Ed Johnson

Photonic crystal enhanced narrow-band infrared emitters

We have experimentally and theoretically developed a unique thermally stimulated midinfrared source that emits radiation within a narrow range of wavelengths (δλ/λ⩽0.2). The emission wavelengths are defined by the periodicity of a metal coated silicon–air photonic crystal etched into the emitter surface. The lattice of the holes in the metal mediate the coupling of light into discrete surface plasmon states. This yields surfaces with spectrally nonuniform infrared reflection properties where over much of the IR 90+% of photons are reflected yet, in a narrow spectral region, 90% absorption is observed. Transfer matrix calculations simulate well the position and strength of the absorption features. This technology will afford tunable infrared emitters with high power in a narrow spectral band that are critical for sensing, spectroscopy, and thermophotovoltaic applications.

Extraordinary emission from two-dimensional plasmonic-photonic crystals

A metallodielectric architecture is employed to readily tailor the spectral properties of a bulk material for application to infrared sources and spectroscopic sensors. We exploit the interaction between surface plasmons at a metal interface with a photonic crystal in silicon to control the spectral response of the surface in reflection, absorption, and emission. The design uses Si-based thermally isolated suspended bridge structures fabricated using conventional photolithography techniques. The tunable narrow spectral response is defined by the symmetry and periodicity of the metallodielectric photonic crystal. Individual subresonances are recognized within this bandwidth. We model their origin through calculations of surface-plasmon modes in the metallic grating overlayer. Periodic arrays of holes in thin metal layers lead to coupled plasmons at the two metal–dielectric interfaces that, in turn, couple to modes in the underlying silicon–air photonic crystal. The model provides crucial physical insight i...

Mechanisms underlying extraordinary transmission enhancement in subwavelength hole arrays

Extraordinary transmission in subwavelength hole arrays has been interpreted by surface-plasmon models and diffraction-based models. To understand controversial mechanisms of transmission enhancement, we simulate hole arrays, using a rigorous Fourier-space scattering matrix simulation. At the enhanced transmission maximum there are large evanescent diffracted fields above the metal surface. These evanescent fields are decomposed into longitudinal and transverse components. Both components are comparable in magnitude. The longitudinal field is 15%-20% larger in the square lattice. Transverse fields are slightly larger in the triangular lattice. The longitudinal and transverse evanescent surface fields are related to bound surface modes of the hole array.

Sharp thermal emission and absorption from conformally coated metallic photonic crystal with triangular lattice

A metallic photonic crystal consisting of a triangular lattice of holes in a silicon layer coated with gold is fabricated at a lattice pitch of 3.75 μm using conventional lithographic methods. The photonic crystal exhibits a deep reflection minimum and sharp thermal emission peak near the lattice spacing. Scattering matrix simulations agree well with measurements. This simple structure with a single patterned metallic layer has no emission sidebands and can be scaled to other lattice spacings to tune the wavelength of the absorption and emission peak.

Angular variation of absorption and thermal emission from photonic crystals

The absorption and thermal exitance of two-dimensional (2D) metallic and metallodielectric photonic crystals (PCs) is simulated with rigorous scattering matrix methods. These PCs have strong thermal exitance and absorption peaks in the normal direction that shift to larger and smaller wavelengths as the angle varies away from the normal direction. These PCs redistribute the thermal emission at different wavelengths into different emission angles. There is partial suppression of photon emission at long wavelengths and enhancement at the shorter wavelength spectral range where the thermal exitance has a maximum. Surface plasmon models describe well the angular dependent absorption. Thermophotovoltaic devices utilizing PCs need to account for the strong spectral variation of the thermal exitance with angle.

Plasmonic photonic crystal MEMS emitter for combat ID

We describe a new class of plasmonic photonic (PPh) crystal structures integrated onto a MEMS platform for high temperature-intensity, high speed, and high efficiency narrow band emitting and signaling applications in the infrared. We exploit 2D organized metallo-dielectric surface structures1,2 for angular and spectral control of reflection, absorption and emission, efficiently in the infrared, with little or no leakage into adjacent visible or near-infrared bands. The 2D PPh structures are built on a MEMS platform, for thermal isolation from the environment. Recent advances2 in the design of the 2D PPh structures allows for tremendous performance enhancement: high temperature/high intensity operation close to 1000 C and high speed (200Hz with 50% modulation), opening new applications in spectroscopy, infrared imaging, and signaling. Demonstrated wafer-level vacuum sealing improves the wall plug efficiency dramatically allowing these devices to be portable, light and battery operated. One potential application for these light-weight, low-power consumption, low-cost IR emitters is signaling and marking in 3-5 or 8- 12 micron thermal bands.