Optical Frequency Comb Generation in Semiconductor Lasers

Optical frequency combs are coherent light sources whose spectra consist of equally spaced lines, providing a ruler in the frequency domain. Semiconductor lasers have emerged as versatile platforms for comb generation, combining compactness with high-speed modulation and integrability. Techniques such as gain switching, optical injection locking and the excitation of dissipative Kerr solitons in microresonators have been adapted to semiconductor gain media, yielding combs with repetition rates from tens of megahertz to tens of gigahertz. Gain switching imposes a periodic modulation of the drive current to generate a comb directly from a laser diode, while optical injection uses an external comb or single-frequency laser to phase-lock and expand the emitted spectrum. More recently, integration of III-V gain elements with high-Q microresonators has enabled turnkey soliton microcombs, reducing power consumption to milliwatt levels and delivering microwave-rate pulse trains on a chip. These advances underpin applications in coherent communications, dual-comb spectroscopy and precision metrology, and pave the way for fully integrated optical clocks and portable sensing systems.

Research from Nature Portfolio

Recent studies have demonstrated that active modulation of injection-locked III-V lasers can pulse-pump high-Q microresonators and generate stable soliton microcombs in the X- and K-band microwave ranges. By synchronising picosecond current pulses with the resonator round-trip time and engineering the pump-pulse phase profile, researchers have reduced the average pumping power by an order of magnitude to just a few milliwatts. This approach has yielded robust soliton formation across crystalline and integrated platforms, delivering low-noise comb spectra with microwave repetition rates and enabling stable trapping of soliton pulses on intracavity pedestals. The work establishes a hybrid comb platform that unites the energy efficiency of gain switching with the spectral purity of Kerr solitons, offering a pathway to chip-scale frequency rulers for next-generation photonic systems.

Optical Frequency Comb Generation in Semiconductor Lasers publication trend

The graph below shows the total number of articles in optical frequency comb generation in semiconductor lasers across all publications each year (not limited to Nature Index journals).

Technical terms

Optical frequency comb: A spectrum of discrete, equally spaced optical lines used as a frequency reference.

Gain switching: A modulation technique in which the drive current of a semiconductor laser is pulsed to create an optical comb.

Optical injection locking: The process of synchronising a slave laser’s frequency and phase to an external optical signal to shape or expand its output spectrum.

Dissipative Kerr soliton: A self-localized waveform in an optical microresonator sustained by a balance between Kerr nonlinearity, dispersion and dissipation.

Dual-comb spectroscopy: A technique that uses two frequency combs with slightly different line spacings to perform high-resolution spectroscopy without moving parts.

References

1. Gain-switched semiconductor laser driven soliton microcombs. Nature Communications (2021).
2. Enhanced optical frequency comb generation by pulsed gain-switching of optically injected semiconductor lasers.. Optics Express (2019).
3. Gain-switched semiconductor lasers with pulsed excitation and optical injection for dual-comb spectroscopy.. Optics Express (2020).
4. Power efficient optical frequency comb generation using laser gain switching and dual-drive Mach-Zehnder modulator.. Optics Express (2019).