Showing papers on "Step-index profile published in 2008"

Glass large-core optical fibers

Abstract: Embodiments of optical fiber may include cladding features that include a material (e.g., fluorine-doped silica glass) that may produce a very low relative refractive index difference with respect to cladding material in which the cladding features are disposed. This relative refractive index difference may be characterized by (ni-n2)/ni, where ni is the index of refraction of the cladding material in which the cladding features are included, and n2 is the index of refraction of the cladding features. In certain embodiments, the relative refractive index difference may be less than about 4.5 x 10'3. In various embodiments, the configuration of the cladding features including, for example, the size and spacing of the cladding features, can be selected to provide for confinement of the fundamental mode yet leakage for the second mode and higher modes, which may provide mode filtering, single mode propagation, and/or low bend loss.

Metamaterial gradient index lens

Abstract: Examples of the present invention include a gradient index element formed from a material such as a metamaterial, the material having an index profile and an index gradient profile, where the index profile includes at least one discontinuity and the index gradient profile is substantially continuous.

Influence of the Medium Refractive Index on the Optical Properties of Single Gold Triangular Prisms on a Substrate

Abstract: The surface plasmon resonance of small metal particles is highly sensitive to the refractive index of the surrounding medium. However, for particles dispersed on a glass surface in a polymer matrix, the effective refractive index is ill-defined. The effects of the substrate and solvent refractive indices on the surface plasmon resonance of individual gold nanoparticles (prisms and decahedra) have therefore been investigated by dark field microscopy. It is found that for any given substrate, e.g., glass or quartz, the surface plasmon band red-shifts when the solvent refractive index is increased as expected. However the sensitivity is reduced from that observed in a homogeneous medium, and the effect of the supporting polymer matrix is found to be of great importance. The effective refractive index dispersion relationship follows an equation of the form neff = (1 − α)nsub + αnmed where the value of α was found to vary from 0.10 to 0.65 depending on whether the particles are embedded in a polymer matrix or ...

Ultrastable in reflection photonic crystal fiber modal interferometer for accurate refractive index sensing

Abstract: A compact in reflection modal interferometer consisting of a stub of large-mode area photonic crystal fiber (PCF) spliced to standard fiber is presented. In the splice, the voids of the PCF are fully collapsed allowing so coupling and recombining PCF core and cladding modes. The interferometer is highly stable over time and can be used for different applications. The measuring of refractive index in the 1.33–1.45 range with high sensitivity is demonstrated. Sensing applications based on refractive index changes are also feasible.

Fiber Cavity Ring-Down Refractive Index Sensor

Abstract: An exploratory study on a novel fiber long-period grating (LPG) cavity ring-down refractive index sensor is conducted. By detecting the ring-down curves at different ambient refractive index levels, the performances of the LPG sensor are investigated. The experimental results demonstrate by using this sensing setup the change of the refractive index in 1.35-1.43 region could be effectively detected.

All-fiber optic sensor for measurement of liquid refractive index

Abstract: A novel intensity modulated fiber optic sensor (FOS) for liquid refractive index measurement is presented in this communication. The sensor principle is based on frustrated total internal reflection effect caused by refractive index change of a medium surrounding an optical fiber tip. Experimental results obtained for liquids of different refractive index confirm the sensor potential to act as a sensitive refractometer.

Dynamics of pump-induced refractive index changes in single-mode Yb-doped optical fibers

Abstract: We quantify the refractive index changes (RIC) in single-mode ytterbium-doped optical fibers induced by optical pulses at 980 nm and, for the first time, report details of the effect dynamics. The RIC dynamics is shown to follow that of the population of the excited/unexcited ion states with a factor proportional to their polarizability difference (PD). The absolute PD value is evaluated in the spectral range of 1460-1620 nm for different fiber samples and is found to be independent on the fiber geometry and on the ion concentration. The PD dispersion profile indicates to a predominant far-resonance UV rather than near-resonant IR transitions contribution to the RIC.

Sensitivity of photonic crystal fiber modes to temperature, strain and external refractive index

Abstract: Several strong narrowband resonances are observed in the transmission spectra of fiber Bragg gratings photo-written in photonic crystal fiber that has a refractive index-neutral germanium/fluorine co-doped core. Experimental results for the strain, temperature and refractive index sensitivities of these mode resonances are reported and compared to those of conventional single mode fiber. In particular, we identify three kinds of resonances whose relative sensitivities to strain, temperature and refractive index are markedly different and present numerical simulations to explain these properties. Potential multiparameter optical sensor applications of these mode resonances are briefly discussed.

Detection of external refractive index change with high sensitivity using long-period gratings in photonic crystal fiber

Abstract: We report that the proposed long-period gratings (LPGs), which were fabricated in an endlessly single-mode photonic crystal fiber (ESM-PCF) via point-by-point residual stress relaxation utilizing focused CO 2 laser irradiation, exhibit a high sensitivity to variations in the external refractive index, with an identified shifting of attenuation band as large as 4.4 pm for 1 × 10 −5 change in the surrounding refractive index over the range from 1.42 to 1.45. Contrary to LPGs inscribed in conventional all-solid optical fiber under similar condition, the mode-coupling resonance band of the ESM-PCF-LPG moves towards longer wavelength with increasing refractive index in the surrounding medium of the fiber cladding. The resonance wavelength has a low-temperature coefficient of 2.2 pm/°C over 30–200 °C.

Refractive index variation in compression molding of precision glass optical components.

Abstract: Compression molding of glass optical components is a high volume near net-shape precision fabrication method. In a compression molding process, a variation of the refractive index occurs along the radial direction of the glass component due to thermal treatment. The variation of refractive index is an important parameter that can affect the performance of optical lenses, especially lenses used for high precision optical systems. Refractive index variations in molded glass lenses under different cooling conditions were investigated using both an experimental approach and a numerical simulation. Specifically, refractive index variations inside molded glass lenses were evaluated by measuring optical wavefront variations with a Shack-Hartmann sensor system. The measured refractive index variations of the molded glass lenses were compared with the numerical simulation as a validation of the modeling approach.

Measurement of CO2-laser-irradiation-induced refractive index modulation in single-mode fiber toward long-period fiber grating design and fabrication.

Abstract: We report a new method to measure the CO2-laser-irradiation-induced refractive index modulation in the core of a single-mode optical fiber for the purpose of design and fabrication of long-period fiber gratings (LPFGs) without applying tension. Using an optical fiber Fabry-Perot interferometer, the laser-induced axial refractive index perturbation was measured. We found that the CO2-laser-irradiation-induced refractive index change in the fiber core had a negative value and that the magnitude was a sensitive function of the laser exposure time following almost a linear relation. Under the assumption of a Gaussian-shaped refractive index modulation profile and based on the first two terms of Fourier series approximation, the measured refractive index perturbations were used to simulate the LPFG transmission spectra. LPFGs with the same laser exposure parameters were fabricated without applying tension, and their spectra were compared with those obtained by simulations.

Low bending loss multimode fiber transmission system

Abstract: A bend-loss tolerant multimode fiber transmission system is provided. The system includes: a transmission fiber having a core and a cladding, and a mode-launching system for selectively exciting only a useful portion of the transmission modes, that portion corresponding to high effective refractive indices relative to a refractive index of the cladding the useful portion corresponding to a substantial number of modes. The mode-launching system may include a lead-in fiber, coupled to the transmission fiber, supporting a number of lead-in modes substantially corresponding to the number of transmission modes in the useful portion. The transmission fiber may have a refractive index profile, within a region of its core that is aligned with the lead-in fiber core, which has a shape that matches a refractive index profile shape in the lead-in fiber core. The transmission fiber core may have a graded refractive index profile that is parabolic or nearly parabolic or truncated.

Periodic arrangements of chiral scatterers providing negative refractive index bi-isotropic media

Abstract: The main goal of this contribution is to show that periodic arrangements of chiral scatterers can be the basis for the development of three dimensional and isotropic negative refractive index artificial media. Three dimensionality and isotropy are key issues in this context since only three dimensional structures can be properly viewed as a ``medium,'' and only in isotropic media the refractive index is unambiguously defined. The proposed arrangements are cubic lattices of chiral split ring resonators conveniently designed to yield an isotropic behavior. The reported structures are shown to provide a significant frequency band of negative refraction with good matching to free space.

Critical dimension where the macroscopic definition of refractive index can be applied at a nanometric scale

Abstract: This Brief Report reports a measurement of the critical dimension where the macroscopic definition of refractive index could be applied at nanometric scale. A fluorescent nanolayer is used as a local probe of the refractive index via its radiative lifetime. By covering the emitting layer with nanofilms of high refractive index material the sphere radius $R$ in which the effective-medium theory has to be applied is estimated as $\ensuremath{\lambda}/4$ in air.

Design and characteristics of refractive index sensor based on thinned and microstructure fiber Bragg grating

Abstract: A refractive index sensor based on the thinned and microstructure fiber Bragg grating (ThMs-FBG) was proposed and realized as a chemical sensing. The numerical simulation for the reflectance spectrum of the ThMs-FBG was calculated and the phase shift down-peak could be observed from the reflectance spectrum. Many factors influencing the reflectance spectrum were considered in detail for simulation, including the etched depth, length, and position. The sandwich-solution etching method was utilized to realize the microstructure of the ThMs-FBG, and the photographs of the microstructure were obtained. Experimental results demonstrated that the reflectance spectrum, phase shift down-peak wavelength, and reflected optical intensity of the ThMs-FBG all depended on the surrounding refractive index. However, only the down-peak wavelength of the ThMs-FBG changed with the surrounding temperature. Under the condition that the length and cladding diameter of the ThMs-FBG microstructure were 800 and 14 μm, respectively, and the position of the microstructure of the ThMs-FBG is in the middle of grating region, the refractive index sensitivity of the ThMs-FBG was 0.79 nm/refractive index unit with the wide range of 1.33-1.457 and a high resolution of 1.2×10−3. The temperature sensitivity was 0.0103 nm/°C, which was approximately equal to that of common FBG.

Novel Method for the Fabrication of Long Optical Fiber Tapers

Abstract: We report a novel fiber taper facility that allows the fabrication of fiber tapers between a few centimeters and tens of meters in length and that can be used for standard and microstructured optical fibers (MOFs). Efficient reduction of error in diameter variation is achieved using the velocity control feedback loop. The experimental results of the tapering of both the step index fiber and the MOF are presented. The observed outer diameter tracking error over the taper length was within 1%.

Photonic Crystal Narrow Filters with Negative Refractive Index Structural Defects

Abstract: This paper presents a proposal of taking the left-handed material as the structural defects of one-dimensional photonic crystals and uses the transfer matrix method to analyze the band-gap of that structure. The simulation result shows that the structure investigated can be considered as a narrow pass band optical filter. By tuning the refractive index of the left-handed material, the ideal transmission rate in the pass band is as higher as 99.99%, while in the band-gap is lower than 0.01%. In addition, we show that the bandwidth can be increased by reducing the cycle number of the photonic crystals.

Negative-Zero-Positive Refractive Index in a Prism-Like Omega-Type Metamaterial

Abstract: Negative-zero-positive index refraction was demonstrated numerically on the basis of full-wave analysis of a microstructured omega-type array and experimentally via angle resolved transmission measurement of a prism-type prototype. The experimental results are interpreted in terms of characteristic impedance and refractive index retrieved by a Fresnel inversion technique. The possibility to balance the dispersion characteristics with a negative-zero-positive index is demonstrated over X - and Ku -bands.

Hybrid particle composite structures with reduced scattering

Abstract: A core-shell composite particle for incorporation into a composite wherein the composite has improved transparency is disclosed. The core-shell composite particle includes a core material having a first refractive index and a shell material having a second refractive index where the core-shell particle has an effective refractive index determined by the first refractive index and the second refractive index. The effective refractive index is substantially equal to the refractive index of the envisioned embedding medium. Methods of forming the core-shell particles are also disclosed.

Numerical analysis of refractive index sensitivity of long-period gratings in photonic crystal fiber

Abstract: The modal coupling properties and resonance spectral response of long-period gratings (LPGs) in index-guiding photonic crystal fiber (PCF) are numerically investigated with respect to its sensitivity to changes in the index of refraction of the measurand in the PCF air channels using a full-vectorial mode solver combined with frequency-domain method. We show that the shift of wavelength resonance of a PCF-LPG structure can be extremely sensitive by appropriately designing the cladding air-channel dimension and geometry as well as the periodicity of the LPG inscribed in an endlessly single mode PCF (ESM-PCF-LPG). Specifically, a sensitivity of 4.3 × 10−8 refractive index unit (RIU) can be obtained in a refractive index range of 1.33 and 1.4 using an ESM-PCF-LPG with hexagonally arrayed 4-ring air channels at the grating periodicity of 1300 μm. A sensitivity of 4.1 × 10−7 RIU can be achieved in the range of 1.0–1.25 employing an ESM-PCF-LPG with similarly arrayed but 5-ring air channels at the grating periodicity of 350 μm. The predicted index sensitivity, coupled with other schemes for selectivity and specificity, opens the ESM-PCF-LPG structure for a variety of sensing and detection applications.

High Sensitive Temperature Sensor Using a Liquid-core Optical Fiber with Small Refractive Index Difference Between Core and Cladding Materials.

Abstract: An intensive temperature sensor based on a liquid-core optical fiber has been demonstrated for the measuring the temperature of the environment. The core of fiber is filled with a mixture of toluene and chloroform in order to make the refractive index of the liquid-core and the cladding of the fiber close. The experiment shows that a temperature sensitivity of about 5 dB/K and a tunable temperature range (from 20 oC to 60 oC) can be achieved. Based on the dielectric-clad liquid core fiber model, a simulation was carried out and the calculated results were in good accord with the experimental measurement.

Antireflection film, optical element and optical system

Abstract: An antireflection film includes a multilayer film having six layers, in total, provided between an optical substrate and an adhesion layer. The respective layers of first to sixth layers are laminated in order from one side of the adhesion layer. A refractive index of the antireflection film as a whole is lower than that of the optical substrate and higher than that of the adhesion layer. The first and third layers are low refractive index layers having a refractive index of 1.35 to 1.50 at d line. The second, fourth and sixth layers are middle refractive index layers having a refractive index of 1.55 to 1.85 at the d line. The fifth layer is a high refractive index layer having a refractive index, at the d line, that is in a range of 1.70 to 2.50 and that is higher than that of the middle refractive index layer.

Laterally emitting step index fiber for e.g. contour illumination of ship, has scattering zone located between core and jacket, where particles are embedded in zone that includes refractive index differing from refractive index of jacket

Abstract: The index fiber has a light guiding core (1) and a transparent and/or translucent jacket (2) made of glass. The core and the jacket include refractive indexes, respectively. A discrete scattering zone (3) located between the core and the jacket is made of glass. Scattering particles are embedded in the scattering zone. The scattering zone includes a refractive index, which differs from the refractive index of the jacket. The particles contain oxides, metals, diamond-like carbon and/or glass ceramic particles. Glass in which scattering centers are embedded is an arsenic-lead silicate glass. An independent claim is also included for a method for producing a laterally emitting step index fiber.

Photonic band gap fiber

Abstract: A photonic band-gap fiber comprises a first core having a refractive index that is not higher than a refractive index of a clad; a second core that is disposed so as to surround the first core and has a refractive index that is lower than the refractive index of the first core; a clad that surrounds the second core; and a periodic structure portion that is disposed in the clad in a vicinity of the second core and is constituted by high-refractive index portions that have a refractive index higher than that of clad and form the periodic structure, and the periodic-structure portion functions as a wave-length filter. By the function of the periodic structure portion as a wave-length filter, it is possible to reduce the propagation loss of the transmission wavelength and increase the propagation loss of the cutoff wavelength.

Gamma radiation-induced refractive index change in Ge- and N-doped silica

Abstract: We measured the change of the refractive index over a wide wavelength range in Ge- and N-doped high purity (fiber optics grade) silica glasses subjected to gamma irradiation. The radiation-induced change of the refractive index tends to be greater in the infrared part of the spectrum compare to the values measured in the UV-visible part of the spectrum. By means of the Kramers–Kronig relations, we estimate that a weak broadening of the optical vibration band of the silica network adds to this effect. The paper also discusses the difference observed in the spectral behavior of the induced refractive index change for both types of doped glass.

Refractive index modulation in periodically poled MgO-doped congruent LiNbO3 crystal

Abstract: An optical diffraction method is exploited to characterize periodically poled MgO-doped congruent LiNbO3 crystal fabricated by electric induced technique. The optical diffraction patterns indicate that the refractive index changes occur in periodic domain structures. Light diffraction from this type of refractive index modulation is simulated, thus providing an effective and nondestructive technique to determine the refractive index changes and domain structures. From the normalized diffraction intensity, we estimate the refractive index change to be in the magnitude of 10−5.

Hollow-Core Photonic Crystal Fibre

Abstract: A hollow core photonic crystal fibre (HCPCF) having a wavelength of operation, the HCPCF comprising: a core region having a first refractive index; a cladding region surrounding the core region and comprising a plurality of microcapillaries arranged in a transverse structure having a pitch, the pitch of the structure being at least five times larger than the wavelength of operation, the cladding region having a second refractive index higher than the first refractive index.