Vittorio M. N. Passaro

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.

Single-mode and polarization-independent silicon-on-insulator waveguides with small cross section

The fabrication restrictions that must be imposed on the geometry of optical waveguides to make them behave as single-mode devices are well known for relatively large waveguides, with shallow etch depth. However, the restrictions for small waveguides (/spl sim/1 /spl mu/m or less in cross section) are not well understood. Furthermore, it is usually a requirement that these waveguides are polarization independent, which further complicates the issues. This paper reports on the simulations of the conditions for both single-mode behavior and polarization independence, for small and deeply etched silicon-on-insulator (SOI) waveguides. The aim is to satisfy both conditions simultaneously. The results show that at larger waveguide widths, waveguide etch depth has little effect on the mode birefringence because the transverse-electric (TE) mode (horizontal-polarized mode) is well confined under the rib region. However, at smaller rib widths, the etch depth has a large influence on birefringence. An approximate equation relating the rib-waveguide width and etch depth to obtain polarization-independent operation is derived. It is possible to achieve single-mode operation at both polarizations while maintaining polarization independence for each of the waveguide heights used in this paper but may be difficult for other dimensions. For example, a 1-/spl mu/m SOI rib waveguide with an etch depth of 0.64 /spl mu/m and rib width of 0.52 /spl mu/m is predicted to exhibit such characteristics.

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 ‰.

Modeling and design of a novel miniaturized integrated optical sensor for gyroscope systems

In this paper, we report, for the first time to our knowledge, the modeling and the design of a miniaturized integrated optical sensor, based on a multiple quantum-well (MQW) microring laser, to be used in gyroscope systems. The device can be fully integrated on a single chip and used either in low (e.g., vehicles for land transport) or high (e.g., ships, airplanes, spaceborne platforms) sensitivity navigation systems. The model includes the influence of some physical effects, such as quantum noise, lock in, thermal effect, and sidewall roughness-induced losses. Very good performance has been obtained in terms of gyro quantum limit, operating regions of detectable velocity, thermal range of operation, and power consumption. The proposed architecture shows significant manifold advantages with respect to other existing optical solutions: no polarization-induced noise, no use of frequency-locking techniques, negligible bending losses, high cavity quality factor, complete evaluation of the rotation speed, predictable thermal variation of the gyro scale factor, and very high dynamic range.

Recent advances in integrated photonic sensors.

Nowadays, optical devices and circuits are becoming fundamental components in several application fields such as medicine, biotechnology, automotive, aerospace, food quality control, chemistry, to name a few. In this context, we propose a complete review on integrated photonic sensors, with specific attention to materials, technologies, architectures and optical sensing principles. To this aim, sensing principles commonly used in optical detection are presented, focusing on sensor performance features such as sensitivity, selectivity and rangeability. Since photonic sensors provide substantial benefits regarding compatibility with CMOS technology and integration on chips characterized by micrometric footprints, design and optimization strategies of photonic devices are widely discussed for sensing applications. In addition, several numerical methods employed in photonic circuits and devices, simulations and design are presented, focusing on their advantages and drawbacks. Finally, recent developments in the field of photonic sensing are reviewed, considering advanced photonic sensor architectures based on linear and non-linear optical effects and to be employed in chemical/biochemical sensing, angular velocity and electric field detection.

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.

Dual grating-assisted directional coupling between fibers and thin semiconductor waveguides

A novel dual grating-assisted directional coupler (DGADC) for coupling an optical fiber with a thin semiconductor waveguide is proposed. As an example, a DGADC in silicon-on-insulator is discussed. Maximum coupling efficiency in excess of 90% can be obtained using this coupler, while the highest coupling efficiency previously reported was only 40%.

Investigation of thermo-optic effect and multi-reflector tunable filter/multiplexer in SOI waveguides

The paper presents an analysis of thermo-optic phase shifters in silicon-on-insulator (SOI) waveguide structures. It gives recommendations to provide high tuning characteristics at minimum power requirements. Then, this analysis is applied to the description of a novel type of reconfigurable optical add/drop multiplexer (ROADM) utilizing multi-reflector (MR) beam expanders and thermo-optic tuning in SOI structures. It is intended for use in high dense wavelength-division-multiplexing (HDWDM) flexible fiber-optic networks having multi-hundreds wavelength channels and advanced ITU grids (12.5 GHz, 25 GHz, 50 GHz).

A high efficiency input/output coupler for small silicon photonic devices

Coupling light from an optical fibre to small optical waveguides is particularly problematic in semiconductors, since the refractive index of the silica fibre is very different from that of a semiconductor waveguide. There have been several published methods of achieving such coupling, but none are sufficiently efficient whilst being robust enough for commercial applications. In this paper experimental results of our approach called a Dual-Grating Assisted Directional Coupler, are presented. The principle of coupling by this novel method has been successfully demonstrated, and a coupling efficiency of 55% measured.

Silicon Photonic Waveguides and Devices for Near- and Mid-IR Applications

Silicon photonics has been a very buoyant research field in the last several years mainly because of its potential for telecom and datacom applications. However, prospects of using silicon photonics for sensing in the mid-IR have also attracted interest lately. In this paper, we present our recent results on waveguide-based devices for near- and mid-infrared applications. The silicon-on-insulator platform can be used for wavelengths up to 4 μm; therefore, different solutions are needed for longer wavelengths. We show results on passive Si devices such as couplers, filters, and multiplexers, particularly for extended wavelength regions and finally present integration of photonics and electronics integrated circuits for high-speed applications.