Elimination of Kerr bistability in an optical fiber ring resonator with a 3 × 3 planar fiber coupler

A special property of a type 3 optical fiber ring resonator with a 3 × 3 planar coupler in which the circulating intensity is independent of the phase change of the ring resonator can be used to eliminate unwanted Kerr bistability. At the same time the device can be used as a two-channel frequency division multiplexer or demultiplexer or a switch. Another method for the elimination of Kerr bistability is the use of two fibers whose nonlinear refractive-index coefficients have opposite signs to build the ring resonator.     

Optical-fiber double-loop resonator with a nonplanar 3 × 3 fiber coupler

We present for the first time to our knowledge a new and simple single-mode optical-fiber double-loop resonator. The double-loop resonator consists of two fiber loops constructed from a nonplanar 3 × 3 directional fiber coupler and two fiber delay lines. When the lengths of the fiber loops are different, additional periodic-resonance notches appear. The depths and the positions of these notches depend on the difference between the phase changes, and the coupling of the two fiber loops. This double-loop resonator can be used as a spectral filter and a sensor.     

Optical vernier filter with two single 3 × 3 planar coupler fiber ring resonators in tandem

A novel and simple optical vernier filter is proposed. It comprises two optical fiber ring resonators in tandem, each connected to a single-mode 3 × 3 planar fiber coupler. The vernier operation increases the effective free spectral range of the device significantly. This device can be used as a filter and wavelength-division demultiplexer.     

Experimental study of a bow-tie-shaped optical fiber ring resonator with two 2 × 2 fiber couplers

An experimental study of a bow-tie-shaped double-coupler fiber ring resonator is presented. Multiple resonances of the transmitted output intensity and the splitting of the main resonance dip or peak have been observed. The experimental results are discussed and compared with theoretical results. The observed output property suggests the possible applications of the resonator as periodic Butterworth-like, narrow-band passing, and blocking filters.     

Transmission performance of one waveguide and double micro-ring resonator using 3×3 optical fiber coupler

Abstract

This paper investigates theoretically the transmission characteristics of one waveguide and double micro-ring resonator using 3 × 3 optical fibre coupler. Our analytical solution of transmittance is suitable for either linearly distributed coupler or circularly symmetric distributed coupler. The all-optical analogue to electromagnetic inducted transparency spectrum of one waveguide and double micro-ring resonators can be controlled by changing the coupling strength between waveguide and micro-rings, the absorption coefficient around micro-rings, as well as the asymmetric coupling coefficients between non-adjacent waveguides. The curves show that the transitions of transmission spectra sensitively depend on asymmetric coupling coefficients.     

Analysis of optical-fiber loop resonators with a collinear 3 × 3 fiber coupler

A theoretical analysis is presented of an optical-fiber loop resonator with a collinear (planar) 3 × 3 fiber coupler in which the cores of the three fibers inside the coupler lie in the same plane. Six different types of the fiber loop resonator (types 1-6) can be constructed in conjunction with different inputs. Expressions for the circulating (resonant) and output intensities and resonance conditions of the six types are derived. Performance parameters such as finesse, cross talk, and maximum output intensity are evaluated when these fiber loop resonators are used as spectral filters and as closely spaced two-channel wavelength-division multiplexerdemultiplexers. Computed results indicate that full resonances cannot be reached simultaneously for both output intensities and that, in general, the output characteristics of the type 5 loop resonator are the best, followed by those of type 6.     

Low-switching power (<45 mW) optical bistability based on optical nonlinearity of ytterbium-doped fiber with a fiber Bragg grating pair

We propose a new optical bistable device (OBD), which is constructed by connecting two symmetrical fiber Bragg gratings with a ytterbium-doped fiber to form a nonlinear Fabry–Perot cavity. The principle of this new OBD is described using the transfer-matrix method, and the two groups of transmitted and reflected optical bistability loops under different parameters are investigated symmetrically. Compared with single fiber Bragg grating switching, whose switching power is greater than 2?kW, this new device has evident merits in reducing the switching power to less than 45?mW.     

A 1 × 4 optical splitter for TE modes based on a silicon photonic crystal self-collimation ring resonator

A 1?×?4 optical splitter (OS) is proposed for TE modes based on a self-collimation (SC) effect ring resonator (SCRR) in an air-hole type silicon photonic crystal. A 1?×?4 OS consists of four beam splitters formed by varying the radii of the air holes. Utilizing multiple-beam interference theory, the theoretical transmission spectra at each port in the OS were analyzed. By forming four splitters in a SCRR properly, self-collimation light can come out from four ports with the light-intensity ratio we set. OSs were investigated using the two-dimensional finite-difference time-domain (FDTD) simulation technique. The simulation results have good agreement with the theoretical prediction. Because of its small dimensions, whole silicon material, and air-hole type, this structure may have an important role in photonic integrated circuits.     

Upconversion emission in antimony–germanate double-clad optical fiber co-doped with Yb3+/Tm3+ ions

In the paper upconversion luminescence properties in Yb³⁺/Tm³⁺ co-doped antimony–germanate glass and double-clad optical fiber were studied. The concentration of lanthanides, which has shown the highest upconversion emission intensity at 478 nm (¹G₄ → ³H₆) and 650 nm (¹G₄ → ³F₄), is 1Yb₂O₃/0.1Tm₂O₃ (mol%) as a result of exciting with a laser diode (976 nm). The lifetime of ²F_5/2 (Yb³⁺) level decreases from 781 μs to 71 μs in the presence of Tm³⁺ 0.1–0.75 mol% respectively. Luminescence decay curve of glass co-doped with 1Yb₂O₃/0.75Tm₂O₃ suggests donor–donor fast migration followed by Tm³⁺ → Yb³⁺ energy transfer. Glass characterized by highest intensity of upconversion luminescence (1Yb₂O₃/0.1Tm₂O₃ mol%) was used as core of double-clad optical fiber made by modified rod-in-tube method. Mechanisms influencing differences in upconversion amplified spontaneous emission of the fabricated optical fiber and bulk glass were discussed. Reabsorption of the amplified spontaneous emission signal along the fibre resulting from Tm³⁺:³H₆ → ¹G₄, transition was observed.     

Beam propagation in an active planar waveguide with an angled bragg grating (α laser)

Abstract

In the angled Bragg grating semiconductor laser (α laser), light does not propagate at a right angle with respect to the two-dimensional corrugated grating of the planar waveguide. A closed-form solution of the coupled-wave theory is used to describe the propagation of both the wave fields with different directions. A constant gain is included. Some properties of the main wave and of the secondary wave are described, which are of interest for the α laser. Additional losses occur during facet reflection of the secondary wave.     

Square-tooth split ring resonator – a novel metamaterial for bandwidth and radiation improvement in microstrip-based radiating structure design

A square multiband truncated microstrip patch antenna was investigated using a square-tooth split ring resonator for multiband applications in both S- and C-bands. The square-tooth split ring resonator is formed from metallic inclusions in a substrate to create a metamaterial. We introduce a new square-tooth split ring resonator which increases the radiation of the antenna as well as the bandwidth. This new design creates a slow wave structure. The square-tooth addition to the split ring resonator works like a slow wave structure. The square-tooth split ring resonator design is compared with the simple split ring resonator design. The square-tooth design has four bands with center frequencies of 3.88, 4.81, 5.4, and 5.62 GHz, whereas design with the simple split ring resonator has just three bands with center frequencies of 3.88, 4.74, and 5.50 GHz. The bandwidth is increased by 20% to 30% using the square-tooth split ring resonator compared to the simple split ring resonator.     

Stochastic dark solitons for a higher-order nonlinear Schrödinger equation in the optical fiber

In this paper, a stochastic higher-order nonlinear Schrödinger equation, which describes the wave propagation in the optical fiber with stochastic dispersion and nonlinearity, is investigated analytically. Via the symbolic computation and white noise functional approach, the stochastic dark one- and two-soliton solutions are obtained, and effects of the Gaussian white noise on the stochastic dark one and two solitons are discussed. For the stochastic dark one soliton, velocity and phase change randomly because of the Gaussian white noise, but the energy, shape and amplitude keep unchanged during the soliton propagation. For the stochastic dark two solitons, effect of the Gaussian white noise leads to the inversion of the velocity directions, while the velocities have the same varying trend so that the interaction appears that the stochastic dark two solitons keep parallel.     

Soliton collisions for a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system for an erbium-doped optical fiber

In this paper, we construct soliton solutions for a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system, which can describe the ultrashort optical pulse propagation in a nonlinear, dispersive fiber doped with two-level resonant atoms. Under certain transformations and constraints, one- and two-soliton solutions are obtained via the Hirota method and symbolic computation, and soliton collisions are graphically presented and analyzed. One soliton is shown to maintain its amplitude and shape during the propagation. Soliton collision is elastic, while bright two-peak solitons and dark two-peak solitons are also observed. We discuss the influence of the coefficients for the group velocity, group-velocity dispersion (GVD), self-phase modulation, distribution of the dopant, and Stark shift on the soliton propagation and collision features, with those coefficients are set as some constants and functions, respectively. We find the group velocity and self-phase modulation can change the solitons’ amplitudes and widths, and the solitons become curved when the GVD and distribution of the dopant are chosen as some functions. When the Stark shift is chosen as a certain constant, the two peaks of bright two-peak solitons and dark two-peak solitons are not parallel. In addition, we observe the periodic collision of the two solitons.     

A decrease in the noise Stokes field modulation during the induced Mandel’shtam-Brillouin scattering in a single-mode optical fiber with high Rayleigh scattering losses

Noise fluctuations of the Stokes field intensity during the induced Mandel’shtam-Brillouin scattering (IMBS) of microsecond pumping radiation pulses in a 300-m-long single-mode optical fiber with 17 dB/km losses were experimentally studied. As the pumping pulse width increases from 20 to 600 μms, the noise modulation amplitude of the IMBS intensity and the IMBS line width tend to decrease. This phenomenon is explained by a distributed feedback mechanism related to the double Rayleigh backscattering of the Stokes component of IMBS.     

Investigation on broadband near-infrared emission in Yb3+/Ho3+ co-doped antimony–silicate glass and optical fiber

In the paper antimony–silicate glass and double-clad optical fiber co-doped with ytterbium and holmium ions were investigated. Absorption spectra in infrared (FT-IR) showed characteristic bands: 445, 605, 1037, 1168 cm⁻¹ coming from the vibration of chemical bonds of SbO₃ and SiO₄, respectively. The combination of relatively low phonon energy with a capability for greater separation (avoiding clustering) of optically active centers in the fabricated glasses should allow an effective expansion of spontaneous emission band. The highest intensity of emission at the wavelength of λ_e = 1950 nm resulting from energy transfer between Yb³⁺ → Ho³⁺ ions was observed in the glass co-doped with 1 mol% Yb₂O₃:0.5 mol% Ho₂O₃. As a result of the optical pumping at the wavelength of 976 nm in the produced optical fiber, strong and narrow band of amplified spontaneous emission (ASE) around 2.1 μm, corresponds to the ⁵I₇ → ⁵I₈ transition, were obtained.     

Squeezed-state generation via atomic collisions in a Bose–Einstein condensate inside an optical cavity

In this paper, we investigate theoretically a system consisting of a one-dimensional Bose–Einstein condensate trapped inside the optical lattice of an optical cavity. In the weak-interaction regime and under the Bogoliubov approximation, the wave function of the Bose–Einstein condensate can be described by a classical field (condensate mode) having some quantum fluctuations (the Bogoliubov mode) about the mean value. Such a system behaves as a so-called atomic parametric amplifier, similar to an optical parametric amplifier, where the condensate and the Bogoliubov modes play, respectively, the roles of the pump field and the signal mode in the degenerate parametric amplifier and the s-wave scattering frequency of atom–atom interaction plays the role of the nonlinear gain parameter. We show that using the nonlinear effect of atomic collisions, how one can manipulate and control the state of the Bogoliubov mode and produce squeezed states.     

Mobilities and dislocation energies of planar faults in an ordered A3B (D019) structure

Present work describes the stability of possible planar faults of the A ₃B (D0 ₁₉) phase with an axial ratio less than the ideal. Mobilities and dislocation energies of various planar faults viz. antiphase boundaries (APBs), superlattice intrinsic stacking faults (SISFs) and complex stacking faults (CSFs) have been computed using complex fourth-order tensor transformations and hard sphere model. Displacements normal to the slip planes for various slip systems (vertical shift) have been used to calculate mobility of dislocations. The energy of the planar faults in Ti ₃Al intermetallic is calculated using some simplifying assumptions. Based on the mobility and energy, stability of planar faults has been explained. These results are compared with single crystal ordered Ti ₃Al alloy having D0 ₁₉ structure.     

Switching of 100-kV pulses in a planar “open” discharge with generation of counterpropagating electron beams

Some results of studying a planar “open” discharge with generation of counterpropagating electron beams at high voltages and appreciable working gas pressures up to atmospheric one are presented. The possibility of its functioning in helium at a voltage above 100 kV is demonstrated, and an increase in the working voltage does not prevent fast breakdown with characteristic switching times of ~1 ns. A specific feature of this type of discharge is the existence of a gas-pressure region, where the discharge-development delay time nonmonotonically depends on the voltage due to the competition between emission processes leading to breakdown.