Showing papers by "Giuseppe Coppola published in 2012"

Critically coupled silicon Fabry-Perot photodetectors based on the internal photoemission effect at 1550 nm

Abstract: In this paper, design, fabrication and characterization of an all-silicon photodetector (PD) at 1550 nm, have been reported. Our device is a surface-illuminated PD constituted by a Fabry-Perot microcavity incorporating a Cu/p-Si Schottky diode. Its absorption mechanism, based on the internal photoemission effect (IPE), has been enhanced by critical coupling condition. Our experimental findings prove a peak responsivity of 0.063 mA/W, which is the highest value obtained in a surface-illuminated IPE-based Si PD around 1550 nm. Finally, device capacitance measurements have been carried out demonstrating a capacitance < 5 pF which has the potential for GHz operation subject to a reduction of the series resistance of the ohmic contact.

Shedding Light on Diatom Photonics by means of Digital Holography

Abstract: Diatoms are among the dominant phytoplankters in the worl's ocean, and their external silica investments, resembling artificial photonics crystal, are expected to play an active role in light manipulation. Digital holography allowed studying the interaction with light of Coscinodiscus wailesii cell wall reconstructing the light confinement inside the cell cytoplasm, condition that is hardly accessible via standard microscopy. The full characterization of the propagated beam, in terms of quantitative phase and intensity, removed a long-standing ambiguity about the origin of the light. The data were discussed in the light of living cell behavior in response to their environment.

A 2.5 ns switching time MachZehnder modulator in as-deposited a-Si:H.

Abstract: A very simple and fast Mach­Zehnder electro-optic modulator based on a p-i-n configuration, operating at λ = 1.55 μm, has been fabricated at 170°C using the low cost technology of hydrogenated amorphous silicon (a-Si:H). In spite of the device simplicity, refractive index modulation was achieved through the free carrier dispersion effect resulting in characteristic rise and fall times of ~2.5 ns. By reverse biasing the p-i-n device, the voltage-length product was estimated to be Vπ∙Lπ = 40 V⋅cm both from static and dynamic measurements. Such bandwidth performance in as-deposited a-Si:H demonstrates the potential of this material for the fabrication of fast active photonic devices integrated on standard microelectronic substrates.

Digital holographic microscopy characterization of superdirective beam by metamaterial

Abstract: Digital holographic microscopy (DHM) has been successfully applied for the first time to characterize the radiative out-of-plane emission properties of a superdirective device. Complementarily to near-field microscopy, DHM allows us to reconstruct the beam in the far-field region. The angular dispersion of the light beam radiated from a grating composed of air and anti-air metamaterial has been determined, and the proposed technique has highlighted a collimation degree higher than 0.04°, as already evaluated in a previous work. Further considerations on the retrieved phase map of the beam in the acquisition plane are presented.

Near-Infrared All-Silicon Photodetectors

Abstract: We report the fabrication and characterization of all-silicon photodetectors at 1550 nm based on the internal photoemission effect. We investigated two types of structures: bulk and integrated devices. The former are constituted by a Fabry-Perot microcavity incorporating a Schottky diode, and their performance in terms of responsivity, free spectral range, and finesse was experimentally calculated in order to prove an enhancement in responsivity due to the cavity effect. Results show a responsivity peak of about 0.01 mA/W at 1550 nm with a reverse bias of 100 mV. The latter are constituted by a Schottky junction placed transversally to the optical field confined into the waveguide. Preliminary results show a responsivity of about 0.1 mA/W at 1550 nm with a reverse bias of 1 V and an efficient behaviour in both C and L bands. Finally, an estimation of bandwidth for GHz range is deduced for both devices. The technological steps utilized to fabricate the devices allow an efficiently monolithic integration with complementary metal-oxide semiconductor (CMOS) compatible structures.

CMOS-compatible electro-optical Mach-Zehnder modulator based on the amorphous silicon technology

Abstract: The realization of on-chip optical interconnects requires the integration of active micro-optical devices with microelectronics. However, it is not clear yet how silicon photonics could be integrated within CMOS chips. In this context the non-crystalline forms of silicon, such as laser-annealed polycrystalline and hydrogenated amorphous silicon (a-Si:H), can deserve some advantages as they can be included almost harmlessly everywhere in a CMOS typical run-sheet, yielding low-cost and flexible fabrication. In particular, a-Si:H can be deposited using the CMOS-compatible low temperature plasma enhanced chemical vapour deposition (PECVD) technique, which brings clear advantages particularly for a back-end photonic integrated circuit (PIC) integration. However, till now a-Si:H has been mainly considered for the objective of passive optical elements within a photonic layer at λ=1.55 μm. Only a small number of examples have been reported, in fact, on waveguide integrated active devices. In this paper we detail about an effective refractive index variation obtained through an electrically induced carrier depletion in an as-deposited a-Si:H-based p-i-n waveguiding device. For this device switch-on and switch-off times of ~2 ns were measured allowing a modulation rate higher than 150 MHz.yy