A novel narrow-band filter based on the dual-core doped photonic crystal fiber is proposed.By optimizing structure parameters of the photonic crystal fiber,the index curves of the fundamental modes for the two cores are crossed at 1.55 μm and the wavelength-selective coupling is achieved.The characteristics of the filter are numerically simulated by the full-vector beam propagation method.And the simulation results show that the coupling length and the bandwidth of the filter are 16.4 mm and 9 nm at-3 dB loss,respectively.It demonstrates the advantages of the filter with a small size,a low transmission loss and the narrow-band width.
A novel broadband directional coupler based on an asymmetric dual-core photonic crystal fibet(PCF)is proposed.The asymmetry in the fiher is introduced by the enlargement of one air-hole in dual-core PCF.Numerical investigation demonstrate that broadband directional coupling with spectral width as large as 370 nm and polarization-dependent loss and uniformity lower than 0.2 and 0.5 dB,respectively,can be achieved.In addition,the proposed fiber shows large tolerance to the variation of the fiber parameters.In particular,the fiber length allows at least 10%derivation from the proposed fiber length of 7.7 mm.
We investigate the coupling characteristics of photonic crystal fiber composed of two cores with different index profiles. The index curves of the fundamental modes of the two cores can cross at a desired wavelength by choosing appropriate index profiles of the cores. As a result, wavelength-selective coupling is achieved. The designed coupler can be applied as an optical fiber bandstop filter with 26-nm bandwidth.
