characteristics of the laser," Choquette says. "This means we can accurately design and fabricate single-mode VCSELs for high-performance optical communication systems." The next step, he says, is to push VCSEL performance toward higher power by considering designs that are much larger in diameter. "Looking beyond that, we also have fundamental problems with high-speed data communica- THE FUTURE IS FIBER-OPTICAL TECHNOLOGIES tion on our circuit boards and in our chips," Choquette says. "This is a tech- nology that could serve as the foundation for a new way of looking at optical interconnects and photonic integrated circuits." 4.6.5 Tiny Laser Bell Labs researchers have built a tiny semiconductor laser that has the poten- tial for advanced optical communication applications, including multiple laser-on-a-chip applications. The device exploits a photonic crystal, a highly engineered material with superior optical properties, and was made in collab- oration with scientists from the New Jersey Nanotechnology Consortium, California Institute of Technology, and Harvard University. "This new laser was made possible by taking advances from many differ- ent areas in physics and incorporating them into one device," says Cherry Murray, senior vice president of physical sciences research at Bell Labs. "This work will open up new directions not only for optoelectronics and sensing but could also provide a new tool to investigate very basic physical phenomena." The laser belongs to a class of high-performance semiconductor lasers, known as quantum cascade (QC) lasers, which were invented at Bell Labs in 1994. QC lasers are made by stacking many ultrathin atomic layers of stan- dard semiconductor materials (such as those used in photonics) on top of each another, much like a club sandwich. By varying the thickness of the layers, it's possible to select the particular wavelength at which a QC laser will emit light, allowing scientists to custom design a laser. When an electric current flows through a QC laser, electrons cascade