156 research outputs found
Experimental Demonstration of Spectral Intensity Optical Coherence Tomography
We demonstrate experimentally quantum-inspired, spectral-domain intensity
optical coherence tomography. We show that the technique allows for both axial
resolution improvement and dispersion cancellation compared to conventional
optical coherence tomography. The method does not involve scanning and it works
with classical light sources and standard photodetectors. The measurements are
in excellent agreement with the theoretical predictions. We also propose an
approach that enables the elimination of potential artifacts arising from
multiple interfaces
Decomposition of the point-dipole field into homogeneous and evanescent parts
In near-field optics the resolution and sensitivity of measurements depend on the abundance of evanescent waves in relation to propagating waves. The electromagnetic field propagator is related to the scalar spherical wave, for which the Weyl expansion is a half-space representation containing both evanescent and homogeneous plane waves. Making use of these results, we decompose the dyadic free-space Green function into its evanescent and homogeneous parts and show that some approaches put forward in the literature are inconsistent with this formulation. We express the results in a form that is suitable for numerical computation and illustrate the field decomposition for a point dipole in some typical cases.Peer reviewe
Degree of polarization in near fields of thermal sources: effects of surface waves
We introduce the concept of degree of polarization for electromagnetic near fields. The approach is based on the generalized Stokes parameters that appear as expansion coefficients of the 3Ă—3 coherence matrix in terms of the Gell-Mann matrices. The formalism is applied to optical near fields of thermally fluctuating half-space sources with particular interest in fields that are strongly polarized owing to resonant surface plasmons or phonons. This novel method is particularly useful when assessing the full vectorial characteristics of random evanescent fields, e.g., for near-field spectroscopy and polarization microscopy.Peer reviewe
Cross-spectral purity of the Stokes parameters in random nonstationary electromagnetic beams
We consider cross-spectral purity in random nonstationary electromagnetic
beams in terms of the Stokes parameters representing the spectral density and
the spectral polarization state. We show that a Stokes parameter being
cross-spectrally pure is consistent with the property that the corresponding
normalized time-integrated coherence (two-point) Stokes parameter satisfies a
certain reduction formula. The current analysis differs from the previous works
on cross-spectral purity of nonstationary light beams such that the purity
condition is in line with Mandel's original definition. In addition, in
contrast to earlier works concerning the cross-spectral purity of the
polarization-state Stokes parameters, intensity-normalized coherence Stokes
parameters are applied. It is consequently found that in addition to separate
spatial and temporal coherence factors the reduction formula contains a third
factor that depends exclusively on the polarization properties. We further show
that cross-spectral purity implies a specific structure for the electromagnetic
spectral spatial correlations. The results of this work constitute foundational
advances in the interference of random nonstationary vectorial light.Comment: 5 pages, 1 figur
Virtually isotropic transmission media with fiber Raman amplifier
We report a theoretical study and simulations of a novel fiber-spin tailoring technique to suppress the polarization impairments, namely polarization mode dispersion and polarization dependent gain (PDG), in fiber Raman amplifiers. Whereas use of depolarizer or multiplexing pump laser diodes with a final degree of pump polarization of 1% for periodically spun fiber results in PDG of about 0.3 dB, we demonstrate that application of just a two-section fiber (where the first part is short and has no spin, and the second one is periodically spun) can reduce the PDG to as low as below 0.1 dB
Effect of backscattering in phase conjugation with weak scatterers
An extension is presented of a recently developed theory (based on the first Born approximation) of cancellation of distortions by phase conjugation. The influence of backscattering of both the incident and the conjugate waves is considered. It is shown that, when backscattering is taken into account, distortions are not eliminated by phase conjugation, except when the conjugate wave is generated without a loss or a gain
Scattering theory of distortion correction by phase conjugation
The correction of wave distortions by the technique of optical phase conjugation is examined first on the basis of a newly derived integral equation for scattering of monochromatic scalar waves in the presence of a phase-conjugate mirror. The solution is developed in an iterative series, and the first- and second-order terms are analyzed and illustrated diagrammatically. A generalization of the integral equation is then presented, which takes into account the electromagnetic nature of light. It is also shown that, if the conjugate wave is generated without losses or gains and with a complete reversal of polarization, a total elimination of distortions may be achieved by this technique under circumstances that frequently occur in practice
Polarization time and length for random optical beams
We investigate the dynamics of the instantaneous polarization state of stationary, partially polarized random electromagnetic beamlike fields. An intensity-normalized correlation function of the instantaneous Poincaré vector is introduced for the characterization of the time evolution of the polarization state. This polarization correlation function enables us to define a polarization time and a polarization length over which the polarization state remains substantially unchanged. In the case of Gaussian statistics, the polarization correlation function is shown to assume a simple form in terms of the parameters employed to characterize partial coherence and partial polarization of electromagnetic fields. The formalism is demonstrated for a partially polarized, temporally Gaussian-correlated beam, and black-body radiation. The results are expected to find a range of applications in investigations of phenomena where polarization fluctuations of light play an important role.Peer reviewe
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