We present characteristics of 850-nm oxide confined vertical-cavity surface-emitting lasers (VCSELs) developed for applications in optical parallel data links and free- space optical interconnects. Low threshold currents of less than 200 (mu) A, wall-plug efficiencies approaching 30%, operating voltages of less than 2 V for 1 mW of optical power, and operation over a wide temperature range, up to 190 degree(s)C, are demonstrated. We optimized VCSEL arrays for operation at elevated temperatures for use in dense free- space interconnects. Excellent performance uniformity-optical power of 1 +/- 0.1 mW at a drive current of 3 mA-across a 20 X 20 array was achieved at 75 degree(s)C. We integrated 2D top emitting VCSEL arrays with top- illuminated metal-semiconductor-metal detectors for future use with CMOS integrated circuits. We discuss design issues encountered in VCSEL-based modules for optical interconnects.

The use of oxide confined VCSELs in datacom applications is demonstrated. The devices exhibit low threshold currents of approximately 3 mA and low electrical series resistance of about 50 (Omega) . The emission wavelength is in the 850 nm range. Life times of the devices are several million hours under normal operating conditions. VCSEL arrays are employed in a high performance parallel optical link called PAROLI^TM. This optical ink provides 12 parallel channels with a total bandwidth exceeding 12 Gbit/s. The VCSELs optimized for the parallel optical link show excellent threshold current uniformity between channels of < 50 (mu) A. The array life time drops compared to a single device, but is still larger than 1 million hours.

Oxide confined VCSELs are being developed at Hewlett-Packard for the next-generation low cost fiber optics communication applications. Compared to the existing 850 nm implant confined VCSELs, the oxide VCSELs have lower operating voltages, higher slope efficiencies, and better modal bandwidth characteristics. Preliminary data on epitaxy and oxidation control uniformity, device performance, and reliability will be discussed.

Optocouplers are used for a variety of applications aboard spacecraft including electrical isolation, switching and power transfer. Commercially available light emitting diode- based optocouplers have experienced severe degradation of light output due to extensive displacement during damage occurring in the semiconductor lattice caused by energetic proton bombardment. A new optocoupler has been designed and fabricated which utilizes vertical cavity surface emitting laser (VCSEL) and resonant cavity photodetector (RCPD) technologies for the optocoupler emitter and detector, respectively. Linear arrays of selectively oxidized GaAs/AlGaAs VCSELs and RCPDs, each designed to operate at a wavelength of 850 nm, were fabricated using an airbridge contacting scheme. The airbridged contacts were designed to improve packaging yields and device reliability by eliminating the use of a polyimide planarizing layer which provided poor adhesion to the bond pad metallization. Details of the airbridged optocoupler fabrication process are reported. Discrete VCSEL and RCPD devices were characterized at temperatures between -100 degree(s)C to 100 degree(s)C. Devices were packaged in a face-to-face configuration to form a single channel optocoupler and its performance was evaluated under conditions of high-energy proton bombardment.

Vertical-Cavity Surface-Emitting Lasers (VCSELs) have rapidly been adopted for use in data communications modules due largely to the improvement in reliability over that of competing compact disc lasers. While very long mean lifetimes for VCSELs have been published elsewhere (> 5 X 10⁶ h MTTF at 40C), telecommunications switching applications require further reduction in the early failure rate to meet targets of < 0.5% failures over 25 years at 50 - 70 degree(s)C. Therefore, a extensive reliability program is needed to measure both the wear-out lifetime and the random failure rate of the devices. The results of accelerated life tests will be presented, and we will discuss the methodology used to estimate the failure rate. Models of current and thermal acceleration will be presented. Degradation mechanisms observed in HP lasers will be briefly discussed. We also present preliminary results from HP oxide-aperture VCSELs.

The fabrication and performance of selectively oxidized 850 nm vertical cavity surface emitting laser (VCSEL) diodes which emit through transparent GaP substrates is reported. Emission through the substrate is advantageous for many VCSEL configurations, such as for the incorporation of optical elements in the substrate or flip-chip integration to microelectronic circuitry. The short wavelength bottom- emitting VCSELs are fabricated by wafer fusion using an inert gas low temperature annealing process. The electrical characteristics of n- and p-type GaAs/GaAs and GaAs/GaP wafer bonded interfaces have been examined to optimize the annealing temperature. A significant reduction of the current-voltage characteristics of the VCSELs bonded to GaP substrates has been achieved whereby the bottom-emitting VCSELs show similar threshold voltage as compared to top- emitting lasers.

An electromagnetic model of Vertical Cavity Surface Emitting Lasers based on semiconductor compounds is developed to study the threshold conditions, the mode field distributions and the noise properties, in particular the linewidth. The model relies on the solution of Maxwell equations by using an expansion in plane waves. The main purpose is the description of the optical field confinement due to the gain mechanism induced by carrier injection. This strongly influences the noise properties and gives rise, in the case of a waveguide device, to the Petermann factor. The solution of the problem is based on an integral equation of the Fredholm type whose eigenvalues are related to the threshold operating conditions and whose eigenvectors give the field distributions. The noise characteristics are analyzed by introducing a Langevin source term in the integral equation.

Vertical-cavity surface-emitting lasers are optimized for fast intrinsic emission dynamics. The structure contains four times three quantum wells in a 2 (lambda) sin-type cavity. We have realized it using the strain-compensated (GaIn)As/Ga(PAs) material system with GaAs/AlAs Bragg mirrors. The laser emission after optical excitation with femtosecond pulses yields a pulse width of 3.2 ps and a peak delay of 4.8 ps to our knowledge the fastest values reported so far, at low temperatures. The design is successfully transferred to higher temperature operation. Picosecond dynamics is demonstrated also at room temperature with a pulse width of 13 ps and a peak delay of 9 ps. Laser operation over a broad temperature range from 140 K up to room temperature is achieved and also shows picosecond emission dynamics.

Active cavity modes are presented as a useful mode set for the analysis of the optical problem in oxide-confined VCSELs. We define the active cavity modes via a novel integral eigenvalue equation containing the VCSEL cavity electromagnetic Green's function and the gain distribution. Photon rate equation parameters, such as the net modal gain and the spontaneous emission into a mode, are calculated using this mode set as a basis. An efficient method for calculating the active cavity modes has been developed in order to allow for rapid iterations with the electronic solver in the laser simulator MINILASE. The details of the implementation of this method are presented, as are sample calculated mode parameters.

Static and dynamic characteristics of weakly index guided VCSELs in a multi-transverse mode regime are analyzed by using a model that takes into account all the transverse modes supported by the waveguide and a consistent spectral gain including many-body effects. Selection of a particular high order transverse mode by using azimuthal dependent current profiling can be obtained over a wide current range. The alternate current modulation of two orthogonal high order transverse modes is studied taking into account thermal effects. This current induced spatial switching leads to high frequency beam steering in the laser azimuthal direction.

Vertical cavity surface emitting lasers (VCSELs) operating near 1310 or 1550 nm have been the subject of intensive research by multiple groups for several years. In the past year at Gore, we have demonstrated the first 1300 nm VCSELs which operate with useful power, high modulation rate, and low voltage over the commercial temperature range of 0 - 70 degree(s)C. These results have been achieved using a new structure in which an 850 nm VCSEL optical pump is integrated with the 1300 nm VCSEL. Electrical drive is applied to the 850 nm pump, and 1300 nm light is emitted from the integrated structure. This approach has resulted in over a milliwatt of single transverse mode power at room temperature, and several hundred microwatts of single transverse mode power at 70 degree(s)C. In addition, these devices demonstrate multi-gigabit modulation and excellent coupling efficiency to single-mode fiber.

It is possible to grow defect-free strained layers on patterned substrates (mesas or grooves) up to thicknesses far exceeding the critical thickness. Defect nucleation and propagation are inhibited in such growth. We have exploited this property to design and fabricate InP-based 1.55 micrometers vertical cavity surface emitting lasers. Careful photoluminescence and TEM studies have confirmed that there are no propagating defects in the GaAs/Al_xGa_1-xAs DBR grown on the patterned active region, or the MQW region. Lasers have been made with InP/InGaAsP bottom mirrors, laterally oxidized InAlAs current confining layers and GaAs/Al_xO_y top DBR mirrors. Lasers with 8 - 40 micrometers diameter have been characterized. A threshold current of 5 mA is observed at 15 degree(s)C for a 8 micrometers diameter device; and up to 60 (mu) W of light output is recorded.

We analyze the performance of InP/GaAs fused 1.55 micrometers vertical-cavity lasers (VCLs) under analog modulation. Our VCLs employ a strain-compensated InGaAsP/InP multi-quantum well (MQW) active region sandwiched between two AlGaAs/GaAs distributed Bragg reflectors. The first AlGaAs layer of the p-doped top mirror is laterally oxidized for optical and electrical confinement. These devices exhibit the lowest threshold current as well as the highest temperature of continuous-wave operation of any electrically pumped long- wavelength VCL. Two different device designs are investigated and compared. Reduction of the MQW barrier strain and enhancement of the optical index guiding by the oxide layer lead to an improvement of VCL performance. However, parasitic effects limit the modulation bandwidth. Higher order harmonic distortion is measured and simulated using a rate equation model. The model includes a non-linear gain function, gain compression, spontaneous emission and Auger recombination as well as carrier density dependent absorption in the quantum wells which reduces the differential gain. The good agreement between measurement and simulation indicates that electron-photon interaction within the quantum wells dominates the non-linear distortion. Multiple higher order response peaks are measured and reproduced by the model.

Monolithic wavelength-graded vertical-cavity surface- emitting laser (VCSEL) and wavelength-selective resonance enhanced photodetector (REPD) arrays have been developed for use in wavelength-division multiplexed optical interconnect architectures. The aim is to achieve a cost-effective wavelength-multiplexed optical interconnect that can carry a large amount of data over longer distances using a single optical fiber. A controllable means for producing wavelength-graded VCSEL and REPD arrays is described, based on the topography-controlled MOCVD growth on a patterned substrate. This technique allows the growth rate of all the epilayers to be scaled, thereby providing closer tracking of the reflectance peak and the gain peak and resulting in more uniform device characteristics. VCSELs and REPDs have been monolithically integrated using the same epilayer structure and the same growth technique. This paper focuses on (1) the characteristics of oxide-confined multi-wavelength VCSEL arrays, (2) the design and comparison of optimized REPD structures at 850 nm and at 980 nm, and (3) wavelength multiplexing and demultiplexing using VCSEL and REPD arrays.

We have designed and fabricated a 64 channel optical module using a self-alignment flip-chip packaging technique for 2D GaAs epitaxial-side emitting vertical-cavity surface- emitting laser (VCSEL) array mounting without substrate removal on Si subcarrier. Light emission is obtained through a wet-chemically etched window in the Si subcarrier. The 2D independently addressable selectively oxidized GaAs laser array is arranged in an 8 X 8 matrix with a device pitch of 250 micrometers and each laser is supplied with two individual top contacts. This metallization scheme allows flip-chip mounting junction-side down on Si subcarrier. The VCSEL array chip is placed above the window in the Si subcarrier and is assembled using a self-aligned bonding technique with PbSn solder bumps. Arrays with 4 micrometers active diameter investigated before and after packaging show quite homogeneous optical and electrical continuous wave output characteristics exhibiting threshold currents of less than 1.1 mA and single-mode output powers of 2 mW. Driving characteristics of the lasers in the array are fully compatible to advanced 3.3 V CMOS technology. The modules are used to demonstrate free-space directional transmission applying beam steering.

A novel dual-purpose Vertical-Cavity Optoelectronic Component (VCOC), functioning either as a laser or a detector, is reported. The device is formed by modifying a conventional vertical-cavity surface-emitting laser so that it can additionally operate as an efficient detector. The modifications to the device, in order to improve photodetection, are achieved by etching its top facet. Avalanche operation under reverse bias is demonstrated for the first time in such a dual purpose component. In order to assess the overall device performance for communication applications, a bi-directional, half-duplex link is established in which a VCOC used as a source transmits signals to one used as a detector at bit rates up to 2 Gb/s.

We report experimental evidence for bandwidth collapse occurring in links employing vertical cavity lasers under conventional launching conditions. Small launch misalignments are found to result in link bandwidths up to 40% below the modal bandwidth of the fiber with eye closure penalties of 4 dB. This effect can cause gigabit/s link lengths to be limited to less than previously thought. By implementing restricted mode launches using angled launch techniques we show that significant performance improvements are achievable. In particular, by adopting an angle of 8 degree(s) between the launch axis and the fiber end face we show that the transmission bandwidth is 100% greater than the 550 Mhz.km fiber bandwidth for a wide range of launch misalignments.

We present a monolithically integrated coupled cavity vertical cavity surface emitting laser or BiVCSEL: this two- terminal electrically injected device exhibits stable laser emission at two design wavelengths simultaneously. The coupling between the two monolithically grown cavities leads to two distinct Fabry-Perot modes whose separation and localization are designed in such a way that the interaction between the two modes leads to dual laser emission. Simultaneous lasing at 925 nm and 955 nm is achieved experimentally with a threshold for dual lasing of 4 kA/cm² and dual lasing is stable over 6 times threshold.

A novel injection multi-active-region cascade laser with high output power, low threshold, small beam divergence, and high inter-modal discrimination is described. The cascade laser is formed by a periodic structure of stacked double- heterostructure diodes electrically connected by low- resistance tunnel junctions. The laser cavity is designed to match the nodes of the optical mode with the tunnel junctions and the antinodes-with the gain layers. We have considered both the cascade vertical-cavity surface-emitting laser (cascade VCSEL) and the cascade edge-emitting laser. In the multi-layer VCSEL with the multi-active-region cavity, the combined effect of increased net gain and distributed feedback allows an increased output from the Fabry-Perot resonator with mirrors of reduced reflectivity. The edge-emitting cascade laser represents a phase-locked laser array with a strong overall inter-element optical coupling. Maximum packing density of the active regions can be achieved in the common confinement cascade laser with weak optical confinement within a single array element. High inter-modal discrimination in the periodic laser structure with concentrated gain and absorption allows us to design a laser that operates in the in-phase mode with the tunnel junctions and gain layers placed in every second node and antinode of the mode, respectively.

Recent work has shown that the etching of deep trenches in close proximity to GaAs VCSEL apertures consistently causes the linear TE polarization of the emission to be pinned in a direction parallel to the line etch. Further enhancement of this polarization pinning has been achieved by post- annealing after etching. Initial studies have been carried out using photoluminescence and Raman measurements of the VCSEL wafer before and after etching as well as after annealing. Modeling the observed shift in the optical cavity (longitudinal) mode has indicated that etching introduces strain perpendicular to the etch in the active region of the VCSEL of 4 X 10⁸ dyn/cm². The strain causes the cavity mode to shift to longer wavelength and reduces the spontaneous emission in the direction perpendicular to the etched trenches. The strain introduced by etching is believed to be the origin of this polarization pinning effect. Measurements of the spontaneous emission profile across the VCSEL facet after etching give valuable information on the mechanisms involved.

On-axis channeling through the use of photoactive layers in VCSEL cavities is proposed to counteract hole burning and mode switching. The photoactive layers act as variable resistivity screens whose radial `aperture' is controlled by the light itself. It is numerically demonstrated that absorption of a small fraction of the light intensity suffices for significant on axis current peaking and single mode operation at currents many times threshold, with minimum efficiency loss and optical mode distortion. Fabrication is implemented during the molecular beam epitaxy phase without wafer post processing, as for oxide apertures.

A microscopic model for polarization switching in optically anisotropic VCSELs is presented. Our approach includes: (1) steady-state microscopic theory for the optical response of semiconductor quantum wells describing the dynamics of charge carriers and of interband polarizations in realistic bandstructures, including Coulomb-interaction correlations; (2) vectorial eigenmode calculation and the resulting expansion of the electromagnetic field in the laser in terms of vectorial eigenmodes of a whole structure, their polarization properties, mode-dependent losses and frequencies; (3) realistic model for optical anisotropies resulting from intentional or unintentional strain in an active quantum-well layer. The resulting steady-state input/output characteristics of linearly polarized microscopic eigenmodes of VCSELs are investigated in details. Linear stability analysis of these modes reveals the polarization switching behavior observed experimentally in practical VCSEL structures. We demonstrate that any nonzero uniaxial strain which may be present in the lattice structure (for instance, left over after the fabrication process) causes the laser to start lasing in a polarization eigenstate which is gain-preferred, but, for larger pumping currents, this polarization becomes unstable and the laser would switch to the orthogonal eigenstate.