Photonic crystal waveguides utilizing a modulated lattice structure.

We experimentally demonstrate a new class of optical waveguide consisting of a-Si/SiO(2) autocloned photonic crystals with modulated lattice structure. The waveguide utilizes the macroscopic form birefringence of photonic crystals and confines light by the difference in the effective refractive index. A monopole modal field with spot diameters of 6.9 micromx6.5 microm was observed at a wavelength of 1.55 microm. The propagation loss of the waveguide at the wavelength was found to be ~4.2 dB/mm at most.

Extremely large group-velocity dispersion of line-defect waveguides in photonic crystal slabs.

We reveal experimentally waveguiding characteristics and group-velocity dispersion of line defects in photonic crystal slabs as a function of defect widths. The defects have waveguiding modes with two types of cutoff within the photonic band gap. Interference measurements show that they exhibit extraordinarily large group dispersion, and we found waveguiding modes whose traveling speed is 2 orders of magnitude slower than that in air. These characteristics can be tuned by controlling the defect width, and the results agree well with theoretical calculations, indicating that we can design light paths with made-to-order dispersion.

All-optical switching by use of cascading of phase-matched sum-frequency-generation and difference-frequency-generation processes in periodically poled LiNbO(3).

We show that all-optical switching is feasible by means of cascading of sum-frequency-generation and difference-frequency-generation processes under phase-matched conditions. Three-terminal switching is demonstrated experimentally with bulk periodically poled LiNbO(3). The cascading under phase-matched conditions facilitates switching with lower power than that required under phase-mismatched conditions.

Analysis of mode coupling behavior in fused polarization-maintaining fiber couplers.

To achieve low excess loss fiber couplers, analysis on mode coupling behavior in fused fiber couplers has been carried out using a combination of a scalar wave finite element method and a step approximation method, with an emphasis on clarifying the excess loss mechanism in fused polarization-maintaining (PANDA) fiber couplers. Numerical analysis has indicated the following results: First, fused PANDA fiber couplers have a critical outer diameter in the biconical taper region,, at which mode couplings between the symmetric fundamental mode and the symmetric next higher-order mode take place. Second, PANDA fiber couplers in which the waist diameter in the biconical taper region is larger than the critical diameter have small excess loss, because the large waist diameter provides the small mode coupling, although too large a waist diameter does not allow power splitting as a coupler. This analysis shows that excess loss in PANDA fiber couplers largely depends on the outer diameter dimension of the biconical taper region and gives an optimal value of such diameter. This is in good agreement with the experimental results.

Low excess loss conditions of polarization-maintaining fiber couplers.

Loss characteristics and field intensity distributions of fused polarization-maintaining fiber couplers are measured. From the results, it is shown that excess loss spectra have a sinusoidal response. Further, the loss peaks of the usual polarization-maintaining and absorption-reducing (PANDA) fiber couplers with indexdepressed stress applying parts are larger than those of PANDA couplers with index-matched stress applying parts. It is also confirmed that low excess loss of <0.1 dB can be obtained for a large waist diameter of the fused region even in conventional PANDA fiber couplers.

New measurement system for fault location in optical waveguide devices based on an interferometric technique.

A new measurement system for fault location in optical waveguide devices is presented. The system consists of a fiber-optic Mach-Zehnder and a bulk-type Michelson interferometers. The spatial resolution of the scatter distribution is <380 microm, which is limited by the averaging time. The minimum detectable backscattered power is -116 dB relative to the light power propagating in the waveguides. Preliminary experimental results using single-mode fibers <10 cm long are demonstrated.