Davide Piccinin

1550-nm volume holography for optical communication devices

The two-lambda method can provide a strategic approach to implement all-optical devices for communication wavelength division multiplexing (WDM) signal processing based on volume holography. By writing holograms at 488 nm in LiNbO/sub 3/:Fe and reading them in the third window of optical communication systems (1550 nm), the feasibility of WDM demultiplexers and holographic memories for digital bytes is here demonstrated.

All-optical free-space processing for optical communication signals

All-optical free-space architecture can find many interesting applications in optical communications in case of packet-oriented data processing. An example of an all-optical system able to perform data processing operations is described and experimented. Logic schemes characterized by high modularity and flexibility are reported. An optical implementation is proposed by using an elementary switching unit realized with CdTe:In crystal. The unit is optically controlled and operates with beams at typical communication wavelengths. Preliminary experimentation in ns regime at 1550 nm is shown.

All-optical pattern recognition for digital real-time information processing

To recognize digital streams of digital data, all-optical and passive techniques able to discriminate optical bit words in real time are presented. Discrimination capability of different correlators, both in free space architectures and in delay lines structures, is theoretically and experimentally analyzed. Experimental performances in word recognition are shown in the case of a volume holographic correlator, in the case of a lithographic phase-only-filter correlator, and in the case of a novel coherent delay lines correlator operating at the wavelength 1550 nm and at the bit rate of 2.5 Gbit/s.

Diffraction of optical communication Gaussian beams by volume gratings: comparison of simulations and experimental results

The diffraction effects induced by a thick holographic grating on the propagation of a finite Gaussian beam are theoretically analyzed by means of the coupled-wave theory and the beam propagation method. Distortion of the transmitted and diffracted beams is simulated as a function of the grating parameters. Theoretical results are verified by experimentation realized by use of LiNbO3 volume gratings read out by a 1550-nm Gaussian beam, typical of optical fiber communications. This analysis can be implemented as a useful tool to aid with the design of volume grating-based devices employed in optical communications.

Fabrication of Optical Wave-Guides in Silica-on-Silicon by Nickel Electroplating and Conventional Reactive Ion Etching

A novel process for the fabrication of deep optical waveguides in silica-on-silicon for optical processing applications has been developed. It makes use of nickel electroplating to conform precisely e-beam written smooth curved structures and to use the deposited nickel to etch deeply (up to 8 µm) into silica layers. It is demonstrated that nickel plating offers substantial advantages in terms of resistance and resist mold fidelity than more conventional etch masks such as patterned metal layers. The etching process, that is based on conventional fluorine reactive ion etching, has been optimized by making use of a design of experiment technique, details of process optimization and comparative analysis of different etching mask performances are also given.

Polarization-independent bidirectional optical switch for communication signals

A 2 X 2 optical switch performing bidirectional cross-bar on optical communication signals at 1550 nm is presented and experimented. The switch is based on electro-optic effect in bulk CdTe crystals. Operation is totally independent by input state of polarization of the optical beams to be addressed. The proposed free-space architecture grants high compactness, reliability and fast response time compared with common switching solutions.

Programmable fiber Bragg gratings for spectral CDMA

Summary form only given.The employment of optical code-division multiple-access (OCDMA) offers high advantages in allocating bandwidth for bursty access networks, where wide bandwidth services are required. Many different optical CDMA implementations have been proposed. Spectral slicing appears an attractive technique because spectral data encoding provides a large number of simultaneous users and transparency to data format and bit-rate. CDMA realized by using a cascade of fiber Bragg gratings (FBGs) allows to combine all the advantages of spectral encoding with the compactness and robustness of a totally guiding structure without free-space architectures losses. In this paper we experiment on FBG technology in order to realize spectral CDMA with programmable encoding. The cascade of 8 FBGs is used in encoding/decoding operation: each grating can be tuned independently by means of piezoelectric elements in order to program the desired user code.

Sputtered tellurite glass thin films for planar optical devices

Tellurium oxide is a promising optical material, conjugating transparency in the infrared with high refractive index, low chromatic dispersion with strong nonlinear response, elevated acousto-optic figure of merit and rare earth doping capability. Reactive sputtering is a suitable technique to obtain thin films of pure TeO2 glass, with tunable stoichiometry, without the need for added components to help vitrification. We report on the growth of tellurite thin films, on the linear and non-linear optical characterization and on the process technology to implement high-contrast planar optics.

1550 nm Volume Holographic Devices for Optical Communication Networks

The present contribution aims to show the feasibility of LiNbO3:Fe volume holography (VH)-based devices for optical fiber communication networks. The VH technique offers a valid alternative to the existing approaches in the building of multiplexers/demultiplexers and databases for individual wavelengths inside an optical wavelength division multiplexing (WDM) system. The use of angle multiplexing jointly with the two-lambda method and the thermal post-fixing technique allow us to achieve efficient and long-lifetime operation in the near-infrared spectral range. Optical fiber communications are rapidly growing in traffic owing to many new important services such as mobile telephony and Internet connections. Increasing capacity demand calls for more transmission bandwidth and higher bit rates. In order to exploit the entire spectrum of the low-loss regions of the fiber attenuation window, Wavelength Division Multiplexing (WDM) transmission mode is today in common use. WDM technology combines multiple optical signals into a single fiber by transmitting each signal on a different wavelength (as happens in the radio spectrum). This means that telecom carriers can multiply the capacity of their fibers without the expensive investment of laying more fiber underground and undersea.

Heteroepitaxial sputtered Ge on Si (100): Nanostructure and interface morphology

Epitaxial growth of Ge thin films onto (100) silicon by DC-Pulsed Magnetron Sputtering was realized and proved by X-ray and electron diffraction. Transmission and high-resolution electron microscopy across the interface region directly confirmed a high degree of epitaxy and show that planar defects and threading dislocations are the relevant lattice imperfections. Electron microscopy shows that a post-deposition rapid thermal annealing process, up to 673 K, is effective to defect annihilation. The films grow single crystalline, slightly misoriented, below 0.1 degrees. A weak roughness around 0.6 nm, was measured both at the Ge-Si interface and at the film surface. The Ge films grown onto n-type Si show the rectifying electrical behaviour typical of p-type semiconductors.