This PDF file contains the front matter associated with SPIE Proceedings Volume 8638, including the Title Page, Copyright Information, Table of Contents, Introduction and Conference Committee listing.

Applications of 850 nm VCSELs have bloomed in recent years arising from their low cost, and the ease of forming one- and two-dimensional arrays. In addition to the traditional measures of device lifetime, operation over a wide temperature range and link length, the figures of merit increasingly include power consumption (pJ/bit), footprint (bits/mm²) and cost ($/Gb/s). As 1 × 12 arrays of 10G VCSELs are widely adopted, there is a clear need for improvement along all these fronts. This is achieved through development of VCSELs operating at higher data rates, and modifications to the oxide VCSEL structure. In this paper, we discuss the development of VCSELs with electrostatic discharge protection, and high bandwidth for operation at 10 – 25 Gb/s.

In May of 2012, Emcore’s VCSEL FAB and VCSEL based transceiver business joined Sumitomo Electric Device Innovations USA (SEDU). After this change of ownership, our high speed VCSEL development effort continues. In this paper, we will report the progress we made in the past year in our 25Gbps to 28Gbps VCSEL. This next generation device is targeted for EDR, 32GFC as well as other optical interconnect applications.

Building coarse wavelength division multiplexing (WDM), 4×10 Gbps VCSEL transmitter modules has the promise for dramatic decreasing power consumption. Over the last years, we have demonstrated continuous improvements of parameters and reliability of wafer fused long-wavelength VCSELs. Progress and challenges in industrial fabrication of wafer-fused VCSELs emitting in the 1310 nm band for high speed WDM applications are reviewed.

Vixar has been developing VCSELs at both shorter (680nm) and longer (1850nm) wavelengths. This paper reports on advances in technology at both of these wavelengths. 680nm VCSELs based upon the AlGaAs/AlGaInP materials system were designed and fabricated for high speed operation for plastic optical fiber (POF) based links for industrial, automotive and consumer applications. High speed testing was performed in a “back-to-back” configuration over short lengths of glass fiber, over 42 meters of POF, with and without I.C. drivers and preamps, and over temperature. Performance to 90°C, 10 Gbps and over 40 meters of plastic optical fiber has been demonstrated. Reliability testing has been performed over a range of temperatures and currents. Preliminary results predict a TT1% failure of at least 240,000 hours at 40°C and an average current modulation of 4mA. In addition, the VCSELs survive 1000 hours at 85% humidity 85°C in a non-hermetic package. 1850nm InP based VCSELs are being developed for optical neurostimulation. The goals are to optimize the output power and power conversion efficiency. 7mW of DC output power has been demonstrated at room temperature, as well as a power conversion efficiency of 12%. Devices operate to 85°C. Over 70mW of pulsed power has been achieved from a 35 VCSEL array, with a pulse width of 10μsec.

Nonpolar and semipolar orientations of gallium nitride offer several advantages for vertical-cavity surface-emitting lasers (VCSELs), including enhanced radiative efficiencies and higher optical gain compared to c-plane oriented VCSELs. Additionally, anisotropic gain within the quantum well plane should result in a consistent and well-defined polarization direction of the emission in nonpolar and semipolar VCSELs. We report the first known electricallyinjected nonpolar m-plane GaN VCSELs, operating under pulsed injection at room temperature. As predicted, m-plane GaN VCSELs exhibit polarization locking, with the polarization direction consistently oriented along the a-direction of the wurtzite crystal structure. We also report a novel fabrication method, utilizing photoelectrochemical etching of a sacrificial InGaN region for substrate removal and cavity length definition. This method allows for the use of dielectric DBR mirrors with freestanding GaN substrates, while maintaining precise control of cavity length by placement of the sacrificial layer during epitaxial growth. Initial device results include a wavelength of 411.9 nm with a FWHM of 0.25 nm and a maximum observed power output of 19.5 uW. Devices exhibit polarization ratios higher than .7 above threshold (with no additional measures taken to account for spontaneous emission or to reduce collection of scattered light).

Comprehensive electro-opto and thermal analysis on GaSb-based vertical-cavity surface-emitting lasers (VCSELs) emitting at 2.6μm are presented. The theoretical models include a 2D/3D drift-diffusion equations for carrier transport coupled with the optical model which describes the spontaneous noise as the driving force for lasing. Optical gain is obtained by Fermi’s golden rule and the self-consistent solution of Schrodinger equation. Self- heating effects of the device are also included self-consistently. These results shed light on the internal device physics such as carrier transport, temperature ditribution, optical gain and losses etc. Based on the simulation, we also discuss the areas for future improvements.

It is well known that high-contrast metastructures can be exploited to perform a controllable coupling between matter and electromagnetic radiation. At optical frequencies this paves the way toward an arbitrarily adjustable spatio-temporal molding of light at the wavelength scale. In detail, high-index-contrast periodic structures such as photonic crystal membranes (PCMs) can be used for controlling the resonant coupling of radiated light to “heavy photons” states in strongly corrugated waveguides, thus putting photons through a slowed-down transport regime which results in an efficient quasi-3D light harnessing. More recently, one-dimensional Si/SiO₂ photonic crystals have been adopted as compact, flexible, and power-efficient mirrors in vertical-cavity surfaceemitting lasers (VCSELs) emitting in the C-band which have been realized within a mass-scale fabrication paradigm by employing standard 200-mm microelectronics pilot lines. The extreme flexibility of such innovative photonic architecture enables to perform a fully-controllable transverse mode filtering, including polarization and far-field control, while the strong near-field mode overlap within mirrors can be exploited to implement unique optical functions such as on-chip optical routing and enhanced sensing capabilities. Furthermore, the device compactness ensures a considerable reduction in footprint, power consumption and parasitics, adding in required features for broadband modulation and high-speed data processing. High fabrication yields obtained via molecular wafer bonding of III-V alloys on silicon conjugate excellent device performances with cost-effective high-throughput production, addressing industrial needs for a fast research-tomarket transfer. In conclusion, photonic crystal VCSELs constitute thus a robust high-performance building block for the follow-through of semiconductor lasers, VCSEL and silicon photonics.

We have conducted a thorough experimental analysis of nano-aperture VCSELs for use in heat-assisted magnetic recording (HAMR). To the best of our knowledge, this is the first study to both explore the impact of magnetic media proximity on VCSEL aperture power throughput and to use statistical methods to simultaneously characterize thousands of aperture designs. To achieve areal recording densities beyond 1 Tb/in2, high anisotropy magnetic materials are required to overcome the super-paramagnetic effect. These require high switching fields which are not conventionally available. Heat assisted magnetic recording (HAMR) is a potential technology to reduce the coercivity of the media and thus the required switching field by localized heating to enable writing of bits. The challenges being faced by this technology are to develop a precise method of delivering light to a very small, sub wavelength bit area with sufficient power through a near field aperture, and the fabrication of a laser source which can be integrated with current write heads used in hard disk drives. The focus of our work is to characterize nano-aperture VCSELs and test their potential application to HAMR. We have fabricated 850 nm VCSELs with large arrays of differently shaped nano-apertures in the gold layer on top of each VCSEL. The focusing and transmission characteristics of differently shaped nano-apertures are compared by simulations and experiments. C-shaped and H-shaped nano-apertures have also been fabricated in a gold layer deposited on a SiO₂ substrate to observe the effect of close proximity of magnetic media (FePt) on the performance of nano-apertures, and polarization effects have also been characterized.

We study theoretically the spectral and polarization threshold characteristics of Vertical-Cavity Surface-Emitting Lasers with nematic and cholesteric liquid crystal overlay: LC-VCSELs. In the first case, we demonstrate the possibility of selecting between two orthogonal directions of linear polarization (LP) of the fundamental mode (x or y LP) by choosing appropriate NLC length and to achieve strong polarization discrimination: threshold gain difference as large as several times the threshold gain. We also demonstrate an active control of light polarization by electro-optically tuning the LC director and show that either polarization switching between x and y LP modes or continuous change of the LP direction is possible. For cholesteric LC-VCSEL we show that it becomes a coupled system with different spectral, threshold and polarization characteristics than the ones of the stand-alone VCSEL. Due to the existence of a band gap for circularly polarized light in the liquid crystal, lasing occurs in almost circularly polarized modes at the LC side.

We demonstrate a miniature VCSEL-based light source with optical power output that varies by less than 50 ppm/°C over a 40°C temperature range. This represents a ten-fold improvement in control accuracy over what is achieved by the best available light sources with semiconductor emitters. A single-mode, polarization-locked, 670-nm VCSEL (Vixar, Inc.) is used to demonstrate the feasibility of the light source. The critical component of our control system is a beamsplitter formed by a wedge of fused silica with a weakly-polarizing, interference coating. A wedge shape eliminates fluctuations in optical power caused by interference fringes and the normal incidence of the exit beam removes polarization dependency as well as the need for an anti-reflective coating. The beamsplitter is in a closed control loop that enables compensation for control errors caused by changes in photodetector responsivity, emission wavelength, and beam divergence with temperature. We also show that careful attention to optical and mechanical alignment is essential to realize the performance enhancements reported herein. Angular tolerances of ±0.05°are required and most coating houses lack the metrology capabilities to characterize the TCB coating with such high tolerances. A discrete-wavelength reflectometer was developed for this purpose.

We present surface micro-machined micro-electro mechanical-system (MEMS) tunable vertical-cavity surfaceemitting lasers (VCSEL) with rectangular and triangular shaped quantum wells (QWs) emitting around 1:95 μm predestined for broadband tunable diode laser absorption spectroscopy. The VCSELs show single-mode operation and high side-mode suppression-ratio SMSR < 50 dB within the whole tuning range of 50nm and 35 nm, the fibre-coupled optical power of 1:0mW and 1:76mW and the threshold current of 2:5mA and 2:0mA for the rectangular and triangular shaped QWs respectively. The 3 dB modulation frequency of the MEMS is 110 Hz.

A technological platform for a vertical cavity surface emitting laser (VCSEL) with tunable polarization is presented. It is realized by integrating an 850nm VCSEL chip in a liquid crystal (LC) cell that uses photo-alignment (PA) to orient the LC. Two kinds of LC are filled in and form a thin layer over the emitter of the VCSEL: nematic LC or chiral nematic LC (cLC). The VCSEL and the nematic LC layer can be electrically driven with separate electrodes. The polarization state of the laser emission can be controlled by applying an appropriate voltage over the nematic LC layer. The chiral nematic LC has a reflection band that contains the VCSEL emission wavelength, so that one circular polarized mode of the laser emission is reflected as a feedback into the VCSEL. We found that the emission from the VCSEL with cLC overlay is circularly polarized.

We demonstrate a giant wavelength-temperature dependence of wavelength of a micromachined 850nm VCSEL with a thermally actuated metal/semiconductor cantilever mirror. The modeling shows a possibility of giant temperature dependence of wavelength of several nm/K, which is determined by cantilever length and metal thickness. The fabricated 850nm VCSEL exhibits a temperature dependence of -1.6 nm/K, and a wavelength tuning of 35 nm in 850 nm band was obtained by changing the device temperature by 12K. In addition, electro-thermal tuning was demonstrated using integrated micro heater. Continuous wavelength shift of 15 nm was obtained with heating power of 40 mW.

A mode hop free single mode tuning < 90nm at 40°C and 45nm at 70°C is demonstrated with a MEMS tunable VCSEL for the first time. The device shows a fiber-coupled output power of 2.9mW at 20°C and 0.5mW at 70°C. The side mode suppression ratio is larger than 40 dB over the entire tuning and temperature range of up to 70°C. The presented technology is cost effective and thus capable for mass production. It is applicable for tuneable VCSELs operating in different wavelength regimes, which are limited by the absorption of the DBR materials only.

In this paper, we demonstrate for the first time the far-field experimental results and the linewidth characteris- tics for widely tunable surface-micromachined micro-electro-mechanical system (MEMS) vertical-cavity surface- emitting lasers (VCSELs) operating at 1550 nm. The fundamental Gaussian mode emission is confirmed by optimizing the radius of curvature of top distributed Bragg reflector (DBR) membrane and by choosing an ap- propriate diameter of circular buried tunnel junctions (BTJs) so that only the fundamental Gaussian mode can sustain. For these VCSELs, a mode-hop free continuous tuning over 100 nm has already been demonstrated, which is achieved by electro-thermal tuning of the MEMS mirror. The fiber-coupled optical power of 2mW over the entire tuning range has been reported. The singlemode laser emission has more than 40 dB of side-mode suppression ratio (SMSR). The smallest linewidth achieved with these of MEMS tunable VCSELs is 98MHz which is one order of magnitude higher than that of fixed-wavelength VCSELs.

For nearly twenty years most models of VCSEL wearout reliability have incorporated Arrhenius activation energy near 0.7 eV, usually with a modest current exponent in addition. As VCSEL production extends into more wavelength, power, and speed regimes new active regions, mirror designs, and growth conditions have become necessary. Even at more traditional VCSEL 850-nm wavelengths instances of very different reliability acceleration factors have arisen. In some cases these have profound effects on the expected reliability under normal use conditions, resulting in wearout lifetimes that can vary more than an order of magnitude. These differences enable the extension of VCSELs in communications applications to even greater speeds with reliability equal to or even greater than the previous lowerspeed devices. This paper discusses some of the new applications, different wearout behaviors, and their implications in real-life operation. The effect of different acceleration behaviors on reliability testing is also addressed.

In comparison to widely used InGaAs Quantum Wells (QW) in high speed VCSELs operating at 25 Gbps and beyond, we present an investigation on the use of GaAs QWs, which have proven their ability to serve reliably in 10 Gbps and 14 Gbps VCSEL products and allow for an evolutionary extension of data rates based on mature technology. As data centers continuously increase in size, the demand for longer reach optical links within these data centers is addressed by the proposal of using small spectral width single-mode VCSELs that offer the potential of significantly reduced chromatic dispersion along optical fibers of several 100 m length. Performance and modeling parameters of single-mode VCSELs are being compared to those of typical multi-mode VCSELs built from identical epitaxy and process technology.

Avago’s 850nm oxide VCSEL for applications requiring modulation at 25-28G has been designed for -3dB bandwidths in excess of 18GHz over an extended temperature range of 0-85C. The VCSEL has been optimized to minimize DBR mirror thermal resistivity, electrical resistance and optical losses from free carrier absorption. The active region is designed for superior differential gain to enable high optical bandwidths. The small-signal modulation response has been characterized and the large-signal eye diagrams show excellent high-speed performance. Characterization data on other link parameters such as relative intensity noise and spectral width will also be presented.

850nm oxide-aperture VCSELs are susceptible to premature failure if operated while exposed to atmospheric water vapor, and not protected by hermetic packaging. The ATLAS detector in CERN’s Large Hadron Collider (LHC) has had approximately 6000 channels of Parallel Optic VCSELs fielded under well-documented ambient conditions. Exact time-to-failure data has been collected on this large sample, providing for the first time actual failure data at use conditions. In addition, the same VCSELs were tested under a variety of accelerated conditions to allow us to construct a more accurate acceleration model. Failure analysis information will also be presented to show what we believe causes corrosion-related failure for such VCSELs.

Systems with arrays of VCSELs can realize multi kilowatt output power. The inherent simplicity of VCSELs enables a performance and cost breakthrough in solutions for thermal processing and the pumping of solid state lasers. The use of an array of micro-optics i.e. one micro-lens per VCSEL enables multiple advantages: firstly it can function as a collimating lens in order to realize a brightness of an array which is similar to the brightness of a single VCSEL. Secondly the micro-lens can be part of an imaging system for tailored intensity distributions. Last but not least the microlens with moderate feedback into the VCSEL can help to select laser modes in order to increase brightness and mode stability. Wafer-level integrated micro-optics allow keeping the VCSEL advantage of realizing complete and operational lasers on wafer level including the micro-optics. This paper presents our approach to bond a 3” GaAs wafer with a micro-optics wafer of the same size. The type of glass used for the optics wafer has been selected to match the coefficient of thermal expansion of GaAs and is suitable for hot pressing of the lens structures. An alignment strategy with corresponding markers on both wafers is used to allow the alignment on a standard mask aligner thus realizing many thousand lens adjustments in a single process step. The technology can be combined with VCSEL wafers with thinned substrate as well as with complete substrate removal. The basic technology and illustrative prototype systems are described here.

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are very attractive to high power light sources owing to the advantageous configuration of two-dimensional arrays and being free from catastrophic optical damage. Although oxideconfined VCSELs have been employed in most of applications with VCSELs, ion-implanted VCSELs have a potential to be the better light sources for high power applications. In spite of the fact, the detailed characteristics of the ionimplanted VCSELs had been researched only in ten milliwatt-class output power. Here we report on a high power VCSEL-array with proton-implanted current apertures. A peak output power of over 40 W under short-pulse operation has been achieved. This is the first demonstration of ten watt-class output power for ion-implanted VCSELs.

High-power red laser sources are used in many applications such as cosmetics, cancer photodynamic therapy, and DNA sequencing in the medical field, laser-based RGB projection display, and bar-code scanning to name a few. Verticalcavity surface-emitting lasers (VCSELs) can be used as high-power laser sources, as efficient single devices can be configured into high-power two-dimensional arrays and scaled into modules of arrays. VCSELs emit in a circular, uniform beam which can greatly reduce the complexity and cost of optics. Other advantages include a narrow and stable emission spectrum, low speckle of the far-field emission, and good reliability. However, developing efficient red VCSEL sources presents some challenges because of the reduced quantum-well carrier confinement and the increased Aluminum content (to avoid absorption) which increases thermal impedance, and also decreases the DBR index contrast resulting in increased penetration length and cavity losses. We have recently developed VCSEL devices lasing in the visible 6xx nm wavelength band, and reaching 30% power conversion efficiency. We fabricated high-power 2D arrays by removing the GaAs substrate entirely and soldered the chips on high thermal conductivity submounts. Such arrays have demonstrated several Watts of output power at room temperature, in continuous-wave (CW) operation. Several tens of Watts are obtained in QCW operation. Results and challenges of these high-power visible VCSEL arrays will be discussed.

High-power, format flexible, 885 nm vertical-cavity surface-emitting laser (VCSEL) arrays have been developed for solid-state pumping and illumination applications. In this approach, a common VCSEL size format was designed to enable tiling into flexible formats and operating configurations. The fabrication of a common chip size on ceramic submount enables low-cost volume manufacturing of high-power VCSEL arrays. This base VCSEL chip was designed to be 5x3.33 mm², and produced up to 50 Watts of peak continuous wave (CW) power. To scale to higher powers, multiple chips can be tiled into a combination of series or parallel configurations tailored to the application driver conditions. In actively cooled CW operation, the VCSEL array chips were packaged onto a single water channel cooler, and we have demonstrated 0.5x1, 1x1, and 1x3 cm² formats, producing 150, 250, and 500 Watts of peak power, respectively, in under 130 A operating current. In QCW operation, the 1x3 cm² VCSEL module, which contains 18 VCSEL array chips packaged on a single water cooler, produced over 1.3 kW of peak power. In passively cooled packages, multiple chip configurations have been developed for illumination applications, producing over 300 Watts of peak power in QCW operating conditions. These VCSEL chips use a substrate-removed structure to allow for efficient thermal heatsinking to enable high-power operation. This scalable, format flexible VCSEL architecture can be applied to wavelengths ranging from 800 to 1100 nm, and can be used to tailor emission spectral widths and build high-power hyperspectral sources.

The introduction of a photonic-crystal to the VCSEL produces single mode emission in a very broad range of applied currents. The mechanism responsible for the discrimination of high-order modes originates from two counter-acting phenomena: 1) the PhC introduces lateral mode confinement through a strong waveguide effect and additionally by the Bragg reflections from a regular net of PhC holes 2) the holes of the PhC destroy the vertical periodicity of the DBR and contribute to the selective reduction in reflectivity of the mirror. As a result, the mode which overlaps the holes of the photonic crystal leaks through and becomes discriminated. We present numerical analysis of the influence of parameters of photonic crystal on the wavelength of emission, modal gain, slope efficiency, emitted power and tuning range in single mode VCSELs. We recognise several mechanisms determining high power emission in the single mode regime, which are: selective leakage, thermal focusing, waveguide effect induced by the photonic-crystal, gain spectrum red shift and its maximum reduction with increase of driving currents. We show that careful design of the photonic crystal allows for 10% increase in the emitted power of a singlemode regime and it allows for broad range of the steering currents from 5 to 50 mA. Such attributes support tuning of the single-mode emission over the 10 nm range of the spectrum.

We report on transverse mode discrimination in long-wavelength wafer-fused vertical-cavity surface-emitting lasers (VCSELs) incorporating ring-shaped air gap patterns at the fused interface between the active region and the top distributed Bragg reflector (DBR). These 60-nm deep patterns were implemented with the aim of favoring the fundamental mode while preserving high output power. The VCSELs under consideration emit in the 1310-nm band and incorporate an AlGaInAs-based quantum well active region, a regrown circular tunnel junction and undoped GaAs/AlGaAs DBRs. A large batch of devices with varying pattern dimensions was investigated by on-wafer mapping, allowing significant statistical analysis leading to conclusions on their typical behavior. We observe experimentally a dependence of the side-mode suppression ratio on the geometrical parameters of the patterns. In particular, we identified a design that statistically increases the maximal single-mode emitted power by more than 20%. Numerical simulations of the patterned-cavity VCSELs based on our fully three dimensional electrical, thermal and optical VCSEL computational model support these observations. They show that patterns with a large inner diameter actually confine the first-order transverse mode and enhance its modal gain. In smaller devices, this mode is pushed out of the optical aperture and suffers larger losses. Optimized parameters were found numerically for enhancing the single-mode properties of the devices with negligible penalty on emitted power and threshold current.

The first error-free data transmission beyond 1 km of multi-mode fiber at bit-rates exceeding 20 Gb/s is demonstrated using a high modulation bandwidth, quasi-single mode (SMSR~20 dB) 850 nm VCSEL. A VCSEL with small ~3 μm aperture shows quasi-single mode operation with a narrow spectral width. The top mirror reflectivity of the VCSEL is optimized for high speed and high output power by shallow etching. A combination of narrow spectral width and high optical power reduces the effects of fiber dispersion and fiber and connector losses and enables such a long transmission distance at high bit-rates.

We present a design of a high speed electro-optically modulated coupled-cavity vertical-cavity surface emitting laser monolithically integrated in a traveling wave electrode structure (TW EOM CC-VCSEL). Such electrical configuration allows to overcome RC time constant limitations of a traditional lumped electrodes design. We use segmented transmission line to match the impedance of the whole structure to the 50 Ω electrical network. We use transmission matrix method to model the response of the device and reflections at the voltage source interface. The CC-VCSEL optical design is based on longitudinal mode switching induced by the electro-optic effect, which has been recently experimentally demonstrated. In the paper we present analysis of electrical equivalent circuits of passive and modulator sections. We optimize our structure with respect to the device physical dimensions, frequency response, microwave reflections and modulation efficiency. We propose two different designs that are theoretically able to reach modulation speeds limited only by carrier extraction time from the quantum wells of the modulator and at the same time having lower than -20 dB reflections to the voltage source. For 1.5 λ long modulator cavity, carrier saturation velocity limits the bandwidth of proposed structures to ≈ 390 GHz.

A new record for energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting lasers (VCSELs) particularly suited for optical interconnects is presented. Error-free performance at 25 Gb/s is achieved with only 56 fJ/bit of dissipated energy per quantum of information. The influence of the oxide-aperture diameter on the energy-efficiency of our VCSELs is determined by comparing the total and dissipated power versus the modulation bandwidth of devices with different aperture diameters. Trade-offs between various parameters such as threshold current, differential quantum efficiency, wall plug efficiency and differential resistance are investigated with respect to energy-efficiency. We show that our present single-mode VCSELs are more energy-efficient than our multimode ones.

We propose the lateral coupling of dual VCSEL cavities using a bow-tie shape connection for increasing the modulation bandwidth. The 3-D modeling shows no-noticeable radiation loss when two oxide-defined VCSEL cavities are coherently coupled. Transverse-mode switching offers a unique modulation concept that makes intensity modulation while total photon density inside the coupled cavities is unchanged under push-pull current modulation. Large modulation bandwidth free from relaxation oscillation frequencies can be expected. We fabricated 980nm laterally coupled cavity VCSELs with a bow-tie shape oxide aperture and demonstrated the transverse-mode switching under push-pull operations.

We present results from our new generation of high performance 850 nm oxide confined vertical cavity surface-emitting lasers (VCSELs). With devices optimized for high-speed operation under direct modulation, we achieve record high 3dB modulation bandwidths of 28 GHz for ~4 μm oxide aperture diameter VCSELs, and 27 GHz for devices with a ~7 μm oxide aperture diameter. Combined with a high-speed photoreceiver, the ~7 μm VCSEL enables error-free transmission at data rates up to 47 Gbit/s at room temperature, and up to 40 Gbit/s at 85°C.

We experimentally investigate high-frequency microwave signal generation using a 1550 nm single-mode VCSEL subject to two-frequency optical injection. We first consider a situation in which the injected signals come from two similar VCSELs. The polarization of the injected light is parallel to that of the injected VCSEL. We obtain that the VCSEL can be locked to one of the injected signals, but the observed microwave signal is originated by beating at the photodetector. In a second situation we consider injected signals that come from two external cavity tunable lasers with a significant increase of the injected power with respect to the VCSEL-by-VCSEL injection case. The polarization of the injected light is orthogonal to that of the free-running slave VCSEL. We show that in this case it is possible to generate a microwave signal inside the VCSEL cavity.