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Using a cascade of an amplitude and a phase regenerator, multilevel signal processing is demonstrated experimentally for a 25-GBd star-8QAM. Improvements in the signal quality by up to 2 dB are obtained.
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Research Interests: Physics, Optics, Telecommunications, Nonlinear dynamics, Computer Aided Design, and 15 moreMedicine, Computer Simulation, Light, Lenses, Optical physics, Computer communication networks, Phase Modulation, Equipment Design, Phase Noise, Equipment Failure Analysis, Electrical And Electronic Engineering, Quadrature Amplitude Modulation, Amplitude Modulation, Amplitude, and Phase shift keying
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ABSTRACT The influence of dispersion of the highly nonlinear fiber in the loop of a nonlinear amplifying loop mirror on its performance as a 2R regenerator for phase-encoded optical signals has been studied.
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This work presents the numerical investigations on the physical limitations and optimization of the nonlinear amplifying loop mirror (NALM) as a regenerator of phase-shift-keyed signals. The NALM consists of a bidirectional amplifier and... more
This work presents the numerical investigations on the physical limitations and optimization of the nonlinear amplifying loop mirror (NALM) as a regenerator of phase-shift-keyed signals. The NALM consists of a bidirectional amplifier and a highly nonlinear fiber (HNLF), combined to a loop by a fiber coupler. The transfer functions for the NALM versus dispersion for an amplifier gain for anomalous
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ABSTRACT Power characteristics and phase functions of a NALM are investigated in simulations and experimentally, showing a phase-preserving nonlinear characteristics suitable for amplitude regeneration of phase-encoded signals. A negative... more
ABSTRACT Power characteristics and phase functions of a NALM are investigated in simulations and experimentally, showing a phase-preserving nonlinear characteristics suitable for amplitude regeneration of phase-encoded signals. A negative power penalty of -1.5 dB was obtained.
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We demonstrate and discuss a state of light with purely transverse angular momentum – a photonic wheel – generated by tight focusing of polarization tailored light. We use an experimental nanoprobing technique to measure the corresponding... more
We demonstrate and discuss a state of light with purely transverse angular momentum – a photonic wheel – generated by tight focusing of polarization tailored light. We use an experimental nanoprobing technique to measure the corresponding distribution.
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In recent years there has been an increasing interest in achieving efficient coupling of a single photon to a single atom in free space. Independent of the particular application at hand, optimizing the efficiency of the coupling is... more
In recent years there has been an increasing interest in achieving efficient coupling of a single photon to a single atom in free space. Independent of the particular application at hand, optimizing the efficiency of the coupling is tantamount to maximizing the electric field component parallel to the dipole moment of the specific atomic transition. In this contribution we present the field distributions which achieve this maximization for several optical focusing devices.
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ABSTRACT We experimentally demonstrate a recently predicted novel beam shift phenomenon, the geometric spin Hall effect of light. This effect is fundamentally different from ordinary beam shifts due to its purely geometric nature.
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Whispering gallery resonators made from nonlinear crystals offer high quality factors combined with small mode volumes leading to an enhanced effective χ(2) nonlinearity. These properties facilitate studying quantum optical effects in the... more
Whispering gallery resonators made from nonlinear crystals offer high quality factors combined with small mode volumes leading to an enhanced effective χ(2) nonlinearity. These properties facilitate studying quantum optical effects in the nonlinear regime with interacting fields differing in frequency by up to four orders of magnitude. Furthermore, the small size results in a large mode spacing allowing for heralded single photon generation in a single mode
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We successfully demonstrate squeezing of nanosecond pulses via self-induced transparency in a system of mercury vapor confined in a hollow core kagome-style fiber.
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ABSTRACT The optical Kerr effect provides an ideal quantum non-demolition interaction. Experiments and proposals using this interaction are reviewed with special emphasis on optical soliton pulses propagating in fibres. The performance of... more
ABSTRACT The optical Kerr effect provides an ideal quantum non-demolition interaction. Experiments and proposals using this interaction are reviewed with special emphasis on optical soliton pulses propagating in fibres. The performance of a quantum non-demolition experiment using the optical Kerr effect may be reduced by self-phase modulation of the probe pulse. Proposals to overcome this limitation are discussed.
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Continuous-variable quantum key distribution is a practical application of quantum information theory that is aimed at generation of secret cryptographic key between two remote trusted parties and that uses multi-photon quantum states as... more
Continuous-variable quantum key distribution is a practical application of quantum information theory that is aimed at generation of secret cryptographic key between two remote trusted parties and that uses multi-photon quantum states as carriers of key bits. Remote parties share the secret key via a quantum channel, that presumably is under control of of an eavesdropper, and which properties must be taken into account in the security analysis. Well-studied fiber-optical quantum channels commonly possess stable transmittance and low noise levels, while free-space channels represent a simpler, less demanding and more flexible alternative, but suffer from atmospheric effects such as turbulence that in particular causes a non-uniform transmittance distribution referred to as fading. Nonetheless free-space channels, providing an unobstructed line-of-sight, are more apt for short, mid-range and potentially long-range (using satellites) communication and will play an important role in the future development and implementation of QKD networks. It was previously theoretically shown that coherent-state CV QKD should be in principle possible to implement over a free-space fading channel, but strong transmittance fluctuations result in the significant modulation-dependent channel excess noise. In this regime the post-selection of highly transmitting sub-channels may be needed, which can even restore the security of the protocol in the strongly turbulent channels. We now report the first proof-of-principle experimental test of coherent state CV QKD protocol using different levels Gaussian modulation over a mid-range (1.6-kilometer long) free-space atmospheric quantum channel. The transmittance of the link was characterized using intensity measurements for the reference but channel estimation using the modulated coherent states was also studied. We consider security against Gaussian collective attacks, that were shown to be optimal against CV QKD protocols . We assumed a general entangling cloner collective attack (modeled using data obtained from the state measurement results on both trusted sides of the protocol), that allows to purify the noise added in the quantum channel . Our security analysis of coherent-state protocol also took into account the effect of imperfect channel estimation, limited post-processing efficiency and finite data ensemble size on the performance of the protocol. In this regime we observe the positive key rate even without the need of applying post-selection. We show the positive improvement of the key rate with increase of the modulation variance, still remaining low enough to tolerate the transmittance fluctuations. The obtained results show that coherent-state CV QKD protocol that uses real free-space atmospheric channel can withstand negative influence of transmittance fluctuations, limited post-processing efficiency, imperfect channel estimation and other finite-size effects, and be successfully implemented. Our result paves the way to the full-scale implementation of the CV QKD in real free-space channels at mid-range distances.
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We present an analysis of the technical challenges faced when deploying long-distance free-space links and orbital angular momentum multiplexing, e.g. for the purpose of communication. Our analysis indicates atmospheric mitigation... more
We present an analysis of the technical challenges faced when deploying long-distance free-space links and orbital angular momentum multiplexing, e.g. for the purpose of communication. Our analysis indicates atmospheric mitigation techniques and the consideration of the modal purity the system design.
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ABSTRACT In this paper, we consider the process of filtering non-Gaussian noise from binary coherent states using two different measurement methods: homodyne detection and on/off detection. Characteristics of homodyne and on/off detection... more
ABSTRACT In this paper, we consider the process of filtering non-Gaussian noise from binary coherent states using two different measurement methods: homodyne detection and on/off detection. Characteristics of homodyne and on/off detection in such a filter are compared and the optimal device is discussed. The performance of the protocol was characterized by measuring the signal state probability before and after filtration. We also measured the success probability (that is, the probability for a positive filter output) as well as the filter sensitivity for extremely weak signal states. All these results will be presented.
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Interferometric surface tests of stigmatic aspherics can be carried out in a null test configuration. Null tests require reference null elements either plane or spherical surfaces or both. A parabolic reflector transforms a plane into a... more
Interferometric surface tests of stigmatic aspherics can be carried out in a null test configuration. Null tests require reference null elements either plane or spherical surfaces or both. A parabolic reflector transforms a plane into a spherical wave which converges to the focus of the paraboloid. Therefore, a spherical ball lens or a steel ball can be placed into the
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Nonlinear electro-optical conversion of microwave radiation into the optical telecommunication band is achieved within a crystalline whispering gallery mode resonator, reaching 0.1% photon number conversion efficiency with MHz bandwidth.
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We present results on nonlinear electro-optical conversion of microwave radiation into the optical telecommunication band with more than 0.1% photon number conversion efficiency with MHz bandwidth, in a crystalline whispering gallery mode... more
We present results on nonlinear electro-optical conversion of microwave radiation into the optical telecommunication band with more than 0.1% photon number conversion efficiency with MHz bandwidth, in a crystalline whispering gallery mode resonator.
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Down-converted photons from counterpropagating whispering gallery modes can be used to generate two-photon interference. We present our experimental scheme and discuss the interference visibility in case of backscattering.
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We report on interferometric characterization of a deep parabolic mirror with a depth of more than five times its focal length. The interferometer is of Fizeau type; its core consists of the mirror itself, a spherical null element, and a... more
We report on interferometric characterization of a deep parabolic mirror with a depth of more than five times its focal length. The interferometer is of Fizeau type; its core consists of the mirror itself, a spherical null element, and a reference flat. Because of the extreme solid angle produced by the paraboloid, the alignment of the setup appears to be very critical and needs auxiliary systems for control. Aberrations caused by misalignments are removed via fitting of suitable functionals provided by means of ray tracing simulations. It turns out that the usual misalignment approximations fail under these extreme conditions.
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ABSTRACT We investigated modes of a birefringent whispering gallery mode resonator whose optical axis is tilted with respect to its symmetry axis. Polarization eigenstates that have not been observed in other WGM configurations will be... more
ABSTRACT We investigated modes of a birefringent whispering gallery mode resonator whose optical axis is tilted with respect to its symmetry axis. Polarization eigenstates that have not been observed in other WGM configurations will be presented.
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We investigate the frequency-resolved intensity noise spectrum of an Yb-doped fiber amplifier down to the fundamental limit of quantum noise. We focus on the kHz and low MHz frequency regime with special interest in the region between 1... more
We investigate the frequency-resolved intensity noise spectrum of an Yb-doped fiber amplifier down to the fundamental limit of quantum noise. We focus on the kHz and low MHz frequency regime with special interest in the region between 1 and 10 kHz. Intensity noise levels up to $$\ge$$ ≥ 60 dB above the shot noise limit are found, revealing great optimization potential. Additionally, two seed lasers with different noise characteristics were amplified, showing that the seed source has a significant impact and should be considered in the design of high power fiber amplifiers.
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We investigate estimation of fluctuating channels and its effect on security of continuous-variable quantum key distribution. We propose a novel estimation scheme which is based on the clusterization of the estimated transmittance data.... more
We investigate estimation of fluctuating channels and its effect on security of continuous-variable quantum key distribution. We propose a novel estimation scheme which is based on the clusterization of the estimated transmittance data. We show that uncertainty about whether the transmittance is fixed or not results in a lower key rate. However, if the total number of measurements is large, one can obtain using our method a key rate similar to the non-fluctuating channel even for highly fluctuating channels. We also verify our theoretical assumptions using experimental data from an atmospheric quantum channel. Our method is therefore promising for secure quantum communication over strongly fluctuating turbulent atmospheric channels.
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Conventional ultra-high sensitivity detectors in the millimeter-wave range are usually cooled as their own thermal noise at room temperature would mask the weak received radiation. The need for cryogenic systems increases the cost and... more
Conventional ultra-high sensitivity detectors in the millimeter-wave range are usually cooled as their own thermal noise at room temperature would mask the weak received radiation. The need for cryogenic systems increases the cost and complexity of the instruments, hindering the development of, among others, airborne and space applications. In this work, the nonlinear parametric upconversion of millimeter-wave radiation to the optical domain inside high-quality (Q) lithium niobate whispering-gallery mode (WGM) resonators is proposed for ultra-low noise detection. We experimentally demonstrate coherent upconversion of millimeter-wave signals to a 1550 nm telecom carrier, with a photon conversion efficiency surpassing the state-of-the-art by 2 orders of magnitude. Moreover, a theoretical model shows that the thermal equilibrium of counterpropagating WGMs is broken by overcoupling the millimeter-wave WGM, effectively cooling the upconverted mode and allowing ultra-low noise detection. By theoretically estimating the sensitivity of a correlation radiometer based on the presented scheme, it is found that room-temperature radiometers with better sensitivity than state-of-the-art high-electron-mobility transistor (HEMT)-based radiometers can be designed. This detection paradigm can be used to develop room-temperature instrumentation for radio astronomy, earth observation, planetary missions, and imaging systems.