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 …

I and i

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Metal interconnections are expected to become the limiting factor for the performance of electronic systems as transistors continue to shrink in size. Replacing them by optical interconnections, at different levels ranging from rack-to-rack down to chip-to-chip and intra-chip interconnections, could provide the low power dissipation, low latencies and high bandwidths that are needed. The implementation of optical interconnections relies on the development of micro-optical devices that are integrated with the microelectronics on chips. Recent demonstrations of silicon low-loss waveguides, light emitters, amplifiers and lasers approach this goal, but a small silicon electro-optic modulator with a size small enough for chip-scale integration has not yet been demonstrated. Here we experimentally demonstrate a high-speed electro-optical modulator in compact silicon structures. The modulator is based on a resonant light-confining structure that enhances the sensitivity of light to small changes in refractive index of the silicon and also enables high-speed operation. The modulator is 12 micrometres in diameter, three orders of magnitude smaller than previously demonstrated. Electro-optic modulators are one of the most critical components in optoelectronic integration, and decreasing their size may enable novel chip architectures.

Micrometre-scale silicon electro-optic modulator

Optical technology is poised to revolutionize short-reach interconnects. The leading candidate technology is silicon photonics, and the workhorse of such an interconnect is the optical modulator. Modulators have been improved dramatically in recent years, with a notable increase in bandwidth from the megahertz to the multigigahertz regime in just over half a decade. However, the demands of optical interconnects are significant, and many questions remain unanswered as to whether silicon can meet the required performance metrics. Minimizing metrics such as the device footprint and energy requirement per bit, while also maximizing bandwidth and modulation depth, is non-trivial. All of this must be achieved within an acceptable thermal tolerance and optical spectral width using CMOS-compatible fabrication processes. This Review discusses the techniques that have been (and will continue to be) used to implement silicon optical modulators, as well as providing an outlook for these devices and the candidate solutions of the future.

/pdf/silicon-optical-modulators-578o7o6kvr.pdf

Silicon optical modulators

Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics1. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III–V semiconductor compounds2,3,4,5,6 and/or electro-optic materials such as lithium niobate7,8,9. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only ∼20 MHz (refs 10, 11), although it has been predicted theoretically that a ∼1-GHz modulation frequency might be achievable in some device structures12,13. Here we describe an approach based on a metal–oxide–semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.

A high-speed silicon optical modulator based on a metal–oxide–semiconductor capacitor

Purpose
A negative correlation exists between advanced maternal age and reproduction. Current data suggest that this correlation is due to a decline in oocyte quality with respect to female age. Since a new individual is derived from the fusion of a single sperm and egg, we tested whether the quality of this material could influence the long-term physiological health of offspring, by examining whether a link between parental age and lifespan of offspring exists.

Maternal non-Mendelian inheritance of a reduced lifespan? A hypothesis

We propose a novel method to monitor the carrier plasma distribution in a bipolar mode field effect transistor light modulator, using standard emission microscopy. Our bi-dimensional maps validate the theoretical predictions of plasma distribution as a function of the device bias. Dynamical measurements provide an experimental evidence of a frequency threshold in the electric field induced plasma distribution. Below 500 kHz generation/recombination processes while above drift phenomena allow the plasma localization in the device. An effective carrier lifetime /spl ges/2 /spl mu/s was extrapolated.

Experimental evidences of carrier distribution and behavior in frequency in a BMFET Modulator

An optoelectronic router integrated in a sol-gel waveguide with a liquid crystal over-layer, working at the wavelength of 1.55 μm, is theoretically discussed. Mode-mixing principle and electro-optic effect of a smectic A * liquid crystal have been employed to reach the optical shift between two output waveguides. The device is composed by: a single mode input optical channel waveguide; a bimodal active region, having a liquid crystal as over-layer; an output Y branch. The active region is designed to allow a π shift between the two supported modes, by means of electro-optic effect of smectic A*. By doing so it is possible to steer light from one output channel to the other one of output Y.

Optoelectronic router in glass waveguide with a liquid crystal cladding

A digital holographic characterization technique is developed for studying changes in the refractive index when polymerization occurs. This all optical characterization technique enables real-time detection of the photopolymer refractive index changes during the recording process. In this paper, two different new photopolymers, sensitive to light at wavelength of 532 nm, were characterized by means of digital holography. We found a very high refractive index variation for both the new photopolymers, thus this materials could be suitable for holographic recordings with the great advantage of being inexpensive and easy to make.

Characterization of photopolymers as optical recording materials by means of digital holography microscopy

Ferroelectric domain micro structuring of bulk Lithium Niobate is very useful for optoelectronic applications such as non-linear optics employing Quasi-Phase-Matching for efficient harmonic and parametric conversion processes or for the fabrication route for production of novel MEMS devices, like micro-cantilever beams. Quasi-Phase-Matching based applications require periodically reversed ferroelectric structures with periods of the order of micrometers. Precise control of the surface quality and of the domain structure of the micro structured materials is required such as in the case of optical MEMS applications. We here report on the application of Digital Holography as metrological tool for the inspection and characterization of the domain structures in bulk Lithium Niobate samples. This technique allows reconstructing both the intensity and the phase of the microstructures under test and it allows determining quantitatively the phase distribution. Several examples of application of the Digital Holography technique for the numerical reconstruction of the micro-topography of domain structure are presented and discussed.

Giuseppe Coppola

Papers

Maternal non-Mendelian inheritance of a reduced lifespan? A hypothesis

Experimental evidences of carrier distribution and behavior in frequency in a BMFET Modulator

Optoelectronic router in glass waveguide with a liquid crystal cladding

Characterization of photopolymers as optical recording materials by means of digital holography microscopy

Characterization of microstructures in lithium niobate crystals by digital holography