Thermal analysis of high-bandwidth and energy-efficient 980 nm VCSELs with optimized quantum well gain peak-to-cavity resonance wavelength offset

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 111, 243508 (2017) and may be found at https://doi.org/10.1063/1.5003288.The static and dynamic performance of vertical-cavity surface-emitting lasers (VCSELs) used as light-sources for optical interconnects is highly influenced by temperature. We study the effect of temperature on the performance of high-speed energy-efficient 980 nm VCSELs with a peak wavelength of the quantum well offset to the wavelength of the fundamental longitudinal device cavity mode so that they are aligned at around 60 °C. A simple method to obtain the thermal resistance of the VCSELs as a function of ambient temperature is described, allowing us to extract the active region temperature and the temperature dependence of the dynamic and static parameters. At low bias currents, we can see an increase of the −3 dB modulation bandwidth f−3dB with increasing active region temperature, which is different from the classically known situation. From the detailed analysis of f−3dB versus the active region temperature, we obtain a better understanding of the thermal limitations of VCSELs, giving a basis for next generation device designs with improved temperature stability

Optimal parameters of monolithic high-contrast grating mirrors

In this Letter a fully vectorial numerical model is used to search for the construction parameters of monolithic high-contrast grating (MHCG) mirrors providing maximal power reflectance. We determine the design parameters of highly reflecting MHCG mirrors where the etching depth of the stripes is less than two wavelengths in free space. We analyze MHCGs in a broad range of real refractive index values corresponding to most of the common optoelectronic materials in use today. Our results comprise a complete image of possible highly reflecting MHCG mirror constructions for potential use in optoelectronic devices and systems. We support the numerical analysis by experimental verification of the high reflectance via a GaAs MHCG designed for a wavelength of 980 nm

19-element vertical cavity surface emitting laser arrays with inter-vertical cavity surface emitting laser ridge connectors

We achieve record concurrent combinations of bandwidth (18 GHz), optical output power (150 mW), and wall plug efficiency (30%) with a unique arrangement of 19-element, electrically parallel 980 nm vertical cavity surface emitting laser (VCSEL) arrays. We use a new two-dimensional, quasi honeycomb geometry with inter-VCSEL ridge connectors—made nonconducting by selective thermal oxidation—to improve heat dissipation and facilitate a single top surface anode contact. Via on-wafer probing we perform static and dynamic measurements over the wide temperature range of 23 °C to 85 °C and extract, report, and discuss key array figures-of-merit.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

30 GHz bandwidth temperature stable 980 nm vertical-cavity surface-emitting lasers with AlAs/GaAs bottom distributed Bragg reflectors for optical data communication

We present a 980 nm vertical-cavity surface-emitting laser (VCSEL) design which achieves 32 GHz small-signal modulation bandwidth (f3db) at 15 °C and record-high 27 GHz at 85 °C. Our devices utilize binary AlAs/GaAs bottom distributed Bragg reflector material layers to improve thermal conductance. We extract key VCSEL figures-of-merit from static optical output power-current-voltage (LIV), spectral emission, and high frequency dynamic measurements and observe highly temperature stable performance for these parameters.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Are Miami blues in Cuba? A review of the genus \u3ci\u3eCyclargus\u3c/i\u3e Nabokov (Lepidoptera: Lycaenidae) with implications for conservation management

We review the genus Cyclargus Nabokov (Lepidoptera: Lycaenidae) based on detailed comparative analyses of wing patterns, genitalia, and mitochondrial COI DNA barcode sequences, and suggest that Cyclargus is composed of four species: C. thomasi (Clench), C. woodruffi (W. Comstock and Huntington), C. ammon (Lucas), and C. dominica (Möschler). The following new subjective synonyms are proposed: C. erembis Nabokov syn. n. and C. kathleena K. Johnson and Matusik syn. n. are C. thomasi noeli (W. Comstock and Huntington); C. sorpresus K. Johnson and Matusik syn. n. and C. shuturn K. Johnson and Bálint syn. n. are C. ammon; and Cyclargus oualiri Brevignon syn. n. is C. woodruffi. Additionally, we report the discovery of C. thomasi noeli in Cuba (where this taxon was previously confused with C. ammon), report C. ammon from Hispaniola for the first time, and document the widespread sympatry of C. thomasi and C. ammon in the northern Caribbean (including south Florida, Cuba, Cayman Islands, Hispaniola, Lucayan Archipelago). Finally, we provide a provisional synonymic list of Cyclargus taxa, which may serve as a taxonomic framework to assist efforts to conserve the Miami blue (C. thomasi bethunebakeri (W. Comstock and Huntington)), a taxon listed as “Endangered” under the Endangered Species Act in the United States

Deep Learning with Coherent VCSEL Neural Networks

Deep neural networks (DNNs) are reshaping the field of information processing. With their exponential growth challenging existing electronic hardware, optical neural networks (ONNs) are emerging to process DNN tasks in the optical domain with high clock rates, parallelism and low-loss data transmission. However, to explore the potential of ONNs, it is necessary to investigate the full-system performance incorporating the major DNN elements, including matrix algebra and nonlinear activation. Existing challenges to ONNs are high energy consumption due to low electro-optic (EO) conversion efficiency, low compute density due to large device footprint and channel crosstalk, and long latency due to the lack of inline nonlinearity. Here we experimentally demonstrate an ONN system that simultaneously overcomes all these challenges. We exploit neuron encoding with volume-manufactured micron-scale vertical-cavity surface-emitting laser (VCSEL) transmitter arrays that exhibit high EO conversion (<5 attojoule/symbol with $V_\pi$=4 mV), high operation bandwidth (up to 25 GS/s), and compact footprint (<0.01 mm$^2$ per device). Photoelectric multiplication allows low-energy matrix operations at the shot-noise quantum limit. Homodyne detection-based nonlinearity enables nonlinear activation with instantaneous response. The full-system energy efficiency and compute density reach 7 femtojoules per operation (fJ/OP) and 25 TeraOP/(mm$^2\cdot$ s), both representing a >100-fold improvement over state-of-the-art digital computers, with substantially several more orders of magnitude for future improvement. Beyond neural network inference, its feature of rapid weight updating is crucial for training deep learning models. Our technique opens an avenue to large-scale optoelectronic processors to accelerate machine learning tasks from data centers to decentralized edge devices.Comment: 10 pages, 5 figure

81 fJ/bit energy-to-data ratio of 850 nm vertical-cavity surface-emitting lasers for optical interconnects

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 98, 231106 (2011) and may be found at https://doi.org/10.1063/1.3597799.Extremely energy-efficient oxide-confined high-speed 850 nm vertical-cavity surface-emitting lasers for optical interconnects are presented. Error-free performance at 17 and 25 Gb/s via a 100 m multimode fiber link is demonstrated at record high dissipation-power-efficiencies of up to 69 fJ/bit (<0.1mW/Gbps) and 99 fJ/bit, respectively. These are the most power efficient high-speed directly modulated light sources reported to date. The total energy-to-data ratio is 83 fJ/bit at 25°C and reduces to 81 fJ/bit at 55°C. These results were obtained without adjustment of driving conditions. A high -factor of 12.0GHz/(mA)0.5 and a -factor of 0.41 ns are measured.EC/FP7/224211/EU/VISIT - Vertically Integrated Systems for Information Transfer/VISITDFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Frequency response of large aperture oxide-confined 850 nm vertical cavity surface emitting lasers

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 95, 131101 (2009) and may be found at https://doi.org/10.1063/1.3231446.Small and large signal modulation measurements are carried out for 850 nm vertical cavity surface emitting lasers (VCSELs). The resonance frequency, damping factor, parasitic frequency, and -factor are extracted. Small signal modulation bandwidths larger than 20 GHz are measured. At larger currents the frequency response becomes partially limited by the parasitics and damping. Our results indicate that by increasing the parasitic frequency, the optical 3 dB bandwidth may be extended to ∼25GHz. A decrease in the damping should enable VCSEL bandwidths of 30 GHz for current densities not exceeding ∼10kA/cm2 and ultimately error-free optical links at up to 40 Gbit/s.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeEC/FP7/224211/EU/VISIT - Vertically Integrated Systems for Information Transfer/VISI

Highly temperature-stable modulation characteristics of multioxide-aperture high-speed 980 nm vertical cavity surface emitting lasers

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Appl. Phys. Lett. 97, 151101 (2010) and may be found at https://doi.org/10.1063/1.3499361.We present multioxide-aperture 980 nm-range vertical cavity surface emitting lasers (VCSELs) with highly temperature stable modulation characteristics operating error-free at 25 Gbit/s at 25 and 85°C. We perform small signal modulation experiments and extract the fundamental physical parameters including relaxation resonance frequency, damping factor, parasitic cut-off frequency, -factor, and -factor, leading to identification of thermal processes and damping as the main factors that presently limit high speed device operation. We obtain very temperature-insensitive bandwidths around 13–15 GHz. Presented results clearly demonstrate the suitability of our VCSELs for practical and reliable optical data transmission systems.EC/FP7/224211/EU/VISIT - Vertically Integrated Systems for Information Transfer/VISITDFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Numerical model for small-signal modulation response in vertical-cavity surface-emitting lasers

We present a numerical model allowing for simulations of small-signal modulation (SSM) response of vertical-cavity surface-emitting lasers (VCSELs). The model of SSM response utilizes only the data provided by a static model of continuous-wave operation for a given bias voltage. Thus the fitting of dynamic measurement parameters is not needed nor used. The validity of this model has been verified by comparing experimental SSM characteristics of a VCSEL with the results of simulations. A good agreement between experiment and simulations has been observed. Based on the results obtained in the simulations of the existing laser, the impact of the number of quantum wells in the active region on the modulation properties has been calculated and analyzed