Towsif Taher

We report the fabrication and characterization of 28-pixel P-SNSPD, reaching 88% system detection efficiency (SDE) at the single photon level. The detector is able to detect single-photon events at 250 Mcps with 50% nominal SDE, using only a single coaxial read-out cable, and maintains a timing jitter below 80 ps until 200 Mcps. Moreover,we achieve 1 Gcps detection rates by using only 4 P-SNSPD detectors and an 1:4 commercially available optical splitter Finally, we show how the P-SNSPD architecture allows us to maintain a very low jitter even at the high detection rates. We finally analyze the PNR capability of the array and measure efficiencies of 75% at 2-photon and 60% at 3-photon at 1550nm.

Phase randomization is essential for the security of practical quantum key distribution (QKD) systems. Commonly, implementations rely on laser sources (either actively phase-randomized, or gain-switched). However, at high repetition rates these show correlations, which can ultimate compromise security and performance. We present a 1.25 GHz fully phase-randomized QKD source based on a super luminescent diode (SLED) operating in the C-band as a compact and cost-effective alternative. The source generates ∼ 100 ps optical pulses with 400 ps time-bin separation, compatible with high-speed time-bin encoding. Interferometric measurements demonstrate > 99% visibility between adjacent time bins, confirming strong first-order coherence within a qubit, while the spontaneous-emission-driven nature of the SLED ensures intrinsic pulse to pulse phase randomization. The broadband architecture further enables operation across multiple ITU channels, supporting wavelength-multiplexed QKD from a single emitter. This work establishes a scalable SLED-based platform for high-speed time-bin QKD systems.