Giuseppe Cusmai

Demonstration of net gain at 1550nm in an erbium-doped polymersingle mode rib waveguide

A polymer-based waveguide optical amplifier doped with Er3+ ions has been modeled, fabricated, and characterized. Propagation losses have been measured using both cutback and Fabry-Perot methods, resulting in similar, reasonable loss values that do not exceed 1.31dBcm−1 at 1540nm. By accounting for overall propagation loss, a net gain of 1.34dB at 1540nm is demonstrated for a 1.6cm long single mode waveguide amplifier.

The role of index contrast in dielectric optical waveguides

The refractive index contrast plays a fundamental role in determining the characteristics of an optical dielectric waveguide and a higher index contrast permits to move towards larger scales of integration and to access new devices and functionalities. In this paper, the impact of the index contrast on the characteristics of dielectric waveguides such as single mode regime, losses, fibre to waveguide coupling efficiency, minimum bending radius, mode hybridness, birefringence, polarisation effects, repeatability and stability, scale of integration, realisable circuits, technological constraints and available materials are investigated. Both classical step index waveguides and multilayer structures that engineers the contrast are considered.

Waveguide index contrast: implications for passive integrated optical components

The index contrast increase of integrated optical waveguides permits to move towards very large scale of integration of photonic integrated circuits, mainly because of the very small bending radius achievable. Furthermore, high index contrast waveguides allow to access new devices, such as ring resonators, more compact and with better spectral characteristics. These two invaluable advantages push to consider new technologies, new materials and new solutions to exploit the integrated optic world. Trying to see the index contrast as a free parameter in the design of a dielectric waveguide, we discuss the general properties and the main impairments of high index contrast waveguides. Not always an increase of the index contrast corresponds to an increase of the waveguide and circuit criticity.

Experimental investigation of ring‐resonators in SiON technology

The ring resonator is an obliged step in the path towards large scale integrated photonic circuits. In this work we focus on passive ring resonators for applications in the modern WDM systems and a ‘best working point’ is suggested. Both a theoretical and an experimental deep investigation is carried out on two basic structures: the single ring phase shifter and the single ring wavelength filter, realized by SiON technology with a 6% index contrast. It is demonstrated that an accurate modelling of directional couplers leads to the proper recovery of the circuit parameters and of the group delay and enables the design of more complex ring‐based structures.

Progress in Large Integration Scale Circuits in SiON Technology

In this contribution the potentialities and the limitation of the silicon oxynitride (SiON) technology are reviewed and a number of integrated optical circuits and devices are presented. Mach-Zehnder, ring resonators, variable bandwidth filters, ring resonators based cross-bar matrices and a DQPSK receiver with interleaver and variable attenuators have been realized, characterized and tested in a 10 Gbit/s WDM system.

The ring-based optical Resonant Router

The Resonant Router (ReR) is an integrated optics crossbar matrix based on ring resonators. Depending on the characteristics of the rings the ReR can operate as cross-connect (X-ReR) or as wavelength router (λ-ReR). The analysis of the device, the spectral characteristics and the impact on a high bit rate signal are presented and discussed both on theoretical and experimental basis. The ReR can add flexibility and extend the capabilities of a node of a transparent optical network.

Experimental confirmation of matched bends

Modal conversion between the fundamental mode and the first-order (leaky) mode has been experimentally investigated in high-index-contrast integrated-optical bent waveguides. The matched bend condition has been experimentally confirmed on cascaded bends, and the effect of both matched and unmatched bends on Y branches has been investigated. Good agreement between theoretical predictions and experimental results for both monomode and multimode waveguides is achieved. It is demonstrated that, in bent waveguides, the modal conversion between the fundamental mode and the first (leaky) mode can be accurately controlled to avoid additional losses and transfer function impairments.

Three-Arm Mach-Zehnder Interferometers

Integrated optical Mach-Zehnder with three arms own remarkable and attractive properties for applications in both linear and nonlinear field. Robustness, compactness, optical performances and flexibility are improved at the expense of a small increase of circuit complexity.

Wavelength Routing by a Matrix of Ring Resonators

The Resonant Router (ReR) is a valid solution for realizing add‐drop multiplexers, cross‐connects and wavelength routers. The characteristics of the ReR, the impact on a high bit rate systems and the technological feasibility are briefly discussed.

Polarization conversion in ring resonators

The effect of the polarization rotation in bent waveguide on the frequency response of optical ring resonators is theoretically and experimentally investigated. A simple model that fairly well agrees with measured spectral responses is proposed.