2,517 research outputs found
On Approaching the Ultimate Limits of Photon-Efficient and Bandwidth-Efficient Optical Communication
It is well known that ideal free-space optical communication at the quantum
limit can have unbounded photon information efficiency (PIE), measured in bits
per photon. High PIE comes at a price of low dimensional information efficiency
(DIE), measured in bits per spatio-temporal-polarization mode. If only temporal
modes are used, then DIE translates directly to bandwidth efficiency. In this
paper, the DIE vs. PIE tradeoffs for known modulations and receiver structures
are compared to the ultimate quantum limit, and analytic approximations are
found in the limit of high PIE. This analysis shows that known structures fall
short of the maximum attainable DIE by a factor that increases linearly with
PIE for high PIE.
The capacity of the Dolinar receiver is derived for binary coherent-state
modulations and computed for the case of on-off keying (OOK). The DIE vs. PIE
tradeoff for this case is improved only slightly compared to OOK with photon
counting. An adaptive rule is derived for an additive local oscillator that
maximizes the mutual information between a receiver and a transmitter that
selects from a set of coherent states. For binary phase-shift keying (BPSK),
this is shown to be equivalent to the operation of the Dolinar receiver.
The Dolinar receiver is extended to make adaptive measurements on a coded
sequence of coherent state symbols. Information from previous measurements is
used to adjust the a priori probabilities of the next symbols. The adaptive
Dolinar receiver does not improve the DIE vs. PIE tradeoff compared to
independent transmission and Dolinar reception of each symbol.Comment: 10 pages, 8 figures; corrected a typo in equation 3
Comparison of direct and heterodyne detection optical intersatellite communication links
The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity
Determination of optical technology experiments for a satellite
Optical technology experiments for satellite - communications, acquisition, tracking, lasers, photometry, and atmospheric
Violation of Bell Inequalities as a Violation of Fair Sampling in Threshold Detectors
Photomultiplier tubes and avalanche photodiodes, which are commonly used in
quantum optic experiments, are sometimes referred to as threshold detectors
because, in photon counting mode, they cannot discriminate the number of
photoelectrons initially extracted from the absorber in the detector. We argue
that they can be called threshold detectors on more account than that. We point
out that their their functioning principle relies on two thresholds that are
usually thought unimportant individually in the context of EPR-Bell discussion.
We show how the combined effect of these threshold can lead to a significant
sampling selection bias in the detection of pairs of pulses, resulting in an
apparent violation of Bell inequalities.Comment: 11 pages, 8 figures, FPP5 conference, Vaxjo (Sweden) August 200
Parametric analysis of microwave and laser systems for communication and tracking. Volume 2 - System selection
System selection criteria of microwave and laser systems for communication and tracking - Vol.
Low Cost and Compact Quantum Cryptography
We present the design of a novel free-space quantum cryptography system,
complete with purpose-built software, that can operate in daylight conditions.
The transmitter and receiver modules are built using inexpensive off-the-shelf
components. Both modules are compact allowing the generation of renewed shared
secrets on demand over a short range of a few metres. An analysis of the
software is shown as well as results of error rates and therefore shared secret
yields at varying background light levels. As the system is designed to
eventually work in short-range consumer applications, we also present a use
scenario where the consumer can regularly 'top up' a store of secrets for use
in a variety of one-time-pad and authentication protocols.Comment: 18 pages, 9 figures, to be published in New Journal of Physic
Optical deep space communication via relay satellite
The possible use of an optical for high rate data transmission from a deep space vehicle to an Earth-orbiting relay satellite while RF links are envisioned for the relay to Earth link was studied. A preliminary link analysis is presented for initial sizing of optical components and power levels, in terms of achievable data rates and feasible range distances. Modulation formats are restricted to pulsed laser operation, involving bot coded and uncoded schemes. The advantage of an optical link over present RF deep space link capabilities is shown. The problems of acquisition, pointing and tracking with narrow optical beams are presented and discussed. Mathematical models of beam trackers are derived, aiding in the design of such systems for minimizing beam pointing errors. The expected orbital geometry between spacecraft and relay satellite, and its impact on beam pointing dynamics are discussed
Timing performance of phased-locked loops in optical pulse position modulation communication systems
An optical digital communication system requires that an accurate clock signal be available at the receiver for proper synchronization with the transmitted signal. Phase synchronization is especially critical in M-ary pulse position modulation (PPM) systems where the optimum decision scheme is an energy detector which compares the energy in each of M time slots to decide which of M possible words was sent. Timing errors cause energy spillover into adjacent time slots (a form of intersymbol interference) so that only a portion of the signal energy may be attributed to the correct time slot. This effect decreases the effective signal, increases the effective noise, and increases the probability of error. A timing subsystem for a satellite-to-satellite optical PPM communication link is simulated. The receiver employs direct photodetection, preprocessing of the detected signal, and a phase-locked loop for timing synchronization. The variance of the relative phase error is examined under varying signal strength conditions as an indication of loop performance, and simulation results are compared to theoretical calculations
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