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Integrated Laser on Lithium Niobate Chip to Spur Advanced Telecom

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In collaboration with industry partners at Freedom Photonics and HyperLight Corp., researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) developed what the collaborators said is the first fully integrated high-power laser on a lithium niobate chip. The technology paves the way for high-powered telecommunications systems, fully integrated spectrometers, optical remote sensing, and efficient frequency conversion for quantum networks, among other applications.

Lithium niobate photonics technologies have seen a number of recent developments, from frequency combs to frequency converters and modulators. But lasers have proved difficult to integrate. An integrated laser would greatly reduce the cost and increase the scalability and stability of long-haul telecommunications networks, data center optical interconnects, and microwave photonics, all of which rely on lasers to generate an optical carrier used in data transmission.
The on-chip laser is combined with a 50 gigahertz electro-optic modulator in lithium niobate to build a high-power transmitter. Courtesy of Second Bay Studios, Harvard SEAS.
The on-chip laser is combined with a 50-GHz electro-optic modulator in lithium niobate to build a high-power transmitter. Courtesy of Second Bay Studios, Harvard SEAS.
“Integrated lithium niobate photonics is a promising platform for the development of high-performance chip-scale optical systems, but getting a laser onto a lithium niobate chip has proved to be one of the biggest design challenges,” said Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering and Applied Physics at SEAS and senior author of the study. “In this research, we used all the nano-fabrication tricks and techniques learned from previous developments in integrated lithium niobate photonics to overcome those challenges and achieve the goal of integrating a high-powered laser on a thin-film lithium niobate platform.”

Loncar and his team used small but powerful distributed feedback lasers for their integrated chip. The devices are prime candidates for integration with the thin-film lithium niobate modulators due to their small footprint, low cost, and high power output, according to the researchers.


The laser uses a high-power indium phosphide (InP)-based platform, which has demonstrated output powers greater than 300 mW and has reported low relative intensity noise. The laser design ensures minimal free-carrier absorption, a lower voltage drop across the diode, and reduced mirror loss. In turn, this results in a longer cavity length, which yields higher power, lower linewidths, and a reduction in spatial hole burning.

On chip, the lasers sit in small wells or trenches etched into the lithium niobate and deliver up to 60 mW of optical power in the waveguides fabricated in the same platforms. The team combined the laser with a 50-GHz electro-optic modulator in lithium niobate to build a high-power transmitter.

“Integrating high-performance plug-and-play lasers would significantly reduce the cost, complexity, and power consumption of future communication systems,” said Amirhassan Shams-Ansari, a graduate student at SEAS and first author of the study. “It’s a building block that can be integrated into larger optical systems for a range of applications in sensing, lidar, and data telecommunications.”

By combining thin-film lithium niobate devices with high-power lasers using an industry-friendly process, the work represents a key step toward large-scale, low-cost, and high-performance transmitter arrays and optical networks. Next, the team aims to increase the laser’s power and scalability for even more applications.

Harvard’s Office of Technology Development has protected the intellectual property arising from the Loncar Lab’s innovations in lithium niobate systems. Loncar is a co-founder of HyperLight Corp., a startup that was launched to commercialize integrated photonic chips based on certain innovations developed in his lab.

The research was published in Optica (www.doi.org/10.1364/optica.448617).


Published: April 2022
Glossary
semiconductor
A semiconductor is a type of material that has electrical conductivity between that of a conductor and an insulator. In other words, semiconductors have properties that are intermediate between metals (good conductors of electricity) and insulators (poor conductors of electricity). The conductivity of a semiconductor can be controlled and modified by factors such as temperature, impurities, or an applied electric field. The most common semiconductors are crystalline solids, and they are...
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...
lithium niobate
A crystalline ferroelectric material used primarily as a substrate and an active medium for thin-film optical modulators and switches. It possesses very high electro-optic and piezoelectric coefficients. LiNbO3.
chip
1. A localized fracture at the end of a cleaved optical fiber or on a glass surface. 2. An integrated circuit.
integrated circuit
Multiple, interconnected circuit elements, contained on or in a common substrate, that function as a unit and not separately.
Research & TechnologyLaserssemiconductorintegrated photonicslithium niobateMaterialsthin filmschiplaser on chipchip laserintegrated circuittelecommunicationsdistributed feedbackindium phosphate. HarvardHarvard SEASMarko LoncarHyperLightAmericasFreedom PhotonicsTechnology News

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