Showing papers on "Step-index profile published in 2013"

Long-Period Fiber Grating Cascaded to an S Fiber Taper for Simultaneous Measurement of Temperature and Refractive Index

Abstract: A novel, low-cost, and simple dual-parameter measurement scheme based on a cascaded optical fiber device composed of a long-period fiber grating (LPFG) and an S fiber taper Mach-Zehnder interferometer (SFT-MZI) is proposed and demonstrated. The crosstalk problem is solved as different resonance peaks of the LPFG and the MZI possess different refractive index (RI) and temperature sensitivities. Experimental results show distinctive spectral sensitivities of -52.57 nm/refractive index unit (RIU) and 45.87 pm/°C by the LPFG, and 311.48 nm/RIU (in the RI range of 1.33-1.37) and 12.87 pm/°C by the SFT-MZI. The simultaneous measurement of external RI and the temperature is experimentally demonstrated by the sensor. The RI and temperature calculated by the sensor matrix agree well with the actual RI and temperature in the experiment.

Performance of Refractive Index Sensors Based On Directional Couplers in Photonic Crystal Fibers

Abstract: We present a systematic analytic and numerical study of the detection limit of a refractive index sensor employing a directional coupler architecture within a photonic crystal fiber (PCF). The device is based on the coupling between the core mode and a copropagating mode of a satellite waveguide formed by a single hole of the PCF infiltrated by a high-index analyte. Using coupled mode theory as well as full simulations, we investigate the influence of changes in the geometrical parameters of the PCF and the analyte's refractive index on sensor performance, including sensitivity, resonance width, and detection limit. We show that regardless of the details of the sensor's implementation, the smallest detectable refractive index change is inversely proportional to the coupling length and the overlap integral of the satellite mode with the analyte, so that best performance comes at the cost of long analyte infiltration lengths. This is experimentally confirmed in our dip sensor configuration, where the lowest detection limit achievable for realistic implementation is estimated to 7 × 10-8 refractive index units (RIU) based on realistic signal to noise ratios in a commercially available PCF.

Refractive Index Sensor Based on S-Tapered Photonic Crystal Fiber

Abstract: The S-tapered PCF interferometer for refractive index sensing was demonstrated in this letter. The whole fabrication process was carried out using a standard splicing machine. It has a compact and stable structure since the S-shape assumes the same function with elongating taper. The sensor exhibits highly SRI sensitivity, which is found to be 8.0 10-5 RIU in 1.38-1.44 and the temperature dependence is only 4.2 pm/°C low 100°C.

Simultaneous measurement of refractive index and temperature using multimode interference inside a high birefringence fiber loop mirror

Abstract: A fiber optic sensor for simultaneous measurement of refractive index and temperature is presented. The sensing probe is realized by introducing a multimode interference device inside a high birefringence fiber loop mirror resulting in a configuration capable of refractive index and temperature discrimination. The multimode interference peak is sensitive to the surrounding refractive index (90 nm/RIU) and slightly responsive to the temperature (0.01 nm/°C). On the other hand, the birefringent fiber loop mirror is highly sensitive to temperature (2.36 nm/°C) and it has almost no response to refractive index. Using a power ratiometric peak detection scheme, a temperature independent refractive index measurement can be achieved with a resolution of ±2.25 × 10−5 RIU.

High-Sensitive Double-Hole Defect Refractive Index Sensor Based on 2-D Photonic Crystal

Abstract: In this paper, we simulate a refractive index sensor based on the 2-D photonic crystal using finite difference time domain methods. The sensor which is called double-hole defect sensor, consists of two waveguides and two-point defect microcavities when the lattice constant is a = 440 nm. In the optimum structure, the sensitivity of the sensor is s = 500 nm/RIU (refractive index unit), whereas the refractive index resolution is very small and Δn = 0.0001 (i.e., resonance wavelength shifts up by 0.05 nm).

Design of Few-Mode Fibers for Mode-Division Multiplexing Transmission

Abstract: We investigate the fiber parameters that meet the design conditions for low bending loss and an effectively few-mode operation on few-mode fibers with a step-index profile and a W-shaped refractive index profile for mode-division multiplexing transmission. We also clarify the limits of effective area enlargement and the difference of the effective index while satisfying the design conditions.

Top-hat beam output of a single-mode microstructured optical fiber: Impact of core index depression

Abstract: A new strategy to obtain a single-mode fiber with a flattened intensity profile distribution is presented. It is based on the use of an OVD-made high index ring deposited on a silica rod having a refractive index slightly lower than the silica used for the microstructured cladding. Using this strategy, we realized the first single-mode fiber with a quasi-perfect top-hat intensity profile around 1 µm. Numerical studies clearly demonstrate the advantage of using a core index depression to insure the single-mode operation of the fiber at the working wavelength.

Mode transition in complex refractive index coated single-mode–multimode–single-mode structure

Abstract: By coating a single-mode-multimode-single-mode (SMS) structure with a high refractive index thin-film it is possible to obtain a transition of modes for specific combinations of thin-film thickness, thin-film refractive index and surrounding medium refractive index, which permits to develop devices with a high sensitivity to specific parameters. In order to gain a better knowledge of the phenomenon the experimental results are corroborated numerically with the Transfer-Matrix-Method. The influence of losses in the thin-film has also been studied. The results obtained prove that a thin-film coated SMS structure is a simple and cost-effective platform for development of sensors and optical filters.

Highly sensitive refractive index sensor based on adiabatically tapered microfiber long period gratings.

Abstract: We demonstrate a refractive index sensor based on a long period grating (LPG) inscribed in a special photosensitive microfiber with double-clad profile. The fiber is tapered gradually enough to ensure the adiabaticity of the fiber taper. In other words, the resulting insertion loss is sufficiently small. The boron and germanium co-doped inner cladding makes it suitable for inscribing gratings into its tapered form. The manner of wavelength shift for refractive indices (RIs) differs from conventional LPG, and the refractive index detection limit is 1.67 × 10−5.

Plastic Optical Fiber Refractive Index Sensor Employing an In-Line Submillimeter Hole

Abstract: An in-line submillimeter hole fabricated by micro-drilling plastic optical fiber (POF) directly has been proposed as a compact refractive index sensor. Since the hole behaves as a concave lens if it is filled with a liquid having lower refractive index than that of the fiber core, transmittance increases in proportion to the refractive index. Analysis of the sensor transmittance has been performed using a simple ray optics model. Through immersing a 1.5-mm POF with a 0.35-mm-radius hole into various liquids, transmittance of the sensor has been measured at 670 nm. It has been shown that the experimental and analytical results are in excellent agreement.

Single-Mode-Multimode Fiber Structure Based Sensor for Simultaneous Measurement of Refractive Index and Temperature

Abstract: A fiber sensor for simultaneous measurement of refractive index (RI) and temperature in solutions based on multimode interference is presented. The intensity and the wavelength of the interference minimum will vary with the RI and the temperature of the solution, respectively. The sensitivity of the RI and the temperature are 94.58 dB/RI and 0.0085 nm/°C, respectively. Its ease of fabrication and low-cost offer the attractive applications in chemical and biological sensing.

Design of Few-Mode Fibers With Arbitrary and Flattened Differential Mode Delay

Abstract: This letter proposes the use of a refractive index profile with a graded core and a cladding trench for the design of few-mode fibers, aiming an arbitrary differential mode delay (DMD) flattened over the C+L band. By optimizing the core grading exponent and the dimensioning of the trench, a deviation lower than 0.01 ps/km from a target DMD is observed over the investigated wavelength range. Additionally, it is found that the dimensioning of the trench is almost independent of the target DMD, thereby enabling the use of a simple design rule that guarantees a maximum DMD deviation of 1.8 ps/km for a DMD target between -200 and 200 ps/km.

Turn-around point long-period fiber grating fabricated by CO2 laser for refractive index sensing

Abstract: Turn-around point long period fiber gratings (TAP-LPFG) are designed by simulations and fabricated by CO 2 laser point-to-point irradiations. It is found that the transmission power of a TAP-LPFG exhibits a large linear range with high sensitivity in response to the surrounding refractive index change. The linear power-refractive index relation enables an intensity based refractive index sensor with significantly simplified calibration and instrumentation. By choosing the grating period, the TAP-LPFG can be designed to operate in different refractive index ranges. The TAP-LPFG sensors are demonstrated for detection of sucrose solutions, refractive index matching liquids and low concentration glucose solutions. Compared with the traditional wavelength-shift based measurement method, intensity based TAP-LPFG sensors may provide a cost effective solution for fast and in situ detection of refractive index changes.

Optimization of Sensors Based on Multimode Interference in Single-Mode–Multimode–Single-Mode Structure

Abstract: By coating a single-mode-multimode-single-mode (SMS) structure with a complex refractive index thin-film the central wavelength of the transmission and attenuation bands of the optical spectrum can be shifted. By adequate selection of multimode segment length and diameter, the thin-film thickness and the thin-film refractive index, the sensitivity of the device to the surrounding medium refractive index, the thickness of the thin-film or the refractive index of the thin-film can be optimized. Experimental results are corroborated numerically with the transfer matrix method.

Characteristics of optical fiber refractive index sensor based on surface plasmon resonance

Abstract: A refractive index optical fiber sensor based on surface plasmon resonance technology is demonstrated. The sensing device is a multimode optical fiber in which half of the core is polished away and a thin-film layer of gold is deposited. We measure the spectrum-difference variations and the resonance wavelength shifts for different refractive index solutions. In terms of the experimental data, the characteristics including resolution, sensitivity, and signal-to-noise ratio for the sensor are obtained. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:574–576, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27397

Three-layered metallodielectric nanoshells: plausible meta-atoms for metamaterials with isotropic negative refractive index at visible wavelengths

Abstract: A three-layered Ag−low-permittivity (LP)−high-permittivity (HP) nanoshell is proposed as a plausible meta-atom for building the three-dimensional isotropic negative refractive index metamaterials (NIMs). The overlap between the electric and magnetic responses of Ag−LP−HP nanoshell can be realized by designing the geometry of the particle, which can lead to the negative electric and magnetic polarizabilities. Then, the negative refractive index is found in the random arrangement of Ag−LP−HP nanoshells. Especially, the modulation of the middle LP layer can move the negative refractive index range into the visible region. Because the responses arise from the each meta-atom, the metamaterial is intrinsically isotropic and polarization independent. It is further found with the increase of the LP layer thickness that the negative refractive index range of the random arrangement shows a large blue-shift and becomes narrow. With the decrease of the filling fraction, the negative refractive index range shows a blue-shift and becomes narrow while the maximum of the negative refractive index decreases.

Dumbbell-Shaped Mach–Zehnder Interferometer With High Sensitivity of Refractive Index

Abstract: We proposed and fabricated a dumbbell-shaped Mach-Zehnder interferometer (MZI) on a single mode fiber using a revised program of the fusion splicer. To the best of our knowledge, it is the first time one has produced and applied the MZI of this configuration to detect liquids refractive indexes. The dumbbell shape has a length of 1.9 mm and a minimum waist diameter of 63 μm. The wavelengths shift with the changing of surrounding refractive indexes, and the refractive index sensitivity is as high as 251 nm per refractive index unit with the linear range of 1.333-1.391 that is tens of times higher than the MZI based on two fiber tapers.

Polarization conversion element

Abstract: A polarization conversion element is disclosed in which an optical waveguide formed on a substrate sequentially includes a first waveguide portion, a polarization rotation portion, and a second waveguide portion, an effective refractive index of a TE mode having the highest effective refractive index in an eigen mode of waveguide light on a sectional surface of the first waveguide portion is higher than an effective refractive index of a TM mode having the highest effective refractive index, an effective refractive index of the TM mode having the highest effective refractive index on a sectional surface of the second waveguide portion is higher than an effective refractive index of the TE mode having the highest effective refractive index, and heights of waveguide structures (for example, cores) of the first waveguide portion and the second waveguide portion are equal to each other.

Athermal photonic waveguide with refractive index tuning

Abstract: In a photonic waveguide, there is provided an undercladding layer and a waveguide core, having a cross-sectional height and width, that is disposed on the undercladding layer. The waveguide core comprises a waveguide core material having a thermo-optic coefficient. A refractive index tuning cladding layer is disposed on top of the waveguide core. The refractive index tuning cladding layer comprises a refractive index tuning cladding material having an adjustable refractive index and an absorption length at a refractive index tuning radiation wavelength. A thermo-optic coefficient compensation cladding layer is disposed on top of the refractive index tuning cladding layer. The thermo-optic coefficient compensation cladding layer comprises a thermo-optic coefficient compensation material having a thermo-optic coefficient that is of opposite sign to the thermo-optic coefficient of the waveguide core material. The thermo-optic coefficient compensation cladding layer provides at least partial compensation for the waveguide core thermo-optic coefficient.

Measurement of $\gamma$ -Radiation Induced Refractive Index Changes in B/Ge Doped Fiber Using LPGs

Abstract: We propose a novel approach to measure in-situ refractive index changes induced by gamma radiation in single mode fibers. The changes are derived from wavelength shifts of resonances of a CO2 laser written long period fiber grating. Using this approach, we estimate the radiation induced refractive index increase in the core of B/Ge co-doped fiber as 2.1×10-5 at 10 kGy and 1.85×10-4 at 1.54 MGy. At doses , the index changes are considered to be governed by glass polarizability changes. Numerical simulations show that saturation of the index change can be observed at doses . Irradiation has a negligible effect on the resonance dip strengths and bandwidths, with the exception of the turnaround point mode.

Multiple lp-mode fiber designs for mode-division multiplexing

Abstract: The specification describes modified step index and GRaded INdex (GRIN) fibers with low core relative delta (near 0.8%) which have desirable properties for transmission. These lower delta fibers have lower attenuation losses due to reduced Rayleigh scattering, which is desirable to improve performance in multiple mode multiplexing. The fiber designs include optimized raised triangle profiles, and depressed cladding profiles, to support two and four LP modes.

Infrared shielding film

Abstract: An infrared shielding film includes a laminated body including a high refractive index layer and a low refractive index layer, the high refractive index layer and the low refractive index layer being alternately laminated and including a high refractive index material and a low refractive index material, respectively, and the high refractive index material and the low refractive index material having mutually different refractive indexes The infrared film also includes a primary reflection unit providing a primary reflection band with reflectivity exceeding 60% in near-infrared region in reflection spectra of the infrared shielding film for incident light angles of 0° and 60° In a short-wavelength side of the primary reflection band, wavelengths exhibiting 70% reflectivity of the peak value in the primary reflection band are referred to as s(0) nm and s(60) nm, respectively, a relationship s(60) nm>700 nm is satisfied

Few mode optical fibers for space division multiplexing

Abstract: The invention relates to an optical fiber com prising an optical core and an optical cladding surrounding the optical core, the optical core having a single α graded-index profile with α ≥ 1, and the optical core having a radius R 1 and a maximal refractive index n 0 , said optical cladding having a refractive index n Cl . Said optical cladding com prises a region of depressed refractive index n trench , having an inner radius R 2 , with R 2 ≥ R 1 , and an outer radius R 3, with R 3 > R 2. According to embodiments of the invention, the α -value of said graded index profile and the optical core radius R 1 are chosen such that R 1 ≥ 13,5 μm and so as to satisfy a criterion C of quality. Thus, the invention provides a few-mode optical fiber, which allow guiding an increased number of LP modes as com pared to prior art FMFs, while reaching the lowest Differential Mode Group Delay. The system reach is thus increased over prior art.

Optical filter and optical apparatus

Abstract: Regarding an optical filter comprising a light-transmitting substrate, a gradient refractive index thin film with a refractive index change in the film thickness direction formed on the substrate and an anti-reflection structure formed on the gradient refractive index thin film, the gradient refractive index thin film is formed so as to have light absorbing characteristic and a refractive index characteristic such that the refractive index change comprising plural changing points with increases and decreases of the refractive index has a tendency to reduce from the side of the substrate toward the side of the anti-reflection structure. The optical filter has excellent environmental resistance and low reflection. The optical filter can be suitably used in an imaging optical system of an optical apparatus or a display of an electronic device.

Low Loss and High Bandwidth Polystyrene-Based Graded Index Polymer Optical Fiber

Abstract: Polystyrene (PS) was selected as a costless polymer matrix for graded index polymer optical fibers (GI POFs) with low attenuation at a wavelength of 670 nm. However, fabricated PS-based GI POFs showed attenuation of more than 300 dB/km. This high attenuation PS-based GI POF had a quite broad molecular weight distribution. In contrast, a PS-based GI POF with a narrow molecular weight distribution showed low attenuation of around 160 dB/km. This is because the refractive index of PS, different from general polymers, is greatly affected by the molecular weight. The PS-based GI POF showed the high thermal stability of this low loss performance at a temperature of 70°C , despite the low glass transition temperature caused by plasticization. The measured refractive index profile was near optimum (g=2.5), and a high bandwidth of 5.8 GHz for a 50 m length was obtained.

Few mode optical fibers

Abstract: A few mode optical fiber comprising: a Ge-free core having an effective area Aeff of LP01 mode wherein 120 μm2 ΔrMIN; and |Δ0−ΔOuter-Clad|>0.05%, the relative refractive index profile of the optical fiber is selected to provide attenuation of 1600 nm.

Multi-core optical fibers with single mode and multimode core elements

Abstract: Multi-core optical fibers are disclosed herein. According to one embodiment, a multi-core optical fiber includes a common outer cladding formed from silica-based glass and having a cladding index of refraction n cl . At least one single mode core element may be disposed in the common outer cladding. The at least one single mode core element may have a maximum index of refraction n 1 sm . In addition, at least one multimode core element may be disposed in the common outer cladding, the at least one multimode core element having a maximum index of refraction n 1 mm . The maximum refractive index n 1 sm of the at least one single mode core element may be greater than the cladding index of refraction n cl , the maximum refractive index n 1 mm of the at least one multi-mode core element may be greater than n cl , and a center-to-center spacing between adjacent core elements is greater than or equal to 25 μm.