Modeling and Experimental Investigation of Non-Adiabatic Optical Fiber Taper
Modeling , Mode interference , Fiber taper , Mode coupling , Laser beam shaping
Mode coupler is an important category of device in the eld of optical sensing and communication. Non-adiabatic ber taper has attracted much attention in recent years as mode coupling device due to its simple fabrication process, compactness and robust performance. While models exist for mode coupling in conventional adiabatic ber taper, there are only commercial numerical softwares for simulations of ber tapers, with little appreciation of the underlying coupling mechanism. In this thesis, a model based on coupled mode theory in non-adiabatic optical ber taper is proposed for the analysis and calculation of the mode coupling phenomena. This method is applicable for a wide range of non-adiabatic ber tapers. The result of the model matches well with the result from numerical simulation, and illustrates the mechanism of mode coupling. Two experiments based on non-adiabatic ber taper are implemented and dis- cussed in this thesis. One is laser beam shaping using abrupt ber taper and the other is mode interference in non-adiabatic ber taper with long uniform region. A at-top beam is observed in the beam shaping experiment. The relation between mode phase and at-top beam is investigated with the model. In the experiment of long taper, we got clear interference spectrum in the range of 1530 1560 nm with bandwidth about 10 nm and atteuation peak over 10 dB. We applied the model in the long ber taper and got good match between modeling and experiment. All this results validate the model and show the potential application of ber taper.