Broadband Wavelength-Tunable Mode Converter Based on Long-Period Fiber Gratings

We investigated theoretically and experimentally the long-period fiber gratings (LPFGs) inscribed in the tapered few-mode fiber (FMF), and successfully generated the LP11 core mode in a broad wavelength range. Simulation and experimental studies have demonstrated that the phase matching curve of the FMF-LPFG can be changed through fiber tapering, thereby moving the dispersion turning point (DTP) to the communication band. The tunable ultra-broadband mode converter can be realized based on the DTP-LPFG. We investigated the relationship between the DTP of the FMF-LPFGs and fiber diameter. The LPFGs were fabricated in the FMF with diameters of
$100~\mu \text{m}$
and
$90~\mu \text{m}$
, with 10-dB bandwidth of 504 nm and 450 nm, respectively. The 10-dB bandwidth of the mode converter and the corresponding wavelength range can be adjusted by changing the fiber diameter.