Showing papers on "Photonic-crystal fiber published in 2012"

Interferometric Fiber Optic Sensors

Abstract: Fiber optic interferometers to sense various physical parameters including temperature, strain, pressure, and refractive index have been widely investigated. They can be categorized into four types: Fabry-Perot, Mach-Zehnder, Michelson, and Sagnac. In this paper, each type of interferometric sensor is reviewed in terms of operating principles, fabrication methods, and application fields. Some specific examples of recently reported interferometeric sensor technologies are presented in detail to show their large potential in practical applications. Some of the simple to fabricate but exceedingly effective Fabry-Perot interferometers, implemented in both extrinsic and intrinsic structures, are discussed. Also, a wide variety of Mach-Zehnder and Michelson interferometric sensors based on photonic crystal fibers are introduced along with their remarkable sensing performances. Finally, the simultaneous multi-parameter sensing capability of a pair of long period fiber grating (LPG) is presented in two types of structures; one is the Mach-Zehnder interferometer formed in a double cladding fiber and the other is the highly sensitive Sagnac interferometer cascaded with an LPG pair.

Linear refractive index and absorption measurements of nonlinear optical liquids in the visible and near-infrared spectral region

Abstract: Liquid-filled photonic crystal fibers and optofluidic devices require infiltration with a variety of liquids whose linear optical properties are still not well known over a broad spectral range, particularly in the near infrared. Hence, dispersion and absorption properties in the visible and near-infrared wavelength region have been determined for distilled water, heavy water, chloroform, carbon tetrachloride, toluene, ethanol, carbon disulfide, and nitrobenzene at a temperature of 20 °C. For the refractive index measurement a standard Abbe refractometer in combination with a white light laser and a technique to calculate correction terms to compensate for the dispersion of the glass prism has been used. New refractive index data and derived dispersion formulas between a wavelength of 500 nm and 1600 nm are presented in good agreement with sparsely existing reference data in this wavelength range. The absorption coefficient has been deduced from the difference of the losses of several identically prepared liquid filled glass cells or tubes of different lengths. We present absorption data in the wavelength region between 500 nm and 1750 nm.

Low loss silica hollow core fibers for 3–4 μm spectral region

Abstract: We describe a silica hollow-core fiber for mid-infrared transmission with a minimum attenuation of 34 dB/km at 3050 nm wavelength. The design is based on the use of a negative curvature core wall. Similar fiber designed for longer wavelengths has a transmission band extending beyond 4 µm.

All-fiber Mach-Zehnder interferometers for sensing applications

Abstract: We propose and demonstrate a thinned fiber based Mach-Zehnder interferometer for multi-purpose sensing applications. The sensor head is formed by all-fiber in-line singlemode-multimode-thinned-singlemode (SMTS) fiber structure, only using the splicing method. The principle of operation relies on the effect that the thinned fiber cladding modes interference with the core mode by employing a multimode fiber as a mode coupler. Experimental results showed that the liquid refractive index information can be simultaneously provided from measuring the sensitivity of the liquid level. A 9.00 mm long thinned fiber sensor at a wavelength of 1538.7228 nm exhibits a water level sensitivity of -175.8 pm/mm, and refractive index sensitivity as high as -1868.42 (pm/mm)/RIU, respectively. The measuring method is novel, for the first time to our knowledge. In addition, it also demonstrates that by monitoring the wavelength shift, the sensor at a wavelength of 1566.4785 nm exhibits a refractive index sensitivity of -25.2935 nm/RIU, temperature sensitivity of 0.0615 nm/°C, and axial strain sensitivity of -2.99 pm/μe, respectively. Moreover, the sensor fabrication process is very simple and cost effective.

Origin of thermal modal instabilities in large mode area fiber amplifiers.

Abstract: We present a dynamic model of thermal modal instability in large mode area fiber amplifiers. This model allows the pump and signal optical intensity distributions to apply a time-varying heat load distribution within the fiber. This influences the temperature distribution that modifies the optical distributions through the thermo-optic effect thus creating a feedback loop that gives rise to time-dependent modal instability. We describe different regimes of operation for a representative fiber design. We find qualitative agreement between simulation results and experimental results obtained with a different fiber including the time-dependent behavior of the instability and the effects of different cooling configurations on the threshold. We describe the physical processes responsible for the onset of the instability and suggest possible mitigation approaches.

Excitation of Orbital Angular Momentum Resonances in Helically Twisted Photonic Crystal Fiber

Abstract: Spiral twisting offers additional opportunities for controlling the loss, dispersion, and polarization state of light in optical fibers with noncircular guiding cores. Here, we report an effect that appears in continuously twisted photonic crystal fiber. Guided by the helical lattice of hollow channels, cladding light is forced to follow a spiral path. This diverts a fraction of the axial momentum flow into the azimuthal direction, leading to the formation of discrete orbital angular momentum states at wavelengths that scale linearly with the twist rate. Core-guided light phase-matches topologically to these leaky states, causing a series of dips in the transmitted spectrum. Twisted photonic crystal fiber has potential applications in, for example, band-rejection filters and dispersion control.

Bismuth-doped optical fibers: a challenging active medium for near-IR lasers and optical amplifiers

Abstract: Optical fibers with the bismuth show promise for developing efficient fiber lasers and amplifiers in extended bands of near IR region, in particular, through a whole spectral range of 1150–1550 nm. Devices capable of operating in this region are required for applications in advanced optical communications, medicine and astrophysics, among others. In this paper, Evgeny Dianov from the Fiber Optics Research Center of the Russian Academy of Sciences in Moscow reviews the luminescent properties and light-emitting mechanisms of bismuth-doped fibres and the progress made towards constructing lasers and amplifiers from such fibers. In particular, the author describes a laser emitting at 1460 nm with a conversion efficiency of 50%, and an amplifier with a peak gain of 24 dB at 1427 nm, a 3 dB bandwidth of 36 nm and a noise figure of 6 dB.

Numerical Analysis of a Photonic Crystal Fiber for Biosensing Applications

Abstract: This paper presents a theoretical study on a photonic crystal fiber (PCF) surface plasmon resonance biosensor. The proposed PCF sensor introduces the concept of simultaneous detection with H E11x and H E11x modes, which opens up some possibilities for multianalyte/multichannel sensing. Analysis was performed which considered the operation of the sensor in both amplitude and wavelength interrogation modes. Typical sensor resolutions of 4×10-5 RIU and 8×10-5 RIU with respect to H E11x and H E11y, respectively, are reported for the amplitude interrogation mode, while resoutions of 5 × 10-5 RIU and 6×10-5 RIU are reported for H E11x and H E11y, respectively, for the wavelength interrogation mode.

Photonic crystal fibers for sensing applications

Abstract: Photonic crystal fibers are a kind of fiber optics that present a diversity of new and improved features beyond what conventional optical fibers can offer. Due to their unique geometric structure, photonic crystal fibers present special properties and capabilities that lead to an outstanding potential for sensing applications. A review of photonic crystal fiber sensors is presented. Two different groups of sensors are detailed separately: physical and biochemical sensors, based on the sensor measured parameter. Several sensors have been reported until the date, and more are expected to be developed due to the remarkable characteristics such fibers can offer.

Optical fiber Fabry-Perot interferometer cavity fabricated by femtosecond laser micromachining and fusion splicing for refractive index sensing

Abstract: We demonstrate a fiber in-line Fabry-Perot interferometer cavity sensor for refractive index measurement. The interferometer cavity is formed by drilling a micro-hole at the cleaved fiber end facet, followed by fusion splicing. A micro-channel is inscribed by femtosecond laser micromachining to vertically cross the cavity to allow liquid to flow in. The refractive index sensitivity obtained is ~994 nm/RIU (refractive index unit). Such a device is simple in configuration, easy for fabrication and reliable in operation due to extremely low temperature cross sensitivity of ~4.8 × 10−6 RIU/°C.

A multi-core holey fiber based plasmonic sensor with large detection range and high linearity

Abstract: We present and numerically characterize a closed-form multi-core holey fiber based plasmonic sensor. The coupling properties of the specific modes are investigated comprehensively by the finite element method. It is found that not only phase matching but also loss matching plays a key role in the coupling process between the fundamental mode and plasmonic mode. The coupling transforms from incomplete coupling to complete coupling with increasing analyte RI. An average sensitivity of 2929.39nm/RIU in the sensing range 1.33-1.42, and 9231.27nm/RIU in 1.43-1.53 with high linearity is obtained. The dynamic sensing range is the largest among the reported holey fiber based plasmonic sensors, to the best of our knowledge.

Physical origin of mode instabilities in high-power fiber laser systems.

Abstract: Mode instabilities, ie the rapid fluctuations of the output beam of an optical fiber that occur after a certain output power threshold is reached, have quickly become one of the most limiting effects for the further power scaling of fiber laser systems Even though much work has been done over the last year, the exact origin of the temporal dynamics of this phenomenon is not fully understood yet In this paper we show that the origin of mode instabilities can be explained by taking into account the interplay between the temporal evolution of the three-dimensional temperature profile inside of the active fiber and the related waveguide changes that it produces via the thermo-optical effect In particular it is proposed that non-adiabatic waveguide changes play an important role in allowing energy transfer from the fundamental mode into the higher order mode As it is discussed in the paper, this description of mode instabilities can explain many of the experimental observations reported to date

Multi-core optical fiber and optical communication systems

Abstract: An apparatus includes an optical fiber having a plurality of optical cores therein. Each optical core is located lateral in the optical fiber to the remaining one or more optical cores and is able to support a number of propagating optical modes at telecommunications wavelengths. Each number is less than seventy.

Low-threshold single-wavelength all-fiber laser generating cylindrical vector beams using a few-mode fiber Bragg grating.

Abstract: We propose and demonstrate a low-threshold single-wavelength all-fiber laser generating cylindrical vector beams using a few-mode fiber Bragg grating. Both radially and azimuthally polarized beams have been generated with very good modal symmetry and polarization purity higher than 94%. The radially and azimuthally polarized modes can be switched by simply adjusting the polarization controllers built in the fiber laser cavity. This fiber laser operates at a single wavelength of 1053 nm with a 3 dB linewidth of less than 0.02 nm, signal-to-background ratio of more than 55 dB, and a threshold as low as 16 mW. A new method for the polarization purity measurement is also proposed.

Magneto-optical fiber sensor based on bandgap effect of photonic crystal fiber infiltrated with magnetic fluid

Abstract: A magnetic field sensor based on combination of the magnetic fluid and the tunable photonic bandgap effect of photonic crystal fiber is proposed. The magnetic fluid with higher refractive index (>1.45) is prepared and filled into the air-holes of photonic crystal fiber to convert the index guiding fiber into photonic bandgap fiber. The proposed sensor takes full advantage of the ultrahigh sensitivity characteristic of photonic bandgap fiber and achieves a high sensitivity and resolution of 1.56 nm/Oe and 0.0064 Oe, respectively, which are 2-3 orders of magnitude better than other sensors based on magnetic fluid.

Supercontinuum generation in ZBLAN fibers—detailed comparison between measurement and simulation

Abstract: We present a detailed comparison between modeling and experiments on supercontinuum (SC) generation in a commercial ZBLAN step-index fiber. Special emphasis is put on identifying accurate material parameters by incorporating measurements of the ZBLAN Raman gain, fiber dispersion, and loss. This identification of accurate parameters is of great importance to substantiate numerical simulations of SC generation in soft-glass fibers. Good agreement between measurement and simulation is obtained when pumping both in the normal and anomalous dispersion regimes.

Fiber-optic bending vector sensor based on Mach–Zehnder interferometer exploiting lateral-offset and up-taper

Abstract: A simple, compact, and highly sensitive optical fiber directional bend sensor is presented. This device consists of a lateral-offset splicing joint and an up-taper formed through excessive fusion splicing method. The lateral-offset splicing breaks the cylindrical symmetry of the fiber and defines a pair of directions along which the bending response of the Mach-Zehnder interferometer transmission spectrum is different and thus could be used for bending vector measurement. For a curvature range from -3 to 3 m(-1), the bending sensitivities at 1463.86 nm and 1548.41 nm reach 11.987 nm/m(-1) and 8.697 nm/m(-1), respectively.

In-Line Fiber Optic Interferometric Sensors in Single-Mode Fibers

Abstract: In-line fiber optic interferometers have attracted intensive attention for their potential sensing applications in refractive index, temperature, pressure and strain measurement, etc. Typical in-line fiber-optic interferometers are of two types: Fabry-Perot interferometers and core-cladding-mode interferometers. It's known that the in-line fiber optic interferometers based on single-mode fibers can exhibit compact structures, easy fabrication and low cost. In this paper, we review two kinds of typical in-line fiber optic interferometers formed in single-mode fibers fabricated with different post-processing techniques. Also, some recently reported specific technologies for fabricating such fiber optic interferometers are presented.

Femtosecond pulse written fiber gratings: a new avenue to integrated fiber technology

Abstract: The use of ultrashort laser pulses for fiber grating inscription has many advantages in comparison to continuous wave and long pulse lasers. The most important one is that it allows inscription in nonphotosensitive fiber materials. In this paper the principal inscription techniques and the physical properties of femtosecond (fs) pulse written in-fiber gratings are reviewed. The role of focusing and order walk-off on the inscribed structures is emphasized. A fs pulse written fiber Bragg grating (FBG) also has a unique coupling behavior, due to a refractive index change that is independent from the fiber geometry. Selected applications of such gratings for sensing and fiber lasers are discussed.

Polyvinyl alcohol coated photonic crystal optical fiber sensor for humidity measurement

Abstract: A polyvinyl alcohol (PVA) coated photonic crystal optical fiber (PCF) sensor has been proposed as a relative humidity (RH) sensor. It was fabricated by collapsing the holes of PCF at both ends to form a Michelson interferometer with cladding mode excitation. PVA was dip coated onto the sensor and the interference shift was measured when the sensor was exposed to varying RH. The sensor with 9% (w/w) coating showed a high sensitivity of 0.60 nm/%RH, displayed little hysteresis, high repeatability, low cross-sensitivity to temperature and ammonia gas and stability over 7 days of testing. A rise/fall time of 300/500 ms was achieved respectively.

Fabrication and characterization of porous-core honeycomb bandgap THz fibers.

Abstract: We present a numerical and experimental investigation of a low-loss porous-core honeycomb fiber for terahertz wave guiding. The introduction of a porous core with hole size of the same dimension as the holes in the surrounding honeycomb cladding results in a fiber that can be drawn with much higher precision and reproducibility than a corresponding air-core fiber. The high-precision hole structure provides very clear bandgap guidance and the location of the two measured bandgaps agree well with simulations based on finite-element modeling. Fiber loss measurements reveal the frequency-dependent coupling loss and propagation loss, and we find that the fiber propagation loss is much lower than the bulk material loss within the first band gap between 0.75 and 1.05 THz.

Temperature sensor based on surface plasmon resonance within selectively coated photonic crystal fiber

Abstract: We demonstrate a temperature sensor based on surface plasmon resonances supported by photonic crystal fibers (PCFs). Within the PCF, to enhance the sensitivity of the sensor, the air holes of the second layer are filled with a large thermo-optic coefficient liquid and some of those air holes are selectively coated with metal. Temperature variations will induce changes of coupling efficiencies between the fundamental core mode and the plasmonic mode, thus leading to different loss spectra that will be recorded. In this paper, variations of the dielectric constants of all components, including the metal, the filled liquid, and the fused silica, are considered. We conduct numerical calculations to analyze the mode profile and evaluate the power loss, demonstrating a temperature sensitivity as high as 720 pm/°C.

Hollow-core photonic crystal fiber Fabry–Perot sensor for magnetic field measurement based on magnetic fluid

Abstract: Based on the characteristic of magnetic-controlling refractive index, the magnetic fluid filled in hollow-core photonic crystal fiber (HC-PCF) can be used as the sensitive medium in the cavity of a fiber Fabry–Perot (F–P) magnetic field sensor. The structure and the sensor principle are introduced. The theoretical simulations of the mode distribution of the HC-PCF filled with the magnetic fluid and the sensor output spectra are discussed in detail. The sensor multiplexing capability is indicated as well. Magnetic field measurement sensitivity is about 33 pm/Oe based on the proposed sensor.

Temperature-Insensitive Magnetic Field Sensor Based on Nanoparticle Magnetic Fluid and Photonic Crystal Fiber

Abstract: A novel magnetic field sensor based on the magnetic fluid and Mach-Zehnder interferometer is proposed. The sensor takes advantage of the tunable refractive index property of the magnetic fluid and the modal interference property of the collapsed photonic crystal fiber. The achieved sensitivity and resolution of the sensor are 2.367 pm/Oe and 4.22 Oe, respectively. The magnetic field sensor is insensitive to the temperature variation with a temperature coefficient of 3.2 pm/°C.

26 mJ, 130 W Q-switched fiber-laser system with near-diffraction-limited beam quality

Abstract: We demonstrate a Q-switched fiber laser system emitting sub-60 ns pulses with 26 mJ pulse energy and near-diffraction-limited beam quality (M2<1.3). In combination with a repetition rate of 5 kHz, a corresponding average output power of 130 W is achieved. This record performance is enabled by a large-pitch fiber with a core diameter of 135 µm. This fiber allows for effective single-mode operation with mode field diameters larger than 90 µm even at average output powers exceeding 100 W.

Giant sensitivity of long period gratings in transition mode near the dispersion turning point: an integrated design approach

Abstract: We report an original design approach based on the modal dispersion curves for the development of long period gratings in transition mode near the dispersion turning point exhibiting ultrahigh refractive index sensitivity. The theoretical model predicting a giant sensitivity of 9900 nm per refractive index unit in a watery environment was experimentally validated with a result of approximately 9100 nm per refractive index unit around an ambient index of 1.3469. This result places thin film coated LPGs as an alternative to other fiber-based technologies for high-performance chemical and biological sensing applications.

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

Abstract: 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.

Microbubble based fiber-optic Fabry-Perot interferometer formed by fusion splicing single-mode fibers for strain measurement.

Abstract: We demonstrate an all-fiber optical Fabry–Perot interferometer (FPI) strain sensor whose cavity is a microscopic air bubble. The bubble is formed by fusion splicing together two sections of single-mode fibers (SMFs) with cleaved flat tip and arc fusion induced hemispherical tip, respectively. The fabricated interferometers are with bubble diameters of typically ∼100 μm. Strain and temperature sensitivities of fabricated interferometers are studied experimentally; a strain sensitivity of over 4 Pm/μe and a thermal sensitivity of less than 0.9 Pm/°C is obtained.

Distributed mode filtering rod fiber amplifier delivering 292W with improved mode stability

Abstract: We demonstrate a high power fiber (85 μm core) amplifier delivering up to 292 Watts of average output power using a mode-locked 30 ps source at 1032 nm. Utilizing a single mode distributed mode filter bandgap rod fiber, we demonstrate 44% power improvement before the threshold-like onset of mode instabilities by operating the rod fiber in a leaky waveguide regime. We investigate the guiding dynamics of the rod fiber and report a distinct bandgap blue-shifting as function of increased signal power level. Furthermore, we theoretically analyze the guiding dynamics of the DMF rod fiber and explain the bandgap blue-shifting with thermally induced refractive index change of the refractive index profile.

Ultrahigh-sensitivity temperature fiber sensor based on multimode interference

Abstract: The proposed sensing device relies on the self-imaging effect that occurs in a pure silica multimode fiber (coreless MMF) section of a single-mode–multimode–single-mode (SMS)-based fiber structure. The influence of the coreless-MMF diameter on the external refractive index (RI) variation permitted the sensing head with the lowest MMF diameter (i.e., 55 μm) to exhibit the maximum sensitivity (2800 nm/RIU). This approach also implied an ultrahigh sensitivity of this fiber device to temperature variations in the liquid RI of 1.43: a maximum sensitivity of −1880 pm/°C was indeed attained. Therefore, the results produced were over 100-fold those of the typical value of approximately 13 pm/°C achieved in air using a similar device. Numerical analysis of an evanescent wave absorption sensor was performed, in order to extend the range of liquids with a detectable RI to above 1.43. The suggested model is an SMS fiber device where a polymer coating, with an RI as low as 1.3, is deposited over the coreless MMF; numerical results are presented pertaining to several polymer thicknesses in terms of external RI variation.