Engineering the optical properties of subwavelength devices and materials

• Main Author: Anant, Vikas, 1980-
• Other Authors: Karl K. Berggren.
• Format: Others
• Language: English
• Published: Massachusetts Institute of Technology 2009
• Subjects: Electrical Engineering and Computer Science.
• Online Access: http://dspace.mit.edu/handle/1721.1/42233; http://hdl.handle.net/1721.1/42233

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007. === Includes bibliographical references (p. 145-154). === Many applications demand materials with seemingly incompatible optical characteristics. For example, immersion photolithography is a resolution enhancing technique used to fabricate the ever-shrinking nanostructures in integrated circuits but requires a material that has-at the same time--a large index of refraction and negligible optical loss. Other applications require devices that have optical properties that seem exorbitant given the constraints posed by the geometry, materials, and desired performance of these devices. The superconducting nanowire single-photon detector (SNSPD) is one such device that, on the one hand, needs to absorb and detect single telecom-wavelength photons (A = 1.55 pm) with near-perfect efficiency, but on the other hand, has an absorber that is subwavelength in its thickness (A/390). For both cases, it is simply not enough to look for alternative materials with the desired optical properties, because the materials may not exist in nature. In fact, it has become necessary to engineer the optical properties of these devices and materials using other means. In this thesis, we have investigated how the optical properties of materials and devices can be engineered for specific applications. In the first half of the thesis, we focused on theoretical schemes that use subwave-length, resonant constituents to realize a material with interesting optical properties. We proposed a scheme that can achieve high index (n > 6) accompanied with optical gain for an implementation involving atomic vapors. We then explored the applicability of this high-index system to immersion lithography and found that optical gain is problematic. We solved the issue of optical gain by proposing a scheme where a mixture of resonant systems is used. We predicted that this system can yield a high refractive index, low refractive index, anomalous dispersion, or normal dispersion, all with optical transparency. In the second half, we studied the optical properties of SNSPDs through theoretical and experimental methods. In the study, we first constructed a numerical model that predicts the absorptance of our devices. We then fabricated SNSPDs with varying geometries and engineered a preprocessing-free proximity-effect correction technique to realize uniform linewidths. We then constructed an optical apparatus to measure the absorptance of our devices and showed that the devices are sensitive to the polarization of single photons. === by Vikas Anant. === Ph.D.