51 research outputs found
Band-edge absorption characteristics of semi-insulating indium phosphide under unified Franz-Keldysh and Einstein models
The foundational Franz-Keldysh effect and Einstein model are applied in this work to characterize semiconductor band-edge absorptionâand its departures from ideality. We unify the Franz-Keldysh and Einstein models to fully characterize the field-induced tunneling of photoexcited electrons from degenerate valence bands into the conduction band, with encroachment into the band gap arising as an Urbach tail. Our unified model is implemented for semi-insulating indium phosphide (SI-InP) with strong agreement seen between the theoretical and experimental results for varied photon energies and electric fields
Pre-distortion adaptive optics for optical feeder links: simulations and performance analyses
Optical feeder links offer immense utility in meeting future communication demandsâhowever, atmospheric turbulence limits their performance. This work targets this challenge through analyses of a bidirectional free-space optical communication (FSOC) link that incorporates pre-distortion adaptive optics (AO) between the next-generation optical ground station at the German Aerospace Center (DLR) Oberpfaffenhofen and the laser communications terminal on Alphasatâa satellite in geostationary orbit (GEO). The analyses are performed via end-to-end Monte Carlo simulations that provide realistic performance estimates of the bidirectional FSOC link for a GEO feeder link scenario. We find that applying pre-distortion AO reduces the total uplink losses of the bidirectional FSOC link by up to 10â
dB and lessens the scintillation at the GEO satellite by an order of magnitude. Moreover, applying pre-distortion AO eases the link budget requirements needed for maintaining 99.9% link uptime by as much as 20-40â
dB, while its use with a laser guide star shows an additional performance improvement of up to 8â
dB. These findings demonstrate the desirability and feasibility of utilizing pre-distortion AO for the realization of optical feeder links
Asymptotically tight performance bounds for equal-gain combining over a new correlated fading channel
A recently proposed fading model which can be used
to describe both line-of-sight and non-line-of-sight components of
a fading channel is analyzed. The outage probability and error
rate performance of equal-gain combining over arbitrary correlated
Beaulieu-Xie fading channels is considered. Asymptoticallytight
closed-form lower and upper bounds are derived and these
analytical results are verified via Monte Carlo simulations.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult
Asymptotically tight performance bounds for selection diversity over Beaulieu-Xie fading channels with arbitrary correlation
A new (Beaulieu-Xie) fading model was recently proposed
to describe line-of-sight and non-line-of-sight components
in wireless channels. In this work, we consider both outage probability
and error rate performance of selective combining over
this new fading channel model with arbitrary channel correlation.
Closed-form expressions are obtained for asymptotically tight
upper and lower bounds. The analytical results are verified by
Monte Carlo simulations.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult
Maximum Likelihood Estimation of the Lognormal-Rician FSO Channel Model
In this work, the on-going challenges are addressed for the application of the lognormal-Rician turbulence model to free-space optical communication systems. Maximum likelihood estimation is applied to characterize the lognormal-Rician turbulence model parameters, and the expectation-maximization algorithm is used to compute maximum likelihood estimates of the unknown parameters. The performance is investigated, by way of the mean square error, and it is found that the proposed technique can accurately characterize free-space optical communication
channels over a wide range of turbulence conditions, with reduced demand on the quantity of data samples.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacultyResearche
Undersampled differential phase shift on-off keying for optical camera communications with phase error detection
This paper introduces the design and implementation
of an optical camera communication (OCC) system. Phase
uncertainty and phase slipping caused by camera sampling are
the two major challenges for OCC. In this paper, we propose
a novel modulation scheme to overcome these problems. The
undersampled differential phase shift on-off keying is capable
of encoding binary data bits without exhibiting any flicker
to human eyes. The phase difference between two consecutive
samples conveys one-bit information which can be decoded by
a low frame rate camera receiver. Error detection techniques
are also introduced to enhance the reliability of the system.
Furthermore, we present the hardware and software design of the
proposed system. This low-cost communication system has been
implemented with a Xilinx FPGA and a Logitech commercial
camera. Experimental results demonstrate that a bit-error rate
of 10-â” can be achieved with 7.15 microwatts received signal
power over a link distance of 15 centimeters.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacult
An investigation of semiconductor nanoparticles for application to all-optical switching
A practical all-optical switch is necessary to alleviate electronic bottlenecks in fibre optic networks. Thus, a new all optical switch is introduced hereâexhibiting femtojoule switching energies and femtosecond switching times. The all optical switches use 40 ÎŒm dielectric spheres to direct high-intensity photonic nanojets into peripheral coatings of semiconductor nanoparticles. Semiconductor nanoparticle coatings of Si, CdTe, InP, and CuO are studied and found to yield switching energies of approximately 1 pJ, 500 fJ, 400 fJ, and 300 fJ with switching times of 2 ps, 2.3 ps, 900 fs, and 350 fs, respectively.Applied Science, Faculty ofEngineering, School of (Okanagan)ReviewedFacultyResearche
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