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. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04038-9͔The planar photonic crystal ͑PC͒ concept is a recent innovation 1 that can permit the miniaturization of integrated optical circuits to a scale comparable to the wavelength of light. In principle, this technology makes it possible to fabricate planar optical circuits with a packing density four to five orders of magnitude higher than the present state of the art, thus realizing the original objective of integrated optics.Waveguiding in a planar circuit requires confinement of the light in three dimensions. This can be achieved by making a three-dimensional ͑3D͒ PC. [2][3][4] However, fabrication of good quality 3D PC structures is a difficult process, and, in terms of fabrication, a more appealing approach is based on the use of the lower-dimensional PCs to achieve confinement of light in all three dimensions. That idea is employed in the case of the thin dielectric slab perforated with twodimensional ͑2D͒ PC. [5][6][7][8][9][10][11][12][13] In the vertical direction, light is confined to the slab due to total internal reflection ͑TIR͒, and in the lateral direction, light is controlled by the means of distributed Bragg reflection due to the presence of the 2D PC. The PC structure that we consider here consists of a periodic arrangement of holes etched into a planar Si slab suspended so that it is surrounded by air on both sides. We have studied the propagation of light in this structure using methods based on plane-wave expansion and the 3D finitedifference time-domain algorithm 9 to analyze Maxwell's equations. Kuchinsky et al. 12 have shown that a Si guide imbedded in a PC slab having a thickness equal to 0.5•pitch of the PC lattice supports two modes: one diffractive, from the periodic PC lattice, and one refractive from the contrast in the index of refraction between the core and the cladding. Johnson et al. 13 have shown in the case of a Si slab perforated with a triangular lattice of holes that there is a thickness limit for the PC waveguide above which the bandgap width significantly decreases. In agreement with that work we find that conditions for waveguiding are more restrictive in a waveguide with a finite third dimension than in a 2D PC of infinite extent in the third dimension. 14,15 The demonstration of waveguiding by photonic band gap ͑PBG͒ confinement is a difficult challenge, but a necessary achievement in order to realize the goal of planar optical circuits with higher levels of integration. A recent letter by Tokushima et al. 16 reports experiments on light propagation in a structure that lies well outside the p...

The dispersion diagram of the leaky modes in the planar photonic crystal waveguide is experimentally obtained for the wavelengths from 1440 to 1590 nm. A small stop band, around wavelength 1500 nm, is detected. The experimentally obtained results are in very good agreement with our three-dimensional finite difference time domain calculations. Propagation losses of the leaky modes are estimated and we have found that they decrease as we approach the ministop band.

We present the development and study of a single bowtie nano-aperture (BNA) at the end of a monomode optical fiber as an interface between near-fields/nano-optical objects and the fiber mode. To optimize energy conversion between BNA and the single fiber mode, the BNA is opened at the apex of a specially designed polymer fiber tip which acts as an efficient mediator (like a horn optical antenna) between the two systems. As a first application, we propose to use our device as polarizing electric-field nanocollector for scanning near-field optical microscopy (SNOM). However, this BNA-on-fiber probe may also find applications in nanolithography, addressing and telecommunications as well as in situ biological and chemical probing and trapping.

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We propose a new concept of fiber-integrated optical nano-tweezer on the basis of a single bowtie-aperture nano-antenna (BNA) fabricated at the apex of a metal-coated SNOM tip. We demonstrate 3D optical trapping of 0.5 micrometer latex beads with input power which does not exceed 1 mW. Optical forces induced by the BNA on tip are then analyzed numerically. They are found to be 10(3) times larger than the optical forces of a circular aperture of the same area. Such a fiber nanostructure provides a new path for manipulating nano-objects in a compact, flexible and versatile architecture and should thus open promising perspectives in physical, chemical and biomedical domains.