Miniaturization of Ultrafast Laser Technology on Photonic Chips

Researchers have devised a novel approach to condense mode-locked lasers onto photonic chips, employing lithium niobate for active mode-locking. This cutting-edge technology holds the promise of scaling down large ultrafast laser experiments into chip-scale dimensions, with further intentions to curtail pulse durations and amplify peak powers.

Caltech has introduced an innovative technique for crafting compact, integrated mode-locked lasers directly on photonic chips, potentially revolutionizing the landscape of ultrafast laser applications by downsizing them while enhancing their performance.

While lasers have become commonplace in various applications, their utility extends far beyond lighting up raves and reading barcodes on consumer products. They play a pivotal role in telecommunications, computing, as well as in scientific research fields such as biology, chemistry, and physics.

The Significance of Ultrashort Laser Pulses

In the latter applications, lasers capable of emitting exceedingly brief pulses—on the order of one-trillionth of a second (one picosecond) or even shorter—prove indispensable. These ultrashort pulses empower researchers to investigate rapid physical and chemical phenomena, such as the formation or rupture of molecular bonds during chemical reactions or the motion of electrons within materials. Moreover, their application in imaging is extensive, owing to their substantial peak intensities and low average power, which mitigate the risk of heat damage to samples, including biological tissues.

Progress in Laser Technology

A paper published in the journal Science details the work of Caltech’s Alireza Marandi, an assistant professor of electrical engineering and applied physics. He describes a groundbreaking method developed by his team to create mode-locked lasers, known as nanophotonic mode-locked lasers, on a photonic chip. These lasers are constructed using nanoscale components, which enable their integration into light-based circuits, akin to the electricity-based integrated circuits found in contemporary electronics.

Marandi elucidates, “Our focus extends beyond merely downsizing mode-locked lasers; we are enthusiastic about crafting high-performance mode-locked lasers on nanophotonic chips and integrating them with other components. This step will usher in a complete ultrafast photonic system on an integrated circuit, bridging the gap between meter-scale experiments and millimeter-scale chips.”

Ultrafast Lasers and Nobel Prize Acknowledgment

The significance of ultrafast lasers for research is underscored by the recent Nobel Prize in Physics, awarded to a trio of scientists for their contributions to lasers that produce attosecond pulses (one attosecond being one-quintillionth of a second). Presently, such lasers are exorbitantly expensive and bulky. Marandi’s research, however, explores methodologies to achieve similar timescales on chips, potentially making them orders of magnitude more cost-effective and compact, with the aim of democratizing access to ultrafast photonic technologies.

Marandi’s team’s innovative nanophotonic mode-locked laser relies on lithium niobate, a synthetic salt with unique optical and electrical properties. In this context, it enables precise control and shaping of laser pulses through the application of an external radio-frequency electrical signal, employing active mode-locking with intracavity phase modulation.

Qiushi Guo, the first author of the paper and a former postdoctoral scholar in Marandi’s lab, remarks, “Around 50 years ago, intracavity phase modulation was used in tabletop experiments to create mode-locked lasers, but it was deemed less favorable compared to other techniques. However, we’ve found it to be an ideal fit for our integrated platform.”

Guo adds, “Beyond its compact size, our laser exhibits a range of intriguing properties. For example, we can precisely tune the repetition frequency of the output pulses across a wide range. This capability can be harnessed to develop chip-scale stabilized frequency comb sources, which are crucial for frequency metrology and precision sensing.”

Future Prospects and Research Impact

Marandi envisions ongoing advancements in this technology to achieve even shorter timescales and higher peak powers, aiming for a remarkable 50 femtoseconds (a femtosecond being one-quadrillionth of a second). This would represent a 100-fold improvement over their current device, which generates pulses lasting 4.8 picoseconds.

The research paper titled “Ultrafast mode-locked laser in nanophotonic lithium niobate” is featured in the November 9 issue of Science.

Reference: “Ultrafast mode-locked laser in nanophotonic lithium niobate” by Qiushi Guo, Benjamin K. Gutierrez, Ryoto Sekine, Robert M. Gray, James A. Williams, Luis Ledezma, Luis Costa, Arkadev Roy, Selina Zhou, Mingchen Liu and Alireza Marandi, 9 November 2023, Science.
DOI: 10.1126/science.adj5438

Co-authors include Benjamin K. Gutierrez (MS ’23), a graduate student in applied physics; electrical engineering graduate students Ryoto Sekine (MS ’22), Robert M. Gray (MS ’22), James A. Williams, Selina Zhou (BS ’22), and Mingchen Liu; Luis Ledezma (PhD ’23), an external affiliate in electrical engineering; Luis Costa, formerly at Caltech and now with JPL, which Caltech manages for NASA; and Arkadev Roy (MS ’23, PhD ’23), formerly of Caltech and now with UC Berkeley.

Funding for the research was provided by the Army Research Office, the National Science Foundation, and the Air Force Office of Scientific Research.

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More about Laser Miniaturization

• Caltech’s Research Page
• Science Journal Article
• Nobel Prize in Physics
• Lithium Niobate