Tunable Wavelength-Selective Coupler Based on Microtapered Long-Period Fiber Gratings

In this letter, the wavelength-selective couplers (WSCs) constructed with two- and three-parallel microtapered long-period fiber gratings (MLPFGs) are experimentally demonstrated, respectively. The MLPFGs are fabricated by periodically tapering the standard single mode fibers. In WSCs constructed with two-parallel MLPFGs, the maximum peak coupling efficiency is ~10.1%, while in WSCs constructed with three-parallel MLPFGs, the maximum peak coupling efficiencies are ~2.9% and ~3.2% for two tapping fibers, respectively. Moreover, we propose an effective and convenient method to tune the WSCs. By simply twisting the WSCs constructed with two-parallel MLPFGs, the wavelength tunability of -0.01985 nm/° with a maximum wavelength tuning range of 6.8 nm is achieved, together with a good linear relationship of the shift at resonance wavelength versus the twist angle.