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The recent breakthrough achieved by scientists at the National Institute of Standards and Technology (NIST) represents a significant advancement in closing the green gap. The NIST team has successfully developed a compact, high-efficiency green laser by modifying a tiny optical component called a ring-shaped microresonator.
This microresonator, small enough to fit on a chip, marks a transformative step forward in addressing the limitations of previous technologies. Traditional compact laser diodes have been effective at emitting infrared, red, and blue wavelengths, but they have needed help efficiently producing green and yellow light.
The new approach developed at NIST involves using an advanced silicon nitride microresonator. This microresonator converts infrared laser light into visible wavelengths through optical parametric oscillation (OPO). In this process, infrared light is introduced into the ring-shaped resonator, which circulates thousands of times until it reaches an intensity that interacts strongly with the silicon nitride. This interaction results in the generation of new wavelengths of light.
This development is particularly notable because it addresses a critical need in various fields. For example, underwater communication systems could benefit from green laser light, as water is nearly transparent to blue-green wavelengths in most aquatic environments.
This would enable more effective communication in underwater settings where traditional methods fall short. Additionally, green lasers could enhance full-colour laser projection displays and improve medical treatments for conditions like diabetic retinopathy, which involves the proliferation of abnormal blood vessels in the eye.
The ability to generate green and yellow laser light has far-reaching implications beyond these immediate applications. One of the most exciting areas is quantum computing and communication. Quantum technologies rely on larger, less efficient lasers, limiting their practicality and deployment outside the laboratory. By developing compact lasers within the green gap, researchers at NIST have made a significant leap toward more portable and practical quantum computing systems. The potential to store and process data using qubits could revolutionise the field.
The NIST team, led by Kartik Srinivasan and affiliated with one of the research institutions, has employed several innovative techniques to achieve this breakthrough. The researchers modified the microresonator in two key ways to fill the green gap. First, they slightly thickened the microresonator. This extended range allowed them to cover the entire green gap spectrum effectively.
Second, the team exposed the microresonator to more air by etching away some of the silicon dioxide layer beneath it. This modification reduced the output colour’s sensitivity to changes in the microring dimensions and the infrared pump wavelength. As a result, the researchers gained greater control over the emitted wavelengths, allowing them to generate a wide range of colours from green to red.
The success of this technology is evident in the fact that the researchers can now produce over 150 distinct wavelengths across the green gap. This achievement represents a significant advancement over previous technologies, which could only generate broad colour bands with limited precision. The ability to fine-tune the wavelengths within the green gap opens up new possibilities for applications that require precise colour control.
Despite the significant progress made, the NIST team is continuing to work on improving the energy efficiency of continuous-gap lasers. Currently, the output power of these lasers is only a small fraction of the input power, which limits their practical applications. Enhancing the coupling between the input laser and the microresonator and improving the methods for extracting the generated light are key areas of focus for future development. This innovation highlights the ongoing evolution of digital technology and its impact on diverse applications, paving the way for future advancements in laser science and technology.
