Multicolor Laser Expands Integrated Photonics Landscape

Though integrated semiconductor lasers have been at the core of integrated photonics, enabling many advancements over the last few decades in information technologies and basic science, integrated lasers continue to lack key functions that are needed for evolving applications, including lidar and AR/VR.

Using a type of integrated semiconductor laser that is based on the Pockels electro-optic effect, a team from the University of Rochester (UR), with researchers at Caltech, the University of California, Santa Barbara, and Clemson University, believes that it has now developed a device with the potential to reshape the landscape of integrated photonics.

The Pockels-based laser is integrated with a lithium-niobate-on-insulator (LNOI) platform. Lithium-niobate is known for its superior optical modulation and frequency conversion capabilities.

The researchers surmised that two major challenges hindering the use of integrated semiconductor lasers were the lack of fast reconfigurability and the narrow spectral window. To overcome these challenges, the team undertook a hybrid integration of a lithium-niobate external cavity with a III-V reflective semiconductor optical amplifier (RSOA) and developed an integrated Pockels laser.

The team’s LNOI external cavity is a Vernier mirror structure consisting of two racetrack resonators. To combine versatile functions into one laser structure, the team designed each resonator for a different purpose: The first resonator was integrated with a micro-heater for broad wavelength tuning via the thermo-optic effect. The second resonator was integrated with driving electrodes designed for high-speed electro-optic tuning.

In addition, the second resonator was tailored to be compatible with the second harmonic generation process. A tunable phase control section was also implemented in the cavity to align the longitudinal laser cavity mode with the Vernier mode.

Using the integrated lithium-niobate/III-V structure, the team to added capabilities to the laser that included fast on-chip reconfigurability with laser-frequency tuning at a record speed of 2.0 exahertz-per-second (EHz/s) and fast switching at a rate of 50 MHz. Both capabilities were made possible by integrating the electro-optic effect into the laser. Due to the low required drive voltages, both capabilities can be directly driven by CMOS signals.

A schematic of an integrated semiconductor laser that has the potential to reshape the landscape of integrated photonics, according to the developing team. The researchers said that the Pockels-based laser is the first multicolor, integrated laser that emits high-coherence light at telecommunication wavelengths and in the visible band, and is the first narrow-linewidth laser with fast reconfigurability at the visible band. The technology provides a fully on-chip laser solution that could be used to probe and manipulate atoms and ions. AR/VR and other applications that operate at short wavelengths could also benefit from the integrated semiconductor laser. Courtesy of Mingxiao Li.

The device co-lases at infrared and visible frequencies via the second-harmonic frequency conversion process.

According to the researchers, the Pockels-based laser is the first multicolor, integrated laser that emits high-coherence light at telecommunication wavelengths and in the visible band, and the first narrow-linewidth laser with fast reconfigurability at the visible band.

Due to its fast frequency chirping capabilities, the laser could benefit lidar systems that incorporate the laser. Further, its frequency conversion capabilities, which surpass the spectral bandwidth limitations of traditional integrated semiconductor lasers, are poised to relieve difficulties in developing new wavelength lasers. The laser’s narrow wavelength and fast reconfigurability provide a fully on-chip laser solution that atomic physicists could use to probe and manipulate atoms and ions. AR/VR and other applications that operate at short wavelengths could also benefit from the integrated semiconductor laser.

The work extends the applications of the LNOI platform and could provide a design path to systems with a range of functions and with potential applications in nonlinear optics, optical signal processing systems, quantum photonics, and optical communications.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-022-33101-6).