The transmission properties of one-dimensional photonic crystals containing double-negative and single- negative materials are studied theoretically.A special kind of photonic band gap is found in this structure. This gap is invariant with scaling and insensitive to thickness fluctuation.But when changing the ratio of the thickness of two media,the width of the gap could be enlarged.The defect modes are analyzed by inducing a linear defect layer in the structure.It is found that the number of defect modes will increase when the thickness of the defect layer becomes larger.
A novel twin-core photonic crystal fiber was proposed to reduce the complexity and cost of fiber Raman amplifiers.By means of a proper design,this fiber could acquire a higher and flatter Raman gain efficiency coefficient curve rR=gR/Aeff over a specified band of wavelength than a conventional fiber.A Raman amplifier was designed with this novel twin-core photonic crystal fiber to operate in C band from 1530 nm to 1565 nm.A remarkable improvement over a conventional fiber Raman amplifier was obtained.It was numerically demonstrated that when pumped with a single source,an average gain of 8.7 dB with a fluctuation of less than 0.9 dB is achievable.
Light trapping within waveguides is a key practice of modern optics,both scientifically and technologically.Photonic crystal fibers traditionally rely on total internal reflection(index-guiding fibers)or a photonic bandgap(photonic-bandgap fibers)to achieve field confinement.Here,we report the discovery of a new light trapping within fibers by the so-called Dirac point of photonic band structures.Our analysis reveals that the Dirac point can establish suppression of radiation losses and consequently a novel guided mode for propagation in photonic crystal fibers.What is known as the Dirac point is a conical singularity of a photonic band structure where wave motion obeys the famous Dirac equation.We find the unexpected phenomenon of wave localization at this point beyond photonic bandgaps.This guiding relies on the Dirac point rather than total internal reflection or photonic bandgaps,thus providing a sort of advancement in conceptual understanding over the traditional fiber guiding.The result presented here demonstrates the discovery of a new type of photonic crystal fibers,with unique characteristics that could lead to new applications in fiber sensors and lasers.The Dirac equation is a special symbol of relativistic quantum mechanics.Because of the similarity between band structures of a solid and a photonic crystal,the discovery of the Dirac-point-induced wave trapping in photonic crystals could provide novel insights into many relativistic quantum effects of the transport phenomena of photons,phonons,and electrons.
Kang XieWei ZhangAllan D BoardmanHaiming JiangZhijia HuYong LiuMing XieQiuping MaoLei HuQian LiTianyu YangFei WenErlei Wang
In this paper, the multimode waveguide lengths and the output port locations of a SOI (silicon on insulator) material-based 1x4 MMI (multimode interference) optical splitter are optimized by means of FD-BPM (finite difference - beam propaga- tion method). An improved 1x4 MMI optical splitter is designed. Compared with an usual optical splitter, a smaller loss 0. 12dB and a better output port power uniformity 0.11dB are achieved for the optical signal transmission.
