The shape of the Brillouin gain spectrum (BGS) that is produced in an optical fiber undergoing strain varying linearly with respect to time, which is a typical example of temporally non-uniform strain, is theoretically derived through an analysis similar to that by which the BGS under spatially non-uniform strain would be derived. The BGS shape that is theoretically derived agrees well with the shape experimentally observed. The characteristics of the BGS deformation and strain measurement error under the temporally linear strain are discussed based on their similarity to the BGS shape derived under spatially linear strain.
A number of distributed fiber optic strain sensing systems are proposed that are based on the frequency shift of the
Brillouin scattered light power spectrum in proportion to the strain produced in the fiber. Although the spectral shape
under a uniform strain distribution is generally given by a Lorentzian function, it is deformed under a non-uniform strain
distribution. It is important to investigate the relationship between the non-uniform strain distribution and the spectral
deformation, because it affects the strain measurement error. We have focused on a linear strain distribution where the
strain changes at a constant rate along the fiber as a typical non-uniform strain distribution. The power spectrum shape is
derived theoretically using the Brillouin frequency shift values at the both ends of the observation section. The power
spectrum of the Brillouin scattered light is then observed experimentally. The experimentally observed power spectrum
shape was in good agreement with that theoretically obtained and the power spectrum was widened according to the
slope of the linear strain distribution.
Anisotropy in the dielectric constant of a medium having a periodic structure whose period is less than the wavelength of light is known as "form birefringence". Axisymmetric periodic media such as annular layers are expected to have axisymmetric birefringence and mode coupling phenomena in such a waveguide is analyzed theoretically. This paper reports the experimental characterization of the axisymmetric birefringence in an axisymmetric optical fiber. An axisymmetric optical fiber is drawn from an annular layered structure preform rod, whose core diameter and the relative refractive index difference between the core and the cladding are 4 ?m and 1.14 %, respectively. There can be 6 modes in total at a wavelength of 1.319 ?m and some of these modes couple with each other during propagation along the test fiber. The polarization behavior through the mode coupling is investigated theoretically and the axisymmetric birefringence of the test fiber is evaluated experimentally to be 4.1 × 10-5 from the fiber length dependence of the output light polarization state. This value is in good agreement with the theoretical value 4.7 × 10-5 estimated from the structural parameters of the preform rod from which the test fiber is drawn. The stress induced birefringence is also evaluated to be 5.9 × 10-8, which coincides with those of the standard single mode fibers and much less than the axisymmetric birefringence by three orders of magnitude.
We demonstrate a novel technique to fabricate a gelatin film containing Au-nano-particles. The technique is based on silver halide photographic development. We investigated third-order non-linearity of the film by forward-four-wave-mixing technique. Peak absorption appeared at the wavelength of 560nm. Self-diffraction by the use of third order nonlinear grating formed by intense pico-second pulses was observed. Experimental diffraction efficiency was proportional to the square of the pump intensity. Third-order susceptibility ?(3) of the film was estimated to be 1.8 10-7esu.
A passive branched optical network integrated for broadcasting and communication utilizing a set of Fabry- Perot etalons with different cavity lengths is proposed and its basic operation including thermal behavior of broadcasting channel is demonstrated.
We report the first demonstration, what is to our knowledge, of resonant second harmonic generation using a photorefractive phase conjugate feedback. Once the phase conjugator turns on, the SH output form self-frequency- doubled NYAB laser starts to increase and reaches up to 9-10 times of that without feedback. In addition, we find that the SH output fluctuates even if the phase conjugate feedback is constant. This phenomena is induced by the self- frequency-scanning of the SH output.
We present what is, to our knowledge, the first report of a single-mode operation of broad-stripe LD using a photorefractive phase conjugator as an external cavity mirror. A single-longitudinal-mode operation of a 190 mW broad-stripe LD with 0.2 nm line-width could be obtained using an external semi-linear type phase conjugate mirror. Its wavelength was locked at 805.5 nm within 0.02 nm over 20 minutes. Further, by varying a LD's temperature, its lasing wavelength could be continuously tuned in the range between 802 nm and 809 nm.
This paper proposes a new model fit type edge feature measurement method. In this new method, an accurate edge model, which explains well the practical edge gray level patterns in an actually observed image, is made by considering the point spread function in the image recording process as well as the edge features, that is, edge position and orientation. This method consists of two preparation steps and a measurement step. Step 1: Gray level patterns with various edge features values are generated on an edge pixel and its surrounding pixels based on this model. Step 2: The gray levels are fed, as teaching signals, into error back propagation type neural networks with a 3-layer structure. The mapping parameters used to determine the edge features are obtained from the gray level patterns. Step 3: The edge features are calculated by feeding the gray levels in an observed image into the networks after learning. Experimental results proved that this method can determine edge position and orientation with a high accuracy of 0.07 pixels and 0.8 degree(s), respectively.
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