Stanley Pau

Full-Stokes imaging polarimeter using an array of elliptical polarizer

In this paper, a full-Stokes imaging polarimeter operating at 580 nm using an array of elliptical polarizers is presented. The division-of-focal-plane polarimeter utilizes a set of four optimized measurements which represent a regular tetrahedron inscribed in the Poincaré sphere. Results from the device fabrication, instrument calibration and characterization are presented. The performance of the optimized full Stokes polarimeter, as defined by size of the standard deviation of the degree of circular polarization, is found to be approximately five times better than the performance of the simple full-Stokes polarimeter.

Imaging nanostructures with coherent phonon pulses

We demonstrate submicron resolution imaging using picosecond acoustic phonon pulses. High-frequency acoustic pulses are generated by impulsive thermoelastic excitation of a patterned 15-nm-thick metal film on a crystalline substrate using ultrafast optical pulses. The spatiotemporal diffracted acoustic strain field is measured on the opposite side of the substrate, and this field is used in a time-reversal algorithm to reconstruct the object. The image resolution is characterized using lithographically defined 1-micron-period Al structures on Si. Straightforward technical improvements should lead to resolution approaching 45nm, extending the resolution of acoustic microscopy into the nanoscale regime.

Integrated waveguide with a microfluidic channel in spiral geometry for spectroscopic applications

The authors fabricated and tested a compact optical sensor with an integrated waveguide and a microchannel in spiral geometry. The multimode waveguide, consisting of an SU-8 core of 40μm thick and 50μm wide and a fluid cladding layer of 60μm thick, realizes a light-fluid interaction length of 110mm within a device area of 4cm2. The waveguide sensor measures changes in liquid sample concentration and is sensitive to changes in liquid refractive index. Absorbance measurements using the spiral waveguide sensor demonstrate increased sensitivity compared with a linear geometry sensor.

Numerical characterization of whispering-gallery mode optical microcavities

We characterize planar microcavities in whispering-gallery mode optical resonances. The microcavity consists of a waveguide and a microdisk, and a nanoscale gap separates the waveguide and the microdisk. The devices can be fabricated on Si-based thin films by using conventional microelectronics techniques. To characterize these types of cavity, we study a broad range of resonator configuration parameters including the size of the microdisk, the width of the gap, and the waveguide dimensions. The finite-element method is used for solving Maxwells equations. The electric fields and the energy density distributions are obtained and compared between the on-resonance and off-resonance situations. A brilliant ring with a strong electric field and a high-energy density is found inside the periphery of the microdisk under first-order resonance. While under second-order resonance, there are two bright rings, and the light intensity in the inner ring is stronger than that in the outer ring. The resonant frequencies and their free spectral ranges are predominantly determined by the size of the microdisk. The gap effect on the resonant frequencies is observable, although it is minor. The gap strongly affects the full width at half-maximum (FWHM), finesse, and quality factor of the resonances. With an increase in the gap width from 100 to 300 nm, both the Q value and finesse increase substantially, while the FWHM decreases. The waveguide width has a visible influence on the Q value, FWHM, and finesse as well.

Patterned color liquid crystal polymer polarizers.

We demonstrate patterned polarizers for visible wavelengths using dichroic dye in a liquid crystal polymer (LCP) host. Contact lithography is used to pattern a thin alignment layer, which subsequently transfers the pattern to the LCP. A gray dichroic dye mixture for the visible spectrum is optimized and implemented along with LCP to fabricate this polarizer. A peak extinction ratio of 41 was measured at a 633 nm wavelength, while simultaneously showing patterns as small as 3 μm. Finally, multi layer films are demonstrated by fabricating a two layer patterned circular polarizer consisting of a quarter-wave retarder and a color polarizer. Our process has applications in three-dimensional displays, interferometry, optical storage, and polarimeters.

Polarization microscope using a near infrared full-Stokes imaging polarimeter

This paper presents a polarization microscope using an infrared (IR) full-Stokes imaging polarimeter. The IR polarimeter utilizes an optimized interference-based micropolarizer design, and provides full-Stokes images with resolution of 1608 × 1208 at 35 frames/second. The device fabrication, instrument calibration, performance evaluation, and measurement results are presented. The measurement error of the imaging polarimeter is less than 3.5%, and the standard deviations are less than 2%.

Imaging capability of patterned liquid crystals

We demonstrate the ability to make high resolution arbitrary patterned optical retarders using liquid crystal polymer (LCP). Contact lithography is used to define unique LCP alignment domains. Patterned LCP retarders are imaged between crossed polarizers to determine pattern visibility as a function of feature size. It was determined that patterned retarders for wavelengths between 250 nm and 2500 nm can be constructed with feature sizes as small as 4 microm. We also showed that multiple patterns can be created on the same substrate using a combination of patterned LCP and opaque features. Our process has applications in displays, double-patterning lithography, and imaging polarimetry.

160-Gb/s all-optical MEMS time-slot switch for OTDM and WDM applications

The authors propose and successfully demonstrate a novel, simple, and low-cost concept of optical time-slot switching, i.e., switching part of one 160-Gb/s optical time-division multiplexing channel to another 160 Gb/s channel all in the optical domain without any optical-electrical-optical conversion and with negligible power penalty.

A planar ion trapping microdevice with integrated waveguides for optical detection

A planar ion trap with an integrated waveguide was fabricated and characterized. The microdevice, consisting of a 1 mm-diameter one-hole ring trap and multi-mode optical waveguides, was made on a glass wafer using microfabrication techniques. The experimental results demonstrate that the microdevice can trap 1.5 μm- to 150 μm-diameter charged particles in air under an alternating electric field with the amplitude and frequency varying from 100 V to 750 V, and 100 Hz to 700 Hz, respectively. The on-chip waveguide is capable of detecting the presence of a particle in the trap, and the particle secular motion frequency was found to depend on the input alternating signal amplitude and frequency.

Tunable light emission from co-assembled structures of benzothiadiazole molecules.

Co-assembled structures possessing tunable light emission from 510-690 nm have been prepared using various compositions of two different 4,7-substituted benzothiadiazole molecules, 1 and 2. The preferential incorporation and co-localization of 1 and 2 to produce co-assemblies are possible because of structural similarities and allow for tuning of morphology and light emission.