On-chip Laser Pushes Photonics Milestones in LiDAR, AR/VR, and Beyond
Shrinking a room-sized laser to the scale of a fingernail, the researchers believe their on-chip laser will “reshape the landscape of integrated photonics.”
Photonics has made tremendous strides in the past decade, now reaching a point where researchers are miniaturizing large laser systems into integrated semiconductor lasers. One challenge of modern room-sized lasers is that these devices cannot be tuned and reconfigured quickly, both of which are essential for prominent use cases such as LiDAR.
To address these outstanding issues, a team of researchers led by the University of Rochester recently published a study describing an innovation that “has the potential to reshape the landscape of integrated photonics.” The team claims to that their newly-developed laser achieves two firsts: it is the first narrow linewidth laser with fast configurability at the visible band and the first multi-color integrated Pockels laser capable of emitting high-coherence light within telecommunication wavelengths. These features allowed the researchers to tune the laser's frequency at record speeds.
The fully on-chip laser is anticipated to affect LiDAR remote sensing in self-driving cars, microwave photonics, atomic physics, and AR/VR. Image used courtesy of the University of Rochester
In this article, we’ll discuss one of the working principles of this study—the Pockels effect—and how University of Rochester researchers leveraged it to build an integrated laser.
What is the Pockels Effect?
The Pockels effect is an electro-optic effect in which the refractive index of a medium is modified in proportion to an externally applied electric field. The effect produces something called birefringence, a relationship between the refractive index and the polarization and direction of light, which is directly proportional to the electric field’s strength. The Pockels effect is only known to occur in non-centrosymmetric materials, with the most popular ones being crystal materials such as lithium niobate.
Anatomy of a Pockels cell. Image used courtesy of Olympus Life Science
Also known as the linear electro-optic effect, the Pockels effect is most commonly used in the form of a Pockels cell. These cells are electro-optical devices that rotate the polarization of lasers and are driven by an external electric field.
University of Rochester Shrinks Benchtop Laser onto a Chip
This week, a research group led by the University of Rochester revealed how they designed a new type of integrated laser based on the Pockels effect. The new laser uses lithium-niobate-on-insulator (LNOI) waveguide elements to form an external cavity that is then coupled with the laser’s gain section.
A diagram of the new laser. Image used courtesy of the University of Rochester
The laser uses this section as a phase shift driven by an electrical signal to harness the Pockels effect. In this way, frequency modulation and frequency tuning is realized on the device by changing the effective optical path length of the laser cavity. This process occurs without introducing any loss, which is an important feature for fast frequency tuning.
The resulting laser was proven to achieve high-frequency modulation at a speed of 2 exahertz/s and fast frequency switching at a rate of 50 MHz.
The laser prototype delivered fast frequency chirping, which determines distance by recording the time between the emission of a short pulse and the return of reflected light. This feature is especially relevant for LiDAR sensor systems. The on-chip laser also displayed the ability to overcome the spectral bandwidth limitations of conventional integrated lasers. Furthermore, the laser operated within narrow wavelengths and offered fast reconfigurability—both useful characteristics to manipulate and probe ions and atoms in atomic physics.
Light-based Use Cases Galore
According to the research group, the new laser is immensely important for applications that require fast and precise frequency control. By miniaturizing a previously large technology, the researchers foresee benefits in use cases like LiDAR, remote sensing, microwave photonics, and AR/VR.