Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on an eavesdropper's power. This article provides a concise up-to-date review of QKD, biased toward the practical side. Essential theoretical tools that have been developed to assess the security of the main experimental platforms are presented (discrete-variable, continuous-variable, and distributed-phase-reference protocols).

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The security of practical quantum key distribution

While organic electronics is mostly dominated by light-emitting diodes, photovoltaic cells and transistors, optoelectronics properties peculiar to organic semiconductors make them interesting candidates for the development of innovative and disruptive applications also in the field of light signal detection. In fact, organic-based photoactive media combine effective light absorption in the region of the spectrum from ultraviolet to near-infrared with good photogeneration yield and low-temperature processability over large areas and on virtually every substrate, which might enable innovative optoelectronic systems to be targeted for instance in the field of imaging, optical communications or biomedical sensing. In this review, after a brief resume of photogeneration basics and of devices operation mechanisms, we offer a broad overview of recent progress in the field, focusing on photodiodes and phototransistors. As to the former device category, very interesting values for figures of merit such as photoconversion efficiency, speed and minimum detectable signal level have been attained, and even though the simultaneous optimization of all these relevant parameters is demonstrated in a limited number of papers, real applications are within reach for this technology, as it is testified by the increasing number of realizations going beyond the single-device level and tackling more complex optoelectronic systems. As to phototransistors, a more recent subject of study in the framework of organic electronics, despite a broad distribution in the reported performances, best photoresponsivities outperform amorphous silicon-based devices. This suggests that organic phototransistors have a large potential to be used in a variety of optoelectronic peculiar applications, such as a photo-sensor, opto-isolator, image sensor, optically controlled phase shifter, and opto-electronic switch and memory.

Organic light detectors: photodiodes and phototransistors.

The scintillation index of plane and spherical light waves as well as of a Gaussian beam, propagating in the clear-water weakly turbulent ocean, is revealed. The results are of utmost importance for underwater optical communications and sensing. An analysis of the threshold between the weak and strong regimes of oceanic turbulence is made, with the accent on the contribution from salinity-induced turbulence. It is found that strong oceanic turbulence can occur at distances as short as several meters, in striking contrast with atmospheric studies for which the typical distances are on the order of a kilometer.

Light scintillation in oceanic turbulence

To improve the performance of sensorless interior permanent magnet synchronous motor (IPMSM) drives, a quadrature phase-locked loop (PLL) with an adaptive notch filter (ANF) is proposed for the model-based sliding-mode observer (SMO). The position estimation error with the sixth harmonic distortion caused by the inverter nonlinearity and the flux spatial harmonics is analyzed. The ANF based on adaptive noise canceling principle combined with the quadrature PLL is proposed to diminish the estimation harmonic error. This method can adaptively compensate the harmonics in the estimated electromotive force to eliminate the corresponding position estimation error. The estimated harmonic coefficients from the ANF can be continuously self-tuned using the least-mean-squares algorithm according to the estimated position information. The effectiveness of the proposed method is verified with the experimental results at a 2.2-kW IPMSM sensorless drive.

Adaptive Compensation Method of Position Estimation Harmonic Error for EMF-Based Observer in Sensorless IPMSM Drives

To improve performance of the field-oriented controlled position sensorless interior permanent magnet synchronous motors (IPMSM) drive, a model-based high-order sliding-mode observer with a software quadrature phase-locked loop (PLL) is proposed. A simplified method of designing the feedback gain matrix of the sliding-mode observer is introduced for easy application. The PLL coefficients are analyzed by considering the expected position estimation error and the operating condition. Compared with the conventional arc-tangent calculation method, the proposed quadrature PLL estimation method can be immune to the influence of the noise and distortion. To achieve the robust high-efficiency operation of the sensorless IPMSM, an enhanced online maximum torque per ampere (MTPA) control strategy without motor parameters dependent is adopted for the vector control drive. The optimal MTPA operation is achieved by searching the optimal current angle online to make the current amplitude be the minimum. The effectiveness of the proposed method is verified with a 2.2-kW IPMSM sensorless drive.

Quadrature PLL-Based High-Order Sliding-Mode Observer for IPMSM Sensorless Control With Online MTPA Control Strategy

It is well know that free-space laser system performance is limited by atmospheric turbulence. Most theoretical treatments have been described for many years by Kolmogorov's power spectral density model because of its simplicity. Unfortunately, several experiments have been reported recently that show that the Kolmogorov theory is sometimes incomplete to describe atmospheric statistics properly, in particular, in portions of the troposphere and stratosphere. We present a non-Kolmogorov power spectrum that uses a generalized exponent instead of constant standard exponent value 11/3, and a generalized amplitude factor instead of constant value 0.033. Using this new spectrum in weak turbulence, we carry out, for a horizontal path, an analysis of long-term beam spread, scintillation index, probability of fade, mean signal-to-noise ratio (SNR), and mean bit error rate (BER) as variation of the spectrum exponent. Our theoretical results show that for alpha values lower than =11/3, but not for alpha close to =3, there is a remarkable increase of scintillation and consequently a major penalty on the system performance. However, when alpha assumes a value close to =3 or for alpha values higher than =11/3, scintillation decreases, leading to an improvement on the system performance.

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Free-space optical system performance for laser beam propagation through non-Kolmogorov turbulence

Atmospheric turbulence induces significant variation on the angle-of-arrival of laser beams used in free space laser
communication. Angle-of-arrival fluctuations of an optical wave in the plane of the receiver aperture can be described
in terms of the phase structure function that already has been calculated by Kolmogorov's power spectral density model.
Unfortunately several experiments showed that Kolmogorov theory is sometimes incomplete to describe atmospheric
statistics properly. In this paper, for horizontal path and weak turbulence, we carry out analysis of angle-of-arrival
fluctuations using a non Kolmogorov power spectrum which uses a generalized exponent factor instead of constant
standard exponent value 11/3 and a generalized amplitude factor instead of constant value 0.033. Also our non
Kolmogorov spectrum includes both inner scale and outer scale effects.

Angle of arrival fluctuations for free space laser beam propagation through non kolmogorov turbulence

Several techniques for phase noise PSD measurement of continuous wave (CW) lasers to be used in coherent transmission systems are analyzed. Between them, we evaluate two novel techniques. The first employs a homodyne optical phase-locked loop, while the second uses a signal source analyzer. Experimental results obtained by these two methods are compared with classical linewidth measurement methods like self-heterodyne and Michelson interferometer. Limits and accuracy of each method are discussed. Furthermore, the comparison shows that, for coherent transmission system applications, only a subset of the analyzed methods is useful for laser phase noise characterization.

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Narrow Linewidth CW Laser Phase Noise Characterization Methods for Coherent Transmission System Applications

Free space laser system performance is limited by atmospheric turbulence that has been described for many years by
Kolmogorov's power spectral density model because of its simplicity. Unfortunately several experiments have been
reported recently that show Kolmogorov theory is sometimes incomplete to describe atmospheric statistics properly, in
particular in portions of the troposphere and stratosphere. In this paper we present a Non-Kolmogorov power spectrum
which uses a generalized exponent instead of constant standard exponent value 11/3 and a generalized amplitude factor
instead of constant value 0.033. Using this new spectrum in weak turbulence, we carry out, for horizontal path, analysis
of Long Term Beam Spread, Scintillation index, Probability of fade, mean SNR and mean BER as variation of the
spectrum exponent.

/pdf/free-space-optical-system-performance-for-laser-beam-1uaap2ae84.pdf

Free space optical system performance for laser beam propagation through non-Kolmogorov turbulence

Atmospheric turbulence has been described for many years by Kolmogorov's power spectral density model because of its simplicity. Unfortunately several experiments have been reported recently that show Kolmogorov theory is sometimes incomplete to describe atmospheric statistics properly, in particular in portions of the troposphere and stratosphere. It is known that free space laser system performance is limited by atmospheric turbulence. In this paper we use a non-Kolmogorov power spectrum which uses a generalized exponent instead of constant standard exponent value 11/3 and a generalized amplitude factor instead of constant value 0.033. Using this spectrum in weak turbulence, we carry out, for a Gaussian beam propagating along a horizontal path, analysis of long term beam spread, scintillation, probability of fade, mean signal to noise ratio and mean bit error rate as variation of the spectrum exponent. Our theoretical results show that for alpha values lower than alpha = 11/3, but not for alpha close to alpha = 3, there is a remarkable increase of scintillation and consequently a major penalty on the system performance. However when alpha assumes values close to alpha = 3 or for alpha values higher than alpha = 11/3 scintillation decreases leading to an improvement on the system performance.

/pdf/free-space-optical-system-performance-for-a-gaussian-beam-4s2y13mi5c.pdf

Valter Ferrero

Papers

Free-space optical system performance for laser beam propagation through non-Kolmogorov turbulence

Angle of arrival fluctuations for free space laser beam propagation through non kolmogorov turbulence

Narrow Linewidth CW Laser Phase Noise Characterization Methods for Coherent Transmission System Applications

Free space optical system performance for laser beam propagation through non-Kolmogorov turbulence

Free Space Optical System Performance for a Gaussian Beam Propagating Through Non-Kolmogorov Weak Turbulence