  Dissipative Kerr solitons (DKSs) have been generated via injection locking of
chipscale microresonators to continuous-wave (CW) III-V lasers. This advance
has enabled fully integrated hybrid microcomb systems that operate in turnkey
mode and can access microwave repetition rates. Yet, CW-driven DKS exhibits low
energy conversion efficiency and high optical power threshold, especially when
the repetition rate is within the microwave range that is convenient for direct
detection with off-the-shelf electronics. Efficient DKS can be generated by
spatiotemporally structured light (i.e., pulsed pumping), which to date however
has required complex cascaded modulators for pulse synthesis. Here we
demonstrate a photonic integrated approach to pulsed pumping. 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 pump a
crystalline and integrated microresonators with coherent picosecond laser
pulses, achieving DKS generation 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 for the first time implement phase
engineering on the pulsed pumping scheme by either accessing a multimode lasing
regime in the gain-switching mode or applying external chirping to support
robust single-soliton generation. Our work leverages the advantages of gain
switching technique and pulse pumping technique, and establishes the merits of
combining distinct compact frequency comb platforms that enhance the potential
of energy-efficient chipscale microcombs.
