12 research outputs found
PPM demodulation: On approaching fundamental limits of optical communications
We consider the problem of demodulating M-ary optical PPM (pulse-position
modulation) waveforms, and propose a structured receiver whose mean probability
of symbol error is smaller than all known receivers, and approaches the quantum
limit. The receiver uses photodetection coupled with optimized phase-coherent
optical feedback control and a phase-sensitive parametric amplifier. We present
a general framework of optical receivers known as the conditional pulse nulling
receiver, and present new results on ultimate limits and achievable regions of
spectral versus photon efficiency tradeoffs for the single-spatial-mode
pure-loss optical communication channel.Comment: 5 pages, 6 figures, IEEE ISIT, Austin, TX (2010
Harvesting Planck radiation for free-space optical communications in the LWIR band
We demonstrate a free-space optical communication link with an optical
transmitter that harvests naturally occurring Planck radiation from a warm body
and modulates the emitted intensity. The transmitter exploits an
electro-thermo-optic effect in a multilayer graphene device that electrically
controls the surface emissivity of the device resulting in control of the
intensity of the emitted Planck radiation. We design an amplitude-modulated
optical communication scheme and provide a link budget for communications data
rate and range based on our experimental electro-optic characterization of the
transmitter. Finally, we present an experimental demonstration achieving
error-free communications at 100 bits per second over laboratory scales
Optical codeword demodulation with error rates below standard quantum limit using a conditional nulling receiver
The quantum states of two laser pulses---coherent states---are never mutually
orthogonal, making perfect discrimination impossible. Even so, coherent states
can achieve the ultimate quantum limit for capacity of a classical channel, the
Holevo capacity. Attaining this requires the receiver to make joint-detection
measurements on long codeword blocks, optical implementations of which remain
unknown. We report the first experimental demonstration of a joint-detection
receiver, demodulating quaternary pulse-position-modulation (PPM) codewords at
a word error rate of up to 40% (2.2 dB) below that attained with
direct-detection, the largest error-rate improvement over the standard quantum
limit reported to date. This is accomplished with a conditional nulling
receiver, which uses optimized-amplitude coherent pulse nulling, single photon
detection and quantum feedforward. We further show how this translates into
coding complexity improvements for practical PPM systems, such as in deep-space
communication. We anticipate our experiment to motivate future work towards
building Holevo-capacity-achieving joint-detection receivers.Comment: 6 pages, 4 figure