Abstract
In this investigation, a convex-shaped fiber ring (CSFR)-based single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) is proposed and experimentally verified. The CSFR, composed of only two optical couplers and forming a double-ring architecture, is employed to serve as a high quality mode filter to eliminate the dense longitudinal modes of the EDFL. The unpumped erbium-doped fiber in the Sagnac loop is utilized to produce the ultra-narrowband auto-tracking filter effect as a saturable absorber to guarantee the SLM out. The experimental results show that the linewidth of the proposed EDFL is 840 Hz with a high optical signal to noise ratio of 63 dB. In addition, the stability of the EDFL with the maximum output power fluctuation of 0.01 dB and the maximum central wavelength variation of 0.01 nm, in both the short-term and the long-term observations. Hence, we obtained a SLM EDFL with extremely high stability, ultra-narrow linewidth and high optical signal to noise ratio (OSNR).
Highlights
Single-longitudinal-mode (SLM) erbium-doped fiber lasers (EDFLs) have attracted a great amount of attention for their favorable applications in the optical fiber communication, the optical fiber sensor, the microwave photonics and the high-resolution spectroscope [1]–[4]
The main cavity of the proposed fiber laser consists of a convex-shaped fiber ring (CSFR) composed of two 2 × 2 optical coupler (OC) (OC2 and OC3) and a Sagnac loop comprised by a 1 × 2 OC (OC4) and a 6-m-long unpumped EDF2 (Nufern EDFC980-HP), apart from a 2-m-long commercial EDF1 (Liekki Er30-4/125), a 980-nm laser diode (LD), a 980/1550-nm wavelength division multiplexer (WDM), a circulator, a fiber Bragg grating (FBG), two optical isolators (ISO1 and ISO2), a polarization controller (PC), a polarization beam splitter (PBS) and a 2 × 2 OC (OC1)
ISO1 and the circulator are employed in the main cavity to ensure the unidirectional operation of the EDFL, which is to avoid the MLM oscillation caused by spatial hole burning
Summary
Single-longitudinal-mode (SLM) erbium-doped fiber lasers (EDFLs) have attracted a great amount of attention for their favorable applications in the optical fiber communication, the optical fiber sensor, the microwave photonics and the high-resolution spectroscope [1]–[4]. The erbium-doped fiber (EDF) ring laser configuration can avoid the spatial gain hole-burning induced by the sanding-wave effect presented in linear cavity fiber lasers and have the advantages of the high output power, the narrow linewidth and the all-fiber format [7], [8].
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