All-fiber Kerr cell

An all-fiber nanosecond Kerr light gate is described that was constructed using microstructured fibers. The switching voltage for a 20?cm long device is as low as Vπ～85 V at a 1.06?μm wavelength. The device is fully spliced. The active element is a three-hole fiber provided with internal electrodes in the side-holes and a liquid core of nitrobenzene, which is fully enclosed. This work allows the exploiting of electrically driven liquid-core fibers and demonstrated the removal of the major limitations of Kerr cells in the past, allowing for integration, safe use, and relatively low switching voltage.     

From Kerr to Heisenberg

In this paper, we consider the space-time of a charged mass endowed with an angular momentum. The geometry is described by the exact Kerr–Newman solution of the Einstein equations. The peculiar symmetry, though exact, is usually described in terms of the gravito-magnetic field originated by the angular momentum of the source. A typical product of this geometry is represented by the generalized Sagnac effect. We write down the explicit form for the right/left asymmetry of the times of flight of two counter-rotating light beams along a circular trajectory. Letting the circle shrink to the origin the asymmetry stays finite. Furthermore it becomes independent both from the charge of the source (then its electromagnetic field) and from Newton’s constant: it is then associated only to the symmetry produced by the gravitomagnetic field. When introducing, for the source, the spin of a Fermion, the lowest limit of the Heisenberg uncertainty formula for energy and time appears.     

Nonlinear magneto-optical Kerr effects

The polarization state of a second-harmonic wave after reflection from a semi-infinite, optically isotropic magnetic medium is considered for the three characteristic uniformmagnetization directions corresponding to the linear magneto-optical Kerr effects. Expressions for the complex amplitudes of the wave field which specify the nonlinear Kerr effects, viz., the polar, meridional, and equatorial effects, are obtained in a first approximation with respect to the magnetization. The dependences of these effects on the angle of incidence of the inducing wave obtained as a result of a numerical experiment are presented. Analytical formulas are found for them at small angles of incidence. A comparative analysis of the linear and nonlinear Kerr effects is made. Zh. éksp. Teor. Fiz. 116, 141–156 (July 1999)     

Mode-locked Kerr frequency combs

We analyze a mode-locked regime in Kerr frequency combs generated in nonlinear microresonators. Using damped driven nonlinear Schr?dinger equations we show that the combs can produce subpicosecond optical pulses when the resonators are characterized with a small enough anomalous group velocity dispersion. We provide an analytical solution of the problem for the case of small damping.     

Second order Kerr deflection

We perform a full second order calculation of the deflection of light along the equatorial plane in the Kerr metric. Previous Kerr deflection calculations were interested in obtaining the correction due to rotation to the Einstein deflection. By expanding to first order in the rotational parameter a, they obtain the Einstein deflection of 4M/r _o and the second order deflection due to rotation of , (where r _o is the point of closest approach). In this paper, we are interested in going beyond the rotational contribution for the purpose of astrophysical applications. We therefore keep all terms up to second order in our final weak field expansion. Besides the rotational contribution, we also obtain an extra second order term of . Since M > a, this extra term is greater than the rotational contribution of in astrophysical applications. When a/M is close to unity the terms are of the same order of magnitude.     

Kerr modulation of planar waveguides

We describe two methods for employing materials with giant Kerr nonlinearities for modulating waveguides. A beam, of relatively intense light, is used to vary the propagation constant of a waveguide with the guiding layer, or the substrate, made from a nonlinear material.     

Anti-PT-symmetric Kerr gyroscope

Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points(EPs).Various EP sensors have been fabricated in recent years,showing strong spectral responses to external signals.Here we propose how to achieve a nonlinear anti-parity-time(PT)gyroscope by spinning an optical resonator.We show that,in the absence of any nonlinearity,the sensitivity or optical mode splitting of the linear device can be magnified up to 3 orders compared to that of the conventional device without EPs.Remarkably,the PT symmetry can be broken when including the Kerr nonlinearity of the materials and,as a result,the detection threshold can be significantly lowered,i.e.,much weaker rotations which are well beyond the ability of a linear gyroscope can now be detected with the nonlinear device.Our work shows the powerful ability of PT gyroscopes in practice to achieve ultrasensitive rotation measurement.     

Efficiency and temporal response of crystalline Kerr media in collinear optical Kerr gating

Optical Kerr gating is widely used in ultrafast measurements ranging from pulse characterization to spectroscopy and microscopy. We examined the efficiency and the temporal response of three cubic lattice Kerr media, YAG, GGG and BGO, and compared them with the well studied fused silica (fast response, low efficiency) and STO (high efficiency, slow response). YAG and GGG emerged as superior materials for ultrafast spectroscopy and microscopy applications thanks to their fast Kerr response and considerably higher gating efficiency than silica at low gating energies. Importantly, it was found that in collinear geometry all tested materials except STO are capable of reaching nearly 100% transmission.     

Intensity noise of Kerr oscillators

Absorbing or emitting elements generate noise waves. The main purpose of this paper is to determine from first principles the spectral density of noise waves relating to nonlinear elements. This was done by considering the combination of linear elements (whose noise properties are well understood) and lossless circuits that are nonlinear because of the Kerr effect. Lossless nonlinear circuits transform noise waves but do not generate noise. A semiclassical theory shows that noise waves remain at the shot noise level (for full population inversion) if the optical gain is considered a function of photon rate (rather than optical intensity). This result, in exact agreement with an independent theory of spectral-hole burning, is conjectured to be general. Intensity fluctuations of a Kerr oscillator are squeezed below the shot-noise level for large Kerr constants.     

Microgeon with a Kerr metric

The structure of electromagnetic and gravitational fields near the singular ring of the Kerr metric is analyzed. An approximate joint solution of the system of Maxwell-Einstein equations is given for a metric with the parameters of an electron; this solution describes a microgeon, a model of an electron. A new interpretation of the two-sheet nature of the Kerr metric is given.     

Intermediate behavior of Kerr tails

The numerical investigation of wave propagation in the asymptotic domain of Kerr spacetime has only recently been possible thanks to the construction of suitable hyperboloidal coordinates. The asymptotics revealed an apparent puzzle in the decay rates of scalar fields: the late-time rates seemed to depend on whether finite distance observers are in the strong field domain or far away from the rotating black hole, an apparent phenomenon dubbed ‘splitting.’ We discuss far-field ‘splitting’ in the full field and near-horizon ‘splitting’ in certain projected modes using horizon-penetrating, hyperboloidal coordinates. For either case we propose an explanation to the cause of the ‘splitting’ behavior, and we determine uniquely decay rates that previous studies found to be ambiguous or immeasurable. The far-field ‘splitting’ is explained by competition between projected modes. The near-horizon ‘splitting’ is due to excitation of lower multipole modes that back excite the multipole mode for which ‘splitting’ is observed. In both cases ‘splitting’ is an intermediate effect, such that asymptotically in time strong field rates are valid at all finite distances. At any finite time, however, there are three domains with different decay rates whose boundaries move outwards during evolution. We then propose a formula for the decay rate of tails that takes into account the inter-mode excitation effect that we study.     

Race for the Kerr field

Roy P. Kerr has discovered his celebrated metric 45 years ago, yet the problem to find a generalization of the Schwarzschild metric for a rotating mass was faced much earlier. Lense and Thirring, Bach, Andress, Akeley, Lewis, van Stockum and others have tried to solve it or to find an approximative solution at least. In particular Achilles Papapetrou, from 1952 to 1961 in Berlin, was interested in an exact solution. He directed the author in the late autumn of 1959 to work on the problem. Why did these pre-Kerr attempts fail? Comments based on personal reminiscences and old notes.     

Vibration and the Kerr effect

The theory of the Kerr effect (electric birefringence) is developed with explicit inclusion of molecular vibration. When the theory is applied to CHCl₃ and CHF₃, it is found that terms with a vibrational origin are an important component of the β-hyperpolarizability extracted from temperature-dependent Kerr studies. It is concluded that these vibrational terms partly account for the difference between β obtained from second-harmonic-generation experiments and from the Kerr constant.     

Femtosecond magneto-optical Kerr microscopy

We have developed a magneto-optical Kerr microscope that allows us to measure the ultrafast magnetization dynamics of ferromagnetic nanostructures. The magneto-optical signal can be recorded in a confocal reflection geometry with an accurate selection of the polarization. The magnetization dynamics is obtained from pump-probe measurements using frequency nondegenerate collinear pump and probe beams with a temporal resolution of 180 fs. Both probe and pump beams are focused to their diffraction limit, leading to an overall spatial resolution of 600 nm. The efficiency of the apparatus is tested by investigating the magnetization dynamics of individual CoPt(3) disks with a submicrometer diameter and a thickness of 15 nm.     

Characterizations of the Kerr metric

For stationary, asymptotically flat solutions of Einstein's equations, covariant functionals of the metric variables are defined which characterize the Kerr metric uniquely. For instance, we obtain a generalization of the Bach tensor to stationary metrics, which vanishes if and only if the solution is Kerr. We also give a new interpretation of the Schwarzschild-to-Kerr-transformation. Our results might be applicable to simplify the proof of the uniqueness theorem for stationary black holes.     

Boosting the Kerr metric

An exact solution of Einstein's equations describing the gravitational wave associated to a ring of massless particles is presented. It has been obtained by boosting the Kerr metric along the axis of symmetry, and considering the limit in which the speed of the boost tends to the velocity of light.     

The Linear Kerr Effect

Russian Physics Journal -     

Causality violation in the Kerr metric

The conjecture that geodesics in the Kerr matric witha > m cannot violate causality in the sense of meeting a turning point before making up for lost time, is found to be untrue for null geodesics.