| Jun 06, 2025 |
First practical QD surface-emitting laser boosts fiber optic efficiency and cost
Quantum dots with precise crystal growth and advanced processing enable compact, energy-efficient, and cost-effective light sources for optical fiber communications.
(Nanowerk News) The National Institute of Information and Communications Technology (NICT) and Sony Semiconductor Solutions Corporation have jointly developed the first practical surface-emitting laser using quantum dots (QDs) as the optical gain medium, targeting applications in optical fiber communications. This advance marks a significant step toward miniaturizing light sources while improving their energy efficiency and scalability.
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The newly developed device is a vertical-cavity surface-emitting laser (VCSEL) that operates at 1,550 nanometers—the standard wavelength used in long-distance optical fiber networks. Until now, VCSELs have been primarily used at shorter wavelengths, such as 850 or 940 nm, due to fabrication constraints at longer wavelengths. Producing devices that operate efficiently at 1,550 nm has required significant innovation in both materials and structural design.
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The research, published in Optics Express ("Electrically pumped laser oscillation of C-band InAs quantum dot vertical-cavity surface-emitting lasers on InP(311)B substrate"), combines two key technological achievements: high-precision crystal growth by NICT and advanced device fabrication by Sony.
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| Schematic of a surface-emitting laser and quantum dots. (Image: National Institute of Information and Communications Technology)
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Overcoming Challenges in Long-Wavelength VCSELs
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VCSELs are compact, energy-efficient lasers that emit light vertically from the surface of a semiconductor wafer. While widely used in short-reach applications such as data centers, their integration into standard telecom wavelengths has been limited by material constraints. At 1,550 nm, it becomes much harder to create distributed Bragg reflectors (DBRs)—the multilayer mirror structures essential to VCSEL operation—due to the limited set of compatible semiconductor materials.
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NICT addressed this bottleneck by developing a high-precision molecular beam epitaxy process for compound semiconductors. This method allows atomic-scale control of material composition, enabling the growth of DBR structures with reflectivity exceeding 99% even at 1,550 nm. NICT also applied strain-compensation techniques to offset lattice strain around the embedded quantum dots. This improvement increased the QD density and enhanced light emission efficiency.
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Device Innovation Through Tunnel Junctions
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Sony contributed an advanced semiconductor processing technique that resolves a key design limitation of surface-emitting lasers. In typical VCSEL configurations, metal electrodes used for injecting current can block the emitted light. To overcome this, Sony implemented a tunnel junction architecture that allows efficient current injection without obstructing light extraction. This required precision fabrication to align and integrate multiple semiconductor layers while maintaining electrical and optical performance.
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The combination of NICT’s and Sony’s technologies enabled stable lasing at 1,550 nm using a threshold current of just 13 mA. The device also demonstrated polarization stability—an important factor for reducing signal distortion in communication systems.
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Toward Scalable, Energy-Efficient Optical Communications
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Using quantum dots as the gain medium in VCSELs provides intrinsic temperature stability and design flexibility. Unlike conventional quantum well lasers, QDs confine charge carriers in all three spatial dimensions, making them less sensitive to thermal fluctuations. This robustness, coupled with the scalable architecture of VCSELs, supports mass production and integration into photonic systems.
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The resulting platform offers a pathway toward low-cost, high-performance lasers for dense optical interconnects, enabling energy-efficient data transmission in next-generation communication infrastructures.
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Outlook
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NICT and Sony aim to further refine quantum-dot-based VCSEL technology for broader deployment in optical networks beyond 5G. Their ongoing work will focus on increasing data capacity while minimizing power consumption, in line with growing demands for efficient, high-throughput communications. Alongside technical development, efforts will be made to accelerate commercialization and social implementation of the technology.
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