Ian D. Henning

A comparison of active and passive optical bistability in semiconductors

A comparison is presented between optical bistability in laser amplifiers and in passive Fabry-Perot cavities. The basis for comparison is afforded by a new analysis of optical amplifiers which encompasses the cases of passive refractive and absorptive bistability as special limiting cases. The results indicate that amplifiers have advantages of lower input intensity requirements (by a factor of 103) and reduced sensitivity to wavelength by comparison with passive cavities; experimental results indicate an input power of -30 dBm is required for active bistability. Facet coating requirements for active and passive optimum configurations are also discussed.

Performance predictions from a new optical amplifier model

We present results of a new model of semiconductor laser amplifiers which differs from previous analyses in that it includes the spectral dependence of material gain and spontaneous emission. The implications of low facet reflectivities are explored in some detail. For reflectivities below about 1 percent, the increased spontaneous emission imposes more stringent limits on current density than realized hitherto. If thermal runaway is to be avoided and gains in the range of 20-30 dB are to be achieved without excessive currents, then facet reflectivities on the order of 0.1-1 percent are probably optimal. Another consequence of including the spectral dependence is that wavelengths longer than that corresponding to the unsaturated gain peak are predicted to experience enhanced amplification at high input powers by comparison to shorter wavelengths.

Gridless optical networking field trial: Flexible spectrum switching, defragmentation and transport of 10G/40G/100G/555G over 620-km field fiber

We report the first gridless networking field trial with flexible spectrum switching nodes over 620 km field fibre links. Successful transport, spectrum switching and defragmentation achieved for mixed line signals including 555G and coherent 100G.

Dynamics of Polarized Optical Injection in 1550-nm VCSELs: Theory and Experiments

We report novel theoretical results obtained from combining the method of largest Lyapunov exponent (LLE) with the spin-flip model (SFM), including noise, to model a vertical-cavity surface emitting laser (VCSEL) subject to polarized optical injection. The LLE is applied to the numerical solutions in order to automatically calculate stability maps that characterize the dynamics. The SFM has been extended and generalized to allow for optical injection of arbitrary polarization. Measurements on a 1550-nm VCSEL have been used to estimate the values of key parameters for use in the model and with these we demonstrate excellent agreement between theory and experiment.

Fully-elastic multi-granular network with space/frequency/time switching using multi-core fibres and programmable optical nodes

We present the first elastic, space division multiplexing, and multi-granular network based on two 7-core MCF links and four programmable optical nodes able to switch traffic utilising the space, frequency and time dimensions with over 6000-fold bandwidth granularity. Results show good end-to-end performance on all channels with power penalties between 0.75 dB and 3.7 dB.

Investigation of vertical cavity surface emitting laser dynamics for neuromorphic photonic systems

We report an approach based upon vertical cavity surface emitting lasers (VCSELs) to reproduce optically different behaviors exhibited by biological neurons but on a much faster timescale. The technique proposed is based on the polarization switching and nonlinear dynamics induced in a single VCSEL under polarized optical injection. The particular attributes of VCSELs and the simple experimental configuration used in this work offer prospects of fast, reconfigurable processing elements with excellent fan-out and scaling potentials for use in future computational paradigms and artificial neural networks.

A Deterministic Distributed TDMA Scheduling Algorithm for Wireless Sensor Networks

Efficient scheduling of time slots in a time division multiple access scheme (TDMA) is important for low power wireless sensor networks. Existing algorithms are either centralized with poor scalability, or distributed but with high complexity. In this paper, we explain how TDMA could be more energy efficient by careful slot scheduling in wireless sensor networks. Then we propose a deterministic distributed TDMA scheduling algorithm (DD-TDMA). In DD-TDMA, each sensor node schedules its own TDMA slot based on its neighborhood information, and packet collisions are gracefully avoided during scheduling. The experimental results show that compared to other centralized and distributed scheduling algorithms, DD-TDMA achieves better performance in terms of schedule length, running time and message complexity.

Contention Reduction in Core Optical Packet Switches Through Electronic Traffic Smoothing and Scheduling at the Network Edge

A contention-aware packet-scheduling scheme for slotted optical packet switching (OPS) networks is proposed, which employs edge-traffic shaping to reduce contention, coupled with a modified type of renegotiated service incorporating rate prediction. Queuing and scheduling of traffic is implemented electronically within the edge nodes, shaping user traffic into streams, which have a fixed bit rate only for a short period, which is renegotiated at regular intervals in response to user requirements and network conditions. Via an appropriate protocol, edge nodes gain knowledge of relevant network scheduling and topology information. This is used to schedule user-data packets appropriately, in order to reduce contention. Simulation and analytical results demonstrate that in the core, under typical conditions, packet loss below 10-8 may be obtained, with a load of 0.8 and with core optical-packet switch buffers having only 20-slot capacity. The tradeoffs between parameters affecting such results are investigated, demonstrating clearly that much more modest optical core buffers than previously thought necessary can provide acceptable performance. The performance and scalability of these proposals are investigated and discussed, demonstrating their feasibility

Different forms of wavelength polarization switching and bistability in a 1.55 μm vertical-cavity surface-emitting laser under orthogonally polarized optical injection

Different forms of wavelength polarization switching and bistability are reported in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) operated just above threshold and subject to orthogonally polarized optical injection into the subsidiary orthogonal polarization mode. This diversity of behavior at the wavelength of 1550 nm offers promise for the use of VCSELs in optical signal processing and optical switching applications.

Optically-pumped dilute nitride spin-VCSEL

We report the first room temperature optical spin-injection of a dilute nitride 1300 nm vertical-cavity surface-emitting laser (VCSEL) under continuous-wave optical pumping. We also present a novel experimental protocol for the investigation of optical spin-injection with a fiber setup. The experimental results indicate that the VCSEL polarization can be controlled by the pump polarization, and the measured behavior is in excellent agreement with theoretical predictions using the spin flip model. The ability to control the polarization of a long-wavelength VCSEL at room temperature emitting at the wavelength of 1.3 µm opens up a new exciting research avenue for novel uses in disparate fields of technology ranging from spintronics to optical telecommunication networks.