DUET is an embodiment of an astronomical telescope without mirrors or lenses. All optics are diffractive. The primary objective is a gossamer membrane annular Gabor Zone Cone which has the characteristic of focusing by wavelength. The secondary is a very high resolution spectrometer. The annulus primary has a diameter sufficiently wide so that the spectral separation of the parent star is resolved to cm/sec Doppler shift as needed to detect Earth analogs in the 10 pc "Neighborhood." Proximate stars are removed by the dual dispersion method permitted with a precise secondary spectrometer. Residual photons detected after coronagraphy come from the exoplanetary system and are natively spectrographic. The optical train allows for new types of coronagraphy, because of a natural bandpass spectral separation. Two types of coronagraph are proposed. The physical embodiment presumes in-space construction. The large primary is delivered as a ribbon on mandrels and is installed over a network of active trusses.
A notional space telescope without any mirrors or lenses is being investigated. DUET (Dual Use Exoplanet Telescope) has a gossamer membrane annular Gabor Zone Plate primary objective that is flat. Highly chromatic stellar imagery is disambiguated in a secondary also made from diffractive elements. The data acquired is intrinsically spectrographic and could (1) detect radial velocity below 5 cm/sec and (2) take direct spectra of a systems exoplanets. DUET is intended as a follow-up to a survey telescope, THE MOST, being developed in tandem which will identify target stellar systems with earth-like exoplanets. DUET observes one star at a time, integrating its light until the exoplanetary system is resolved. DUET utilizes a battery of coronographic methods including angular differential imaging, interferometric nulling, and phased Fraunhofer line subtraction. The potential performance has been given preliminary laboratory tests which are detailed in Conference AS11451-192.
A novel telescope, The Dual Use Exoplanet Telescope (DUET), is designed to directly take spectra of an exoplanet with extremely high resolution spectroscopy based on the primary objective --- a lightweight annular Gabor Zone-Plate (GZP). The zone-plate functions as a converter that transforms incident starlight directly into a spectrogram. In this paper, we will present the design of an annular GZP hologram based on the interference of two spherical waves. We will show, through an analytical solution, that the focal-length of the zone-plate can be tailored by tuning the radius-ofcurvature of the two spherical waves. The grating period of the GZP hologram is variable and decreasing from center to outer region, which brings the incoming star-light to focus. A desirable focal-length and the spherical symmetry of a zone-plate hologram will result in an unusual on-axis dispersive behavior of the incoming star-light. Furthermore, the preliminary laboratory tests of the GZP hologram will be presented. We will illustrate a successful implementation of a scale model optical system for realizing such a telescope GZP-hologram. Particularly, we will demonstrate that a GZPhologram can achieve a spectral dispersion of =430-650nm over an on-axis distance of 19cm.
Planck’s law predicts the distribution of radiation energy, color and intensity, emitted from a hot object at thermal equilibrium. The Law also sets the upper limit of radiation intensity, the blackbody limit. Recent experiments reveal that micro-structured tungsten can exhibit significant deviation from the blackbody spectrum. However, whether thermal radiation with weak non-equilibrium pumping can exceed the blackbody limit in the far field remains un-answered. Here, we use a tungsten photonic-crystal with a partially coated black surface to show that far-field thermal radiation can exceed the blackbody limit by > 8 times at 1.7 micrometer resonant wavelength. This finding is attributed to non-linear Bloch-waves and the excitation of dipole-active tungsten resonators throughout the photonic-crystal. This discovery could help create super-intense LED-like thermal light sources and even thermal emitters with laser-like input-output characteristics.
Today, one major obstacle for a broader impact and utilization of three-dimensional photonic-crystals (3D PC) is the lack of a scheme for low cost and large scale fabrication. In this work, we proposed a novel lithographic method to realize 3D PC that is inherently a low-cost and wafer-scale method. This method combines a 2D optical mask and off-axis double optical exposures to create 3D PCs having slanted rods and SP2 lattice symmetry. Three types of SP2 PC were successfully fabricated with a minimum feature size of d=1.5 micrometer over a large scale of 8x10 mm2, without any observable fabrication defects. The optical performances of the SP2 PCs were studied by FTIR reflectance measurements, indicating photonic band gap. Furthermore, this holographic method is ideal for creating a new class of slanted-rod based PC, such as topological PC in 3D, for new scientific discovery.
KEYWORDS: Reactive ion etching, Absorption, Silicon, Etching, Photonic crystals, Solar energy, Solar cells, Scanning electron microscopy, Ultraviolet radiation, Reflection
We show a unique design of teepee-like photonic crystal (TP-PC) structure that possesses a true gradient, Gaussian-type surface profile for smooth and accurate index matching between air and silicon for near-perfect light trapping. Such funnel-like, inverse-conical topography is capable of achieving near-zero optical reflection and near-unity solar absorption with excellent angular response over the entire visible light wavelength range. The fabrication only requires standard microelectronics reactive-ion etching (RIE) process. We demonstrate how various process parameters, such as RIE gas mixture ratio, RIE power, thickness of silicon dioxide (SiO2) coatings, and lattice constant of the photonic crystal, can impact the details of the “Gaussian” profile and further improve the optical performance of the TP-PC structure at broad-λ, broad-θ, especially in the ultraviolet (UV) wavelength range. Our finite-difference time-domain (FDTD) simulation of the TP-PC structure reveals existence of multiple absorption resonances in the 800- to1100-nm wavelength range. Poynting vector plots show that such strong absorption enhancements at the resonant frequencies are due to long-lifetime photonic modes arising from parallel-to-interface refraction of the incoming sunlight and formation of vortex-like energy flow pattern inside the TP-PC structure. Our design will lead the way for future development of ultrathin, high-efficiency c-Si solar photovoltaics.
We report the observation of unusual thermal radiation at elevated temperatures (T=400-900K) from a three-dimensional metallic photonic-crystal composite that includes a micro-cavity. Upon thermal excitation by a heating element of a large heat-mass and a constant temperature (heat bath), its emissive power at resonant wavelengths exceeds a blackbody’s at nominally the same surface temperature. The possible explanations include, but are not limited to, angular concentration of light emission, slightly lower lattice-temperature for a reference blackbody and also a significant pumping of hot electrons at resonance such that our sample’s electron-temperature is higher than its latticetemperature.
For monitoring the optical properties of material under a dynamical processing, we design a compact in-situ ellipsometry
by using a liquid crystal (LC) phase retarder. Since the key issue of an accurate ellipsometer is the alignment of each
optical component in the system, hence we not only proposed the alignment procedure, we also calibrated the phase
retardation of LC retarder for this in-situ ellipsometry. The azimuths of polarizers and phase retarders can be aligned by
the analytical solutions of the azimuthal deviations. The phase retardation can be directly determined by the intensity
ratio technique.
To achieve the full complex modulated range of the cascaded twisted nematic liquid crystal spatial light modulator (TNLC-SLM), we propose and demonstrate a novel amplitude compensated technique. Optical reconstructions of complex digital holograms with higher image quality are discussed in both analytical and experimental results.
In this contribution, we propose a design algorithm to create three-dimensional objects by
using CGH technique with the Iterative Fourier Transform Algorithm (IFTA) for designing
computer generated phase holograms. One example of the designed phase hologram is
simulated, and computer simulated reconstruction are presented. In addition, we measure the
phase and amplitude modulated characteristic of reflective LCSLM by Michelson
Interferometer. By using this commercial device, designed CGHs can be dynamically
displayed and the real-time reconstruction of 3D images can be optically achieved by a
Fourier transform lens. We also will demonstrate experimentally the optical reconstruction
for real-time 3D images.
The modulation transfer function (MTF) of a pixelated digital micromirror device spatial light modulator has been defined and derived as a function of the fill factor and the shape of the micromirror. Based on the formula, we have investigated the dependence of the MTF on the orientations and spatial frequency of the input patterns.
We propose and demonstrate a versatile holographic storage system using a single-mode polarization-maintained (PM) fiber guided reference beam. By properly allocating the output coupler of the single-mode fiber, the system provides the ability of angular multiplexing recording with no upper limit of the angle tuning range of the reference beam. In addition, this system can easily achieve different holographic storage architectures including transmission, reflection, and 90-deg geometries.
We present a study of the grating detuning effect on the volume holographic data storage using photopolymer recording material. By using the Bragg matching condition, the angle shift and the decay of the diffraction efficiency of the reconstructed beam is obtained. Then the distortion of the readout page is described. And a method for pre-compensation of the incident angles of the reading beam is presented.
We demonstrate a real-time optical image recognition system using photorefractive thin plates. The effects of donor/acceptor concentration ratio in thin lithium niobate crystal plates on the photorefractive response time and the grating diffraction efficiency are presented.
We present theoretical and experimental investigations on diffraction properties of transmission-type gratings in photorefractive crystals under the conditions of strong beam coupling effect between two writing beams. By using the coupled-recording-wave approach, the diffraction efficiency is derived as a function of intensity ratio of the two writing beams, the beam coupling constant, and the phase-shift between the interference fringes. Two configurations are discussed with (pi) /2 and -(pi) /2 phase shift between the interference fringes and the refractive index gratings. The theoretical results suggest that the case of (pi) /2 phase shift has the optimum conditions for high-fidelity holographic storage of the gray-level images. On the other hand, the case of -(pi) /2 phase shift is suitable for information processing in the Fourier plane. The experimental results are in agreement with the theoretical predictions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.