公益財団法人

セコム科学技術振興財団

研究成果報告書

研究課題名
光信号の符号化・暗号化／復号化技術と高セキュリティ・低消費電力な光通信の実現
Encoding/scrambling and decoding of optical signals, and realization of high-security andlow-power-consumption optical communication

研究期間
平成２５年 ４月 ～ 平成２９年 ３月

報告年月
平成２９年 ６月
研究代表者
立命館大学 理工学部 電気電子工学科 教授
瀧口 浩一

Professor, Department of Electrical and Electronic Engineering, College of Science and Engineering,
Ritsumeikan University
Koichi Takiguchi

Abstract
It is important to devise new and practical technology including optical logical processing, with which high-speed
optical communication signals can be encoded and decoded directly in the optical domain, and investigate
low-power-consumption optical devices that can carry out the optical logical processing. In this research, byverifying application possibility of the optical logical processing to optical communication systems, we intended tocontribute to the future realization of highly secure and low-power-consumption optical communication systems,
and safe and secure society. Specific research contents are described below.
In the preliminary research stage, we comprehensively compared characteristics between two kinds of opticalexclusive OR (XOR) circuits, which we devised for encoding and decoding technology, by carrying out simulationand preliminary experiments. In consequence, we adopted the circuit, which was composed of a balanced
photo-detector (PD) and a Mach-Zehnder interferometer-type optical intensity modulator, due to its stable
operation and simple configuration. We carried out subsequent investigation using this circuit configuration. Inaddition, we sped up the optical XOR circuit so that it could process 40 Gbit/s on-off keying (OOK) signals. In the
full-fledged research stage, we first evaluated the fundamental characteristics of the optical XOR circuit in detail,which we realized in the preliminary research stage, and simulated and measured the operation of the optical XOR
circuit to various kinds of pseudo-random sequences . Then, we investigate codes to improve the security of the
optical logical processing, and considered application fields of the optical logical processing. We finally tried tointegrate the components of the optical XOR circuit.
We summarize the contents of the full-fledged research below.
We constructed a bit error rate measurement set-up for 40 Gbit/s OOK signals, and quantitatively evaluatedoperation of the optical XOR circuit.
We investigated the properties of several pseudo-random sequences used for encoding and decoding of signals.
We actually inputted the above-mentioned pseudo-random sequences into the optical XOR circuit, and measured
the operational characteristics of the circuit. We carried out sub-system experiments.
We proposed a time-varying code with a view to improving security of the optical logical processing, andevaluated the properties of the code.
We examined application of the optical logical processing to new fields including error correction of opticalsignals, which can also contribute to security and have low-power-consumption characteristics.
We considered further operation stabilization and miniaturization of the optical logical circuit by trying tointegrate the circuit. In particular, we tried to fabricate an integrated-photonic XOR circuit by utilizing the availabletechnology. However, the fabricated circuit did not work.
In addition to the above-described contents, during the full-fledged research period, we discussed the researchwith experts in optical communication system fields when needed, and could get useful advice.

To sum up, although we could realize a practical high-speed optical XOR circuit based on the combined
technology of photonics and electronics, and could evaluate the circuit characteristics in detail, we could not haveenough time to investigate application fields of the optical logical processing technology. Also, we could notachieve the realization of an integrated-photonic XOR circuit, which was an important goal in the last year. Please
note, however, that we could get challenging tasks and useful knowledge to develop application fields and torealize an integrated-photonic XOR circuit in the future.