Visible-wavelength super-refraction in photonic crystal superprisms

Abstract

We demonstrate the fabrication of superprism devices in photonic crystal waveguides with excellent transmission through 600 rows of 160 nm diameter holes. Broadband spectral and angular measurements allow mapping of the chromatic refractivity. This shows the ability of such devices to super-refract by more than 1°/ nm close to the principal band gaps, 10ϫ more than equivalent gratings, and 100ϫ more than equivalent prisms. Simple theories based on plane-wave models give excellent agreement with these results. © 2004 American Institute of Physics.[DOI: 10.1063/1.1772521] Photonic crystal (PC) waveguides promise many ways to miniaturize and integrate photonic devices on high functionality optical chips. An extremely wide range of components can benefit from the competing interplay between multiple diffraction and interference in such periodically patterned nanostructures. This results in many enhanced optical properties around the critical band gaps in the photonic bandstructure which can break conventional optical "design rules" such as multirefringence, 1 slow light, 2-4 enhanced nonlinear conversion, 5 and superprisms. 6-9 While considerable theoretical effort has been developed in the past few years to raise the prospect of enhanced performance, 10,11 very few devices have actually been realized, spectrally tested and robustly compared to these theories. In particular, the role of the photonic band gaps in relation to the superprism phenomena have not been highlighted.In this letter, we show state-of-the-art fabrication of PCs in the visible optical region based on a silicon platform. Planar waveguides are deposited and subsequently patterned with a range of periodic arrays of holes in different geometries, and up to 600 rows of holes across. Broadband optical characterization on a range of such devices allows us to clearly identify their excellent transmission properties, exhibiting strong band gaps with high transmission in the intervening spectral regions. A chromatic refraction technique combining angular scans with transmission spectroscopy allows us to map the super-refraction properties. Our results compare well with a simple two-dimensional (2D) plane wave theory, thus enabling further optimization of the devices.The devices are fabricated in a standard silicon microfabrication process line, compatible with very large-scale integrated electronics, on n-type silicon wafers. They are based on our previous designs 1,2,12 with silicon nitride waveguides (Si 3 N 4 250 nm nominal thickness, n = 2.02) embedded in silicon dioxide ͑SiO 2 ͒ substrate and cladding layers (1.7 m and 75 nm thick, respectively, n = 1.46). The PC sections are defined using electron-beam lithography and subsequent dry etching to give large aspect ratio holes through the core waveguide layers. In this letter, we will concentrate on a particular set of devices with hole diameter d = 160 nm, in a rectangular array of periodicity with a = 310 nm, b = 465 nm (aspect ratio 1:1.5), with 600 rows of holes giving a total device length of 186 m...

Highly engineered mesoporous structures for optical processing

“…Applications utilizing the photonic band structure include optical time-delay devices, dispersion compensators and superprisms. Superprisms are PC devices that are able to refract incoming light over much greater angles than their conventional glass prism counterparts, with clear applications in wavelength division multiplexing systems (Baumberg et al 2004). If, and when, we are able to produce perfect three-dimensional PC structures, a whole new world is opened up to us.…”

Signatures of light-beam spatial filtering in a three-dimensional photonic crystal

“…Perhaps the best-known propagation effect in PCs is the so-called self-collimation or the disappearance of diffraction [5][6][7][8][9][10], where, due to the flattening of the segments of the spatial dispersion curve the spatial envelope of the Bloch mode propagates without diffractive broadening. The dispersion curve can also present strongly tilted segments, which leads to super-refraction and negative refraction effects [11,12]. It has been recently proposed that the PCs can lead to the modification of the angular spectra of the transmitted beams [13], the effect that could be at the basis of an interesting type of spatial filter.…”

Realisation of ultra-low loss photonic crystal slab waveguide devices

“…The second class of applications include devices such as PC superprisms [3,4] and optical time-delay elements [5,6] which make use of the dispersive properties of PCs. These require low loss transmission through the bulk of the phonic crystal across hundreds or even thousands of lattice periods.…”