Study of Transverse Effects in Optical Bistable Ring Resonators Using the Finite Element Method

Abstract

An extension of the finite-element/finite-difference propagation algorithm has been applied to simulate the propagation of a laser beam in a nonlinear optical bistable ring resonator. Agreement with established results has been shown, applying an inherently versatile numerical technique offering a high level of efficiency.     

A Diode-laser-bar Pumped Stable CW Nd: YAG Slab Laser and its Frequency Doubling

Abstract

A high power Nd: YAG mini-slab laser transversely pumped by two diode laser arrays has been investigated. The simplicity and compactness of this pumping scheme provides intrinsic stability in both the output power and the beam pointing. A linearly polarized TEM₀₀ mode output power of 3·6 W at 1064 nm was achieved with a linear cavity, and 1 W of single frequency green light at 532 nm was generated by intracavity doubling in a ring cavity.     

Pulse Asymmetry in the Colliding-pulse Mode-locked Dye Laser

Abstract

The design and performance characteristics of a group velocity dispersion-compensated colliding-pulse passively mode-locked ring dye laser are discussed. Pulses as short as 19 fs have been observed and analyses of experimental autocorrelations—both intensity and interferometric—together with spectral data that show evidence of pulse asymmetry are presented.     

Speckle Displacement by a Surface Rotation and Conical Diffraction Phenomena

Abstract

The null displacement ring observed in the speckle pattern when a translucent rough surface is rotated is closely related to the conical diffraction phenomena of the gratings. When the mth diffraction order coincides with the null displacement ring, the displacement of this order and the speckle displacement are null.     

Transfer characteristics and propagation effects of a multi-resonance ring resonator-based optical device

Abstract

We describe the linear and nonlinear optical transfer characteristics of a multi-resonance device consisting of two optical ring resonators coupled one to the other and to an optical waveguide. The propagation effects displayed by the device are compared with those of a sequence of fundamental ring resonators coupled to a waveguide.     

Dual wavelength demultiplexer based on metal–insulator–metal plasmonic circular ring resonators

Abstract

In this paper, we investigated a plasmonic demultiplexer structure based on Metal–Insulator–Metal (MIM) waveguides and circular ring resonators. In order to achieve the structure of demultiplexer, two improved ring resonators have been used, which input and outputs MIM waveguides coupled by the ring resonators. To improve the transmission efficiency, a reflector was introduced at the right end of the input and output waveguides. By substituting the ring core with dielectric, the possibility of tuning the resonance wavelength of the proposed structure is illustrated, and the effect of various parameters such as radius and refractive index in transmission efficiency is studied in detail. This is useful for the design of integrated circuits in which it is not possible to extend the dimension of the ring resonator to attain a longer resonance wavelength. Transmission efficiency and quality factor of the single ring are 84% and 110, respectively. The simulation results using finite difference time domain method shows that in the proposed demultiplexer, which is composed of two rings with different core refractive indexes, the average power efficiency, bandwidth for each output channel, and the mean value of crosstalk are estimated 80%, 17 nm, and ?26.95 dB, respectively. It is revealed that the significant features of the device are high transmission efficiency, low crosstalk, high-quality factor, and tunability for desired wavelengths. Therefore, the proposed structure has the potential to be applied in plasmonic integrated circuits.     

Crystal growth and structure of L-methionine L-methioninium hydrogen maleate—a new NLO material

Abstract

A new organic nonlinear optical (NLO) crystal from the amino acid family, viz., L-methionine L-methioninium hydrogen maleate (LMMM), has been grown by slow evaporation method from aqueous solution. Bulk crystals were grown using submerged seed solution method. The structure was elucidated using the single crystal x-ray diffraction data. The compound crystallized in the space group P2₁ and the unit cell contains a protonated L-methioninium cation and a zwitterionic methionine residue plus a maleate anion. The backbone conformation angles Ψ¹ and Ψ² are in cis and trans configurations for both the methionine and methioninium residues, respectively. Amino and carboxyl groups of the methioninium and methionine residues are connected through N–H…O hydrogen bonds leading to a ring R₂²(10) motif.     

Kinetic and Stability Study of an Investigative Antirhinovirus Compound

Abstract

A hydrolytic acid and base catalyzed ring opening reaction has been demonstrated for a 1,2,4-oxadiazole antiviral compound (WIN 63843) resulting mainly in an amidoxime product. Decomposition products and related impurities were detected using a gradient HPLC method. The hydrolysis reaction was first-order for 35% ethanol/buffer solutions in a 50°C chamber or a light cabinet (1000 ft-candles), the greatest stability being between pH 4 and 6. Furthermore, increasing ethanol concentrations resulted in a great decrease in reaction rates. Therefore, for oral or aerosol solution formulations, light protection, pH control between 4 and 6 and the highest permissible ethanol concentrations would be advantageous. This study has shown that the highly electronegative trifluoromethyl group at the 5 position increases the lability of a 1,2,3-oxdiazole compound.     

Observation of Fibre Laser Instabilities Through Modulation of the Cavity Optical Length

Abstract

A Nd-doped, single-mode, double-clad fibre laser (FL) is coiled around a resonant piezoelectric ceramic ring; this induces modulation of the cavity optical length and two distinct classes of laser intensity instabilities are observed as the ring drive voltage V _P-P is increased. The first class involves a slowly varying intensity, with characteristic time scale in the microsecond range. For fixed drive-voltage frequency f _m ≈ 20 kHz, we consistently observe subharmonics f _m/2 and f _m/4 in the FL output intensity spectrum; noise in the system precludes the observation of higher subharmonic bifurcations. Small-amplitude random relaxation oscillations of the unmodulated FL are strongly amplified as V _P-P is increased and transition to a state of large-amplitude chaotic relaxation oscillations occurs for V _P-P ≈ 4 V; a value of 2·6 has been measured for the correlation dimension of the chaotic attractor. The second class of laser instability occurs simultaneously for V _P-P ? 10 V, and the FL output consists of a train of pulses about 2 ns wide at a repetition rate close to the cavity frequency f _cav ≈ 15 MHz and modulated by the slowly varying chaotic envelope described above.     

Diels-Alder Reaction of [60]Fullerene with Dienes Having an Ester Substituent at 1-Position

Abstract

Treatment of [60]fullerene with ethyl trans, trans-hexa-2,4-dienoate (1) and methyl trans, trans-octa-2,4-dienoate (2) at 70 ～ 100 °C afforded products 3 and 4, respectively, which are resulted from Diels-Alder addition of the dienoates to a 6/6 ring junction of [60]fullerene.     

Effect of heat treatment on mechanical properties of alloy 909

Abstract

Alloy 909 is a Ni–Fe–Co alloy that exhibits a low coefficient of thermal expansion and high strength at elevated temperatures. These characteristics are suitable for demanding high temperature uses such as turbine components for aerospace and energy generation. The mechanical properties are achieved by heat treatment (solution and aging) that affects the microstructural characteristics such as grain size and precipitation of intergranular and transgranular particles. This work summarises the results of trials conducted to determine the conditions that assure the desired mechanical properties in high temperature ring rolled pieces. Results of tensile, hardness and stress rupture tests are complemented by microstructural analyses. These studies allowed for establishing a robust method for the manufacture of rings; no degradation of the product, either metallurgical or due to properties, has been reported after the method was implemented.     

Output Characteristics of an Optical Fibre Ring Resonator Using a Planar or Nonplanar 3 × 3 Fibre Coupler: A Comparison

Abstract

A comparison is made between the output characteristics of type 1 optical fibre ring resonators with a different type of 3 × 3 fibre coupler, that is a planar or a nonplanar coupler. Three different nonplanar couplers are formed when the central fibre 1 of a loosely coupled planar 3 × 3 fibre coupler is displaced normally from the common plane. Such a 3 × 3 fibre coupler can be identified by the value of its relative coupling ratio m ₃. The dependence of the output intensities of the ring resonator on the coupling length kd and the relative coupling ratio m ₃ of the 3 × 3 fibre coupler is investigated. The former dependence can be used as a guide to obtain suitable output characteristics of a fibre ring resonator for a specific application, while the latter can be used to choose the right type of 3 × 3 fibre coupler to build a fibre ring resonator. It is found that the output characteristics of a fibre ring resonator with a 3 × 3 planar (m ₃ = 0) or an equilateral triangular (m ₃ = 1) fibre coupler are usually better than those of the others.     

Out of roundness distortion of bearing rings owing to internal stresses from tube bending

Abstract

The out of roundness distortion of bearing rings owing to relaxation of internal stresses was investigated experimentally and numerically. Internal stresses in the rings were owing to bending of the tubes from which the rings were produced. This three point bending operation can be regarded as an idealised tube straightening operation. Bending is a typical deformation mode in real tube straightening. The experiments and simulations included the following steps: three point bending of tube, ring turning, and soft annealing heat treatment (also representing the heating in a hardening operation). The ring distortion was measured after ring turning and after soft annealing. A considerable out of roundness was found in both steps but the major contribution was owing to the elastic deformation of the ring at the final stage of turning when the ring was cut off from the tube.     

Stable Modelocking of a Coupled Cavity Moving Mirror Ring Dye Laser

Abstract

We report the stable operation of a new modelocked standing-wave ring dye laser operating with a repetition rate of 250 MHz. Two external cavities are coupled to a bidirectionally operating continuously pumped ring dye laser. When a moving mirror is placed in one of the external cavities, the laser produces pulses 6 ps in duration. The operation is stable with the modelocked pulses arriving in a constant intensity envelope 5 ms in duration at a repetition rate of 90 Hz.     

One- and two-photon lasers with injected signal in a high-Q fabry-Pérot cavity

Abstract

Explicit models are derived for good cavity one- and two-photon lasers with an injected signal in a Fabry-Pérot cavity. The steady solutions and their stability properties are obtained analytically and compared with the corresponding ring cavity model ones. Only quantitative differences between both types of cavities are found. In particular we show that (i) the Fabry-Pérot cavity reduces significantly the domain of self-pulsing with respect to the ring cavity, and for the two-photon laser case (ii) larger output can be extracted from a Fabry-Pérot cavity than from a ring cavity under certain conditions, something impossible in free-running lasers. We conclude that ring cavity models are sensible models for describing qualitatively Fabry-Pérot experimental configurations.     

Enhancement of Phase Modulation Detection Sensitivity in Ring Photorefractive Configurations

Abstract

An adaptive ring photorefractive configuration, which can increase remarkably the sensitivity of the homodyne detection of high frequency light phase modulation, is proposed and analysed. For typical BaTiO₃ photorefractive crystals, the enhancement factor can reach 100. However, the practical results can be limited by the light losses in the ring cavity and, in particular, inside the photorefractive sample.     

Design of a compact dual-mode ring resonator bandpass filter with harmonic suppression

Abstract

An approach to suppress the harmonic responses in a dual-mode circular ring resonator bandpass filter is presented. Feed lines with one-sided coupling arms are suitably relocated around the ring resonator to introduce phase interference between two degenerate modes for simultaneously suppressing the second and third harmonics. Three open loop resonators at the rim of the ring are adopted to further suppress the second harmonic. By fabricating on a FR4 glass-epoxy base, this approach is demonstrated to have effectiveness in broadening the filter's rejection band in both simulations and measurements without affecting the fundamental response or increasing the device size.     

Preformulation Studies on Imexon

Abstract

Imexon is an aziridine containing iminopyrrolidone that, through aziridine ring opening, is able to induce oxidative stress resulting in apoptosis. The main objective of this research was to conduct extensive preformulation studies on Imexon in order to understand the factors that affect its stability. The results obtained indicate that the stability of Imexon is dependant on pH, ionic strength, temperature, buffer species, and initial concentration. Degradation of Imexon follows apparent first-order degradation kinetics with the primary degradation product resulting from opening of the aziridine ring. In order to maximize stability, ionic strength, temperature, and initial concentration should be minimized, with an optimal range pH between 7.2 and 9.0. Experimentation with other aqueous solutions indicates that Imexon has increased stability in D5W as opposed to normal saline, while it undergoes rapid degradation in 6% H₂O₂. Imexon is not ionizable between pH 5.0 to 8.5 and has an aqueous solubility of approximately 25 mg/mL over this range. Solid-state characterization has concluded that Imexon is a crystalline solid that begins decomposition at 165°C, prior to melting.     

Dynamic materials modelling concepts applied to analysis of hot rolling of commercial aluminium alloys

Abstract

A typical industrial hot rolling operation applied to a commercial Al–1%Mg alloy has been analysed in terms of some concepts from dynamic materials modelling (DMM), particularly the so called dissipator co-content J and the efficiency of power dissipation through microstructural changes η. The calculation of the parameter η for every deformation condition of the hot rolling schedule has been conducted assuming that this variable depends not only on the mean deformation temperature and strain rate but also on the strain applied to the material. All the analysis has been conducted on the basis of a constitutive equation previously determined for this material on a rational basis, which is capable of describing the strain, strain rate, and temperature dependence of the flow stress. It has been determined that, for this material, η can be significantly dependent on strain under certain deformation conditions, particularly low deformation temperatures and relatively high strain rates. It has also been shown that for the materials analysed, η is much more dependent on deformation temperature than on strain rate. A comparative analysis carried out with aluminium of various purities indicates that η is much lower for the alloy when it is deformed under similar conditions. In this sense, it has been suggested that such results could be interpreted in terms of the impurity content of the material and the interaction of the alloying atoms with the dislocation structure developed during high temperature deformation. However, this is only possible if the hypothesis advanced by Prasad and co-workers, that the power dissipation efficiency is associated with the dynamic microstructural processes that occur during deformation, is considered valid. The present results indicate that, contrary to previous findings, in terms of DMM concepts there are no specific conditions of temperature and strain rate for the optimum processing of the materials investigated.     

Modulational method of eliminating the zero shift of a fiber ring interferometer induced by polarization nonreciprocity

A new method is proposed to eliminate the zero shift of a fiber ring interferometer induced by polarization nonreciprocity. This method is based on periodic modulation of the polarization state of nonmonochromatic radiation at the entrance to the interferometer ring system. Numerical estimates are given. Pis’ma Zh. Tekh. Fiz. 25, 78–82 (August 26, 1999)