Guided wave evanescent field devices

In a dielectric optical waveguide surrounded by air, a fraction of the light is guided outside the device in the form of an evanescent field. The effective area of the waveguide modes, the amount of power in the evanescent field, and the propagation constant are each a function of the waveguide dimensions and optical properties. As a result, guided wave evanescent field devices can be used to efficiently couple light to atomic vapors or other guided wave devices. These devices are interesting because they may be useful for implementing quantum logic operations by using the interaction between the guided mode and atomic vapors to implement the quantum Zeno effect. This work has studied three guided wave evanescent field devices as part of an ongoing effort to demonstrate two-photon absorption at low power levels.;The first device, the holey fiber cavity, was a microcavity formed by placing a short section of microstructured fiber between two moveable mirrors. Small-diameter solid-core fiber was used because it confined the guided mode to a small effective area with some power in the evanescent field. The optical and spectral properties of this device were investigated. It was found that losses at the fiber-minor interface limited the attainable quality factors.;The second device, the microtoroidal resonator, has been used extensively for various nonlinear effects because of its high quality factor and small mode volume. Coupling is generally achieved via the evanescent field of the resonator mode by positioning a tapered optical fiber nearby. As a first step in using these devices in more elaborate experiments, the coupling and resonant characteristics of these devices have been studied. Contact and variable-gap coupling has been demonstrated in the near-infrared and the free spectral ranges and loaded quality factors of a sample of microtoroids have been measured.;The third device, tapered optical fiber, consists of standard optical fiber that has been heated and pulled to form a submicron-diameter section. Low-loss transitions between this region, the taper waist, and the original fiber can be achieved by ensuring the change in diameter is gradual. In the submicron taper waist region the optical mode is predominantly guided by the silica-air interface, which results in a small mode area with a fraction of the power in the evanescent field. The interaction between atomic vapors and guided optical modes in this device has been studied. A strong interaction corresponding to the single-photon transition in rubidium has been observed. Additionally, an effect has been characterized in which the transmission properties are altered by atoms accumulating on the surface of the fiber and it has been found that this phenomenon is a function of input power.;All of these research topics represent a first step in evaluating devices for improved quantum logic gates using two-photon absorption and the quantum Zeno effect.