We present a comprehensive description of electric properties of vertical-cavity surface-emitting lasers (VCSELs). A complete drift-diffusion model is developed and applied for carrier transport in a ...multilayer semiconductor laser heterostructure with a p-n junction. We address the impact of interface grading in distributed Bragg reflectors (DBRs), modulation doping of the DBRs and surrounding layers of the quantum well as well as drastically material-dependent carrier mobilities and recombination constants. Solution of the drift-diffusion model yields spatial profiles of the nonequilibrium carrier concentrations and current. The focus is made on oxide-confined GaAs/AlGaAs VCSELs. We evaluate both depletion and diffusion capacitance of the device and show that both contributions to the capacitance as well as the differential series resistance critically depend on the injection current and VCSEL chip design such that, in general, VCSEL cannot be properly modeled by an equivalent circuit approximation. Solution for the current profile demonstrates significant enhancement of the current density at the edges of the oxide-confined aperture (current crowding). We show that, as long as the mesa diameter is small, the effective RC-product can be kept low at small aperture diameters.
In this article, we report on energy efficient (6.2 mW/Gbit/s) transmitter and receiver assemblies capable of NRZ 80 Gbit/s and 72 Gbit/s fiber data transmission through 2 and 50 m of MMF, ...respectively. The optical link studied consisted of a 130 nm BiCMOS driver and transimpedance amplifier, ~30 GHz VCSEL, and ~27 GHz PD.
We report the observation of narrow tilted lobes in the far-field emission pattern of leaky oxide-confined vertical-cavity surface-emitting lasers (VCSELs). The VCSEL cavity is surrounded by two ...selectively oxidized aperture layers, which are intentionally designed to produce a high lateral leakage of the high-order transverse modes of the vertical cavity. The device operates in the fundamental transverse mode at oxide aperture diameters below 5~\mu \text{m} and currents up to 4 and 5 mA. At higher currents or larger aperture diameters, an additional high-order transverse optical mode evolves. This mode is revealed by the appearance of a shorter wavelength emission line in the electroluminescence spectra of the device, resulting in multi-mode lasing and in the related changes in the near- and far-field patterns. In the far-field pattern, the evolution of the high-order mode is revealed by the evolution of the two overlapping emission lobes at moderate (~5°) tilt angles with respect to the normal to the surface and by the appearance of a multi-spot or a ring pattern in the CCD camera images. Most importantly, the appearance of this high-order transverse mode is accompanied by an observation of much narrower lobes in the far-field pattern observed at significantly larger tilt angles (~35°). The tilt angle and the narrow angular width of these emission lobes in the far-field spectrum are in agreement with those calculated in the 3-D cold cavity modeling of the optical modes of the device. These narrow tilted lobes revealed in this paper are the fingerprints of the leakage effect in specially designed oxide-confined VCSELs with their intensity being proportional to the optical power leaving the aperture region in the direction parallel to the surface and propagating into the oxidized region. The effect can be applied for engineering of single-mode VCSELs, coherently-coupled 2-D VCSEL arrays, laterally integrated VCSEL-photodetector chips, and VCSELs integrated to slow light waveguides, for coupled optical gates for optical computers and other types of photonic integrated circuits.
Key components of the optical interconnects are the fully integrated optical transmitter and receiver subassemblies. The required features of such components include high bit rate and energy ...efficient operation in the wide range of operating conditions as well as small dimensions. In this paper, operation of the transmitter and receiver micromodules integrated with the driving electronics into the TO-can packages is demonstrated. The evaluated TOSA and ROSA 850 nm link had a convolved -3 dB bandwidth of ~ 21 GHz. Data transmission utilizing TOSA and ROSA pair up to 28 Gb/s is demonstrated in temperature range of 25°C/85°C with the nominal and up 43% reduced power consumption as well as the limited to 330 mVpp driving voltage. Results of the multiple TOSA and ROSA link measurements show limited performance spread. Finally, error-free operation up to 38 Gb/s is presented. The obtained results indicate a high potential of 850 nm VCSEL and PIN-based TO-can assemblies for the next generation of energy-efficient high bit rate optical interconnects.
We report on 4× VCSEL multi-aperture arrays in the SWDM range suitable for high power high coupling efficiency multimode fiber (MMF) transmission at current densities as low as 6.7kA/cm 2 at 25 Gbaud ...(4mW optical power in the MMF) and 16.5kA/cm 2 at 50 Gbaud (7mW).
Novel trends and concepts in the design and fabrication of vertical cavity surface-emitting lasers (VCSELs) and their integration in optical networks and implementation in integrated photonics ...applications are discussed. To serve these goals and match the growing bandwidth demands, significant changes are to be implemented in the device design. New lateral leakage-mediated single-mode VCSELs, including both devices confined by oxide layers and those confined by alloy-intermixed regions, are likely to be good candidates for light sources for the data networks of the future. An overview of the records in VCSEL transmission distances and transmission speeds is discussed in this context.
To cope with the ever increasing data traffic demands in modern data centers, new approaches and technologies must be explored. Short range optical data links play a key role in this scenario, ...enabling very high speed data rate links. Recently, great research efforts are being made to improve the performance of vertical-cavity surface-emitting lasers (VCSELs) based transmission links, which constitute a cost-effective solution desirable for massive deployments. In this paper, we experimentally demonstrate intensity-modulation direct-detection transmissions with a data rate of 107.5 Gb/s over 10 m of OM4 multimode fiber (MMF) using a multimode VCSEL at 850 nm, and up to 100 m of OM4 MMF using a single-mode VCSEL at 850 nm. Measured bit error rates were below 7% overhead forward error correction limit of 3.8e-03, thus, achieving an effective bit rate of 100.5 Gb/s. These successful transmissions were achieved by means of the multiband approach of carrierless amplitude phase modulation.
We address the design and performance issues of 640-nm range GaInP-AlGaInP laser diodes based on a longitudinal photonic bandgap crystal (PBC). The all-epitaxial design is based on selective ...filtering of high-order modes and allows extending of the fundamental mode over a PBC waveguide achieving very large vertical modal spot size. At the same time the robustness of the narrow far-field vertical beam divergence is remarkably high with respect to layer thickness variations. Optimal design ensures that all high-order optical modes show high absolute values of leakage loss (> 30 cm/sup -1/), which are order (orders) of magnitude higher than the leakage loss for the fundamental mode. This PBC-induced "resonant tunneling effect" for high-order modes leads to preferential excitation of the fundamental mode and the high-order modes are not excited even at the highest injection current densities. Broad-area (100 /spl mu/m) devices show vertical beam divergence of 8' (full-width at half-maximum) and lateral beam divergence of 7'-8'. The far-field pattern is circular shaped and stable upon an increase in injection current. Differential quantum efficiency is as high as 85 %. Maximum pulsed total optical output power is 20 W for 100-tim-wide stripe lasers with uncoated fac.
980 nm vertical-cavity surface-emitting lasers based on submonolayer growth of quantum dots show clearly open eyes and operate error free with bit error rates better than 10 at 25 and 85degC for 20 ...Gb/s without current adjustment. The peak differential efficiency only reduces from 0.71 to 0.61 W/A between 25 and 85degC; the maximum output power at 25degC is above 10 mW.
980-nm VCSELs based on submonolayer growth show for 20-Gbit/s large-signal modulation clearly open eyes without adjustment of the driving conditions between 25degC and 120degC. To access the limiting ...mechanism for the modulation bandwidth, a temperature-dependent small-signal analysis is carried out on these devices. Single-mode devices are limited by damping, whereas multimode devices are limited by thermal effects, preventing higher photon densities in the cavity.
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