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Date of publication xxxx 00, 0000, date of current version xxxx 00, 0000.

In the paper, a hybrid Mach-Zehnder interferometer (MZI) and Rayleigh backscattering (RB) injection is designed and applied in the erbium-doped fiber (EDF) ring laser configuration. The MZI scheme and RB-induced signal can accomplish the single-longitudinal-mode (SLM) oscillation and narrow the linewidth to kHz target for each generated wavelength over the available wavelength-tuning bandwidth. In the measurement, the output power, optical signal to noise ratio (OSNR) and wavelength linewidth of the designed fiber laser are also executed and discussed.

An erbium-doped fiber (EDF) laser with quad-ring is designed to reach the broad continuous-wave (CW) tunability and single-longitudinal-mode (SLM) behavior. Here, while a C-band erbium-based gain medium is exploited, the tunable scope can be extended from C- to part of L-bands and narrow the linewidth to several kHz by the presented compound-ring configuration. Additionally, the optical signal to noise ratio (OSNR), output power, and stability behavior of every lasing wavelength are also demonstrated.

In this paper, an erbium-doped fiber (EDF) octa-ring laser system with continuous-wave (CW) tunability and stable single-longitudinal-mode (SLM) output is presented and investigated. The octa-ring configuration can cause a mode-filter operation based on the Vernier effect for dense side-mode suppression and gain extension. Therefore, the available wavelength-tuning bandwidth of the laser can be achieved from 1519.0 to 1575.0 nm by utilizing conventional C-band EDF based gain-medium. Moreover, the output power, output stability, optical signal to noise ratio (OSNR) and laser linewidth of the demonstrated EDF laser are also executed and discussed.INDEX TERMS Erbium-doped fiber (EDF), fiber laser, tunability, single-longitudinal-mode (SLM), octa-ring.