Mechanical Microbending Long-period Fiber Grating Devices

Long-period fiber gratings (LPFG) can couple core mode with special cladding modes, and produces stop-band transmission spectra with bandwidth of tens of nanometers. LPFG has the advantages of low additional loss, easy-to-connect. It has been widely used in passive fiber devices, such as fiber filter, fiber Add-Drop Multiplexer, fiber coupler and so on. Long-period fiber grating coupler has advantages of being adjustable and flexible. Recently, mechanically induced micro-bending long-period fiber grating (MBLPFG), have drawn lots of interests, because it has advantages of being reconfigurable, easy to adjust and low cost.This paper analyzed in detail the mechanism of MBLPFG, studied the relations of resonant wavelength with the grating period. Then the structure of pressing set of MBLPFG, which had a large cross coupling coefficient at 1550 nm and a low additional loss, was designed. The relations of bandwidth with period number, transmission spectrum with pressure were studied. And over coupling and polarization characteristics were also investigated.Then a new kind of long-period fiber grating coupler, which consists of two mechanically induced MBLPFGs, was investigated. This kind of coupler had the advantages of being erasable, reconfigurable, easy to assemble and low cost. The structure of this coupler and pressing set were designed. The influences of coupling ratio by pressure, period number and refractive index of matching liquid were also studied. Through continuous experimentation and improvement, a coupling ratio of about 13% was achieved at 1550 nm.Although the efficiency of the coupler is still low due to the poor manufacture conditions. Hard works are still needed for MBLPFG coupler to achieve wider application. But as a new device with unique advantage of being reconfigurable, it is worth further studying. It is believed that this kind of coupler will certainly have its value through continuous improvement.