This paper presents a holographic fabrication of a new type of photonic crystal, called graded photonic super-crystals with graded basis, dual period and dual symmetry. Pixel-by-pixel phase coding of laser beams in a spatial light modulator can produce the highest resolution in produced photonic super-lattice. Two-level designs in phase pattern are used to generate graded photonic super-crystals where graded square lattice clusters are orientated in four, five or six-fold symmetry. Further phase engineering in a super-cell of 12x8 pixels can produce small-period square lattice orientated in a large period rectangular pattern.
Coupling of light to surface plasmons at metal cathode represents a significant light loss in organic light-emitting diode. The newly discovered graded photonic super-crystals with dual periodicity and dual basis, present great opportunity to improve the light out-coupling (The light extraction efficiency) from organic light-emitting diodes. These graded photonic super-crystals can be holographically fabricated by eight beam interference lithography. In this paper, we have computed, through electrodynamic simulation, the light extraction efficiency of planar, organic light-emitting diodes where the Al cathode is patterned with the graded photonic super-crystals. When the cathode of an organic light-emitting device is patterned in the graded photonic super-crystals, a light extraction efficiency up to 70% in the visible range can be achieved.
Transparent conducting oxides are part of a robust material class that is capable of supporting near-IR surface plasmon resonances (SPRs) which are strongly dependent on size, structure, and doping of the material. This study presents the implementation of holographic lithography to structure large area square lattice cylindrical hole arrays on the transparent conducting oxide thin film, aluminum doped zinc oxide (AZO). For fabricated structures on a glass substrate, SPR are indirectly measured by FTIR transmission and verified with electromagnetic simulations using a finite difference time domain method. Furthermore, it is shown that the SPR excited are standing wave resonances in the (1,1) direction of the lattice array located at the interface of the patterned AZO and glass substrate. This research extends the robust CMOS compatible fabrication techniques of holographic lithography into tunable conductive materials,and contributes to the core technology of future integrated photonics.
Laser shock micro-forming is a non-thermal laser forming method that use laser-induced shockwave to modify surface
properties and to adjust shapes and geometry of work pieces. In this paper, we present an adaptive optical technique to
engineer spatial profiles of the laser beam to exert precision control on the laser shock forming process for free-standing
MEMS structures. Using a spatial light modulator, on-target laser energy profiles are engineered to control shape, size,
and deformation magnitude, which has led to significant improvement of the laser shock processing outcome at micrometer
scales. The results presented in this paper show that the adaptive-optics laser beam forming is an effective method
to improve both quality and throughput of the laser forming process at micrometer scales.
A method of fabricating large-volume three-dimensional (3D) photonic crystal and quasicrystal templates using holographic lithography is presented. Fabrication is accomplished using a single-beam and single exposure by a reflective optical element (ROE). The ROE is 3D printed support structure which holds reflecting surfaces composed of silicon or gallium arsenide. Large-volume 3D photonic crystal and quasicrystal templates with 4-fold, 5-fold, and 6-fold symmetry were fabricated and found to be in good agreement with simulation. Although the reflective surfaces were setup away from the Brewster's angle, the interference among the reflected s and p-polarizations still generated bicontinuous structures, demonstrating the flexibility of the ROE. The ROE, being a compact and inexpensive alternative to diffractive optical elements and top-cut prisms, facilitates the large-scale integration of holographically fabricated photonic structures into on-chip applications.
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.
In this paper, we proposed highly efficient all-dielectric Huygens’ metasurfaces working at mid-IR frequencies. The meta-atom of the designed Huygens’ metasurface is a cubic dielectric resonator or its variety, which is made from PbTe that possesses a high refractive index of around 5 at mid-IR frequencies. By overlapping spectrally both the magnetic and electric dipole modes of the high-index dielectric resonators, a full phase coverage of 2π and an equal-magnitude transmission could be achieved, which are essential conditions for realizing a metasurface. Two Huygens’ metasurfaces for beam bending are designed with a phase change between two consecutive meta-atoms of π/4 and π/3, respectively. The simulation results agree well with the design theory.
In this paper, we proposed metasurfaces working at two THz wavelengths simultaneously (in a broadband manner for each wavelength). The performance of the proposed metasurfaces at both wavelengths could be manipulated individually. A unit cell of the metasurface is first designed. Based on the unit cell structure, two functional metasurface devices are realized, which can arbitrarily deflect the incident THz waves at the two design wavelengths. The simulation results of these two proposed designs agree well with the theoretical predictions.
In this paper, we proposed a novel cross-polarization converter that simultaneously works at two frequencies in the reflection mode, which is constructed of an L-shape perforated graphene sheet printed on a dielectric spacer backed by a gold layer. For the normal incidence, the optical rotation at these two working frequencies originates from the simultaneous excitation of both eigenmodes characterized as the localized surface plasmon resonances. In addition, both working frequencies can be tuned within a large frequency range by varying the Fermi energy of the graphene, which opens up tremendous opportunities to develop voltage-controlled tunable devices at mid-IR frequencies.
In this paper, we proposed novel graphene-based tunable plasmonic metamaterial structures to realize transparency windows. The proposed structures are composed of a graphene layer perforated with a quadrupole slot structure and a dolmen-like slot structure, which could achieve single and multiple transparency windows, respectively. In both complementary structures, the transparency windows could be dynamically manipulated by varying the Fermi energy levels of the graphene layer through electrical gating. The presented complementary graphene-based metamaterial structures with multiple tunable transparency windows could open up new opportunities for potential applications in tunable multi-wavelength slow light devices and optical sensors.
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.
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.
We demonstrate that the refractive indices of important functional metal oxides (TiO2, SnO2, and ZnO) can be engineered “at will” for applications in photonics engineering. The tailoring of the refractive indices is accomplished by 3D nanostructuring in the sub-wavelength regime (50nm or less) using the method of block-copolymer templating combined with a low cost solution processing approach. Using this method, the index of refraction of the demonstrated metal oxides and their doped variants can be engineered to be as low as 1.25. We will present both numerical simulations and experimental data demonstrating the unrestricted integration of functional metal oxides with a D-shaped optical fiber for applications in chemical and biological sensing. Using the developed refractive index engineering scheme, we introduce a novel hydrogen sensor by integrating a palladium doped TiO2 nanomaterial with D-shaped optical fiber and provide sensor characterization up to 700°C for applications in the energy sector.
Gradient index (GRIN) structures have attracted great interests since their invention. Especially, the recent advance in
the fields of transformation optics, plasmonics, and nanofabrication techniques has opened new directions for the
applications of GRIN structures in nano-photonic devices. In this paper, we apply Luneburg lens and its transformed
counterpart to realize efficient coupling to plasmonic nano-waveguides. We first briefly present the general structures of
Luneburg lens and generalized Luneburg lens, as well as the design process of flattened Luneburg lens applying quasiconformal
mapping techniques. After that, we study the performance of these lenses for coupling electromagnetic signals
to nano-waveguides (the metal-insulator-metal (MIM) nano-waveguide), and different schemes are investigated.
In this paper, a novel design of broadband monopole optical nano-antennas is proposed. It consists of a corrugated halfelliptical patch inside an elliptical aperture. Full-wave electromagnetic simulations have been used to investigate the performance of the nano-antenna. The predicted performance of the proposed monopole nano-antenna is remarkably broadband. Moreover, the proposed broadband nano-antenna can respond to light waves with different polarizations. The proposed optical antenna will pave the way towards the development of high performance optical antennas and optical systems.
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.
In this work, we present a method of holographically fabricating photonic structures in photosensitive polymer
using a phase pattern displayed on a spatial light modulator (SLM) as a digitally programmable phase mask. The phase
pattern can be programmed in hexagonal and square symmetries. By changing the gray level of the pixelated units in the
displayed phase pattern, we can achieve a digital control of the phases of one or more of the interfering beams, thus
changing the interference pattern. By using the phase pattern on the SLM as a tunable phase mask, different photonic
crystal templates can be fabricated.
In this paper, we report novel designs of tunable THz plasmonic devices. The designed devices will be able to dynamically control and change the spectrum responses of extraordinary THz wave transmissions. The tuning of the devices is accomplished by electrowetting-controlled liquid metals morphing. Different THz device configurations are investigated and numerical simulations have been conducted to theoretically predict the feasibility of proposed structures. Since all of these devices will be constructed by liquid metals, their geometrical shapes can be actively modulated by electrowetting. In this way, THz devices with tunable wave transmission property can be realized. These new THz devices are expected to be applied in various areas of sensing, communication, and imaging.
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.
Abstract: Here we present holographic fabrications of large area nano-optical device templates, including nano-antenna and photonic quasi-crystals using a single reflective optical element (ROE) through single beam and a single exposure process. These ROEs consist of several silicon wafers arranged with 5 or 6-fold symmetry, supported by two plastic platforms. By changing the polarization of the incident beam, various photonic quasi-crystal including spiral quasicrystals can be fabricated using the 5-fold symmetrically arranged optical element. Using the single optical element with silicon chips arranged in 6-fold symmetry, large areas of nano gap arrays can be fabricated holographically. These nanogaps and their shapes can be controlled through the phase delay of one laser beam. The nano gap arrays will be used for fabrication of nano-antennas arrays after metal depositions.
It is well-known that the conventional lens design suffers from the aberration, which will lead to imperfect imaging. One
way to solve this problem is to use gradient index (GRIN) lenses such as Luneburg lens. However, the spherical
geometry of Luneburg lens imposes difficulty for manufacturing. Also, it is desired to design the Luneburg lens with
arbitrary focal length. To address these issues, in this paper, we propose to apply the transformation optics techniques to
the general Luneburg lens design. In this way, the spherical lens surface will be transformed to flattened shapes, which
can be practically fabricated on a flat substrate. Specifically, three-dimensional (3D) Luneburg lenses with different
focal lengths will be studied. Moreover, discussion on the fabrications of proposed lens has been included. It is desired
to ensure that the modified design lies within the available material properties of various polymer photoresists.
Traditional optical components have many drawbacks such as bulky size and suffering from the diffraction limits. In
order to solve these problems, optical antennas have been proposed recently. It overcomes the constraints imposed by
conventional optical devices, allowing unprecedented control of light-matter interactions within sub-wavelength volume.
Up until now, almost all of the existing optical antennas can only operate at single fixed frequency. This has highlighted
the need for designing optical antennas covering multiple working frequencies or broad frequency band to achieve more
design and application flexibility. Motivated by this factor, in this paper, we design and investigate new optical antennas
with multi-frequency and broadband operations. Specifically, we investigate several optical antenna topologies to
introduce multiple resonant peaks. Potential candidate designs include the stepped-junction optical antenna, and the
multi-junction optical antenna. Moreover, based on the concept of multiple-pair nano-dimer structure, broadband optical
antennas are investigated, which can further enable us to control light over broad spectrum.
Study of structures that demonstrate negative refraction is important in the search for metamaterials suitable for
imaging capabilities below the diffraction limit. In this work, we study negative refraction behavior for the third
photonic band of two dimensional elliptical rod photonic crystals in a centered rectangular lattice in air background
using analysis of the equifrequency contours of this band combined with FDTD simulations. Hyperbolic equifrequency
contours on the third photonic band indicate both negative and positive refraction at different angles. FDTD simulations
are used to verify negative and positive refraction in the third band and search for potential imaging capabilities. If these
behaviors are found, this photonic crystal design could potentially find use in sub-diffraction limit imaging applications.
In this paper, we investigated the design of a photonic-crystal based three-dimensional (3D) cloaking structure
with low-cost and improved performance. The carpet cloaking structure with truly 3D geometry is designed
at optical frequencies. Compared with microwave cloaks where materials with large anisotropy are needed,
the designed 3D cloak can be constructed using isotropic dielectric materials with small material parameter
variations, which makes it suitable for practical implementation. By applying two-layer phase mask based
holographic lithography, the designed cloaking structures can be fabricated rapidly and at low-cost, which will
pave the way towards the mass production of invisibility cloak.
This paper presents a photonic bandgap simulation for real holographic 3D photonic crystals instead of optimal photonic
crystal structures. The holographic photonic crystals are formed through five-beam interference generated by multi-layer
phase mask. The photonic bandgap depends on the relative phase difference among the interfering beams. A maximum
bandgap of 20% of the middle bandgap can exist in these structures which can be formed through single beam, single
phase mask, and single laser exposure process. We also fabricate the multi-layer phase mask by placing a spacer layer
between gratings. Using the multi-layer phase mask, photonic crystal templates are holographically fabricated in a
photosensitive polymer.
In this paper we demonstrate an approach for laser holographic manufacturing of three-dimensional photonic lattice
structures using a single specially designed, diffraction optical element mask. The mask is fabricated by recording
gratings in a photosensitive polymer using a two-beam interference method and has four diffraction gratings in the
sample plane, with a same distance from the opening center and oriented four-fold symmetrically. Four first-order
diffracted beams by the gratings and one non-diffracted central beam overlap and form three-dimensional interference
pattern. The phase of one side beam is delayed by inserting a thin piece of microscope glass slide into the beam. By
rotating the glass slide thus tuning the phase of the side beam, the five beam interference pattern changes from facecenter
tetragonal symmetry into desired diamond-like lattice symmetry. The three-dimensional interference pattern is
recorded in a photosensitive polymer, showing the phase tuning related changes of photonic lattice structures. Combing
an amplitude mask with the phase mask by putting the amplitude mask in the central opening of the diffraction optical
element mask, line defects are produced within the photonic crystal template.
We report a new design and fabrication of an integrated two-layer phase mask for five-beam holographic fabrication of
three-dimensional photonic crystal templates. The fabricated phase mask consists of two layers of orthogonally oriented
gratings produced in a polymer. The vertical spatial separation between two layers produces a phase difference among
diffractive laser beams, which has enabled a holographic fabrication of diamond-like photonic crystal templates through
single-beam and single-exposure process. The reported method simplifies the fabrication of photonic crystals and is
amendable for massive production and chip-scale integration of three-dimensional photonic structures.
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