A polarization-dependent supercontinuum spectrum source of light from the UV to infrared region has been generated in our photonic crystal fiber with birefringence B=2.23×10 3.By tuning the polarization direction of the input pulse,it is found that the width of the supercontinuum spectrum changes dramatically with the input polarization directions.At the same time,we qualitatively explain the blue-shift peak and the red-shift peak in the experimental spectrum using phase matching conditions on dispersive waves,stoke waves and the pump wave.In addition,we also found that supercontinuum spectrum generation,to some extent,is dependent on the pump wavelength and average power of the pump.The spectrum is broadened with the increase of average power,but unchanged after average power reaches a certain value;when the pump wavelength is located in the anomalous dispersion and further away from the zero-dispersion wavelength,the spectrum of the supercontinuum is wider.
WANG XiaoYanLI ShuGuangHAN YingDU YingXIA ChangMingHOU LanTian
A simplified structure of birefringent chalcogenide As 2 Se 3 photonic crystal fiber(PCF) is designed.Properties of birefringence,polarization extinction ratio,chromatic dispersion,nonlinear coefficient,and transmission are studied by using the multipole method,the finite-difference beam propagation method,and the adaptive split-step Fourier method.Considering that the zero dispersion wavelength of our proposed fiber is about 4 μm,we have analysed the mechanism of spectral broadening in PCFs with different pitches in detail,with femtosecond pulses at a wavelength of 4 μm as the pump pulses.Especially,mid-infrared broadband polarized supercontinuums are obtained in a 3-cm PCF with an optimal pitch of 2 μm.Their spectral width at 20 dB reaches up to 12 μm.In the birefringent PCF,we find that the supercontinuum generation changes with the pump alignment angle.Research results show that no coupling between eigenpolarization modes are observed at the maximum average power(i.e.,37 mW),which indicates that the polarization state is well maintained.
This paper proposes three kinds of tapered holey fibres with a multi-layer of holes whose pitch of air holes at the end of untapered and tapered are 5.8 μm and 1.8 μm. The central wavelength which locates in the anomalous dispersion region is 1.55 μm. An adaptive split-step Fourier method is numerically used to study the pulse propagation in tapered holey fibres. For the considered convex tapered holey fibre, at a wavelength of 1.55 μm, a compression factor of 136.7 can be achieved by initial width of 800 fs propagation through a length of 0.8 m. It demonstrates that in anomalous dispersion region, pulse can be compressed with the increase of nonlinearity coefficient and the decrease of dispersion coefficient.
A kind of improved high birefringence photonic crystal fibre (PCF) is proposed in this paper.The characteristics of birefringence,dispersion and leakage loss are studied by the multipole method.Numerical results show that the improved PCF possesses the properties of a flat dispersion and single mode operation.Moreover,with the operating wavelength λ=1.55 μm,the modal birefringence increases greatly in comparison with that of the original PCF,and the leakage loss is about 10 4 times smaller than that of the original PCF because the modification gives rise to the strong confinement of guided modes.It is expected that the improved PCF can be used as high birefringence and dispersion flattened fibres.
The propagation of femtosecond laser pulses with wavelengths of 1550 nm, 1064 nm, 800 nm and 700 nm, respectively, which are in the normal dispersion region of the nano-structured photonic crystal fiber (N-PCF) with interesting broadband normal dispersion and highly nonlinear properties, is studied. For the effect of chirp variation mainly induced by group velocity dispersion (GVD) and self-phase modulation (SPM), after propagation over a short length, the wave breaking occurs. Namely, oscillatory structures are presented near pulse edges and sidelobes appear in the pulse spectrum. In the case of 800 nm, after the propagation of 20 mm, a super flat spectrum is obtained. The bandwidth of the super flat spectrum is associated with the dispersion length and the nonlinear length. By choosing N-PCF and laser pulse with appropriate parameters, a broadband super flat spectrum in a short length can be achieved.
A terahertz photonic crystal fibre (THz-PCF) is designed for terahertz wave propagation.The dispersion property and model birefringence are studied by employing the finite element method.The simulation result reveals the changing patten of dispersion parameter versus the geometry.The influence of the large frequency band of terahertz on birefringence is also discussed.The design of low loss,high birefringence THz-PCFs with zero dispersion frequency at 0.3 THz is presented.
