Increase of Recognizable Label Number with Optical Passive Waveguide Circuits for Recognition of Encoded 4- and 8-Bit BPSK Labels

Optical label processing is expected to reduce power consumption in label switching network nodes. Previously, we proposed passive waveguide circuits for the recognition of BPSK labels with a theoretically infinite contrast ratio. The recognizable label number was limited to four and eight for 4-bit and 8-bit BPSK labels, respectively. In this paper, we propose methods to increase the recognizable label number. The proposed circuits can recognize eight and sixteen labels of 4-bit BPSK codes with a contrast ratio of 4.00 and 2.78, respectively. As 8-bit BSPK codes, 64, 128, and 256 labels can be recognized with a contrast ratio of 4.00, 2.78, and 1.65, respectively. In recognition of all encoded labels, that is, 16 and 256 labels for 4-bit and 8-bit BPSK labels, a reference signal is employed to identify the sign of the optical output signals. The effect of phase deviation and loss along the optical waveguides of the devices is also discussed.