## 1 Introduction  
Microwave photonics is key technology for the development of flexible radiofrequency (RF) payloads. Photonics technology offers critical advantages, such as enhanced system reconfigurability, reduced size, weight, and power consumption (SWaP), as well as increased bandwidth, all of which are essential for modern satellite applications [1, 2, 3]. Integrated microwave photonics (iMWP) further enhances these benefits by combining microwaves and photonic integration, enabling functions such as signal generation and processing directly on a photonic integrated circuit (PIC) to improve scalability, stability, and overall system cost efficiency, while offering even greater SWaP reductions [4]. Different photonic integration platforms supporting PIC design and fabrication have been developed, each offering standardized process design kits (PDKs). Among these platforms, it is worth highlighting thin-film lithium niobate (TFLN) [5, 6], indium phosphide (InP) [7, 8], and silicon nitride (Si\({}_{3}\)N\({}_{4}\)) [9, 10], as well as hybrid solutions such as InP/Si\({}_{3}\)N\({}_{4}\)[11, 12], providing a range of options for tailored iMWP implementations. In a photonic-based RF payload, the RF signal generation unit is a key module [1]. This unit is responsible for the generation and distribution of the local oscillator (LO) signal. To achieve RF signals over a broad frequency range, optical heterodyning is a commonly employed technique. This process involves mixing two optical wavelengths on a high-speed photodetector (HS-PD), which generates an RF beat signal at a frequency corresponding to the difference between the two wavelengths [13; 14; 15; 16; 17]. To date, the two main photonic integration platforms that have been used for optical heterodyne RF signal generation are monolithic InP and hybrid InP/Si\({}_{3}\)N\({}_{4}\). An example of a monolithic implementation, detailed in [14], utilizes an InP-based photonic integrated circuit for terahertz (THz) signal generation. This chip integrates two distributed feedback (DFB) lasers to generate electrical signals within the THz range. An experimental setup for THz transmission was also developed, featuring a transmitter based on a waveguide-integrated PIN photodiode and a receiver employing an InGaAs/InAlAs-based photoconductor. On the other hand, RF signal generation was recently demonstrated using a hybrid InP/Si\({}_{3}\)N\({}_{4}\) integrated circuit, highlighting the wide RF frequency tuning range, from 5 GHz to 155 GHz [17]. A key distinction between InP DFB lasers and hybrid InP/Si\({}_{3}\)N\({}_{4}\) lasers is their optical linewidth in free-running conditions. The DFB lasers have optical linewidths in the tens-of-MHz range, requiring the use of a stabilization scheme to reduce their optical linewidth [18], thereby lowering the electrical linewidth of the generated RF signal. In contrast, the signals generated by the InP/Si\({}_{3}\)N\({}_{4}\) dual-laser module presented in [17] showed an electrical linewidth of less than 150 kHz under free-running conditions, with a long-term drift of less than 12 MHz, without requiring phase-locking techniques. This improved performance is attributed to the low propagation losses (0.1 dB/cm) of the TriPlex(r) Sti\({}_{3}\)N\({}_{4}\) waveguides [19], which enable longer cavity lengths and high Q-factor resonators, resulting in narrower linewidths. Furthermore, lasers with intrinsic linewidths as narrow as 40 Hz have been successfully demonstrated on this platform [20]. In this paper, we report for the first time, to the best of our knowledge, the generation of dual local oscillator signals from a hybrid multi-laser module. This module serves as the core component of a photonic RF channel multiplexing/demultiplexing subsystem designed for flexible satellite payloads under the THORMUX (Tunable Photonic RF De-multiplexer for Broadband Satellites) project, funded by the European Space Agency (ESA).