It’s not easy making green.
For years, scientists have been able to produce high-quality lasers that emit red and blue light, but creating tiny lasers that generate yellow and green light has been a challenge. This lack of miniature green lasers, known as the “green gap,” has limited opportunities in various fields, such as underwater communications and medical treatments.
Despite the existence of green laser pointers for the past 25 years, they only emit a narrow spectrum of green light and are not integrated into chips for more diverse functionalities.
Now, researchers at the National Institute of Standards and Technology (NIST) have successfully closed the green gap by modifying a small optical component called a ring-shaped microresonator that can fit on a chip.
The development of a miniature green laser source could revolutionize underwater communication, as blue-green wavelengths are highly efficient in water. This breakthrough also opens up possibilities for applications in full-color laser projection displays and medical treatments like diabetic retinopathy.
Miniature lasers in the green wavelength range are crucial for advancements in quantum computing and communication, allowing for data storage in qubits. Current quantum applications rely on larger, less versatile lasers that are limited to laboratory use only.
Leading the way in this research is a team led by Kartik Srinivasan of NIST and the Joint Quantum Institute (JQI). They have successfully used silicon nitride microresonators to convert infrared laser light into various visible colors, including green.
The team achieved this by slightly modifying the microresonator to generate light at wavelengths as short as 532 nanometers, covering the entire green gap. By exposing the microresonator to more air and making adjustments to its dimensions, they were able to produce over 150 distinct wavelengths within the green gap.
Efforts are now focused on enhancing the energy efficiency of producing green-gap laser colors, aiming to increase the output power significantly. Better coupling between the input laser and the waveguide, along with improved methods of extracting generated light, could lead to a substantial improvement in efficiency.
The researchers, along with collaborators from Meta’s Reality Labs Research, have published their findings in the journal Light: Science and Applications.