ECCS-0801869 A. Heberle, University of Pittsburgh Objective: Mode-locking of lasers is an important technique for generation of frequency combs and trains of picosecond or femtosecond optical pulses. So far, only longitudinal modes have been locked reliably, leading to pulses traveling around the laser cavity in direction of to the light beam.
Intellectual Merit: The goal of this experimental research program is the investigation of a new process, lateral two-dimensional mode-locking in monolithic vertical-cavity surface-emitting lasers (VCSEL?s), and the fabrication/exploration of novel devices for picoseconds or even femtosecond pulse and frequency comb generation. The project aims to demonstrate that lateral mode-locking of round VCSEL?s produces solitons that move in circles around the emission aperture. This work will not only provide understanding of ultrafast dynamics and soliton propagation in VCSEL?s, but it will add ultrafast mode-locking and frequency comb generation to this increasingly important class of lasers. It is expected, for example, that laterally mode-locked VCSEL?s will provide two orders of magnitude better control of the pulse repetition rate than conventional, longitudinally mode-locked monolithic semiconductor lasers, in which the repetition rate can be tuned by only about 0.5%. Mode-locked VCSEL?s could have significant applications for optical communication, sensing, and displays in which the blue and green colors are generated by frequency doubling.
Broader Impact: The project gives graduate and undergraduate students hands-on experience in several important fields: femtosecond technology, photonics, nanoscience, and semiconductor technology. It also supports the interdisciplinary photonics course program and the early lab experience program that involves underrepresented minorities at the University of Pittsburgh
This project was aimed at development of small, compact lasers that could produce very short-duration pulses, namely, durations of a few picoseconds (trillionths of seconds). This would be extremely valuable because most lasers which produce ultrashort pulses at present are large and bulky. The project was partially successful. When small solid-state lasers were pumped with a light pulse from another laser, they emitted pulsed light pulses on very short time scales, but the emitted pulses were not regular in time. This was found to be due to the fact that the solid state laser devices we were using did not have perfect circular symmetry. We were able to map out all the optical characteristics of one of these lasers and show that the properties agreed with the theory which took into account the imperfections. We also did extensive studies on the time dependence of the laser light emission and the recovery of the initial state of the laser after it was pumped. The results of our studies were used to create new designs for solid state pulsed lasers. Our ability to do optical studies on these ultrafast time scales was also used for exploratory studies on other solid state systems, namely quantum dots and microcavities, which have special properties which can also be useful for controlling optical signals. This project was also a fantanstic educational experience for five graduate students to be able to learn and work with state-of-the-art ultrafast optics, including both experiments and theory/design work. This has prepared them to work in the optics and semiconductor industry. Some of the technology was also used for advanced in-class demonstrations at the University of Pittsburgh.
