All-Optical Spiking Neuron Based On Passive Micro-Resonator

Neuromorphic photonics that aims to process and store information simultaneously like human brains has emerged as a promising alternative for the next generation intelligent computing systems. The implementation of hardware emulating the basic functionality of neurons and synapses is the fundamental work in this field. However, previously proposed optical neurons implemented with SOA-MZIs, modulators, lasers or phase change materials are all dependent on active devices and quite difficult for integration. Meanwhile, although the nonlinearity in nanocavities has long been of interest, the previous theories are intended for specific situations, e.g., self-pulsation in microrings, and there is still a lack of systematic studies in the excitability behavior of the nanocavities including the silicon photonic crystal cavities. Here, we report for the first time a universal coupled mode theory model for all side-coupled passive microresonators. Attributed to the nonlinear excitability, the passive microresonator can function as a new type of all-optical spiking neuron. We demonstrate the microresonator-based neuron can exhibit the three most important characteristics of spiking neurons: excitability threshold, refractory period and cascadability behavior, paving the way to realize all-optical spiking neural networks.Comment: 8 pages, 7 figure

Improved receiver design for layered ACO-OFDM in optical wireless communications

Layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) is recently proposed for intensity-modulated directed-detected optical wireless communications, which achieves higher spectral efficiency compared with the conventional ACO-OFDM, since different layers of ACO-OFDM signals are combined to utilize more subcarriers. In this letter, an improved receiver is proposed for LACO-OFDM, which distinguishes different layers of ACO-OFDM signals in the time domain. After that, the structure of ACO-OFDM signals in each layer is exploited to further reduce the noise and inter-layer interference, resulting in the improved performance. Simulation results show that the proposed receiver for LACO-OFDM achieves significant gain over its conventional counterpart

Monolithically integrated selectable repetition-rate laser diode source of picosecond optical pulses.

We describe the characterization of a monolithically integrated photonic device for short pulse generation featuring a mode-locked laser diode, a Mach-Zehnder modulator (MZM), and a semiconductor optical amplifier (SOA). The integrated device is designed for fabrication by a generic foundry scheme with a view to ease of design, testing, and manufacture. Trains of 6.8 ps pulses are generated at repetition rates that are electronically switchable from 14 GHz to 109 MHz. The SOA boosts the peak power by 7.4 dB, and the pulses are compressible to 2.4 ps by dispersion compensation using single-mode telecommunications fiber.This research leading to these results has received support from the UK EPSRC COPOS award EP/H022384/1 and from the European Commission’s Seventh Framework Programme FP7/2007-2013 under grant agreement NMP 228839 EuroPIC.This is the author accepted manuscript. The final published version can be found on the publisher's website at: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-39-14-414

Layered ACO-OFDM for intensity-modulated direct-detection optical wireless transmission

Layered asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with high spectral efficiency is proposed in this paper for optical wireless transmission employing intensity modulation with direct detection. In contrast to the conventional ACO-OFDM, which only utilizes odd subcarriers for modulation, leading to an obvious spectral efficiency loss, in layered ACO-OFDM, the subcarriers are divided into different layers and modulated by different kinds of ACO-OFDM, which are combined for simultaneous transmission. In this way, more subcarriers are used for data transmission and the spectral efficiency is improved. An iterative receiver is also proposed for layered ACO-OFDM, where the negative clipping distortion of each layer is subtracted once it is detected so that the signals from different layers can be recovered. Theoretical analysis shows that the proposed scheme can improve the spectral efficiency by up to 2 times compared with conventional ACO-OFDM approaches with the same modulation order. Meanwhile, simulation results confirm a considerable signal-to-noise ratio gain over ACO-OFDM at the same spectral efficiency

Miniaturized Computational Photonic Molecule Spectrometer

Miniaturized spectrometry system is playing an essential role for materials analysis in the development of in-situ or portable sensing platforms across research and industry. However, there unavoidably exists trade-offs between the resolution and operation bandwidth as the device scale down. Here, we report an extreme miniaturized computational photonic molecule (PM) spectrometer utilizing the diverse spectral characteristics and mode-hybridization effect of split eigenfrequencies and super-modes, which effectively eliminates the inherent periodicity and expands operation bandwidth with ultra-high spectral resolution. These results of dynamic control of the frequency, amplitude, and phase of photons in the photonic multi-atomic systems, pave the way to the development of benchtop sensing platforms for applications previously unfeasible due to resolution-bandwidth-footprint limitations, such as in gas sensing or nanoscale biomedical sensing

16-user OFDM-CDMA optical access network

We demonstrate a 16×2.5 Gb/s (40 Gb/s aggregate) OFDM-CDMA PON for next-generation access applications. Four-channel error-free transmission over 25 km SMF shows 6 dB coding gain, with 0.1 dB dispersion and 0.9 dB crosstalk penalties

Metasurface spectrometers beyond resolution-sensitivity constraints

Optical spectroscopy plays an essential role across scientific research and industry for non-contact materials analysis1-3, increasingly through in-situ or portable platforms4-6. However, when considering low-light-level applications, conventional spectrometer designs necessitate a compromise between their resolution and sensitivity7,8, especially as device and detector dimensions are scaled down. Here, we report on a miniaturizable spectrometer platform where light throughput onto the detector is instead enhanced as the resolution is increased. This planar, CMOS-compatible platform is based around metasurface encoders designed to exhibit photonic bound states in the continuum9, where operational range can be altered or extended simply through adjusting geometric parameters. This system can enhance photon collection efficiency by up to two orders of magnitude versus conventional designs; we demonstrate this sensitivity advantage through ultra-low-intensity fluorescent and astrophotonic spectroscopy. This work represents a step forward for the practical utility of spectrometers, affording a route to integrated, chip-based devices that maintain high resolution and SNR without requiring prohibitively long integration times