Programmable Thermo-induced Long Period Fiber Grating In Liquid Core Optical Fiber

Reconfigurable optical devices that can respond dynamically to variable demands are re-quired for the development of efficient and flexible all-fiber systems and optical networks.Al-though silica fibers are the excellent platform for low loss waveguiding,they are somewhat limited in terms of their functionality owing to their low linear,nonlinear and thermal optical coefficients,for example.Therefore,in order to introduce some reconfigurable behavior into these fibers they are often infiltrated with materials that have tunable optical properties such as liquids,polymers,and liquid crystals.By incorporating those materials,the reconfigurability of optical fiber can be greatly enchanced and can respond to physical parameters like temperature,electric and magnetic fields.Temperature has been one of the most important tuning method for optics devices.However,as of to date,temperature tuning has been limited to adjusting the operation wavelength and not the device function.It it possible that we can use precise,local temperture to define a hybrid material optics device?Based on this hypothesis,we realised the programmable thermo-induced long period fiber grating(TI-LPFG)by applying a well-controlled temperture gradient on liquid core optical fiber(LCOF).5 key parameters of LPFG including period,modulation depth,length,duty ratio and phase shift can all be digitally programmed.This work has expanded the horizon of tradi-tional usage of hybrid material optical fiber and put it into the programmable thermo-induced optics device for the first time.The main work of this thesis consists of the following:1.A new method of LCOF fabrication.We proposed an LCOF fabrication technique which enables fast and robust LCOF.Although LCOF has a long history along the development of optical fiber itself,it ceased to grow as the comercial silica based fiber has conquered the world.LCOF was only used in laboratory environment.Recently as the fast growing interest on Optofluidics,LCOF has come back as a very good container for the light-matter interaction,and has been widely used in fiber laser and fiber nonlinearity area.However,the research on the easy-realised fabrication of LCOF has been rarely reached.In the first part of our research,we proposed a novel fabrication method of LCOF,which provides long-time stable operation and good repeatability.The resulted LCOF shows low attenuation and good stability in the months-long experiment.2.The first real-time programmable TI-LPFG.Dynamic LPFGs were induced in the LCOF using the programmble thermal distribution.LPFGs are of great interest for the development of in-fiber notch filters,optical fiber sensors and spatial mode converters,and a variety of fabrication methods exist for their inscription into solid fibers such as UV radiation,stress,and/or structural-induced index changes.However,the reconfigurability of these permanently inscribed gratings is inherently quite limited.In contrast,here we demonstrate large,dynamic tuning of both the spectral profile and band rejection strength by digitally programming the heating profile along the LCOF.The grating period,strength,length and phase shift inside the grating can all be digitally controlled.The coupling efficiency can be as high as 30 dB,and the insertion loss is less than 0.5 dB.The proposed TI-LPFG could provide unprecedented flex-ibility in filtering in wavelength domain,pulse shaping in time domain and selectively mode conversion capability.The proposed TI-LPFG shows the highest temperature sensitivity and widest tuning range the author has known,which is 132.9 nm/~?C and beyond 200 nm respectively.The sensitivity,which shows the temperature tuning capability is 3 orders'higher than nomal silica based LPFG.Owning to the high TOC of the liquid core,the temperature change that needed to realise the TI-LPFG is only around 2.75~?C,and the corresponding power consumption is only around 55 mW.Together with the very low temperature change to tune the TI-LPFG,the operation stability could be ensured.The excellent support from the theoretical analysis and simulation.To better explain the behavior of our TI-LPFG and understand the device,theoretical and simulation including mode analysis in LCOF,phase matching curve of LCOF and the temperature sensitivity of the TI-LPFG were carried out.All simulation and analysis fitted well with the experiment results.3.Programmable phase shift LPFG and optical fiber interferometer.Based on the pro-grammable TI-LPFG,we have shown advanced programming capability of the device and so-phisticated spectrum shaping technique.The programmable phase shift inside the TI-LPFG has been realised for the first time in our research.Such technique relies on the arbitray phase shift inserted into the LPFG,with programmable phase shift value and position.Multiple phase shift can be achieved easily to enable more advanced filtering profile.Moreover,by inserting a long gap inside the TI-LPFG,we have made an interference-length programmable interferometer.Our proposed device has a great potential to be the building block of optical fiber filter device and dynamic optical information processing in the future.