Passively mode-locked monolithic two-section gain-guided tapered quantum-dot lasers: II. Record 15 Watt peak power generation

In recent years, quantum-dot (QD) mode-locked semiconductors lasers have shown great potential as ultrashort pulse laser sources [1]. For instance, the generation of ultrashort transform-limited pulses with pulse durations of 360 fs has been previously demonstrated in tapered index-guided mode-locked quantum-dot lasers without any dispersion compensation - however, peak power reached only 2.25 W, for a typical average power of 15.6 mW [2]. In our recent work, we have shown that output average/peak power and pulse energy can be greatly increased using a tapered (or flared) gain-guided structure [3]. In [3], two-section devices incorporating 5 or 10 QD layers with a total length of 2.78mm were used, resulting in pulse repetition rates of the order of 14.6 GHz. With an absorber-to-gain lengths ratio of 17, the highest peak power achieved was 3.6W from both QD structures. On the other hand, a maximum average power of 209 mW corresponding to 14.2 pJ pulse energy with 6-ps pulse duration was achieved for the 5-layer QD laser. The generation of high-peak-power pulses is vital for a variety of applications such as biomedical nonlinear microscopy and imaging, where a combination of high peak power and average power (up to the limit tolerable by the bio-sample) are most effective in enhancing the nonlinear effects required. In this paper, we report the highest peak power (to our knowledge) of 15 W directly from a monolithic quantum-dot tapered laser, with sub-picosecond pulse width.