Periodic Index Changes Research Articles

High strength coupling and low polarization-dependent long-period fiber gratings based on the helicoidal structure

A compact helicoidal long-period fiber grating (HLPFG) was fabricated by twisting a single mode fiber with CO 2 laser beam exposure and its characteristic was experimentally investigated. The eccentricity between the core and the cladding of a fiber is introduced from the screw-type deformation. This helically induced significant periodic index change along the fiber produces strong mode coupling between the core and the cladding of − 20 dB with a short grating length of ∼ 1 cm . The novel resonance wavelength shift of a HLPFG was analyzed with co-directional or contra-directional torsion to the helix.

Widely tunable asymmetric long-period fiber grating with high sensitivity using optical polymer on laser-ablated cladding

We demonstrate high-efficiency, wideband-tunable, laser-ablated long-period fiber gratings that use an optical polymer overlay. Portions of the fiber cladding are periodically removed by CO(2) laser pulses to induce periodic index changes for coupling the core mode into cladding modes. An optical polymer with a high thermo-optic coefficient with a dispersion distinct from that of silica is used on a deep-ablated cladding structure so that the effective indices of cladding modes become dispersive and the resonant wavelengths can be efficiently tuned. The tuning efficiency can be as high as 15.8 nm/ degrees C, and the tuning range can be wider than 105 nm (1545-1650 nm).

Theoretical investigation of a notch filter using a long-period grating based on the sampling theorem

A notch filter using a different grating scheme is investigated theoretically. The grating is the thermo-optic index change induced by individually controllable heaters that are periodically arranged on the filter surface. If the index change pattern induced by the heaters is in the form of sampling a periodic index change, the transmission spectrum of the filter has the same resonance band as that generated by the periodic index change. Simulation results show that the attenuation, bandwidth, and center wavelength of a resonance band are independently adjustable. In addition, it is shown that the transmission spectrum may be tailored to arbitrary predictable shapes. Finally, the realization of the filter is discussed.