# Photonic Integrated Circuits for NGPON2 ONU Transceivers (Invited)
## 5 Conclusions  
PICs are a promising technology with great potential in several fields including telecom, sensing, and bio-photonics. In this work, we have reviewed the PON technology standards and evaluated the challenges and benefits of meeting its requirements with the prospective usage of PIC. Depending on the requirements, the type of materials, and components, a tailored approach has to be carefully specified. The different materials used in the available solutions for implementing PIC result in different behaviors, steps, processes, and capabilities. The main constraint of PIC is still the limited gain band of the active devices which are in its core. This may imply advanced processing and/or packaging  
Figure 9: Representation of average price evolution of PON technology for GPON, XGSPON, and NGPON2 bulk type BOSA (not PIC based). Pricing was empirically collected along the years from several providers and averaged in the graph.  
techniques to be able to cope with the existing standards, e.g., regrowth and hybrid packaging. After carefully choosing the standard to be followed and the packaging approach, its control complexity also has to be cautiously considered to guarantee that the solution is feasible and adapted. Specifically, for PON the most stringent requirements are the cost and robustness of the proposed solution. We have discussed several of the challenges to be considered when equating the introduction of PIC in the next-generation PONs, like productization, wideband wavelength range (O, C, and L-bands), laser control, and tunability mechanisms.  
PON standards have different flavors that result in quite different requirements, especially regarding the wavelength ranges to be covered by the two traffic directions, i.e., the upstream and downstream. For instance, GPON and XGSPON have specifications of \(>\)200 nm spacing between upstream and downstream, while NGPON2 requires around 60 nm for the same parameter. Due to technological inherent limitations of some technologies, hybrid integration may be required, e.g., XGSPON and GPON. Smaller bands will ease this process and therefore potentiate monolithic PIC implementation, simplifying packaging and deployment, e.g., NGPON2.  
PICs have typically two major interfaces, electrical and optical, each with different requirements, techniques, and available materials to be used. Packaging and technical considerations such as size, power, RF compliance, and sealing are relevant. In a nutshell, the manufacturability is anticipated to be one of the most critical steps for the technology to be successful, especially in PON.  
In our vision, the use of PICs in PON and other subsystems is very close to being an effective reality with prospective advantages.  
This is a review paper, each author contributed to all chapters. C.P. and A.T. prepared the manuscript, i.e., writing, review and editing. All authors have read and agreed to the published version of the manuscript.  
This work is supported by the European Regional Development Fund (FEDER), through the Competitiveness and Internationalization Operational Programme (COMPETE 2020) of the Portugal 2020 framework [Project Virtual Fiber Box with Nr. 033910 (POCI-01-0247-FEDER-033910)]; plugPON (POCI-01-0247-FEDER-047221); FEDER through the Regional Operational Programme of Centre (CENTRO 2020) of the Portugal 2020 framework [Project HeatIT with Nr. 017942 (CENTRO-01-0247-FEDER-017942)]; and IT (UID/EEA/50008/2019).  
The authors declare no conflict of interest.