-We analyse the effect of crosstalk noise on the performance of free space optical interconnects (FSOIs). In addition to "diffraction-caused" crosstalk, we consider the effect of "stray-light" crosstalk noise which, to the best of our knowledge, has not been addressed previously. Simulations were performed on a microlens based FSOI system using the modal composition and beam profiles experimentally extracted from a commercial Vertical-Cavity Surface-Emitting Laser. We demonstrate that this crosstalk noise introduces significant degradation to interconnect performance, particularly for multi-transverse mode laser sources. A simple behavioural model is also developed which accurately approximates the crosstalk noise for a range of optical sources and interconnect configurations.

Free-space optical interconnects (FSOIs), made up of dense arrays of vertical-cavity surface-emitting lasers, photodetectors and microlenses can be used for implementing high-speed and high-density communication links, and hence replace the inferior electrical interconnects. A major concern in the design of FSOIs is minimization of the optical channel cross talk arising from laser beam diffraction. In this article we introduce modifications to the mode expansion method of Tanaka et al. [IEEE Trans. Microwave Theory Tech. MTT-20, 749 (1972)] to make it an efficient tool for modelling and design of FSOIs in the presence of diffraction. We demonstrate that our modified mode expansion method has accuracy similar to the exact solution of the Huygens-Kirchhoff diffraction integral in cases of both weak and strong beam clipping, and that it is much more accurate than the existing approximations. The strength of the method is twofold: first, it is applicable in the region of pronounced diffraction (strong beam clipping) where all other approximations fail and, second, unlike the exact-solution method, it can be efficiently used for modelling diffraction on multiple apertures. These features make the mode expansion method useful for design and optimization of free-space architectures containing multiple optical elements inclusive of optical interconnects and optical clock distribution systems.

Single-phase Ba(Cd1∕3Ta2∕3)O3 powder was produced using conventional solid state reaction methods. Ba(Cd1∕3Ta2∕3)O3 ceramics with 2wt% ZnO as sintering additive sintered at 1550°C exhibited a dielectric constant of ∼32 and loss tangent of 5×10−5 at 2GHz. X-ray diffraction and thermogravimetric measurements were used to characterize the structural and thermodynamic properties of the material. Ab initio electronic structure calculations were used to give insight into the unusual properties of Ba(Cd1∕3Ta2∕3)O3, as well as a similar and more widely used material Ba(Zn1∕3Ta2∕3)O3. While both compounds have a hexagonal Bravais lattice, the P321 space group of Ba(Cd1∕3Ta2∕3)O3 is reduced from P3̱m1 of Ba(Zn1∕3Ta2∕3)O3 as a result of a distortion of oxygen away from the symmetric position between the Ta and Cd ions. Both of the compounds have a conduction band minimum and valence band maximum composed of mostly weakly itinerant Ta5d and Zn3d∕Cd4d levels, respectively. The covalent nature of the directional d-electron bonding in these high-Z oxides plays an important role in producing a more rigid lattice with higher melting points and enhanced phonon energies, and is suggested to play an important role in producing materials with a high dielectric constant and low microwave loss.

No abstract

The effect of transmitter and receiver array configurations on the performance of free-space optical interconnects (FSOIs) was investigated. Experimentally measured, spectrally resolved, near-field images of vertical-cavity surface-emitting laser (VCSEL) transverse modes were used as extended sources in our simulation model and combined with laser relative intensity noise and the receiver noise to determine the optimal array geometry. Our results demonstrate the importance of stray-light cross talk in both square and hexagonal configurations. By changing the array lattice geometry from square to hexagonal, we obtained an overall optical signal-to-noise ratio improvement of 3 dB. We demonstrated that the optical signal-to-noise ratio is optimal for the hexagonal channel arrangement regardless of the transverse mode structure of the VCSEL beam. We also determined the VCSEL drive current required for the best performance of the FSOI system.