Endlessly Single-mode Photonic Crystal Fiber Research Articles

High sensitivity trace carbon monoxide gas sensor based on endlessly single-mode photonic crystal fiber Sagnac interferometer

Abstract In this paper, a novel carbon monoxide (CO) gas sensor based on α-Fe2O3/MgO is presented and constructed. The endlessly single-mode photonic-crystal fibers (ESPCF) was sandwiched between the four-core fibers (FCF) to form the ESPCF-FCF-ESPCF structure, which was embedded it in the Sagnac loop to construct the Sagnac interferometer. The crystal structure, composition and morphology of α-Fe2O3/MgO sensing film were characterized by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM), respectively. The results indicated that the α-Fe2O3/MgO sensing film was uniformly coated on the outside surface of two ESPCFs, with a thickness of about 1 μm. When these sensing films adsorbed CO, the monitoring wavelength showed blueshift and the maximum sensitivity was 99.42 pm/ppm. The response time and recovery time were respectively 90 s and 100 s respectively. The Sagnac fiber-optic sensor exhibt high sensitivity, good selectivity and strong stability, and it can effectively realize the monitoring of carbon monoxide.

Experimental realization of D-shaped photonic crystal fiber SPR sensor

A novel surface plasmon resonance sensor based on a D-shaped, all-glass, endless single-mode photonic crystal fiber is experimentally demonstrated in this paper, which provides a new approach to realizing a high-performance photonic crystal fiber surface plasmon resonance sensor. In order to achieve the best performance, the side-polished position of the D-shaped photonic crystal fiber is theoretically and experimentally obtained. The proposed sensor can be used in wavelength and intensity interrogations simultaneously, and the experimental results of wavelength interrogation agree well with theoretical results. By combining the two interrogation methods, we present a two-feature interrogation method to improve the resolution. As a new interrogation method, the two-feature resolution is determined to be 6.53 × 10−5 RIU, which is higher than those of the wavelength and intensity interrogations.

Enhanced modes excitation in photonic crystal fiber by long-period gratings for sensing application

Evanescent-wave sensing platform is proposed by two interrogating schemes, core-cladding coupling and core-cladding-core coupling and re-coupling, in endlessly single-mode photonic crystal fiber (ESM-PCF) with long-period gratings (LPGs). The sensing characteristics are experimentally investigated by stress relaxation technique and point-by-point grating inscription via CO2 laser. It shows that the evanescent wave in cladding mode is significantly increased due to LPGs, compared with in core mode only. The introduced concept will further help explore the PCF evanescent-wave sensing and its applications.

High-temperature fiber-optic Fabry-Perot interferometric sensors.

A photonic crystal fiber (PCF) based high-temperature fiber-optic sensor is proposed and experimentally demonstrated. The sensor head is a Fabry-Perot cavity manufactured with a short section of endless single-mode photonic crystal fiber (ESM PCF). The interferometric spectrum of the Fabry-Perot interferometer is collected by a charge coupled device linear array based micro spectrometer. A high-resolution demodulation algorithm is used to interrogate the peak wavelengths. Experimental results show that the temperature range of 1200 °C and the temperature resolution of 1 °C are achieved.

Photonic Crystal Fiber-Based Modal Interferometer for Refractive Index Sensing

A core-cladding-mode interferometer is fabricated by splicing a single-mode fiber to an endlessly single-mode photonic crystal fiber (ESM-PCF). The optimum collapsed length of ESM-PCF is investigated to ensure a higher order cladding mode of ESM-PCF to be excited, serving as a sensing beam. At the end of ESM-PCF, a spherical end-facet with big radius is proposed to ensure from where the higher order cladding mode is to be reflected and then it interferes with the core mode serving as a reference beam. Such a device has an enhanced refractive index sensitivity of ~ 199 nm/RIU, offering potentials in biological and chemical applications.

Launch device using endlessly single-mode PCF for ultra-wideband WDM transmission in graded-index multi-mode fiber

We demonstrated ultra-wideband wavelength division multiplexing (WDM) transmission from 850 to 1550 nm in graded-index multi-mode fiber (GI-MMF) using endlessly single-mode photonic crystal fiber (ESM-PCF) as a launch device. Effective single-mode guidance is obtained in multi-mode fiber at all wavelengths by splicing cm-order length ESM-PCF to the transmission fiber. We achieved 3 × 10 Gbit/s WDM transmission in a 1 km-long 50-μm-core GI-MMF. We also realized penalty free 10 Gbit/s data transmission at a wavelength of 850 nm by optimizing the PCF structure. This method has the potential to achieve greater total transmission capacity for MMF systems by the addition of more wavelength channels.

High-temperature measurement by using a PCF-based Fabry–Perot interferometer

A new method for fabricating a fiber-optic Fabry–Perot interferometer (FPI) for high-temperature sensing is presented. The sensor is fabricated by fusion splicing a short section of endlessly single-mode photonic crystal fiber (ESM-PCF) to the cleaved end facet of a single-mode fiber (SMF) with an intentional complete collapse at the splice joint. This procedure not only provides easier, faster and cheaper technology for FPI sensors but also yields the FPI exhibiting an accurate and stable sinusoidal interference fringe with relatively high signal-to-noise ratio (SNR). The high-temperature response of the FPI sensors were experimentally studied and the results show that the sensor allows linear and stable measurement of temperatures up to 1100°C with a sensitivity of ∼39.1nm/°C for a cavity length of 1377um, which makes it attractive for aeronautics and metallurgy areas.

High-Temperature Annealing Behaviors of CO$_{2}$ Laser Pulse-Induced Long-Period Fiber Grating in a Photonic Crystal Fiber

High-temperature annealing behaviors of long-period fiber grating (LPFG) induced by high-frequency CO2 laser pulse in an endlessly single-mode photonic crystal fiber (ESM-PCF) are investigated in this paper. We find that the change difference of effective refractive index between the air holes cladding and the solid core of the ESM-PCF both in grating fabricating and in annealing processes with different mechanisms would cause resonant wavelength red shift. Through annealing the gratings under high temperature at 600°C-650°C, its stability, linearity, and repeatability to temperature and tensile strain responses under high temperature condition can be greatly enhanced. Our study shows that the changes in fiber glass structure would have significant influence on the optical properties of ESM-PCF LPFG and thus will help understanding of the forming mechanisms and physical characteristics of ESM-PCF LPFG. In addition, ESM-PCF LPFGs can be used as temperature or strain sensors after annealing at high temperature of 600°C-650°C.

In-line fiber Fabry-Perot refractive-index tip sensor based on endlessly photonic crystal fiber

This paper, for the first time to the best of our knowledge, presents a novel fiber-optic refractive-index sensor which is based on an intrinsic Fabry-Perot interferometer (IFPI) formed by a section of endlessly single-mode photonic crystal fiber (EPCF) and conventional single-mode fiber. Such an IFPI sensor has the advantages of easy fabrication, low joint and transmission losses, low-cost and good fringe visibility due to the use of the EPCF. This miniature fiber-optic sensor is demonstrated for the measurement of the refractive index change of glycerin solution by measuring its fringe visibility change solely. The experimental data agree well with the theoretical results and the refractive-index resolution and repeatability of ∼2 × 10 −5 and ±0.5%FS in the linear operating range, are achieved. In addition, such a sensor can be used as an excellent temperature sensor with a cavity-length-temperature sensitivity of 4.16 nm/°C and repeatability of ±0.15%FS when tested from 20 °C to 100 °C. Therefore, simultaneous measurement of refractive index and temperature can be realized by determination of the fringe visibility and the cavity length change of such a PCF-based IFPI, respectively, providing a practical way to measure refractive index with self-temperature compensation.

Photonic crystal fiber interferometer composed of a long period fiber grating and one point collapsing of air holes

We present an all-fiber interferometer fabricated with a single piece of an endless single-mode photonic crystal fiber (PCF) by an electric arc discharge. By forming a long period grating (LPG) at a point and collapsing the air holes at another point along the PCF, the simple but effective interferometer could be implemented. The LPG made a strong wavelength selective mode coupling between the core and cladding modes in the interesting wavelength range, while the air-hole collapse induced wavelength independent mode couplings. By cascading them, we could implement the all-fiber interferometer. As a potential application of the proposed all PCF interferometer, strain sensing is experimentally demonstrated.

Strain and Temperature Characteristics of a Long-Period Grating Written in a Photonic Crystal Fiber and Its Application as a Temperature-Insensitive Strain Sensor

Strain and temperature characteristics of a long-period grating (LPG) written in an endless-single-mode photonic crystal fiber (ESM-PCF) are investigated theoretically and experimentally. By use of a dispersion factor , a deeper understanding of the behavior of LPG in the ESM-PCF is achieved. The negative strain sensitivity of the LPG is explained by the negative value of the dispersion factor . Our analysis clearly reveals the significant effect of the waveguide dispersive characteristics of the cladding modes on the strain and temperature characteristics of the LPG in the ESM-PCF. By selecting an appropriate grating period, a simple, low-cost LPG sensor with approximately zero temperature sensitivity but large strain sensitivity is realized.

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.

Formation of transverse structure of CW light beams in photonic crystal fibers with saturable gain

Transverse beam dynamics in a nonlinear photonic crystal fiber is studied numerically. The field decomposition in terms of Laguerre-Gaussian functions is used to simulate the propagation of a beam along the fiber. Symmetry breakdown due to the competition of transverse modes is demonstrated. Both the few-mode photonic crystal fiber and the endlessly single-mode photonic-crystal fiber are considered. In the photonic crystal fiber with broad gain region, the resulting beam structure is shown to depend strongly upon the initial conditions.

Wide-passband, temperature-insensitive, and compact π-phase-shifted long-period gratings in endlessly single-mode photonic crystal fiber

We demonstrate what is believed to be the first fabrication of a wide-passband, temperature-insensitive, and compact spectral filter based on a pi-phase-shifted long-period grating in an endless single-mode photonic crystal fiber. By introducing a pi-phase shift in the middle of a 12-period long-period grating, two symmetrical rejection bands at wavelengths of 1252.65 and 1418.7 nm are obtained with isolation higher than 18 dB and a passband bandwidth of 84.15 nm. The pi-phase-shifted long-period gratings are inscribed by the relaxation of mechanical stress with the focused pulses of a CO2 laser and a point-by-point technique without geometric deformation. The length of the spectral filter is approximately 6.6 mm with a sensitivity of 8 pm/ degrees C at a medium temperature range of 23-190 degrees C.