Programmable pulse width and wavelength tunable Er-doped active mode-locked laser for quantum applications

We demonstrate pulse width and wavelength tunable Er-doped mode lock laser (PWT-MLL) using pulsed modulation as opposed to sinusoidal modulation. We develop a theoretical model based on discrete coupled modes and solve it numerically to study the effect of pulsed modulation on the pulse width tunability of our proposed PWT-MLL. We also study the impact of intra-cavity filter on the performance of our laser. Using two types of optical bandpass filters (OBPFs)—a fixed filter with a 3 dB bandwidth of 0.7 nm and a tunable filter with a 3 dB bandwidth of 0.25 nm—we achieve both temporal and wavelength tunability at a fixed repetition rate. The pulse width of the laser is tunable from 2.3 ns to 370 ps in the case of a tunable filter and from 700 ps to 91 ps in the case of a fixed filter. The wavelength can be tuned across the entire C-band. Our results demonstrate that supermode noise suppression ratio (SMSR) and signal-to-noise ratio (SNR) are significantly influenced by pulse modulation duty cycles. Using Tunable Fiber Bragg grating (TFBG), the average SMSR was approximately 27 dB across all duty cycles. In contrast, the Dense Wavelength Division Multiplexing (DWDM) filter maintained a high SMSR only down to a 20 % duty cycle before declining sharply. In both configurations, the average SNR was close to 50 dB.