We provide a numerical model to investigate the performance of a visible light communication-based vehicle-to-vehicle (V2V) communication system that incorporates organic light emitting diode (OLED) transmitters and discrete multitone modulation to overcome the bandwidth limitations of the organic devices. Different application scenarios using vehicle’s headlights and taillights as optical transmitters are considered. The results indicate the potential of using OLEDs for cooperative intelligent transportation system applications to achieve transmission of low-to-moderate data rates, providing evidence that the proposed OLED-based V2V system can achieve data communication of several Mbps. In the scenario that involves transmitting data to the leading car using the OLED headlights as transmitters, we show that the data rate can exceed 5 Mbps, despite the low modulation bandwidth of the OLED. When transmitting data to the trailing car using the taillights, we show that the transmission rate can reach 2 Mbps. We also discuss the trade-off between vehicle distance and communication performance and show that, even for distances up to 40 m, data rates on the order of several hundred kbps can be supported.
A systematic design process of slow light photonic crystal slab waveguides is presented with the aim of maximizing the storage capacity. Dispersion effects and propagation losses characteristics are included in order to increase the design accuracy. Our procedure allows the optimization of the structure at the same time by varying as many as ten design parameters. We show that storage capacities of almost 32bits at 40Gb/s and 65bits at 100Gb/s can be obtained.
In this paper, we consider the propagation of slow light optical pulses inside photonic crystal slab waveguides (PCSW)
both from a theoretical and an application point-of-view. The numerical model used relies on a nonlinear envelope
propagation equation that includes the effects of second and third order dispersion, optical losses and self phase
modulation. Pulse propagation is examined both in the linear and nonlinear regime. It is numerically shown that for rates
of 10Gb/s, the order of nanosecond delays can be achieved through the PCSW defect modes without excessive pulse
broadening in the nonlinear regime. In the nonlinear case, it is shown that soliton pulses exhibit less broadening than
pulses in the linear case. In comparing the linear and the non-linear case we consider launching pulses with the same
initial full width at half maximum or the same RMS width. The influence of optical losses on the soliton pulse
broadening factor is also incorporated and discussed providing a more practical perspective. The results demonstrate the
potential of implementing a variety of linear and nonlinear signal processing applications in PCSWs, such as optical
buffering.
During the European collaborative project
OMEGA, two optical-wireless prototypes have been
developed. The first prototype operates in the near-infrared
spectral region and features Giga Ethernet connectivity, a
simple transceiver architecture due to the use of on-off
keying, a multi-sector transceiver, and an ultra-fast switch
for sector-to-sector hand over. This full-duplex system,
composed by one base station and one module, transmits
data on three meters.
The second prototype is a visible-light-communications
system based on DMT signal processing and an adapted
MAC sublayer. Data rates around to 100 Mb/s at the
physical layer are achieved. This broadcast system,
composed also by one base station and one module, transmits
data up to two meters.
In this paper we present the adapted optical wireless
media-access-control sublayer protocol for visible-light
communications. This protocol accommodates link
adaptation from 128 Mb/s to 1024 Mb/s with multi-sector
coverage, and half-duplex or full-duplex transmission.
Coupled optical cavities are constantly attracting increased attention in telecommunication applications. For an infinite
chain of optical cavities, also known as the coupled resonator optical waveguide (CROW), the tight binding approximation has been used in order to evaluate its dispersion characteristics and the modal fields. In this paper, the accuracy of the tight binding formalism is investigated for a finite chain of optical cavities of arbitrary length. This approximation allows the derivation of simple analytical formulas for the resonant frequencies and the corresponding modal fields, which involve only the resonant frequency of the isolated cavity and the coupling coefficients between two consecutive coupled cavities. The equations for the modal fields involve an expansion in terms of displaced versions of the field distribution of the mode of the isolated cavity and simple trigonometric functions. These analytical results are compared with the numerical results of the plane wave expansion method in the case of a finite photonic crystal chain of coupled resonators and an excellent agreement is observed even if the cavities are placed close together. The results clearly indicate the usefulness and accuracy of the tight binding formalism for the description of coupled
optical resonators.
This paper studies the non-linear tolerance of several modulation formats in a four-span WDM system (8x10Gb/s) using low chromatic dispersion fiber. The narrow spacing between the channels (50 GHz) makes FWM to be the most detrimental effect experienced in each span made of G.655 fiber (80 km, D=2ps/nm.km) compensated by 0.8 km of DCF. A particular attention to the Q factor computed in the simulations enables a fair comparison between IMDD (Intensity Modulated Direct Detection) and phase modulated formats. It is shown that the various amplitude modulation alternatives result in more or less the same performance. Phase modulation schemes drastically increase the system performance leading to an increase of the Q-factor by almost 3dB.
The performance of high-powered Wavelength Division Multiplexed (WDM) optical networks can be severely degraded due to the Four Wave Mixing (FWM) induced distortion. FWM distortion depends on the statistics of the signals carried by the WDM channels and hence the Gaussian approximation may not be valid. This implies that the well known Q-factor method can not be used to yield an accurate value for the performance of the system in terms of the Bit-Error Rate (BER) of the receiver. To evaluate the BER, one must determine the probability density function (PDF) of the decision variable in the presence of FWM noise, which is related to the signal statistics in a complex manner and can not be evaluated in closed form. In this paper, the Multi-Canonical Monte Carlo Method (MCMC) is used to calculate the PDF of the decision variable of a receiver, limited by FWM noise. Compared to the conventional Monte Carlo method previously used in the literature to estimate this PDF, the MCMC method is much faster and can accurately estimate very low Bit Error Rates. The method takes into account the correlation between the components of the FWM noise unlike the Gaussian model, which is shown not to provide accurate results. The impact of traffic burstiness in the performance of a FWM limited WDM receiver is also investigated using MCMC. It is shown that the traffic load can significantly affect the performance of the system.
Photonic Crystals (PCs) are a promising technology for the realization of high-density optical integrated
circuits. Photonic Crystal-based couplers have been proposed as a compact means of achieving Wavelength
Multiplexing and Demultiplexing. However, the performance of such devices can be limited by fabrication
imperfections such as rod size non-uniformities. In this paper, Coupled Mode Theory (CMT) is applied in order to study
the implication of the variation of the size of the rods. CMT can provide a useful insight in the effect of size variations,
and unlike other numerical methods such as the Finite Difference Time Domain (FDTD), it does not require excessive
computational time. Using CMT, the relation between the size non-uniformities and the coupler's insertion loss and
extinction ratio is analyzed. It is shown even a small size variation of the order of 2%-3% can degrade the performance
of the device.
Arrayed Waveguide Gratings (AWGs) are key components in current and future optical network realizations. In order to prevent the need of accurate wavelength control the transfer function of the AWG should ideally have a rectangular shape. Several techniques have been proposed in order to flatten the Gaussian-like transfer function of the conventional AWG. In this paper we propose a new technique is based on the modification of the arrayed waveguide lengths and their positions on the Free Propagation Regions. The above technique is similar to the deterministic tapering technique used in the design of antenna arrays, since the spatial transfer function of the latter has the same characteristics as the spectral transfer function of an AWG. Therefore, problem is reduced to that of matching the integral of a sinc function with a discrete step function and the optimal waveguide lengths are obtained by solving a set of equations numerically. The performance of this technique (in terms of transfer function flatness, sidelobe level and insertion losses compared to a conventional AWG) depends on the values given to several initial design parameters related to the AWG geometry. The results obtained show that it is feasible to fabricate AWGs with rectangular transfer function with proper adjustment of certain structural parameters.
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