We demonstrate controlled squeezing of visible light waves into nanometer-sized optical cavities. The light is perpendicularly confined in a few-nanometer-thick SiO2 film sandwiched between Au claddings in the form of surface plasmon polaritons and exhibits Fabry-Perot resonances in a longitudinal direction. As the thickness of the dielectric core is reduced, the plasmon wavelength becomes shorter; then a smaller cavity is realized. A dispersion relation down to a surface plasmon wavelength of 51 nm for a red light, which is less than 8% of the free-space wavelength, was experimentally observed. Any obvious breakdowns of the macroscopic electromagnetics based on continuous dielectric media were not disclosed for 3-nm-thick cores.

Light scattering by individual Ag nanoparticles and structures have been studied spectroscopically. Individual particles were selected and manipulated with a micromanipulator installed inside a scanning electron microscope (SEM). With typical particle dimensions of some 100 nm, the plasma resonances of particles and the coupled modes of particle pairs were observed in the visible region. The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy; the effect that would be averaged out for experiments on ensembles. With a simple approximation to take the glass substrate into account, the results are in good agreement with the analytical calculations by Mie scattering, and with numerical calculations by the finite-difference time-domain method, both of which are performed with the morphological parameters obtained from the SEM observation for the corresponding particle or particle pair.

We observe coherent resonant coupling of optical whispering-gallery modes in fluorescence from dye doped polymer bispheres with diameters ranging from 2 to 5 mm. By monitoring the frequencies of fluorescence peaks of individual spheres, we sort out two spheres with appropriate size matching and bring them into contact. Wave optics calculation also gives good agreement with the experiment. By taking into account harmonic coupling of the whispering-gallery modes, the obtained features of normal mode splitting are well explained by the tight-binding photon picture. [S0031-9007(99)09349-7] PACS numbers: 42.60.DaManipulation of light path in micrometer length scale has recently attracted considerable attention from both fundamental and application points of view. Conventionally, the manipulation is based on the photonic crystal concept [1][2][3]. In photonic crystals, which have periodic modulation of the refractive index, propagation of the light wave is governed by a weak potential. Correspondingly, such an approach can be referred to as a nearly free photon approach analogous to the nearly free electron approach in band theory. Alternatively the micromanipulation of light can be achieved by exploring the possibility of confining the light in a small unit of the wavelength size. Light propagates through the system of such units due to the coupling between the nearest neighbors. This approach is referred to as the tight-binding photon approach [4]. Within the tight-binding photon approach we can guide the optical waves by connecting the units in the arbitrarily shaped microstructures.The microspheres are the most natural choice of the unit to be employed in the tight-binding photon device. It is known that a dielectric sphere acts as a unique optical microcavity which has very long photon storage time within a small mode volume [5][6][7][8]. In particular, Q factors of the order of 10 10 have been observed for whispering gallery modes (WGM's) in quartz spheres with a diameter of several tens of micrometers [9-13], and the mode structure of a pair of these large spheres in contact has been studied [14]. However, in order to explore the feasibility of micromanipulation of light, one has to confirm the existence of the coherent coupling between spheres of the size of a few times of optical wavelength. Lorenz-Mie theory predicts long photon lifetime even for small spheres, giving, for example, nearly 30 ps for a 4 mm sphere with a refractive index of 1.59. This has allowed one to propose such relatively small spheres to be employed as "photonic atoms" [15] for the tight-binding scheme. However, the coherent coupling between two adjacent microspheres of such size range have not been realized until now. The coherent coupling results in the splitting of the corresponding WGM's and is a manifestation of the well-known phenomena of the normal mode splitting (NMS) in coupled harmonic oscillators. However, although some attempts have been made [16], NMS has not yet been observed because of the difficulty in the precise size con...

Electronic devices and their highly integrated components formed from semiconductor crystals contain complex three-dimensional (3D) arrangements of elements and wiring. Photonic crystals, being analogous to semiconductor crystals, are expected to require a 3D structure to form successful optoelectronic devices. Here, we report a novel fabrication technology for a semiconductor 3D photonic crystal by uniting integrated circuit processing technology with micromanipulation. Four- to twenty-layered (five periods) crystals, including one with a controlled defect, for infrared wavelengths of 3-4.5 microm, were integrated at predetermined positions on a chip (structural error <50 nm). Numerical calculations revealed that a transmission peak observed at the upper frequency edge of the bandgap originated from the excitation of a resonant guided mode in the defective layers. Despite their importance, detailed discussions on the defective modes of 3D photonic crystals for such short wavelengths have not been reported before. This technology offers great potential for the production of optical wavelength photonic crystal devices.