Abstract
Dissipative Kerr soliton generation using self-injection-locked III-V lasers has enabled fully integrated hybrid microcombs that operate in turnkey mode and can access microwave repetition rates. Yet, continuous-wave-driven soliton microcombs exhibit low energy conversion efficiency and high optical power threshold, especially when the repetition frequencies are within the microwave range that is convenient for direct detection with off-the-shelf electronics. Here, by actively switching the bias current of injection-locked III-V semiconductor lasers with switching frequencies in the X-band and K-band microwave ranges, we pulse-pump both crystalline and integrated microresonators with picosecond laser pulses, generating soliton microcombs with stable repetition rates and lowering the required average pumping power by one order of magnitude to a record-setting level of a few milliwatts. In addition, we unveil the critical role of the phase profile of the pumping pulses, and implement phase engineering on the pulsed pumping scheme, which allows for the robust generation and the stable trapping of solitons on intracavity pulse pedestals. Our work leverages the advantages of the gain switching and the pulse pumping techniques, and establishes the merits of combining distinct compact comb platforms that enhance the potential of energy-efficient chipscale microcombs.
Highlights
Dissipative Kerr soliton generation using self-injection-locked III-V lasers has enabled fully integrated hybrid microcombs that operate in turnkey mode and can access microwave repetition rates
A soliton microcomb, the bias current of a semiconductor laser is modulated at a frequency close to the microresonator free spectral range (FSR)
Because the intrinsic linewidths of the semiconductor laser modules used in this study are of a few megahertz, we use a 1550-nm external cavity diode laser (ECDL) to injection-lock the semiconductor lasers, narrowing the linewidths of the slave lasers to ~20 kHz and ensuring the pulse-to-pulse coherence during gain switching
Summary
While we still cannot observe any wide soliton steps with the single-mode-lasing GSL pulses with average power up to 200 mW, we can generate a single-soliton microcomb (whose spectrum is presented in Fig. 4d) by using 40 mW of the offset-injection-locked GSL. This power level is fourfold larger than that for the DFB GSL because of the subharmonic pumping scheme and the CW component contained in the FP GSL. The demonstrated power threshold that is below the output power of the DM GSL shows promise for direct pulse-driven soliton generation if integrated dispersion compensation[45] is implemented
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