Ahmed Hisham Morshed

VIOLET/BLUE EMISSION FROM EPITAXIAL CERIUM OXIDE FILMS ON SILICON SUBSTRATES

Violet/blue photoluminescence was observed from epitaxial cerium oxide films on silicon substrates. The films were deposited on silicon (111) substrates under ultrahigh vacuum conditions using pulsed laser ablation of a cerium oxide target and treated by rapid thermal annealing in argon. High resolution transmission electron microscopy and x-ray diffraction measurements indicated the formation of a single crystal cerium oxide phase Ce6O11 different from CeO2 in the annealed films. The emission might be due to charge transfer transitions from the 4f band to the valence band of the oxide.

Effect of the fabrication and design parameters on the performance of multimode interference devices made by ion exchange: a detailed study

A comprehensive and rigorous study of the performance of MMI devices fabricated by ion exchange on a glass substrate is presented. The effect of both design and fabrication parameters on the performance of the devices is investigated and a physical interpretation of the effect of these parameters on the behavior of devices is given. A novel stable and efficient approach for solving the nonlinear ion exchange diffusion equation is proposed and exploited in this study. Based on this study an optimal design for a 3 dB ion-exchanged power splitter with low insertion loss and wide bandwidth is proposed.

Optimization of optical wide band 3-dB MMI splitter with graded-index side diffusions

The design of a 3-dB multimode-inter

Intensity-based optical fiber intrusion detector

erencebased symmetrical optical splitter for realization by ion exchange on glass substrates is optimized for wide band peformance taking the graded-index side diffusions into consideration. The depth of diffusion and width of the multimode waveguide section for best coupler performance are determined based on a modified model of ion-e.xchanged waveguides which takes into account the effective index grading in the lateral direction due to the finite width of the waveguide and the presence of side diffusions. The performance of the devices is simulated using the beam propagation method and compared to that of a conventional step-index design. Couplers with larger bandwidths are obtained using optimized designs. Index Terms 3-dB symmetrical optical splitter, multimodeinterference, wide band performance, ion exchange on glass, graded-index side diffusions.

Self-imaging in single mode-multimode-single mode optical fiber sensors

An intensity-based optical fiber sensor using single-mode-multimode-single-mode fiber sections concatenation is proposed and investigated for use as an intrusion detector. The sensor is composed with simple FC/PC connections between the fiber sections. It is found to be sensitive to intrusion disturbances applied to the multimode fiber section. The transmission spectra of the device under different conditions are measured and its operation as intrusion detector is demonstrated using a single-mode laser source. More than 1 dB variation in the detected power level was observed at a wavelength of 1543 nm. The device proposed is a simple intensity-based sensor, which can be used as a stand-alone device to detect intrusion events over its length or possibly interrogated in a quasidistributed intrusion detection system based on optical time domain reflectometry.

Modeling the field diffracted from photo mask at oblique incidence

Multimode interference in optical waveguides has interesting self-imaging properties, which have extensively been investigated and utilized in many integrated optical devices. Although these investigations started with most interest in step-index integrated waveguides, they have later included graded-index waveguides, where the dependence of the interference images on the refractive index grading of the waveguides was observed and utilized in the design and optimization of devices. Later on, multimode interference has also been explored in optical fibers in order to realize fiber devices, including sensors. A basic structure of these devices has been the Single mode — Multimode — Single mode (SMS) fiber section concatenation, where multimode interference in the multimode section leads to the formation of a self-image of the single mode fiber excitation onto the output single mode fiber core. This paper reports on the investigation of the self-imaging properties of these optical fiber structures and their possible use as sensors. Self-imaging in symmetrically excited multimode optical fibers is analytically studied, revealing the effect of refractive index grading on the characteristics of SMS fiber devices. The theoretical results are verified by numerical simulations using the beam propagation method. The experimental investigation of an SMS structure proposed as a bending sensor is then described and a discussion of the results obtained and possible application of the device is presented.

Modeling mask scattered field at oblique incidence

In optical lithography, light diffracted from photo mask structures has been customarily assumed to be constant with the angle of incidence of the light illuminating the photo mask. As numerical aperture increases to unity and beyond, to cope with the continuous demand for shrinking integrated circuits, device dimensions, and densities, this approximation is no longer valid. In this paper we use the physical theory of diffraction to study, understand, and model the variation of light diffracted from photo mask structures of the order of the wavelength, with the angle of light incidence. We present a semianalytical model that is fast, accurate, and compatible with existing professional software in this domain. The accuracy of the model is studied using the finite-difference time-domain technique and is shown to be below 5% at the image plane, within angles of incidence between +/-20 degrees .

Optimized 3D design of an MMI splitter with ion exchange technology

In optical lithography light diffracted from the mask has been customary assumed to have constant amplitude with the angle of incidence of the light illuminating the mask. This approximation, known as constant scattering coefficient approximation, has been successfully used at small NA. As the NA increases to unity and beyond, to cope with the continuous demand for shrinking integrated circuits device dimensions and densities, the validity of this approximation becomes questionable. In this paper, we study diffracted field variation with the angle of incidence using physical theory of diffraction. An asymptotic theory like the physical theory of diffraction allows us to better understand, quantify, and model using analytical formulae, induced effects of light diffraction from mask at oblique incidence. This paper presents a semi analytical model that describes diffracted field variation with angle of incidence. The model accuracy is validated by comparison with rigorous field simulations using Panoramic software.

Stable optical filter using porous silicon technology

Multimode interference (MMI) couplers are important integrated optical components for the optical signal processing and routing. The realization of these components by ion exchange on glass substrates is particularly attractive for low cost integration. The design and analysis of MMI devices have generally been based on the self imaging principle in step-index waveguides, whereas waveguides fabricated by ion exchange on glass are practically graded-index due to the nature of the thermal diffusion of exchanged ions. In addition, the ion exchange process results in a guide with depth that depends on the mask opening (the guide width) which causes a high insertion loss at the interface between single mode and multimode sections of the MMI. To overcome these problems 3D simulation of the ion exchanged MMI structures is strongly required. In this work such 3D simulation is achieved on two levels. First the non-linear diffusion equation describing the ion exchange process is solved numerically using a finite-difference method with a modified algorithm to ensure solution stability for an extended range of nonlinearity. The resultant index distribution is used in a wide angle 3D BPM to simulate the optical field propagation in the structure. This allows accurate prediction of the structure performance under different fabrication and excitation conditions. Based on this simulation technique, 3 dB MMI splitter design with tapered access guides is optimized by both geometrical mask design and process parameter variations. The optimization shows that both the tapering and the use of annealing process can significantly improve the performance of the devices.

Rotation sensing with a low-cost simple FOG

A stable multilayer IR optical filter is designed based on the porous silicon technology. The filter stability is achieved based on the mechanical properties of porous silicon that are used to tailor the stresses inside the mutilayer structure. The filter, working at the wavelength of 1.55 µm, have been designed to be matched with spot sizes of 7 µm and 8.5 µm which makes it compatible with single mode fiber used in optical communications