Proceedings Article | 25 October 1996
Proc. SPIE. 2849, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications II
KEYWORDS: Lithography, Mirrors, Switches, Waveguides, Crystals, Dielectrics, Photonic crystals, Integrated optics, Tunable filters, Nanolithography
Photonic crystals were investigated experimentally in a scaled setup with microwaves in the form of 2D arrays of dielectric rods of high permittivity surrounded by air and are reported in the literature. These crystals render perfect mirrors for a band of wavelengths. Having an impurity built into the structure, transmission filters with a specific narrow bandwidth can be generated. The predominant feature of these structures is, that devices of high finesses are obtained with as few as 6 planes of dielectric rods. The grid constant of the rods is < (lambda) /3, with (lambda) the wavelength used in the device. The rod diameter is < (lambda) /6 and the length of the rods should exceed 2 (lambda) . Therefore photonic crystal elements extend only a few micrometers in the x-, y-, and z- dimension. In combination with monomode-waveguides and applying some areas filled with non-linear optical materials, tunable filters and switches for the routing of light can be built in a very compact way. It is the first time, that 3D additive lithography with electron-beam induced deposition is employed to generate photonic crystals. This technique allows to generate insulating or conductive structures from wires with > 80 nm diameter and micrometers dimensions with a surface roughness below 3 nm. It offers the freedom to taylor the refractive index of the material by selecting precursor materials, deposition conditions, and exposure mode. A scanning electron microscope with VIDAS-beam control system is used for this lithography. A custom designed lithography function allows to control position, dwelltime, and sequence of the pixels. Using a program generated database, which contains all pixel and time information required, 3D structures are generated with the deposition process. The devices are placed with nm precision in waveguide patterns. Macro-controlled construction of arrays of dielectric rods of high aspect ratios is presented, which resemble perfect or imperfect photonic crystals. Using specialized crystals, filters and tunable filters dense devices for routing of light or optical metrology can be fabricated.
