Ju Hee Back

Modern information and communications security has relied on public-key cryptosystems-such as RSA and ECC-based on computational complexity. With the accelerating global research and investment in quantum computing, however, warnings that these traditional schemes could be fundamentally broken by quantum algorithms such as Shor’s algorithm[1] are becoming increasingly realistic. As a result, quantum key distribution (QKD), which provides security independent of computational complexity by harnessing quantum-mechanical principles, has emerged as a promising alternative. QKD has advanced from laboratory experiments to inter-city trials, nationwide fiber-optic networks, and satellite links. Nevertheless, challenges in manufacturing, especially cost, size, and power consumption, continue to hinder the commercialization of QKD. To mitigate these issues, photonic integrated circuit (PIC) transmitters and receivers based on silicon, InP, SiN, and LiNbO_3 platforms have been developed[2,3,4]; to our knowledge, no commercial form-factor transmitter integrating both the light source and the modulator has been reported. In this work, we present the first QKD transmitter that hybrid-integrates a laser source, asymmetric delay interferometer, variable optical attenuator, and phase modulator into a CFP2 form-factor. We first measure and report the performance of each component, including the pulse characteristics depending on the system rate, the interferometer characteristics, the maximum optical attenuation, and the phase modulator’s half-wave voltage (V_pi). Furthermore, using the integrated transmitter, we implement a phase-encoding BB84 system, measure the interference visibility as a function of the phase modulator’s drive voltage and the sifted-key rate, then calculate the resulting quantum bit error rate (QBER) and secret-key rate (SKR).