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Enlightra, DESY Hamburg Develop Improved, Scalable Comb Lasers

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JOEL WILLIAMS, NEWS EDITOR
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Laser technology startup Enlightra has collaborated with DESY Hamburg to develop comb lasers that are more stable and efficient by design. The work demonstrated microresonators with programmable synthetic reflection, providing tailored injection feedback to the driving laser. The technology is a marked improvement compared to conventional self-injection locking, and can be produced using standard lithographic production.

Comb lasers are sources of multiple colors with equidistant spacing ranging from 100 GHz to 1 THz. The technology is highly valuable for optical communications to achieve the data necessary of AI applications.
The key components of Enright’s laser comb. On the left a conventional distributed feedback laser on the right Enlightra’s patented photonic integrated circuit cable of producing 100s of wavelengths from a single laser. Courtesy of Enlightra.
The key components of Enlightra's laser comb. A conventional distributed feedback laser (left). Enlightra’s patented photonic integrated circuit capable of producing hundreds of wavelengths from a single laser (right). Courtesy of Enlightra.

One of the key aspects of a comb laser’s usefulness is its color purity. While lasers may seem like they have very pure color, for the most part, the beam is made up of many different shades of very similar colors. In the case of applications such as optical communications, it is desirable to have a laser that emits many different, pure colors. This is where comb lasers come in.

To improve purity for comb lasers, self-injection locking has been the standard method. The method uses ring resonators to filter out noise. Through Rayleigh backscattering, light bounces off of random imperfections within the ring and is sent back to the laser to do the injection locking.

“The problem with relying on random imperfections is that they can depend on the color and that they are not very strong,” said John Jost, cofounder of Enlightra and one of the authors of the paper. “With some limits, you want to send more light back to the laser, as this helps a lot with the injection locking.”

One of the key advancements of this research was engineering how the light scatters backward within the ring resonator. This was achieved by engineering the inner surface of a ring with a pattern that strongly scattered only one particular color. As the light goes around the ring, it feels the pattern and enables more light to be sent back for injection locking than it typically could, Jost told Photonics Media.


“This greatly improved the injection locking,” Jost said.
Enlightra’s comb laser supports integrated light sources for optical I/O solutions and distributed computing and memory architectures. Courtesy of Ethan Beaney.
Enlightra’s comb laser supports integrated light sources for optical I/O solutions and distributed computing and memory architectures. Courtesy of Ethan Beaney.

The authors conducted various tests with different customized nanostructured ring resonators. They used a semiconductor laser diode butt-coupled to the photonic chip with the ring resonator. The technology was demonstrated in the C-Band but works equally well in all the telecommunications bands. The actual resonator was built in an integrated photonic chip with silicon nitride photonic crystal ring resonators, embedded in silica cladding.

“The photonic integrated circuits used in this work were fabricated at industrial foundries, so the technology is already ready to scale,” Jost said. “The ability to engineer the scattering of the light opens up a whole new door for more advanced designs that will allow us to tailor to our needs the comb laser spectrum in ways before not thought possible.”

The laser can be incorporated with a broad variety of photonic integrated circuits. For example, it could support fast optical I/O units or optical field-programmable gate arrays. The technology will be beneficial for data intensive applications, such as generative AI, and novel disaggregated computer and memory architectures.

According to Jost, he and his team already have more ideas than they can possibly try. 
 
The research was published in Nature Photonics (www.doi.org/10.1038/s41566-023-01367-x).

Published: January 2024
Glossary
integrated photonics
Integrated photonics is a field of study and technology that involves the integration of optical components, such as lasers, modulators, detectors, and waveguides, on a single chip or substrate. The goal of integrated photonics is to miniaturize and consolidate optical elements in a manner similar to the integration of electronic components on a microchip in traditional integrated circuits. Key aspects of integrated photonics include: Miniaturization: Integrated photonics aims to...
frequency comb
A frequency comb is a precise and regular series of equally spaced spectral lines, or frequencies, that are generated with great accuracy. The term "frequency comb" is often associated with the Nobel Prize-winning technique known as frequency comb spectroscopy, developed by John L. Hall and Theodor W. Hänsch in the 1990s. The technology has since become a powerful tool in various scientific and technological applications. Key points about frequency combs: Origin and development: The...
efficiency
As applied to a device or machine, the ratio of total power input to the usable power output of the device.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
wavelength
Electromagnetic energy is transmitted in the form of a sinusoidal wave. The wavelength is the physical distance covered by one cycle of this wave; it is inversely proportional to frequency.
Research & Technologyintegrated photonicsLaserscombfrequency combring resonatormicroresonatorphotonic integrated circuitsPICsFPGAEnlightraDESY HamburgEuropeefficiencyphotonicsintegratedwavelengthnanostructureNature PhotonicsJohn JostTechnology News

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