48,843 research outputs found
Atmospheric channel effects on terrestrial free space optical communication links
Abstract. This paper illustrates the challenges imposed by the atmospheric channel on the design of a terrestrial laser communication link. The power loss due to scattering effect is described using the Kim/Kruse scattering model while the effect and the penalty imposed by atmospheric turbulence is highlighted by considering the bit error rate (BER) of an On-Off Keying modulated link in an optical Poisson channel. The power loss due to thick fog can measure over 100 dB/km while snow and rain result in much lower attenuation. We show that non-uniformity in the atmospheric temperature also contributes to performance deterioration due to scintillation effect. At a BER of 10-4, for a channel with a turbulence strength of>0.1, the penalty imposed by turbulence induced fading is over 20 photoelectron counts in order to achieve the same level of performance as a channel with no fading. The work reported here is part of the EU COST actions and EU projects.
Performance of free space optical communication using M-array receivers at atmospheric conditions
Abstract: In free space optical (FSO) communication links, atmospheric parameters including absorption, scattering and turbulence have significant impacts on the quality of laser beams propagating through the atmosphere. Absorption and/or scattering, due to atmospheric particles result in optical losses, whereas turbulence contributes to the intensity scintillation that can severely impair the operation of FSO communications systems. In this paper, using a modified model we analyze the atmospheric effects on the signal-to-noise ratio (SNR) and the bit error rate (BER) of an FSO system. We show that there is an improvement in BER when using M-array receivers instead of one a single receiver
A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using integrated path differential absorption LiDAR limb sounding
We propose a new satellite mission to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 µrad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively. This novel concept presents significant challenges, including the performance of the lasers in space, the tracking between the main spacecraft and the retroreflectors, the refractive effects of turbulence, and the design of the telescopes to achieve a high signal-to-noise ratio for the high precision measurements. The mission concept was conceived at the Alpbach Summer School 2010
Long-distance quantum communication with atomic ensembles and linear optics
Quantum communication holds a promise for absolutely secure transmission of
secret messages and faithful transfer of unknown quantum states. Photonic
channels appear to be very attractive for physical implementation of quantum
communication. However, due to losses and decoherence in the channel, the
communication fidelity decreases exponentially with the channel length. We
describe a scheme that allows to implement robust quantum communication over
long lossy channels. The scheme involves laser manipulation of atomic
ensembles, beam splitters, and single-photon detectors with moderate
efficiencies, and therefore well fits the status of the current experimental
technology. We show that the communication efficiency scale polynomially with
the channel length thereby facilitating scalability to very long distances.Comment: 2 tex files (Main text + Supplement), 4 figure
Free space laser telecommunication through fog
Atmospheric clearness is a key issue for free space optical communications
(FSO). We present the first active method to achieve FSO through clouds and
fog, using ultrashort high intensity laser filaments. The laser filaments
opto-mechanically expel the droplets out of the beam and create a cleared
channel for transmitting high bit rate telecom data at 1.55 microns. The low
energy required for the process allows considering applications to
Earth-satellite FSO and secure ground based optical communication, with
classical or quantum protocols.Comment: 4 pages + 2 pages supplementary text and movie
Polarization Imperfections of Light in Interferometry
DisertaÄŤnĂ práce pojednává o polarizaÄŤnĂch nedokonalostech optickĂ˝ch komponentĹŻ, kterĂ© jsou vyuĹľĂvány ke kontrole a k transformaci polarizaÄŤnĂho stavu svÄ›tla. ZĂskanĂ© teoretickĂ© vĂ˝sledky jsou pak vyuĹľity ve vybranĂ˝ch aplikacĂch, jeĹľ ke svĂ© ÄŤinnosti vyuĹľĂvajĂ právÄ› polarizace svÄ›tla. KonkrĂ©tnÄ› se jedná o zaĹ™ĂzenĂ měřĂcĂ vibrace oscilujĂcĂch objektĹŻ, dále o interferenÄŤnĂ měřenĂ dvojlomu v transparentnĂch materiálech a koneÄŤnÄ›, o vybraná tĂ©mata z optickĂ© kvantovĂ© komunikace.The emphasis of the dissertation is put on the investigating of polarization imperfections of optical components which are used to control and transform polarization of light. The theoretical results of this investigation are then applied to different applications which exploit light polarization, namely to the arrangements for high-resolution measurement of vibrating targets, to interferometric measurements for the determination of stress-induced birefringence in transparent materials and to the selected topics in quantum optical communication.
Free-space quantum links under diverse weather conditions
Free-space optical communication links are promising channels for
establishing secure quantum communication. Here we study the transmission of
nonclassical light through a turbulent atmospheric link under diverse weather
conditions, including rain or haze. To include these effects, the theory of
light transmission through atmospheric links in the elliptic-beam approximation
presented by Vasylyev et al. [D. Vasylyev et al., Phys. Rev. Lett. 117, 090501
(2016); arXiv:1604.01373] is further generalized.It is demonstrated, with good
agreement between theory and experiment, that low-intensity rain merely
contributes additional deterministic losses, whereas haze also introduces
additional beam deformations of the transmitted light. Based on these results,
we study theoretically the transmission of quadrature squeezing and Gaussian
entanglement under these weather conditions.Comment: 14 pages, 8 figure
Current optical technologies for wireless access
The objective of this paper is to describe recent activities and investigations on free-space optics (FSO) or optical wireless and the excellent results achieved within SatNEx an EU-framework 6th programme and IC 0802 a COST action. In a first part, the FSO technology is briefly discussed. In a second part, we mention some performance evaluation criterions for the FSO. In third part, we briefly discuss some optical signal propagation experiments through the atmosphere by mentioning network architectures for FSO and then discuss the recent investigations in airborne and satellite application experiments for FSO. In part four, we mention some recent investigation results on modelling the FSO channel under fog conditions and atmospheric turbulence. Additionally, some recent major performance improvement results obtained by employing hybrid systems and using some specific modulation and coding schemes are presented
A Raman anemometer for component-selective velocity measurements of particles in a flow
An anemometer for the measurement of the velocity of particles of different components in a flow, separate and apart from that of the flow itself, is described. As a component-selective mechanism Raman scattering is used. The velocity is measured by relating the autocorrelated scattering signal to the known laser beam profile
- …