An efficient all-fiber variable optical attenuator via acoustoopticmode coupling

A novel broad-band variable optical attenuator is realized using acoustooptic mode coupling on a cladding etched single-mode fiber. Broad-band coupling bandwidth with low attenuation ripples is achieved by matching both the group index and dispersion parameter between the core and the LP₁₁^cl cladding modes. A single-section device exhibits a 10-dB dynamic range with attenuation ripples of <0.5 dB over a spectral range of >100 nm, a response time of 20 μs, an insertion loss of 0.3 dB, and a maximum power consumption of only 3.4 mW. Attenuation of 22 dB is obtained for a cascaded two-section device