Showing papers on "Fiber Bragg grating published in 2010"
TL;DR: In this paper, a non-periodic pattern of the grating surface is proposed to give full control over the phase front of reflected light while maintaining a high reflectivity, which could have a substantial impact on a number of applications that depend on low-cost, compact optical components.
Abstract: Sub-wavelength dielectric gratings have emerged recently as a promising alternative to distributed Bragg reflection dielectric stacks for broadband, high-reflectivity filtering applications. Such a grating structure composed of a single dielectric layer with the appropriate patterning can sometimes perform as well as 30 or 40 dielectric distributed Bragg reflection layers, while providing new functionalities such as polarization control and near-field amplification. In this Letter, we introduce an interesting property of grating mirrors that cannot be realized by their distributed Bragg reflection counterpart: we show that a non-periodic patterning of the grating surface can give full control over the phase front of reflected light while maintaining a high reflectivity. This new feature of dielectric gratings allows the creation of miniature planar focusing elements that could have a substantial impact on a number of applications that depend on low-cost, compact optical components, from laser cavities to CD/DVD read/write heads.
561 citations
TL;DR: A compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA) is demonstrated using a two-reflection peak fiber Bragg grating as the external cavity mirror.
Abstract: We demonstrate a compact Q-switched dual-wavelength erbium-doped fiber (EDF) laser based on graphene as a saturable absorber (SA). By optically driven deposition of graphene on a fiber core, the SA is constructed and inserted into a diode-pumped EDF laser cavity. Also benefiting from the strong third-order optical nonlinearity of graphene to suppress the mode competition of EDF, a stable dual-wavelength Q-switching operation has been achieved using a two-reflection peak fiber Bragg grating as the external cavity mirror. The Q-switched EDF laser has a low pump threshold of 6.5mW at 974nm and a wide range of pulse-repetition rate from 3.3 to 65.9kHz. The pulse duration and the pulse energy have been characterized. This is, to the best of our knowledge, the first demonstration of a graphene-based Q-switched laser.
449 citations
TL;DR: In this paper, an all-fiber tunable passively Q-switched erbium-doped fiber (EDF) laser is presented, where saturable absorbers are constructed by optically driven deposition of single-wall carbon nanotubes on fiber connectors.
Abstract: An all-fiber tunable passively Q-switched erbium-doped fiber (EDF) laser is presented. Saturable absorbers are constructed by optically driven deposition of single-wall carbon nanotubes on fiber connectors. A low pump threshold of 11.1 mW is achieved. Self-mode-locking effect is also observed, and it could be suppressed by splicing an extra unpumped EDF into the laser ring cavity. The laser can be tuned by applying axial strain on the fiber Bragg grating which serves as a narrowband external mirror of the cavity.
253 citations
TL;DR: The FBG fabricated in the microfiber has high potential in various types of optical fiber sensor applications and may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter.
Abstract: Fiber Bragg grating (FBG) is fabricated in the microfiber by the use of femtosecond laser pulse irradiation. Such a grating can be directly exposed to the surrounding medium without etching or thinning treatment of the fiber, thus possessing high refractive index (RI) sensitivity while maintaining superior reliability. The grating in the microfiber may have a number of propagation modes in its transmission spectrum, depending on the fiber diameter, and the higher order of mode has larger RI sensitivity. The RI sensitivity also depends on the fiber diameter and a smaller diameter corresponds to a large sensitivity. The maximum sensitivity obtained is approximately 231.4 nm per refractive index unit at the refractive index value of approximately 1.44 when the fiber diameter is approximately 2 microm. The FBG fabricated in the microfiber has high potential in various types of optical fiber sensor applications.
233 citations
TL;DR: In this paper, a fiber in-line Mach-Zehnder interferometer with a microcavity formed by removing part of the fiber core near the core and cladding interface by femtosecond laser micromachining is presented.
Abstract: We report a compact fiber in-line Mach-Zehnder interferometer for refractive index sensing with high sensitivity and precise sensing location. One arm of the interferometer contains a microcavity formed by removing part of the fiber core near the core and cladding interface by femtosecond laser micromachining, and the other arm remains in line with the remaining part of the fiber core. Such a fiber in-line Mach-Zehnder interferometer exhibits an extremely high refractive-index-sensitivity of −9370 nm/RIU (refractive index unit) within the refractive index range between 1.31 and 1.335.
216 citations
TL;DR: This work reports a series of grating structures that were realized by exploiting flexibilities in the point-by-point technique of fabricating fibre-Bragg gratings using an ultrafast laser, including gratings with controlled bandwidth, and amplitude- and phase-modulated sampled (or superstructured) gratings.
Abstract: The point-by-point technique of fabricating fibre-Bragg gratings using an ultrafast laser enables complete control of the position of each index modification that comprises the grating. By tailoring the local phase, amplitude and spacing of the grating’s refractive index modulations it is possible to create gratings with complex transmission and reflection spectra. We report a series of grating structures that were realized by exploiting these flexibilities. Such structures include gratings with controlled bandwidth, and amplitude- and phase-modulated sampled (or superstructured) gratings. A model based on coupled-mode theory provides important insights into the manufacture of such gratings. Our approach offers a quick and easy method of producing complex, non-uniform grating structures in both fibres and other mono-mode waveguiding structures.
186 citations
TL;DR: An efficient single frequency fiber laser by using a newly-developed Er(3+)/Yb(3+) co-doped single mode phosphate glass fiber with the net gain coefficient of 5.2 dB/cm and propagation loss coefficient has been demonstrated.
Abstract: An efficient single frequency fiber laser by using a newly-developed Er(3+)/Yb(3+) co-doped single mode phosphate glass fiber with the net gain coefficient of 5.2 dB/cm and propagation loss coefficient of 0.04 dB/cm has been demonstrated. Over 300 mW stable continuous -wave single transverse and longitudinal mode seed lasering at 1.5 microm has been achieved from a 2.0 cm-long active fiber. The measured slope efficiency and the calculated quantum efficiency of laser emission are found to be 30.9% and 0.938 +/- 0.081, respectively. It is found that the linewidth of the fiber laser is less than 2 kHz, and the measured relative intensity noise (RIN) is around -120 dB/Hz in the frequency range of 50 to 500 kHz.
159 citations
TL;DR: In this article, the physical principles underlying the different techniques for distributed sensing are discussed, a classification is done based on the backscattered wavelength; this is important to understand its possibilities and performances.
Abstract: Obtaining the strain data all along the optical fiber, with adequate spatial resolution and strain accuracy, opens new possibilities for structural tests and for structural health monitoring. Formerly, only point sensors, as strain gages or fiber Bragg grating, were available, and information about the response to loads was restricted only to those points on which the sensors were bonded. Unless a sensor was located near the damage initiation point, details about the failure initiation and growth were lost. With a distributed system, the information is given as an array of data with the position in the optical fiber and the strain or temperature data at this point. In this article, the physical principles underlying the different techniques for distributed sensing are discussed, a classification is done based on the backscattered wavelength; this is important to understand its possibilities and performances. The definition of performance for distributed sensors is more difficult than for traditional point...
158 citations
TL;DR: The use of a short section of polarization-maintaining fiber as a birefringent medium to construct an all-fiber Lyot filter inside the cavity of a fiber laser allows mode-locked operation of an all -fiber all-normal dispersion Yb-f fiber oscillator without the use of an bulk bandpass filter and using standard components.
Abstract: We propose the use of a short section of polarization-maintaining fiber as a birefringent medium to construct an all-fiber Lyot filter inside the cavity of a fiber laser. This allows mode-locked operation of an all-fiber all-normal dispersion Yb-fiber oscillator without the use of a bulk bandpass filter and using standard components. Moreover, filter bandwidth and modulation depth is easily controlled by changing the length and splice angle of the polarization-maintaining-fiber section, leading to an adjustable filter. At mode-locked operation, the 30% output fiber port delivers 1 nJ pulses that are dechirped to 230 fs duration.
155 citations
TL;DR: The multiplexed sapphire sensors present a significant advancement over traditional single-point sensors for critical high temperature applications.
Abstract: In this Letter we present a high temperature multipoint sensing method using sapphire fiber air gap-based extrinsic Fabry–Perot interferometers. Three sensors are fabricated and tested in a single sensing link. Experimental results show that the air gap-based high temperature sensors have a very high temperature sensitivity (>20 nm/°C) and resolution (<0.3°C) and are capable of operating at temperatures well above 1000°C. The multiplexed sapphire sensors present a significant advancement over traditional single-point sensors for critical high temperature applications.
137 citations
TL;DR: Carrier envelope offset self-referencing and long-term phase locking to an rf reference is demonstrated, exemplifying the suitability of this system for generating vacuum and extreme-UV frequency combs via enhancement in passive cavities and high harmonic generation.
Abstract: We report on a high-power fiber frequency comb exhibiting linear chirped-pulse amplification up to 80 W and generating 120 fs pulses. By proper matching of the group delay between the fiber stretcher and compressor, a compression ratio of 3100 could be achieved. Carrier envelope offset self-referencing and long-term phase locking to an rf reference is demonstrated, exemplifying the suitability of this system for generating vacuum and extreme-UV frequency combs via enhancement in passive cavities and high harmonic generation.
TL;DR: An optical fiber refractometer based on a cladding-mode Bragg grating that consists of a long-period grating followed by a fiber Bragggrating and can be multiplexed on a fiber in wavelength domain.
Abstract: We demonstrate an optical fiber refractometer based on a cladding-mode Bragg grating. It consists of a long-period grating (LPG) followed by a fiber Bragg grating (FBG). The LPG partially couples light from the core mode to a cladding mode, both of which are reflected by the FBG. Part of the cladding mode reflection is coupled back to the core mode through the original LPG and used for refractive index sensing. The core mode reflection is used to compensate for the temperature cross sensitivity of the refractometer. The sensors operate in the reflection mode and can be multiplexed on a fiber in wavelength domain.
TL;DR: In this paper, an optical bend sensor based on a Bragg grating inscribed in an eccentric core polymer optical fiber was presented, which exhibits the strong fiber orientation dependence, the wide bend curvature range of ±22.7 m-1, and high bend sensitivity of 63 pm/m-1.
Abstract: We report on an optical bend sensor based on a Bragg grating inscribed in an eccentric core polymer optical fiber. The device exhibits the strong fiber orientation dependence, the wide bend curvature range of ±22.7 m-1, and high bend sensitivity of 63 pm/m-1.
TL;DR: A compact, lightweight, and efficient fiber laser lidar system has been developed to measure water vapor profiles in the lower atmosphere of Earth or Mars and has made preliminary atmospheric measurements.
Abstract: A compact, lightweight, and efficient fiber laser lidar system has been developed to measure water vapor profiles in the lower atmosphere of Earth or Mars. The line narrowed laser consist of a Tm:germanate fiber pumped by two 792 nm diode arrays. The fiber laser transmits ~0.5 mJ Q- switched pulses at 5 Hz and can be tuned to water vapor lines near 1.94 μm with linewidth of ~20 pm. A lightweight lidar receiver telescope was constructed of carbon epoxy fiber with a 30 cm Fresnel lens and an advanced HgCdTe APD detector. This system has made preliminary atmospheric measurements.
TL;DR: In this paper, a hybrid structure made of a long period grating (LPG) and a tilted fiber Bragg grating was proposed to measure the curvature of a beam by the reflected power difference between the core and the recoupled cladding modes.
TL;DR: This paper describes steps involved in the design and realization of a new type of pressure sensor based on the optical fiber Bragg grating, which consists of increasing sensitivity, resistance to electromagnetic interference, dimensions, and potential increased accuracy.
Abstract: This paper describes steps involved in the design and realization of a new type of pressure sensor based on the optical fiber Bragg grating. A traditional pressure sensor has very limited usage in heavy industrial environments, particularly in explosive or electromagnetically noisy environments. Utilization of optics in these environments eliminates all surrounding influences. An initial motivation for our development was the research, experimental validation, and realization of a complex smart pressure sensor based on the optical principle. The main benefit of this solution consists of increasing sensitivity, resistance to electromagnetic interference, dimensions, and potential increased accuracy.
TL;DR: A flexible 2D optical fiber-based pressure sensing surface suitable for biomedical applications that meets the requirements of various biomedical applications with respect to human skin pressure measurements, including amputee sockets, shoe sensors, wearable sensors, wheelchair seating-system sensors, hospital-bed monitoring sensors.
Abstract: We report on the development of a flexible 2D optical fiber-based pressure sensing surface suitable for biomedical applications. The sensor comprises of highly-sensitive Fiber Bragg Grating elements embedded in a thin polymer sheet to form a 2x2 cm2 sensing pad with a minimal thickness of 2.5mm, while it is easily expandable in order to be used as a building block for larger surface sensors. The fabricated pad sensor was combined with a low physical dimension commercially available interrogation unit to enhance the portability features of the complete sensing system. Sensor mechanical properties allow for matching human skin behavior, while its operational performance exhibited a maximum fractional pressure sensitivity of 12 MPa−1 with a spatial resolution of 1×1cm2 and demonstrated no hysteresis and real time operation. These attractive operational and mechanical properties meet the requirements of various biomedical applications with respect to human skin pressure measurements, including amputee sockets, shoe sensors, wearable sensors, wheelchair seating-system sensors, hospital-bed monitoring sensors.
TL;DR: In this article, the authors demonstrate an optical time-domain distributed fiber sensor showing the highest spatial resolution ever reported based on Brillouin dynamic grating in a polarization-maintaining fiber.
Abstract: We demonstrate an optical time-domain distributed fiber sensor showing the highest spatial resolution ever reported based on Brillouin dynamic grating in a polarization-maintaining fiber. In our scheme, the acoustic gratings containing the information on the local Brillouin frequency are generated by a long pump pulse in one polarization, and read out by a short probe pulse in the orthogonal polarization at a clearly distinct optical frequency from the pump. In the experiment, distributed temperature measurements over a 20 m fiber are performed with 1.2 cm spatial resolution.
TL;DR: Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements as mentioned in this paper, where the fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber.
Abstract: Optical fiber sensors based on stimulated Brillouin scattering have now clearly demonstrated their excellent capability for long-range distributed strain and temperature measurements The fiber is used as sensing element, and a value for temperature and/or strain can be obtained from any point along the fiber After explaining the principle and presenting the standard implementation, the latest developments in this class of sensors will be introduced, such as the possibility to measure with a spatial resolution of 10 cm and below while preserving the full accuracy on the determination of temperature and strain
TL;DR: In this paper, a substrate-free metal-cavity surface-emitting microlaser with both top and sidewall metal and a bottom distributed Bragg reflector as the cavity structure is presented.
Abstract: We propose and realize a substrate-free metal-cavity surface-emitting microlaser with both top and sidewall metal and a bottom distributed Bragg reflector as the cavity structure. The transfer-matrix method is used to design the laser structure based on the round-trip resonance condition inside the cavity. The laser is 2.0 μm in diameter and 2.5 μm in height, and operates at room temperature with continuous-wave mode. Flip-bonding the device to a silicon substrate with a conductive metal provides efficient heat removal. A high characteristic temperature about 425 K is observed from 10 to 27 °C.
TL;DR: An ultracompact optical fiber sensor based on a Mach-Zehnder interferometer (MZI) embedded in fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement as mentioned in this paper.
Abstract: An ultracompact optical fiber sensor based on a Mach-Zehnder interferometer (MZI) embedded in fiber Bragg grating (FBG) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement. By use of the resonant wavelength of the FBG and the interference dip of the MZI, the RI and temperature of the surrounding medium can be unambiguously determined. The interesting properties of the sensor include good operation linearity, extremely high RI sensitivity up to ~ -9148 nm/RI unit in the RI range between 1.30 and 1.325, and precise sensing location, determined by the MZI cavity created.
TL;DR: A new method to extend the range of Brillouin optical time domain analysis (BOTDA) systems is proposed that exploits the virtual transparency created by second-order Raman pumping in optical fibers and can be increased up to 100 km with 2 meter resolution.
Abstract: We propose and experimentally demonstrate a new method to extend the range of Brillouin optical time domain analysis (BOTDA) systems. It exploits the virtual transparency created by second-order Raman pumping in optical fibers. The idea is theoretically analyzed and experimentally demonstrated in a 50 km fiber. By working close to transparency, we also show that the measurement length of the BOTDA can be increased up to 100 km with 2 meter resolution. We envisage extensions of this technique to measurement lengths well beyond this value, as long as the issue of relative intensity noise (RIN) of the primary Raman pump can be avoided.
TL;DR: A widely tunable erbium-doped all-fiber laser has been demonstrated, based on a novel tunable filter using multimode interference effects (MMI), which is very simple and inexpensive, but also quite efficient as a wavelength Tunable filter.
Abstract: A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter.
TL;DR: A fiber Bragg grating written in a photosensitive microfiber using KrF excimer laser via a uniform phase mask is demonstrated and two Bragg gratings in microfibers having different diameters are fabricated.
Abstract: A fiber Bragg grating written in a photosensitive microfiber using KrF excimer laser via a uniform phase mask is demonstrated. We have successfully fabricated two Bragg gratings in microfibers having different diameters. In the reflection spectrum of a microfiber Bragg grating (MFBG), we observed two reflection peaks,which agrees with our numerical simulation results. Compared with the fundamental mode reflection, the higher-order reflection mode is more sensitive to the refractive index (RI) variation of the surrounding fluid due to its larger evanescent field. The measured maximum sensitivity is ~102 nm/RIU (RI unit) at an RI value of 1.378 in an MFBG with a diameter of 6 μm.
TL;DR: The most frequently used vibration optical fiber sensors are reviewed, classifying them by the sensing techniques and measurement principles, and the main techniques, intensity modulation, fiber bragg gratings and Fabry-Perot Interferometry, will be reviewed here.
Abstract: Condition monitoring of heavy electromechanical equipment is commonly accomplished in the industry using vibration analysis. Several techniques, mainly based on capacitive and piezoelectric accelerometers, have been applied for predictive maintenance. However, the negative influence of the electromagnetic interference (EMI) can be a real problem when electrical signals are used to detect and transmit physical parameters in noisy environments such as electric power generator plants with high levels of EMI. Optical fiber sensors are increasingly used because of the nonelectrical nature of signals. In this paper, the most frequently used vibration optical fiber sensors will be reviewed, classifying them by the sensing techniques and measurement principles. The main techniques, intensity modulation, fiber bragg gratings and Fabry-Perot Interferometry, will be reviewed here.
TL;DR: Theoretical modeling of a surface plasmon resonance (SPR) based fiber optic sensor with a conducting metal oxide [indium tin oxide (ITO)] as the SPR active material reveals that the proposed sensing probe can be utilized for sensing in the IR region, where most of the gases show their absorption regime.
Abstract: Theoretical modeling of a surface plasmon resonance (SPR) based fiber optic sensor with a conducting metal oxide [indium tin oxide (ITO)] as the SPR active material is proposed. The theoretical analysis reveals that the proposed sensing probe can be utilized for sensing in the IR region, where most of the gases show their absorption regime. Comparison of sensitivity predicts that an ITO-layer-coated SPR-based fiber optic sensor is about 60% more sensitive than a gold-coated fiber optic sensor. The physical reasons behind sensitivity enhancement are provided. Apart from this, various advantageous features of the ITO over the noble metals, silver and gold, are addressed.
TL;DR: A multiplexible pressure sensor technology for a high-temperature environment using a single fiber and a single-fiber feedthrough is demonstrated using an ultrafast laser and shows stable and reproducible operation above 800 degrees C.
Abstract: We present fiber Bragg grating pressure sensors in air-hole microstructured fibers for high-temperature operation above 800 degrees C. An ultrafast laser was used to inscribe Type II grating in two-hole optical fibers. The fiber Bragg grating resonance wavelength shift and peak splits were studied as a function of external hydrostatic pressure from 15 psi to 2000 psi. The grating pressure sensor shows stable and reproducible operation above 800 degrees C. We demonstrate a multiplexible pressure sensor technology for a high-temperature environment using a single fiber and a single-fiber feedthrough.
TL;DR: Two different laser configurations for high-power tunable thulium fiber lasers are reported on: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating.
Abstract: Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150W of average power, >50% slope efficiency, narrow output linewidth, and >100nm tunability in the wavelength range around 2μm.
TL;DR: In this paper, the authors demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber.
Abstract: We demonstrate a high-repetition-rate soliton fiber laser that is based on highly doped anomalously dispersive erbium-doped fiber. By splicing an 11mm single-mode fiber to the erbium-doped fiber, the thermal damage of the butt-coupled saturable Bragg reflector (SBR) is overcome. The laser generates 187fs pulses at a repetition rate of 967MHz with a measured long-term stability of more than 60 h.
TL;DR: In this paper, the authors demonstrate simultaneous measurement of three parameters viz. refractive index of surrounding medium, temperature, and strain using etched-core fiber Bragg grating sensors using an asymmetric nonadiabatic taper and measuring difference in their Bragg wavelength shifts due to different parameters.
Abstract: This study demonstrates simultaneous measurement of three parameters viz. refractive index of surrounding medium, temperature, and strain using etched-core fiber Bragg grating sensors. Simultaneous measurement is achieved by exciting higher order modes in the sensor using an asymmetric nonadiabatic taper and measuring difference in their Bragg wavelength shifts due to different parameters. In order to simultaneously measure three parameters, three different order modes were excited in the sensor. The ability to measure multiple parameters is useful in bio-chemical measurements as it allows us to compensate for the change in Bragg wavelength with respect to change in temperature or strain. Thus, the sensors do not need to be stabilized.