Band-rejection filtering based on lossy torsional acousto-optic coupling in a single polarization fiber

Abstract

We propose and demonstrate novel band-rejection filtering scheme based on lossy torsional acousto-optic (AO) coupling in a single polarization fiber. Simulation results show that the polarization insensitive notch depth of -30 dB is achievable for a 2-m-long fiber in the state-of-the-art fiber manufacturing technology. More efficient band-rejection in excess of -44 dB could be also feasible in practical fiber length. Good agreement between our numerical simulations and proof-of-principle experiments is obtained in optical communication C-band. The measured notch depth is -29.4 dB for a low loss polarization mode after propagating an AO interaction length of 49.8 cm. The filtered wavelength could be tuned linearly by the variable acoustic transducer frequency with the slope of 0.61 nm/kHz, and the polarization dependence of notch depth was measured to 0.8 dB in our setup. Our experiments confirm the validity and practicality of the approach, and illustrate the in-fiber torsional AO band-rejection filter with simpler device configuration is achievable.

Recent progress of dynamic mode manipulation via acousto-optic interactions in few-mode fiber lasers: mechanism, device and applications

“…(ω′, k′), (ω 0 , k 0 ) and (ω a , k a ) are the frequency and the wavenumber of diffracted light, incident light and acoustic wave, respectively, as shown in Figure 2B. In fiber acoustooptics, the practical applications based on acoustically induced refractive index modulation depend on different kinds of acoustic vibrations including longitudinal mode [65][66][67]84], torsion mode [113][114][115][116][117] and flexural mode [43,59,71,[107][108][109]112], as depicted in Table 1.…”