We investigated several curved vane baffle designs coated with specular black paint as an inexpensive manufacturing alternative to traditional diffuse baffles vanes to reduce stray light and heat due to absorption in a standard Cassegrain telescope design configuration. The heat absorption is a very large problem in infrared systems and the specular designs solve this part of the problem. Our study involved simulating two different types of baffle systems, diffuse and specular painted vanes on the main barrel baffle. The first type of baffle consisted of evenly and non-evenly spaced diffusely black coated straight planar vanes on the main barrel baffle and a second type using specular black paint on curved vanes. TracePro, a stray light simulation software from Lambda Research Corporation, was used to simulate and compare each of the nine baffle systems for stray light rejection. The diffuse black painted straight vane baffle design was used as the baseline design to compare results to the other eight designs. In all designs except for the baseline design, TracePro's local downhill simplex optimization method was used to optimize each vane curvature and spacing in the main barrel baffle to reject incoming stray light. These curved vanes were designed to reject stray light back out of the main barrel baffle rather than to be absorbed by diffuse black paint.
A secure border necessitates the development of new technology for remote sensing and surveillance. We investigate
and develop wireless sensor network systems consisting of spatially distributed sensor nodes that can monitor various
environmental parameters including temperature, humidity, motion, and vibration, etc. The sensors, nodes and
transceivers have low-power consumption and are powered by solar energy so that the systems can work over long time
periods with minimal human intervention and maintenance. This paper presents the technology development, wireless
sensor integration, power management, and communication architecture, as well as a demonstration of environmental
monitoring.
An ultrafast optical pump and probe technique known as picosecond ultrasonics is used to generate and detect coherent acoustic phonon pulses in nanostructured films grown on Si wafers. By detecting the phonons after they have diffracted across a millimeter thick wafer, it is possible to measure the scattered phonons in the acoustic far field. Numerical backpropagation algorithms can then be used in order to reconstruct the object which scattered the acoustic phonon pulses. We describe measurements and simulations of experiments performed on surface and sub-surface nanostructures. Results with ~500 nm image resolution are shown, and plans for improving that resolution by an order of magnitude will be described.
KEYWORDS: Resonators, Waveguides, Optical microcavities, Systems modeling, Energy coupling, Finite element methods, Energy efficiency, Chemical elements, Scattering, Wave propagation
Photon tunneling between an optical resonator and a light-delivery coupler is strongly dependent on the gap dimension which can vary from zero to size of an optical wavelength involved. In this systematic report, we investigate the gap effects of whispering-gallery modes in two modeling systems: a waveguide-coupling resonator of 2μm and 10μm in diameter, respectively. Maxwell's equations which govern the EM wave propagation and photon tunneling in the microsystems are solved using the finite element method. The simulation accuracy and sensitivity is examined. It is found that when the maximum element size in the computationally sensitive regions is below 1/8 of the wavelength involved, the calculations are accurate. An optimal gap exists for maximum energy coupling and is a strong function of the wavelength of the resonant mode. The Q factor increases exponentially with increasing gap and saturates as the gap approaches the optical wavelength. An optimum gap can be defined at the half maximum energy coupling where both the Q factor and coupling efficiency are high. We also calculate the effects of gap width on the resonance shift. We find that the resonance wavelength is increased (decreased) with decreasing gap width for the 10μm (2μm) diameter resonator with narrow gap widths.
In this paper, we present the design, fabrication and characterization of the whispering-gallery mode (WGM) miniature sensors for potential use in biosensing at the nanometer scale. In order to understand and investigate the characteristics of WGM resonances, we designed and fabricated a number of sensors with different dimensions. Each sensor is a micro/nano-structure consisted of a microdisk as the resonating cavity and a micro waveguide for light delivery and collection. In addition to the waveguides having uniform cross-section dimensions, tapered waveguide was also considered in our studies. A simulation model was employed to characterize the EM field and radiation energy density of the designed sensors. The gap effects on WGM resonance in terms of quality factor and full width at half maximum (FWHM) were evaluated. Following the design and characterization, the sensors were fabricated in 1.3μm-thick Si3N4 film using 248nm optical lithography and conventional silicon IC processing. Top and down SEM measurements of the fabricated sensors were conducted and the data for the sensors in one device are given.
This report characterizes the whispering-gallery mode (WGM) resonators with the design of waveguide and microdisk coupling microstructure. In order to understand and optimize the design, studies over a broad range of resonator configuration parameters including the microdisk size, the gap separating the microdisk and waveguide, and the waveguide width are numerically conducted. The finite element method is used for solving the Maxwell's equations which govern the propagation of electromagnetic (EM) field and the radiation energy transport in the micro/nano-structured WGM systems. The EM field and the radiation energy distributions in the WGM resonator are obtained and compared between the on-resonance and off-resonance cases. A very brilliant ring with strong EM field and high radiation intensity is found inward the peripheral surface of the microdisk under the first-order resonance. While under the second-order resonance, there are two bright rings; and the outer ring inward the peripheral surface is thin and weaker than the internal ring. The microdisk size affects significantly the resonant frequencies and their intervals. The gap also has a slight effect on the resonant frequencies. The effect of waveguide width on the resonant frequencies is negligible. However, the gap as well as the waveguide width does obviously influence the qualify factor and the finesse of the resonant modes.
We demonstrate a technique to print. high-density windows using attenuated phase shift mask, negative photoresist and ArF exposure tool and compare our result with that obtained using a binary mask and positive photoresists.
Microcavity lasers have been predicted to offer low threshold current, high quantum efficiency and high modulation bandwidth. In this report we review the physics underlying microcavity device behavior. Specifically we cover dipole-field coupling for both localized (point) dipoles and extended dipoles. In general, optical pumping of the devices is required to create extended dipoles. We also outline the difference between the weak (irreversible) coupling regime and the strong (reversible) regime. For photonic application the intermediate, superradiant regime is perhaps more interesting than the strong coupling regime. Finally, we describe our recent experimental efforts to make high quantum efficiency devices by creating extended excitonic dipoles in electrically pumped devices.
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