The objective of this work is to the study of the Purcell effect in submicron metallo-dielectric submicron laser cavities.
Intellectual Merit: The proposed research will investigate the spontaneous emission rate of a laser when optical modes are sustained in a very small cavity. The PI proposes to characterize the effect novel submicronlaser cavities by measuring the spontaneous emission rate under a range of conditions, varying temperature, size, material, cavity design and pumping schemes.
Broader Impact: The advancement of nanolasers will enable compact sensing instruments and impact multiple fields such as environmental, chemical sciences and homeland security. In addition the project will help train and educate both graduates and grade students through research and outreach programs lead by the PI who has an exceptional record in the dissemination of research finds.
Intellectual Merit: The research investigates the fact that the spontaneous emission rate of a laser is affected by its surrounding environment. This effect is particularly important when optical modes are sustained in a very small cavity. We developed and characterized metallo-dielectric-semiconductor lasers with submicron size in all three dimensions. Those cavities, which can function at room temperature, are a very good vehicle to study the Purcell effect with the ultimate goal to achieve lasing without threshold. To achieve this goal we designed, fabricated and tested a novel nanoscale continuous wave coaxial metal-dielectric-semiconductor laser that utilizes Purcell effect to operate without threshold at telecommunication wavelength (see primary image). According to classical laser theory, in a nanolaser, too many of the photons would give off their energy as they strike the metal parts of the cavity’s walls. Consequently, the device wouldn’t support the degree of spatial and temporal coherence needed to spark amplification inside the cavity and emission of a coherent beam. We got the photons moving in the right direction by formulating the device as a coaxial waveguide: in this case, a metallic rod surrounded by an indium-gallium-arsenic-phosphide semiconductor ring that is coated in metal. To form the lasing cavity, the waveguide is capped at both ends with low-index dielectric plugs. One plug, made of silicon dioxide coated in silver, forms a totally reflecting mirror; the other plug, which allows the pump beam to enter and the laser light to escape, is filled with air. This setup is sufficient to ensure that the laser cavity can emit energy only in the transmission mode wherein the amount of light amplification is always high enough to overcome energy losses from the cavity itself. The laser emitted coherent beams when excited by a pump source with an incident power of only 720 picowatts (see additional image). The metallic coating around the semiconductor ring serves as a heat sink. Because of the lack of threshold, these devices can be modulated much quicker than the existing lasers, and can thus become a backbone for future communication devices. The significance of the thresholdless operation is important because it heralds the day when arrays of lasers will send and receive optical signals, powered only by the minuscule amounts of energy available in semiconductors. The small size of nanolasers will have impact on ultra-high-resolution imaging, sensing and displays. We feel this is just a beginning of a new family of light emitters with superior characteristics that are breaking new grounds, and many advances in this new area are yet to come. Broader Impact: The advancement of nanolasers integrated with CMOS electronics will enable high speed and energy efficient communications on a chip, which will have a significant impact on the future computing systems. They will also have a significant impact on compact sensing instruments and impact multiple fields such as environmental, chemical sciences and homeland security. The results from this effort will have an important bearing for submicron photonic components. In addition the project helped to train and educate both graduates and undergraduate students through research and outreach programs lead by the PI who has over 20 years record in the dissemination of research finds. He has served as a mentor to many students and teachers through various NSF programs such as REU and RET.
