometers diameter core fibers is 0.75 mW for a non-heat-sinked device with 8 micrometers alignment tolerances. The easy fiber attachment is applicable to 2D laser arrays and mass production. The large alignment tolerances will improve reliability and drastically reduce packaging costs making vertical-cavity lasers very attractive for short distance optical interconnects.

We have reduced the threshold voltages and currents of vertical cavity surface emitting lasers by using dielectric high reflectivity mirrors which were deposited after the diode fabrication step. This device fabrication sequence is able to correct for inaccuracies in the crystal growth and allows the future development of more complex laser structures. The quantum- well based laser diodes were demonstrated at 0.72 micrometers , 0.85 micrometers , and 1.55 micrometers . Threshold currents and voltages of our 0.85 micrometers lasers were 2.8 mA at 1.7 V pulsed, and 4 mA when cw- pumped. The threshold currents of 5x7 micrometers ² area 1.55 micrometers devices were 17 mA.

Optoelectronic integrated circuits based on arrays of vertical- cavity surface emitting lasers (VCSELs) are evolving into functional chips enhancing the performance of fiber optic networks, optical data storage, laser printing and scanning, visual displays, and optoelectronic computing and other systems. This evolution involves the development of advanced manufacturing technology germane to packaged arrays of VCSELs comprising micro- optic lens arrays and interface electronics. In this paper we describe Photonics Research's LASE-ARRAY commercial manufacturing efforts. Specifically we will discuss commercial manufacturing advancements in molecular beam epitaxial growth, full-wafer processing, interface electronics, microoptic lens arrays, packaging and implementation of statistical process control. Yield and reliability will also be discussed. Last we discuss emerging applications for the LASE-ARRAY technology.

A new approximate analytical approach is developed and applied to investigate thermal properties of top-surface-emitting vertical- cavity diode lasers (VCSELs) mounted substrate-down. Multilayer structure of distributed-Bragg reflectors is taken into account by considering anisotropic thermal conductivity. Design conditions for minimal thermal resistance in short- and long- wavelength systems are specified for devices with various active- region diameters. Our results indicate that difficulties with obtaining the cw operation of long-wavelength VCSELs are primarily associated with intrinsic properties rather than with their thermal resistance.

This paper reviews the progress in the technology and application of vertical cavity surface emitting semiconductor laser (VCSEL) arrays. I focus on the capability to obtain high-performance, high-yield, uniformly operating arrays. Both 1D individually addressable arrays and 2D matrix-addressable VCSEL arrays are described. These arrays are made possible by the novel geometry of VCSELs and the advances in the field of epitaxial growth. Applications envisioned include high-speed parallel optical data links (exploiting both 1D and 2D arrays) and imaging, microscopy and computational technologies which readily benefit from 2D addressable sources. The characteristics of VCSEL devices and arrays for use as transmitter sources as optical interconnects and for display and/or imaging applications are stressed.

Since the advent of semiconductor lasers, the reduction of threshold current has been an important research theme, because zero-bias modulation and low consumption of power are expected. To reduce threshold current, many approaches have been reported for edge-emitting lasers and surface-emitting lasers. Recently, with the growing interest in 2D optical interconnect systems, which lead to a lot of channels, surface-emitting-lasers and related optical functional devices have been extensively studied. To integrate these surface-emitting devices into a 2D array, each device has to achieve high light-output power in low current level. For this purpose, threshold reduction in surface-emitting- laser type optical devices is particularly important. This paper reviews recent activity on low-threshold surface-emitting-laser type optical devices, which includes photon recycling and microcavity, and also describes the record low threshold current of 190 (mu) A under pulsed operation at room temperature in an airpost microcavity laser with the diameter of 5 micrometers .

An optical logic system is being developed to test the packaging and operation of free space optical logic systems. It uses symmetric-self-electro-optic effect devices as the logic elements and vertical cavity surface emitting lasers (VCSELs) to provide the optical inputs. This paper discusses the issues involved with incorporating the VCSEL array into the system. Issues that are investigated include beam combining, electrical drive, and VCSEL polarization. We find that current experimental devices are appropriate for early system experiments although issues such a multimode operation and the resulting current dependent polarization need to be addressed for practical systems.

Vertical cavity surface emitting lasers (VCSELs) have the potential to provide massively parallel 2D free space chip-to- chip and fiber guided board to board optical interconnections. We describe the construction and performance of two prototype optical data links (2D-ODL). One prototype used direct modulation of a 2 X 18 array of fiber pigtailed VCSELs. The other 2D-ODL attempted to use an 8 X 18 VCSEL array as an optical power source for a symmetric self-electooptic effect device reflection modulator array.