Widely tunable single-/dual-wavelength fiber lasers with ultra-narrow linewidth and high OSNR using high quality passive subring cavity and novel tuning method

Abstract

High stability single- and dual-wavelength compound cavity erbium-doped fiber lasers (EDFLs) with ultra-narrow linewidth, high optical signal to noise ratio (OSNR) and widely tunable range are demonstrated. Different from using traditional cascaded Type-1/Type-2 fiber rings as secondary cavities, we nest a Type-1 ring inside a Type-2 ring to form a passive subring cavity to achieve single-longitudinal-mode (SLM) lasing with ultra-narrow linewidth for the first time. We also show that the SLM lasing stability can be further improved by inserting a length of polarization maintaining fiber in the Type-2 ring. Using a uniform fiber Bragg grating (FBG) and two superimposed FBGs as mode restricting elements, respectively, we obtain a single-wavelength EDFL with a linewidth as narrow as 715 Hz and an OSNR as high as 73 dB, and a dual-wavelength EDFL with linewidths less than 1 kHz and OSNRs higher than 68 dB for both lasing wavelengths. Finally, by employing a novel self-designed strain adjustment device capable of applying both the compression and tension forces to the FBGs for wavelength tuning, we achieve the tuning range larger than 10 nm for both of the EDFLs.

Six-Wavelength-Switchable SLM Thulium-Doped Fiber Laser Enabled by Sampled FBGs and 3 × 3 Coupler Based Dual-Ring Compound Cavity Filter

“…Second, the passband v  of the DRCC should be comparable with the FSR of the AMRC, which guarantees that only one longitudinal mode is located at the passband of the DRCC. The passband bandwidth of the DRCC can be calculated according to the following equation [13,26]:…”

“…To further enable SLM lasing for the wavelength-switchable laser, it is critical to find effective mode-selection mechanisms against the resulting small FSR due to the elongated laser cavity length. Effective mode-selection techniques include the use of ultra-narrow bandwidth filters or an unpumped doped fiber as a self-tracking narrowband reflection filter [23,24], and the incorporation of the compound-cavity or the multi-ring compound cavity (MR-CC) [12,13,[25][26][27][28]. The fiber rings used in MR-CC are generally based on optical couplers (OCs), which makes this method a more affordable and easier alternative for use in the 2 μm band, where there is a lack of optimized components.…”

Wavelength-Switchable Single-Longitudinal- Mode Thulium-Doped Fiber Laser With Sampled Fiber Bragg Grating

“…, where c, n, L and δ are the speed of light in vacuum, the effective index of refraction (1.44), the length of R-2 and the one-way loss of the passive resonant cavity, respectively [29] . The one was loss can be expressed as:…”

Five-Wavelength-Switchable Single-Longitudinal-Mode Thulium-Doped Fiber Laser Based on a Passive Cascaded Triple-Ring Cavity Filter

“…Then, SLM operation can be obtained when the effective FSR is wider than half the 3 dB-bandwidth of the wavelength selector [15]. The primary passive subring cavities in an MR-CC are generally composed of one or multi-cascaded/parallel single-coupler-based fiber rings (single-coupler ring, SCR) [16]- [18], dual-coupler ring (DCR) [13], [16], three nested couplers ring [19], or a combination of DCR and SCR [20]. Apart from quantitatively determining the parameters of compound rings based on the Vernier effect, the filtering performance for the desired mode can also be determined by obtaining the optimized parameters This work is licensed under a Creative Commons Attribution 4.0 License.…”