A course has been developed for students interested to learn practical design procedures for automotive lighting applications. The course covers topics such as imaging and non-imaging optics, LED lighting, plastic optics, plastic part design, optical manufacturing, injection molding, optical tolerancing, computer aided lighting and computer aided design, and economical aspects of product development. The students work through several projects on rear lighting and forward lighting. The present paper summarizes the pedagogy in optics education in the second offering of the course, inspired by the experiences from the first offering, the feedback from students, and the feedback from industry. Challenges faced during teaching the course, both technical and pedagogical, are discussed.
Gradient Index (GRIN) Optics is a challenging frontier of lens design. We have developed a free, online toolbox for generating gradient optics dynamic linked library (GODLL) files representing an arbitrary, user-defined gradient index profile for use with Zemax OpticStudio. In order to show the accuracy, user-experience and the procedure for usage of GODLL, we have demonstrated the performance of our toolbox using several popular or extreme examples consisting of Maxwells Fisheye Lens, Luneberg Lens, and a typical SELFOC lens.
The work presented here shows a compact lens system that demonstrates improved imaging quality performance while focusing on as-built performance and design for manufacturing. Using Zemax, we consider an approach for optimizing for as-built performance and incorporate the approach into the design process for a mobile phone camera. The optimized design consists of 6 plastic aspheric lenses, an infrared glass filter, and a 12 MP CMOS image sensor. The optical system demonstrates high-resolution imaging and has a field-of-view of 87.6°, an F-number of 2.0, a maximum distortion of less than 2.5%, and a total track length of 6.630 mm.
With the recent addition of Moore's high-yield feature in Zemax, a convenient path to optimiza- tion for as-built performance while reducing computation time has been introduced. In order to analyze the cost and outcome of optimization with the new feature and other approaches, we consider a side-by-side comparison of the conventional approach, high-yield approach, and other alternatives. The benchmark design under consideration is a basic Double Gauss lens due to the extensive studies of its variants since its conception. A total of eight approaches are considered, and the resulting designs and their tolerance sensitivities are presented in order to provide recommendation of a favorable approach.
We have fabricated biaxial hyperbolic metamaterials (BHMMs) using layered structures consisting of titanium dioxide (TiO2) and copper (Cu). In order to enable the biaxial property, an oblique angle deposition (OAD) technique is applied to deposit the dielectric layer. We have characterized the biaxial hyperbolic dispersion using variable angle spectroscopic ellipsometry (VASE) measurements in the wavelength range 400 nm to 900 nm. A noticeable difference be- tween in-plane permittivity components of the fabricated BHMM is observed to be 0.13 at 633 nm. The experimental characterization results have been in good agreement with the predictions of effective medium approximation (EMA) with an MSE of 18.
A multilayer hyperbolic metamaterial (HMM), fabricated from alternating thin films of metal and dielectric, displays a hyperbolic, anisotropic dispersion relation due to the coupling of excited surface plasmons. The design, fabrication, and characterization of an HMM based on TiO2 / Cu alternating layers with a metal-to-dielectric fill factor of 67% is presented. The layers were deposited onto glass and silicon substrates using physical vapor deposition (PVD) with an electron beam evaporator and then characterized using ellipsometry. According to the effective medium theory, this design shows an epsilon-near-zero (ENZ) line near the Helium-Neon wavelength of 633 nm. Our experimental measurements are in good agreement with the theoretical predictions.
Disordered one-dimensional photonic bandgap (PBG) structures could prove useful in designing broadband reflectors capable of filtering chosen polarizations of incoming light. By capitalizing on the similarities between defects and disorder, it is possible to construct a 1D PBG structure such that the layers are non-uniform but the structure can retain its most novel properties. This is done by allowing the thickness of the layers in the structure to deviate uniformly around an average thickness by a preselected amount of deviation. A mathematical model using the Transfer Matrix Method for simulation has been previously constructed by this group. This model has been verified using FDTD simulation as well. The PBG structure was then fabricated consisting of TiO2 deposited by electron-beam physical vapor deposition (e-beam PVD) first at normal incidence and then at a 70o oblique angle. This pattern was repeated to create six bilayers of TiO2 films. This alternating pattern gives rise to the novel structure of a PBG structure by creating a repeating pattern of amorphous and biaxial, columnar, birefringent TiO2 ,which is analogous to using two different materials. Through testing using a polarizer, analyzer, and HeNe laser with a wavelength of 632.8 nm, it has been found that the sample does in fact match well with the expected theoretical results and acts as a broadband reflector for the TM polarization designed for a 70º incidence angle. The average layer thickness of the fabricated TiO2 PBG is 22.7 nm.
We have designed a light-guide for lighting applications, including automotive headlamps. The light-guide is designed based on a free-form slab. Our intention has been to optimize the design for creating legal patterns. One of our objectives has been to investigate how the changes in the shape of the freeform light-guide affects the light pattern, and how the light source geometry affects the design. For prototyping purpose, we use a particular polymer that exhibits optical performance close to acrylic (PMMA).
A one-dimensional, single-material polarizing photonic bandgap structure is designed and fabricated using e-beam PVD and oblique angle deposition technique. In order to obtain high- and low-index layers, we deposited alternate layers of titanium dioxide (TiO2) at deposition angles of 0° and 70°on top of a fused silica substrate. This approach is chosen since at deposition angle of zero degree, deposited TiO2 using e-beam PVD, show a negligible birefringence while the obliquely deposited TiO2 acts as a biaxial material with significant birefringent behavior. As a result, deposition of a bilayer film at two angles is analogous to using two different materials with the advantage of simplifying fabrication and modeling this polarizing device. The bandgap of the bilayer structure is modeled in a way that only a specific wavelength with certain polarization, p polarization, could pass through while the s polarization is reflected. For modeling we used Transfer Matrix Method and numerical FDTD analysis to simulate behavior of the 1D photonic band gap structure. The simulations produce better than 98% reflection for s polarization and almost no reflection for p polarization for the center wavelength of 632.8 nm. The fabricated device shows 94% reflection for s polarization and less than 6% reflection for p polarization at the red HeNe laser wavelength at an incident angle of 70°. The results demonstrate that a 1D multi-layer photonic crystal, fabricated from a single material, can be designed to selectively reflect or transmit p or s polarization of an incident light beam.
We investigate negative index of refraction in plasmonic metamaterials with an emphasis on distinguishing and isolating contributions to negative refraction from spatial dispersion, as a function of metamaterial dimensions on the scale of the wavelength. We explain the design approach using genetic algorithm and provide sample applications including negative refraction.
We explain the design of one dimensional Hyperbolic Metamaterials (HMM) using a genetic algorithm (GA) and provide sample applications including the realization of negative refraction. The design method is a powerful optimization approach to find the optimal performance of such structures, which “naturally” finds HMM structures that are globally optimized for specific applications. We explain how a fitness function can be incorporated into the GA for different metamaterial properties.
We investigate a novel light conversion scheme in nanostructures for the highly demanding field of plasmonic solar cells. In our study, we incorporate vertical nanorods made of semiconductor materials, which are coupled optically to plasmonic nanoantennas for optimal absorption of sunlight. Utilizing the unique properties of localized surface plasmon resonances, we create dedicated nanoantenna elements such that the emission pattern is effectively directed toward the absorber material. In our approach, we use a computational finite element method to investigate the effects of size and shape of metallic nanoparticles to obtain an asymmetric radiation pattern that matches the geometry of our design.
Recent progress in the area of hyperbolic metamaterials (HMMs) has sparked interest in transparent conducting oxides (TCOs) that behave as plasmonic media in the near-IR and at optical frequencies for imaging and sensing applications. It has been shown that by depositing alternating layers of negative-epsilon/positive-epsilon materials, a medium can be created with unusual index values such as near zero. HMMs support high-k waves corresponding to a diverging photonic density of states (PDOS), the quantity determining phenomena such as spontaneous and thermal emission. Also, modeling such structures allows evanescent fields containing sub-wavelength information to be coupled to propagating radiation. We investigate the optical, electronic, and physical properties of radio frequency plasma-assisted molecular beam epitaxial (RF-MBE) growth of alternating layers of ZnO and TCO of uniform thickness for HMM applications. Preliminary work creating HMMs with ZnO and Al-doped ZnO (AZO) has shown a negative real part of the permittivity at near-IR whose modulus is proportional to the number density of Al dopant. However, increasing the Al content of the AZO increases the transmission losses to unacceptable levels for device applications at industry standard wavelengths. A TCO with conductivity and physical structure superior to that of AZO is gallium-doped ZnO (GZO). Uniformly grown GZO has been demonstrated to possess improved crystal quality over AZO due to the higher diffusivity of Al in the ZnO. AZO and GZO HMM structures grown by RF-MBE are characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Hall effect, four-point probing, deeplevel transient spectroscopy (DLTS), ellipsometry, visible and ultraviolet spectroscopy (UV-VIS) and in-situ reflection high energy electron diffraction (RHEED).
We investigate the incorporation of an epsilon-near-zero (ENZ) material into a waveguide structure in order to suppress dispersion associated with the interaction of light with material in the core, guiding layer. ENZ metamaterials can provide a mechanism for air-core waveguides by introduction of a cladding medium exhibiting a refractive index less than unity. We study the application of aluminum zinc oxide (AZO), a transparent conducting oxide, as the candidate for ENZ waveguides. For this purpose, we design a metamaterial cladding layer with ENZ properties derived from nanoparticles of AZO, and investigate the resulting loss and dispersion of guided optical signals.
We investigated the optical characteristics and polarization insensitivity of an epsilon-near-zero metamaterial structure comprising aluminum-doped zinc oxide nanoparticles (NPs) hosted by a medium of ligands. By the use of an equivalent circuit model for the pairs of NPs, or dimers, and also of fullwave simulations, we studied the response of this self-assembled metamaterial for near-infrared applications. Considering the coupling of localized surface plasmons, we demonstrated the dominance of a certain dimer configuration and then applied this result to the whole medium as a simplifying approximation for a random structure. The consequent results showed a polarization insensitivity and also a general redshift in the plasmon resonance of the structure.
Transparent conducting oxides (TCO) are an interesting class of plasmonic materials, which are under intensive
study for their use in low-loss metamaterials and a range of applications such as sensing, imaging and transformation
optics. Here, using both full-wave simulations and an equivalent circuit model for pairs of nanoparticles
of aluminum doped zinc oxide (AZO), we study the plasmonic effects for low loss low index metamaterials for
infrared applications. The behavior of localized surface plasmon resonances (LSPR) of AZO nanoparticle dimers
embedded in a host polymer medium is investigated for different dimer orientations with respect to the indicent
electromagnetic wave. In doing this, the role of dressed polarizability to enhance and quench the plasmonic
effects is also considered. The effects of the nanoparticles relative size and the spacing between them are studied.
Understanding these resonances and their dependence on dimer orientations, provides a means to design metamaterial
structures for use in the near infrared (NIR) region with epsilon-near-zero properties leading also to
low index metamaterials. In our studies, we demonstrate how nanospheres with radii less than 100 nm that are
distributed with an average spacing less than their diameter, can result in an effective medium with refractive
index less than one. We utilize a full-wave frequency domain finite element method in conjunction with an
equivalent-circuit model for the nanoscale dimers in order to describe the spectral response of the bulk low index
properties. We also present a statistical analysis to obtain the effective refractive index for incident light having