We investigate the transmission of focused beams through single subwavelength holes in a silver film. We use radially and azimuthally polarized light to excite higher-order waveguide modes as well as to match the radial symmetry of the aperture geometry. Remarkably, the transmission properties can be described by a classical waveguide model even for thicknesses of the silver film as thin as a quarter of a wavelength.
Tailored polarization patterns for performance optimization of optical devices
In the case of strong focusing the smallest possible focal spot can be reached, provided one uses a specially designed polarization pattern. Other optical set-ups also employing high numerical aperture imaging are likewise expected to improve performance under polarization optimization. We propose a strategy for calculating the polarization pattern required for system optimization. A single element modulating only the polarization and not amplitude and phase may lead to satisfactory performance in some cases.
Design considerations for the absolute testing approach of aspherics
using combined diffractive optical elements
Gufran S. Khan,
Klaus Mantel,
Irina Harder,
Norbert Lindlein,
Johannes Schwider
Aspheric optical surfaces are often tested using diffractive optics as null elements. For precise measurements, the errors caused by the diffractive optical element must be calibrated. Recently, we reported first experimental results of a three position quasi-absolute test for rotationally invariant aspherics by using combined-diffractive optical elements (combo-DOEs). Here we investigate the effects of the DOE substrate errors on the proposed calibration procedure and present a set of criteria for designing an optimized combo-DOE. It is demonstrated that this optimized design enhances the overall consistency of the procedure. Furthermore, the rotationally varying part of the surface deviations is compared with the rotationally varying deviations obtained by an N-position averaging procedure and is found to be in good agreement. (c) 2007 Optical Society of America.
Single-photon quantum key distribution in the presence of loss
We investigate two-way and one-way single-photon quantum key distribution (QKD) protocols in the presence of loss introduced by the quantum channel. Our analysis is based on a simple precondition for secure QKD in each case. In particular, the legitimate users need to prove that there exists no separable state (in the case of two-way QKD), or that there exists no quantum state having a symmetric extension (one-way QKD), that is compatible with the available measurements results. We show that both criteria can be formulated as a convex optimization problem known as a semidefinite program, which can be efficiently solved. Moreover, we prove that the solution to the dual optimization corresponds to the evaluation of an optimal witness operator that belongs to the minimal verification set of them for the given two-way (or one-way) QKD protocol. A positive expectation value of this optimal witness operator states that no secret key can be distilled from the available measurements results. We apply such analysis to several well-known single-photon QKD protocols under losses.
Improved absolute frequency measurement of the In-115(+) 5s(2)
S-1(0)-5s5p P-3(0) narrowline transition: Progress towards an optical
frequency standard
Y. H. Wang,
T. Liu,
R. Dumke,
A. Stejskal,
Y. N. Zhao,
J. Zhang,
Z. H. Lu,
L. J. Wang,
Th. Becker, et al.
We report on an improved absolute frequency measurement of the 5s(2 1)S(0)-5s5p(3) P-0 narrowline clock transition at 236.5 nm, for a single, trapped, and laser-cooled In-115 ion. Using a narrowline laser as the local oscillator, a linewidth of 43 Hz for the transition is resolved. The uncertainty of the transition frequency's centroid is 18 Hz, leading to a fractional uncertainty of 1.4 x 10(-14). For absolute frequency measurement, we use an optical frequency comb locked to a cesium clock as the reference. The transition frequency is found to be 1267402452900967(63) Hz, averaged over 13 days of separate measurements. The accuracy is about 5.0 x 10(14). We discuss possibilities for further improvement.
Enhancement of optical absorption and photocurrent of 6H-SiC by laser
surface nanostructuring
Nanoscale ripple structures with spatial periods of up to 155 nm are generated by a single beam ultrashort pulsed laser structuring of 6H-SiC surface. The period of nanoripples does not depend on the laser fluence and the number of pulses. Optical absorption and photocurrent measurements on SiC samples are investigated before and after laser nanostructuring. Nearly 40% enhancement of optical absorption and a factor of 3 increase of photocurrent are achieved after laser nanostructuring. (c) 2007 American Institute of Physics.
Security of coherent-state quantum cryptography in the presence of
Gaussian noise
We investigate the security against collective attacks of a continuous variable quantum key distribution scheme in the asymptotic key limit for a realistic setting. The quantum channel connecting the two honest parties is assumed to be lossy and imposes Gaussian noise on the observed quadrature distributions. Secret key rates are given for direct and reverse reconciliation schemes including post-selection in the collective attack scenario. The effect of a nonideal error correction and two-way communication in the classical post-processing step is also taken into account.
Experimental demonstration of macroscopic quantum coherence in Gaussian
states
Christoph Marquardt,
Ulrik L. Andersen,
Gerd Leuchs,
Yuishi Takeno,
Mitsuyoshi Yukawa,
Hidehiro Yonezawa,
Akira Furusawa
We witness experimentally the presence of macroscopic coherence in Gaussian quantum states using a recently proposed criterion [E. G. Cavalcanti and M. D. Reid, Phys. Rev. Lett. 97 170405 (2006)]. The macroscopic coherence stems from interference between macroscopically distinct states in phase space, and we prove experimentally that a coherent state contains these features with a distance in phase space of 0.51 +/- 0.02 shot noise units. This is surprising because coherent states are generally considered being at the border between classical and quantum states, not yet displaying any nonclassical effect. For squeezed and entangled states the effect may be larger but depends critically on the state purity.
Second-harmonic generation by an astigmatic partially coherent beam
We investigate second-harmonic generation by an astigmatic partially coherent beam. An explicit expression for the second-order correlation function of the second-harmonic field is obtained. The properties of the generated field and the conversion efficiency for second-harmonic generation are studied numerically. We find that using an astigmatic instead of astigmatic partially coherent pump beam can increase the conversion efficiency of the second-harmonic generation. (c) 2007 Optical Society of America.
Numerical study of guided modes in arrays of metallic nanowires
C. G. Poulton,
M. A. Schmidt,
G. J. Pearce,
G. Kakarantzas,
P. St. J. Russell
We numerically investigate the band structure and guided modes within arrays of metallic nanowires. We show that bandgaps appear for a range of array geometries and that these can be used to guide light in these structures. Values of attenuation as low as 1.7 dB/cm are predicted for arrays of silver wires at communications wavelengths. This is more than 100 times smaller than the attenuation of the surface plasmon polariton modes on a single silver nanowire. (c) 2007 Optical Society of America.
Exact frequency comb mode number determination in precision optical
frequency measurements
J. Zhang,
Z. H. Lu,
Y. H. Wang,
T. Liu,
A. Stejskal,
Y. N. Zhao,
R. Dumke,
Q. H. Gong,
L. J. Wang
We demonstrate a method to determine the absolute mode number of a frequency comb when it is used for high-precision laser frequency measurement, without the help of wavemeters. Our technique involves changing the repetition rate of the frequency comb in a two-step process. Guidelines for choosing the correct repetition rates for different laser linewidths are given. As a demonstration, the absolute frequencies of two lasers with different linewidths are measured with our method.
Optimization of a nonlinear amplifying loop mirror for amplitude
regeneration in phase-shift-keyed transmission
Klaus Sponsel,
Kristian Cvecek,
Christian Stephan,
Georgy Onishchukov,
Bernhard Schmauss,
Gerd Leuchs
We present the numerical optimization of the transmission characteristics of a nonlinear amplifying loop mirror for amplitude regeneration of phase-encoded optical transmission formats. Adjusting the splitting factor, the amplifier gain and the phase bias, minimal phase distortions can be achieved while strong amplitude fluctuations are regenerated. The limiting effects of noise from the built-in amplifier and of amplified Rayleigh backscattering are also discussed.
Scintillation index of elliptical Gaussian beam in turbulent atmosphere
Yangjian Cai,
Yuntian Chen,
Halil T. Eyyuboglu,
Yahya Baykal
A tensor method is used to formulate the on-axis scintillation index for an elliptical Gaussian beam (EGB; astigmatic Gaussian beam) propagating in a weak turbulent atmosphere. Variations of the on-axis scintillation of an EGB are studied. It is interesting to find that the scintillation index of an EGB can be smaller than that of a circular Gaussian beam in a weakly turbulent atmosphere under certain conditions and is closely related to the ratio of the beam waist size along the long axis to that along the short axis of the EGB, the wavelength, and the structure constant of the turbulent atmosphere. (C) 2007 Optical Society of America.
Degree of polarization for partially coherent general beams in turbulent
atmosphere
The degree of polarization is found for optical excitations of cosh-Gaussian, cos-Gaussian and annular-Gaussian beams in a turbulent atmosphere. The related formulation is based on the beam coherence polarization matrix. The self and mutual coherence functions appearing in the beam coherence polarization matrix are evaluated, when the above mentioned excitations exhibit partial source coherence for self and cross fields. Plots showing the variation of the degree of polarization are provided versus the propagation length when the source size, displacement parameter, structure constant and the degree of source coherence for self and cross fields change.
Absolute frequency and isotope shift measurements of the cooling
transition in singly ionized indium
Y. H. Wang,
R. Dumke,
J. Zhang,
T. Liu,
A. Stejskal,
Y. N. Zhao,
Z. H. Lu,
L. J. Wing,
Th. Becker, et al.
EUROPEAN PHYSICAL JOURNAL D
44
(2)
307-311
(2007)
| Journal
We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In(+) 5s(2) (1)S(0) (F - 9/2)-5s5p (3)P(1) (F = 11/2) transition near 230.6 urn. The laser-induced fluorescence from a single In(+) in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes 115In(+) and 113In(+) are measured to be 1299 648 954.54(10) MHz and 1299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.
Dynamic and steady state current response to light excitation of
multilayered organic photodiodes
E. S. Zaus,
S. Tedde,
J. Fuerst,
D. Henseler,
G. H. Doehler
JOURNAL OF APPLIED PHYSICS
101
(4)
044501
(2007)
| Journal
Measurements of current transients are used to gain insight into the mechanism of charge transport and extraction of photodiodes based on bulk heterojunction blends of poly-3-hexyl-thiophene and [6,6]-phenyl C-61 butyric acid methyl ester. It is shown that the implementation of an appropriate hole conducting layer leads to a reduction of the dark current in the reverse direction. It is observed that the dynamic response to light excitation is strongly influenced by the thickness of the hole conducting layer, the light intensity, and the applied bias. Charge accumulation at the interface is assumed to result in the characteristic shape of the transients. The shape of the switch-off transient can be understood qualitatively by an equivalent circuit diagram. (c) 2007 American Institute of Physics.
2R-regeneration of an RZ-DPSK signal using a nonlinear amplifying loop
mirror
K. Cvecek,
K. Sponsel,
G. Onishchukov,
B. Schmauss,
G. Leuchs
The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for return-to-zero differential-phase-shift-keyed signals has been investigated experimentally. The measured power characteristics and phase functions show that the signal amplitude is regenerated while the signal phase is preserved in the setup. A significant eye-opening improvement and a negative power penalty of about 1.5 dB were obtained.
Efficient terahertz emission from ballistic transport enhanced
n-i-p-n-i-p superlattice photomixers
S. Preu,
F. H. Renner,
S. Malzer,
G. H. Doehler,
L. J. Wang,
M. Hanson,
A. C. Gossard,
T. L. J. Wilkinson,
E. R. Brown
The authors report on photomixing terahertz sources that overcome the transit time versus RC-time trade-off and allow for independent optimization of both of them, using a n-i-p-n-i-p superlattice. Furthermore, they take advantage of ballistic transport for reduced transit times. Apart from more favorable material parameters, In(Al)GaAs photomixers benefit from the advanced telecommunication laser technology around 1.55 mu m as compared to GaAs. In such devices, a terahertz-power output of 1 mu W has been achieved at 0.4 THz at a photocurrent of 3.8 mA. A comparison between corresponding GaAs- and InGaAs-based n-i-p-n-i-p photomixers reveals an improvement of performance by at least an order of magnitude for the latter one. (c) 2007 American Institute of Physics.
Bound soliton pairs in photonic crystal fiber
A. Podlipensky,
P. Szarniak,
N. Y. Joly,
C. G. Poulton,
P. St. J. Russell
We demonstrate experimentally the formation and stable propagation of bound soliton pairs in a highly nonlinear photonic crystal fiber. The bound pairs occur at a particular power as the consequence of high-order soliton fission. They propagate over long distances with constant inter-soliton frequency and time separation. During propagation, the soliton self-frequency shift causes the central frequency of the pairs to move towards longer wavelength. The formation and characteristics of the bound soliton pairs are confirmed numerically. We believe this to be the first experimental observation of such bound soliton pairs. (c) 2007 Optical Society of America.
A new 4 pi geometry optimized for focusing on an atom with a dipole-like
radiation pattern
N. Lindlein,
R. Maiwald,
H. Konermann,
M. Sondermann,
U. Peschel,
G. Leuchs
Focusing electromagnetic radiation efficiently onto an atom requires an open geometry, which is as close to the full solid angle as possible. Additionally, the radiant intensity should be as close as possible to a dipole radiation in order to have a similar field distribution as in the emission process. Here, we propose to make use of a novel combination of a parabolic mirror and a diffractive optical element.
Generation of polarization squeezing with periodically poled KTP at 1064
nm
Mikael Lassen,
Metin Sabuncu,
Preben Buchhave,
Ulrik L. Andersen
We report the experimental demonstration of directly produced polarization squeezing at 1064 nm from a type I optical parametric amplifier (OPA) based on a periodically poled KTP crystal (PPKTP). The orthogonal polarization modes of the polarization squeezed state are both defined by the OPA cavity mode, and the birefringence induced by the PPKTP crystal is compensated by a second, but inactive, PPKTP crystal. Stokes parameter squeezing of 3.6 dB and anti squeezing of 9.4 dB is observed. (c) 2007 Optical Society of America.
A periodic structure mimics a metamaterial
Carsten Rockstuhl,
Ulf Peschel,
Falk Lederer
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
24
(10)
A62-A67
(2007)
We show that properties attributed to planar metamaterials that support resonances due to an appropriately shaped unit cell can also be identified in a medium that exhibits a resonance evoked by its period only. By choosing a subwavelength period, the effective material parameters of such a medium can be retrieved from the complex reflected and transmitted amplitude. The parameters exhibit Lorentzian line shapes in the spectral vicinity of the resonances associated with the period. If this material is stacked to form a three-dimensional medium, a stop gap is observed in transmission in the frequency range where the real part of one effective material parameter becomes negative. The resonance at the origin of the response is related to the excitation of a higher-order Bloch mode. Because their negligible excitation is a prerequisite for deriving effective material parameters, the analyzed structure mimics only the response of a metamaterial but cannot be regarded as a metamaterial. (c) 2007 Optical Society of America.
Achieving Gaussian outputs from large-mode-area higher-order-mode fibers
We describe an alternative to fiber-gratings for converting higher-order LP0m (m > 1) fiber modes into a nearly fundamental Gaussian shape at the output of a fiber. This schematic enables the use of light propagation in higher-order modes of a fiber, a fiber-platform that has recently shown great promise for achieving very large mode areas needed for future high-power lasers and amplifiers. The conversion will be done by using a binary phase plate in the near field of the fiber, which emits the LP0m mode. Since the binary phase plate alone cannot increase the quality factor M-2 of the laser beam because of some broad sidebands, a filtering of the sidebands is done in the Fourier plane of a telescope. Of course, this will cost some of the total light power, but on the other side the M-2 factor can be reduced to nearly the ideal value near 1.0, and it is shown that similar to 76% of the total light power can be conserved for all investigated modes (2 <= m <= 8). A tolerance analysis for the phase plate and its adjustment is made, and different optical imaging systems to form a magnified image of the fiber mode on the phase plate are discussed in order to have more tolerance for the adjustment of the phase plate. (c) 2007 Optical Society of America.
Demonstration of deterministic and high fidelity squeezing of quantum
information
Jun-ichi Yoshikawa,
Toshiki Hayashi,
Takayuki Akiyama,
Nobuyuki Takei,
Alexander Huck,
Ulrik L. Andersen,
Akira Furusawa
By employing a recent proposal [R. Filip, P. Marek, and U.L. Andersen, Phys. Rev. A 71, 042308 (2005)] we experimentally demonstrate a universal, deterministic, and high-fidelity squeezing transformation of an optical field. It relies only on linear optics, homodyne detection, feedforward, and an ancillary squeezed vacuum state, thus direct interaction between a strong pump and the quantum state is circumvented. We demonstrate three different squeezing levels for a coherent state input. This scheme is highly suitable for the fault-tolerant squeezing transformation in a continuous variable quantum computer.
Atomic scale structure and optical emission of AlxGa1-xAs/GaAs quantum
wells
C. Ropers,
M. Wenderoth,
L. Winking,
T. C. G. Reusch,
M. Erdmann,
R. G. Ulbrich,
M. Grochol,
F. Grosse,
R. Zimmermann, et al.
A combined study of the optical and structural properties of AlGaAs/GaAs quantum wells is presented. Microphotoluminescence experiments, magnetomicrophotoluminescence, and atomically resolved cross-sectional scanning tunneling microscopy were performed on the same quantum well sample. Constant-current topographs with aluminum and/or gallium sensitivity are used to directly extract disorder potentials. Using these potentials, exciton absorption spectra, microphotoluminescence spectra, and diamagnetic shifts of individual exciton states are calculated in an envelope function approximation. Very good agreement between the theoretical and experimental results is found.
Narrow linewidth light source for an ultraviolet optical frequency
standard
T. Liu,
Y. H. Wang,
R. Dumke,
A. Stejskal,
Y. N. Zhao,
J. Zhang,
Z. H. Lu,
L. J. Wang,
Th. Becker, et al.
We report an ultra-narrow linewidth light source applicable for a frequency standard in the ultraviolet. The laser is a Nd:YAG laser that emits at 946 nm with 300-mW output power. It is locked to a high-finesse cavity. The minimum Allan deviation is 1.3 x 10(-14) for an integration time of 1 s, which corresponds to a laser linewidth of 2.8 Hz. The cavity drift is measured by a frequency comb and a single-ion spectrum for different time scales. In order to investigate broadening mechanisms due to the fiber transport and doubling systems, the laser light is frequency doubled with two independent systems and compared. The measured minimum beat-note between the two laser fields is less than 1 Hz. By carrying out a high-resolution scan on a trapped single indium ion, we observe a linewidth of 260 Hz on the ion clock transition. Possible reasons for the broadening effects are discussed.
Design of a mode converter for efficient light-atom coupling in free
space
M. Sondermann,
R. Maiwald,
H. Konermann,
N. Lindlein,
U. Peschel,
G. Leuchs
In this article, we describe how to develop a mode converter that transforms a plane electromagnetic wave into an inward-moving dipole wave. The latter one is intended to bring a single atom or ion from its ground state to an excited state by absorption of a single photon wave packet with near-100% efficiency.
Connection of anisotropic conductivity to tip-induced space-charge
layers in scanning tunneling spectroscopy of p-doped GaAs
S. Loth,
M. Wenderoth,
R. G. Ulbrich,
S. Malzer,
G. H. Doehler
The electronic properties of shallow acceptors in p-doped GaAs{110} are investigated with scanning tunneling microscopy (STM) at low temperature. Shallow acceptors are known to exhibit distinct triangular contrasts in STM images for certain bias voltages. Spatially resolved I(V) spectroscopy is performed to identify their energetic origin and behavior. A crucial parameter-the scanning tunneling microscope tip's work function-is determined experimentally. The voltage dependent potential configuration and band bending situation are derived. Ways to validate the calculations with the experiment are discussed. Differential conductivity maps reveal that the triangular contrasts are only observed with a depletion layer present under the STM tip. The tunnel process leading to the anisotropic contrasts calls for electrons to tunnel through vacuum gap and a finite region in the semiconductor.
Models for guidance in kagome-structured hollow-core photonic crystal
fibres
G. J. Pearce,
G. S. Wiederhecker,
C. G. Poulton,
S. Burger,
P. St. J. Russell
We demonstrate by numerical simulation that the general features of the loss spectrum of photonic crystal fibres (PCF) with a kagome structure can be explained by simple models consisting of thin concentric hexagons or rings of glass in air. These easily analysed models provide increased understanding of the mechanism of guidance in kagome PCF, and suggest ways in which the high-loss resonances in the loss spectrum may be shifted. (C) 2007 Optical Society of America.
Paraxial propagation of a partially coherent Hermite-Gaussian beam
through aligned and misaligned ABCD optical systems
Yangjian Cai,
Chiyi Chen
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
24
(8)
2394-2401
(2007)
| Journal
Paraxial propagation of a partially coherent Hermite-Gaussian beam through aligned and misaligned ABCD optical systems is investigated based on the generalized Collins formula for treating the propagation of a partially coherent beam through such optical systems. Analytical formulas for the cross-spectral density of a partially coherent Hermite-Gaussian beam propagating through such optical systems are derived. As an application example, we derive the propagation formulas for a partially coherent flattened Gaussian beam by expressing it as a superposition of a series of partially coherent Hermite-Gaussian beams by using polynomial expansion. The focusing properties of a partially coherent Hermite-Gaussian beam focused by a thin lens are studied as a numerical example. (c) 2007 Optical Society of America.
Propagation of Bessel and Bessel-Gaussian beams through an unapertured
or apertured misaligned paraxial optical systems
Propagation of Bessel and Bessel-Gaussian beams through an unapertured or apertured misaligned paraxial optical system is investigated. Analytical formulas for Bessel and Bessel-Gaussian beams propagating through an unapertured misaligned paraxial optical system are derived based on the generalized diffraction integral formula for treating the propagation of a laser beam through a misaligned paraxial optical system in the cylindrical coordinate system. By expanding the hard aperture function into a finite sum of complex Gaussian functions, some approximate analytical formulas are derived for Bessel and Bessel-Gaussian beams propagating through an apertured misaligned paraxial optical system. Some numerical examples are illustrated. The present analytical formulas provide a convenient and effective way for studying the propagation and transformation of Bessel and Bessel-Gaussian beams through an unapertured or apertured misaligned paraxial optical system. (C) 2007 Elsevier B.V. All rights reserved.
Modified hollow Gaussian beam and its paraxial propagation
A model named modified hollow Gaussian beam (HGB) is proposed to describe a dark hollow beam with adjustable beam spot size, central dark size and darkness factor. In this modified model, both the beam spot size and the central dark size will be convergent to finite constants as the beam order approaches infinity, which are much different from that of the previous unmodified model, where the beam spot size and the central dark size will not be convergent as the beam order approaches infinity. The dependences of the propagation factor of modified and unmodified HGBs on the beam order are found to be the same. Based on the Collins integral, analytical formulas for the modified HGB propagating through aligned and misaligned optical system are derived. Some numerical examples are given. (c) 2007 Elsevier B.V. All rights reserved.
Propagation of laser array beams in a turbulent atmosphere
The propagation of phase-locked and non-phase-locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens-Fresnel integral. The beamlet used in our paper for constructing the laser array beams is of elliptical Gaussian mode. Analytical formulae for the average irradiance of phase-locked and non-phase-locked radial and rectangular laser array beams are derived through vector integration and tensor operation. The irradiance properties of these laser array beams in a turbulent atmosphere are studied numerically. It is found that both phase-locked and non-phase-locked radial and rectangular laser array beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The propagation properties are closely related to the parameters of laser array beams and the structure constant of the turbulent atmosphere.
Experimental observation of fractional Fourier transform for a partially
coherent optical beam with Gaussian statistics
Fei Wang,
Yangjian Cai
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND
VISION
24
(7)
1937-1944
(2007)
| Journal
We report the experimental observation of the fractional Fourier transform (FRT) for a partially coherent optical beam with Gaussian statistics [i.e., partially coherent Gaussian Schell-model (GSM) beam]. The intensity distribution (or beam width) and the modulus of the square of the spectral degree of coherence (or coherence width) of a partially coherent GSM beam in the FRT plane are measured, and the experimental results are analyzed and agree well with the theoretical results. The FRT optical system provides a convenient way to control the properties, e.g., the intensity distribution, beam width, spectral degree of coherence, and coherence width, of a partially coherent beam. (c) 2007 Optical Society of America.
2R-Regeneration of an 80-Gb/s RZ-DQPSK signal by a nonlinear amplifying
loop mirror
K. Cvecek,
K. Sponsel,
R. Ludwig,
C. Schubert,
C. Stephan,
G. Onishchukov,
B. Schmauss,
G. Leuchs
The performance of a nonlinear amplifying loop mirror as a 2R-regenerator for an 80-Gb/s return-to-zero differential-quadrature-phase-shift-keyed signal has been investigated. experimentally. A significant eye-opening improvement and a negative power penalty of up to 2.6 dB were obtained.
Off-axis Gaussian Schell-model beam and partially coherent laser array
beam in a turbulent atmosphere
Yangjian Cai,
Qiang Lin,
Yahya Baykal,
Halil T. Eyyuboglu
The propagation of an off-axis Gaussian Schell-model (GSM) beam in a turbulent atmosphere is investigated based on the extended Huygens-Fresnel integral formula. Analytical formulae for the cross-spectral density and corresponding partially coherent complex curvature tensor of an off-axis GSM beam propagating in a turbulent atmosphere are derived. Based on these formulae, the propagation properties of such kind of beam in a turbulent atmosphere are investigated in detail. Furthermore, the methods are extended to investigate the propagation properties of a partially coherent laser array beam in a turbulent atmosphere. The properties of an off-axis GSM beam and a partially coherent laser array beam in a turbulent atmosphere are closely related with the beam parameters and the structure constant of the turbulent atmosphere. (c) 2007 Elsevier B.V. All rights reserved.
An efficient Fredholm method for the calculation of highly excited
states of billiards
Hakan E. Tureci,
Harald G. L. Schwefel
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
40
(46)
13869-13882
(2007)
| Journal
A numerically efficient Fredholm formulation of the billiard problem is presented. The standard solution in the framework of the boundary integral method in terms of a search for roots of a secular determinant is reviewed first. We next reformulate the singularity condition in terms of a flow in the space of an auxiliary one-parameter family of eigenproblems and argue that the eigenvalues and eigenfunctions are analytic functions within a certain domain. Based on this analytic behavior, we present a numerical algorithm to compute a range of billiard eigenvalues and associated eigenvectors by only two diagonalizations.
Quantum reconstruction of an intense polarization squeezed optical state
Ch. Marquardt,
J. Heersink,
R. Dong,
M. V. Chekhova,
A. B. Klimov,
L. L. Sanchez-Soto,
U. L. Andersen,
G. Leuchs
We perform a reconstruction of the polarization sector of the density matrix of an intense polarization squeezed beam starting from a complete set of Stokes measurements. By using an appropriate quasidistribution, we map this onto the Poincare space, providing a full quantum mechanical characterization of the measured polarization state.
Precision measurement of the refractive index of carbon dioxide with a
frequency comb
We report a higher precision measurement of the refractive index of carbon dioxide using a frequency comb as the light source in a Mach-Zehnder interferometer setup. The experimental sensitivity can reach the level of 8.8 X 10(-9). Taking into account the measurement accuracy of temperature and pressure, the experimental accuracy has a value of 1.2 X 10(-8). The measurement result has a deviation from the commonly quoted result [Old et al., J. Opt. Soc. Am. 61, 89 (1971)] by 6.4 X 10(-7) at 800 nm. (c) 2007 Optical Society of America.
Reduction from Eu3+ to Eu2+ in BaAl2O4 : Eu phosphor prepared in an
oxidizing atmosphere and luminescent properties of BaAl2O4 : Eu
Mingying Peng,
Guangyan Hong
JOURNAL OF LUMINESCENCE
127
(2)
735-740
(2007)
| Journal
A reduction phenomenon of Eu3+ -> Eu2+ was observed for the first time when Eu3+ ions were doped into an AlO4-tetrahedron-containing compound BaAl2O4 in an oxidizing atmosphere of air by high-temperature solid-state reaction. X-ray powder diffraction patterns and photoluminescent spectra are used to confirm the compound structure and detect the simultaneous existence of both divalent and trivalent europium ions, respectively. The abnormal Eu3+ -> Eu2+ reduction is explained by a charge compensation model. Spectroscopic properties of BaAl2O4:Eu are discussed and Eu2+ emission spectrum shows consistence with the results reported by Katsumata et a]. [J. Cryst. Growth 198/199 (1999) 869.] and Lin et al. [Mater. Chem. Phys. 70 (2001) 156.]. (C) 2007 Elsevier B.V. All rights reserved.
Quantum key distribution with passive decoy state selection
We propose a quantum key distribution scheme which closely matches the performance of a perfect single photon source. It nearly attains the physical upper bound in terms of key generation rate and maximally achievable distance. Our scheme relies on a practical setup based on a parametric downconversion source and present day, nonideal photon-number detection. Arbitrary experimental imperfections which lead to bit errors are included. We select decoy states by classical postprocessing. This allows one to improve the effective signal statistics and achievable distance.
Ideal bend contour trajectories for single-mode operation of low-loss
overmoded waveguides
Christian Koos,
Christopher G. Poulton,
Lars Zimmermann,
Lenin Jacome,
Juerg Leuthold,
Wolfgang Freude
Bend designs for single-mode operation of low-loss overmoded waveguides are presented. A class of contour trajectories for minimum radiation loss is derived analytically, and numerical optimization is used to find ideal trajectory parameters. Three-dimensional finite-difference time-domain simulations predict bend losses below 0.1 dB for 180 degrees-bends of overmoded silicon-on-insulator waveguides with a radius of R = 1.5 mu m. These findings are supported experimentally.
High numerical aperture imaging with different polarization patterns
The modulation transfer function (MTF) is calculated for imaging with linearly, circularly and radially polarized light as well as for different numerical apertures and aperture shapes. Special detectors are only sensitive to one component of the electric energy density, e. g. the longitudinal component. For certain parameters this has advantages concerning the resolution when comparing to polarization insensitive detectors. It is also shown that in the latter case zeros of the MTF may appear which are purely due to polarization effects and which depend on the aperture angle. Finally some ideas are presented how to use these results for improving the resolution in lithography. (c) 2007 Optical Society of America
An efficient source of continuous variable polarization entanglement
Ruifang Dong,
Joel Heersink,
Jun-Ichi Yoshikawa,
Oliver Gloeckl,
Ulrik L. Andersen,
Gerd Leuchs
We have experimentally demonstrated the efficient creation of highly entangled bipartite continuous variable polarization states. Exploiting an optimized scheme for the production of squeezing using the Kerr non-linearity of a glass fibre we generated polarization squeezed pulses with a mean classical excitation in (S)over-cap(3). Polarization entanglement was generated by interfering two independent polarization squeezed fields on a symmetric beam splitter. The resultant beams exhibit strong quantum noise correlations in the dark (S)over-cap(1)-(S)over-cap(2) polarization plane. To verify entanglement generation, we characterized the quantum correlations of the system for two different sets of conjugate Stokes parameters. The quantum correlations along the squeezed and the anti-squeezed Stokes parameters were observed to be - 4.1 +/- 0.3 and - 2.6 +/- 0.3 dB below the shot noise level, respectively. The degree of correlations was found to depend critically on the beam-splitting ratio of the entangling beam splitter. Carrying out measurements on a different set of conjugate Stokes parameters, correlations of -3.6 +/- 0.3 and -3.4 +/- 0.3 dB have been observed. This result is more robust against asymmetries in the entangling beam splitter, even in the presence of excess noise.
Temporal dynamics of the alpha factor in semiconductor optical
amplifiers
Jin Wang,
Ayan Maitra,
Chris G. Poulton,
Wolfgang Freude,
Juerg Leuthold
JOURNAL OF LIGHTWAVE TECHNOLOGY
25
(3)
891-900
(2007)
| Journal
The temporal evolution of the a-factor during pump-probe experiments in semiconductor optical amplifiers (SOAs) is not constant but varies strongly with time. It even takes on negative values for short periods of time. As a consequence, cross-phase modulation (XPM) effects usually lag behind cross-gain modulation effects by several picoseconds. This delay has important consequences for ultrafast operation of all-optical devices based on SOAs. It. actually means that not every scheme will be suited for ultrafast operation. In order to properly model the XPM and phase variations within an SOA during a pump-probe experiment, a new parameterization for the alpha-factor is introduced. Inclusion of this model leads to an excellent agreement with the recent 160-Gb/s experiments for both phase and amplitude evolutions of the respective signals with time.
Sequential attacks against differential-phase-shift quantum key
distribution with weak coherent states
QUANTUM INFORMATION & COMPUTATION
7
(7)
665-688
(2007)
We investigate limitations imposed by sequential attacks on the performance of differential-phase-shift quantum key distribution protocols that use pulsed coherent light. In particular, we analyze two sequential attacks based on unambiguous state discrimination and minimum error discrimination, respectively, of the signal states emitted by the source. Sequential attacks represent;I special type of intercept-resend attacks and, therefore, they provide ultimate upper bounds on the maximal distance achievable by quantum key distribution schemes.
Quenching of the deuteron in flight
M. Dillig,
C. Rothleitner
INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS
16
(1)
69-80
(2007)
| Journal
We investigate the Lorentz contraction of a deuteron in flight. Starting from the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a 3-dimensional quasi potential equation, we apply it for the deuteron bound in an harmonic oscillator potential (for an analytical result) or by the Bonn NN potential for a more realistic estimate. We find substantial quenching with increasing external momenta and a significant modi. cation of the high momentum spectrum of the deuteron.
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