All-fiber polarizer based on a null taper coupler

An entirely new type of single-mode all-fiber polarizer is reported. The polarizer is based on a narrow circularly fused null taper coupler, which was twisted through 45 degrees after being made. The polarizing effect is due to the excitation of hybrid second modes in the coupler waist. An extinction ratio of 15 dB and an insertion loss of 0.2 dB have been obtained, with scope for further improvement.