Slow light boosts VCSEL performance to 100GHz
Researchers in the US have developed a vertical-cavity surface-emitting laser (VCSEL) that has a record bandwidth of 100GHz. This can help boost the performance of datacentre interconnects and reduce the power consumption.
The design combines multiple transverse coupled cavities, which enhances the optical feedback of the laser. This overcomes the 3dB bandwidth, known as the speed limit of VCSELs, that limited by thermal effects, parasitic resistance, capacitance and nonlinear gain effects.
Direct modulation of VCSELs cannot exceed about 30GHz due to nonlinear optical amplification effects known as gain relaxation oscillations. As feedback inside the laser needs to be carefully managed, the researchers introduced a multi-feedback approach by combining multiple coupled cavities. This allowed them to strengthen the feedback known as slow-light, extending the temporal laser bandwidth beyond the known limit of the relaxation oscillation frequency. This means the direct feedback from each cavity only needs to be moderate and can be controlled precisely via the coupled cavities, allowing for a higher degree of design freedom. Following this coupled cavity scheme, a resulting modulation bandwidth in the 100 GHz range is expected.
“Here we introduce a paradigm-shift in laser design. We utilize a novel coupled cavities approach to carefully control the feedback to the laser achieved by significantly slowing the laser light down. This coupled cavity approach adds a new degree of freedom for laser design, with opportunities in both fundamental science and technology.” – Volker Sorger, associate professor of electrical and computer engineering at the George Washington University.
“This invention is timely since demand for data services is growing rapidly and moving towards next generation communication networks such as 6G, but also in automotive as proximity sensor or smart phone’s face ID. Furthermore, the coupled cavity system paves a way for emerging applications in quantum information processors such as coherent Ising machines.”
The paper, “Hexagonal Transverse Coupled Cavity VCSEL Redefining the High-Speed Lasers,” was published in the journal Nanophotonics.
https://dx.doi.org/10.1515/nanoph-2020-0437
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