Christopher Middlebrook

Direct-write electron-beam lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens

This article describes a method for performing direct-write lithography of an IR antenna-coupled microbolometer onto the surface of a hemispherical lens. Antennas on a dielectric half-space receive power more efficiently from the substrate side than from the air side. The use of a hemispherical lens facilitates reception through the substrate as well as elimination of trapped surface waves that would normally occur in the substrate. Using direct-write lithography onto the surface of the hemispherical lens eliminates the potential of an air gap between the antenna and lens. Additionally, the accuracy of alignment between the antenna and the center of the lens is controlled at the lithographic step. As a result, there is increased responsivity is observed in the antenna-coupled microbolometer when illuminated from the substrate-side compared to air-side illumination.

Optical-electrical printed wiring board for high-speed computing applications

Abstract. Optical-electrical printed wiring boards were fabricated featuring mechanical transfer (MT)-compatible interconnections for out-of-plane optical signal routing with an average optical link loss of 10.7 dB. Commercially available components were integrated into an optical layer for out-of-plane optical routing, including light turning devices that feature spherical micro lens arrays, a total internal reflection mirror, and alignment slots compatible with standard MT connectors. The feasibility of the optical-electrical printed wiring board is discussed in detail to demonstrate its compatibility with common printed circuit board manufacturing processes. The optical-electrical printed wiring board prototypes survived thermal cycling (−40°C to 85°C) and humidity exposure (95% humidity) showing an overall degradation of <3  dB of optical performance. Operational failure (>18  dB) occurred after environmental aging life testing at 110°C for 216 h.

Chemical inertness of UV-cured optical elastomers within the printed circuit board manufacturing process for embedded waveguide applications

Embedding polymer optical waveguides (WGs) into printed circuit boards (PCBs) for intra-board or board-to-board high speed data communications requires polymer materials that are compatible and inert when exposed to common PCB manufacturing processes. Ensuring both WG functionality after chemical exposure and maintaining PCB manufacturing integrities within the production process is crucial for successful implementation. The PCB manufacturing flow is analyzed to expose major requirements that would be required for the successful implementation of polymer materials for embedded WG development. Chemical testing and analysis were performed on Dow Corning ® OE-4140 UV-Cured Optical Elastomer Core and Dow Corning® OE-4141 UV-Cured Optical Elastomer Cladding which are designed for low loss embedded optical WGs. Contamination testing was conducted to demonstrate polymer compatibility in both cured and uncured form. Various PCB chemicals were treated with uncured polymer material and tested for effective contamination. Fully polymerized multimode WGs were fabricated and exposed to PCB chemicals at temperatures and durations comparable to PCB manufacturing conditions. Chemical analysis shows that the chosen polymer is compatible and inert with most common PCB manufacturing processes.

Non-moving Hadamard matrix diffusers for speckle reduction in laser pico-projectors

Personal electronic devices such as cell phones and tablets continue to decrease in size while the number of features and add-ons keep increasing. One particular feature of great interest is an integrated projector system. Laser pico-projectors have been considered, but the technology has not been developed enough to warrant integration. With new advancements in diode technology and MEMS devices, laser-based projection is currently being advanced for pico-projectors. A primary problem encountered when using a pico-projector is coherent interference known as speckle. Laser speckle can lead to eye irritation and headaches after prolonged viewing. Diffractive optical elements known as diffusers have been examined as a means to lower speckle contrast. This paper presents a binary diffuser known as a Hadamard matrix diffuser. Using two static in-line Hadamard diffusers eliminates the need for rotation or vibration of the diffuser for temporal averaging. Two Hadamard diffusers were fabricated and contrast values measured showing good agreement with theory and simulated values.

Fan-out routing and optical splitting techniques for compact optical interconnects using single-mode polymer waveguides

Polymer waveguide (WG) S-bends are necessary for fan-out routing techniques and optical splitting in high-density optical interconnects. Designing and manufacturing of optimal S-bends are critical for minimizing optical link loss while maintaining overall size and layout constraints. Complete structural loss analysis is demonstrated theoretically and shown experimentally utilizing both radial and transitional loss in single-mode (SM) polymer WG radial arc, cosine, and raised-sine S-bend profiles. SM polymer WG straights were first fabricated to measure standard propagation loss. SM WG S-bends were fabricated incorporating straight lead-in and lead-out sections to incorporate transitional loss present in workable designs. S-bend designs were measured at different dimensions and matched to theoretical losses. Compact cosine and radial arc S-bends exhibited the lowest structure loss for low and high NA WGs, respectively. High-speed performance of SM WG straights and S-bends was measured at 10 Gbit/s demonstrating low error rate. Optical splitters designed with S-bends and tapers were also evaluated and fabricated. Trade-off between optimal loss and minimal device size is discussed.

Laser speckle contrast reduction measurement using diffractive diffusers

In order to produce future generation micro-projection systems that can function independently or in conjunction with small personal communication devices lasers are the preferred source of illumination over LEDs. Lasers are much brighter and require less power than LEDs allowing for larger screen sizes and smaller battery requirements. In order to illuminate the spatial light modulator used in the micro-projection system micro-optical elements are used within the illumination path of a projector system to shape the RGB laser sources. Due to the diffractive nature of the optical elements and the high coherence of the lasers a speckle pattern is produced in the final image reducing the overall image quality. Diffractive diffusers are typically used in combination with micro-lens arrays in a time varying fashion in an attempt to reduce the spatial coherence of the laser sources and hence reduce the speckle. Previous reduction techniques have successfully used pseudo-random hadamard matrix diffusers to greatly minimize the contrast of the pattern. This paper examines new reduction methods involving diffractive diffusing elements and presents measurements in the reduction of speckle contrast for each technique.

A case study on blackout restoration as an educational tool

New exercises are needed to stimulate interest in power engineering, especially providing links to the other areas of electrical engineering such as computers or controls. While de-regulation has revitalized many technical challenges in power system engineering, power faculty members need updated resources to interest students in power engineering as a career. This paper describes a case study developed at Michigan Technological University (MTU). This exercise provides an educational opportunity for electrical engineering students at the sophomore/junior level to expand their knowledge about power systems in general, and more specifically power system blackout restoration. Besides offering explanations of concepts, this case study uses the dynamic environment of HTML to help create links for more detailed and often more visual representations for key concepts. The end goals for the students are (1) to complete open-ended exercises to see how they can immediately apply their newly acquired knowledge, and (2) an introduction to advanced power system subjects.

Highly linear dual ring resonator modulator for wide bandwidth microwave photonic links

A highly linear dual ring resonator modulator (DRRM) design is demonstrated to provide high spur-free dynamic range (SFDR) in a wide operational bandwidth. Harmonic and intermodulation distortions are theoretically analyzed in a single ring resonator modulator (RRM) with Lorentzian-shape transfer function and a strategy is proposed to enhance modulator linearity for wide bandwidth applications by utilizing DRRM. Third order intermodulation distortion is suppressed in a frequency independent process with proper splitting ratio of optical and RF power and proper dc biasing of the ring resonators. Operational bandwidth limits of the DRRM are compared to the RRM showing the capability of the DRRM in providing higher SFDR in an unlimited operational bandwidth. DRRM bandwidth limitations are a result of the modulation index from each RRM and their resonance characteristics that limit the gain and noise figure of the microwave photonic link. The impact of the modulator on microwave photonic link figure of merits is analyzed and compared to RRM and Mach-Zehnder Interference (MZI) modulators. Considering ± 5 GHz operational bandwidth around the resonance frequency imposed by the modulation index requirement the DRRM is capable of a ~15 dB SFDR improvement (1 Hz instantaneous bandwidth) versus RRM and MZI.

Using the 3D beam propagation method to model the effects of lithographic roughness on the attenuation of highly multimodal polymer waveguides

Waveguide sidewall surface roughness is a primary cause of attenuation in lithographically defined, multimode, polymer optical waveguides. Techniques that are currently employed to analyze the effect of roughness on highly multimode waveguides such as coupled mode theory are not easily adaptable to more complicated structures. For example, this technique cannot be used for waveguides that utilize bends, where the modal distribution can not be easily calculated. In this paper, the beam propagation method is used to find sidewall roughness losses empirically. Straight waveguides of different roughnesses are first modeled, and the modeled results are compared to the attenuation of manufactured straight waveguides. The roughness that closely matches the manufactured waveguides attenuation is then verified further by matching the attenuation of waveguides containing 90° bends.

Optical filtering of RF signals through contrasting fiber dispersion slopes

The authors present a photonic filter that uses a difference in dispersion slopes in different fiber lengths to create a tunable notch filter. The use of differing dispersion slopes allows for a relative propagation delay in one output of a dual output Mach-Zehnder modulator.The performance of this filter has been simulated and shown to reduce co-site interference. Fibers or other optical waveguides with large dispersion slopes can be used to reduce the length of fiber necessary to achieve wide tuning ranges. Filters with wider pass bands and deeper nulls can be achieved by increasing the number of delay paths through the use of multiple optical splitters and combiners. Future work implementing photonic crystals or waveguides may be used in order to generate this filter structure over shorter physical path lengths, further reducing the size and weight of the system.