Fast all-optical processing is expected for packet routing in high-speed photonic networks. In photonic label networks, recognition of optical labels is one of the key functions. We propose a scalable passive waveguide device to recognize binary phase shift keying (BPSK) labels. The label recognition device consists of cascaded asymmetric X-junction couplers. The proposed basic device recognizes four labels consisting of parallel four pulses. Since an output is obtained at only one output port out of four ports with high contrast ratio, the device can be scaled up for labels of a larger number of bits. The devices for four, eight and sixteen labels are theoretically analyzed. To confirm the operation in the devices, the label recognition of four- and eight-bit labels is numerically simulated by finite-difference beam propagation method (FD-BPM). Expanded circuits based on the four-bit basic device to increase the number of recognizable labels are also presented.
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