Presenting the new lithium niobate laser technology
Researchers from Switzerland have developed a new type of laser based on lithium niobate (LiNbO3) that can control the frequency or intensity of light transmitted through a device. Supported by the EU-funded projects MICROCOMB, OMT, HOT and QUSTEC, their work could have a major impact on optical ranging technology. Lithium niobate – a synthetic salt consisting of niobium, lithium and oxygen – is used extensively in the telecommunications market. It is one of the most widely used materials for high-speed electro-optical modulators. As a news item posted on ‘Optics.org’ reports, its usefulness lies in the ability to “handle a lot of optical power” and to “change its optical properties when an electric field is applied to it.” However, as the researchers explain in their study published in the journal ‘Nature’, even though “recent advances have demonstrated tunable integrated lasers based on LiNbO3, the full potential of this platform to demonstrate frequency-agile, narrow-linewidth integrated lasers has not been achieved.”
Combining lithium niobate with silicon nitride
To remedy this, the research team combined lithium niobate with silicon nitride (Si3N4) to create a new type of hybrid integrated tuneable laser. First, photonic integrated circuits based on silicon nitride were manufactured at OMT and HOT project coordinator and MICROCOMB project partner Swiss Federal Institute of Technology Lausanne (EPFL), Switzerland. The circuits were then bonded with lithium niobate wafers at MICROCOMB, OMT and HOT project partner IBM Research Europe, also based in Switzerland. The study authors describe their approach: “Our platform is based on heterogeneous integration of ultralow-loss Si3N4 photonic integrated circuits with thin-film LiNbO3 through direct bonding at the wafer level, in contrast to previously demonstrated chiplet-level integration, featuring low propagation loss of 8.5 decibels per metre, enabling narrow-linewidth lasing (intrinsic linewidth of 3 kilohertz) by self-injection locking to a laser diode. The hybrid mode of the resonator allows electro-optic laser frequency tuning at a speed of 12 × 1015 hertz per second with high linearity and low hysteresis while retaining the narrow linewidth.” The team’s approach yielded qualities that are needed for lasers used in light detection and ranging applications. The resulting laser demonstrated low frequency noise – suggesting a stable frequency – and fast wavelength tuning. The researchers then used the laser to measure distances with high precision in an optical ranging experiment. “What is remarkable about the result is that the laser simultaneously provides low phase noise and fast petahertz-per-second tuning, something that has never before been achieved with such a chip-scale integrated laser,” notes study senior author Prof. Tobias J. Kippenberg of EPFL in the news item. Besides integrated lasers, the hybrid platform developed with support from MICROCOMB (Applications and Fundamentals of Microresonator Frequency Combs), OMT (OMT - Optomechanical Technologies), HOT (Hybrid Optomechanical Technologies), and QUSTEC (QUSTEC: international, interdisciplinary and intersectoral doctoral programme in Quantum Science and Technologies) could also be used to develop integrated transceivers for telecommunications and microwave-optical transducers for quantum computing. For more information, please see: MICROCOMB project OMT project website HOT project website QUSTEC project website
Keywords
MICROCOMB, OMT, HOT, QUSTEC, laser, integrated laser, tuneable laser, lithium niobate, silicon nitride
