Tetsuro Yabu

All-optical logic gates containing a two-mode nonlinear waveguide

We propose a new element containing a two-mode nonlinear waveguide consisting of Kerr-like material for all-optical logic circuits. The proposed element, incorporated into the Mach-Zehnder interferometer, functions like a phase shifter. Although the optical waves propagating in the proposed element are monochromatic and identical in polarization, its function is insensitive to the relative phase difference between the incident beams. Using this element, we can realize various logic functions. In this paper, we demonstrate such logic circuits as inverters, distributors, and AND gates.

New design method for low-loss Y-branch waveguides

We propose a new method to design low-loss Y-branch waveguides. In conventional design methods, a specific geometry of branching structure is given first, and then structural parameters describing the details of the proposed geometry (for example, location, sizes, and refractive index of microprisms or phase-adjusting elements) are determined by ray optics or other means. In this paper, we take quite a different approach. Given a complex field distribution, one complex refractive index distribution that supports it is determined uniquely, according to the scalar Helmholtz equation. Using this relation, we first make up an ideal field distribution for dividing optical waves smoothly in the branching region. Next, we calculate the refractive index distribution corresponding to the ideal field. Finally, the imaginary part of the refractive index is set to be zero and its real part is discretized into three levels from the practical viewpoint. Numerical simulations show that the present design method offers extremely low-loss Y-branch waveguides.

Symmetric three-branch optical power divider with a coupling cap

Proposed is a new fork-type three-branch optical power divider consisting of two different dielectric materials. The structure is composed of a symmetric Y-branch waveguide with a phase front retarder and a center branch located a coupling gap apart. The present power divider suffers minimum radiation losses as compared to previously reported fork-type three-branch devices consisting of two dielectric materials. Numerical simulations are carried out with a finite difference beam propagation analysis for representative three different sets of significant structural parameters as the refractive index and waveguide width. Numerical results also contain the power dividing characteristics for the case where sharp wedges of index distribution are blunted.

Novel design method for 4-branch optical power splitters

We propose a new method to design 4-branch power splitters. In the method, the index distribution of 4-branch region is calculated from the field distribution synthesized to achieve lossless 4-branch splitting.

Polarization dependence of Raman gain efficiency distribution and its suppression technique

The polarization dependence of the Raman gain efficiency distribution is investigated theoretically and experimentally. The simple technique for suppressing the polarization fluctuations of Raman gain efficiency is also proposed.

Simple technique for measuring nonlinear index n 2 distribution by using bidirectional OTDR

A simple technique is proposed for measuring nonlinear index n2 distribution by using bidirectional OTDR. The n2 is estimated easily from the relative-index difference, core diameter and MFD, which can be measured by OTDR.

Polarization dependence of resonance wavelength of LPFG using photoelastic effect

The polarization dependence of resonance wavelength of LPFG utilizing the photoelastic effect has been investigated based on the simple model. Our model for LPFG is in good agreement with the experimental results.

Temperature dependence of chromatic dispersion distribution along a single-mode fiber using OTDR

Temperature dependence of the chromatic dispersion distribution of the fiber is examined using OTDR for the first time. The relationship between MFD and relative-index difference due to temperature change is also clarified experimentally.

Raman gain efficiency distribution measurement of optical fiber cable installed in the field using indirect OTDR technique

A novel indirect OTDR technique for measuring Raman gain efficiency distribution is applied to optical fiber cables installed in the field. Field measurements are successfully made on a 17-km long test fiber.

New all-optical XOR logic circuit suppressing influence of temporal misalignment between data streams

We propose a new all-optical XOR circuit that can suppress the influence of temporal misalignment between two data streams. An XOR output is obtained for temporally misaligned data with our present circuit.