Single longitudinal mode laser generation using coupled microfiber Mach–Zehnder interferometer filter

The fabrication and operation of a single longitudinal mode (SLM) laser using a compact coupled microfiber Mach–Zehnder interferometer (CM-MZI) in an erbium doped fiber (EDF) laser cavity is demonstrated. The CM-MZI is created by first fabricating an optical microfiber using the flame-brushing technique before being cut and rejoined to form a half-loop, which is the basis for the CM-MZI structure. The CM-MZI is inserted into an EDF laser cavity; the filtering effect of the CM-MZI induces a stable SLM lasing output with a consistent 3 dB bandwidth of 0.02 nm at different a pumping power and signal-to-noise ratio of ~50 dB. The output also exhibits minimal wavelength and power fluctuations of 0.02 nm and 0.15 dB, respectively, over a time period of 60 min.