Francesco Dell'Olio

Optical sensing by optimized silicon slot waveguides

A theoretical investigation of silicon-on-insulator nanometer slot waveguides for highly sensitive and compact chemical and biochemical integrated optical sensing is proposed. Slot guiding structures enabling high optical confinement in a low-index very small region are demonstrated to be very sensitive to either cover medium refractive index change or deposited receptor layer thickness increase. Modal and confinement properties of slot waveguides have been investigated, considering also the influence of fabrication tolerances. Waveguide sensitivity has been calculated and compared with that exhibited by other silicon nanometer guiding structures, such as rib or wire waveguides, or with experimental values in literature.

Photonic technologies for angular velocity sensing

Photonics for angular rate sensing is a well-established research field having very important industrial applications, especially in the field of strapdown inertial navigation. Recent advances in this research field are reviewed. Results obtained in the past years in the development of the ring laser gyroscope and the fiber optic gyroscope are presented. The role of integrated optics and photonic integrated circuit technology in the enhancement of gyroscope performance and compactness is broadly discussed. Architectures of new slow-light integrated angular rate sensors are described. Finally, photonic gyroscopes are compared with other solid-state gyros, showing their strengths and weaknesses.

Ammonia Optical Sensing by Microring Resonators

A very compact (device area around 40 μm2) optical ammonia sensor based on a microring resonator is presented in this work. Silicon-on-insulator technology is used in sensor design and a dye doped polymer is adopted as sensing material. The sensor exhibits a very good linearity and a minimum detectable refractive index shift of sensing material as low as 8×10-5, with a detection limit around 4 ‰.

High performance InP ring resonator for new generation monolithically integrated optical gyroscopes

An InP ring resonator with an experimentally demonstrated quality factor (Q) of the order of 10(6) is reported for the first time. This Q value, typical for low loss technologies such as silica-on-silicon, is a record for the InP technology and improves the state-of-the-art of about one order of magnitude. The cavity has been designed aiming at the Q-factor maximization while keeping the resonance depth of about 8 dB. The device was fabricated using metal-organic vapour-phase-epitaxy, photolithography and reactive ion etching. It has been optically characterized and all its performance parameters have been estimated. InP waveguide loss low as 0.45 dB/cm has been measured, leading to a potential shot noise limited resolution of 10 °/h for a new angular velocity sensor.

Efficient Chemical Sensing by Coupled Slot SOI Waveguides

A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed. The sensor is based on an asymmetric directional coupler employing slot optical waveguides. The use of a nanometer guiding structure where optical mode is confined in a low-index region permits a very compact sensor (device area about 1200 μm2) to be realized, having the minimum detectable refractive index change as low as 10-5. Silicon-on-Insulator technology has been assumed in sensor design and a very accurate modelling procedure based on Finite Element Method and Coupled Mode Theory has been pointed out. Sensor design and optimization have allowed a very good trade-off between device length and sensitivity. Expected device sensitivity to glucose concentration change in an aqueous solution is of the order of 0.1 g/L.

High-Q Spiral Resonator for Optical Gyroscope Applications: Numerical and Experimental Investigation

This paper reports the numerical and experimental results of a high-Q silica-onsilicon spiral resonator to be used in microoptical gyroscopes having a potential resolution <; 10 °/h. First, demonstration of a Ge:SiO2 waveguiding spiral cavity as sensing element for gyro applications is given, and results of its optical characterization are provided. Quality factor, finesse, free spectral range, and thermal stability have been measured, clearly showing the potential of the device for gyro applications. The effect of coupling tuning through micrometer scale heaters and the supported eigenstates of polarization have also been experimentally investigated. The thermal stabilization of the silica chip is realized using a thermoelectric cooler co-packaged with the resonant cavity. The Q-factor of the spiral exceeds 106, and the thermal drift of the resonance frequency is very low (<; 20 kHz/s). An original formula estimating the bias drift due to the Kerr effect has been derived, proving that a bias drift of 0.2 °/h can be achieved by controlling the polarization noise. The resolution of the angular velocity sensor has been numerically estimated by exploiting the experimental results. We demonstrate that the resolution of our device can be improved to values less than 10 °/h, by decreasing both the propagation loss within the resonator (<; 0.05 dB/cm, which is currently achievable) and the cavity insertion loss to 1-2 dB (typical value).

Fast light generation through velocity manipulation in two vertically-stacked ring resonators

Speed manipulation of optical pulses is a very attractive research challenge enabling next-generation high-capacity all-optical communication networks. Pulses can be effectively slowed by using different integrated optical structures such as coupled-resonator waveguiding structures or photonic crystal cavities. Fast light generation by means of integrated photonic devices is currently a quite unexplored research field in spite of its crucial importance for all-optical pulse processing. In this paper, we report on the first theoretical demonstration of fast light generation in an ultra-compact double vertical stacked ring resonator coupled to a bus waveguide. Periodic coupling between the two rings leads to splitting and recombining of symmetric and anti-symmetric resonant modes. Re-established degenerate modes can form when a symmetric and an anti-symmetric mode having different resonance order exhibit the same resonance wavelength. Under degenerate mode conditions, wide wavelength ranges where the group velocity is negative or larger than the speed of light in vacuum are generated. The paper proves how this physical effect can be exploited to design fast light resonant devices. Moreover, conditions are also derived to obtain slow light operation regime.

Scaling and Optimization of MOS Optical Modulators in Nanometer SOI Waveguides

In this paper, a very accurate model of optical modulators in silicon-on-insulator technology is developed and validated using experimental results reported in literature. Using an optimized nanometer MOS structure, a significant bandwidth increase (around 45%), length decrease (around four times), and power consumption reduction (three times) with respect to the state-of-the-art have been obtained.

A High-

The design, fabrication, and optical characterization of the sensing element of a photonic InP-based gyroscope intended for applications in the field of aerospace and defense are reported in this paper. The sensing element is a spiral resonator coupled to a straight bus waveguide through a multimode interference coupler and exhibits a Q factor of approximately 600 000 with a footprint of approximately 10 mm 2. The design of each component of the sensor is based on some well-established numerical methods such as the Finite Element Method, the beam propagation method, and the film mode matching method. The spiral cavity was designed using the standard transfer matrix method. The selected fabrication process, which is an enhanced version of the standard COBRA process, allows the monolithic integration of the sensing element with the other active components of the gyroscope, e.g., lasers, photodiodes, and modulators. Each component of the fabricated sensing element was optically characterized using an appropriate setup, which was also used for the optical characterization of the whole sensor. Based on the results of the characterization, the gyro performance was evaluated, and a way to improve both the resolution and the bias drift, i.e., down to 10°/h and 1°/h, respectively, was also clearly identified. The achieved results demonstrate, for the first time, the actual feasibility of a photonic gyro-on-chip through a well-established InP-based generic integration process.

Q

An integrated optical gyroscope based on a passive silica-on-silicon resonator with a footprint of about 20 cm2 is reported in this paper. The optical characterization of the cavity has been carried out and the main experimental results are discussed. We derive the sensor performance in terms of minimum detectable angular velocity (or resolution) δΩ, underlining also the impact of the insertion loss in the silica-on-silicon device. Finally, we describe some technical approaches for improving the resolution.