Er'el Granot

Bio: Er'el Granot is an academic researcher from Ariel University. The author has contributed to research in topics: Dispersion (optics) & Brillouin scattering. The author has an hindex of 15, co-authored 132 publications receiving 801 citations. Previous affiliations of Er'el Granot include Israel Atomic Energy Commission & Tel Aviv University.

Efficient impulse response reconstruction from the amplitude spectrum

Abstract: We suggest adopting an efficient digital signal processing algorithm, which includes several fast Fourier transforms, to efficiently reconstruct the impulse response of a diffusive medium from its amplitude spectrum. It is also demonstrated that the singularities, which appear in the phase spectrum reconstruction, can be easily eliminated through the implementation of at least two types of data padding.

Making the \(\mathbb {PT}\) Symmetry Unbreakable

Abstract: It is well known that typical \(\mathbb {PT}\)-symmetric systems suffer symmetry breaking when the strength of the gain-loss terms, i.e., the coefficient in front of the non-Hermitian part of the underlying Hamiltonian, exceeds a certain critical value. In this article, we present a summary of recently published and newly produced results which demonstrate various possibilities of extending the \(\mathbb {PT}\) symmetry to arbitrarily large values of the gain-loss coefficient. First, we recapitulate the analysis which demonstrates a possibility of the restoration of the \(\mathbb {PT}\) symmetry and, moreover, complete avoidance of the breaking in a photonic waveguiding channel of a subwavelength width. The analysis is necessarily based on the system of Maxwell’s equations, instead of the usual paraxial approximation. Full elimination of the \( \mathbb {PT}\)-symmetry-breaking transition is found in a deeply subwavelength region. Next, we review a recently proposed possibility to construct stable one-dimensional (1D) \(\mathbb {PT}\)-symmetric solitons in a paraxial model with arbitrarily large values of the gain-loss coefficient, provided that the self-trapping of the solitons is induced by self-defocusing cubic nonlinearity, whose local strength grows sufficiently fast from the center to periphery. The model admits a particular analytical solution for the fundamental soliton, and provides full stability for families of fundamental and dipole solitons. It is relevant to stress that this model is nonlinearizable, hence the concept of the \(\mathbb {PT}\) symmetry in it is also an essentially nonlinear one. Finally, we report new results for unbreakable \(\mathbb {PT}\)-symmetric solitons in 2D extensions of the 1D model: one with a quasi-1D modulation profile of the local gain-loss coefficient, and another with the fully-2D modulation. These settings admit particular analytical solutions for 2D solitons, while generic soliton families are found in a numerical form. The quasi-1D modulation profile gives rise to a stable family of single-peak 2D solitons, while their dual-peak counterparts tend to be unstable. The soliton stability in the full 2D model is possible if the local gain-loss term is subject to spatial confinement.

Optical wavelength converter with a dynamic Brillouin filter and an electronic compensating device

Abstract: We present an experimental and theoretical study of a highly robust wavelength converter at 10Gbit/s that is based on a narrow bandstop Brillouin filter. The wavelength conversion takes place in a semiconductor optical amplifier in a cross-gain-phase process, which operates in a weak-modulation mode. The signal then undergoes a carrier reduction by a spectrally narrow bandstop filter. Since we use a Brillouin grating as the narrow filter, the signal is distorted owing to the filter's finite spectral width (~20 MHz). To overcome this problem, we use a relatively slow electronic mechanism to effectively narrow the filter's spectral width and to improve its signal-to-noise ratio. We elaborate on this electronic mechanism by developing the underlying theory and showing how it is implemented in practice. Although we focus on an application for wavelength conversion, this technology can be implemented in many other cases in which an effective narrowing of a bandstop filter is required.

Forbidden activation levels in a non-stationary tunneling process

Abstract: Tunneling in the presence of an opaque barrier, part of which varies in time, is investigated numerically and analytically in one dimension. Clearly, due to the varying barrier a tunneling particle experiences spectral widening. However, in the case of strong perturbations, the particles’ activation to certain energies is avoided . We show that this effect occurs only when the perturbation decays faster than t −2 .

Inducing and harnessing stimulated Brillouin scattering in photonic integrated circuits

Abstract: We review recent progress in inducing and harnessing stimulated Brillouin scattering (SBS) in integrated photonic circuits. Exciting SBS in a chip-scale device is challenging due to the stringent requirements on materials and device geometry. We discuss these requirements, which include material parameters, such as optical refractive index and acoustic velocity, and device properties, such as acousto-optic confinement. Recent work on SBS in nano-photonic waveguides and micro-resonators is presented, with special attention paid to photonic integration of applications such as narrow-linewidth lasers, slow- and fast-light, microwave signal processing, Brillouin dynamic gratings, and nonreciprocal devices.

Ultrasound-mediated biophotonic imaging: A review of acousto-optical tomography and photo-acoustic tomography

Abstract: This article reviews two types of ultrasound-mediated biophotonic imaging–acousto-optical tomography (AOT, also called ultrasound-modulated optical tomography) and photo-acoustic tomography (PAT, also called opto-acoustic or thermo-acoustic tomography)–both of which are based on non-ionizing optical and ultrasonic waves. The goal of these technologies is to combine the contrast advantage of the optical properties and the resolution advantage of ultrasound. In these two technologies, the imaging contrast is based primarily on the optical properties of biological tissues, and the imaging resolution is based primarily on the ultrasonic waves that either are provided externally or produced internally, within the biological tissues. In fact, ultrasonic mediation overcomes both the resolution disadvantage of pure optical imaging in thick tissues and the contrast and speckle disadvantages of pure ultrasonic imaging. In our discussion of AOT, the relationship between modulation depth and acoustic amplitude is clarified. Potential clinical applications of ultrasound-mediated biophotonic imaging include early cancer detection, functional imaging, and molecular imaging.

Optical solitons in PT periodic potentials

Abstract: We investigate the effect of nonlinearity in novel parity-time (PT) symmetric potentials. We show that new types of nonlinear self-trapped modes can exist in optical PT synthetic lattices.

Optical nonlinearities in fibers: review, recent examples, and systems applications

Abstract: Optical nonlinearities give rise to many ubiquitous effects in optical fibers. These effects are interesting in themselves and can be detrimental in optical communications, but they also have many useful applications, especially for the implementation of all-optical functionalities in optical networks. In the present paper, we briefly review the different kinds of optical nonlinearities encountered in fibers, pointing out the essential material and fiber parameters that determine them. We describe the effects produced by each kind of nonlinearity, emphasizing their variations for different values of essential parameters. Throughout the paper, we refer to recent systems applications in which these effects have been dealt with or exploited.