Spacing adjustable and switchable multi-wavelength Erbium-doped fiber laser based on the parallel filter of photonic crystal fibers and polarization hole burning effect

Abstract

Polarization hole burning (PHB) is an important approach widely used to generate multi-wavelength output in erbium-doped fiber laser (EDFL). In this work, we demonstrated a potential approach for multi-wavelength EDFL generation based on a parallel filter and the PHB effect. The parallel filter comprises two in-line Mach-Zehnder interferometers (MZIs) namely (MZI-1 and MZI-2) which are parallel connected between two 3-dB optical fiber couplers (OCs). Here, MZI-1 consists of a segment of non-linear photonic crystal fiber (NLPCF) fused spliced between two single mode fibers (SMFs). MZI-2 was realized by the core-offset fusion splicing of a piece of an NLPCF between two SMFs. The core offset technique in NLPCF splicing enabled the manipulation of the optical path difference between the two arms of the parallel filter. The two MZIs configured as parallel filters were initially utilized as transmission spectrum filters to simultaneously generate dual-wavelength EDFL at 1530.4 and 1525.6 nm. Then, the proposed parallel filter, when combined with polarization controllers (PCs), produces the PHB effect, which reduces mode competition and allows for spacing adjustment and switchable multi-wavelength operation. The free spectral range (FSR) of the parallel filter can be altered among single, dual, triple, and quadruple wavelengths by adjusting the PC1 incorporated within the ring cavity. The spacing adjustable wavelength operation can subsequently be modified from 1.2 to 5 nm by altering the FSR of MZI-2, which was accomplished by adjusting PC2 embedded in the MZI-2 arm. The results indicate that the proposed parallel filter offers a potential candidate for stable, switchable, and controllable generation of multi-wavelength EDFL.