Every laser has its limitations in terms of repetition rate and pulse characteristics, but bringing five lasers together in one system could make those limitations vanish. A device developed at the University of Southampton does just that to generate wide-bandwidth optical signals with arbitrary amplitude and phase profiles — flexibility that could be useful for telecommunications, metrology, sensing and materials processing. The new method relies on the coherent combination of multiple semiconductor lasers, each operating in CW mode at different frequencies. Through the precise control of the amplitude and phase of each laser’s output, it is possible to produce a range of complex pulsed optical waveforms. The researchers used the device to generate 100-GHz pulses. An example of custom-shaped pulses at a 100-GHz repetition rate. Courtesy of the University of Southampton. “By combining a larger number of input lasers, shorter or more complicated-shape pulses and/or more power can be obtained,” said doctoral candidate David Wu. “It can also generate pulses with a very low-level of noise (down to the quantum limit) and very high (greater than one THz) repetition frequencies.” Any application that requires optical pulses typically needs waveforms of a specific repetition rate, pulse duration and pulse shape. It is often challenging to design and manufacture a laser with these parameters exactly as required. Even when a suitable solution exists, size, complexity and ease of operation are further critical considerations. Key to making the new combinative approach work is to phase-lock the semiconductor lasers to an optical frequency comb, which ensures the individual lasers have well-defined mutual coherence. The lasers could all be integrated into a chip to create a compact, low-cost pulse generator. “We believe that this work is likely to be of direct interest to scientists working in virtually any field of optics where pulsed laser sources are used,” said principal research fellow Dr. Radan Slavik. Funding came from the British Engineering and Physical Sciences Research Council. The research was published in Optica (doi: 10.1364/optica.2.000018). For more information, visit www.southampton.ac.uk.