Robert P. Dahlgren

Non-imaging optical concentrators for low-cost optical interconnect

In this work we report on a non-imaging optical concentrator for high-speed polymer optical fiber (POF), which has applications in chip-to-chip, consumer display, and backplane data transport. High-speed operation places demands on the ability of coupling from large-core media to small apertures typical of 10 Gbps optoelectronics. Design and fabrication of concentrators made by single point diamond turning and injection molding will be discussed, and comparison of experimental data to simulation will show good coupling efficiency with a wide tolerance to fiber misalignment.

Aspheric nonimaging concentrators for multimode fiber coupling

Robust and efficient optical coupling from laser-to-fiber and from fiber-to-detector is an important consideration for loss limited optical data links. Standard chip scale package process flow used by the semiconductor industry is based upon machine vision assisted pick-and-place die attach and wirebonding operations. To realize scalable heterogeneous integration of optical elements, mass production must be done within the framework of existing manufacturing equipment and avoid active opto-mechanical alignment steps. This publication reports on the performance of a set of a refractive, hemi-aspheric, nonimaging optical concentrators that are simple and amenable to standard package integration flow with passive alignment. A set of lenses are made by single-point diamond-turning and injection molding of unfilled polyetherimide, which is relatively transparent at the link operating wavelength of 850 nm. The goal of the design is to balance the absolute coupling at optimum alignment with wide margins for angular and linear misalignment.

Tolerancing and corner cases in optical simulation

Our work discusses the tolerance modeling of an optical fiber that is inserted into a cylindrical alignment bore. We note that some commercial optical simulation software suites have the mechanical tolerance operands entered in Cartesian coordinates and if radial variation is entered as simple X and Y de-centering, there arises a kind of corner condition where fiber in the opto-mechanical model is offset more than is possible in the physical implementation resulting in an overly-conservative estimate of the worst-case coupling efficiency. Approaches to avoid this over estimation are presented and discussed.

Methodology to Simulate Parasitic Reflection and Birefringence in Optical Pickup Units and Sensors

A novel technique is presented for the computation of the polarization transfer function of optical assemblies with finite reflection coefficients, birefringence, and other parasitic imperfections. The methodology is directly applicable to optical data storage modeling, such as CD/DVD recording optics and the physical recording process

3D scanning and printing of airfoils for modular UAS

The NASA Ames Research Center has been developing small unmanned airborne systems (UAS) based upon remotecontrolled military aircraft such as the RQ-14 DragonEye and RQ-11 Raven manufactured by AeroVironment. The first step is replacing OEM avionics with COTS avionics that do not use military frequencies for command and control. 3D printing and other rapid prototyping techniques are used to graft RQ-14 components into new “FrankenEye” aircraft and RQ-11 components into new “FrankenRaven” airframes. To that end, it is necessary to design new components to concatenate wing sections into elongated wingspans, construct biplane architectures, attach payload pods, and add control surfaces. When making components such as wing splices it is critical that the curvature and angles of the splice identically match the existing wing at the mating surfaces. The RQ-14 has a thick, simple airfoil with a rectangular planform and no twist or dihedral which make splice development straightforward. On the other hand the RQ-11 has a much thinner sailplane-type airfoil having a tapered polyhedral planform. 3D scanning of the Raven wings with a NextEngine scanner could not capture the complex curvature of the high-performance RQ-11 airfoil, resulting in non-matching and even misshapen splice prototypes. To characterize the airfoil a coordinate measuring machine (CMM) was employed to measure the wing’s shape, fiducials and mounting features, enabling capture of the subtle curves of the airfoil and the leading and trailing edges with high fidelity. In conclusion, both rapid and traditional techniques are needed to precisely measure and fabricate wing splice components.

Remotely sensing the photochemical reflectance index, PRI

In remote sensing, the Photochemical Reflectance Index (PRI) provides insight into physiological processes occurring inside leaves in a plant stand. Developed by1,2, PRI evolved from laboratory reflectance measurements of individual leaves. Yet in a remotely sensed image, a pixel measurement may include light from both reflecting and transmitting leaves. We compared values of PRI based upon polarized reflectance and transmittance measurements of water and nutrient stressed leaves. Our results show the polarized leaf surface reflection should be removed when calculating PRI and that the leaf physiology information is in leaf interior reflectance, not leaf transmittance.

Matrix operators for complex interferometer analysis

A modeling methodology and matrix formalism is presented that permits analysis of arbitrarily complex interferometric waveguide systems, including polarization and backreflection effects. Considerable improvement results from separation of the dependencies on connection topology from the dependencies on the devices and their specifications. A non-commutative operator and embedding matrices are introduced allowing a compact depiction of the salient optical equations, and straightforward calculation of the amplitude and intensity transfer functions.