Support for a general factor of well-being

Well-being is typically defined as positive feeling (e.g. happiness), positive functioning (e.g. competence, meaning) or a combination of the two. Recent evidence indicates that well-being indicators belonging to different categories can be explained by single “general” factor of well-being (e.g. Jovanovic, 2015). We further test this hypothesis using a recent well-being scale, which includes indicators of positive feeling and positive functioning (Huppert & So, 2013). While the authors of the scale originally identified a two-factor structure, in view of recent evidence, we hypothesize that the two-factor solution may be due to a method effect of different items being measured with different rating scales. In study 1, we use data from the European Social Survey round 3 (n = 41,461) and find that two factors have poor discriminant validity and, after using a bifactor model to account for different rating scales, only the general factor is reliable. In study 2, we eliminate method effects by using the same rating scale across items, recruit a new sample (n = 507), and find that a one-factor model fits the data well. The results support the hypothesis that well-being indicators, typically categorized as “positive feeling” and “positive functioning,” reflect a single general factor

Impact of Damping on High-Speed Large Signal VCSEL Dynamics

An investigation of the optimal relaxation oscillation damping for high-speed 850-nm vertical-cavity surface-emitting laser (VCSEL) under large signal operation is presented, using devices with K-factors ranging from 0.1 to 0.4 ns. Time-domain measurements of turn-on transients are used to quantify damping dependent rise times, overshoots, and signal amplitudes. Optical eye diagrams together with timing jitter and bit error rate measurements reveal a tradeoff between the rise time and the duration of the relaxation oscillations. To produce a high-quality eye at a specific data rate, a proper amount of damping is needed to simultaneously obtain sufficiently high bandwidth and low timing jitter. We found that for error-free transmission, a VCSEL with a 0.3 ns K-factor achieved the best receiver sensitivity at 10 and 25 Gb/s, whereas a less damped VCSEL with a 0.2 ns K-factor achieved the best sensitivity at 40 Gb/s

Impact of Damping on Large Signal VCSEL Dynamics

The dependence of large signal VCSEL dynamics on damping is studied through time-domain measurements of turn-on transients and timing jitter for VCSELs having K-factors from 0.1 to 0.4 ns

High-Speed VCSELs with Strong Confinement of Optical Fields and Carriers

We present the design, fabrication, and performance of our latest generation high-speed oxide-confined 850-nm verticalcavity surface-emitting lasers. Excellent high-speed properties are obtained by strong confinement of optical fields and carriers. Highspeed modulation is facilitated by using the shortest possible cavity length of one half wavelength and placing oxide apertures close to the active region to efficiently confine charge carriers. The resulting strong current confinement boosts internal quantum efficiency, leading to low threshold currents, high wall-plug efficiency, and state-of-the-art high-speed properties at low bias currents. The temperature dependent static and dynamic performance is analyzed by current-power-voltage and small-signal modulation measurements

High Speed VCSELs and VCSEL Arrays for Single and Multicore Fiber Interconnects

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

Energy Efficiency of VCSELs in the Context of Short-Range Optical Links.

We present results from an investigation of the energy efficiency of VCSELs under large signal modulation. We show that the most important factor influencing the energy consumption of the VCSELs is the required optical modulation amplitude, which drives other VCSEL design requirements. The required optical modulation amplitude also depends on the optical link design. Through this dependence it is possible to better understand the energy consumption of complete short range optical links

High-speed 850 nm VCSELs with 28 GHz modulation bandwidth for short reach communication

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 similar to 4 mu m oxide aperture diameter VCSELs, and 27 GHz for devices with a similar to 7 mu m oxide aperture diameter. Combined with a high-speed photoreceiver, the similar to 7 mu m VCSEL enables error-free transmission at data rates up to 47 Gbit/s at room temperature, and up to 40 Gbit/s at 85 degrees C

25 Gbit/s transmission over 500 m multimode fibre using 850 nm VCSEL with integrated mode filter

An integrated mode filter in the form of a shallow surface relief was used to reduce the spectral width of a high-speed 850 nm vertical-cavity surface-emitting laser (VCSEL). The mode filter reduced the RMS spectral width from 0.9 to 0.3 nm for a VCSEL with an oxide aperture as large as 5 mu m. Because of reduced effects of chromatic and modal fibre dispersion, the mode filter significantly increases the maximum error-free (bit error rate < 10(-12)) transmission distance, enabling transmission at 25 Gbit/s over 500 m of multimode OM3+ fibre