Ilaria Cristiani

University of Pavia | UNIPV · Department of Electrical, Computer and Biomedical Engineering

We report here a broadband Si-rich silicon nitride wavelength converter based on intermodal four-wave mixing with on-chip mode multiplexing and de-multiplexing functionalities. L- to U-band wavelength conversion of 40-Gbps QPSK optical signals is demonstrated.

Intermodal four-wave mixing (FWM) processes have recently attracted significant interest for all-optical signal processing applications thanks to the possibility to control the propagation properties of waves exciting distinct spatial modes of the same waveguide. This allows, in principle, to place signals in different spectral regions and satisfy...

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physi...

In this work, we show the design of a silicon photonic-based polarization converting device based on the integration of semiconduction InP nanowires on the silicon photonic platform. We present a comprehensive numerical analysis showing that full polarization conversion (from quasi-TE modes to quasi-TM modes, and vice versa) can be achieved in devi...

Multimode devices and components have attracted considerable attention in the last years, and different research topics and themes have emerged very recently. The multimodality can be seen as an additional degree of freedom in designing devices, thus allowing for the development of more complex and sophisticated components. The propagation of diffe...

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physi...

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physi...

Yield stress materials deform as elastic solids or flow as viscous liquids, depending on the applied stress, which also allows them to trap particles below a certain size or density threshold. To investigate the conditions for such a transition at the microscale, we exploit an optofluidic microrheometer, based on the scattering of an infrared beam...

We propose and demonstrate an on-chip optofluidic device allowing active oscillatory microrheological measurements with sub-μL sample volume, low cost and high flexibility. Thanks to the use of this optofluidic microrheometer it is possible to measure the viscoelastic properties of complex fluids in the frequency range 0.01–10 Hz at different tempe...

The viscosity of gel-forming fluids is notoriously complex and its study can benefit from new model systems that enable a detailed control of the network features. Here we use a novel and simple microfluidic-based active microrheology approach to study the transition from Newtonian to non-Newtonian behavior in a DNA hydrogel whose structure, connec...

We present a simple and practical strategy that allows to design high-efficiency grating couplers. The technique is based on the simultaneous apodization of two structural parameters: the grating period and the fill-factor, along with the optimization of the grating coupler etching depth. Considering a 260 nm Si-thick Silicon-on-insulator platform,...

We report the design and experimental characterization of a SOI grating coupler which shows, for the first time to our knowledge, a coupling loss below 1 dB (0.89 dB) without the use of any back-reflector.

During the last decade Silicon photonics emerged as mature technology in the field of integrated optics for the fabrication of low-cost optical integrated circuits [1]. Silicon-on-insulator (SOI) represents the ideal platform for the realization of optical circuits characterized by a strong optical confinement, because of the large index contrast b...

We report on the experimental characterization, in the telecom C-band, of group-velocity dispersion (D) in 100-nm high rectangular strip waveguides realized by silicon-on-insulator technology. We compare the experimental results with numerical predictions, showing that 100-nm high waveguides exhibit normal dispersion and that the absolute value of...

In the present work, an integrated optofluidic chip for fluid viscosity measurements in the range from 1 mPa·s to 100 mPa·s is proposed. The device allows the use of small sample volumes (< 1 μL) and the measurement of viscosity as a function of temperature. Thanks to the precise control of the force exerted on dielectric spheres by optical beams,...

Optical resonators are fundamental building-blocks for the development of Si-photonics-integrated circuits, as tunable on-chip optical filters. In addition to the specific spectral shape, which may vary according to a particular application, extremely low losses from these devices are a crucial requirement. In the current state-of-the-art devices,...

Scientific Reports 6 : Article number: 23946; 10.1038/srep23946 published online: 04 April 2016 ; updated: 19 January 2017 . This Article contains errors.

Optoelectronic tweezers (OET) are a promising technique for the realization of reconfigurable systems suitable to trap and manipulate microparticles. In particular, dielectrophoretic (DEP) forces produced by OET represent a valid alternative to micro-fabricated metal electrodes, as strong and spatially reconfigurable electrical fields can be induce...

The application of an external field can modify the optical properties of a material. By controlling the strength and frequency of the external field, the amplitude, phase, or polarization of the optical beam can be controlled and modulated. The most important modulation methods are those using electric fields, but both acoustic fields and magnetic...

The field of nonlinear optics ranges from fundamental studies of the interaction of intense laser light with matter to applications such as frequency conversion, non-resonant amplification, all-optical switching. The treatment developed in this chapter restricts the attention to those topics that are of interest for applications, and limits the not...

In this chapter, after presenting Maxwell equations inside matter and describing reflection and refraction processes, the interaction of optical waves with simple optical components such as mirrors, prisms, and lenses is examined. The different methods for measuring the power spectrum of an optical beam are described and compared in Sect. 2.3. In S...

We realized an integrated microfluidic chip that allows measuring both optical deformability and acoustic compressibility on single cells, by optical stretching and acoustophoresis experiments respectively. Additionally, we propose a measurement protocol that allows evaluating the experimental apparatus parameters before performing the cell-charact...

Tutte le sorgenti di luce utilizzate prima dell’invenzione del laser sono basate sul seguente meccanismo: si fornisce energia ad un insieme di atomi che, una volta eccitati, riemettono spontaneamente l’energia acquisita sotto forma di onde elettromagnetiche a frequenze ottiche. I processi di emissione spontanea di atomi diversi sono mutuamente indi...

In questo capitolo, dopo aver introdotto le equazioni di Maxwell nella materia, vengono descritte leproprietà dei componenti ottici diusopiù comune nella Fotonica. La trattazione assume che le proprietà ottiche dei materiali isotropi siano tutte descrivibili con un solo parametro, l’indice di rifrazione,che è una funzione della frequenza dell’onda...

In questo capitolo vengono descritte le tecniche di modulazione di segnali luminosi. Modulare un’onda elettromagnetica significa introdurre una variazione di ampiezza (o di fase o di stato di polarizzazione) che segua l’andamento di un campo esterno. Ad esempio, nel caso delle comunicazioni ottiche, il campo esterno è una sequenza temporale di impu...

In questo capitolo, dopo aver derivato dalle equazioni di Maxwell l’equazione delle onde, viene introdotta l’onda piana e ne vengono discusse le proprietà. Successivamente è definito lo spettro di frequenza ed è ricavata la relazione che lega la durata di un impulso luminoso alla larghezza spettrale.La propagazione di onde monocromatiche viene affr...

Questo capitolo descrive il funzionamento dei principali dispositivi optoelettronicibasati su materiali semiconduttori, tra cui in particolare i diodi laser.Condizione necessaria perché si possa avere amplificazione ottica è che il semiconduttore presenti una ricombinazione elettronelacuna che sia radiativa, cioè che generi un quanto di radiazione...

Le fibre ottiche sono guide d’onda dielettriche nelle quali un fascio di luce si propaga con basse perdite senza allargarsi per diffrazione. Le fibre ottiche maggiormente diffuse sono realizzate in vetro e trasmettono in modo molto efficiente la radiazione nella regione dell’infrarosso vicino. In questo capitolo vengono illustrate le proprietà prin...

Le applicazioni del laser si possono dividere in tre categorie principali: a) applicazioni alle tecnologie dell’informazione e delle comunicazioni (“Information and Communication Technology”, ICT), che comprendono le comunicazioni ottiche, le memorie ottiche, le stampanti laser, e l’elaborazione ottica dei dati; b) strumentazione diagnostica e sens...

The development of compact, low power, silicon photonics CMOS compatible components for all-optical signal processing represents a key step towards the development of fully functional platforms for next generation all-optical communication networks. The wavelength conversion functionality at key nodes is highly desirable to achieve transparent inte...

We present the characterization of Silicon-on-insulator (SOI) photonic-crystal based 2D grating-couplers (2D-GCs) fabricated by CEA-Leti in the frame of the FP7 Fabulous project, which is dedicated to the realization of devices and systems for low-cost and high-performance passives-optical-networks. On the analyzed samples different test structures...

Here we show the results of an experimental analysis dedicated to investigate the impact of optical non linear effects, such as two-photon absorption (TPA), free-carrier absorption (FCA) and free-carrier dispersion (FCD), on the performance of integrated micro-resonator based filters for application in WDM telecommunication systems. The filters wer...

The most important family of photonic devices is based on semiconductor materials. Semiconductor lasers have high efficiency and long lifetime, are fabricated by the same epitaxial growth techniques used in silicon microelectronics, can be designed to emit at almost any wavelength in the visible and near infrared range. In this chapter, after an in...

All the light sources utilized before the invention of the laser are based on spontaneous emission processes from excited atoms. Since each atom emits in a random direction with a random phase, conventional light sources are intrinsically chaotic. The laser is a completely different light source, because it is based on stimulated emission instead o...

Light is an electromagnetic phenomenon that is described, in common with radio waves, microwaves and X-rays, by Maxwell equations. This chapter briefly reviews those aspects of electromagnetic theory that are particularly relevant for optics. The propagation of quasi-collimated monochromatic light beams, Gaussian waves, is treated by using the para...

This chapter concisely describes the most important applications of photonics, which are based on the optical methods and devices discussed in Chaps. 1–7. Section 8.1 deals with the applications to information and communication technology. After introducing the design principles of digital information transmission and recording, the structure and p...

L’invenzione del laser ha generato una vera rivoluzione nella scienza e nella tecnologia e ha dato luogo alla nascita di una nuova disciplina chiamata Fotonica. Le applicazioni della Fotonica che hanno un impatto cruciale in molti ambiti della nostra vita sono le comunicazioni in fibra ottica su cui si basa il funzionamento di Internet e del traffi...

This extended and revised edition will serve as a concise, self-contained, up-to-date introduction to Photonics for undergraduate students. It can also be used as a primer by researchers and professionals who start working in the field. Blending theory with technical descriptions, the book covers a wide range of topics, including the general mechan...

In this work we demonstrate, for the first time, successful four wave mixing (FWM) based wavelength conversion of Binary Phase Shift Keyed (BPSK) and Quadrature Phase Shift Keyed (QPSK) signals, at 20 Gb/s bitrate, in a 1-mm long amorphous silicon waveguide. A maximum FWM-efficiency of -26 dB was achieved by employing a pump power of just 70 mW, es...

Here we present the results of a study concerning the effect of temperature on cell mechanical properties. Two different optofluidic microchips with external temperature control are used to investigate the temperature-induced changes of highly metastatic human melanoma cells (A375MC2) in the range of ~0 – 35 °C. By means of an integrated optical st...

Optical tweezers represent a powerful tool for a variety of applications both in biology and in physics, and their miniaturization and full integration is of great interest so as to reduce size (towards portable systems), and to minimize the required intervention from the operator. Optical fibers represent a natural solution to achieve this goal, a...

In the last decade silicon on insulator-based waveguides have progressively attracted the attention of the nonlinear-optics research community. Due to the strong refractive index contrast of such waveguides and thanks to the very high nonlinear refractive index of silicon, strong nonlinear effects can be achieved in SOI structures, even at moderate...

Acoustophoresis is a widely reported and used technique for microparticle manipulation and separation. In the study described here, acustophoresis is employed to prefocus the flow (i.e., focusing occurring upstream of the analysis region) in a microfluidic chip intended for optical trapping and stretching. The whole microchip is made of silica with...

We present a theoretical optimisation of 1D apodized grating couplers in a “pure” Silicon-On-Insulator (SOI) architecture, i.e. without any bottom reflector element, by means of a general mutative method. We perform a comprehensive 2D Finite Difference Time Domain study of chirped and apodized grating couplers in 220 nm SOI, and demonstrate that th...

A compact silicon ring resonator is demonstrated that allows simple electrical tuning of the ring coupling coefficient and Q -factor and therefore the resonant enhancement of on-chip nonlinear optical processes. Fabrication-induced variation in designed coupling fraction, crucial in the resonator performance, can be overcome using this post-fabrica...

Cellular mechanical properties constitute a good marker to characterize tumor cells, to study cell population heterogeneity and to highlight the effect of drug treatments. In this work, we describe the fabrication and validation of an integrated optofluidic chip capable of analyzing cellular deformability on the basis of the pressure gradient neede...

Optical stretching is a powerful technique for the mechanical phenotyping of single suspended cells that exploits cell deformability as an inherent functional marker. Dual-beam optical trapping and stretching of cells is a recognized tool to investigate their viscoelastic properties. The optical stretcher has the ability to deform cells through opt...

We present a novel optofluidic device for real-time sorting on the basis of cell mechanical properties, measured by optical stretching. The whole mechanism, based on optical forces, does not hamper the viability of the tested cells, which can be used for further analysis. The device effectiveness is demonstrated by extracting a sample population en...

In this work we fabricate and validate two optofludic devices for the manipulation and analysis of single cells. The chips are fabricated by femtosecond laser micromachining exploiting the 3D capabilities of the technique and the inherent perfect alignment between microfluidic channels and optical networks. Both devices have been validated by probi...

Bit Error Ratio Raw measurements for the idler signal for BPSK and QPSK signals

By bridging the dimensional gap between fiber mode and Silicon On Insulator (SOI) layer thickness, 1D and 2D-Grating couplers (GCs) represent promising solutions to the challenge of coupling light into silicon photonics circuits. Considerable work has been done over the last decade towards optimization 1D-GCs, that nevertheless [1-2] exhibit a very...

The development of highly non-linear silicon devices is a fundamental step towards the realization of low power optical signal processing devices. In order to achieve this final goal several constraints have to be overcome. In particular, the next generation of opto-electronic integrated devices must be ultra-compact, compatible with foundry model...

Polarization-diversity couplers are low-cost industrially-scalable passive devices that can couple light of unknown polarization from a telecom fiber-mode to a pair of TE-polarized wave-guided modes in the Silicon-on-Insulator platform. These couplers offer significantly more relaxed alignment tolerances than edge-coupling schemes, which is advanta...

Manipulation, sorting and recovering of specific live cells from samples containing less than a few thousand cells is becoming a major hurdle in rare cell exploration such as stem cell research or cell based diagnostics. Moreover the possibility of recovering single specific cells for culturing and further analysis would be of great impact in many...

Aluminum Gallium Arsenide (AlGaAs) is an attractive platform for the development of integrated optical circuits for all-optical signal processing thanks to its large nonlinear coefficients in the 1.55-μm telecommunication spectral region. In this paper we discuss the results of the nonlinear continuous-wave optical characterization of AlGaAs wavegu...

We present here a fully integrated fluorescence activated cell sorter (FACS), able to perform analysis at single cell level. This optofluidic device is obtained on a fused silica substrate with the use of femtosecond laser micromachining.

In this paper, we determine the optical nonlinear coefficient of hydrogenated amorphous silicon (a-Si:H) waveguides. Up to date, the data reported in the scientific literature for similar structures show a very large variability and the final assessment of their nonlinear performance is still an open issue. We performed a complete and careful chara...

Polarization-diversity couplers, which are designed to couple the unknown polarization state of an optical fiber into the TE-polarized modes of integrated waveguides, are important for the development of practical all-optical circuits. We describe the use of a full 3D finite difference time domain (FDTD) calculation campaign to rigorously optimize...

We report on the experimental demonstration of a novel silicon based fully integrated nonlinear Mach Zehnder device. A standard silicon waveguide is used as a nonlinear arm, conversely a large mode SU-8 waveguide acts as a purely linear arm. Given this asymmetry, an intensity dependent phase shift can be introduced between the two interferometric a...

A new approach to measure the refractive index of a given material, in its whole transparency window and within a single-shot, is proposed. This method, which requires the use of only few and common optical elements, is based on the analysis of the transmission function of a single etalon fabricated with the material under test, and can be used als...

The photorefractive effect induced by 775-nm laser light on doped lithium niobate crystals is investigated by the direct observation in the far field of the transmitted-beam distortion as a function of time. Measurements performed at various Zr-doping concentrations and different light intensities show that the 775-nm light beam induces a steady-st...

Here we report on a novel and fully-integrated biophotonic system exploiting a miniaturized fiber-based optical-tweezer to produce 3D-trapping of single cells. We also demonstrate its use for fluorescence and Raman measurements of single cells

3D finite difference time domain calculations are used to optimize the coupling between a single-mode telecom fibre and a silicon-on-oxide 2D-grating coupler. By simultaneously varying the hole-radius and grating-pitch of the photonic crystal array that makes up the active region of the coupler, the maximum in coupling efficiency is tuned to 1550nm...

Hydrogenated amorphous silicon (a-Si:H) is emerging as a promising new platform for silicon photonics. Low temperature required for its deposition provides an excellent compatibility with complementary metal-oxide-semiconductor (CMOS) processes. Besides, recent works have pointed out that a-Si:H exhibits an enhanced nonlinear efficiency that, combi...

Micro-ring resonators in silicon photonic circuits have been widely studied and implemented in systems for biosensing [1], telecommunications [2] and generation of photon pairs for quantum optics experiments [3]. The resonator Q-factor, defined by the roundtrip loss and coupling coefficient, is typically a static property of the device realised in...

Current frontier of cellular biology is the manipulation, analysis and sorting of single cells. Populations of cells in culture and in organisms, although considered nominally identical, often present some heterogeneity whose analysis may unravel the complexity of many biological phenomena [1]. Optical stretching is a powerful technique to study th...

In this paper, a comparison of the photorefractivity produced in Mg-doped and Zr-doped crystals as a function of the wavelength used to induce the photorefractive effect is shown.This paper shows very similar performances between Mg-doped and Zr-doped samples, even if some small differences in the wavelength dependence of photorefractivity appear,...

form only given. Silicon photonics is a well established platform for the development of fully integrated optical devices for optical communication systems. In particular, the strong modal confinement typical of silicon waveguides enables the exploitation of nonlinear effects with much lower optical power levels. Different structures for all-optica...

We investigate the applicability of highly reduced lithium niobate samples doped with iron for the use as optoelectronic tweezers. Increasing the reduction degree of Fe-doped lithium niobate is well known to increase the photoconductivity and reduce the writing time of internal space-charge fields. Based on our measurements of the photorefractive p...

Optofluidic microsystems are key components towards lab-on-a-chip devices for manipulation and analysis of biological specimens. In particular, the integration of optical tweezers (OT) in these devices allows stable sample trapping, while making available mechanical, chemical and spectroscopic analyses.

Supplementary Video S2

Supplementary Video S1

We present novel miniaturized optical tweezers fabricated by two photon lithography on optical fibers. The integration of micro-tweezers in a microfluidic chip allows 3D trapping and spectroscopic analysis at a single cell level

We present a new class of integrated optical devices, fabricated by femtosecond laser micromachining, that allows for mechanical probing, fluorescence detection and sorting of single cells by means of optical forces inside a microfluidic chip.

We present the characterization of the ultrafast nonlinear dynamics of a CMOS-compatible horizontal-slot waveguide with silicon nanocrystals. Results are compared to strip silicon waveguides, and modeled with nonlinear split-step calculations. The extracted parameters show that the slot waveguide has weaker carrier effects and better nonlinear figu...

The combination of high power laser beams with microfluidic delivery of cells is at the heart of high-throughput, single-cell analysis and disease diagnosis with an optical stretcher. So far, the challenges arising from this combination have been addressed by externally aligning optical fibres with microfluidic glass capillaries, which has a limite...

The main trend in optofluidics is currently towards full integration of the devices, thus improving automation, compactness and portability. In this respect femtosecond laser microfabrication is a very powerful technology given its capability of producing both optical waveguides and microfluidic channels. The current challenge in biology is the pos...

We describe a wavelength conversion experiment (generation of a pulse at the wavelength λp - Δλ from a signal at λp+Δλ under the action of a pump at λp) performed through cascaded second-order process in a lithium niobate channel waveguide. With a 58-mm-long Ti diffused channel waveguide, λp=1.1 μm (the wavelength of phase matching for the first st...

The carrier lifetime in SiGe planar waveguides with Si cladding was measured with a pump-and-probe technique, using an ultrashort 810 nm laser pulse and a CW 1.55 μm probe, as a function of layer thickness d and Ge concentration x. The measured lifetimes are in the range of 20-90 ns. The obtained interface recombination velocity S is a growing func...

Le fibre ottiche sono guide d’onda dielettriche nelle quali un fascio di luce si propaga con basse perdite senza allargarsi per diffrazione. Le fibre ottiche maggiormente diffuse sono realizzate in vetro e trasmettono in modo molto efficiente la radiazione nella regione dell’infrarosso in cui il coefficiente di attenuazione mostra il valore minimo....

In questo capitolo vengono descritte le tecniche di modulazione di segnali luminosi. Modulare un’onda elettromagnetica significa introduire una variazione di ampiezza (o di fase o di stato di polarizzazione) che segua l’andamento di un campo esterno. Ad esempio, nel caso delle comunicazioni ottiche, il campo esterno è una sequenza temporale di impu...

Le applicazioni del laser si possono dividere in tre categorie principali: a) applicazioni alle tecnologie dell’informazione e delle comunicazioni (“Information and Communication Technology”, ICT), che comprendono le comunicazioni ottiche, le memorie ottiche, le stampanti laser, e l’elaborazione ottica dei dati; b) strumentazione diagnostica e sens...