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IEICE Technical Report; IEICE Tech. Rep.

Optimization of signal amplitudes for dynamic range of analog-to-digital convertor in digital coherent reception of ultra-high QAM optical signals

Yasuhiro Kawabata, Koji Igarashi

Published Oct 11, 2018• 0 citations
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Abstract Data security is a key feature of future communications networks. Physical layer introduces rich physical mechanisms to increase the complexity of deciphering and provides extensive protection, but faces challenges in compatibility with commercial systems. Quantum noise stream cipher (QNSC) has been proposed as a promising solution to overcome this problem by fusing the stream cryptography regime with the quantum noise masking physical mechanism. However, it has limitations in terms of digital to analog conversion and clock data synchronization of ultra-high-order ciphertext as well as flexible control of masking noise. Here we report a 147.9-Gbps device-compatible quadrature amplitude modulation (QAM) QNSC secure scheme over 75-km fiber. Thanks to delta-sigma modulator, the transmission of 220 × 220-order QAM-QNSC signal are established through the low-order digital signal. We develop a theoretical model for flexibly regulating the transmission rate and security performance. Broadband optical chaos introduces true randomness and acts on the masking noise.
This letter first reports a digital coherent quantum noise stream cipher (QNSC) experiment over 300km fiber without intermediate amplifiers. With the help of Raman fiber amplifiers, ultra-low loss fiber, and the optimized fuzzy C-means clustering algorithm, the results show the system can carry 10.2 Tbit/ s·km data, which is significantly improved in the single polarization and single wavelength digital coherent context without intermediate amplifiers. We further analyze the transmission and security performances under the 16 quadrature amplitude modulation (QAM) scenario in detail. The number of masked signals of 16 QAM/QNSC is 3843.2.
Optical transmission over space links between satellites in intra-orbital constellations or inter-orbital constellations and optical ground stations are currently attracting a lot of attention, both for their ultra-high capacities reaching multi-tera-bits/sec and for their use in quantum key distribution for coding to transmitting over public channels.This paper outlines the followings: (i) Multi-dimensional considerations to reach Tera-bits/sec that include multiplexing of polarized modes, high-order modulation formats, high speed integrated photonic complex modulations, digital signal processing techniques etc.; (ii) Continuous variable quantum key distribution (CV-QKD) achieved through constant amplitude zero auto-correlation (CAZAC) sequence for quantum level signaling with phase-coded BB84protocol, decorrelation , high order sampling rate and digital signal processing for quantum key recovery.(iii) Discussion of advantages and disadvantages of both coherent and self-coherent reception techniques for space transmission channels for multi-photons to subphoton energy reception and transmission; (iv) Presentation of initial transmission results and Terabits/s optical transmission systems; (vi) Analytical considerations of CV-QKD space self-homodyne and homodyne reception system employing CAZAC and crosscorrelation decoding as a photonic-pre-processor.