We introduce a new III-V-on-Silicon (Si) heterogeneous integration platform, where the III-V material is bonded to the back of a processed Si photonic wafer. This "Back-Side-on-Buried Oxide" (BSoBOX) process is fully compatible with active, multilayer Si photonics platforms. This work describes the process flow and reports on O-band hybrid distributed feedback (DFB) lasers of various grating periods fabricated on this platform. A comprehensive set of measurements show that the quarter-wave shifted DFB lasers have comparable performance to front-side platforms. Single-mode emission with a side mode suppression ratio around 50 dB was measured between 20°C - 60°C. The DFB lasers had threshold currents as low as 32 mA and produced output powers in the Si waveguide from a single-end of about 15 mW at 170 mA before the devices began to mode hop. Output powers of ${\sim 20}$ mW were measured before the onset of thermal roll-off and operation up to 80°C was achieved. The characteristic temperatures and thermal impedance of the lasers were evaluated and future improvements are discussed.

The evolution beyond 5G towards 6G will accelerate the transformations begun by 5G to deploy new approaches to define delivery services. The network should be accessible anywhere, always-on and with the guarantee performances. This poses new challenges to the transport network that should assure available connectivity among the functions at different levels of granularity. The transport network should be so flexible to guarantee on-demand the connectivity among the processing functions that automatically will be required and, at the same time, should assure extreme performance. Optical network and Dense Wavelength Division Multiplexing technology are relevant candidates to match high bandwidth and low latency, but new challenges are required to assure the suitable cost and size for the wireless access networks. The current optical technology, suitable used in aggregation and long-haul transport network, cannot be simply downsized to be used in the access area, but novel paradigm should be considered for the optics as well. Integrated photonics seems a promising direction to realize low cost and low size optical components for the transport network. Moreover, this technology enables a certain level of remote tunability and reconfiguration of optical equipment that allow to simplify and reduce cost of installation in field and operation of the transport network. In this paper relevant optical components for transport networks are analyzed using the integrated photonics to assess the technology challenges.

5G and its evolution towards 6G is unlocking new use cases that will require the reconsideration of the existing network architectures and its operation. As the network will be required to support new service types and radio protocol splits, the traditional physical point to point connections will need to be replaced with a transport network up to the antenna site to guarantee low latency services and high bandwidth. Optical based transport is a key enabler to realize such a convergent network, where the traditional fixed infrastructure in use for mobile services and mobile infrastructure should also support enterprises services. The Software Defined Network (SDN) and Network Function Virtualization (NFV) technology plays a key role to evolve towards digitalization. It allows to simplify the creation of new services and to implement a real decoupling between the infrastructure and the network functions that run virtually, on generic processing units located everywhere in the network. Supporting automation is a key requirement that traditional optical technology is not able to meet. In this paper the reference scenarios for the access network are presented with the analysis of their requirements and the enabling optical solutions based on integrated silicon photonics.

We report on the performance of a silicon photonic integrated circuit for laser frequency chirping, developed for FMCW LIDAR applications. An external laser source is fiber coupled to the photonic circuit and frequency chirping is achieved with a silicon IQ modulator and a monolithically integrated III-V/Si semiconductor optical amplifier to compensate for IQ modulator losses. A chirp distortion of 1.8% over 5% to 95% of the chirp ramp period was measured with a delayed self-heterodyne interferometric method. The high chirp linearity of our circuit is confirmed by FMCW ranging measurements using 2-18 m long fiber delay lines. The resulting beat frequency follows a linear dependency with the fiber delay line length (R²=0.999).

We present a new platform integrating heterogeneous III-V/silicon gain devices at the backside of silicon-on-insulator wafers. The fabrication relies on commercial silicon photonic processes. The performances of lasers and SOAs fabricated accordingly are reported.

We demonstrate the first backside-processed hybrid silicon discrete mode laser. It operates in the O-band with a total waveguide-coupled output power >43 mW, 850 kHz linewidth, and a side mode suppression ratio of 60 dB.