Objective: The objective of this research is to develop CMOS compatible electronically controlled leaky wave optical antennas, based on planar dielectric waveguides with a set of silicon perturbations. Distributed electronic tuning of various parameters like permittivity and losses in all the semiconductor perturbations results in controlling the propagation phase and attenuation constants of the leaky wave radiation, and hence the output radiation power and profile. Intellectual Merit: The proposed research leads to highly directive optical antennas with tunable capabilities, that require a single feed point, instead of resorting to optical arrays that require a large number of electronically controlled optical waveguides and relative phase shifts. The intellectual merit of the proposed research lies in achieving this goal by using a dielectric waveguide with semiconductor perturbations in which the tuning of the carrier concentrations leads to tunable leaky wave radiation. Broader Impact: The proposed research will eventually lead to fast electronic control of the power radiated, enabling the development of novel optical modulators and switches. CMOS compatibility, integrated electronic control, low cost and possible system integration are key attributes of the proposed photonic devices, with applications in optical communications, microwave photonics and chip scale optical sensing. The educational outreach activities aim at making this subject accessible and attractive to a broad audience through live demonstrations, public lab tours, and web based distant learning tools. In particular, preparation of special demonstrations and summer programs will attract traditionally under-represented groups and facilitate the increase of enrollments to the physical sciences and engineering nationwide.
This research aimed at exploring a new route to design highly directive CMOS (i.e. low cost silicon based) compatible optical antennas as viable solution for low cost optical radiators with modulation properties. Tunable radiation is realized using periodic semiconductor (it is silicon in this research) perturbations integrated in a silicon nitride waveguide that will lead to the electronically controlled leaky wave radiation. This type of optical antenna (please see Fig. 1) is referred to as Optical Leaky Wave Antenna (OLWA). Semiconductor materials can conduct electrical charges and hence facilitate electronic/optical tuning of the propagation constant of the radiating leaky wave by carrier plasma dispersion effect and thus by tuning the semiconductor complex refractive index. Based on these tunable parameters we developed CMOS compatible planar dielectric silicon nitride waveguides with novel controlled (electronically or optically) silicon perturbations to provide OLWAs with control on radiation angle, beam width and directivity. Furthermore, two novel methods of resonator integration have been proposed in order to boost the radiation control capability. The prototype of a dielectric silicon nitride optical leaky wave antenna with silicon perturbations was fabricated and characterized. A fabrication recipe was developed and optimized to achieve desired feature size. The radiation features of an OLWA based on a silicon nitride waveguide and Si perturbations is experimentally and theoretically demonstrated for the first time. Intellectual merit: As a result of this project a new theory for optical leaky wave antennas in resonators has been developed. The new schemes of antennas inside resonators for in enhanced electronic control of radiation have been devised and proved. These schemes open up new ways to achieve fast modulators with high modulation depth. New fabrication recipes for low loss, low stress thick silicon nitride films for optical applications have been developed. For the first time dielectric antennas with semiconductor perturbations have been experimentally demonstrated. This shows that electronic control can be put on silicon perturbations. As the gate size of CMOS approaches a few tens on nanometers, using dielectric waveguides with semiconductor perturbations paves the way of integrating optics and electronics and hence new approaches in photonic device design. As a further development, novel trench waveguides have been fabricated for sensing applications. These novel fabrication technology and integrated waveguide concepts have lead to another NSF project related to manufacturing of photonic materials. Broader Impact: Six PhD students have conducted research on this project and been trained on theoretical optics, antennas, modeling and simulations, nano fabrication, e-beam lithography, and optical characterization and testing. Graduated students continue to contribute to the society at government laboratories (Sandia National Labs) and private industries in Orange County and in the Bay area, CA. Three undergraduate engineering students and three high school students have been trained during their internships on science and technology, training them in photonic devices, lasers, integrated optics, testing and measurement and theoretical characterization and modeling. The internship program covered 4-6 week during summer quarters. The interns have been guided by the PIs and graduate students. Graduate students also benefited mainly by improving their communication skills, conveying their professional skills in an interactive manner. Moreover the research group visited a local high school to stimulate interest in science and to encourage students from underrepresented minorities to pursue a career in science and technology. Results have been disseminated via several prestigious academic meetings. These meetings include OSA CLEO Conference on Lasers and Electro-Optics (2010), SPIE Photonics West (2011), IEEE Photonics Conference (2011), IEEE Antennas and Propagation Society International Symposium (2012), SPIE Photonics West (2012), IEEE Antennas and Propagation Society International Symposium (2013), URSI Raido Science Meeting (2014), OSA Advanced Photonics for Communications (2014), SPIE Photonics West (2015). Overall this research produced more than 16 journal papers and conference proceedings.
