This PDF file contains the front matter associated with SPIE Proceedings Volume 9381 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Besides the mature and steadily growing datacom market for which VCSELs are key components in Transceivers, Active Optical Cables (AOC), Mid Board Optical Modules (MBOM) or Embedded Optical Modules (EOM), VCSELs have proven to be key components also for other volume applications. Laser mice emerged 2004, just after the burst of the dotcom bubble and the related downturn in the Datacom industry, and dominated the shipped quantities for some years, accompanied by various smaller applications like atomic clock, oxygen sensing, encoders, and many more. Over the past years, two other major applications came into focus: optical interconnects in high performance computers or datacenters and smart sensors for mobile devices. In addition, VCSELs are penetrating into more and more power applications, primarily for illumination or IR heating. We present recent developments in technology, products, and addressed market segments that will have a major impact on the VCSEL industry.

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are key components enabling power- and cost-efficient, high-density, ultra-high bandwidth parallel optical interconnects for data center and high-performance computing applications. This paper presents recent developments at TE Connectivity (TE) in the area of 25 Gb/s per channel-class VCSEL and optical transmitter technology for applications such as 100G and 400G Ethernet and Enhanced Data Rate InfiniBand pluggable and mid-board connectivity solutions.

Mode partition noise (MPN) can become the dominant limitation in 850 nm VCSEL-based multi-mode fiber (MMF) links at high data rates. Fluctuations in the partition of energy between the transverse modes of the VCSEL combined with the chromatic dispersion in the fiber leads to intensity noise at the receiver. The impact of MPN on non-equalized and equalized links has been studied with a numerical model of the VCSEL and MMF. The MPN in 25 Gb/s VCSELs has been investigated by examining noise in individual mode groups isolated using a thin film Fabry-Perot filter. The measured k factor below 0.15 should enable links significantly longer than 100 m at 25 Gb/s and higher data rates.

We present different concepts for long wavelength buried tunnel junction VCSELs for the spectroscopically important range above 2 μm. This includes GaSb-based laser using GaInAsSb quantum wells, InP-based lasers with V-shaped quantum wells and InP-based lasers using type-II quantum wells. For InP-based devices, emission wavelengths up to 2.36 μm are presented, with single-mode output powers of roughly 500 μW and side-mode suppression ratios of more than 30 dB. GaSb-based VCSELs are presented with single-mode emission at 2.6 μm, a side-mode suppression ratio of more than 20 dB and a peak output power of 400 μW.

In this article we propose a long wavelength VCSEL by VCSEL Optoelectronic Oscillator to generate high frequency carriers. Stability and quality are key factors to use Vertical-Cavity Surface-Emitting Lasers (VCSELs) in VCSEL Based Optoelectronic Oscillators (VBO). To enhance the performance of a 2.49 GHz VBO presented in [1]. The use of the optical injection locking technique applied to the VBO laser pump contributes to the VCSEL Relative Intensity Noise (RIN) reduction, and the increase of the modulation bandwidth that leads to a carrier phase noise reduction. The Injection Locked VCSEL Based Oscillator (ILVBO) performance will be presented and discussed taking into account the injection locking conditions of the laser source.

Heat assisted magnetic recording (HAMR) is a next generation technology proposed for achieving magnetic storage densities beyond 1 Tb/in². However, the commercialization of heat-assisted magnetic recording faces substantial technical challenges that must be resolved before widespread adoption of the technology can commence. Foremost of these challenges is the development of a precise method of delivering light to a very small, sub wavelength bit area with sufficient power to heat a high coercivity magnetic medium above its Curie temperature. Complex fabrication processes, low power transfer efficiency and high heat dissipation are the biggest problems faced in current HAMR light delivery systems. A nano-aperture vertical cavity surface emitting laser (VCSEL) is a potential candidate as a light delivery system in HAMR. We have fabricated 850 nm VCSELs with C-shaped nano-apertures on their output facets to be used as near-field transducers in order to produce a small localized optical spot; we then characterized their performance and compared power requirements with successful HAMR demonstrations with control C-shaped nano-aperture near-field transducers fabricated on glass substrates. Laser light at 850 nm wavelength was focused onto a magnetic medium, through the nano-apertures, and an external magnetic field of magnitude much lower than the coercivity (at room temperature) of the magnetic medium was simultaneously applied. Magnetic force microscopy images of the medium showed that C-apertures are capable of producing a magnetic spot much smaller than the diffraction limit using localized plasmonic effects. The power density required at this wavelength for HAMR process was experimentally measured using a pump-probe optical setup.

This paper reports a method and system comprising a light source, an electronic method, and a calibration procedure for stabilizing the optical power of vertical-cavity surface-emitting lasers (VCSELs) and laser diodes (LDs) without the use thermoelectric coolers (TECs). The system eliminates the needs for custom interference coatings, polarization adjustments, and the exact alignment required by the optical method reported in 2013 [1]. It can precisely compensate for the effects of temperature and wavelength drift on photodiode responsivity as well as changes in VCSEL beam quality and polarization angle over a 50°C temperature range. Data obtained from light sources built with single-mode polarization-locked VCSELs demonstrate that 30 ppm/°C stability can be readily obtained. The system has advantages over TECstabilized laser modules that include: 1) 90% lower relative RMS optical power and temperature sensitivity, 2) a five-fold enhancement of wall-plug efficiency, 3) less component testing and sorting, 4) lower manufacturing costs, and 5) automated calibration in batches at time of manufacture is practical. The system is ideally suited for battery-powered environmental and in-home medical monitoring applications.

In this paper, we study the critical parameters of 1550 nm vertical-cavity surface-emitting lasers (VCSEL) for several applications in space environment like satellite (telecommunications and observation) and deep space (probes and rover). The analysis is focus in the main parameters degrading the VCSEL behavior in wide application field. These parameters are the optical output power, the threshold current and the relative noise intensity (RIN) according to the temperature that affects the storage and mostly the operation of the laser diode. Characterization processes and results are presented here.

Finisar has developed a line of high power, high efficiency VCSEL arrays. They are fabricated at 860nm as traditional P side up top emitting devices, leveraging Finisar’s existing VCSEL fab and test processes for low cost, high volume capability. A thermal camera is used to accurately measure temperature profiles across the arrays at a variety of operating conditions and further allowing development of a full reliability model. The arrays are shown to demonstrate wear out reliability suitable for a wide range of applications. Typical 1/e^2 beam divergence is near 16 degrees under CW operating conditions at peak wall plug efficiency, narrowing further under pulsed drive conditions.

Vertical-cavity surface-emitting lasers (VCSELs) are attractive for many pumping and direct-diode applications due to combined advantages in low cost, high reliability, narrow and thermally stable spectrum, high power scalability, and easy system integration, etc. We report our progress on electrically pumped, GaAs-based, high- power high-brightness VCSELs and 2D arrays in the infrared wavelength range. At 976nm, over 5.5W peak CW output and 60% peak power conversion efficiency (PCE) were demonstrated with 225um oxide-confined device. For 5x5mm arrays, peak PCE of 54% and peak power of >450W at 976nm, peak PCE of 46% and peak power of >110W at 808nm were achieved respectively under QCW conditions. External cavity configuration was used to improve the VCSEL brightness. Single mode output of 280mW and 37% PCE were realized from 80um device. For large 325um device, we obtained single mode (M²=1.1) CW output of 2.1W, corresponding to a brightness of 160MW/cm²*sr. Three major areas of applications using such VCSELs are discussed: 1. High brightness fiber output; 2. High power, high efficiency green lasers from 2^nd harmonic generation. 3.34W green output with 21.2% PCE were achieved; 3. Pumping solid state lasers for high energy pulse generation. We have demonstrated Q-switched pulses with 16.1mJ at 1064nm and 4.9mJ with 1W average power at 473nm.

A unique architecture for two-dimensional arrays of VCSELs that allow for simultaneous high-power output and highbandwidth modulation has been developed for a variety of applications. The arrays use integrated micro-lenses for beam shaping and control, and to enable incoherent beam combining to make compact, high-brightness sources with low coherence noise. The fabrication and performance of the laser arrays are reviewed and sample applications are discussed.

Our recent work on high speed 850 nm VCSELs and VCSEL arrays is reviewed. With a modulation bandwidth approaching 30 GHz, our VCSELs have enabled transmitters and links operating at data rates in excess of 70 Gbps (at IBM) and transmission over onboard polymer waveguides at 40 Gbps (at University of Cambridge). VCSELs with an integrated mode filter for single mode emission have enabled transmission at 25 Gbps over >1 km of multimode fiber and a speed-distance product of 40 Gbps·km. Dense VCSEL arrays for multicore fiber interconnects have demonstrated 240 Gbps aggregate capacity with excellent uniformity and low crosstalk between the 40 Gbps channels.

High-speed and “green” ~850 nm vertical-cavity surface-emitting lasers (VCSELs) have lately attracted lots of attention due to their suitability for applications in optical interconnects (OIs). To further enhance the speed and its maximum allowable linking distance of VCSELs are two major trends to meet the requirement of OI in next generation data centers. Recently, by use of the advanced 850 nm VCSEL technique, data rate as high as 64 Gbit/sec over 57m and 20 Gbit/sec over 2km MMF transmission have been demonstrated, respectively. Here, we will review our recent work about 850 nm Zn-diffusion VCSELs with oxide-relief apertures to further enhance the above-mentioned performances. By using Zn-diffusion, we can not only reduce the device resistance but also manipulate the number of optical modes to benefit transmission. Combing such device, which has excellent single-mode (SMSR >30 dB) and high-power (~7mW) performance, with advanced modulation format (OFDM), record-high bit-rate-distance-product through MMF (2.3 km×28 Gbit/sec) has been demonstrated. Furthermore, by selective etching away the oxide aperture inside Zn-diffusion VCSEL, significant enhancement of device speed, D-factor, and reliability can be observed. With such unique VCSEL structure, >40 Gbit/sec energy-efficient transmission over 100m MMF under extremely low-driving current density (<10kA/cm2) has been successfully demonstrated.

We address demands and challenges for GaAs–based Vertical–Cavity Surface–Emitting Lasers (VCSEL) in data communication. High speed modulation (~50Gb/s) at a high reliability can be realized with a proper VCSEL design providing a high differential gain. In cases where extreme temperatures are required electrooptic modulation in duo– cavity VCSELs can be applied as the modulation speed and the differential gain are decoupled. Single mode operation of VCSELs is necessary to counteract the chromatic dispersion of glass fibers and extend distances to above 1 km while using standard multimode fibers. Oxide layer engineering or using of photonic crystals can be applied. Parallel error–free 25Gb/s transmission over OM3 and OM4 multimode fiber (~0.5 and 1 km, respectively) is realized in large aperture oxide–engineered VCSEL arrays. Passive cavity VCSELs with gain medium placed in the bottom DBR and the upper part made of dielectric materials a complete temperature insensitivity of the emission wavelength can be realized. Engineering of the oxide aperture region enables near field vertical cavity lasers. Such devices can operate in a high– order transverse mode with an effective mode angle beyond the angle of the total internal reflection at the semiconductor–air interface. Near filed coupling to optical fibers and waveguides becomes possible in this case.

Vertical-cavity surface-emitting lasers (VCSELs) are decisive cost-effective, energy-efficient, and reliable light sources for short-reach (up to ~300 m) optical interconnects in data centers and supercomputers. To viably replace copper interconnects and advance to on-chip integrated photonics, reliable VCSELs ideally must be able to operate highly energy efficient, but at large bit rates and without cooling up to 85 °C, with immunity to temperature variations. Our 980 nm VCSELs achieve such temperature-stable, energy-efficient, and high-speed operation coincidently. Record low 139 fJ/bit of dissipated heat for 35 Gbit/s error-free data transmission at 85 °C is reported. Careful design of both the VCSEL’s epitaxial structure and device geometry is of essence. Introducing a suitable gain-to-etalon wavelength offset simultaneously improves the temperature-stability, the maximum bit rate at high temperatures, and the energy efficiency. Tuning the photon lifetime additionally increases the bandwidth by changing the relation between damping and resonance relaxation frequency. Systematic temperature-dependent and oxide aperture-diameter-dependent measurements, including static L-I-V curves and emission spectra, small signal analysis, and data transmission experiments are reported. The modulation bandwidth, the parasitic cut-off frequency, the relaxation resonance frequency, lumped-circuit elements, and the K- and D-factors are derived, useful for energy-efficient optical interconnects based on 980 nm VCSELs.

Spintronic lasers offer promising perspectives for new concepts superior to options of purely charge-based devices. Especially spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) exhibit ultrafast spin and polarization dynamics. Using pulsed spin-injection, oscillations in the circular polarization degree can be generated, which have the potential to exceed frequencies of 100 GHz. The oscillations evolve due to coupling of the carrier-spin-photon system for linear modes via birefringence in the VCSEL's cavity. They are independent of the conventional relaxation oscillations and thus their usage can be the cornerstone for ultrafast directly modulated spin-VCSELs in the near future. After giving a short overview of the state of scientific and technical knowledge we will outline a method to control the polarization oscillations by multiple spin-injection pulses. It is possible to switch these oscillations on and off, depending on phase and amplitude conditions of two consecutive excitation pulses. Even half-cycles can be generated, which is the basis for short polarization pulses, only limited by the polarization oscillation resonance frequency. We investigate influences of the birefringence, which directly determines the oscillation frequency, by means of calculations with the spin-flip-model and experimental verification using 850 nm VCSELs. Furthermore we discuss experimental possibilities of increasing the birefringence and therefore the oscillation frequency, such that ultrashort pulses come into reach.

In the talk we show the process of modeling complete physical properties of VCSELs and we present a step-by-step development of its complete multi-physics model, gradually improving its accuracy. Then we introduce high contrast gratings to the VCSEL design, which strongly complicates its optical modeling, making the comprehensive multi-physics VCSEL simulation a challenging task. We show, however, that a proper choice of a self-consistent simulation algorithm can still make such a simulation a feasible one, which is necessary for an efficient optimization of the laser prior to its costly manufacturing.

Vertical-cavity surface-emitting lasers (VCSELs) enable a range of applications such as data transmission, trace sensing, atomic clocks, and optical mice. For many of these applications, the output power and beam quality are both critical (i.e. high output power with good beam quality is desired). Multi-mode VCSELs offer much higher power than single-mode devices, but this comes at the expense of lower beam quality. Directly observing the resolved mode structure of multi-mode VCSELs would enable engineers to better understand the underlying physics and help them to develop multi-mode devices with improved beam quality. In this work, a low-cost, high-resolution (<3 pm) Echelle grating spectrometer system is used to map the two-dimensional VCSEL near-field emission profile. The system spectrally disperses the VCSEL beam and images it with high magnification onto a CMOS camera. The narrow spectral content of each LP mode allows direct observation of the modal content of the VCSEL.

A high electro-optical conversion efficiency of a VCSEL (Vertical-Cavity Surface-Emitting Lasers) is one of the key requirements for their application in high power systems for heating, illumination and pumping applications. The substantial amount of degrees of freedom in the epitaxial and structural design of a VCSEL demands numerical guidance in form of technology computer aided design (TCAD) modeling for a straight forward and successful optimization of the devices. We set up a full electro-thermal optical model for the simulation of VCSEL devices. The electro-thermal part of the simulation follows a drift-diffusion model complemented by a customized, energy resolved, semi-classical carrier capture theory in the QW regions. Optical modes, eigensolutions of the vectorial electromagnetic wave equation, stem from a finite element vectorial solver. The electro-thermal and optical models are linked via the photon-rate equation using QW gain spectra (screened Hartree-Fock approximation) and iterated to self-consistency in a Gummel-type iteration scheme. For comparison and calibration, experimental reference data was extracted from oxide-confined, top-emitting VCSEL devices with an emission wavelength of 808 nm. Our simulations are in good agreement with the electro-optical characteristics of the experimental reference. With the calibrated, microscopic model, routes of design adjustment for efficiency optimization are explored. Exemplarily, the maximum VCSEL efficiency of the simulated reference design increases by 10% (absolute) when free hole absorption is switched off. Accordingly, with the combination of an electro-thermal and optical description, a balancing of the tradeoffs of pDBR doping towards reduced free carrier absorption results in a noteworthy efficiency improvement which is validated with experimental data.

In this paper we present the simulation results of an oxide-confined, InGaAs/GaAs based vertical-cavity surface-emitting laser with three different configurations of the oxide apertures. We analyze the impact of the number and position of oxide layers on the carrier distribution in the laser's active region, distribution of the optical modes, and modulation properties.

We study theoretically and experimentally spectral and polarization characteristics of hybrid systems of VCSELs integrated within liquid crystal (LC) cells. Three cases are considered: Nematic or cholesteric LC on top of VCSEL, coupled-cavity system with the second cavity next to the VCSEL’s one filled in with nematic LC and a system with a nematic LC inside the VCSEL cavity. For the case of nematic liquid crystal - VCSEL coupled cavity system we demonstrate selection between two orthogonal directions of linear polarization of the fundamental mode by changing the LC length or by electro-optical tuning of the LC director. For the case of cholesteric liquid crystal-VCSEL system we demonstrate lasing on circularly polarized (CP) modes due to the LC band gap for CP light. The transition from nematic to isotropic phase of the LC when increasing temperature leads to a drastic change of the polarization of the generated light from left-handed circular to linear polarization. Finally, we investigate the possibility of efficient wavelength tuning by utilizing electrooptical effect in nematic LC layer integrated next to the active region in a VCSEL cavity.

Distributed Bragg reflectors (DBRs) are typically used as the highly reflecting mirrors of vertical-cavity surface-emitting lasers (VCSELs). In order to provide optical field confinement, oxide apertures are often incorporated in the process of the selective wet oxidation of high aluminum-content DBR layers. This technology has some potential drawbacks such as difficulty in controlling the uniformity of the oxide aperture diameters across a large-diameter (≥ 6 inch) production wafers, high DBR series resistance especially for small diameters below about 5 μm despite elaborate grading and doping schemes, free carrier absorption at longer emission wavelengths in the p-doped DBRs, reduced reliability for oxide apertures placed close to the quantum wells, and low thermal conductivity for transporting heat away from the active region. A prospective alternative mirror is a high refractive index contrast grating (HCG) monolithically integrated with the VCSEL cavity. Two HCG mirrors potentially offer a very compact and simplified VCSEL design although the problems of resistance, heat dissipation, and reliability are not completely solved. We present an analysis of a double HCG 980 nm GaAs-based ultra-thin VCSEL. We analyze the optical confinement of such a structure with a total optical thickness is ~1.0λ including the optical cavity and the two opposing and parallel HCG mirrors.

Small, single mode VCSELs have been pursued almost since the inception of the device, but have been difficult to realize. Here we present data on lithographic and oxide-free VCSELs as small as 2 μm in diameter that produce single transverse mode powers of 8 mW and have high efficiency. The efficiencies reach 46% power conversion with greater than 73 % slope efficiency, with threshold current as low as 300 μA. Smaller VCSELs of 1 μm diameter produce 37 % power conversion efficiency with greater than 79 % slope efficiency, and single mode power over 5 mW. The keys to the high performance are the lithographic control and oxide elimination that reduce the electrical and thermal resistances.

Despite many unique advantages, vertical cavity surface emitting lasers (VCSELs) have been available mostly on rigid, planar wafers over restricted areas, thereby limiting their usage for applications that can benefit from large-scale, programmable assemblies, hybrid integration with dissimilar materials and devices, or mechanically flexible constructions. Here, materials design and fabrication strategies that address these limitations of conventional VCSELs are presented. Specialized design of epitaxial materials and etching processes, together with printing-based deterministic assemblies and substrate thermal engineering, enabled defect-free release of microscale VCSELs and their device- and circuit-level implementation on non-native, flexible substrates with performance comparable to devices on the growth substrate.

Energy-efficient oxide-confined vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm, particularly well suited for optical interconnects operating at up to 85°C are presented. The modulation bandwidth f_3dB of our VCSELs increases at low currents with increasing temperature up to 23 GHz at 85°C. The impact of cavity photon lifetime and oxide-aperture diameter on the energy efficiency, temperature stability, and static and dynamic properties of our VCSELs are analyzed. Error-free 40 Gb/s operation at 85°C with an energy-to-data ratio below 100 fJ/bit and a current density close to 10 kA/cm² is predicted based on small signal modulation experiments.

The polarization of the beam emitted from telecom-wavelength vertical-cavity surface-emitting lasers (VCSELs) is studied in detail. Stokes parameters are extracted separately for the two polarization submodes of the fundamental spatial mode LP01. This characterization was performed at room temperature and for a significant number of devices. This led to the discovery of stable optical modes with a polarization that differs from the linear case. This crucial result was obtained without immersing the devices in an external magnetic field or driving them under external optical injection. In addition, the polarization can be tuned directly with the drive current. Moreover, the polarization handedness can be switched electrically. A theoretical investigation shows that some of the equations forming the basis of the spin-flip model should be reconsidered. In particular, a generalization of this theory is discussed and fantastic agreement is found with the experimental results. This work paves the way for a broad range of novel applications with the VCSEL technology, in particular for spintronics, bio-chemical sensing and telecommunication.

Oxide–confined vertical cavity surface emitting lasers (VCSEL) are inherently leaky structures, despite the fact that the oxidized periphery region surrounding the all–semiconductor core has a lower refractive index. The reason is that the VCSEL modes in the non–oxidized core region can be coupled to tilted modes in the selectively oxidized periphery as the orthogonality between the core mode and the modes at the periphery is broken by the oxidation–induced optical field redistribution. Engineered VCSEL designs show that the overlap between the VCSEL mode of the core and the tilted mode in the periphery can reach >30% resulting in significant leakage. Three–dimensional modeling confirms that the leakage losses are much stronger for high order transverse modes which have a higher field intensity close to the oxidized region. Single mode lasing in the fundamental mode can thus proceed up to large aperture diameters. A 850–nm GaAlAs leaky VCSEL based on this concept is designed, modeled and fabricated, showing single–mode lasing with aperture diameters up to 5 μm. Side mode suppression ratio >20dB is realized at the current density of 10kA/cm² in devices with the series resistance of 90 Ω.

Vertical-cavity surface-emitting lasers (VCSELs) based on the InGaAlAs-materials system on GaAs substrates are the key component for short-reach data and computer communications systems. Several different modulation schemes have been developed to realize high data bit rates based on various oxide-confined near-infrared VCSEL designs operated under direct current modulation. However, one open question to resolve is the optimal gain-to-cavity wavelength detuning to employ for temperature-stable high-speed performance. We investigate the static and dynamic characteristics of 850 nm high-speed oxide-confined VCSELs with different negative gain-to-cavity wavelength detunings. Our oxideconfined 850 nm VCSELs with a more common ~10 nm negative gain-to-cavity detuning demonstrate the conventional optical mode behavior with a classical single-resonance frequency response. With a larger (≥ 20 nm) negative detuning, our devices with large oxide-aperture size (>6 μm) show an anomalous start of lasing via higher order modes with a subsequent switching to lasing via the lowest order modes at higher currents. At intermediate currents, co-lasing via two types of transverse modes and a two-resonance modulation response is observed. The increase of operation temperature as well as the reduction in the oxide-aperture area resulted in classical lasing of index-guided VCSELs. The observed optical mode behavior can be attributed to the specific index guiding profile caused by the oxide-apertures, low internal optical losses, and the large gain-to-cavity detuning. Moreover, one can suggest that the complex shape of the modulation response results from the mode competition for the available gain during an interesting co-lasing operating regime.

We have measured the effect of the temperature on the polarization-resolved characteristics of a 1550-nm singletransverse mode vertical-cavity surface-emitting laser (VCSEL). Two double polarization switchings (PS) are observed. For low temperatures a PS from longer to shorter wavelengths (Type II PS) followed by the opposite PS (Type I) is observed. For higher temperatures Type I followed by Type II PS are measured. A simple expression relating the spin flip rate to the dichroism, differential gain, threshold current and PS current is derived. With this expression the dependence of the spin-flip rate on the temperature is obtained.