John E. Sipe

Bio: John E. Sipe is an academic researcher from University of Toronto. The author has contributed to research in topics: Nonlinear optics & Photon. The author has an hindex of 83, co-authored 719 publications receiving 27000 citations. Previous affiliations of John E. Sipe include Bell Labs & Lehigh University.

Long-period fiber gratings as band-rejection filters

Abstract: We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB.

Laser-induced periodic surface structure. I. Theory

Abstract: We develop a theory for laser-induced periodic surface structure by associating each Fourier component of induced structure with the corresponding Fourier component of inhomogeneous energy deposition just beneath the surface. We assume that surface roughness, confined to a region of height much less than the wavelength of light, is responsible for the symmetry breaking leading to this inhomogeneous deposition; we find strong peaks in this deposition in Fourier space, which leads to predictions of induced fringe patterns with spacing and orientation dependent on the angle of incidence and polarization of the damaging beam. The nature of the generated electromagnetic field structures and their relation to the simple "surface-scattered wave" model for periodic surface damage are discussed. Our calculation, which is for arbitrary angle of incidence and polarization, applies a new approach to the electrodynamics of randomly rough surfaces, introducing a variational principle to deal with the longitudinal fields responsible for local field, or "depolarization," corrections. For a $p$-polarized damaging beam our results depend on shape and filling factors of the surface roughness, but for $s$-polarized light they are essentially independent of these generally unknown parameters; thus an unambiguous comparison of our theory with experiment is possible.

Laser-induced periodic surface structure. II. Experiments on Ge, Si, Al, and brass

Abstract: We report the results of a detailed investigation into the properties of the periodic damage structure that can be produced on nominally smooth surfaces of solids when they are irradiated with a single beam of intense laser radiation. The study is primarily concerned with extracting information from the Fourier transform of the damage structure as observed via the Fraunhofer diffraction pattern produced by reflecting a cw laser beam from the surface. In particular, the patterns produced in Ge, Si, Al, and brass by pulsed 1.06- and 0.53-\ensuremath{\mu}m radiation are compared as a function of the angle of incidence and polarization of the beam. We find that all materials contain similar and much more intricate detailed structure than has been previously appreciated. Whereas periodic ripple patterns oriented perpendicular to the polarization at near-normal incidence are commonly reported, the diffraction patterns reveal that in fact there exists a continuous distribution of periodic structure oriented at all angles with respect to the polarization. At near-normal incidence there are two dominant sets of "fringes" running perpendicular to the polarization, while for a $p$-polarized beam incident at g35\ifmmode^\circ\else\textdegree\fi{} there exist three dominant periodic structures; two which run perpendicular to the polarization and one which is oriented parallel to it. For $s$-polarized light incident at angles g35\ifmmode^\circ\else\textdegree\fi{} there are two dominant patterns which form a cross-hatched pattern with axes oriented at 45\ifmmode^\circ\else\textdegree\fi{} to the plane of incidence. A study of the evolution of the patterns on a shot-to-shot basis indicates that both the initial and laser-induced surface roughness play important roles in the evolution of the damage. We conclude with a comparison of our experimental results with those predicted by the theory developed in the preceding paper. Excellent agreement is found.

Second-order optical response in semiconductors

Abstract: We present a new general formalism for investigating the second-order optical response of solids, and illustrate it by deriving expressions for the second-order susceptibility tensor ${\ensuremath{\chi}}_{2}(\ensuremath{-}{\ensuremath{\omega}}_{\ensuremath{\Sigma}};{\ensuremath{\omega}}_{\ensuremath{\beta}},{\ensuremath{\omega}}_{\ensuremath{\gamma}}),$ where ${\ensuremath{\omega}}_{\ensuremath{\Sigma}}={\ensuremath{\omega}}_{\ensuremath{\beta}}+{\ensuremath{\omega}}_{\ensuremath{\gamma}},$ for clean, cold semiconductors in the independent particle approximation. Based on the identification of a polarization operator $\mathbf{P}$ that would be valid even in a more complicated many-body treatment, the approach avoids apparent, unphysical divergences of the nonlinear optical response at zero frequency that sometimes plague such calculations. As a result, it allows for a careful examination of $\mathit{actual}$ divergences associated with physical phenomena that have been studied before, but not in the context of nonlinear optics. These are (i) a coherent current control effect called ``injection current,'' or ``circular photocurrent,'' and (ii) photocurrent due to the shift of the center of electron charge in noncentrosymmetric materials in the process of optical excitation, called ``shift current.'' The expressions we present are amenable for numerical calculations, and we demonstrate this by performing a full band-structure calculation of the shift current coefficient for GaAs.

Nonlinear optical susceptibilities of semiconductors: Results with a length-gauge analysis.

Abstract: We present a simple prescription for the derivation of electronic contributions to the nonlinear optical response of crystals in the independent particle approximation. Semiconductor Bloch equations are found that include previously neglected effects of intraband motion. Applying perturbation theory to clean, cold semiconductors we find expressions for the susceptibilities lacking the unphysical divergences at zero frequency that have plagued other calculations. For these materials we present well-behaved, general expressions for ${\mathrm{\ensuremath{\chi}}}^{(2)}$ and ${\mathrm{\ensuremath{\chi}}}^{(3)}$ for arbitrary frequency mixing and give an explicit demonstration of the finite zero-frequency value of ${\mathrm{\ensuremath{\chi}}}^{(3)}$. We further show how second-order photogalvanic effects are contained in certain physical zero-frequency divergences of ${\mathrm{\ensuremath{\chi}}}^{(2)}$, and consider the corresponding physical zero-frequency divergences of ${\mathrm{\ensuremath{\chi}}}^{(3)}$.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Spintronics: Fundamentals and applications

Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

Plasmonics: Fundamentals and Applications

Abstract: Fundamentals of Plasmonics.- Electromagnetics of Metals.- Surface Plasmon Polaritons at Metal / Insulator Interfaces.- Excitation of Surface Plasmon Polaritons at Planar Interfaces.- Imaging Surface Plasmon Polariton Propagation.- Localized Surface Plasmons.- Electromagnetic Surface Modes at Low Frequencies.- Applications.- Plasmon Waveguides.- Transmission of Radiation Through Apertures and Films.- Enhancement of Emissive Processes and Nonlinearities.- Spectroscopy and Sensing.- Metamaterials and Imaging with Surface Plasmon Polaritons.- Concluding Remarks.

Graphene photonics and optoelectronics

Abstract: The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.