Superprism Structures Research Articles

Design of flat-band superprism structures for on-chip spectroscopy.

We present a systematic design procedure of photonic crystal (PhC) superprism structures for on-chip spectroscopic applications. In specific, we propose a new figure of merit, namely the angular-group-dispersion-bandwidth-product (AGDBP) to quantitatively describe the spectroscopic performance of PhC superprism structures, and an optimum PhC structure for spectroscopic applications should have large angular group dispersion over a large bandwidth, i.e., a flat-top dispersion profile. We demonstrate the advantage of such a new design consideration by optimizing the geometry of a two-dimensional parallelogram-lattice PhC superprism structure. The performance of such a superprism spectrometer is further analyzed numerically using finite-difference time-domain simulations, which out-performs current implementations in terms of the number of achievable output spectral channels.

Tunable superprism effect in photonic crystals

AbstractWe present a review of the field of tunable superprism structures. Such structures enable an active tuning of the group propagation angle by combining the large angular dispersion near the bandgap of a photonic crystal with a tuning of the optical material properties. The tuning is significantly enhanced compared to the change of the group propagation angle in a bulk material allowing for compact devices on the sub‐millimeter scale. Tunable superprism structures can be employed for many key components of optical circuitry and optical communications. Controlled deflection or refraction of light as well as spatial beam switching are only some possible tasks such devices could accomplish. We give a survey of geometries, switching mechanisms, and materials that have been investigated theoretically or experimentally for tunable photonic bandgap (PBG) structures and tunable superprism structures. A detailed theoretical investigation is presented for all‐optical switching in a one‐dimensional tunable superprism structure employing an optically non‐linear organic material. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical Study of Light Refraction in Three-Dimensional Photonic Crystals

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A rigorous theory for solving general 3-D photonic crystal refraction problem is developed. The power flow direction and transmission intensity of each mode refracted at a periodic surface are rigorously analyzed and determined from matrix equations. We further illustrate how to apply our method to design a low-index-contrast 3-D superprism structure that exhibits efficient transmission over a wide angular scanning range at wavelengths near 1550 nm. </para>

Fabrication of polymer photonic crystal superprism structures using polydimethylsiloxane soft molds

We presented a soft lithography technique of fabricating polymer photonic crystal superprism structures using elastomeric polydimethylsiloxane templates. Dense two-dimensional photonic crystal superprism structures with feature sizes of 150–500nm and aspect ratios of up to 1.25 were replicated. Large field size and easy fabrication are two major advantages when compared with other imprint technology. Atomic force microscopy images showed that the molded structures had high fidelity to the masters. Less than 3% reduction of the depth in the molded structures was achieved with respect to the master. The increase of the surface roughness from the master to the molded structures is minimal. The issue of pattern collapse during pattern transfer of submicron structures was analyzed against the pattern dimensions and aspect ratios; and the experimental results were found in agreement with a prior theory. We also experimentally demonstrated the superprism effect in two-dimensional photonic crystal structure at near-infrared wavelength. The propagation beam changed 39° in the photonic crystal with respect to the input wavelength varying from 1546to1572nm. Such an effective, low cost, and high throughput soft lithography technique could find wide use in making photonic crystal based nanostructures.

Compact wavelength demultiplexing using focusing negative index photonic crystal superprisms

Here, we demonstrate a compact photonic crystal wavelength demultiplexing device based on a diffraction compensation scheme with two orders of magnitude performance improvement over the conventional superprism structures reported to date. We show that the main problems of the conventional superprism-based wavelength demultiplexing devices can be overcome by combining the superprism effect with two other main properties of photonic crystals, i.e., negative diffraction and negative refraction. Here, a 4-channel optical demultiplexer with a channel spacing of 8 nm and cross-talk level of better than -6.5 dB is experimentally demonstrated using a 4500 microm(2) photonic crystal region.

Multilayer thin-film structures with high spatial dispersion.

We demonstrate how to design thin-film multilayer structures that separate multiple wavelength channels with a single stack by spatial dispersion, thus allowing compact manufacturable wavelength multiplexers and demultiplexers and possibly beam-steering or dispersion-control devices. We discuss four types of structure--periodic one-dimensional photonic crystal superprism structures, double-chirped structures exploiting wavelength-dependent penetration depth, coupled-cavity structures with dispersion that is due to stored energy, and numerically optimized nonperiodic structures utilizing a mixture of the other dispersion effects. We experimentally test the spatial dispersion of a 200-layer periodic structure and a 66-layer nonperiodic structure. Probably because of its greater design freedom, the nonperiodic structure can give both a linear shift with wavelength and a larger usable shift than the thicker periodic structure gives.