In photonic label routing networks, recognition of optical labels is one of the key functions. We have proposed waveguide-type optical circuits for recognition of optical labels encoded in quadriphase-shift-keying (QPSK) form. A basic device for the circuits consists of a 3-dB directional coupler, two Y-branches, and an asymmetric X-junction coupler. We employed a scheme of complete interference of optical waves between each coded pulse and a reference pulse in our previously reported paper. The contrast ratio of the output at the destination output port to the outputs at the other ports was reported to decrease to 1.6, 1.28, and 1.13 for two-, three-, and four-stage circuits for recognition of 16, 64, and 256 QPSK labels, respectively. We find optimum circuits with improved contrast ratio of 1.8, 1.6, and 1.47 for 16, 64, and 256 labels, respectively. The recognition operation with the improved circuits is numerically confirmed using the beam propagation method. Noise tolerance of the proposed circuits is also clarified by numerical simulation. The improved circuits are optimum from the viewpoint of efficient use of optical power and noise tolerance.
Linear and non-linear optical properties of Manganese-phthalocyanine (MnPc) thin films in the near infrared
(NIR) are reported. MnPc thin films are prepared by vapor deposition on glass and the effects of growth
conditions on the optical properties are also studied. First, Morphology of the MnPc film is studied using
atomic force microscope and the structure of the film is studied using theta-2theta scan X-ray diffraction. The
MnPc films consist of grains with sizes of several tens of nanometers. The grain size depends on the substrate
temperature of the vapor deposition process. The growth conditions also affect the reflection intensity from the
{1 0 0} facet of MnPc. The films are studied using spectroscopic ellipsometry for the NIR region (1200-1800 nm)
in wide wavelength range (0.6-6.5 eV) with various incidence angles (60-80°). The nonlinear optical properties of
saturable absorption are also studied by the Z-scan method with a CW laser with a wavelength of 1550 nm. The
substrate temperature affects Δ and ψ more drastically than the deposition rate and this is most pronounced
in the NIR region. From the saturable absorption experiments, the same trend that the substrate temperature
drastically affects the nonlinear coefficient of MnPc, was also evident.
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