Waveguide-type optical circuits for the recognition of optical 8PSK-coded labels

Abstract

This paper discusses optical label recognition for photonic label routing. The label recognition is one of the key functions in photonic label routing related functions including optical label extraction, recognition of the label and label rewriting. In a previous study, we have proposed a basic waveguide-type circuit for the recognition of an optical label encoded in quadri-phase-shift-keying (QPSK) format, which consists of a 3-dB directional coupler, two Y-branches and an asymmetric X junction coupler. In order to increase the number of labels represented by the same symbol number, we propose 8PSK recognition circuits based on the QPSK recognition circuit. The input-output relation of the proposed circuits is theoretically discussed and the noise tolerance is also investigated. From the theoretical analysis, the proposed optical-waveguide circuits recognize the 8PSK labels by detecting the position of the output port having either the maximum or minimum intensity. The bit-error performance of the proposed circuits is clarified by computer simulation. It is found that the minimum-output detection scheme for a one-symbol 8PSK label is superior from the viewpoint of noise tolerance. The proposed method also addresses the scalability of two-symbol 8PSK coded labels. The maximum-output detection scheme demonstrates improved scalability performance.