Showing papers on "Step-index profile published in 2017"
TL;DR: In this paper, a surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated, which consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum.
Abstract: A surface plasmon resonance-based fiber-optic sensor for simultaneous measurement of refractive index and temperature of liquid samples is proposed and experimentally demonstrated. The sensor consists of a gold-coated MM-SM-MM optical fiber structure, whose sensitive section was partially covered with polydimethylsiloxane (PDMS) to generate two independent SPR resonance dips in the fiber transmission spectrum. One of the dips is generated by the bare gold-coated fiber section whose wavelength resonance is tuned by the refractive index and temperature of the surrounding medium. The other dip that is exclusively used to monitor the temperature variations of the liquid sample, whose central wavelength at 900 nm corresponds to PDMS refractive index at 20 °C, is produced by the polymerized gold-coated fiber section. The high refractive index and temperature sensitivity achieved, 2323.4 nm/RIU and −2.850 nm/°C respectively, the small size, the ease fabrication process, and the bio-compatibility of the proposed device are appealing characteristics that makes it ideal for practical bio-sensing applications.
175 citations
TL;DR: In this paper, the authors report the first extended study of the inscription of Bragg gratings in surface-core fibers and their application in refractive index and directional curvature sensing.
44 citations
TL;DR: In this paper, a novel refractive index (RI) sensor based on middle-tapered multicore fiber (TMCF) was proposed and experimentally demonstrated, which achieved a sensitivity around 171.2 nm/RIU for a refractive indices range from 1.3448 to 1.3774.
42 citations
TL;DR: In this article, a novel long-period fiber grating via periodically embedding no-core fiber (NCF) has been achieved, which can exhibit an extremely high loss resonant dip (>20dB).
Abstract: A novel long-period fiber grating via periodically embedding no-core fiber (NCF) has been achieved. The 11-period SMF-NCF-SMF-long period fiber grating (SNS-LPG) can exhibit an extremely high loss resonant dip (>20 dB). Theoretical analysis shows good agreement with the measured transmission spectrum. We investigated both refractive index and temperature sensitivity of SNS-LPG. The fabricated sensor achieve an average wavelength sensitivity of 141.837 nm/RIU in the range of 1.333–1.400 RIU, and exhibit lower temperature sensitivity (−6.43 pm/ °C and 0.005 dB/ °C).
37 citations
TL;DR: In this paper, the authors investigated theoretically the reflectivity, quality factor, and eigenfrequency for a single slab with zero refractive index and demonstrated that optical bound states in the continuum can be achieved by the various zero-refractive-index slabs made of epsilon-near zero, impedance-machted zero-index, or mu-near-zero materials.
Abstract: We have investigated theoretically the reflectivity, quality factor, and eigenfrequency for a single slab with zero refractive index. We demonstrate that optical bound states in the continuum can be achieved by the various zero-refractive-index slabs made of epsilon-near-zero, impedance-machted zero-index, or mu-near-zero materials. Moreover, by analytically investigating the frequency of the resonant reflection and resonant transmission, when the quality factor becomes infinity, these two frequencies are precisely equal. For the mu-near-zero slab, the bound states in the continuum are observed at arbitrary incident angles by analyzing the behaviors of complex eigenfrequencies. Our findings may lead to unprecedented high-quality resonators in metamaterials.
30 citations
TL;DR: A novel coupling scheme to excite short-range surface plasmons, whereby the radially polarized hybrid mode propagating inside the nanowire section excites the plasmonic mode close to the fiber endface, which is in turn superfocused down to nanoscale dimensions at the tip apex.
Abstract: We propose and experimentally demonstrate a monolithic nanowire-enhanced fiber-based nanoprobe for the broadband delivery of light (550–730 nm) to a deep subwavelength scale using short-range surface plasmons. The geometry is formed by a step index fiber with an integrated gold nanowire in its core and a protruding gold nanotip with sub-10 nm apex radius. We present a novel coupling scheme to excite short-range surface plasmons, whereby the radially polarized hybrid mode propagating inside the nanowire section excites the plasmonic mode close to the fiber endface, which is in turn superfocused down to nanoscale dimensions at the tip apex. We show that in this all-integrated fiber-plasmonic coupling scheme the wire length can be orders of magnitude longer than the attenuation length of short-range plasmon polaritons, yielding a broadband plasmon excitation and reducing demands in fabrication. We observe that the scattered light in the far-field from the nanotip is axially polarized and preferentially excit...
28 citations
TL;DR: A compact eccentric long period grating with enhanced sensitivity in low refractive index region is demonstrated with a period designed at 15 µm for coupling light to high order cladding modes and is significantly improved with the eccentric localized inscription induced by the femtosecond laser.
Abstract: We demonstrate a compact eccentric long period grating with enhanced sensitivity in low refractive index region. With a period designed at 15 µm for coupling light to high order cladding modes, the grating is more sensitive to surrounding refractive index in low refractive index region. The intrinsically low coupling coefficients for those high order cladding modes are significantly improved with the eccentric localized inscription induced by the femtosecond laser. The fabricated grating is compact with a length of 4.05 mm, and exhibits an average sensitivity of ~505 nm/RIU in low refractive index region (1.3328-1.3544). The proposed principle can also work in other refractive index region with a proper choice of the resonant cladding modes.
26 citations
TL;DR: The proposed refractive index sensor constructed by a short section of single eccentric hole-assisted dual-core fiber spliced between two single-mode fibers has outstanding advantages, such as simple fabrication, good mechanical strength, and excellent microfluidic channel, and will be of importance in biological detection, chemical analysis, and environment monitoring.
Abstract: We propose a novel and simple in-fiber refractive index sensor based on resonant coupling, constructed by a short section of single eccentric hole-assisted dual-core fiber (SEHADCF) spliced between two single-mode fibers. The coupling characteristics of the SEHADCF are calculated numerically. The strong resonant coupling occurs when the fundamental mode of the center core phase-matches to that of the suspended core in the air hole. The effective refractive index of the fundamental mode of the suspended core can be obviously changed by injecting solution into the air hole. The responses of the proposed devices to the refractive index and temperature are experimentally measured. The refractive index sensitivity is 627.5 nm/refractive index unit in the refractive index range of 1.335–1.385. The sensor without solution filling is insensitive to temperature in the range of 30–90°C. The proposed refractive index sensor has outstanding advantages, such as simple fabrication, good mechanical strength, and excellent microfluidic channel, and will be of importance in biological detection, chemical analysis, and environment monitoring.
25 citations
TL;DR: In this article, a high sensitivity method for the measurement of the internal refractive index using a photonic crystal fiber long period grating was reported, where a side lobe appeared near the resonant dip through the analysis of the characteristics of transmission spectra showing variation in the refractive indices.
Abstract: A high sensitivity method is reported for the measurement of the internal refractive index using a photonic crystal fiber long period grating. Long period gratings of different lengths were inscribed in photonic crystal fibers, and the air holes of the fiber had varying refractive indices. A side lobe appeared near the resonant dip through the analysis of the characteristics of transmission spectra showing variation in the refractive index. The resonant dip and its side lobe provided varying sensitivities to the internal refractive index values. The sensitivity of the side lobe was as high as 2343 nm/refractive index unit (RIU), which exceeded the value for the resonant dip (2047 nm/RIU) for refractive indices from 1.3333–1.3792. Due to the high resolution of 8.5 × 10−6 RIU, this method offers promising applications for biological and chemical analysis in which high-precision refractive index measurements are required.
23 citations
TL;DR: In this article, the use of a polymer fiber as a refractive index sensor is proposed, where a fiber Bragg grating is inscribed near the fiber tip and the fiber is cut shorter thus creating a Fabry-Perot cavity.
20 citations
TL;DR: An optical fiber sensor based on fewmode fiber and spherical structure is proposed and demonstrated in this paper, where temperature and refractive index can be measured simultaneously, since the interference spectrums between certain high core mode and different order cladding modes of the few-mode fiber have different sensitivities for the two parameters.
TL;DR: In this paper, an optical sensor based on the interference pattern created by an all-fiber Mach-Zehnder setup is presented, which is produced by the combination of the core and cladding modes that are excited on a fiber with reduced diameter fusion spliced to a single-mode fiber with a 4- $\mu \text{m}$ core axial offset.
Abstract: We report an optical sensor based on the interference pattern created by an all-fiber Mach–Zehnder setup. This pattern is produced by the combination of the core and cladding modes that are excited on a fiber with reduced diameter fusion spliced to a single-mode fiber with a 4- $\mu \text{m}$ core axial offset. Discrete measurements of refractive index and temperature are achieved with sensitivities of 8.8 nm/refractive index units and 39.2 pm/°C, respectively, and also distributed measurements of liquid level up to 120 mm are made with a sensitivity of 6 pm/mm.
TL;DR: In this paper, a heterogeneous 12-core 4-LP-mode fiber having two different types of cores and trench-assisted graded-index profiles was designed. And the numerical analyses based on the coupled-mode equation show that the inter-core crosstalk levels of the proposed fiber are lower than $-$ 55 dB/km, regardless of modes, as long as the fiber is not bent tightly with a bending radius of $\times$ 10 $-$ 3 $\mu {\rm m}$ $-$ 2 and 42.2, respectively.
Abstract: We design a heterogeneous 12-core 4-LP-mode fiber having two different types of cores and trench-assisted graded-index profiles. For the optimum design of the index profiles of these two heterogeneous cores, we first investigate the impacts of various geometric parameters on the effective refractive index of each LP mode, maximum differential modal delay (DMD), and bending losses of the guiding and higher order modes. We then design a heterogeneous 12-core 4-LP mode fiber having a cladding diameter of 242 $\mu {\rm m}$ . The numerical analyses based on the coupled-mode equation show that the inter-core crosstalk levels of the proposed fiber are lower than $-$ 55 dB/km, regardless of modes, as long as the fiber is not bent tightly with a bending radius of $\times$ 10 $-$ 3 $\mu {\rm m}$ $-$ 2 and 42.2, respectively.
TL;DR: In this paper, a simple structure for the refractive index sensing by splicing a segment of capillary with two segments of single-mode fibers (SMFs) is demonstrated, where two mode coupling regions can be formed with tapered air-cavities on both sides of the capillary.
Abstract: We demonstrate a simple structure for the refractive index sensing by splicing a segment of capillary with two segments of single-mode fibers (SMFs). By selecting appropriate splicing parameters, two mode coupling regions can be formed with tapered air-cavities on both sides of the capillary. This simple structure allows us the light propagation in the capillary with a ring mode distribution, while the high-order mode distributed in the capillary will be affected by the surrounding environment. With the inner diameter of the capillary increases, there is an enhancement of interaction between ring modes and the surrounding environment. Therefore, we can realize a tailored sensitivity based on the inner capillary diameter. Maximum refractive index sensitivities of 789, 1196, and 1684 nm/RIU can be obtained in the refractive index range from 1.3360 to 1.4365 when the inner diameter is 5, 15, and 25 μm, respectively. The distinguishing feature of such a capillary-based fiber sensor is that it can be used for the refractometry with a tailored high sensitivity through choosing the inner capillary diameter.
TL;DR: In this article, a photonic device for launching light from a singlemode fiber to a hollow-core photonic-crystal fiber, based on inserting a glass-fiber ''nanospike'' into the hollow core, is presented.
Abstract: Splicing optical fibers for good transmission is important, and can be tricky. This study presents a photonic device for launching light from a single-mode fiber to a hollow-core photonic-crystal fiber, based on inserting a glass-fiber ``nanospike'' into the hollow core. Optomechanics and the adiabatic evolution of the optical mode are exploited to achieve self-aligned, efficient light coupling in a compact, ready-to-use integrated device. This hardware would naturally see application in telecommunications, light-gas interaction and spectroscopy, and nonlinear and quantum optics.
TL;DR: In this paper, a high sensitive connector offset optical fiber sensor is employed to detect the refractive index of liquid, which is formed by lateral core offset fusion splicing of no-core fiber between the single mode fibers and cladding modes.
Abstract: In this paper, a high sensitive connector offset optical fiber sensor is employed to detect the refractive index of liquid. The configuration chosen for this experiment is formed by lateral core offset fusion splicing of no-core fiber (NCF) between the single mode fibers (SMF) and cladding modes are excited by misalignment. The sensing principle for refractive index detection is based on Mach-Zehnder Interferometer (MZI) principle and the experiment is carried out by immersion of device in NaCl solutions of different refractive indices. Such refractive index sensor exhibits high sensitivity 197.33 nm/RIU for the surrounding refractive index variation from 1.333 to 1.380, and the result shows the excellent agreement with theoretical analysis. Compared to other sensors, the proposed device has the potential to provide high sensitivity, ease of fabrication, low cost, compact size, and linear response. Thus, it can be used in many applications such as bio-sensors, chemical sensor, temperature sensor, and pressure sensor.
TL;DR: Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results, which show that the diameter of SDNCF has significant influence on the sensitivity.
Abstract: A high sensitivity refractive index sensor based on a single mode-small diameter no core fiber structure is proposed. In this structure, a small diameter no core fiber (SDNCF) used as a sensor probe, was fusion spliced to the end face of a traditional single mode fiber (SMF) and the end face of the SDNCF was coated with a thin film of gold to provide reflective light. The influence of SDNCF diameter and length on the refractive index sensitivity of the sensor has been investigated by both simulations and experiments, where results show that the diameter of SDNCF has significant influence. However, SDNCF length has limited influence on the sensitivity. Experimental results show that a sensitivity of 327 nm/RIU (refractive index unit) has been achieved for refractive indices ranging from 1.33 to 1.38, which agrees well with the simulated results with a sensitivity of 349.5 nm/RIU at refractive indices ranging from 1.33 to 1.38.
TL;DR: In this article, a high-power spectrally flat 2-5-μm supercontinuum (SC) laser is reported in a piece of As2S3 chalcogenide step-index fiber.
Abstract: In this paper, a high-power spectrally flat 2–5 μm supercontinuum (SC) laser is reported in a piece of As2S3 chalcogenide step-index fiber. A fluoride fiber-based SC laser which spans from 2–4.2 μm is used as the pump light. Two pump coupling systems between the fluoride and As2S3 fibers, one based on aspheric lens coupling and the other using all-fiber mechanical splicing are investigated. With the setup of aspheric lens coupling, the obtained SC laser has a 10 dB spectral bandwidth of 3000 nm spanning from 2050 to 5050 nm, corresponding to an average power of 57.6 mW. While with the all-fiber mechanical splicing, the 10 dB spectral bandwidth of the SC laser shrinks slightly, spanning from 2140 to 4980 nm range, but the average output power is further scaled to a record power of 97.1 mW. It is found that the dominant nonlinearities for continuous spectral broadenings in the As2S3 fiber are self-phase modulation and stimulated Raman scattering in the normal dispersion regime. This paper presents an all-fiber mid-infrared SC laser with spectrum beyond 5 μm for the first time. It also offers a practical solution for robust and reliable high power 2–5 μm broadband fiber laser.
TL;DR: An anti-resonant reflecting guidance coated with a few layers of graphene has been proposed and experimentally demonstrated for the simultaneous measurement of the refractive index and liquid flow rate as discussed by the authors.
Abstract: An anti-resonant reflecting guidance coated with a few layers of graphene has been proposed and experimentally demonstrated for the simultaneous measurement of the refractive index and liquid flow rate. A few layers of graphene were coated on the surface of a hollow core photonic crystal fibre. The refractive index and liquid flow rate can be detected by using the resonant condition of the Fabry–Perot resonator and the effective refractive index of the graphene layers heated by a visible laser beam, which are interrogated through the wavelength shift and visibility of the lossy dip in the transmission spectrum. The experimental results show that the sensitivity of up to 1328 nm/RIU and −2.99 dB/(µL/s) are achieved for the refractive index and flow rate measurement in the refractive index range from 1.345 to 1.363 RIU, respectively. The proposed sensor appears to have potential applications for precise measurement in chemistry, medicine, and biology.
TL;DR: In this article, a fiber-optic quasi-Michelson interferometer (QMI) was used for micro-displacement measurement with a micro-structure of a reflection taper tip containing a refractive index modification as a coupling window over the interface between core and cladding of the fiber.
TL;DR: An ultrasensitive magnetic field sensor is proposed and investigated experimentally and the sensitivity is considerably enhanced compared with those of previously designed, similar structures.
Abstract: An ultrasensitive magnetic field sensor is proposed and investigated experimentally. The no-core fiber is fusion-spliced between two pieces of single-mode fibers and then immersed in magnetic fluid with an appropriate value of refractive index. Under the refractive-index-matched coupling condition, the guided mode becomes leaky and a coupling wavelength dip in the transmission spectrum of the structure is observed. The coupling wavelength dip is extremely sensitive to the ambient environment. The excellent sensitivity to the refractive index is measured to be 116.681 μm/RIU (refractive index unit) in the refractive index range of 1.45691–1.45926. For the as-fabricated sensors, the highest magnetic field sensing sensitivities of 6.33 and 1.83 nm/mT are achieved at low and high fields, respectively. The sensitivity is considerably enhanced compared with those of previously designed, similar structures.
TL;DR: In this paper, a high sensitive refractive index composite fiber sensor comprising the polymer micro-fiber fabricated by directly drawing method from poly(methyl methacrylate) colloid was built by means of micro-manipulation under microscope.
Abstract: This paper reports a high sensitive refractive index composite fiber sensor comprising the polymer micro-fiber fabricated by directly drawing method from poly(methyl methacrylate) colloid. Through the evanescent wave coupling method, the whole sensing system was built by means of micro-manipulation under microscope. The dip wavelength in the measured spectrum caused by the models interference shifted obviously when the surrounding refractive index changed. The approximate linear relationship between surrounding refractive index and dip wavelength shift was obtained experimentally. The measurement sensitivity have been demonstrated up to 1490 nm/RIU with the surrounding refractive index ranging from 1.3333 to 1.3403 by using the polymer micro-fiber with a diameter of 6.6 μm.
TL;DR: A realistic induced birefringence profile inside the fibre which is generated by a bending operation is determined, not only in the cladding but also in graded index core region as well.
TL;DR: In this paper, a spiral shaped plastic optical fiber (POF) was constructed and applied for sensing of the refractive index of a sucrose solution, which is based on evanescent wave interaction between the light travelling within the fiber and the medium surrounding it.
Abstract: A spiral shaped plastic optical fiber (POF) has been constructed and applied for sensing of the refractive index of a sucrose solution. The sensing mechanism is based on evanescent wave interaction between the light travelling within the fiber and the medium surrounding it. Difference in output voltage is observed as the concentration of sucrose solution is varied from 10% to 50%, demonstrating a uniform relation among them. By varying the pitch of the spiral shape and applying strain to the same, the sensitivity of the POF is refined. This spiral-shaped POF sensor is comparatively easy to fabricate, has low cost of operation, and provides real-time sensing-based data.
TL;DR: In this article, a chemical sensor based on defective 1-D photonic crystals in total internal reflection geometry, where a gradient refractive index (GRIN) defect layer is located at the end of the structure, is presented.
Abstract: In this paper, we introduce and analytically demonstrate a novel chemical sensor based on defective 1-D photonic crystals in total internal reflection geometry, where a gradient refractive index (GRIN) defect layer is located at the end of the structure. This configuration creates an open sensing interface for real-time detection with ultrahigh sensitivity. Using the GRIN lens in the structure not only helps to tune the resonance wavelength to a desired value but also as a consequence of its special refractive index distribution function, a ring-shaped reflectance distribution appears on the output plane of the structure that plays a key role in finding the optimized refractive index of the defect layer and achieving the best resonance of the cavity modes. The resonance angle of the cavity modes is highly sensitive to the effective refractive index of the fluid flowing above the sensor. The refractive index variation of $\Delta n_{F}=10^{-8}RIU$ that causes $\Delta \theta =3.2\times 10^{-6}$ degrees shift at the resonance angle can be detected by this sensor.
TL;DR: The effect of the variable Rayleigh scattering-loss coefficient is shown to be more noticeable in the fibers with a quadratic refractive index profile, whereas it is negligible in actual multimode step-index fibers.
Abstract: The recently developed diffraction technique of analytical investigation of the Rayleigh backscattering produced by an incident fundamental mode in a multimode optical fiber with an arbitrary refractive index profile is supplemented by taking into account the Rayleigh scattering-loss coefficient, which could be variable within the fiber cross section. The relative changes in various radial and azimuthal modes’ excitation levels, due to some typical radial dependences of this coefficient, are computed for the quadratic- and step-index fibers. It is stated that the excitation efficiency could either rise or decay for different modes. The effect of the variable Rayleigh scattering-loss coefficient is shown to be more noticeable in the fibers with a quadratic refractive index profile, whereas it is negligible in actual multimode step-index fibers.
Patent•
06 Mar 2017
TL;DR: In this article, an optical coupler configured to cause an NA of light, which exits a taper fiber, to be smaller as compared with a conventional ocular coupler is presented.
Abstract: Provided is an optical coupler configured to cause an NA of light, which exits a taper fiber, to be smaller as compared with a conventional optical coupler A taper fiber has a high refractive index part which is provided inside a core of the taper fiber and which has a refractive index smaller than a refractive index n core of the core An exit end surface of each GI fiber is bonded to an entrance end surface of the taper fiber so that at least a part of the exit end surface of the each GI fiber overlaps with a section of the high refractive index part A relative refractive index difference of the taper fiber is smaller than 0076%
TL;DR: In this article, a high-linearity refractive index (RI) sensor based on an analyte-filled defect hollow core Bragg fiber (DHCBF) for large dynamic ranges was proposed.
Abstract: We propose a high-linearity refractive index (RI) sensor based on an analyte-filled defect hollow core Bragg fiber (DHCBF) for large dynamic ranges. A resonant wavelength induced by the transverse coupling between core modes and defect modes is used as the characteristic wavelength for realizing a high-linearity RI sensor. The numerical results show that the linear correlation between characteristic wavelength and analyte RI can be significantly improved by optimizing structural parameters of a defect layer, which would be beneficial to the enlargement of dynamic measurement range. Furthermore, we numerically demonstrated an RI sensor with the sensitivity of 2062 nm/RIU and the adjusted R-Square value of 0.99967 in the measurement range of 1.324-1.432, by using an analyte-filled DHCBF with a low RI-contrast cladding. Compared with that based on a standard HCBF, our proposed high-linearity RI sensor can achieve high sensitivity in a larger dynamic range.
01 Jul 2017
TL;DR: The grating slot waveguide is designed and numerically simulated to obtain a narrow resonant band at a stop-band of the transmission spectra for a realization of a refractive index sensor.
Abstract: The grating slot waveguide is designed and numerically simulated to obtain a narrow resonant band at a stop-band of the transmission spectra for a realization of a refractive index sensor. The sensing principle has depended on a detection of the shift in the resonant band for a change in the refractive index of a biomaterial. The Q factor of the resonant peak is found out to be 21637. The theoretical value of the limit of detection has calculated as 3.684 × 10−4 RIU.