Light-induced metal-like surface of silicon photonic waveguides

The surface of a material may exhibit physical phenomena that do not occur in the bulk of the material itself. For this reason, the behaviour of nanoscale devices is expected to be conditioned, or even dominated, by the nature of their surface. Here, we show that in silicon photonic nanowaveguides, massive surface carrier generation is induced by light travelling in the waveguide, because of natural surface-state absorption at the core/cladding interface. At the typical light intensity used in linear applications, this effect makes the surface of the waveguide behave as a metal-like frame. A twofold impact is observed on the waveguide performance: the surface electric conductivity dominates over that of bulk silicon and an additional optical absorption mechanism arises, that we named surface free-carrier absorption. These results, applying to generic semiconductor photonic technologies, unveil the real picture of optical nanowaveguides that needs to be considered in the design of any integrated optoelectronic device

Light Dependence of Silicon Photonic Waveguides

In OPN’s December “Optics in 2015” review of interesting research conducted in the previous year, Stefano Grillanda and Francesco Morichetti explore the crucial impact of surface effects in the behavior of light in nanoscale optoelectronic waveguides, such as those in integrated photonic chips—creating a metal-like “skin” of conductivity on the surface of the waveguid

Breakthroughs in Photonics 2013: Toward Feedback-Controlled Integrated Photonics

We present an overview of the main achievements obtained in 2013 on the monitoring, stabilization, and feedback loop control of passive and active photonic integrated circuits. Key advances contributed to the evolution of photonic technologies from the current device level toward complex, adaptive, and reconfigurable integrated circuits

NURBS-based kinematic limit analysis of FRP-reinforced masonry walls with out-of-plane loading

A three-dimensional (3D) general upper-bound limit analysis procedure for the determination of the collapse load of out-of-plane loaded masonry walls with Fiber Reinforced Polymer (FRP) reinforcement strips is presented. The geometry of a given FRP reinforced masonry wall of arbitrary shape is represented by its Non-Uniform Rational B-Spline (NURBS) description in the three-dimensional Euclidean space. The NURBS parameter space is partitioned by means of a number of possible fracture lines and the original reinforced wall geometry is subdivided into an initial set of rigid elements, accordingly. An upper-bound limit analysis formulation, accounting for the main characteristics of both masonry material and FRP reinforcement by means of homogenization techniques, is deduced. Internal dissipation is allowed along element edges only and the effect of vertical loads and membrane stresses is considered as well. Numerical experiments show that a good estimate of the load bearing capacity is obtained provided that the initial arrangement of yield lines is adjusted by means of a suitable Genetic Algorithm (GA)

Novel non-linear static numerical model for curved masonry structures based on a combined adaptive limit analysis and discrete FE computations

A new procedure for a fast and comprehensive description of the collapse behavior of curved masonry structures is presented. The first step provides the identification of the exact collapse mechanism and the load-bearing capacity through adaptive NURBS limit analysis. This method is based on the discretization of the masonry vault through very few curved elements, assumed as rigid blocks with internal dissipation allowed only at interfaces, whose shape is iteratively modified until interfaces coincide with the correct position of cracks. On the obtained mechanism, a kinematic non-linear analysis with rigid-softening behavior can be also applied to better understand how the load-bearing capacity decreases during the evolution of the mechanism. A finite element (FE) non-linear static analysis is then applied to obtain the force-displacement curve according to the real elastic-softening behavior. The NURBS optimized model is converted into a discrete FE model composed of three-dimensional elastic units joint together by interfaces where the non-linear mechanical properties are lumped. Within this assumption, non-linear interfaces are applied along the cracks previously found through the limit analysis in a fully automatic way, preventing any mesh dependency effect. Furthermore, the combination of such approaches allows overcoming the respective drawbacks of the methods. Selected masonry arches and vaults are here studied to present the reliability of the presented coupled approach.NSFC - National Natural Science Foundation of China(51576043

Non-invasive monitoring and control in silicon photonics by CMOS integrated electronics

As photonics breaks away from today's device level toward large scale of integration and complex systems-on-a-chip, concepts like monitoring, control and stabilization of photonic integrated circuits emerge as new paradigms. Here, we show non-invasive monitoring and feedback control of high quality factor silicon photonics resonators assisted by a transparent light detector directly integrated inside the cavity. Control operations are entirely managed by a CMOS microelectronic circuit, hosting many parallel electronic read-out channels, that is bridged to the silicon photonics chip. Advanced functionalities, such as wavelength tuning, locking, labeling and swapping are demonstrated. The non-invasive nature of the transparent monitor and the scalability of the CMOS read-out system offer a viable solution for the control of arbitrarily reconfigurable photonic integrated circuits aggregating many components on a single chip

A variable delay integrated receiver for differential phase-shift keying optical transmission systems

An integrated variable delay receiver for DPSK optical transmission systems is presented. The device is realized in silicon-on-insulator technology and can be used to detect DPSK signals at any bit-rates between 10 and 15 Gbit/s

Automated routing and control of silicon photonic switch fabrics

Automatic reconfiguration and feedback controlled routing is demonstrated in an 8×8 silicon photonic switch fabric based on Mach-Zehnder interferometers. The use of non-invasive Contactless Integrated Photonic Probes (CLIPPs) enables real-time monitoring of the state of each switching element individually. Local monitoring provides direct information on the routing path, allowing an easy sequential tuning and feedback controlled stabilization of the individual switching elements, thus making the switch fabric robust against thermal crosstalk, even in the absence of a cooling system for the silicon chip. Up to 24 CLIPPs are interrogated by a multichannel integrated ASIC wire-bonded to the photonic chip. Optical routing is demonstrated on simultaneous WDM input signals that are labelled directly on-chip by suitable pilot tones without affecting the quality of the signals. Neither preliminary circuit calibration nor lookup tables are required, being the proposed control scheme inherently insensible to channels power fluctuations