Symposium Background: Photonic Source Technologies: Surface Emitting Semiconductor Lasers
Dr. Kenichi Iga is responsible for one of the world's major technological breakthroughs that impacts society every day — the vertical-cavity surface-emitting laser, or VCSEL for short. Lasers are ubiquitous in our modern world, many of them found in places and in forms we might never realize. Most people know about laser printers, pointers, and CD/DVD players, but may not stop to think about the scanner in the supermarket checkout line, the fiber optic based data networks that bring them the internet, cable TV, and reliable wireless communications, or even the optical computer mouse on their desktop — all technologies made possible by extremely small and efficient semiconductor lasers.
All these technologies use semiconductor lasers (also called laser diodes) of various types. Until the perfection of the VCSEL, however, all laser diodes shared one thing in common: they emitted their laser light from their edges, rather than from the surface of the semiconductor chip. It may seem a trivial difference, but developing a laser diode that emits light from its surface required overcoming significant scientific and technological challenges with great pay-off in component manufacturing, practical systems implementations cost and improved performance efficiencies.
VCSELs are easier to test during production, as their surface-emitting nature allows for a large numbers of VCSELs to be manufactured and tested together on a single chip without requring the extra steps of cleaving as is done with edge emitting lasers. They are also more efficient, requiring less operating current to transmit data at higher speeds than edge emitting lasers do. The low divergence of the laser beam from large emitting surface and its near-circular shape makes VCSELs ideal for high-speed optical data communication over fiber optics both in communication networks and in large parallel processed server farms used in various search engines and sophisticated numerical modeling tools.
But today’s VCSELs didn't simply appear fully-formed from a flash of inspiration—they're the product of a long evolution and experimental process that Dr. Iga began almost forty years ago. He first proposed the concept of a surface emitting laser in 1977, but the journey from concept to practical reality proved challenging.
For more than ten years, Dr. Iga proceeded in carefully reasoned steps, first demonstrating a pulsed surface emitting laser in 1979 that operated only at very low temperatures, then experimenting with different semiconducting materials and structures before achieving a working continuous-wave room-temperate VCSEL in 1989. This achievement required the development of advanced optically active semiconductor materials, including new high reflectivity semiconductor mirrors called Distributed Bragg Reflectors, which together form the resonant cavity and the required positive feedback for lasing to occur.
Dr. Iga's dedicated work provided the solid foundation for today's generation of advanced VCSELs for various applications. Because the researchers who followed him built upon that foundation so successfully, Dr. Iga is often considered not merely at the “father” of the VCSEL, but as its “grandfather,” in recognition of the overwhelming importance and primacy of his pioneering work pursued, while others overlooked this important innovation.
Image copied from the Prof. Iga’s publications.