High peak power and sub-picosecond Fourier-limited pulse generation from passively mode-locked monolithic two-section gain-guided tapered InGaAs quantum-dot lasers

Abstract

We report on the development of a new generation of high power ultrashort pulse quantum dot lasers with tapered gain section. Two device designs are proposed and fabricated, with different total lengths and absorber to gain section length ratios. These designs have been informed by numerical simulations of the dynamic mode locking regimes and their dependence on the structural parameters. One device design demonstrated a record high peak power of 17.7 W with 1.26 ps pulse width and a second design enabled the generation of a Fourier limited 672 fs pulse width with a peak power of 3.8 W. A maximum output average power of 288 mW with 28.7 pJ pulse energy was also attained. In addition, the integrated timing jitter of 2.6 ps and far field patterns are demonstrated.

Ultra‐Short‐Pulse QD Edge‐Emitting Lasers

“…The simulations propose two specific waveguide designs to simultaneously attain short pulses and high peak power: first, based on [52], a short cavity length is preserved and a gain-to-absorber length ratios of 5 : 1 and 4 : 1 are chosen. Secondly, based on [52] a considerably decrease in pulse width is expected [44] if the laser operates in a condition where the QD GS net gain is close to its maximum value because of the small available density of states and the high cavity losses; this ensures a very small differential gain that highly reduces the gain saturation due to total carrier density depletion [53]. A further increase in the gain saturation energy is expected by implementing a large full taper angle of 2 • .…”

“…In this way, the ratio between the gain and absorption saturation energies is consequently highly improved [50] where gain saturation balancing the absorption bleaching in the absorber is mainly due to spectral-hole-burning nonlinearities allowing ultra-short pulse generation. In the simulations, the maximum peak power is found for a 4 mm [53][54][55]. The first electrode is the absorber section whereas the second electrode denotes the tapered gain section.…”

“…The laser under investigation is the fully gain-guided structure with a gain-toabsorber length ratio of 5 : 1 that has been introduced in Section 2.5.1 [53,54,59]. The absorber is reverse biased with 6 V. On the basis of the knowledge obtained by the absorber R-SEED concept in Section 2.4.2, where the absorber section had been exploited as a photocurrent control element, in the following, the absorber section is exploited as a saturable absorber, a photodiode, and as a laser control element.…”

“…19 Autocorrelation time trace for tapered laser with 5 : 1 gain-to-absorber length ratio indicating shortest obtained pulse width of 672 fs[53,54].and is observed at a gain current of 575 mA and at a reverse bias of 6 V[52,53]. The corresponding pulse trace is depicted inFigure 2.19.Together with a spectral width of 2.8 nm, the time-bandwidth-product (TBP) amounts to 0.36 indicating nearly transform-limited pulses.…”

“…Stable ML is indicated by a low −20 RF spectrum for the mode-locked tapered laser with a gain-to-absorber length ratio of 5 : 1 indicating ML with a strong RF suppression >51 dB. Inset: zoom into fundamental beat frequency depicting a low linewidth of 11 kHz[53,54]. 21 Autocorrelation time trace for tapered laser with 4 : 1 gain-to-absorber length ratio for the highest peak power of 17.7 W and for an injection current of 1.5 A and a reverse bias of 4 V. Left inset: RF spectrum depicting the fundamental beat frequency[53,55].…”