InP-based VCSELs (Vertical Cavity Surface Emitting Lasers) are interesting light sources for applications in spectroscopy and fiberoptical communication. Reviewed are devices with a buried tunnel junction (BTJ) and a dielectric backside reflector directly integrated on a electroplated gold-heatsink in the InGaAlAs/InP material system covering the wavelength range from 1.3 to 2.0 μm. The BTJ accomplishes both current confinement to the active region and wave-guiding by the refractive index distribution to achieve low threshold currents. Furthermore it allows for substitution of p-doped device parts by more suitable n-doped material. This approach already proved excellent device performance such as 7 mW output power (multi-mode) and good high temperature characteristics such as 0.5 mW at 80°C for 1.55 μm. Modulation at 10 Gbit/s was also demonstrated. Since the BTJ VCSEL concept covers a wide wavelength range, there is a high-potential field of applications in Tunable Diode Laser Absorption Spectroscopy (TDLAS). Demonstrated are representative measurements of NH3 and HCl. A specialty of TDLAS with VCSELs is the ability for rapid concentration determination with a time resolution up to the megahertz regime. Recent results and further developments of the device structure are also discussed.

We demonstrate novel electrically pumped 1300 nm and 1550 nm VCSELs with two InP/air-gap DBRs. The active regions comprise conventional InGaAsP multiple quantum wells. A tunnel junction is placed between the active region and top DBR to convert electrons into holes, thus minimizing the use of p-type material in the structure to reduce the free-carrier loss and achieve current confinement. The whole structure was grown in a single growth run by low pressure MOCVD. For both 1300 and 1550 nm emission wavelengths, air-gap DBR VCSELs exhibit roomtemperature, CW threshold current density as low as 1.1 kA/cm², differential quantum efficiency greater than 30%, and CW operation up to 85°C. The single-mode output power was 1.6 mW from a 1300 nm VCSEL with a 6.3 μm aperture; and 1.1 mW from a 1550 nm VCSEL with a 5.7 μm aperture under room temperature CW operation

We present the design and characteristics of an optically pumped vertical external cavity surface emitting laser emitting near 1550 nm. The InP-based laser was grown by Metalorganic vapor-phase epitaxy including an InGaAsP gain element and an InP/InGaAsP mirror. The gain element comprises 20 strain compensated quantum wells on top of a distributed Bragg reflector. As an external mirror we used a concave spherical mirror, which also provides the outcoupling of light. Gain is achieved by optical pumping with a high power, 1250 nm fiber Raman laser focused on the gain chip. Essential for achieving high output power is to reduce the temperature of the gain material and this is accomplished by bonding an intra-cavity silicon heat spreader to the surface of the gain element. The maximum output power is 260 mW at multi transverse mode operation and 230 mW at single transverse mode operation with a near Gaussian beam profile (M²=1.22) at 240 K. At room temperature the output power was limited to 12 mW. The maximum output power greatly depends on the operating temperature and studies of pump induced thermal effects show that thermal lensing imposes limitations on the attainable power.

Honeywell continues to be the world’s leading supplier of VCSELs operating at 850 nm. This paper will cover new commercial application areas for 850-nm VCSELs, and will present new findings in VCSEL reliability science. In particular, newly-developing applications drive requirements for ever more reliable VCSEL design and fabrication, and for improvements in controls for ESD (electrostatic discharge) and EOS (electrical overstress) at manufacturing facilities both for VCSEL components and for higher-level assemblies employing VCSEL components. Honeywell efforts toward improvement of reliability and toward reduction of ESD exposure are described, as is an alternative approach to improving reliability of systems containing VCSELs without compromising their performance.

By continuing on the VCSEL studies, TrueLight’s VCSEL was proven to be a highly reliable product for Datacom applications as well as to have cost-effective advantages in manufacturing. In this paper, we will show the fabrication technologies for several Gigabits approach as well as for very low cost sensor applications. We will also show recent achievements in studies of extended operating temperature, single mode emission and long wavelength VCSEL emitted at about 1300 nm.

Injection locking has been actively researched for its possibility to improve laser performance for both digital and analog applications. When a modulated follower laser (also termed "slave" laser) is locked to the master laser, its nonlinear distortion and frequency chirp may be reduced. As well, the resonance frequency can increase to several times higher than its free running case. In this paper, we show that the frequency response (S21) of an injection-locked laser is similar to a parasitic-limited laser with a high resonance frequency. The S21 was studied experimentally and the condition to achieve a flat, enhanced frequency response was identified. For analog applications, a record 112 dB-Hz2/3, single-tone third harmonic spur-free dynamic range of a 1.55 um VCSEL was demonstrated. An improvement was attained for a wide injection parameter space. Furthermore, the RIN of the VCSEL was found to be 10 dB lower at 2 GHz for certain injection condition. In a 50 km 2.5 Gb/s digital link, a 2 dB power penalty reduction at 10-9 bit-error-rate was also demonstrated. As a novel application, an injection-locked uncooled tunable VCSEL was shown to have a reasonable modulation performance in a wide ambient temperature range. The VCSEL was locked to a designated wavelength and the injection compensated the temperature-induced performance degradation. This concept can be extremely attractive for low-cost DWDM transmitters.

Oxide-confined, polyimide-planarized 850 nm vertical cavity surface emitting lasers (VCSELs) with excellent high-speed performance were fabricated and characterized. The reproducible, simple process provides good metal adhesion to photodefined polyimide offering low capacitance without implantation or semi-insulating substrates. Microwave measurements are used to extract parameters for a physically based equivalent circuit for the VCSEL.

Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers (VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain best current confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy to integrate with classical software for circuit studies, this model which is widely adaptable for different structures takes into account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10 GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic values for the VCSEL intrinsic parameters. Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current and voltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz for monomodal emitter.

We present in this paper the MOCVD growth and characterization of high performance 850nm InGaAsP/InGaP strain-compensated MQWs vertical-cavity surface-emitting lasers (VCSELs). These VCSELs exhibit superior characteristics, with threshold currents ~0.4 mA, and slope efficiencies ~ 0.6 mW/mA. The threshold current change is less than 0.2 mA and the slope efficiency drops by less than ~30% when the substrate temperature is raised from room temperature to 85°C. These VCSELs also demonstrate high speed modulation bandwidth up to 12.5Gbit/s from 25°C to 85°C.

Photonic crystal confinement in vertical cavity surface-emitting lasers (VCSELs) is a robust and reliable technology for achieving operation in the fundamental lateral mode and is potentially applicable to a variety of materials systems and operating wavelengths. We demonstrate photonic crystal VCSELs operating in a single transverse mode with over 30 dB side mode suppression and over 1 mW of output power. These lasers have been subjected to a post-process technique to introduce the etched holes making up the photonic crystals that surround a centralized defect in which lasing occurs. We also show that coupling between adjacent defects in a photonic lattice is possible, further increasing the power available in the devices.

An all-epitaxial process is described for obtaining an intracavity aperture in GaAs-based vertical-cavity surface-emitting lasers (VCSELs) that lead to simultaneous current and optical confinement. The laser structure starts with 30 pairs of n-type GaAs/AlAs bottom DBR mirrors, a full-wave cavity including three 6nm In_0.2Ga_0.8As quantum wells at the center, and 1.5 pairs of p-type GaAs/AlGaAs DBR mirrors. A tunnel junction is deposited thereafter, which includes AlGaAs etch-stop, 30nm p+ (Be = 5×10¹⁹ cm^-3) GaAs, 10nm n+ (Si = 5×10¹⁹ cm^-3) In_0.1Ga_0.9As, and 30nm n+ (Si = 1×10¹⁹ cm^-3) GaAs. Apertures are defined by removal of the tunnel junction layers outside the aperture via ex-situ lithography and wet etching. The VCSEL structure is completed by an MBE regrowth of 15 pairs of n-type GaAs/AlAs DBRs. Simple post-grown processing includes metal ring contact deposition and device isolation (wet-etching through the cavity.) The current confinement in the area far from the aperture is shown to be excellent from the measurement of the same-size dummy mesas and metal contacts next to the working devices on the same wafer. At room temperature, a 10 μm circular-aperture VCSEL lases under pulsed current injection with a threshold current of 2.6mA. Some limitations in the continuous wave operating characteristics will be described and are believed to arise from Be diffusion. Replacing Be with a less diffusive C dopant can greatly improve the device performance.

Antiresonant reflecting optical waveguide (ARROW) vertical cavity surface emitting lasers (VCSELs) are designed for high power single mode operation. Scalar wave and finite-difference time domain (FDTD) studies indicate large modal discrimination in favor of the fundamental mode for large aperture (8 um) ARROW VCSELs. The modal discrimination mechanisms are identified through the total modal loss and quality factor calculations including polarization dependence. A novel design is presented, utilizing metal absorption loss to help suppress higher-order modes.

Closely packed VCSEL arrays phase lock due to active lateral interactions from cross gain and cross hole-burning. Breaking the lattice symmetry either by geometry, or by staggered application of two biases IA, IB creates a "two cavity species" photonic lattice. The relative phase among locked cavities is controlled by the applied bias ratio IA/IB. While uniform arrays allow only in- or out- of phase locking, two-species lattices allows a small but continuous range of phase shifts for the Bragg steering condition, without movable parts.

Laser sources emitting at 460nm have been developed through intracavity doubling of an extended cavity, surface emitting semiconductor laser. These lasers are compact, spectrally pure, efficient, and have a high quality beam. The basic design is similar to previously reported work[1] at 488nm using Novalux Extended Cavity Surface Emitting Laser (NECSEL) structures. The choice of nonlinear material was found to be critical, with periodically poled materials providing distinct benefits over bulk materials. Output powers exceeded 20mW. The reliability of the completed lasers was found to be excellent.

This talk will present a new category of optical interconnection solutions based on an intelligent active cable concept. The inset of the Smart cables is to be fully plug-compatible with existing electrical copper-based cable sockets. By powering upt the Smart cables through the electrical socket the new cable can have active fiber optic elements or active cable equalization to extend the reach of conventional passive copper cables. Specific characterization data will be provided on Alvesta four-channel transceiver solution.

We have improved the design of our red emitting VCSELs to be less sensitive to leakage induced optical losses in the output reflector. The current designs produce in excess of 0.2mW at 652nm and 50 degrees C. We also have devices emitting 6.5mW at 668nm at 20 degrees C. We use a simple model to predict the device performance improvements of minor modifications to the device design. By reducing the bias voltage from the current high levels, we predict that c.w. powers in excess of 0.5mW at 80 degrees C and up to 17mW at 20 degrees C should be possible without any further design or material improvements.

Data patterns are shown to affect the far field distribution of vertical cavity surface emitting lasers (VCSELs). Two data patterns with different frequency content resulted in different beam profile distributions even though both patterns had 50% duty cycles resulting in the same thermal dissipation. The effect of gain switching and varying high and low drive levels was also investigated. Angle dependent waveforms displayed overshoot on axis and undershoot off axis. The potential impact of pattern dependent launch conditions is discussed.

1.3 μm VCSELs have been under development for several years. In this work, we discuss several requirements and characteristics that allow a device to be manufacturable in high volume with excellent yield.

We report our results on InGaNAs/GaAs vertical-cavity surface-emitting lasers (VCSELs) for fiber-optic applications in the 1.3 μm range. The epitaxial structures were grown on (100) GaAs substrates by MBE or MOCVD. The nitrogen composition of the InGaNAs/GaAs quantum-well (QW) active region is 0 to 0.02. Long-wavelength (up to 1.3 μm) room-temperature continuous-wave (RT CW) lasing operation was achieved for MBE and MOCVD-grown VCELs. For MOCVD-grown devices with n- and p-doped distributed Bragg reflectors (DBRs), a maximum optical output power of 0.74 mW was measured for In_0.36Ga_0.64N_0.006As_0.994/GaAs VCSELs. The MBE-grown devices were made with intracavity structure. Top-emitting multi-mode 1.3 μm In_0.35Ga_0.65N_0.02As_0.98/GaAs VCSELs with 1mW output power have been achieved under RT CW operation. Emission characteristics of InGaNAs/GaAs VCSELs were measured and analyzed.

We have optimized the doping levels in distributed Bragg reflectors (DBRs) and GaInNAs/GaAs quantum well (QW) structures in order to enhance their optical output power. We achieved high output power GaInNAs vertical-cavity surface-emitting lasers (VCSELs) emitting at 1260nm. The continuous wave (CW) output power of the devices reached 3.0mW at room temperature, with a slope efficiency of 0.28W/A. The devices consisted of conventional n-type and ptype doped DBRs with GaInNAs/GaAs 3QWs, and they were grown by metalorganic chemical vapor deposition (MOCVD).

Following the success in fiber based DataCom, VCSELs start to conquer additional market shares in a variety of other applications like free space optics (FSO), lighting, printing, and sensing. U-L-M photonics presents a new family of commercial high power VCSELs emitting powers of up to 50 mW cw at RT based on top-emitting technology. The devices are available at 850 nm emission wavelength. All devices can be operated passively cooled and provide modulation bandwidths of up to 1 GHz. Wallplug efficiencies are in excess of 25 %. Even higher output power of 250 mW cw from a 80 μm active diameter bottom-emitting VCSEL operating at 980 nm has already been obtained although just beeing passively cooled. Further power up scaling is achieved by arrangement of multiple VCSELs in 2D arrays. For the first time we demonstrate cw output power of 10 Watt cw at RT from compact monolithic VCSEL module of 14 mm² chip area. Transfer of the technology to other wavelengths, e.g. 808 nm and 945 nm, is presented, too, and shows perspectives towards homogeneous optical pumping of solid state lasers. Almost identical device performance levels can be presented for the entire wavelength span. All discussed results are based on highest quality epitaxy optimized for maximum intrinsic efficiency and differential slope efficiency. Oxide confinement is used for current constriction that provides most efficient electrical pumping of the active area. In combination with advanced mounting techniques all mentioned aspects sum up to allow for cost effective VCSEL products in the medium and high power laser regime. The circular output beam in addition to simple heat sinking offers attractive solutions for advanced system integration.

Recent data on 10 Gb/s oxide VCSELs are presented. We cover failure analysis results on VCSELs that failed in the field, including failures due to electrostatic discharge (ESD) and those inherent to the limitations of the present mesa structure used in oxide VCSELs. An ongoing experiment to overcome these limitations is discussed.

The reliability of novel, electrically pumped, vertical cavity 980-nm InGaAs lasers is demonstrated through accelerated life testing (ALT). The ALT methodology is used to detect failure modes as well as to obtain failure statistics. The time-to-failure (TTF) distribution and acceleration model are determined from over 200 devices tested from multiple wafers and assembly lots to account for process variation. The failure mode observed was gradual power degradation, while all other laser diode characteristics, e.g., threshold current, operating current and wavelength, remained stable. Laser output power degraded linearly in t^1/2, where t is the stress time. The acceleration model best fitting the data is Black's equation with thermal activation energy of 0.89 eV and current density coefficient of 2.9. Verification of the acceleration model was confirmed through life testing over 500 devices at field operating conditions. The high level of reliability demonstrated meets strict telecommunications requirements.

Based on design guidelines from a three-dimensional, fully vectorial model, we have fabricated vertical-cavity surface-emitting lasers (VCSELs) with a monolithically integrated dielectric surface grating for polarization control. For VCSELs with emission wavelengths of 850 and 980 nm we have achieved orthogonal polarization suppression ratios (OPSRs) above 15 dB for all modes up to thermal rollover, which very well agrees with theory. It is shown both theoretically and experimentally that the grating has no influence on the emission far-field. The surface grating has also been combined with a surface relief to stabilize the polarization and to increase the fundamental mode output power at the same time.

Proton implanted VCSEL has been demonstrated with good reliability and decent modulation speed up to 1.25 Gb/s. However, kinks in current vs light output (L-I) has been always an issue in the gain-guided proton implant VCSEL. The kink related jitter and noise performance made it difficult to meet 2.5 Gb/s (OC-48) requirement. The kinks in L-I curve can be attributed to non-uniform carrier distribution induced non-uniform gain distribution within emission area. In this paper, the effects of a Ti/ITO transparent over-coating on the proton-implanted AlGaAs/GaAs VCSELs (15um diameter aperture) are investigated. The kinks distribution in L-I characteristics from a 2 inch wafer is greatly improved compared to conventional process. These VCSELs exhibit nearly kink-free L-I output performance with threshold currents ~3 mA, and the slope efficiencies ~ 0.25 W/A. The near-field emission patterns suggest the Ti/ITO over-coating facilitates the current spreading and uniform carrier distribution of the top VCSEL contact thus enhancing the laser performance. Finally, we performed high speed modulation measurement. The eye diagram of proton-implanted VCSELs with Ti/ITO transparent over-coating operating at 2.125 Gb/s with 10mA bias and 9dB extinction ratio shows very clean eye with jitter less than 35 ps.

A quantitative analysis of Wavelength Modulation Spectroscopy (WMS) signals at various harmonic detection orders for use in precision, non-intrusive measurements is performed. A theoretical analysis of fitting of WMS signals is developed. The detailed structures of WMS signals at various harmonic detection orders are studied and analyzed, using statistical measures. It is shown that the variance of errors increases with mesmatches in linewidth in a particular (N^th order) harmonic signal. However, this rate of increase in variance is characteristic of the harmonic detection order used, thereby demonstrating the advantage in measurements at different harmonics. It is shown that for a constant error in estimation of linewidth of a profile, the variance of errors can be higher for higher detection orders. Therefore, mismatches in fits are more prominent at some optimal detection order. The methods developed can be used to examine subtle effects such as Dicke narrowing in certain molecular spectra. These small perturbations of lineshape profile reveal details of the molecular collision kinetics, and hence yield precise measurements that are difficult to achieve by other techniques.