A. Di Donato

Calibration Protocol for Broadband Near-Field Microwave Microscopy

In this paper, we describe how to define and build a set of known loads to be used in near-field microwave microscopy. Such loads are necessary to set up a microwave calibration kit, enabling local quantitative measurements by the microscope. The proposed protocol is validated through the microscopy system we have recently developed that combines a scanning tunneling microscope and a 70-GHz vector network analyzer.

High Resolution Scanning Microwave Microscopy for Applications in Liquid Environment

In this work, we demonstrate a hybrid scanning tunneling microscope/near field scanning microwave microscope featuring nanometric resolution in liquid environment. The system performs an ultra-broadband microwave analysis, since the frequency is swept (up to 50 GHz) for each spatial point of the sample under measurement. A conversion in time-domain allows to disentangle near-field and far-field probe-sample interactions. Results are reported for highly oriented pyrolitic graphite immersed in water, and demonstrate microwave nanometric resolution in spite of the presence of the losses induced by the aqueous environment.

Full-wave analysis of photonic bandgap integrated optical components by the TLM-IE method

This paper presents the full-wave analysis of commonly encountered optical periodic structures by the novel transmission-line matrix/integral equation (TLM-IE) method. The TLM-IE is a three-dimensional full-wave hybrid technique that combines the advantages of the numerical TLM method in dense finite regions and those of the IE method in open regions where simple Green functions are available. The pre- and postprocessing tools of the TLM-IE solver provide visualization and physical insight into the dynamics of electromagnetic propagation in such devices. The aim of this effort is twofold: 1) to analyze the diffraction and reflection characteristics of photonic bandgap gratings and 2) to define optimization guidelines for the Q factor of integrated dielectric resonators.

Investigation of Fullerene Exposure of Breast Cancer Cells by Time-Gated Scanning Microwave Microscopy

Nanoparticles are receiving increasing attention as carriers of active drugs or biochemical signals. Among them, fullerene C60 is particularly attractive since its cage structure helps it to carry other molecules and its lipophilicity helps it to penetrate through a cell membrane. This paper explores the potential of time-gated broadband near-field scanning microwave microscopy for detecting fullerene inside Michigan Cancer Foundation-7 breast cancer cells. It demonstrates measurement of relative variation of electromagnetic properties across the sample surface, while explaining the difficulty for measurement of absolute electromagnetic properties. The results are compared with scanning capacitance microscopy, atomic force microscopy, and scanning tunneling microscopy performed on the same samples.

Infrared Imaging of Fixed-Cells through Micro-Cavity Fiber Optic Scanning Microscopy

Noninvasive, lens-free microscopy methods helps biologists to measure quantitative contrast phase imaging without damaging the cells. An extrinsic scanning micro-cavity in optical fiber is proposed to achieve surface imaging at infrared wavelengths. The micro-cavity is realized by approaching a single mode fiber with a numerical aperture NA to a sample and it is fed by a low-coherence source. The measurement of the reflected optical intensity provides a map of the sample reflectivity, whereas from the analysis of the reflected spectrum in the time/spatial domain, we disentangle the topography and contrast phase information. The latter describes the contrast variation of the reflected spectrum from the cavity due to changes in topography and surface refractive index. The interference of diffracted waves defines the transverse field behavior of the electromagnetic field inside the micro-cavity, affecting in this way the transverse resolution, that is not defined by the numerical aperture NA of the fiber and consequently by the conventional Rayleigh limit (about 0.6λ/NA). The resolution in the normal direction is limited mainly by the source bandwidth and demodulation algorithm. The system shows a compact and simple architecture.

Quantitative endoscopy by FOLCI-based distance sensor

In medical endoscopy, quantifying anatomical dimensions would be of great help, but the appropriate tools are not yet available. We present a novel method for the calibration and size measurement of endoscopic images. We realized an optical sensor, based on Fiber Optic Low Coherence Interferometry (FOLCI), capable of measuring the absolute distance between the tip of an endoscopic probe and an anatomical object under inspection. We showed that this sensor provides very sensitive and accurate (error lower than 0.1 mm) measurements of biological samples. The sensing fiber of the sensor was introduced in the operative channel of an Olympus rhinoscope. After calibrating the endoscope magnification system as a function of the distance, our system was capable of providing the size of any object included in the field of view of the endoscope. Tests performed on planar targets and pig trachea showed the accuracy of the system to be adequate for allowing quantitative dimensional information.

Structured beam diffraction

We report on the observation of a modulated pattern induced by a single laser beam in a polymeric film. In spite of the simple geometrical configuration, the analysis of the far field diffraction pattern allows a sensitive retrieving of the wavelength of the recording beam and of its incidence angle, pointing out the high information content of the recorded spot. A theoretical model is presented which satisfactorily explains the observed behavior. It takes into account the interaction of structured light with structured matter with the same symmetries and spatial modulation frequencies close to each other. This result shows a feature of the interaction between structured light and structured matter which has not been explored yet.

Synthetic holography based on scanning microcavity

Synthetic optical holography (SOH) is an imaging technique, introduced in scanning microscopy to record amplitude and phase of a scattered field from a sample. In this paper, it is described a novel implementation of SOH through a lens-free low-coherence system, based on a scanning optical microcavity. This technique combines the low-coherence properties of the source with the mutual interference of scattered waves and the resonant behavior of a micro-cavity, in order to realize a high sensitive imaging system. Micro-cavity is compact and realized by approaching a cleaved optical fiber to the sample. The scanning system works in an open-loop configuration without the need for a reference wave, usually required in interferometric systems. Measurements were performed over calibration samples and a lateral resolution of about 1 μm is achieved by means of an optical fiber with a Numerical Aperture (NA) equal to 0.1 and a Mode Field Diameter (MDF) of 5.6 μm.

Analytical study of the optical spectrum shift in a modulating channel

In this work, an analytical model of the frequency shift experienced by an optical signal passing through a traveling wave modulating channel is derived. The model starts from the well-known coupled-mode theory but holds for an arbitrary temporal envelope of the optical signal and for any time dependence of the slowly varying modulating field; it provides an analytical and accurate explanation of various effects such as those due to losses or microwave-optical group velocity mismatch. The practical example of a modulated optical Gaussian pulse is provided.

Parasitic Coupling Effects in Multimode Buried Channel Waveguides Arrays for O-PCB Interconnects

The use of buried channel waveguides in optical printed circuits boards (O-PCB) offers the possibility of overcoming some problems and limitations encountered in high-frequency electrical interconnects. Although the use of optical waveguides reduces significantly crosstalk and electromagnetic interferences, parasitic coupling effects between the buried channels may appear when waveguide arrays are realized. In this paper, we analyze theoretically and experimentally the conditions inducing crosstalk effects in a multimode array, realized by means of a conventional photolithographic patterning technique. In particular, the results show how the common configuration used to pattern an array of optical waveguides produces a parasitic slab waveguide close to the core channels, accounting for a substantial increase of the coupling effects.