| Photonic crystal fiber?PCF?has been a research hotspot in the field of optical fiber technology since it was proposed due to its endlessly single mode,high birefringence,ultra-flat dispersion,and controllable transmission performance.The high birefringence photonic crystal fibers?HB-PCFs?are reported that they possess the functions of polarization maintaining,dispersion compensation,and optical sensing,which have attracted intensive attention of researchers.In recent years,with the development of numerical methods,people can design and simulate micro-structured fibers very conveniently.Some HB-PCFs with new structures and functional materials are designed and applied to optical communication,non-linear optics,fiber sensing and so on,which greatly broadens its applications and development prospects.In order to make full use of the design flexibility and general applicability of PCF,this article designs a new asymmetric structure for HB-PCF,analyses and optimizes its optical performance,and then extends the research on sensing performance.The main contents are as follows:?1?The chapter reviews research background and development history of PCFs.They are classified according to different working mechanisms,and their characteristics and advantages are presented.Then it briefly describes the applications of PCFs in various fields,as well as the corresponding structural characteristics and design methods.The research progress,main performance indexes and applications of HB-PCF are listed,and it further clarifies the significance of this study.?2?The next chapter summarizes several theoretical characterization methods of PCFs,introduces the basic concepts and mathematical expressions of plane wave expansion,effective refractive index method,finite difference time domain method,finite element method,which lay a theoretical foundation for structural design and simulations in the following chapters.?3?In this work,a new design of a HB-PCF with multimode and low confinement loss is proposed.The core is designed as an elliptical region,which is enclosed by twelve small holes.At 1.55?m,the birefringence of the fundamental mode(LP01)and the second-order mode(LP11)are 1.70×10-2 and 1.85×10-2,respectively.Meanwhile,the confinement losses maintain on orders of 10-5 dB/km(LP01)and 10-1 dB/km(LP11).?4?Based on the optimized structure,we continue to study its application in optical sensing.The calculation shows that the birefringence is 0.01 and the refractive index sensitivity is 0.03/RIU at 1.55 um.Given the advantages of multi-band application of HB-PCF,the operating frequency is extended to 1-3 THz.The simulations show that the devise can provide more than 0.05 birefringence in terahertz band,and also its sensitivity is higher than 0.03/RIU,whose performance is obviously improved. |
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