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Sixth Symposium on Novel Optoelectronic Detection Technology and Applications

High-speed nonreciprocal modulation in bidirectional links based on periodically poled lithium niobate modulator

Zexu Wang, Feifei Yin, Kun Xu, Yitang Dai

Published May 11, 2026• 0 citations

Abstract

Non-reciprocal modulation in bidirectional links eliminates the modulation speed limitation caused by preventing electrical signals from simultaneously modulating light in both directions, thereby enabling the system to operate at higher speeds. Conventional lithium niobate modulators only support this functionality under specific conditions. The periodically poled lithium niobate (PPLN) based modulator we propose supports non-reciprocal modulation across expanded application scenarios. Simulation results demonstrate that the PPLN modulator achieves high-speed modulation for both continuous wave and pulsed light. A polarization encoder based on a Sagnac interferometer using the PPLN modulator enables random modulation of four polarization states at a system repetition frequency of 10GHz, with an average polarization extinction ratio exceeding 20dB.

DOI: 10.1117/12.3103307

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Non-reciprocal modulation in bidirectional links eliminates the modulation speed limitation caused by preventing electrical signals from simultaneously modulating light in both directions, thereby enabling the system to operate at higher speeds. Conventional lithium niobate modulators only support this functionality under specific conditions. The periodically poled lithium niobate (PPLN) based modulator we propose supports non-reciprocal modulation across expanded application scenarios. Simulation results demonstrate that the PPLN modulator achieves high-speed modulation for both continuous wave and pulsed light. A polarization encoder based on a Sagnac interferometer using the PPLN modulator enables random modulation of four polarization states at a system repetition frequency of 10GHz, with an average polarization extinction ratio exceeding 20dB.

In polarization-encoding quantum key distribution (QKD) systems, achieving high-speed, robust, and low-error polarization modulation helps to increase the secure key rate (SKR). Moreover, the advanced QKD protocols place higher demands on the system’s photon preparation capability, which implies providing additional polarization states for practical implementation. Here, we redesign the Sagnac interferometer and utilize the non-reciprocity of the lithium niobate modulator to eliminate the reverse modulation that limits the modulation speed. The proposed scheme enables high-speed, robust, and low-error modulation with arbitrary polarization states. The average bit error rate (BER) for the 10 min measurement is 0.2332% with a system repetition frequency of 16.5 GHz.

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