A low-cost multimode optical fiber based sensor has been reported for measuring the refractive index (RI) of liquid samples. In this sensor, a light is coupled from a multimode optical fiber to a customized U-shaped g...
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A low-cost multimode optical fiber based sensor has been reported for measuring the refractive index (RI) of liquid samples. In this sensor, a light is coupled from a multimode optical fiber to a customized U-shaped glass tube, and light emerging out of the U-shaped glass tube is guided onto a photodetector with the help of another multimode fiber. The intensity of light detected by the photodetector is found to vary with the RI of liquid sample that comes into contact with the U-shaped glass tube. A sensor response has also been observed by changing the bending radius of the glass tube and the depth of surrounding liquid medium. The proposed sensor is expected to be more rugged and reliable, as compared to a tapered optical fiber and the U-shaped optical fiber refractometers.
Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over t...
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Complex structural dynamics at the nanoscale requires sufficiently small probes to be visualized. In conventional imaging using electron microscopy, the dimension of the probe is large enough to cause averaging over the structures present. However, by converging ultrafast electron bunches, it is possible to select a single nanoscale structure and study the dynamics, either in the image or using electron diffraction. Moreover, the span of incident wave vectors in a convergent beam enables sensitivity levels and information contents beyond those of parallel-beam illumination with a single wave vector Bragg diffraction. Here, we report the observation of propagating strain waves using ultrafast Kikuchi diffraction from nanoscale volumes within a wedge-shaped silicon single crystal. It is found that the heterogeneity of the strain in the lateral direction is only 100 nm. The transient elastic wave gives rise to a coherent oscillation with a period of 30 ps and with an envelope that has a width of 140 ps. The origin of this elastic deformation is theoretically examined using finite element analysis;it is identified as propagating shear waves. The wedge-shaped structure, unlike parallel-plate structure, is the key behind the traveling nature of the waves as its angle permits "transverse" propagation;the parallel-plate structure only exhibits the "longitudinal" motion. The studies reported suggest extension to a range of applications for nanostructures of different shapes and for exploring their ultrafast eigen-modes of stress strain profiles.
This paper is concerned with the stability characteristics of nonlinear surface waves propagating along a left-handed substrate (LHM) and a non-linear dielectric cover. These characteristics have been simulated numeri...
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This paper is concerned with the stability characteristics of nonlinear surface waves propagating along a left-handed substrate (LHM) and a non-linear dielectric cover. These characteristics have been simulated numerically by using the perturbation method. The growth rate of perturbation is computed by solving the dispersion equation of perturbation. I found that the stability of nonlinear surface waves is affected by the frequency dependence of the electric permittivity εh and magnetic permeability μh of the LHM. The spatial evolution of the steady state field amplitude is determined by using computer simulation method. The calculations show that with increasing the effective refractive index nx at fixed saturation parameter μp, the field distribution is sharpened and concentrated in the nonlinear medium. The waves are stable of forward and backward behavior. At higher values of nx, attenuated backward waves are observed.
The localization of electromagnetic waves in defect-free circular photonic crystals (CPCs) is investigated using a multiple-scattering method. It is shown that electromagnetic waves of certain freqencies are localized...
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The localization of electromagnetic waves in defect-free circular photonic crystals (CPCs) is investigated using a multiple-scattering method. It is shown that electromagnetic waves of certain freqencies are localized in some special regions inside a perfect CPC with a high order of rotational symmetry. Localized modes with a high Q factor, greater than 106, are obtained. In particular, some unique localized modes such as circular modes and localized modes for both polarized waves are found in the present system, which are completely different from those in defect-free photonic quasicrystals and periodic structures. Their physical properties are also analyzed.
We introduce a Z-scan technique as a tool to characterize small phase shift (< 1 rad) and photodarkening, both effects induced inside photosensitive materials by light illumination. Theoretical analysis supported b...
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We introduce a Z-scan technique as a tool to characterize small phase shift (< 1 rad) and photodarkening, both effects induced inside photosensitive materials by light illumination. Theoretical analysis supported by experiments is presented for permanent refraction and absorption Gaussian profiles. Simple relations are derived in order to estimate the changes in the linear coefficients. Particularly, we investigate quantitatively the photoinduced modifications in the linear optical constants of As(2)S(3) caused by subbandgap irradiation (17 ps, 1064 nm). (C) 2009 Optical Society of America
We present, for the first time to our knowledge, the fabrication and electro-optic (EO) tuning of single-crystalline organic microring resonators. In recent years, optical microring resonators have proven to be highly...
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We present, for the first time to our knowledge, the fabrication and electro-optic (EO) tuning of single-crystalline organic microring resonators. In recent years, optical microring resonators have proven to be highly suitable building blocks for the realization of very large-scale integrated photonic circuits. In particular, microresonators based on organic materials are very promising for ultrafast EO applications, due to the electronic nature of the EO response preserving the modulation performances beyond 100 GHz. In contrast to polymer waveguiding structures realized previously, our crystalline thin-film devices feature an excellent long-term stability of the chromophore orientation and superior photochemical stability, and they do not require high-field poling prior to operation. The introduced thin-film fabrication method significantly reduces fabrication complexity of organic crystalline EO waveguides, compared to previously developed techniques. We have fabricated crystalline COANP (2-cyclo-octylamino-5-nitropyridine) microring resonators with resonance contrast up to 10 dB, ring waveguide propagation losses of about 10 dB/cm, a free spectral range of 1.6 nm, a finesse of up to 20, and a corresponding Q-factor of about 20,000, measured in the telecom wavelength range around 1.55 mu m. We have demonstrated resonance wavelength tuning at the rate of 0.13 GHz/V (1.1 pm/V). (C) 2009 Optical Society of America
Palladium (Pd) nanoparticles exhibit broad optical resonances that have been assigned to so-called localized surface plasmons (LSPs). The resonance's energy varies with particle shape in a similar fashion as is we...
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Palladium (Pd) nanoparticles exhibit broad optical resonances that have been assigned to so-called localized surface plasmons (LSPs). The resonance's energy varies with particle shape in a similar fashion as is well known for LSPs in gold and silver nanoparticles, but the line-shape is always anomalously asymmetric. We here show that this effect is due to an intrinsic Fano interference caused by the coupling between the plasmon response and a structureless background originating from interband transitions. The conclusions are supported by experimental and numerical simulation data of Pd particles of different shape and phenomenologically analyzed in terms of the point dipole polarizability of spheroids. The latter analysis indicates that the degree of Fano asymmetry is simply linearly proportional to the imaginary part of the interband contribution to the metal dielectric function.
A mathematical approach is presented that is based on coupled-mode theory (CMT);it is extended to infinite perfect photonic structures and combined with the supercell method for analysis of infinite photonic crystals ...
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A mathematical approach is presented that is based on coupled-mode theory (CMT);it is extended to infinite perfect photonic structures and combined with the supercell method for analysis of infinite photonic crystals with introduced point (0D) and linear (1D) defects. This approach shows a strong advantage over most existing techniques in regards to time and consumption of resources, and thus allows one to quickly analyze operational characteristics of different photonic devices [photonic crystal fibers (PCFs), phased arrays of VCSELs, etc.] over a wide range of physical parameters. (C) 2009 Optical Society of America
Realization of chip-based all-optical and optoelectronic computational networks will require ultracompact Si-compatible modulators, ideally comprising dimensions, materials, and functionality similar to electronic com...
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Realization of chip-based all-optical and optoelectronic computational networks will require ultracompact Si-compatible modulators, ideally comprising dimensions, materials, and functionality similar to electronic complementary metal-oxide-semiconductor (CMOS) components. Here we demonstrate such a modulator, based on field-effect modulation of plasmon waveguide modes in a MOS geometry. Near-infrared transmission between an optical source and drain is controlled by a gate voltage that drives the MOS into accumulation. Using the gate oxide as an optical channel, electro-optic modulation is achieved in device volumes of half of a cubic wavelength with femtojoule switching energies and the potential for gigahertz modulation frequencies.
We have proposed an ultracompact all-optical photonic crystal AND gate based on nonlinear ring resonators, consisting of two Kerr nonlinear photonic crystal ring resonators inserted between three parallel line defects...
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We have proposed an ultracompact all-optical photonic crystal AND gate based on nonlinear ring resonators, consisting of two Kerr nonlinear photonic crystal ring resonators inserted between three parallel line defects. We have employed a Si nanocrystal as the nonlinear material for its appropriate nonlinear properties. The gate has been simulated and analyzed by finite difference time domain and plane wave expansion methods. The proposed logic gate can operate with a bit rate of about 120 Gbits/s. (c) 2008 Optical Society of America
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