One technology for 5G wireless networks. In

One of the main possible applications of SP technology, as mentioned above, is it as enabling technology for 5G wireless networks. In this section I’m going to present a case study on its application as a transceiver between base station and the antennas in a communication network, based on the technology introduced in the previous section.?To achieve the goals of 5G mentioned in section 1 (increased bandwidth, low latency, faster bit transmission), there is a need of rethinking and reorganizing the radio access networks (RANs).

Since the number of connected devices is expected to increase hugely, radio-over-fiber links (RoF, i.e. light is modulated by a radio signal and transmitted over an optical fiber link) appear to be the solution: given the large number of required links, therefore, a cheap, scalable SP transceiver is needed. ?In Ref. 6, a III-V-on-silicon distributed feedback laser is used as a transmitter (fig. 17).

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The laser is built by an adhesive wafer bonding on a InP/AlGaInAs multi-quantum-well epitaxial stack to a integrated circuit based on silicon photonics. The silicon waveguides are 400 nm thick, 180 nm deep, and a DFG grating is defined in them, below the III-V gain material. Light is coupled from the gain section to the Si waveguide by a tapering in two steps, that minimizes reflections and guarantees no light losses due to coupling to higher order modes.

At the receiver side a high-bandwidth waveguide-couples Ge-on-Si photodetector (to translate the signal from optical to electrical) are used (fig. 18). More specifically, the RX is a 14 ?m Ge-on-Si waveguide-coupled avalanche photodetector on a SP integrated circuit, where the Germanium slab (400 nm thick and 1000 nm wide) is p-doped, built over a n-doped Silicon waveguide.

The receiver works in avalanche operation at low voltages, in order to improve the link gain without needing very high power.?These devices appear to be a scalable and a cost-effective solution for future mass usage. They have been tested for 1) a 64-QAM OFDM signal at 3.5 and 5 GHz and for 2) a 16 Gbps 16-QAM at 20 GHz data signal, showing both the feasibility of a high bit rate transmission with these devices, as well as good linear behavior and low noise level.?The bit-error rate (BER) for experiment n.2 has been found to be below 2.

5 · 10?8 and of 5 · 10?5 respectively with and without the presence of an equalizer. The received constellation is reported in fig. 19, along with an electrically transmitted back-to-back 4 GBd for comparison purpose.

The obtained results from the study show that the silicon photonics transceivers can be used to transmit a high complex-modulated data (as this is the case of a quadrature-to-amplitude modulation) of on a high frequency carrier. Is it then possible to operate at a frequency of about 28 GHz, that is the range of interest of fifth generation wireless networks.