Photonic Integrated Local Oscillator Signal Generation for Satellite Communications

Recently, satellite telecommunications have experienced the necessity to dramatically increase their transmission capacity to tackle with the demand for higher mobile network data rates. An increase of the capacity is often associated with an increase in size, mass, and power consumption, commonly known as SWaP. Low SWaP requirements are especially critical for novel Very High Throughput Satellites (VHTS), where new technologies are required to increase the capacity and flexibility of the communication payloads. Microwave Photonics (MWP) has arisen as a promising technique to overcome this challenge, and specifically the Integrated Microwave Photonics (iMWP) technology. iMWP enables handling of wider bandwidths as well as increasing the system agility while maintaining a low SWaP by making use of a photonic integrated approach. Photonic integration enables a significant improvement in terms of SWaP because of a reduced footprint while maintaining the quality of the RF signals generated. MWP enable radiofrequency (RF) local oscillator (LO) signal generation, using tunable lasers, that range from a few MHz up to the THz range, which is far beyond the specs of conventional RF-based LO generators. However, the main disadvantage of this approach is when the integrated lasers operate under the free-running condition, resulting in a large phase noise of the beat note and a long-term drift of the generated signal. In this paper we analyze the suitability of the most important photonic integration platforms, including monolithic InP, hybrid InP/Polymer and hybrid $\operatorname{InP} / \mathrm{Si}_{3} \mathrm{~N}_{4}$, to be used for LO signal generation. We will present some of the most relevant results focusing on the RF carrier generation and stability of the generated signals as well as ways to mitigate the drift and improve the performance.