Recent developments in photoalignment of liquid crystals (LCs) brought to the market photoreversible materials such as azobenzene-based PAAD complex dyes , which quickly found broad photonics applications for constructing diffraction elements and waveplates [2,3]. Despite extensive investigations of photoaligned LC systems, there is little information on the optical properties such thin PAAD layers.
Here we report an experimental investigation of optical properties, such as refractive indices and absorption coefficients for different PAAD materials, namely PAAD-22D, 22E and 22N. Photoinduced phase gratings were recorded in 20-50 nm thick PAAD layers with no evidence of a corresponding surface relief, which is a typical feature in thicker azobenzene films. Therefore, the formation of the gratings is attributed to optically induced birefringence. The investigated materials exhibited different values of birefringence, reaching 0.025, and significantly different temporal response to laser irradiation. Moreover, the diffracted power was observed to be very sensitive to the polarisation of the probe beam with respect to that of the pump beam.
We also studied photoinduced diffraction in PAAD-LC systems, where we observed the formation of a stable and strong diffraction pattern. The gratings can be rewritten by illumination with another light pattern or switched off by reorienting liquid crystals with a bias voltage. A diffraction efficiency of more than 5% was measured in a cell containing PAAD-22D in combination with 8μm thick LC-E7 layer. Finally, we compare the dynamics of light induced response in the PAAD layers and PAAD-LC cells and investigate their respective memory effects.
 Beam Engineering for Advanced Measurements Company, Winter Park, FL 32789.
 Vernon, J. P., et al., Opt. Express 21, 1645 (2013).
 Nersisyan, S. R., et al. Opt. Express 21, 8205 (2013).
We investigate geometries for efficient coupling of single ions to fiber-coupled light fields for applications in quantum sensing, quantum metrology, and quantum information processing. Specifically, we discuss the integration of fiber-tip microcavities into radio-frequency ion traps. The distortions of the trapping fields induced by the presence of the optical fibers are simulated for a range of ion trap geometries and the most promising arrangements are identified. Finally, we investigate the use of fiber-tip microcavities with non-spherical mirrors for enhanced ion-light coupling at the center of the trap by appropriate shaping of the cavity modes.
We present the design and fabrication of a dual air-bridge waveguide structure integrated with MEMS functionality. The structure is designed to function as a tunable optical buffer for telecommunication application.
The optical buffer structure is based on two parallel waveguides made of high refractive index material with subwavelength dimensions. They are suspended in air, and are separated by a sub-micron air gap. Due to the fact that the size of the waveguides is much smaller than the wavelength of light that propagates in the structure, a significant fraction of the optical mode is in the air gap between the waveguides. By changing the size of the air gap using MEMS techniques, we can vary this fraction and hence the effective refractive index of the waveguide structure, thus generating tunable optical delay.
The optical buffer structure was grown on an InP substrate by molecular beam epitaxy, and the device layer was made of InGaP. An InGaAs layer was sandwiched between the device layer and the substrate to serve as a sacrificial layer. The sub-micron waveguides, their supports in the form of side pillars with tapered shapes in order to minimize optical losses, and the MEMS structures were patterned using electron beam lithography and plasma etching. Electrodes were integrated into the structure to provide electrostatic actuation. After the sample patterning, the waveguide structure was released using HF etch. Our simulations predict that by varying the waveguide separation from 50 nm to 500 nm, we could achieve a change in propagation delay by a factor of two.
We present the design and fabrication of a tunable optical buffer device based on III-V semiconductor platform for
telecommunication applications. The device comprises two indium phosphide suspended parallel waveguides with cross
sectional dimension of 200 nm by 300 nm, separated by an air gap. The gap between the waveguides was designed to be
adjustable by electrostatic force. Our simulation estimated that only 3 V is required to increase the separation distance
from 50 nm to 500 nm; this translates to a change in the propagation delay by a factor of 2. The first generation of the
suspended waveguide structure for optical buffering was fabricated. The sample was grown on an InP substrate by
molecular beam epitaxy. The waveguide pattern is written onto a 300 nm thick InP device layer by electron beam
lithography and plasma etching. Electrodes were incorporated into the structure to apply voltages for MEMS actuation.
We investigate theoretically and experimentally the possibility of electrostatic actuation of nanomechanical optical fibers with integrated electrodes. The fiber has two optically guiding cores suspended in air by thin flexible membranes. This fiber structure allows for control of the optical properties via nanometer-range mechanical core movements. The electrostatic actuation of the fiber is generated by electrically charged electrodes embedded in the fiber cladding. Fiber designs with one to four electrodes are analyzed and, in particular, a quadrupole geometry is shown to allow for all-fiber optical switching in a 10cm fiber with an operating voltage of 25 - 30V. A multi-material fiber draw technique is demonstrated to fabricate a fiber with well-defined dual core structure in the middle and four continuous metal electrodes in the cladding. The fabricated fiber is analyzed and compared with the modeled requirements for electrostatic actuation.