A chip-scale laser can achieve ultrafast frequency control for diverse applications in precision optical metrology [Image: J. Adam Fenster/University of Rochester]
Researchers in the United States have engineered a chip-based laser device that could deliver simpler and more compact systems for precise optical metrology (Light Sci. Appl., doi: 10.1038/s41377-025-01872-4). The streamlined solution provides the performance needed for the most demanding applications, including the navigation systems in autonomous vehicles and the finely tuned instrumentation needed for optical clocks and quantum information processing.
A more precise beam
Although optical metrology has become a vital tool in many areas of science and technology, current solutions require bulky and expensive equipment to control the exact parameters of the laser beam. Existing lasers also lack the high-speed frequency control needed to support state-of-the-art protocols for lidar, requiring complex feedback systems to achieve the reliability required for self-driving cars.
In the hybrid design demonstrated by the team, the gain provided by a semiconductor optical amplifier is coupled into an external cavity made from lithium niobate, an electro-optic material that is known for its ability to modulate the frequency of optical signals. Such integrated lasers have been demonstrated before, but they have not yet achieved the narrow linewidths or frequency control needed for precision metrology.
To improve performance, the researchers formed a Bragg reflector in the cladding layer of silicon oxide, which has a much lower refractive index than lithium niobate. The ultranarrow reflection spectrum produced by this novel design yields a linewidth as narrow as 167 Hz, which is better than previous demonstrations.
The ultranarrow reflection spectrum produced by this novel design yields a linewidth as narrow as 167 Hz, which is better than previous demonstrations.
High-speed frequency control is achieved by using the electro-optic properties of lithium niobate to tune the center frequency of the Bragg reflector. This strategy achieves a broad tuning range of around 10 GHz at modulation frequencies of up to 1 GHz, allowing the frequency to be chirped at a record-high rate of 2 × 1019 Hz/s. The output from the integrated device can also be varied at frequencies of more than 10 GHz—orders of magnitude higher than any other laser.
Testing the laser
The researchers tested the performance of the device by incorporating it into a lidar system that can detect both the location and velocity of surrounding objects. This lab-based demonstration measured velocities of 40 m/s at distances of down to 0.4 m—a significant improvement on conventional ranging systems—and can determine distances with a resolution below 20 mm.
The high modulation speed offered by the laser also enables the frequency to be stabilized without any external equipment for light control. By directly locking the laser to a reference gas cell, the team reduced the fluctuation in the laser frequency to ±6.5 MHz over a period of 60 minutes. “Since the majority of optical metrology applications require frequency-stabilized lasers for proper operation, this simplified architecture could significantly enhance both the integration and performance of these measurement systems,” the researchers conclude.
