We investigate the combined effect of the diffraction-caused crosstalk noise (DCCN) and the stray-light crosstalk noise
(SLCN) on the performance of FSOI system. A numerical simulator was employed in this study to investigate OI
channel design. We determine that there exists an optimal focal length, which maximises the signal-to-noise ratio (SNR)
by minimising the combined effects of DCCN and SLCN. For the fundamental mode, the optimal focal length is
approximately 750 &mgr;m for both LG01 and LG10 modes, the optimal focal length occurs between f = 650 &mgr;m and f =
700 &mgr;m, depending on the interconnection distance and array pitch.
We investigate the effect of transmitter and receiver array configurations on the stray-light and diffraction-caused crosstalk in free-space optical interconnects. The optical system simulation software (Code V) is used to simulate both the stray-light and diffraction-caused crosstalk. Experimentally measured, spectrally-resolved, near-field images of VCSEL higher order modes were used as extended sources in our simulation model. Our results show that by changing the square lattice geometry to a hexagonal configuration, we obtain the reduction in the stray-light crosstalk of up to 9 dB
and an overall signal-to-noise ratio improvement of 3 dB.
In this paper we investigate for the first time the effect of the crosstalk introduced due to laser beam imaging in a free-space optical interconnect (FSOI) system. Due to the overfill of the transmitter microlens array by the vertical cavity surface emitting laser (VCSEL) beam, one part of the signal is imaged by the adjacent microlens to another channel, possibly far from the intended one. Even though this causes increase in interchannel and intersymbol interference, to our knowledge this issue has been neglected so far. The numerical simulation has been performed using a combination of exact ray tracing and the beam propagation methods. The results show that some characteristics of stray-light crosstalk are similar to that of diffraction-caused crosstalk, where it is strongly dependent on the fill factor of the microlens, array pitch, and the channel density of the system. Despite the similarities, the stray-light crosstalk does not affect by an increase in the interconnection distance. As simulation models for optical crosstalk are numerically intensive, we propose here a crosstalk behavioral model as a useful tool for optimization and design of FSOIs. We show that this simple model compares favorably with the numerical simulation models.