SPR-Assisted Photonic Crystal Fiber-Based Dual-Wavelength Single Polarizing Filter With Improved Performance

The article introduces a photonic crystal fiber (PCF)-based single polarizing filter for a dual-communication band with strongest filter intensity and broad-bandwidth of crosstalk (CT) more than 20 dB, working on the surface plasmon resonance (SPR) principle. The finite-element method (FEM) is used to investigate the filter characteristics of gold-coated PCF. The proposed PCF shows single-polarization filtering in two communication bands of 1.63 and
$1.378~\mu \text{m}$
. In phase-matching conditions, the core-guided propagation mode coupled with the surface plasmon polariton (SPP) mode results in the occurrence of SPR. The
$y$
-polarized core mode is coupled with the
$y$
-polarized SPP mode and therefore the light energy is transferred from the
$y$
-polarized core mode to the
$y$
-polarized SPP mode, hence the confinement loss of
$y$
-polarized core mode is much higher than that of the
$x$
-polarized core mode. Therefore, the single polarization filter can be retaining the core guided mode always in the
$x$
-polarized direction for a wide-wavelength range. In the optimized PCF, the confinement loss of the core mode in the
$y$
-polarized direction reaches an extremely higher value of 2953 dB/cm at 1.63
$\mu \text{m}$
and 450.8 dB/cm at 1.378
$\mu \text{m}$
, but in the
$x$
-polarized direction loss is only 149.3 dB/cm at 1.63
$\mu \text{m}$
and 4.658 dB/cm at 1.378
$\mu \text{m}$
. Besides, the CT reaches the maximum value of 2435 dB at
$1.63~\mu \text{m}$
and 387.5 dB at
$1.378~\mu \text{m}$
with the fiber length of 1 mm, and the corresponding bandwidth of CT above 20 dB is 591 nm. Moreover, it is easier to operate the SPR-PCF-based polarization filter devices.