Hexa-ring structured erbium fiber laser with wideband tunability and single-frequency operation

In this demonstration, an erbium-doped fiber (EDF) laser incorporating a hexa-ring configuration is designed and experimentally investigated, when C-band erbium gain is applied. Through the compound-ring-induced mode-filtering effect based on the Vernier mechanism, the prevalent multi-longitudinal-mode (MLM) oscillations are entirely suppressed, enabling stable single-longitudinal-mode (SLM) operation. Based on the hexa-ring design, the tuning range of the proposed EDF laser can be extended to 1518.0 to 1571.0 nm, accompanied by a narrow 3-dB linewidth of 0.312 kHz. Furthermore, the output features, including power, optical signal to noise ratio (OSNR), and stability, are evaluated and discussed.