Cryptography is the art of providing secure communication between different parties such that no unauthorized party has access to the content of the messages. Although cryptography is as old as communication itself, the strive for unconditionally secure and practical encryption algorithms is still open. In fact, the only classical cryptographic method whose security is proved is the so-called one-time-pad protocol, which requires secure distribution of long keys that cannot be used more than once. Quantum cryptography (quantum key distribution), whose security is guaranteed by the laws of quantum mechanics, can be used as a complement to the one-time-pad securely distribute the keys among authorized parties. Up-to-date, the most robust strategy for fiber-based implementation of quantum key distribution is time-bin encoding, where single-photon qubit states are encoded by the presence of photons in one of the two possible time slots, namely time-bins, or a superposition of these two states. The functioning of protocols based on time-bin encoding generally relies on ultra-stable interferometric measurements in unbalanced Mach-Zehnder interferometers. This interferometric stability can be easily achieved by integrated photonic circuits. However, state analysis at the receiver can be jeopardized by the inherent birefringence of integrated optical platforms. Therefore, femtosecond laser micromachining that realizes waveguides with low values of birefringence, as well as enabling the fabrication of low-loss devices with 3D structures, is considered a promising technology for prototyping quantum photonic circuits. In this work, we designed and …