Dynamic properties of silicon-integrated short-wavelength hybrid-cavity VCSEL

We present a vertical-cavity surface-emitting laser (VCSEL) where a GaAs-based "half-VCSEL" is attached to a dielectric distributed Bragg reflector on silicon using ultra-thin divinylsiloxane-bis-benzocyclobutene (DVS-BCB) adhesive bonding, creating a hybrid cavity where the optical field extends over both the GaAs- and the Si-based parts of the cavity. A VCSEL with an oxide aperture diameter of 5 mu m and a threshold current of 0.4 mA provides 0.6 mW output power at 845 nm. The VCSEL exhibits a modulation bandwidth of 11 GHz and can transmit data up to 20 Gbps

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

High-speed 850 nm VCSELs operating error free up to 57 Gbit/s

Error-free transmission is demonstrated at bit rates up to 57 Gbit/s back-to-back, up to 55 Gbit/s over 50 m fibre and up to 43 Gbit/s over 100 m fibre using an oxide-confined 850 nm high-speed vertical cavity surface-emitting laser with a photon lifetime optimised for high-speed data transmission

40 Gb/s data transmission over a 1-m-long multimode polymer spiral waveguide for board-level optical interconnects

Optical interconnects have attracted considerable attention for use in short-reach communication links within high performance electronic systems, such as data centres, supercomputers and data storage systems. Multimode polymer waveguides in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly-multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER<10-12) 40 Gb/s data transmission over a 1 m long multimode polymer spiral waveguide and present thorough studies on the waveguide bandwidth performance. The frequency response of the waveguide is investigated under a wide range of launch conditions and in the presence of input spatial offsets which are expected to be highly-likely in real-world systems. A robust bandwidth performance is observed with a bandwidth-length product of at least 35 GHz×m for all launch conditions studied. The reported results clearly demonstrate the potential of this technology for use in board-level interconnects, and indicate that data rates of at least 40 Gb/s are feasible over waveguide lengths of 1 m.This work was supported by the U.K. EPSRC through the Centre for Advanced Photonics and Electronics (CAPE), and the Swedish Foundation for Strategic Research.This is the final version of the article. It was first published by IEEE at http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=696085

56 Gb/s PAM-4 data transmission over a 1 m long multimode polymer interconnect

Advanced modulation formats can enable >40 Gb/s data rates in waveguide-based optical interconnects without the need for high-specification optoelectronic components. Record 56 Gb/s PAM-4 data transmission is demonstrated over a 1 m-long multimode polymer waveguide.The authors acknowledge Dow Corning for providing the polymer samples, IQE for supplying the VCSEL epitaxial material, the Swedish Foundation for Strategic Research for financial support and Tektronix for the loan of the DSA.This is the author accepted manuscript. The final version is available from OSA Publishing via http://dx.doi.org/10.1364/CLEO_SI.2015.STu4F.

Assessment of VCSEL thermal rollover mechanisms from measurements and empirical modeling

We use an empirical model together with experimental measurements for studying mechanisms contributing to thermal rollover in vertical-cavity surface-emitting lasers (VCSELs). The model is based on extraction of the temperature dependence of threshold current, internal quantum efficiency, internal optical loss, series resistance and thermal impedance from measurements of output power, voltage and lasing wavelength as a function of bias current over an ambient temperature range of 15-100 degrees C. We apply the model to an oxide-confined, 850-nm VCSEL, fabricated with a 9-mu m inner-aperture diameter and optimized for highspeed operation, and show for this specific device that power dissipation due to linear power dissipation (sum total of optical absorption, carrier thermalization, carrier leakage and spontaneous carrier recombination) exceeds power dissipation across the series resistance (quadratic power dissipation) at any ambient temperature and bias current. We further show that the dominant contributors to self-heating for this particular VCSEL are quadratic power dissipation, internal optical loss, and carrier leakage. A rapid reduction of the internal quantum efficiency at high bias currents (resulting in high temperatures) is identified as being the major cause of thermal rollover. Our method is applicable to any VCSEL and is useful for identifying the mechanisms limiting the thermal performance of the device and to formulate design strategies to ameliorate them

Impact of photon lifetime on thermal rollover in 850-nm high-speed VCSELs

We present an empirical thermal model for VCSELs based on extraction of temperature dependence of macroscopic VCSEL parameters from CW measurements. We apply our model to two, oxide-confined, 850-nm VCSELs, fabricated with a 9-mu m inner-aperture diameter and optimized for high-speed operation. We demonstrate that for both these devices, the power dissipation due to linear heat sources dominates the total self-heating. We further show that reducing photon lifetime down to 2 ps drastically reduces absorption heating and improves device static performance by delaying the onset of thermal rollover. The new thermal model can identify the mechanisms limiting the thermal performance and help in formulating the design strategies to ameliorate them