The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions in surface
electrode ion traps is a key component to achieving scalability for quantum information processing. Diffractive optical
elements (DOEs) present a promising approach as compared to bulk optics because of their small physical profile and
their flexibility in tailoring the optical wavefront. The precise alignment of the optics for coupling fluorescence to and
from the ions, however, poses a particular challenge. Excitation and manipulation of the ions requires a high degree of
optical access, significantly restricting the area available for mounting components. The ion traps, DOEs, and other
components are compact, constraining the manipulation of various elements. For efficient fluorescence collection from
the ions the DOE must be have a large numerical aperture (NA), which results in greater sensitivity to misalignment.
The ion traps are sensitive devices, a mechanical approach to alignment such as contacting the trap and using precision
motors to back-off a set distance not only cannot achieve the desired alignment precision, but risks damage to the ion
We have developed a non-contact precision optical alignment technique. We use line foci produced by off-axis linear
Fresnel zone plates (FZPs) projected on alignment targets etched in the top metal layer of the ion trap and demonstrate
micron-level alignment accuracy.
Designing and integrating micro-optical components into atom and ion traps are enabling steps toward miniaturizing
trap dimensions in quantum computation applications. The micro-optic must have a high numerical aperture for precise
illumination of the ion and should not introduce scatter. Due to the extreme optical efficiency requirements in trapped
ion and atom-based quantum information processing, even slight losses from integrated micro-optics are detrimental.
We have designed and fabricated aspheric micro-lenses through grayscale transfer into a fused silica in an effort to
realize increased transmissive efficiency and decreased scatter compared to an equivalent diffractive optical element.
The fabricated grayscale lens profile matched the desired lens profile well, and the measured and predicted optical
performances were in good agreement. The pattern was transferred via coupled plasma reactive-ion etching smoothly
into the fused silica with a RMS roughness ~ 35 nm. The micro-lens had a diameter of 88 um and 14.2 um sag, with an
as-designed focal length of 149 um and spot diameter of 2.6 um. The maximum measured efficiency was ~80% (86% of
theoretical, possibly due to rms roughness). This realized efficiency is superior to the equivalent diffractive lens
efficiency, designed to the same use parameters. The grayscale approach demonstrated an increase in collection
efficiency, at the desired optical focal length, providing the potential for further refinement.
Conductive polymers with high solids loading (> 40wt.%) are challenging to pattern to single micron feature sizes and require unique techniques or templates to mold the material. The development of a conductive polymer optical tag is discussed for identifying the presence of hydrofluoric acid (HF) and leverages free standing silicon fins as a template utilizing deep reactive ion etching (DRIE) techniques will be discussed. This work is aimed towards a future flexible conductive polymer tag to be transferred via adhesive or epoxy for a novel sensor surface. The advantage to this technique over wafer thinning is a higher throughput of device manufacture without damage to the silicon fins or polymer due to chemical-mechanical interactions or added protective layers. The gratings consist of a high spatial frequency (1.15 μm pitch) grating consisting of lines of conductive polymer and lines of silicon which are free standing. A novel running bond pattern aims to minimize the intrinsic stress and allows the conductive polymer to infiltrate without distorting the template. The polymer conductivity mechanism has been designed to break down under a chemical binding to fluorine; changing its conductivity upon exposure, and results in a change in the polarization response. The use of the polarization response makes the signal more robust to intensity fluctuations in the background or interrogation system. Additionally, the use of optical interrogation allows for standoff detection in instances where hazardous conditions may be present. Examples of material and device responses will be shown and directions for further investigation are discussed.
Resonant subwavelength gratings have been designed and fabricated as wavelength-specific reflectors for application as
a rotary position encoder utilizing ebeam based photolithography. The first grating design used a two-dimensional
layout to provide polarization insensitivity with separate layers for the grating and waveguide. The resulting devices had
excellent pattern fidelity and the resonance peaks and widths closely matched the expected results. Unfortunately, the
gratings were particularly angle sensitive and etch depth errors led to shifts in the center wavelength of the resonances.
A second design iteration resulted in a double grating period to reduce the angle sensitivity as well as different materials
and geometry; the grating and waveguide being the same layer. The inclusion of etch stop layers provided more accurate
etch depths; however, the tolerance to changes in the grating duty cycle was much tighter. Results from these devices
show the effects of small errors in the pattern fidelity. The fabrication process flows for both iterations of devices will be
reviewed as well as the performance of the fabricated devices. A discussion of the relative merits of the various design
choices provides insight into the importance of fabrication considerations during the design stage.
In this work, we describe the most recent progress towards the device modeling, fabrication, testing and system
integration of active resonant subwavelength grating (RSG) devices. Passive RSG devices have been a subject of
interest in subwavelength-structured surfaces (SWS) in recent years due to their narrow spectral response and high
quality filtering performance. Modulating the bias voltage of interdigitated metal electrodes over an electrooptic thin
film material enables the RSG components to act as actively tunable high-speed optical filters. The filter characteristics
of the device can be engineered using the geometry of the device grating and underlying materials.
Using electron beam lithography and specialized etch techniques, we have fabricated interdigitated metal electrodes on
an insulating layer and BaTiO<sub>3</sub> thin film on sapphire substrate. With bias voltages of up to 100V, spectral red shifts of
several nanometers are measured, as well as significant changes in the reflected and transmitted signal intensities around
the 1.55um wavelength.
Due to their small size and lack of moving parts, these devices are attractive for high speed spectral sensing applications.
We will discuss the most recent device testing results as well as comment on the system integration aspects of this