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 different modes can be used to increase the fiber optic capacity, but also to introduce novel intermodal interactions, as well as allowing for complex manipulation of optical modes for a variety of applications. In this roadmap we would like to give to the readers a comprehensive overview of the most recent developments in the field, presenting contributions coming from different research topics, including optical fiber technologies, integrated optics, basic physics and telecommunications.

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 induced in a photoconductive layer by means of light-driven phenomena. In this paper we report, and compare with the experimental data, the results obtained by analyzing the spatial configurations of the DEP-forces produced by a 532 nm laser beam, with Gaussian intensity distribution, impinging on a Fe-doped Lithium Niobate substrate. Furthermore, we also present a promising preliminary result for water-droplets trapping, which could open the way to the application of this technique to biological samples manipulation.

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, most low-loss filters have only been demonstrated by exploiting ad hoc lithographic and etching techniques, which are not compatible with the standard CMOS (complementary metal-oxide semiconductor) process-flow available at Si-photonic foundries. In this paper, we describe the design and optimization of optical micro-resonators, based on Si-waveguides with a height lower than the standard ones (i.e., less than 220 nm), prepared on SOI (silicon on insulator) platform, which allow the realization of high-performance optical filters with an insertion loss lower than 1 dB, using only previously validated lithographic etch-depths.

The carrier lifetime in ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ planar waveguides with Si cladding was measured as a function of layer thickness $d$ and Ge concentration $x$ by using an optical pump-and-probe technique. The measured lifetimes are in the range of $20–90\mathrm{ns}$ . The obtained interface recombination velocity $S$ increases with both $d$ and $x$ , taking values in the range from $300\text{to}4000\mathrm{cm}∕\mathrm{s}$ .

Wavelength conversion in the transmission of a message masked by optical chaos is experimentally demonstrated. In our setup, chaos is generated by a distributed-feedback laser subject to delayed optical feedback, and hides a message by additive chaos masking. The optical wavelength is converted, along the transmission line, by four-wave mixing in a semiconductor optical amplifier. At the receiver, the message is extracted by master-slave synchronization. Our experiments demonstrate that secure communications based on chaos are compatible with channel switching as required in reconfigurable optical networks.