Detecting WDM visible light signals by a single multi-color photodiode with MIMO processing.

For the first time, to the best of our knowledge, we experimentally demonstrate that multiple-input-multiple-output (MIMO) processing allows using a single photodiode to detect simultaneously a wavelength-division multiplexing (WDM) visible light communications (VLC) signal. The photodiode has a triple junction, and when it is illuminated by a WDM signal, the junctions produce inherently three photocurrents that are unusable for detecting any of the WDM signals. However, by means of linear MIMO processing, we are able to recover the transmitted signals exactly. Bit error rate measurements confirm the effectiveness of the proposed solution. This opens a new scenario for practical WDM-VLC systems.

Electrical filter-based and low-complexity DPSK coherent optical receiver.

Direct-detection of differential phase shifted keying (DPSK) optical signals is implemented either by ad hoc optical filtering or one-bit delayed optical interferometers. We show a coherent receiver where the filtering is performed in the electrical domain after down-converting the incoming signal to the baseband or to an intermediate frequency. This can be particularly advantageous whenever optical filters cannot be used or when extremely narrow filtering (sub-GHz) would be required [for example ultra-dense wavelength division multiplexing (WDM) passive optical networks]. Electrical filters can be realized more accurately than their optical counterpart. In addition, in a coherent receiver, this operation is colorless and avoids digital signal processing. We show experimentally this reduced complexity receiver and compare it with the classical one based on the delay and multiply block.

System feasibility of using stimulated Brillouin scattering in self coherent detection schemes.

We demonstrate the first self-coherent detection of 10 Gbit/s BPSK signals based on narrow-band amplification of the optical carrier by means of Stimulated Brillouin effect in a common fiber. We found that this technique is very effective only if it is combined with proper line coding and high-pass electrical filtering at the receiver. In this case we obtain OSNR-performance close to the ideal coherent receiver.

A 80 km reach fully passive WDM-PON based on reflective ONUs.

We propose a novel line coding combination (Inverse RZ coding in downlink and RZ in uplink) that extends the reach of WDM Passive Optical Networks based on Reflective SOAs with no in-line amplification. We achieved full downstream remodulation even when feeding the reflective SOA with power levels as low as -35 dBm, thus increasing the system power budget. We experimentally assessed this scheme for a fully passive, full-duplex and symmetrical 1.25 Gb/s WDM-PON over a 80 km G.652 feeder.