Mode-locked ring laser with output pulse width of <0.5 ps

The output pulse width of a mode-locked ring laser composed of an erbium-doped fiber amplifier, Mach-Zehnder type optical modulator, and optical band-pass filter depends largely on the repetition frequency and the wavelength characteristics of these optical circuit elements. In previous experiments, the output pulse width was of the order of 5 ps at a repetition frequency of 5 GHz. The principal reason was that the narrow passage band of the optical circuit elements made it extremely difficult to generate the ultra-short optical pulse. Consequently, we examined how to narrow the optical pulse width by flattening the wavelength characteristics of these optical circuit elements. By using the all-optical circuit devices with wider wavelength passage band than previously possible comprising a mode-locked ring laser, we achieved an output pulse width of narrower than 0.5 ps at a repetition frequency of 5 GHz; the pulse peak power was more than +25 dBm, and the time bandwidth product was 0.32. We successfully tested an ultra-short optical pulse source with an output pulse width of less than 0.5 ps with no external pulse compression using a mode-locked ring laser