http://fcbt.mse.gatech.edu/PDF/Bersra2007.pdf

A review on fundamentals and applications of electrophoretic deposition (EPD)

Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components1,2,3. Furthermore, it is highly desirable to use silicon—the dominant material in the microelectronic industry—as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon4,5, but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III–V compound semiconductors6,7, but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers8,9,10,11,12,13,14,15 in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction16 of efficient optical switching in silicon using resonant structures.

All-optical control of light on a silicon chip

Direct observations of sunspot numbers are available for the past four centuries1,2, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades3.

/pdf/unusual-activity-of-the-sun-during-recent-decades-compared-wrgvwl8y45.pdf

Unusual activity of the Sun during recent decades compared to the previous 11,000 years

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

Nonlinear Optical Crystals: A Complete Survey

We present a temperature-dependent Sellmeier equation for the refractive index of stoichiometric LiTaO3. The extraordinary refractive index, for the range 0.39-4.1 microm and for temperatures of 30-200 degrees C, are based on previously published data [Jpn. J. Appl. Phys. 41, 465 (2002)] and on measured data derived from quasi-phase-matched (QPM) resonances. We used the new Sellmeier coefficients that we obtained to calculate the QPM wavelengths for an optical parametric oscillator (OPO) based on periodically poled stoichiometric LiTaO3 pumped at 1064 nm. The measured wavelengths of the OPO were in good agreement with our predictions.

Temperature-dependent Sellmeier equation for the refractive index of stoichiometric lithium tantalate

This article presents a unified formulation and review of an extensive class of radiation effects and devices based on free or quasifree electrons. The effects and devices reviewed include slow-wave radiators [such as \ifmmode \check{C}\else \v{C}\fi{}erenkov, Smith-Purcell, and TWT (traveling-wave tube) effects and devices], periodic bremsstrahlung radiators [such as undulator radiation, magnetic bremsstrahlung FEL's (free-electron lasers), and coherent bremsstrahlung in the crystal lattice], and transverse-binding radiators [such as the CRM (cyclotron resonance maser) and channeling radiation]. Starting from a general quantum-electrodynamic model, both quantum and classical effects and operating regimes of these radiation devices are described. The article provides a unified physical description of the interaction kinematics, and presents equations for the characterization of spontaneous and stimulated radiative emission in these various effects and devices. Universal relations between the spontaneous and stimulated emission parameters are revealed and shown to be related (in the quantum limit) to Einstein relations for atomic radiators and (in the classical limit) to the relations derived by Madey for magnetic bremsstrahlung FEL for on-axis radiative emission. Examples for the application of the formulation are given, estimating the feasibility of channeling radiation x-ray laser and optical regime Smith-Purcell FEL, and deriving the gain equations of magnetic bremsstrahlung FEL and CRM for arbitrary electron propagation direction, structure (wiggler) axis, and radiative emission angle.

Spontaneous and stimulated emission from quasifree electrons

Planar waveguides of TiO2‐organically modified silanes deposited on glass substrates were prepared by the sol‐gel method, either in a pure form or doped by red perylimide laser dye, and their optical properties characterized. The refractive index increases and film thickness decreases as TiO2 contents rise. Waveguiding in the pure film and the trapped luminescence in the doped films were measured. Typically three guided modes were observed.

Sol‐gel glass waveguides prepared at low temperature

The analysis of parallel waveguides can be performed either by expressing the coupling of energy between individual, primary guides (coupled-mode approach) or by directly analyzing a structure consisting of all the guides and their surrounding media (normal-mode approach). A comparison of these two approaches, as well as the derivation of relations enabling the conversion of data, when possible, from one approach to the other, are presented in this paper. Finally, the results are used to investigate the dependence of the coupling coefficient on the spacing between the guides. Although the derivations are performed for 2-D (slab) configurations, the results pertain to 3-D guides as well, by applying an effective refractive-index method. It is also shown that normal-mode analysis predicts incomplete transfer of energy for strongly coupled guides, even for perfectly symmetric configurations.

Relation between normal-mode and coupled-mode analyses of parallel waveguides

Glass waveguiding films were prepared from titania and modified silica using the sol‐gel method and doped by the laser dye rhodamine B. The guided and amplified fluorescence (pumped by a double frequency Nd‐YAG laser) was coupled out either by static grating written on the film or by a prism. The gain of the emitted superradiance was determined from the amplified spontaneous emission intensity dependence on the pumped strip length. A maximum net gain of 54 dB/cm was measured.

Shlomo Ruschin

Papers

Temperature-dependent Sellmeier equation for the refractive index of stoichiometric lithium tantalate

Spontaneous and stimulated emission from quasifree electrons

Sol‐gel glass waveguides prepared at low temperature

Relation between normal-mode and coupled-mode analyses of parallel waveguides

Light amplification in a dye-doped glass planar waveguide