A research group at Technische Universiteit Eindhoven and JDS Uniphase Corp., both in Eindhoven, the Netherlands, has demonstrated that coupled microring lasers exhibit bistable operation with picosecond switching times, making them suitable for use in the development of digital optical processing systems for telecommunications data. A description of the devices appears in the Nov. 11 issue of Nature.The group employed contact lithography and reactive ion etching to create two 16-µm-diameter InP/InGaAsP ring lasers operating at slightly different wavelengths and coupled by a 2-µm-wide InGaAsP waveguide. In operation, one of the coupled emitters injection-locks its counterpart so that the laser radiation in the slave circulates only clockwise or counterclockwise. Which laser dominates can be selected by injecting radiation close to the wavelength and polarization of the preferred emitter into the waveguide.The scientists report that pulses with an average energy of 5.5 fJ could switch the state of the system between the lasers, which operated at 1453.5 and 1464.6 nm. Switching times were less than 20 ps.Courtesy of Cobra Research Institute, Technische Universiteit Eindhoven.