Jeffrey Lutkenhaus

Digitally tunable holographic lithography using a spatial light modulator as a programmable phase mask

In this paper, we study tunable holographic lithography using an electrically addressable spatial light modulator as a programmable phase mask. We control the phases of interfering beams diffracted from the phase pattern displayed in the spatial light modulator. We present a calculation method for the assignment of phases in the laser beams and validate the phases of the interfering beams in phase-sensitive, dual-lattice, and two-dimensional patterns formed by a rotationally non-symmetrical configuration. A good agreement has been observed between fabricated holographic structures and simulated interference patterns. The presented method can potentially help design a gradient phase mask for the fabrication of graded photonic crystals or metamaterials.

Holographic fabrication of 3D photonic crystals through interference of multi-beams with 4 + 1, 5 + 1 and 6 + 1 configurations

In this paper, we are able to fabricate 3D photonic crystals or quasi-crystals through single beam and single optical element based holographic lithography. The reflective optical elements are used to generate multiple side beams with s-polarization and one central beam with circular polarization which in turn are used for interference based holographic lithography without the need of any other bulk optics. These optical elements have been used to fabricate 3D photonic crystals with 4, 5 or 6-fold symmetry. A good agreement has been observed between fabricated holographic structures and simulated interference patterns.

Reconfigurable surface plasmon polariton wave adapter designed by transformation optics

In this paper, we propose a reconfigurable surface plasmon polariton (SPP) wave adapter designed by transformation optics, which can control the propagation of SPP waves on un-even surfaces. The proposed plasmonic device is constructed using homogeneously tunable materials (e.g. liquid crystals) so that the corresponding SPP wave transmission can be reconfigured by applying different voltages. Additionally, modified designs optimized for practical fabrication parameters are investigated. Their performance is verified by full-wave simulations. The proposed devices will pave the way towards developing tunable plasmonic devices.

Holographic Fabrication of Designed Functional Defect Lines in Photonic Crystal Lattice Using a Spatial Light Modulator

We report the holographic fabrication of designed defect lines in photonic crystal lattices through phase engineering using a spatial light modulator (SLM). The diffracted beams from the SLM not only carry the defect’s content but also the defect related phase-shifting information. The phase-shifting induced lattice shifting in photonic lattices around the defects in three-beam interference is less than the one produced by five-beam interference due to the alternating shifting in lattice in three beam interference. By designing the defect line at a 45 degree orientation and using three-beam interference, the defect orientation can be aligned with the background photonic lattice, and the shifting is only in one side of the defect line, in agreement with the theory. Finally, a new design for the integration of functional defect lines in a background phase pattern reduces the relative phase shift of the defect and utilizes the different diffraction efficiency between the defect line and background phase pattern. We demonstrate that the desired and functional defect lattice can be registered into the background lattice through the direct imaging of designed phase patterns.

Flexible Holographic Fabrication of 3D Photonic Crystal Templates with Polarization Control through a 3D Printed Reflective Optical Element

In this paper, we have systematically studied the holographic fabrication of three-dimensional (3D) structures using a single 3D printed reflective optical element (ROE), taking advantage of the ease of design and 3D printing of the ROE. The reflective surface was setup at non-Brewster angles to reflect both s- and p-polarized beams for the interference. The wide selection of reflective surface materials and interference angles allow control of the ratio of s- and p-polarizations, and intensity ratio of side-beam to central beam for interference lithography. Photonic bandgap simulations have also indicated that both s and p-polarized waves are sometimes needed in the reflected side beams for maximum photonic bandgap size and certain filling fractions of dielectric inside the photonic crystals. The flexibility of single ROE and single exposure based holographic fabrication of 3D structures was demonstrated with reflective surfaces of ROEs at non-Brewster angles, highlighting the capability of the ROE technique of producing umbrella configurations of side beams with arbitrary angles and polarizations and paving the way for the rapid throughput of various photonic crystal templates.

Spatial light modulator based holographic fabrication of 3D spatially varying photonic crystal templates

In this work, we present holographic fabrication of spatially varying photonic crystal templates of gradient index structures in photosensitized polymer using the interference of multiple beams with specified phases generated by an engineered grayscale phase patterns displayed on a phase only spatial light modulator (SLM) in conjunction with a 4f imaging system. Simple spatially varying 3D structures are fabricated by the interference of four 1st order beams with desired phases plus a central 0th order beam generated by pixel-by-pixel assignment of the gray levels of cells and supercells within the phase pattern displayed on the SLM. Additionally, a low order simple gradient or vortex phase can be added to a multi-beam-generating phase pattern to also create an angularly varying 3D structure. We also demonstrate 2D and 3D spatially variant wave fields that can be used to fabricate photonic crystal templates in photoresist with variation in lattice orientation and spacing using interference of modified beams with specified phases produced by an engineered phase pattern displayed on a SLM. With control of the phases of interfering beams using an SLM, holographic fabrication of spatially varying photonic lattices becomes possible.

Fabrication of 4, 5, or 6-fold symmetric 3D photonic structures using single beam and single reflective optical element based holographic lithography

Here we present the holographic fabrication of large area 3D photonic structures using a single reflective optical element (ROE) with a single beam, single exposure process. The ROE consists of a 3D printed plastic support that houses 4, 5, or 6-fold symmetrically arranged reflecting surfaces which redirect a central beam into multiple side beams in an umbrella configuration to be used in multi-beam holography. With a circular polarized beam incident to silicon wafer reflecting surfaces at the Brewster angle, multiple linearly s-polarized side beams are generated. 3D photonic crystal structures of woodpile, Penrose quasi-crystal, and hexagonal symmetry were produced with ROEs that have 4+1, 5+1 and 6+1 beam configurations, respectively. Since the ROE design can be readily changed and implemented for different photonic crystal structures, this fabrication method is more versatile and cost effective than currently comparable single optical methods like prisms and phase masks.

Design and fabrication of local fill fraction in photonic crystal templates using a spatial light modulator

We report the fabrication of designed defects and regions in photonic crystal templates with differing filling fractions using a spatial light modulator. For the hexagonal lattice, phase patterns with local variance of diffraction efficiency are created using phase tiles from other phase patterns with known diffraction efficiencies. Six-fold symmetric phase patterns are used to generate six beams with locally specified phases. Fourier transform simulations of designed phase patterns are used to guide the filtering process and also give insight into the interference pattern in the 4f plane. Photonic crystal templates are fabricated using exposure of photoresist to the interference patterns generated from the phase patterns with local diffraction efficiency variance displayed on a spatial light modulator. It is shown that local control of filling fraction is achievable using this method. For the square lattice, line defects in polymer lattices are produced using line phase defects in a checkerboard phase pattern. The shifting of the lattice due to the defect phase is investigated. The shifting of lattice around the defects in 2+1 interference is less than that produced by 4+1 interference due to the alternative shifting in lattice in the 2+1 interference. By 45 degree defect orientation and 2+1 interference, the defect orientation can be aligned with the background lattice, the shifting is alternative in lattice, and the shifting is only in one side of the defects, in agreement with the theory prediction.

Fabrication of defects in periodic photonic crystals using a phase only spatial light modulator

Here we present single exposure holographic fabrication of embedded defects in photonic crystal structures in a negative photoresist using a spatial light modulator (SLM). A phase pattern is engineered to form a desired interference pattern and displayed on a phase-only SLM. The resulting first order beams at the Fourier plane are used to recreate the interference pattern. Negative and positive defects are added to the photonic crystal in the following ways. A void-type defect is produced in two dimensional photonic crystal structures by replacing the phase of the engineered phase pattern with a constant value at the points where the defect is desired. And a positive bump defect can be made by allowing the zeroth order beam to interfere with the first order beams. Through these methods, it is possible to fabricate arbitrary shaped defect structures in photonic crystals through a single exposure process, thus improving cost effectiveness and simplifying the fabrication process of integrated photonics.

Holographic fabrication of woodpile-type photonic crystal templates using silicon based single reflective optical element

In this work, we present the holographic fabrication of woodpile-type photonic crystal templates in photosensitive polymer using a silicon-on-PDMS based reflective optical element. The reflective optical element is fabricated from four silicon chips placed inside a polydimethylsiloxane (PDMS) mold, which reflects a circularly or elliptically polarized beam into four linearly polarized side beams, arranged four-fold symmetrically about a central beam, with electric fields normal to the incident plane, and also reduces the laser intensity of the side beams. With a single beam and a single reflective optical element, we can generate the desired laser beam intensities and polarization of each beam, thereby creating woodpile-type photonic crystal templates, and improving the contrast of 3D structures.