NEW CONCEPT FOR CONTROLLING MODES IN A FABRY-PEROT

Dartmouth College, Hanover NH

Investigators

Abstract

A Fabry-Perot consists of two parallel mirrors used to define modes in lasers, tunable filters, spectrum analyzers, and some modulators. The mirrors are usually dielectric quarter wave stacks that reflect in a distributed way, throughout their thickness. The objective of this project is to demonstrate that the effective penetration length into the quarter wave stack mirror (also called a distributed Bragg reflector) can become large and negative, zero, or large and positive, depending on careful control of the refractive indices. This concept will then be applied to: a) producing single mode semiconductor lasers and b) investigating high speed spatial light modulators. Intellectual merit: this project stems from a new analytic solution to the effective penetration length in these distributed mirrors and the discovery of both a pole and a zero in the solution. The existence of these regimes has been checked by computer and implies a number of important applications in optical devices and systems. Defining and demonstrating these applications is the exciting challenge. For example, this will be the first time that control of a Fabry-Perot mode spacing is achieved by controlling the refractive index in its mirrors. Furthermore, a negative penetration length implies superluminal reflection, which is an important intellectual challenge to explain and find applications for. To achieve this regime with high reflectivity requires the distributed reflector be deposited on metal (or a metal film) or to use a large number of layer-pairs. In either case, careful control of the refractive indices of the films is required. This is the technical challenge that will be undertaken in the laboratory. It will be helped by a thin film measurement technique introduced by author in 1983 and will use a thin film deposition technology that was developed at Dartmouth. Broader impact: Controlling the effective penetration length of a distributed mirror offers a wide range of applications. These include: inexpensive single mode semiconductor lasers, mode-locked semiconductor lasers with more power per pulse, simpler fabrication of fiber Fabry-Perot tunable filters, a practical variable optical attenuator, better Fabry-Perot optical sensors, simpler fabrication of VCSEL's, and resonant photo-detectors. Finally, nonlinear and electrically driven waveguide modulators and spatial light modulators become practical. The concept pioneered here can also be used to achieve in-plane right angle bends in waveguides, which usually requires nanostructure photonic bandgap materials. This research will also have a positive impact on training engineering personnel, since the P. I. is a woman and the Ph. D. graduate student proposed to initiate the research is also a woman. Dartmouth as a college is involved in state-of-the-art research and provides a model for teaching-research institutions.