Showing papers on "Photonic crystal published in 2000"
TL;DR: This work describes a technique—three-dimensional holographic lithography—that is well suited to the production of three-dimensional structures with sub-micrometre periodicity, and has made microperiodic polymeric structures, and used these as templates to create complementary structures with higher refractive-index contrast.
Abstract: The term 'photonics' describes a technology whereby data transmission and processing occurs largely or entirely by means of photons. Photonic crystals are microstructured materials in which the dielectric constant is periodically modulated on a length scale comparable to the desired wavelength of operation. Multiple interference between waves scattered from each unit cell of the structure may open a 'photonic bandgap'--a range of frequencies, analogous to the electronic bandgap of a semiconductor, within which no propagating electromagnetic modes exist. Numerous device principles that exploit this property have been identified. Considerable progress has now been made in constructing two-dimensional structures using conventional lithography, but the fabrication of three-dimensional photonic crystal structures for the visible spectrum remains a considerable challenge. Here we describe a technique--three-dimensional holographic lithography--that is well suited to the production of three-dimensional structures with sub-micrometre periodicity. With this technique we have made microperiodic polymeric structures, and we have used these as templates to create complementary structures with higher refractive-index contrast.
1,737 citations
TL;DR: Single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 µm are described, produced by growing silicon inside the voids of an opal template of close-packed silica spheres that are connected by small ‘necks’ formed during sintering, followed by removal of the silica template.
Abstract: Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials1,2, a special class of photonic crystals in which three-dimensional, periodic dielectric constant variations controllably prohibit electromagnetic propagation throughout a specified frequency band. This can result in the localization of photons3,4,5,6, thus providing a mechanism for controlling and inhibiting spontaneous light emission that can be exploited for photonic device fabrication. In fact, carefully engineered line defects could act as waveguides connecting photonic devices in all-optical microchips7, and infiltration of the photonic material with suitable liquid crystals might produce photonic bandgap structures (and hence light-flow patterns) fully tunable by an externally applied voltage8,9,10. However, the realization of this technology requires a strategy for the efficient synthesis of high-quality, large-scale photonic crystals with photonic bandgaps at micrometre and sub-micrometre wavelengths, and with rationally designed line and point defects for optical circuitry. Here we describe single crystals of silicon inverse opal with a complete three-dimensional photonic bandgap centred on 1.46 µm, produced by growing silicon inside the voids of an opal template of close-packed silica spheres that are connected by small ‘necks’ formed during sintering, followed by removal of the silica template. The synthesis method is simple and inexpensive, yielding photonic crystals of pure silicon that are easily integrated with existing silicon-based microelectronics.
1,520 citations
18 Feb 2000
TL;DR: In this paper, the optical properties of a photonic crystal fiber including a plurality of longitudinal holes are altered by virtue of the change in cross-sectional area of holes in that region.
Abstract: A photonic crystal fibre including a plurality of longitudinal holes (220), in which at least some of the holes have a different cross-sectional area in a first region (200) of the fibre, that region having been heat-treated after fabrication of the fibre, from their cross-sectional area in a second region of the fibre (190), wherein the optical properties of the fibre in the heat-treated region (200) are altered by virture of the change in cross-sectional area of holes (230) in that region (200).
1,394 citations
TL;DR: In this article, the authors demonstrate that light propagation in strongly modulated two-dimensional (2D)/3D photonic crystals becomes refractionlike in the vicinity of the photonic bandgap.
Abstract: Although light propagation in weakly modulated photonic crystals is basically similar to propagation in a diffraction grating in which conventional refractive index loses its meaning, we demonstrate that light propagation in strongly modulated two-dimensional (2D)/3D photonic crystals becomes refractionlike in the vicinity of the photonic bandgap. Such a crystal behaves as a material having an effective refractive index controllable by the band structure. This situation is analogous to the effective-mass approximation in electron-band theory. By utilizing this phenomenon, negatively refractive material can be realized, which has interesting optical properties such as mirror-image refraction.
1,310 citations
TL;DR: In this article, a single defect is created inside a two-dimensional photonic bandgap structure, and photons propagating through a linear waveguide are trapped by the defect, which then emits them to free space.
Abstract: By introducing artificial defects and/or light-emitters into photonic bandgap structures1,2, it should be possible to manipulate photons. For example, it has been predicted2 that strong localization (or trapping) of photons should occur in structures with single defects, and that the propagation3,4 of photons should be controllable using arrays of defects. But there has been little experimental progress in this regard, with the exception of a laser5 based on a single-defect photonic crystal. Here we demonstrate photon trapping by a single defect that has been created artificially inside a two-dimensional photonic bandgap structure. Photons propagating through a linear waveguide are trapped by the defect, which then emits them to free space. We envisage that this phenomenon may be used in ultra-small optical devices whose function is to selectively drop (or add) photons with various energies from (or to) optical communication traffic. More generally, our work should facilitate the development of all-optical circuits incorporating photonic bandgap waveguides and resonators.
1,056 citations
TL;DR: An artificial crystal structure has been fabricated exhibiting a full three-dimensional photonic bandgap effect at optical communication wavelengths, encouraging us to create an ultra-small optical integrated circuit including a three- dimensional photonic crystal waveguide with a sharp bend.
Abstract: An artificial crystal structure has been fabricated exhibiting a full three-dimensional photonic bandgap effect at optical communication wavelengths. The photonic crystal was constructed by stacking 0.7-micrometer period semiconductor stripes with the accuracy of 30 nanometers by advanced wafer-fusion technique. A bandgap effect of more than 40 decibels (which corresponds to 99.99% reflection) was successfully achieved. The result encourages us to create an ultra-small optical integrated circuit including a three-dimensional photonic crystal waveguide with a sharp bend.
1,033 citations
TL;DR: Based on spectral measurements of the polarization mode beating, it is estimated that the strongly anisotropic photonic crystal fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.
Abstract: We report a strongly anisotropic photonic crystal fiber. Twofold rotational symmetry was introduced into a single-mode fiber structure by creation of a regular array of airholes of two sizes disposed about a pure-silica core. Based on spectral measurements of the polarization mode beating, we estimate that the fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.
860 citations
TL;DR: In this paper, the authors describe the measured group-velocity dispersion characteristics of several air-silica photonic crystal fibers with anomalous group velocity dispersion at visible and near-infrared wavelengths.
Abstract: We describe the measured group-velocity dispersion characteristics of several air-silica photonic crystal fibers with anomalous group-velocity dispersion at visible and near-infrared wavelengths. The values measured over a broad spectral range are compared to those predicted for an isolated strand of silica surrounded by air. We demonstrate a strictly single-mode fiber which has zero dispersion at a wavelength of 700 mm. These fibers are significant for the generation of solitons and supercontinua using ultrashort pulse sources.
683 citations
TL;DR: In this article, a systematic analysis of waveguides in photonic-crystal slabs is presented, and the considerations that must be applied to achieve single-mode guided bands in these systems are discussed.
Abstract: Linear waveguides in photonic-crystal slabs, two-dimensionally periodic dielectric structures of finite height, are fundamentally different from waveguides in two-dimensional photonic crystals. The most important distinctions arise from the fact that photonic-crystal slab waveguides must be index-confined in the vertical direction ~while a band gap confines them horizontally!. We present a systematic analysis of different families of waveguides in photonic-crystal slabs, and illustrate the considerations that must be applied to achieve single-mode guided bands in these systems. In this way, the unusual features of photonic-crystal waveguides can be realized in three dimensions without the fabrication complexity required by photonic crystals with complete three-dimensional band gaps.
618 citations
TL;DR: It is shown that complete photonic bandgaps—non-directional and for any polarization—to be realized with small air holes in silicon nitride, glass, and even glass make photonic quasicrystals promising for application in a range of optical devices.
Abstract: Photonic crystals are attracting current interest for a variety of reasons, such as their ability to inhibit the spontaneous emission of light1,2. This and related properties arise from the formation of photonic bandgaps, whereby multiple scattering of photons by lattices of periodically varying refractive indices acts to prevent the propagation of electromagnetic waves having certain wavelengths. One route to forming photonic crystals is to etch two-dimensional periodic lattices of vertical air holes into dielectric slab waveguides3,4,5,6,7. Such structures can show complete photonic bandgaps8,9,10, but only for large-diameter air holes in materials of high refractive index (such as gallium arsenide, n = 3.69), which unfortunately leads to significantly reduced optical transmission when combined with optical fibres of low refractive index. It has been suggested that quasicrystalline (rather than periodic) lattices can also possess photonic bandgaps11,12,13,14. Here we demonstrate this concept experimentally and show that it enables complete photonic bandgaps—non-directional and for any polarization—to be realized with small air holes in silicon nitride (n = 2.02), and even glass (n = 1.45). These properties make photonic quasicrystals promising for application in a range of optical devices14,15,16,17,18.
506 citations
TL;DR: In this paper, theoretical studies on waveguides and waveguide bends in two-dimensional photonic crystal slabs are presented, focusing on using the frequency range where the waveguide mode is non-leaky.
Abstract: We present theoretical studies on waveguides and waveguide bends in two-dimensional photonic crystal slabs. The waveguides are created by either filling up or decreasing the sizes of air holes. Our designs focus on using the frequency range where the waveguide mode is nonleaky. It is shown that high transmission through the sharp bend can be obtained for some frequency ranges in the triangular lattice slabs. The waveguides in square lattice slabs are also investigated.
TL;DR: In this paper, the authors have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement.
Abstract: We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference time-domain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides.
TL;DR: This approach enables to answer questions such as When does ultrarefraction occur?
Abstract: We describe methods of investigating the behavior of photonic crystals. Our approach establishes a link between the dispersion relation of the Bloch modes for an infinite crystal (which describes the intrinsic properties of the photonic crystal in the absence of an incident field) and the diffraction problem of a grating (finite photonic crystal) illuminated by an incident field. We point out the relationship between the translation operator of the first problem and the transfer matrix of the second. The eigenvalues of the transfer matrix contain information about the dispersion relation. This approach enables us to answer questions such as When does ultrarefraction occur? Can the photonic crystal simulate a homogeneous and isotropic material with low effective index? This approach also enables us to determine suitable parameters to obtain ultrarefractive or negative refraction properties and to design optical devices such as highly dispersive microprisms and ultrarefractive microlenses. Rigorous computations add a quantitative aspect and demonstrate the relevance of our approach.
TL;DR: In this paper, a two-dimensional confinement by photonic crystals in the plane of propagation, and total internal reflection to achieve confinement in the third dimension were demonstrated. But they were not shown to guide light at 1550 nm around sharp corners where the radius of curvature is similar to the wavelength of light.
Abstract: Photonic crystal planar circuits designed and fabricated in silicon on silicon dioxide are demonstrated Our structures are based on two-dimensional confinement by photonic crystals in the plane of propagation, and total internal reflection to achieve confinement in the third dimension These circuits are shown to guide light at 1550 nm around sharp corners where the radius of curvature is similar to the wavelength of light
TL;DR: In this article, a liquid crystal was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 and a band gap wavelength range of 3.3-5.7 µm.
Abstract: The photonic band gap of a two-dimensional photonic crystal is continuously tuned using the temperature dependent refractive index of a liquid crystal. Liquid crystal $E7$ was infiltrated into the air pores of a macroporous silicon photonic crystal with a triangular lattice pitch of 1.58 $\ensuremath{\mu}$m and a band gap wavelength range of 3.3--5.7 \ensuremath{\mu}m. After infiltration, the band gap for the H polarized field shifted dramatically to 4.4--6.0 \ensuremath{\mu}m while that of the E-polarized field collapsed. As the sample was heated to the nematic-isotropic phase transition temperature of the liquid crystal $(59\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ the short-wavelength band edge of the H gap shifted by as much as 70 nm while the long-wavelength edge was constant within experimental error. Band structure calculations incorporating the temperature dependence of the liquid crystal birefringence can account for our results and also point to an escaped-radial alignment of the liquid crystal in the nematic phase.
TL;DR: The fabrication of a waveguide-coupled photonic crystal slab with a strong 2D bandgap at wavelengths of about 1.5 µm is reported, which is capable of fully controlling light in all three dimensions and raises the prospect of being able to realize unusual photonic-crystal devices, such as thresholdless lasers.
Abstract: Optoelectronic devices are increasingly important in communication and information technology. To achieve the necessary manipulation of light (which carries information in optoelectronic devices), considerable efforts are directed at the development of photonic crystals—periodic dielectric materials that have so-called photonic bandgaps, which prohibit the propagation of photons having energies within the bandgap region. Straightforward application of the bandgap concept is generally thought to require three-dimensional (3D) photonic crystals1,2,3,4,5; their two-dimensional (2D) counterparts confine light in the crystal plane6,7, but not in the perpendicular z direction, which inevitably leads to diffraction losses. Nonetheless, 2D photonic crystals still attract interest8,9,10,11,12,13,14,15 because they are potentially more amenable to fabrication by existing techniques and diffraction losses need not seriously impair utility. Here we report the fabrication of a waveguide-coupled photonic crystal slab (essentially a free-standing 2D photonic crystal) with a strong 2D bandgap at wavelengths of about 1.5 µm, yet which is capable of fully controlling light in all three dimensions. These features confirm theoretical calculations16,17 on the possibility of achieving 3D light control using 2D bandgaps, with index guiding providing control in the third dimension, and raise the prospect of being able to realize unusual photonic-crystal devices, such as thresholdless lasers1.
TL;DR: This procedure for achieving photonic crystal fibers with nearly zero ultraflattened group-velocity dispersion permits remarkably improved suppression of third-order dispersion, particularly in the low-dispersion domain.
Abstract: We present a procedure for achieving photonic crystal fibers with nearly zero ultraflattened group-velocity dispersion. Systematic knowledge of the special guiding properties of these fibers permits the achievement of qualitatively novel dispersion curves. Unlike the behavior of conventional fibers, this new type of dispersion behavior permits remarkably improved suppression of third-order dispersion, particularly in the low-dispersion domain.
TL;DR: The eigenmode splitting due to coupling of the evanescent defect modes in three-dimensional photonic crystals was well explained with a theory based on the classical wave analog of the tight-binding formalism in solid state physics.
Abstract: We have experimentally observed the eigenmode splitting due to coupling of the evanescent defect modes in three-dimensional photonic crystals. The splitting was well explained with a theory based on the classical wave analog of the tight-binding (TB) formalism in solid state physics. The experimental results were used to extract the TB parameters. A new type of waveguiding in a photonic crystal was demonstrated experimentally. A complete transmission was achieved throughout the entire waveguiding band. We have also obtained the dispersion relation for the waveguiding band of the coupled periodic defects from the transmission-phase measurements and from the TB calculations.
TL;DR: In this paper, the authors proposed an accurate vector analysis of the lowest electromagnetic modes of photonic crystal fibers, and the likeness of their propagation characteristics to those of step index fibers was emphasized.
NEC1
TL;DR: In this article, the authors demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC).
Abstract: We have demonstrated 1.55 μm wavelength lightwave propagation through a 120° sharply bent waveguide formed in a triangular-lattice two-dimensional photonic crystal (2D PC). Such propagation has not previously been experimentally confirmed. The photonic crystal was fabricated in a silicon-on-insulator (SOI) wafer with the top silicon layer of the wafer used as a core layer. A 877-μm-long single-line-defect waveguide was formed in the PC with a sharp 120° bend near the middle of the waveguide. A tapered-hemispherical-end fiber was coupled to the input end of the waveguide for the light input, and the output from the other end of the waveguide was directly observed by scanning its near-field profile with another tapered-hemispherical-end fiber.
TL;DR: In this article, the authors showed that multilayer photonic crystals active within a broad range of wavelengths in the visible spectrum can be easily produced from a simple system comprised of a block copolymer and two homopolymers.
Abstract: Interest in the photonic properties of dielectrically struc-tured materials is growing rapidly. This is fueled by the potential application of such materials in a broad range of fields. Much recent work has focused on lithographically fabricated photonic materials, [1,2] and on self-assembled colloidal crystals [3,4] and inverse opal structures. [5±7] The former need to be fabricated on small-area flat surfaces, the latter tend to have long timescales inherent in the fabrication and both have limited tunability with respect to the precursor materials. Our recent work [8,9] has shown that self-assembled block copolymer systems can exhibit a one-dimensionally periodic lamellar structure with component domains having widths large enough (l/4n) to act as visible light photonic materials. Their use in photonics would bring many advantages in terms of materials properties, process-ability, as well as cost, and would enable the fabrication of large-area conformable photonic materials. In this communication we show that multilayer photonic crystals active within a broad range of wavelengths in the visible spectrum can easily be produced from a simple system comprised of a block copolymer and two homopolymers. Ternary blends of a poly(styrene-b-isoprene) (S/I) di-block copolymer, polystyrene, and polyisoprene were solution cast from cumene. As the samples begin to dry they selectively reflect light, giving the appearance of green or red color. After drying, each sample showed a single well-defined peak in reflectivity in the visible wavelength range (350±600 nm) and a corresponding drop in the transmission profile. This implies that the reflection was fairly efficient and that the color observed in the samples was not due to significant absorption. In Figure 1a, we show typical reflec-tivity curves for several blend samples. The relative width of the reflectivity peaks (or transmission dips), Dl/l, varies approximately from 0.15 to 0.25, widening as the fraction of homopolymer in the blend increases. The wavelength of the reflectivity peak versus the homopolymer composition is plotted in Figure 1b. There is a monotonic increase in the peak reflective wavelength with the fraction of homopoly-mer. Scanning electron microscopy (SEM) of the samples confirmed that a lamellar morphology was present in the samples , with typical grain sizes of the order of several micro-meters. The backscattered electron imaging (BEI) image of a sample containing 40 % homopolymer is shown in Figure 2a. The bright regions correspond to the OsO 4 stained polyisoprene domains and the dark regions are the un-stained polystyrene. The lamellar repeat from the …
TL;DR: In this article, the frequency band structure of an infinite photonic crystal and the transmission, reflection and absorption coefficients of light by a slab of this crystal are calculated using a new version of a program.
TL;DR: It is shown that scattering on plane stacking faults located perpendicular to the direction of growth results in a strong anisotropy of diffraction pattern as well as in appearance of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the Direction of growth.
Abstract: Self-organized synthetic opals possessing a face centered cubic (fcc) lattice are promising for fabrication of a three-dimensional photonic crystal with a full photonic band gap in the visible. The fundamental limiting factor of this method is the large concentration of lattice defects and, especially, planar stacking faults, which are intrinsic to self-assembling growth of colloidal crystal. We have studied the influence of various types of defects on photonic band structure of synthetic opals by means of optical transmission, reflection and diffraction along different crystallographic directions. We found that in carefully chosen samples the stacking probability alpha can be as high as 0.8-0.9 revealing the strong preference of fcc packing sequence over the hexagonal close-packed (hcp). It is shown that scattering on plane stacking faults located perpendicular to the direction of growth results in a strong anisotropy of diffraction pattern as well as in appearance of a pronounced doublet structure in transmission and reflection spectra taken from the directions other than the direction of growth. This doublet is a direct manifestation of the coexistence of two crystallographic phases--pure fcc and strongly faulted. As a result the inhomogeneously broadened stop-bands overlap over a considerable amount of phase space. The latter, however, does not mean the depletion of the photonic density of states since large disordering results in filling of the partial gaps with both localized and extended states.
TL;DR: In this article, three laser beams interfere into a glass cell filled with a liquid photopolymerizable resin to form a hexagonal periodic structure, and two beams of another laser also interfere to form layers which cross perpendicular to the rod array.
Abstract: Three-dimensional (3D) photonic crystal structures can be fabricated into photopolymerizable resins by using laser beam interference with high precision. Three laser beams interfere into a glass cell filled with a liquid photopolymerizable resin to form a hexagonal periodic structure. Rods are formed in a hexagonal arrangement after being photopolymerzed according to the 3D periodic light distribution which results from the laser’s interference. Two beams of another laser also interfere to form layers which cross perpendicular to the rod array. After photofabrication, the nonsolidified resin is removed by ethanol. The lattice constant can be selected by tuning the angles of the incident beams and the laser wavelength. We have fabricated a 500 μm×500 μm×150 μm photonic crystal structure, the lattice constant of which is 1 μm and contains 150 lateral layers.
TL;DR: In this article, a simple scheme is devised to include these losses into purely two-dimensional calculations by using an imaginary index, which is shown to agree with corresponding experimental transmission through near-infrared photonic crystals, reproducing the contrasting behavior of the dielectric and air band edges.
Abstract: Radiation losses occurring in photonic crystals etched into planar waveguides are analyzed using a first-order perturbation approximation. Assuming the incoherent scattering limit, the model indicates that losses diminish as the cladding index approaches the core index. A simple scheme is devised to include these losses into purely two-dimensional calculations by using an imaginary index. Such calculations are shown to agree with corresponding experimental transmission through near-infrared photonic crystals, reproducing the contrasting behavior of the “dielectric” and “air” band edges.
TL;DR: This work presents what is to their knowledge the first theoretical analysis of air-guiding photonic bandgap fibers and explains the operational principle of the fibers and obtains detailed information about the properties of the air-guided modes.
Abstract: We present what is to our knowledge the first theoretical analysis of air-guiding photonic bandgap fibers The fibers are characterized by a large hollow core and a microstructured cladding exhibiting photonic bandgap effects Using an efficient, full-vectorial numerical method, we explain the operational principle of the fibers and obtain detailed information about the properties of the air-guided modes This information includes accurate determination of the modes' spectral extent, cutoff properties, and mode-field distributions
TL;DR: In this article, a three-dimensional periodic dielectric structure with a large complete photonic band gap (PBG) is presented, distinguished by a sequence of planar layers, identical except for a horizontal offset, and repeating every three layers to form an fcc lattice.
Abstract: A three-dimensionally periodic dielectric structure with a large complete photonic band gap (PBG) is presented. The structure is distinguished by a sequence of planar layers, identical except for a horizontal offset, and repeating every three layers to form an fcc lattice. The layers can be thought of as an alternating stack of the two basic two-dimensional (2D) PBG slab geometries: rods in air and air cylinders in dielectric. These high-symmetry planar cross-sections should simplify the integration of optical devices and components by allowing modification of only a single layer, using simple defects of the same form as in the corresponding 2D systems. A process for fabricating the structure with conventional planar microfabrication technology is described. Gaps of over 21% are obtained for Si/air substrates. Reasonable gaps, over 8%, can be achieved even for the moderate index ratio of 2.45 (Si/SiO2).
TL;DR: In this article, the authors proposed and demonstrated two different methods to split electromagnetic waves in three-dimensional photonic crystals, and showed that the guided mode in a coupled-cavity waveguide can be splitted into the planar or planar waveguide channels without radiation losses.
Abstract: We proposed and demonstrated two different methods to split electromagnetic waves in three-dimensional photonic crystals. By measuring transmission spectra, it was shown that the guided mode in a coupled-cavity waveguide can be splitted into the coupled-cavity or planar waveguide channels without radiation losses. The flow of electromagnetic waves through output waveguide ports can also be controlled by introducing extra defects into the crystals. Our results may have an important role in the design of efficient power splitters in a photonic circuit.
TL;DR: In this paper, the effect of two-photon absorption and Kerr nonlinearity on the optical properties of a one-dimensional photonic crystal made with amorphous silicon and SiO2 was studied.
Abstract: We study the effect of two-photon absorption and Kerr nonlinearity on the optical properties of a one-dimensional photonic crystal made with amorphous silicon and SiO2. A stop band appearing near 1.5 μm is monitored with a weak probe beam and modulated by changes in the refractive index caused by a pump pulse at 1.71 μm with 18 GW/cm2 peak intensity. Nonlinear optical characterization of the sample using Z-scan points out to two-photon absorption as the main contributor to free carrier excitation in silicon at that power level. Modulation in the transmittance near the band edge is found to be dominated by the optical Kerr effect within the pulse overlap (∼400 fs) whereas free carrier index changes are observed for 12 ps.