Resonance control of a silicon micro-ring resonator modulator under high-speed operation using the intrinsic defect-mediated photocurrent

Overlaying 5G radio access networks on wavelength division multiplexed optical access networks with carrier distribution

As 5G communication matures, the requirement for advanced radio access networks (RAN) drives the evolution of optical access networks to support these needs. Basic RAN functions, mobile front-haul to the backbone and interconnected front-end remote radio units, must support and enable data rate surges, low-latency applications, RF coordination, etc. Wavelength division multiplexed optical access networks (WDM-OANs) provide sufficient network capacity to support the addition of RAN services, especially in unused portions of WDM. We propose and demonstrate a method for RAN overlay in WDM-OANs that employ distributed carriers. In such systems, the carrier is modulated at the central office for direct-detected downstream digital data services; later the same carrier is remodulated for the uplink. We propose the use of silicon photonics to intercept the downstream and add 5G signals. We examine the distributed-carrier power budget issues in this overlay scenario. The carrier power must be harvested for direct detection of both digital and RoF services, and yet hold in reserve sufficient power for the uplink remodulation of all services. We concentrate on the silicon photonics subsystem at the remote node to add RoF signals. We demonstrate the overlay with a fabricated chip and study strategic allocations of carrier power at the optical network units housing the radio units to support the overlay. After the successful drop and reception of both conventional WDM-OAN and the newly overlaid RoF signals, we demonstrate sufficient carrier power margin for the upstream remodulation.

Enhancing bulk defect-mediated absorption in silicon waveguides by doping compensation technique

Silicon waveguide photodiodes (SiWG PD) based on the bulk defect-mediated absorption (BDA) of sub-bandgap photons are suitable to realize in-line optical power monitors for silicon photonic integrated circuits. Deep-level states to enable the BDA can be induced by exploiting the ion implantation steps that are used to embed PN junctions for carrier-depletion-based modulators. This manner usually exhibits limited responsivities since relevant processing conditions are optimized for the modulation rather than the BDA. In this letter, we solve this issue with the doping compensation technique. This technique overlaps P-type and N-type implantation windows at the waveguide core. The responsivity is enhanced due to the increased density of lattice defects and the reduced density of free carriers in the compensated silicon. Influences of the dimension of the dopant compensation region on responsivity and operation speed are investigated. As the width of this region increases from 0 μm to 0.4 μm, the responsivity at -5 V is improved from 2 mA/W to 17.5 mA/W. This level is comparable to BDA based SiWG PDs relying on dedicated ion bombardments. On the other hand, a bit-error-rate test at 10 Gb/s suggests that the device with 0.2-μm-wide compensation region exhibits the highest sensitivity.