Multi-wavelength switchable erbium-doped fiber laser based on a hybrid filter incorporating a bi-tapered Mach–Zehnder interferometer and Sagnac loop

Abstract

A multi-wavelength switchable C-band erbium-doped fiber laser based on a hybrid comb filter composed of a Sagnac loop and Mach–Zehnder interferometer (MZI) is designed and experimentally demonstrated. In the designed ring cavity fiber laser, the MZI is composed of bi-tapered single-mode fiber fabricated by etching with hydrofluoric acid. In the experiment, the wavelength intervals in the comb spectra of the Sagnac loop and MZI are 3.4 and 18.8 nm, respectively, and by combining the Sagnac loop and MZI, measurements of the hybrid comb spectrum are obtained. When the pump power is 91 mW, lasing occurs at 1529.2 nm. Adjustment of the variable attenuator (VA) can provide 1541.9 and 1558.6 nm single-wavelength switchable lasers, for which the maximum peak power difference is less than 3.59 dB, the signal-to-noise ratio (SNR) exceeds 19.25 dB, and the peak power fluctuation is less than 0.34 dB over a 30 min scan time at 26 °C. For dual-wavelength switchable laser emission, four different sets of wavelengths can be realized, and the SNR exceeds 15.57 dB with power fluctuations of less than 1.6 dB, under the same monitoring conditions. By further adjusting the VA, stable and tunable triple-wavelength lasing is also realizable; under these conditions, the SNR exceeds 15.02 dB and the power fluctuation is less than 0.91 dB. Furthermore, four- and five-wavelength lasing can also be achieved by adjusting the VA again, with SNRs exceeding 19.05 and 14.98 dB, respectively.