A high-quality source of single photons is hard to come by. But there may be a solution in the pipeline in the form of an integrated optical chip. “Unfortunately, nature is reluctant to create photons one at a time — they tend to come out in bunches,” said Thomas Meany, a doctoral student at Macquarie University in Sydney and member of a research team studying this topic. “This is a serious impediment we have to overcome in order to make photon sources a useful tool.” Such sources are vital to advanced quantum technologies, such as the simulation of complex molecules, secure communications and quantum computing. Artist rendering of the four-way multiplexed light source. It shows on-chip photon generation and routing. Courtesy of Macquarie University. The researchers combined optical materials and components into one device to exploit the best of each technology, as there is no single optical device that can perform all of the required operations. Passive glass routers created by femtosecond laser writing were combined with nonlinear waveguides in a highly advanced chip and fast optical switching elements. Photons were generated in a lithium niobate chip developed by a research group from Université Nice Sophia Antipolis. To embed this chip into the larger experiment, Macquarie produced femtosecond laser-written glass circuits. “Our chip allows the generation of up to four photons simultaneously, but as they appear randomly, we can’t predict where or when the next photon will appear,” said Dr. Olivier Alibart of the Université Nice Sophia Antipolis. “Lithium niobate is a wonderful nonlinear optical material, but it doesn’t interface easily with other components.” He added that the team’s strategy has been to use the laser-written waveguides to deliver pump light to the chip as well as “guide the outgoing single photons toward the switching array that selects the correct output channel.” Experiments conducted last year by the University of Sydney demonstrated that photons from two sources could be combined on a silicon chip using ultrafast optical switches to break the intrinsic noise limit of photon sources. This new study takes this a step further, proving that the approach is scalable and can be applied to other types of waveguides. The research was published in Laser & Photonics Reviews (doi: 10.1002/lpor.201400027). For more information, visit: www.mq.edu.au.