Benedetto Troia

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.

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.

Recent advances in gas and chemical detection by Vernier effect-based photonic sensors.

Recently, the Vernier effect has been proved to be very efficient for significantly improving the sensitivity and the limit of detection (LOD) of chemical, biochemical and gas photonic sensors. In this paper a review of compact and efficient photonic sensors based on the Vernier effect is presented. The most relevant results of several theoretical and experimental works are reported, and the theoretical model of the typical Vernier effect-based sensor is discussed as well. In particular, sensitivity up to 460 μm/RIU has been experimentally reported, while ultra-high sensitivity of 2,500 μm/RIU and ultra-low LOD of 8.79 × 10−8 RIU have been theoretically demonstrated, employing a Mach-Zehnder Interferometer (MZI) as sensing device instead of an add drop ring resonator.

Device-level characterization of the flow of light in integrated photonic circuits using ultrafast photomodulation spectroscopy

Advances in silicon photonics have resulted in rapidly increasing complexity of integrated circuits. New methods are desirable that allow direct characterization of individual optical components in-situ, without the need for additional fabrication steps or test structures. Here, we present a new device-level method for characterization of photonic chips based on a highly localized modulation in the device using pulsed laser excitation. Optical pumping perturbs the refractive index of silicon, providing a spatially and temporally localized modulation in the transmitted light enabling timeand frequency-resolved imaging. We demonstrate the versatility of this all-optical modulation technique in imaging and in quantitative characterization of a variety of properties of silicon photonic devices, ranging from group indices in waveguides, quality factors of a ring resonator to the mode structure of a multimode interference device. Ultrafast photomodulation spectroscopy provides important information on devices of complex design, and is easily applicable for testing on the device-level. Integrated silicon-based photonics has developed into a mature technology platform with a multitude of applications [1-4], including telecommunications, healthcare diagnostics and optical sensors. As technology progresses, device designs become increasingly complex and integrate more functions onto a single device [5]. Characterization of fabricated devices is an important step in the design cycle as it highlights differences between the intended design

Photonic resonant microcavities for chemical and biochemical sensing

Nowadays, photonic sensors represent an efficient and intriguing solution for advanced chemical and biochemical sensing in liquid and gas. In this article, a detailed investigation of photonic sensors based on resonant microcavities is presented. Photonic device architectures, optical sensing principles, technologies and materials are presented, emphasizing their role in optical sensing mechanisms. In conclusion, interesting experimental results are reviewed in order to show the main applications of photonic resonant microcavities in several fields, such as medicine, chemistry and biotechnology, to name a few.

Photonic Crystals for Optical Sensing: A Review

The development and integration of Microfluidic and Photonic technologies, with specific reference to the CMOS-compatible silicon-on-insulator (SOI) technology, allows to enhance sensing performance in terms of sensitivity, limit-of-detection (LOD) and detection multiplex‐ ing capability. Photonic sensors have been the subject of intensive research over the last decade especially for detection of a wide variety of biological and chemical agents. In this context, photonic Lab-on-a-chip systems represent the state-of-the-art of photonic sensing since they are expected to exhibit higher sensitivity and selectivity as well as high stability, immunity to electromagnetic interference and product improvements, such as smaller integration sizes and lower costs.

Generalized modelling for the design of guided-wave optical directional couplers

In this Letter we propose a rigorous and generalized approach for the design of integrated optical bent directional couplers (DCs) based on the coupled mode theory and super mode theory. The full vectorial finite-element method is used for the calculation of effective indices of optical modes propagating into the waveguides constituting the DCs. The flexibility and robustness of this general modelling approach is demonstrated by simulating several directional coupling configurations, as those based on cosine S-bend and double arc bent waveguides. Furthermore, some numerical results have been validated by comparison with the three-dimensional semi-vectorial beam propagation method.

Germanium-on-silicon Vernier-effect photonic microcavities for the mid-infrared.

We present Vernier-effect photonic microcavities based on a germanium-on-silicon technology platform, operating around the mid-infrared wavelength of 3.8 μm. Cascaded racetrack resonators have been designed to operate in the second regime of the Vernier effect, and typical Vernier comb-like spectra have been successfully demonstrated with insertion losses of ∼5  dB, maximum extinction ratios of ∼23  dB, and loaded quality factors higher than 5000. Furthermore, an add-drop racetrack resonator designed for a Vernier device has been characterized, exhibiting average insertion losses of 1 dB, extinction ratios of up to 18 dB, and a quality factor of ∼1700.

Design Rules for Raman Lasers Based on SOI Racetrack Resonators

In this paper, the detailed modeling of Raman lasers in silicon-on-insulator guided-wave racetrack resonant microcavities is developed. Modeling based on full-vectorial equations and systematic design rules are presented for the first time. Simulation results are compared with experimental and theoretical results in literature, demonstrating a very good agreement. Moreover, parametric investigations including waveguide sizes, pump and Stokes coupling factors, cavity shape, polarization states, and waveguide orientation are presented, and their influence on the laser features are discussed.

Cascade-coupled racetrack resonators based on the Vernier effect in the mid-infrared

In this paper we report the experimental demonstration of racetrack resonators in silicon-on-insulator technology platform operating in the mid-infrared wavelength range of 3.7-3.8 μm. Insertion loss lower than 1 dB and extinction ratio up to 30 dB were measured for single resonators. The experimental characterization of directional couplers and bending losses in silicon rib waveguides are also reported. Furthermore, we present the design and fabrication of cascade-coupled racetrack resonators based on the Vernier effect. Experimental spectra of Vernier architectures were demonstrated for the first time in the mid-infrared with insertion loss lower than 1 dB and maximum interstitial peak suppression of 10 dB.