In 1996, Honeywell was the first company to commercialize VCSEL technology, and today it is the world's largest VCSEL component supplier. This paper will focus on the aspects of VCSEL manufacture that are important to maintain highly reliable and producible components. For current VCSEL products, we will address the evolution of VCSEL reliability and its effect on performance in data communications systems. New applications in both the data communications and sensor markets are being enabled by the VCSEL technology. This paper will also discuss new VCSEL structures, packages and wavelengths that are being commercialized by Honeywell to address these emerging markets.

We discuss the reliability of the oxide VCSELs made by Agilent Technologies (formerly part of Hewlett Packard). Measurements of operating temperature in fiber optic modules are given; these temperatures are higher than generally assumed. General challenges with oxide VCSEL reliability are introduced, and different types of failures are discussed. Long-term oxide VCSEL lifetest results are presented, along with observations about the thermal and current acceleration models. Production monitoring strategies are discussed, and the basic degradation phenomenology is briefly shown.

System architects in the communications and computing industries have been waiting for the arrival of cost effective fiber optic links to relieve the copper BW*distance constraint for intra and short reach inter-system connections. Parallel optics has been targeted at this application space for several years, but up until the current generation of systems, these applications largely remained copper. The current change-over in interconnect media is partially due to the engineering challenge in meeting performance requirements with electrical interconnects as well as the progress in parallel fiber optic components. Gore has been investigating aggressively in the research and development of the technologies required for producing high bandwidth, reliable, and cost effective parallel fiber optic links. The first commercialization of this effort will be the nLIGHTEN parallel optical modules. This paper details the design, fabrication, and operation of this high performance, short haul communication system.

Ion-implanted vertical cavity surface emitting lasers are analyzed by photocurrent spectroscopy. The photoelectric quantum efficiency of such a device was found to reveal information on the presence of defect levels within the device. Photocurrent spectra of the samples, that are in part aged, were measured. For aged devices we find up to a tenfold increase of the magnitude of a defect band energetically situated below the laser emission. We show that photocurrent spectroscopy, that so far has been successfully applied for studying aging properties of high-power diode lasers, has also a remarkable potential as analytical tool for vertical cavity surface emitting lasers.

The impressive performance improvements of laterally oxidized VCSELs come at the expense of increased fabrication complexity for 2-dimensional arrays. Since the epitaxial layers to be wet-thermally oxidized must be exposed, non-planarity can be an issue. This is particularly important in that electrical contact to both the anode and cathode of the diode must be brought out to a package. We have investigated four fabrication sequences suitable for the fabrication of 2- dimensional VCSEL arrays. These techniques include: mesa etched polymer planarized, mesa etched bridge contacted, mesa etched oxide isolated (where the electrical trace is isolated from the substrate during the oxidation) and oxide/implant isolation (oxidation through small via holes) all of which result in VCSELs with outstanding performance. The suitability of these processes for manufacturing are assessed relative to oxidation uniformity, device capacitance, and structural ruggedness for packaging.

We demonstrate a technique to apply real-time optical flux monitoring by in situ atomic absorption when the only available optical path through a molecular beam epitaxial growth chamber reflects from the substrate. Thin-film interference effects in the reflected signal were virtually eliminated during growth by using a collinear beam that has a wavelength very close to that of the group-III absorption line. This method enables atomic absorption monitoring to be applied to heterostructure growths without the need for real- time reflectance analysis. We demonstrated the technique by monitoring Ga flux during GaAs growth using a Mn lamp for the off-resonance source. The short-term uncertainty in the flux measurement was 0.6% (one standard deviation). Theoretical calculations indicated that approximately 0.2% and 0.3% maximum instantaneous error can be attained for Ga and Al, respectively, during the growth of vertical cavity surface emitting layers.

The characterization of 1.55 micrometer room temperature (RT) electrically pumped monolithic vertical cavity surface emitting lasers (VCSELs) on InP is reported. By combining high refractive index-contrast AlGaAsSb/AlAsSb distributed Bragg mirrors (DBRs) and Esaki-junction-based active region, these results demonstrate that VCSELs operating at 1.55 micrometer and employing a reasonable number of mirror periods can be grown in a single epitaxial step. Regarding our first results with the same type of structure, some improvements have been achieved on the threshold current density (approximately equals 1 kA/cm²), and on the voltage drop in the DBRs. We also present in this paper the thermal conductivity of the As- Sb materials measured on both bulk layers and DBR stacks. The main performance-limiting factor appears to be the combination between the low thermal conduction of the quaternary alloys lattice-matched to InP, and the high energy-band offset between the high- and the low-index materials.

We review a relatively simple model for VCSEL polarization noise, which is based on the adiabatic elimination of the carrier spin dynamics, and show how this 2-dimensional model can often be further simplified to a 1-dimensional (Kramers) model. Experimental verification for the validity of these models comes from a series of experiments on proton-implanted and etched-post VCSELs. We quantify the amount of linear and nonlinear birefringence and dichroism, we demonstrate a polarization-type of four-wave mixing, and discuss the correlated modal intensity fluctuations in the two polarization modes. Finally, we discuss the jump statistics of a VCSEL with stochastic polarization switches, and present a time-resolved observation of the polarization evolution during such a switch.

Top-emitting intra-cavity VCSELs have been fabricated by reactive-ion etching of a double mesa and applying p and n contact metallizations at the bottom of both mesas, respectively, where highly doped layers are inserted into the cavity on either side of the active region. The VCSELs are designed to emit around 980 nm, and use two strained InGaAs quantum wells and AlAs/GaAs DBR mirrors. Efficient lateral current constriction is realized by selective oxidation of two AlAs layers in the second mesa. A sealing method has been developed to prevent simultaneous oxidation of the top-DBR. A novel asymmetric contacting scheme is introduced in order to avoid current crowding at the inner edges of the oxidized AlAs layers and to stabilize the polarization. Devices with various mesa shapes and either symmetric or asymmetric contacts have been fabricated on the same wafer. Experimental analysis of these VCSELs demonstrates polarization control by asymmetric current injection, where the polarization perpendicular to the current path is favored due to anisotropy of both gain and optical losses. The strength of this effect relative to others (anisotropic loss in rectangular mesas, crystal anisotropy) and its use in electrically controlled polarization switching is explored.

Polarization control is reported for a 2-D independently addressable VCSEL array. Polarization pinning for emitters on the same die at several orientations is achieved by etching trenches close to the contact metallization of each emitter in the array using focused ion beam etching. Polarization extinction ratios in excess of 50 are achieved over a wide range of orientations and bias currents. No significant effects are observed on threshold current subsequent to the etching of polarization pinning trenches.

We report on two AlGaInP-based visible VCSEL designs based on different current confinement schemes, ion implantation and selective oxidation, and we compare the respective performances with a particular interest on the modulation properties. The implanted device operated continuous wave (CW) up to 40 degrees Celsius. Threshold current of 7 mA, threshold voltage of 2.5 V and maximum optical power of 0.3 mW were measured at room temperature. The small signal modulation responses were fitted using a 3-poles model, allowing the estimation of various parameters such as resonance frequency, damping factor and parasitic cut-off. The maximum 3dB- bandwidth was shown to be 2.1 GHz, limited both by thermal and parasitic effects. 'Error-free' transmission at 1 Gb/s was demonstrated through 50-meter of graded-index POF. The selectivity oxidized devices achieve much higher output power (1.8 mW for the 10 micrometer opening diameter) with threshold current as low a 1.5 mA and threshold voltage of 2.1 V at room temperature, and operate CW up to 49 degrees Celsius. The maximum 3 dB-bandwidth was 4.5 GHz. Modulation current efficiency factor up to 2.8 GHz/(root)[mA] was measured.

This paper presents results that have emerged from the European funded ESPRIT Project, Bright Red Surface Emitting Lasers (BREDSELS-23455). The project's main objective has been to develop arrays of Vertical Cavity Surface Emitting Lasers (VCSEL's) emitting in the region of 650 nm. These VCSEL arrays, suitably coupled to plastic fiber ribbon, are potentially ideal sources for high-speed plastic optical fiber networks. Linear 1 X 8 VCSEL arrays have been fabricated from wafers grown in multi-wafer MOVPE reactors. Individual VCSELs are shown to generate a peak room temperature power of 2 mW at 674 nm and are capable of operating continuous wave to a temperature of 60 degrees Celsius. The use of selective oxidation in the fabrication process is found to be essential in terms of providing effective heat sinking to the active region, while free carrier absorption is found to be a significant loss mechanism. A detailed description of the device results including modal behavior is presented along with the initial results from the plastic fiber ribbon module.

The semiconductor laser simulator Minilase has been integrated with a novel optical mode solver in order to simulate vertical cavity surface emitting lasers. The electronic and optical solvers are reviewed, and the interaction between the two solvers is presented in detail. The combined simulator recalculates the optical modes in response to changing electronic conditions without requiring prohibitively large computational resources.

The time evolution of the first three higher order transverse modes is studied for proton-implanted VCSELs using a spatially resolved multi-mode rate equation model. The cylindrically symmetrical model includes spatial hole burning, thermal lensing, current spreading, carrier diffusion and gain saturation. This role of thermal effects and gain non- linearity are studied for transverse mode competition in proton-implanted VCSELs by operating the device with long electrical pulses. Limitations in the single mode operation resulting from the spatial hole burning and thermal effects are observed.

It is demonstrated numerically that photoactive layers placed in a VCSEL cavity can eliminate the power modulation during laser switch on. As well known, the transient response is generated by the cavity relaxation oscillations (omega) _R, stemming from accelerated carrier depletion with increasing laser power. The presence of photoactive layers with appropriately chosen parameters reverses the sign of the depletion rate. The relaxation frequency then becomes pure imaginary, and the laser cavity behaves as an overdamped oscillator that asymptotes to the final steady-state without power modulation or 'spiking.' Superior bandwidth is anticipated by frequency response analysis.

We have studied the spontaneous emission of polarized excitons in the GaInP/AlGaInP VCSEL from 30 K to room temperature. It is observed that the spontaneous emission peak enters and leaves the resonant regime. At the resonant regime, the emission intensities of the perpendicular and horizontal polarized exciton are enhanced at different ratio to those in non-resonant regime. These experiment results are explained through the dressed exciton theory of the semiconductor microcavity device. From this theory, the intensity enhancement and the polarization dependence are understood as cooperative emission and the microcavity anisotropy.

Vertical cavity surface emitting lasers (VCSEL) operating around 850 nm are finding escalating markets in fiber optical communication applications, currently mainly at data rates between 1 and 2,5 Gbit/s. More than 3 million device hours without failures at temperatures up to 100 degrees Celsius proves that the reliability of the VCSEL satisfies the requirements for these applications. Results for oxidized as well as implanted devices are discussed and designs for both common anode and common cathode driving conditions are described. We demonstrate the application of our VCSEL design to arrays with passive alignment for parallel data communication over fiber ribbon. As examples of visible components for communication over plastic optical fiber, results for resonant cavity light emitting diodes will be shown and compared to red VCSELs.

Standards activities for the next generation of Ethernet, 10 Gigabit Ethernet, are underway. Vertical Cavity Surface Emitting Lasers (VCSELs) offer significant advantages for realizing cost-effective, high speed optical data links. The progress towards achieving 10 Gb/s VCSEL-based links is reviewed.

The advent of the vertical cavity surface-emitting laser (VCSEL) has spurred numerous applications requiring low-cost high performance laser sources. Gigabit Local Area Networks (LAN) utilizing multimode fiber-optic communication systems have predominantly pushed VCSEL technologies to their current state. In order for VCSEL technologies to continue driving the optical networking interconnect solutions, new datacom applications have been proposed. Course Wavelength Division Multiplexing (CWDM) is one such application being proposed that has the potential to significantly increase both the capacity and distance of optical interconnects, while still maintaining a low cost. Designing CWDM (Course Wavelength Division Multiplexing) systems for integration into a small and low cost package suitable for LAN applications has many challenges. These challenges include producing multi- wavelength VCSEL arrays, miniature multiplexers and demultiplexers, passive alignment, and thermal management. The first section of this paper will describe the VCSEL wavelengths and thermal requirements necessary to achieve an 8-channel CWDM system. The second section will describe the optical multiplexer and demultiplexer technologies. The final section will discuss several specific applications and products that VCSEL CWDM systems can address.

The presentation gives an overview of the ongoing Army Research Laboratory (ARL)/University of Maryland research effort on vertical-cavity-surface-emitting-laser (VCSEL) interconnects and OE processing and why this technology is of interest. ARL is conducting a research and development effort to develop VCSELs, VCSEL arrays, and their hybridization with complimentary metal-oxide-semiconductor (CMOS) electronics and microwave monolithic integrated circuits (MMICs). ARL is also very active in the design, modeling, and development of diffractive optical elements (DOEs). VCSEL-CMOS flip-chip optoelectronic circuits and DOEs are of interest together with detector-CMOS flip-chip circuits to provide digital and analog optoelectronic interconnects in optoelectronic processing architectures. Such optoelectronic architectures show promise of relieving some of the information flow bottlenecks that are emerging in conventional digital electronic processing as the electronic state of the art advances at a rapid pace and the electronic interconnects become a significant limitation. Such optoelectronic interconnects are also of interest in the development of analog optoelectronic processing architectures that are very difficult to implement in conventional electronic circuitry due to the incorporation of dense arrays of interconnects between electronic elements. VCSEL-MMIC- detector flip-chip circuits are of interest for the incorporation of optoelectronic interconnects into analog RF systems where the optoelectronic interconnect offers advantages of size, weight, bandwidth, and power consumption. VCSEL-MMIC interconnects may also play a role in future high- speed digital optoelectronic processing.

The Large Hadron Collider (LHC) will become operational in 2005 at The European Laboratory for Particle Physics (CERN). The LHC will be the highest energy proton-proton collider in the world. One of the electronic particle detectors which will operate at the LHC is called ATLAS. The environment for electronics placed within ATLAS is extremely hostile due to the high levels of radiation and the general lack of access to components during the expected 10 year lifetime of the experiment. It is planned to use custom radiation tolerant VCSEL-based optical links to transfer data from the ATLAS inner detector to remote data acquisition electronics. A low mass, non-magnetic and radiation tolerant VCSEL packaging has been developed for the most hostile region in the center of ATLAS where the inner detector is located. The performance of the package is reported on. Qualification tests of commercial VCSELs are also described. The VCSELs were irradiated with neutrons (up to 8.10¹⁴ n(1MeV)/cm²) and annealing studies carried out. Post-irradiation accelerated lifetime tests equivalent to a minimum of 3700 LHC operation years at a 0 degree Celsius operation temperature are reported on. The characteristics of VCSELs when operated in a strong magnetic field (up to 6 T) are also studied.

High beam qualities at high optical output powers make VCSELs attractive light sources for various applications like printing, engraving or pumping of solid state lasers. We report on mounted AlGaAs-GaAs two-dimensional VCSEL arrays of 0.123 mm² size emitting 1.4 W cw optical output power at 10 degrees Celsius. The emitting wavelength of these bottom emitting VCSELs is 980 nm. Maximum power is achieved at a current of 3.3 A and an applied voltage of 2.8 V. The power density spatially averaged over the cleaved laser chip is as high as 1.1 kW/cm². Narrow circular far-fields below 12 degrees FWHM allow easy focusing of the light to a spot size of less than 100 micrometer resulting in a power density of above 10 kW/cm². Mounting of the VCSEL array is very convenient since there is no need to take care of precise facet alignment as required for conventional edge emitting laser arrays. Simple mounting on copper heat sinks or microchannel coolers leads to inexpensive laser modules with output powers in the Watt regime. Lifetime testing for more than 7000 hours at room temperature performed at 1 A current corresponding to an output power of about 440 mW has shown a degradation rate of about 1% per 1000 hours which is very promising for industrial applications. So far, we have successfully employed VCSEL arrays for foil marking and free space data transmission.

We present the investigation of several methods to increase the active diameter of single transverse mode oxide confined VCSELs in both the 850 and 980 nm wavelength regimes. Among the concepts considered are mode intensity specific shallow surface etched reliefs, monolithically increased cavity lengths, current confinement matching the fundamental mode intensity distribution and saturable absorbers. All approaches are introduced in theoretical considerations and corresponding measurement results are presented. Additionally, numerical simulations are performed to gain an increased understanding of some of the mode selection mechanisms. The considered concepts are evaluated in terms of decrease of the series resistance (for impedance matching/driving reasons) and device lifetime (as derived from maximum current densities). The results obtained are also compared to other approaches found in literature (e.g. metal apertures, photocurrent feedback, Fabry-Perot etalon, half-symmetric cavity). Conventional devices with optimized thin oxide aperture location have shown single-mode output powers above 4 mW with an active diameter of 3.5 micrometer. A record high single-transverse mode output power of 5 mW at a series resistance of 98 (Omega) is obtained for a 7 micrometer aperture device by increasing the cavity length monolithically by 4 micrometer.

A simple model is used to design and optimize masks that when etched onto the aperture of a normally multi-mode gain guided vertical-cavity surface-emitting laser, VCSEL, cause the device to lase in a single transverse mode. After etching, Gaussian beam profiles for the LP01 mode are achieved over the entire operating current range with greater than 16 dB modal suppression. To date single mode emission at 2 mW has been achieved with pinning of the nearfield width. The modelling shows that the etching introduces a spatial filter on the higher order modes. The power in the fundamental mode remains constant before and after etching.

Vertical cavity surface emitting lasers (VCSELs) which operate in multiple transverse optical modes have been rapidly adopted into present data communication applications which rely on multi-mode optical fiber. However, operation only in the fundamental mode is required for free space interconnects and numerous other emerging VCSEL applications. Two device design strategies for obtaining single mode lasing in VCSELs based on mode selective loss or mode selective gain are reviewed and compared. Mode discrimination is attained with the use of a thick tapered oxide aperture positioned at a longitudinal field null. Mode selective gain is achieved by defining a gain aperture within the VCSEL active region to preferentially support the fundamental mode. VCSELs which exhibit greater than 3 mW of single mode output power at 850 nm with mode suppression ratio greater than 30 dB are reported.

Optical Translation Measurement (OTM), developed by GOU Lite Ltd, is a novel Doppler based motion measurement method. An OTM sensor includes a laser diode, detectors and optics integrated into a small transistor-style package. The sensor measures the relative motion of surfaces placed adjacent (up to a few millimeters) to its aperture. The OTM sensor is thus a compact 3D Doppler motion sensor, measuring two transverse (perpendicular to illumination beam) and one longitudinal directions of motion. Integration of low power (less than 1 mW) VCSELs enables low cost, low power consumption sensors. OTM is characterized by high SNR, high accuracy, resolution of a few wavelengths, and independence of the measurement from the distance to and the type of the surface. OTM is an 'enabling technology,' with potential wide-spread use both in traditional encoding tasks and in new applications.

Stable phase-locking of a VCSEL array of N equals 16 emitters with the master laser on the same chip is demonstrated. To accomplish the injection-locking a very small portion of the master radiation is seeded frontally into the 16 slave lasers. All VCSELs are driven by one voltage source with small individual series resistors to compensate for frequency differences. The beams are collimated by a microlens array and are commonly focused. A factor 14 increase of the peak power density of the superimposed beams compared to the unlocked operation is achieved (overall system coherence 85%) without any phase control. The coherent operation is stable for hours without any sophisticated voltage or temperature control. By slightly varying the current of each emitter within the locking range a maximum phase shift of (pi) can be achieved for each emitter. In this way residual phase differences between the individual beams can be compensated. The fraction of the master power necessary to lock one slave laser is below 10^-3. Therefore, scaling to very large arrays is possible. Apart from simply increasing the peak power density of the chip, a promising perspective for data transmission applications is the GHz-modulation of the system coherence. The locking of the array can be switched by a very small (2%) modulation of the master current thereby switching the peak power density by a factor of nearly N.

In this contribution, we bring forward and compare the polarization switching (PS) dynamics and the polarization modulation characteristics of gain- and index-guided VCSELs. We then discuss the steady-state and dynamic characteristics of both types of VCSELs. Finally we focus on the polarization modulation limit and the average mode hopping frequency, which both scale over 8 orders of magnitude when the switching current is varied from just above threshold up to 2 times the threshold current.