Towards a unified understanding of event-related changes in the EEG:the Firefly model of synchronization through cross-frequency phase modulation

Although event-related potentials (ERPs) are widely used to study sensory, perceptual and cognitive processes, it remains unknown whether they are phase-locked signals superimposed upon the ongoing electroencephalogram (EEG) or result from phase-alignment of the EEG. Previous attempts to discriminate between these hypotheses have been unsuccessful but here a new test is presented based on the prediction that ERPs generated by phase-alignment will be associated with event-related changes in frequency whereas evoked-ERPs will not. Using empirical mode decomposition (EMD), which allows measurement of narrow-band changes in the EEG without predefining frequency bands, evidence was found for transient frequency slowing in recognition memory ERPs but not in simulated data derived from the evoked model. Furthermore, the timing of phase-alignment was frequency dependent with the earliest alignment occurring at high frequencies. Based on these findings, the Firefly model was developed, which proposes that both evoked and induced power changes derive from frequency-dependent phase-alignment of the ongoing EEG. Simulated data derived from the Firefly model provided a close match with empirical data and the model was able to account for i) the shape and timing of ERPs at different scalp sites, ii) the event-related desynchronization in alpha and synchronization in theta, and iii) changes in the power density spectrum from the pre-stimulus baseline to the post-stimulus period. The Firefly Model, therefore, provides not only a unifying account of event-related changes in the EEG but also a possible mechanism for cross-frequency information processing.

A unidirectional scheme for high-fidelity optical-carrier dissemination using phase-modulation, homodyne coherent-detection, and frequency entrainment

We report for the first time an ultra-stable optical-carrier dissemination technique for transmission over a 20km unidirectional fibre link. The optical-linewidth of the recovered carrier matches closely that of the original carrier. © 2014 OSA.

Self-phase modulation dependent dispersion mitigation in high power SSB and DSB + dispersion compensated modulated radio-over-fiber links

The joint effect of fiber chromatic dispersion and fiber nonlinearity onto single-sideband and double-sideband modulated radio-over-fiber links is investigated. Experimental and simulated results show that modulation suppression caused by the chromatic dispersion in radio-over-fiber links can be successfully eliminated in both schemes only when the system is in the linear regime. Under nonlinear transmission the received microwave carrier power depends on the optical incident power.

Cost-efficient OFDM generation at 60-GHz by heterodyne technique with direct modulation and envelope detector

A cost-effective radio over fiber system to up-convert and transmit multigigabit signals at 60 GHz is presented. A low intermediate frequency OFDM signal is used to directly modulate a laser, which is combined with an independent unmodulated laser. The generated millimeter wave frequency can be adjusted by tuning the frequency separation between the lasers. Since no external modulator is required, this technique is low-cost and it is easily integrable in a single chip. In this paper, we present numerical results showing the feasibility of generating an IEEE 802.15.3c compliant 3.5-Gbps 60-GHz OFDM. We show that received signal quality is not limited by the lasers' linewidth but by the relative intensity noise. © 2013 IEEE.