Rare-earth ion-doped crystals exhibit exceptionally narrow optical transitions at low temperatures (around 3K). These unique properties make them ideal for foundational quantum technology applications, including quantum memories, quantum sensors, and quantum-enabled signal processing architectures. Over the past decades, our team, in a long-standing collaboration with Thales Research & Technology and IRCP, has developed a number of state-of-the-art signal processing designs, including a spectral analyzer demonstrator at the industrial level and an agile photonic filter. Nevertheless, the development of cutting-edge architectures goes hand-in-hand with ongoing exploration of alternative materials, always with specific applications in mind. With this internship, we want to continue our exploration focusing on Tm:YGG and Er:YSO, in the perspective of optimizing our spectrum analyzer designs.