Quantum key distribution (QKD) promises unconditional security based on quantum mechanics principles. Fiber-based and free space-based QKD systems have been implemented, but the chip-based implementation of QKD systems is essential for large-scale deployment of QKD systems. Silicon pho-tonics technology platform is a potential candidate for on-chip QKD because of its advantages, such as being a low-cost CMOS-compatible fabrication process, robust, and compactness. Proof of concept on-chip QKD has already been implemented using polarization encoding and time-bin encoding in the silicon photonics platform. Time-bin encoding is preferred because polarization encoding suffers from birefringence in fiber optics communication systems. One of the essential components in the time-bin encoding QKD system is the delay line interferometer (DLI). The desired long waveguide delay line can be implemented in a compact spiral architecture. However, fabrication imperfection leads to unpredictable delay outcomes. Thermal optic tuning of long waveguide delay line is found to be an inefficient solution for this remedy. Therefore, a plenty of scope is there for the design and demonstration of tunable delay lines by integrating thermo-optically/electro-optically actuated resonant/non-resonant silicon photonic components.In this talk, we will discuss various configurations of on-chip delay line devices and their merits/demerits. We will also present the design, fabrication, and characterization of passive spiral waveguides and their time delay measurements.