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Streamlined Microcomb Design Provides Control With The Flip of a Switch

Lasers developed at the University of Rochester offer a new path for on-chip frequency comb generators.

University of Rochester researchers created a chip-scale microcomb laser with an innovative design that allows users to control the optical frequency comb simply by switching on a power source. (Image: University of Rochester / J. Adam Fenster)

Light measurement devices called optical frequency combs have revolutionized metrology, spectroscopy, atomic clocks, and other applications. Yet challenges with developing frequency comb generators at a microchip scale have limited their use in everyday technologies such as handheld electronics.

In a study published in Nature Communications, researchers at the University of Rochester describe new microcomb lasers they have developed that overcome previous limitations and feature a simple design that could open the door to a broad range of uses.

What are Microcombs?

Optical frequency combs generate a spectrum of light consisting of multiple coherent beams, each tuned to a different frequency or color, in evenly spaced distances. The resulting shape resembles the teeth on a hair comb. In recent years, scientists have been working to create miniaturized versions of this technology, or microcombs, that can fit on small chips.

But while scientists have made progress in prototyping microcombs, they have had limited success producing viable versions that can be applied in practical devices. Obstacles include low power efficiency, limited controllability, slow mechanical responses, and the need for sophisticated system pre-configuration.

A Simplified Approach

A team of researchers led by Qiang Lin, a Professor in Rochester’s Department of Electrical and Computer Engineering and at the Institute of Optics, created a unique approach to solve these challenges in a single device.

According to Jingwei Ling, an Electrical and Computer Engineering Ph.D. Student in Lin’s lab and the Lead Author of the paper, previous approaches usually rely on a single-wavelength laser injected into a nonlinear converter that can transfer the single wavelength into multiple wavelengths, forming the optical comb.

“We eliminated the single wavelength because that’s going to degrade the system’s efficiency,” says Ling. “We instead have all the comb itself being amplified in a feedback loop inside the system, so all the wavelengths get reflected and enhanced inside a single element.”

The simplicity of the “all in one” microcomb laser results in lower power demands, lower costs, high tunability, and a turnkey operation.

“It is easy to operate,” says coauthor Zhengdong Gao, also an Electrical and Computer Engineering Ph.D. Student in Lin’s lab. “The previous methods make it hard to excite the comb, but with this method we only need to switch on the power source, and we can control the comb directly.”

Hurdles remain for implementing these microcomb lasers, particularly with developing fabrication techniques to create such tiny components within the tolerances necessary for manufacturing. But the researchers are hopeful that their devices can be used for applications such as telecommunications systems and light detection and ranging (LiDAR) for autonomous vehicles.

The Defense Advanced Research Projects Agency and the National Science Foundation supported this research.

This research was performed by Qiang Lin and a team of researchers from the University of Rochester. For more information, download the Technical Support Package (free white paper) below. ADTTSP-08245

Topics:
Aerospace Computers Electronic equipment Electronics Electronics & Computers Integrated circuits Lasers & Laser Systems Measurements Optics Optics Semiconductors & ICs Sensors and actuators Spectroscopy Test & Measurement
This Brief includes a Technical Support Package (TSP).
Document cover
Electrically Empowered Microcomb Laser

(reference ADTTSP-08245) is currently available for download from the TSP library.

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    Magazine cover
    Aerospace & Defense Technology Magazine

    This article first appeared in the August, 2024 issue of Aerospace & Defense Technology Magazine (Vol. 9 No. 5).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document presents research on an electrically empowered microcomb laser, addressing significant challenges in microcomb technology, such as complex soliton initialization, low power efficiency, and limited reconfigurability. The authors introduce a novel on-chip microcomb laser that combines the advantages of integrated laser structures with enhanced tunability and performance, making it suitable for a wide range of applications, including communication, metrology, and sensing.

    The microcomb laser utilizes a thin-film lithium niobate-on-insulator (LNOI) platform, integrating III-V gain chips with photonic integrated circuits. This integration allows for efficient mode-locking and the generation of soliton microcombs. The device is designed to be flexibly mode-locked using either active-driving or passive-feedback approaches, enabling ultra-fast tuning and reconfiguration. The authors highlight the laser's ability to achieve individual comb linewidths as low as 600 Hz and a frequency tuning rate of 39.58 GHz, showcasing its high power efficiency and robust operation.

    The document details the device fabrication process, which involves e-beam lithography and etching techniques to create waveguides and electrodes. The authors emphasize the importance of optimizing the roundtrip length of the main laser cavity to enhance the comb spectrum and coherence. They also discuss the use of group-delay tuning elements to further improve performance.

    The research findings indicate that the demonstrated integrated comb laser significantly outperforms conventional on-chip mode-locked semiconductor lasers, offering greater reconfigurability and efficiency. The authors envision this technology as a promising avenue for generating soliton microcombs on demand, with potential applications in ranging, communication, optical and microwave synthesis, and metrology.

    In conclusion, the document outlines a significant advancement in microcomb laser technology, presenting a chip-scale solution that combines simplicity, robustness, and enhanced tunability. The work is supported by various funding agencies, including DARPA and the National Science Foundation, and was conducted at the Cornell NanoScale Facility and the Cornell Center for Materials Research. The authors express gratitude to collaborators and acknowledge the contributions of peer reviewers, emphasizing the collaborative nature of this research.

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