Fabry-Perot resonator composed of a photoinduced birefringent fiber grating

The periodic mode coupling between the x- and y-polarization modes that is induced by a photoinduced birefringent fiber grating is analyzed through the use of the coupled-mode theory. A novel Fabry-Perot resonator composed of a photoinduced birefringent fiber grating is proposed and theoretically investigated. In the ideal case, the x- and y-polarization resonances of the resonator coincide with each other because of the polarization power exchange by the photoinduced birefringent grating, which results in the total resonator output's being polarization independent. However, if there are some external perturbations (e.g., temperature change or strain), the phase matching is detuned, which could destroy the coincidence between the two polarization resonances, which can further result in the total output resonance's having two peaks. The separation between these two resonant peaks depends on perturbations of the environment (temperature changes or strain).     

Simultaneous determination of size and wavelength-dependent refractive indices of thin-layered droplets from optical resonances

A technique for determining the size and wavelength-dependent refractive indices of a droplet coated with a thin layer is presented. The existence of a layer on the droplet is identified by a procedure that involves separate alignments of independently measured TE- and TM-mode resonances with computed homogeneous-sphere resonances. The procedure also yields the mode and the order numbers associated with the measured resonances. The observed resonances are then aligned with layered-sphere resonances of the same mode and order numbers to determine the core radius, layer thickness, and constants of core and shell dispersion formulas that minimize the difference between the observed and the calculated positions of resonances. The technique has been tested with synthetic data with various levels of random errors as well as with experimental data from two droplets under identical conditions. The results show that the core radius, layer thickness, and core and layer refractive indices can be determined with relative errors of 3.5 × 10(-4), 4.5 × 10(-2), 2.3 × 10(-4), and 4.4 × 10(-3), respectively, with the technique.     

Simultaneous temperature and strain measurements performed by a step-changed arc-induced long-period fiber grating

A compact sensor based on step-changed arc-induced long-period fiber gratings was implemented to discriminate between temperature and strain. The proposed sensor consists of a single long-period grating with two sections written consecutively in the SMF-28 fiber using the electric arc discharge technique. The two sections have the same period but different fabrication parameters. The operation of the sensor relies on the existence of a difference between the values of temperature and strain sensitivity of two neighboring resonances observed in the spectrum of the step-changed grating. The temperature and strain resolutions obtained for the sensor are 0.2 degrees C and 35 micro epsilon, respectively.     

Optical response of a d-fiber antenna in a finite-element analysis intended for radio-over-fiber applications

An all-fiber antenna with a piezoelectric polymer-coated circular-core D fiber has been characterized by finite-element analysis. The response of the D-fiber antenna was determined over a wide frequency range from 1 to 500 MHz. The modeling predicts an electric-field-induced phase shift of 2.43 x 10(-5) rad/(V/m)/m at 5 MHz. At frequencies higher than 8 MHz the optical response is dominated by radial resonances of the D-fiber-coating composite. From the simulation results a minimum detectable electric field of 41-muV/m has been achieved with a 1-km length of coated D fiber. In addition, a D-fiber antenna network intended for microcellular communications has been analyzed by shot-noise-limited detection.     

Propagation and coupling of hybrid modes in twisted fibers

The first-order paraxial approximation is used to obtain the distributions of the electric and magnetic fields for the core and cladding hybrid fiber modes. The coupling coefficients of these modes are found for fibers subject to twist. The longitudinal electric field component determines the mode coupling in twisted fibers. It is shown that in the first-order paraxial approximation the cladding hybrid modes propagating in a twisted fiber rotate along the direction of the twist at the same rate as the core mode, independently of the azimuthal and radial mode numbers. Four hybrid modes constituting one linearly polarized mode have different longitudinal components, and the corresponding cladding-mode resonances of a long-period fiber grating undergo different shifts owing to different mode self-coupling coefficients. This results in the removal of mode degeneracy and splitting of resonances of long-period gratings in twisted fibers.     

High-sensitivity sensor of low relative humidity based on overlay on side-polished fibers

A low relative humidity (RH) sensor based on overlay on side-polished fiber is presented. The evanescent field from a single-mode optical fiber is coupled to a TiO/sub 2/ waveguide overlay. The transmission response exhibits sharp resonances whose central wavelengths are linearly shifted with RH. This behavior is due to the porous columnar nanostructure of the TiO/sub 2/ film. The water is adsorbed in the pores of the nanostructure changing the refractive index of the layer and causing a shift of the wavelength resonances. The response of the sensor is determined by the shape and size of the pores. The optical fiber evanescent field sensor developed has a linear response and high sensitivity (0.5 nm/% RH) for low RH (RH/spl sim/0%-15%) at 26.1/spl deg/C/spl plusmn/0.6/spl deg/C. The lack of hysteresis in the adsorption-desorption cycle has been checked. The development of a sensor with tailored response is envisaged using properly techniques to control the porosity of the material.     

Motion transduction in nanoelectromechanical systems (NEMS) arrays using near-field optomechanical coupling

Development of efficient and sensitive motion transducers for arrays of nanoelectromechanical systems (NEMS) is important for fundamental research as well as for technological applications. Here, we report a single-wire nanomechanical transducer interface, which relies upon near-field optomechanical interactions. This multiplexed transducer interface comes in the form of a single-mode fiber taper on a fiber-optic cable. When the fiber taper is positioned sufficiently close to the NEMS array such that it can attain evanescent optical coupling with the array, individual NEMS resonances can be actuated using optical dipole forces. In addition, sensitive detection of nanomechanical motion can be realized when the evanescent waves confined around the taper are scattered by the motion. We have measured resonances from an array of 63 NEMS resonators with a displacement sensitivity of 2-8 pm·Hz(-1/2) at a detection power of ~100 μW (incident on the entire array).     

Realization of a bragg reflection filter wavemeter

We present the preliminary results of a metrological standard for fiber Bragg gratings. This device is based on well-established wavemeter concepts and allows for the a priori determination of Bragg resonances that are verifiable and accurate. Although the concept is demonstrated here with small-fringe-number samplings, the production and detection of images of 50,000 metering fringes was easily accomplished with a nonidealized imaging system. Thus, since the system is characteristically similar to a standard wavemeter, increased fringe counts produce accurate frequency counter ratios for the determination of Bragg resonances, allowing for its application as a universal metering tool for many holographic systems.     

Analysis of time-dependent scattering spectra for studying processes associated with microdroplets

Techniques are presented for analysis of time-dependent scattering spectra from single droplets undergoing physical changes. Times of appearance of resonances in experimental spectra are aligned with theoretical resonances, and the size and refractive index of a droplet as functions of time are determined from the minimum errors in alignment between observed and theoretical resonances. The techniques have been applied to time-dependent elastic scattering spectra obtained from single droplets evaporating under quasi-steady conditions and during unsteady growth. The results of quasi-steady evaporation data show that size and refractive index can be determined with relative errors of 1 x 10(-4). The quasi-steady evaporation data of a droplet are used to identify the resonances observed during the unsteady growth of the same droplet, and the size and refractive index at each resonance are calculated from the identity of the resonance.     

Lambda/4 resonance of an optical monopole antenna probed by single molecule fluorescence

We present a resonant optical nanoantenna positioned at the end of a metal-coated glass fiber near-field probe. Antenna resonances, excitation conditions, and field localization are directly probed in the near field by single fluorescent molecules and compared to finite integration technique simulations. It is shown that the antenna is equivalent to its radio frequency analogue, the monopole antenna. For the right antenna length and local excitation conditions, antenna resonances occur that lead to an enhanced localized field near the antenna apex. Direct mapping of this field with single fluorescent molecules reveals a spatial localization of 25 nm, demonstrating the importance of such antennas for nanometer resolution optical microscopy.     

Stability of short, single-mode erbium-doped fiber lasers

We conducted a detailed study of the stability of short, erbium-doped fiber lasers fabricated with two UV-induced Bragg gratings written into the doped fiber. We find that the relative intensity noise of single-longitudinal-mode fiber grating lasers is approximately 3 orders of magnitude lower than that of a single-frequency 1.523-mum helium-neon laser. The frequency noise spectrum contains few resonances, none of which exceeds 0.6 kHz/Hz(1/2) rms; the integrated rms frequency noise from 50 Hz to 63 kHz is 36 kHz. We also demonstrate a simple method for monitoring the laser power and number of oscillating modes during laser fabrication.     

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.     

Generation of infrared surface plasmon resonances with high refractive index sensitivity utilizing tilted fiber Bragg gratings

We demonstrate the use of tilted fiber gratings to assist the generation of localized infrared surface plasmons with short propagation lengths and a sensitivity of dlambda/dn = 3,365 nm in the aqueous index regime. It was also found that the resonances could be spectrally tuned over 1,000 nm at the same spatial region with high coupling efficiency (in excess of 25 dB) by altering the polarization of the light illuminating the device.     

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.     

Design rules for lossy mode resonance based sensors

Lossy mode resonances can be obtained in the transmission spectrum of cladding removed multimode optical fiber coated with a thin-film. The sensitivity of these devices to changes in the properties of the coating or the surrounding medium can be optimized by means of the adequate parameterization of the coating refractive index, the coating thickness, and the surrounding medium refractive index. Some basic rules of design, which enable the selection of the best parameters for each specific sensing application, are indicated in this work.     

Measuring evaporation rates of laser-trapped droplets by use of fluorescent morphology-dependent resonances

Morphology-dependent resonances (MDRs) are used to measure accurately the evaporation rates of laser-trapped 1- to 2-mum droplets of ethylene glycol. Droplets containing 3 x 10(-5) M Rhodamine-590 laser dye are optically trapped in a 20-mum hollow fiber by two counterpropagating 150-mW, 800-nm laser beams. A weaker 532-nm laser excites the dye, and fluorescence emission is observed near 560 nm as the droplet evaporates. A complete series of first-order TE and TM MDRs dominates the fluorescent output. MDR mode identification sizes the droplets and provides accurate evaporation rates. We verify the automated MDR mode identification by counting fringes in a videotape of the experiment. The longitudinal spring constant of the trap, measured by analysis of the videotaped motion of droplets perturbed from the trap center, provides independent verification of the laser's intensity within the trap.     

Plasmon-induced transparency by detuned magnetic atoms in trirod metamaterials

We demonstrate theoretically an analog of electromagnetically induced transparency (EIT) in the plasmonic metamaterial with the unit cell consisting of three parallel metallic rods. The electromagnetic mechanism for the EIT-like transmission is discussed based on our investigation of the localized surface plasmon resonances in three trirod configurations. We find that the transmission minima surrounding the transparency window on both sides correspond to two detuned magnetic resonances, which arise respectively from the antiphase plasmon couplings between a long rod and a short rod and between two short rods. A decrease of more than 10 times in the group velocity can be achieved for the trirod structure at the transparency window in the optical regime, and the EIT-like response can be well described by the theoretical model of two harmonic oscillators. This work not only reveals the EIT-like transmission in plasmonic metamaterial consisting of detuned magnetic "atoms," but also provides further insight into the plasmons' interactions, especially for metallic nanostructures comprising multiple metallic elements.     

Fano-Enhanced Circular Dichroism in Deformable Stereo Metasurfaces

2D metasurfaces have emerged as a paradigm-shifting platform for light management with considerable miniaturization and alleviated fabrication challenges than their 3D counterparts. However, the appearance of in-plane mirror symmetry and reduced dimensions impose fundamental restraints to advanced chiroptical responses and reconfiguration capabilities. Here, a new concept of Fano-enhanced circular dichroism by introducing a reconfigurable stereo metasurface, which possesses deformable out-of-plane twists that are readily achieved by a simple nano-kirigami fabrication method, is demonstrated. The stereo height and twisting geometries can be reproducibly controlled, providing a facile and automated fashion to tailor the distinct profiles of Fano resonances under circularly polarized incidence. As a result, a recorded high efficiency of circular dichroism generation per unit sample thickness is achieved with Fano resonances in opposite lineshapes. Leveraging this feature, large-range reconfiguration of circular dichroism at optical wavelengths is demonstrated through reversible compression of the stereo metasurfaces with a fiber tip. The studied stereo metasurface unfolds a new degree of freedom for advanced photonic applications in a quasi-flat optical platform, and the proposed concept of Fano-enhanced circular dichroism opens new venues to explore interesting fundamental phenomena of chiral optics.     

Effects of fiber gripping methods on the single fiber tensile test: I. Non-parametric statistical analysis

Single fiber tensile tests using two different gripping methods were carried out on various fiber lengths. One method (the glue-tab grip method) consists of mounting a fiber onto a rigid tab as specified in ASTM C1557-03 using an adhesive, while the other (the direct grip method) involves directly clamping a fiber using poly(methyl methacrylate) blocks. The tensile moduli obtained by the glue-tab grip as a function of the fiber gauge length are clearly different from those of the direct grip for fiber length between 2 and 10 mm, based on graphical statistical analyses using kernel density and q–q plots. This difference is caused by the gripping effect. In addition, the tensile strains and strengths obtained by the glue-tab grip were different from those of the direct grip at the short fiber gauge lengths (i.e., 2–10 mm). The differences between the tensile properties (i.e., modulus, strain, and strength) for the two grips measured with the 60-mm fiber length were not statistically significant compared to the results with the short fiber lengths.     

Test of the FDTD accuracy in the analysis of the scattering resonances associated with high-Q whispering-gallery modes of a circular cylinder

Our objective is the assessment of the accuracy of a conventional finite-difference time-domain (FDTD) code in the computation of the near- and far-field scattering characteristics of a circular dielectric cylinder. We excite the cylinder with an electric or magnetic line current and demonstrate the failure of the two-dimensional FDTD algorithm to accurately characterize the emission rate and the field patterns near high-Q whispering-gallery-mode resonances. This is proven by comparison with the exact series solutions. The computational errors in the emission rate are then studied at the resonances still detectable with FDTD, i.e., having Q-factors up to 10(3).