Jack Feinberg

Bio: Jack Feinberg is an academic researcher from University of Southern California. The author has contributed to research in topics: Photorefractive effect & Fiber Bragg grating. The author has an hindex of 44, co-authored 161 publications receiving 6740 citations. Previous affiliations of Jack Feinberg include University of Colorado Boulder & University of Mons.

Self-pumped, continuous-wave phase conjugator using internal reflection

Abstract: Continuous-wave phase conjugation of an image-bearing beam is demonstrated using a single-domain crystal of BaTiO(3) and nothing else. The device operates by four-wave mixing using the photorefractive effect but without any external pumping beams or external mirrors. The customary pumping beams are derived from the incident beam and are internally reflected inside the crystal adjacent to an edge. The device is self-starting and has a phase-conjugate reflectivity of 30%. Imaging applications are discussed.

Photorefractive effects and light‐induced charge migration in barium titanate

Abstract: We propose a new theoretical model for the light‐induced migration of charges which mediates the ’’photorefractive effect’’ (light‐induced refractive index change) in barium titanate and other crystals. We also present experimental results of various effects of this light‐induced charge migration in a single‐domain crystal of barium titanate, specifically, (1) energy transfer between two intersecting optical beams, (2) optical four‐wave mixing and optical‐beam phase conjugation, (3) erasure of spatial patterns of photorefractive index variations, and (4) photoconductivity. The theoretical model predicts the observed dependences of these effects on (1) beam intensities, directions, and polarizations, (2) crystal orientation, and (3) on an externally applied dc electric field. Time dependences of transients as well as steady‐state magnitudes are predicted. In this model, identical charges migrate by hopping between adjacent sites, with a hopping rate proportional to the total light intensity at the starting site. The net hopping rate varies with the local electric potential that is calculated self‐consistently from the charge migration pattern. In barium titanate the charges are positive with a density of (1.90.2) ×1016 cm−3 at 514 nm. The origin of the charges and sites is at present unknown. The hopping rate constant determined from optical beam interactions is used to predict the observed photoconductivity of 1.3×10−10 cm Ω−1 W−1 at 514 nm.

Asymmetric self-defocusing of an optical beam from the photorefractive effect

Abstract: A new kind of optical self-defocusing is described that in steady state is independent of optical beam power and is strongly asymmetric. The physical mechanism responsible is the photorefractive effect. We present a theory that explains the observed dependence of this self-defocusing on polarization, angle of incidence, beam size, and crystal orientation. Experimental results, using a single-domain crystal of BaTiO3, are presented that show excellent quantitative agreement with the theory. Possible device applications are discussed, including an optical diode and a low-power bistable device with permanent memory.

Phase-conjugating mirror with continuous-wave gain

Abstract: We demonstrate a phase-conjugating mirror that has a continuous-wave power reflectivity much greater than unity (gain ~100). This mirror uses nonresonant degenerate four-wave mixing in a single crystal of barium titanate (BaTiO3). With our mirror we have (1) observed cw self-oscillation in an optical resonator formed by this mirror and a normal mirror, (2) demonstrated a cw oscillator that, in spite of phase-distorting material placed inside the resonator, will always emit a TEM00 mode, and (3) demonstrated an optical image amplifier. This mirror will work at any visible wavelength and with weak (milliwatt or weaker) pump beams.

Photorefractive properties of strontium‐barium niobate

Abstract: We have grown and optically characterized strontium‐barium niobate crystals, including both undoped and cerium‐doped crystals having two different Sr/Ba ratios (61/39 and 75/25). By measuring the coupling of two optical beams in the crystals, we have determined the following photorefractive properties: the effective density, sign, and spectral response of the dominant charge carrier, the grating formation rate, dark conductivity, and carrier diffusion length. We find that electrons are the dominant photorefractive charge carriers in all of our samples; the typical density of photorefractive charges is ∼1×1016 cm−3 in the undoped samples. The grating formation rate increases with intensity, with a slope of ∼0.3 cm2/(W s) over an intensity range of ∼1–15 W/cm2 in undoped samples. Cerium doping improves both the charge density (increased by a factor of ∼3) and the response rate per unit intensity (∼5 times faster).

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 …

Optical fibre long-period grating sensors: characteristics and application

Abstract: Recent research on fibre optic long-period gratings (LPGs) is reviewed with emphasis placed upon the characteristics of LPGs that make them attractive for applications in sensing strain, temperature, bend radius and external index of refraction. The prospect of the development of multi-parameter sensors, capable of simultaneously monitoring a number of these measurands will be discussed.

Analysis and applications of optical diffraction by gratings

Abstract: Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.