Research On Microfiber/helical-fiber Long-period Grating Devices Utilizing The Arc-discharge Fabrication Method

Long-period fiber grating?LPFG?is a kind of devices which rely on the coupling of modes to manipulate light energy for optical fiber sensing and communication applications.It is widely used in optical fiber band-stop filter,gain equalizer,optical add / drop multiplexer,optical light and dispersion compensator,and etc.Since the resonant peaks of LPFG are very sensitive to external environments,they can be exploited in the field of optical sensing for measurements of temperature,strain,twist,refractive index,or biological and chemical parameters.Multi-parameter measurement is also an interesting research topic.How to develop new fiber optic devices is key for the applications.Microfiber long-period grating and twisted long-period fiber grating,acting as a new type of structures,have been attracting research attention.In this paper,the fabrication or development of LPFGs are introduced.The arc discharge method is developed.Both the spectral and sensing characteristics are studied.The proposed devices are featured with flexibility,low cost,and high reproducibility for fabrication as well as excellent sensing characteristics as detailed in the main context of this thesis.The thesis mainly includes the following aspects:?1?A novel kind of microfiber long-period grating is proposed.Compared to the counterparts which are fabricated with CO₂ and femtosecond lasers,there is only the coupling between the fundamental mode LP01 and the symmetric higher-order mode LP02.It is shown that only 11 cycles can induce the resonant dip of higher than 30 dB with a transmission loss smaller than 1.0dB.The advantage lies on high repeatability,stability,flexibility and low production costs.Secondly,high-order diffraction of the microfiber long-period grating is realized,which enable the period elongated to 400 ?m-1000 ?m.The fabrication limitation induced by the minimum period due to the size of the laser spot or arc is solved.Thirdly,it is found that the fabricated microfiber longperiod grating has high refractive index?RI?sensitivity and a very low temperature coefficient,showing high potential for biochemical sensing applications.?2?A helical all-solid band-gap fiber is proposed and realized.We explain the principle of grating formation,and its coupling effect mainly comes from the core mode and the orbital resonance mode.The sensing characteristics including the torsion,tension,refractive index and temperature are investigated.Finally,we investigated helically twisted single-mode fiber grating devices.The cascaded gratings are studied these structures can be widely used in tunable optical filtering,optical fiber sensing,and communication areas.