Single-/dual-wavelength switchable and tunable compound-cavity erbium-doped fiber laser with super-narrow linewidth

Abstract

A single-/dual-wavelength switchable and tunable erbium-doped fiber laser (EDFL) with super-narrow linewidth has been proposed and experimentally demonstrated at room temperature. The fiber laser is based on a compound cavity simply composed of a ring main cavity and a two-ring subring cavity (TR-SC). Regardless of single-or dual-wavelength operation, the EDFL could always work well in single-longitudinal-mode (SLM) state at every oscillating wavelength. In dual-wavelength operation, the spacing could be tuned from 0 nm to 4.83 nm. In single-wavelength operation, the EDFL could lase at a fixed wavelength of 1 543.65 nm or another wavelength with a tunable range of 4.83 nm. The super-narrow linewidths of 550 Hz and 600 Hz for two wavelengths are obtained. The proposed EDFL has potential applications in microwave/terahertz-wave generation and high-precision distributed fiber optical sensing.Dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber lasers (EDFLs) are considered to be excellent sources for applications such as wavelength division multiplexing transmission system, fiber sensing, optical signal processing, LIDAR, and microwave photonic generation [1][2][3][4][5] . The single-/dual-wavelength switchable operation is another crucial target for research of EDFLs [6] .In order to achieve SLM operation for EDFLs, many configurations have been proposed in the past few decades, such as distributed feedback [7,8] , short-cavity distributed Bragg reflector [9] , conventional linear and ring cavities incorporating complicated ultra-narrow-band filters [10][11][12][13] , and compound cavity [14][15][16][17] . Due to the drastic mode competition induced by homogenous gain broadening effect in EDF, stable dual-wavelength SLM oscillation is not easy to achieve. In recent years, many researchers have reported different techniques to demonstrate stable dual-wavelength SLM EDFLs, such as a novel symmetrical fiber Bragg grating (FBG) structure as compact dual-wavelength laser cavity [2] , a reconfigurable dual-pass Mach-Zehnder interferometer (MZI) filter [18] , an unpumped polarization-maintaining EDF saturable absorber filter [19] , two superimposed FBGs and an in-line two-taper MZI filter [20] , a 70 cm long EDF loop attached to a microfiber coupler as wavelength filter [21] , a polarization-maintaining chirped Moiré FBG as ultra-narrow filter [22] , and a special U-bending apparatus based filter [23] . However, all of the techniques cannot achieve continuously tunable wavelength-spacing, switchable single-/dual-wavelength operation and narrow linewidth lasing simultaneously.In this paper, we propose and demonstrate a single-/dualwavelength switchable and tunable SLM EDFL with super-narrow linewidth based on a compound cavity which consists of a ring main cavity and a two-ring subring cavity (TR-SC). The performance of this EDFL is investigated in detail.The configuration of the proposed EDFL is shown in Fig.1. The fiber laser is based on a compound cavity consisting of a main cavity and a TR-SC. In the main ...