Stanford team develops chip-scale Ti:sapphire laser

27 Jun 2024

New source can be pumped optically using ”cheap green laser diodes”.

Researchers at Stanford University, California, have developed and built a Ti:sapphire laser on a chip. The prototype is four orders of magnitude smaller (10,000x) and three orders less expensive (1,000x) than any Ti:sapphire laser ever produced.

“This is a complete departure from the old model,” said Jelena Vučković, the Jensen Huang Professor in Global Leadership, a professor of electrical engineering, and senior author of the paper introducing the chip-scale Ti:sapphire laser published yesterday in Nature. “Instead of one large and expensive laser, any lab might soon have hundreds of these valuable lasers on a single chip. And you can [drive it] with a green laser pointer.”

“When you leap from tabletop size and make something producible on a chip at such a low cost, it puts these powerful lasers within reach for a lot of different important applications,” said Joshua Yang, a doctoral candidate in Vučković’s lab and co-first author of the study along with Vučković’s Nanoscale and Quantum Photonics Lab colleagues, research engineer Kasper Van Gasse and postdoctoral scholar Daniil M. Lukin.

In technical terms, Ti:sapphire lasers are so valuable because they have the largest “gain bandwidth” of any laser crystal, explained Yang. In simple terms, gain bandwidth translates to the broader range of wavelengths the laser can produce compared to other lasers. It’s also ultrafast, Yang said; pulses of light issue forth every quadrillionth of a second.

But Ti:sapphire lasers are also hard to come by. Even Vučković’s lab, which perfroms quantum optics experiments, only has a few such lasers to share. The new Ti:sapphire laser fits on a chip that is measured in square millimeters, promising simpler mass-production.

How it works

To fashion the new laser, the researchers began with a bulk layer of titanium-sapphire on a platform of silicon dioxide (SiO₂), on a true sapphire crystal. They then grind, etch, and polish the Ti:sapphire to an extremely thin layer, just a few hundred nanometers thick. Into that thin layer, they then pattern a waveguide.

“Mathematically speaking, intensity is power divided by area. So, if you maintain the same power as the large-scale laser, but reduce the area in which it is concentrated, the intensity goes through the roof,” said Yang. “The small scale of our laser actually helps us make it more efficient.”

The remaining element is a microscale heater that warms the light traveling through the waveguides, allowing the Vučković team to change the wavelength of the emitted light between 700 and 1,000 nanometers.

Applications

In quantum physics, the new laser offers an inexpensive and practical solution that could dramatically scale down state-of-the-art quantum computers. In neuroscience, the Stanford researchers can foresee immediate application in optogenetics, a field that allows scientists to control neurons with light guided inside the brain by relatively bulky optical fiber.

Next up, the team will be working on perfecting their chip-scale Ti:sapphire laser and on ways to mass-produce them, thousands at a time, on wafers. Yang will earn his doctorate this summer based on this research and is working to bring the technology to market. “We could put thousands of lasers on a single four-inch wafer,” said Yang. “That’s when the cost per laser starts to become almost zero. That’s pretty exciting.”