Piece Of Single-mode Fiber Research Articles

A Novel In-Line Fiber Mach–Zehnder Interferometer Temperature Sensor Made of Thermally Expanded Core Fiber

A novel in-line fiber temperature sensor by splicing a piece of single mode fiber between two thermally expanded core fibers at their core-expanded ends is proposed and demonstrated. This structure forms an all fiber Mach–Zehnder interferometer due to the interference between the core mode and the cladding modes of the single mode fiber. The fabricated sensor is applied to measure temperature changes. The temperature sensitivity of the sensor at a length of 6.3cm is about 65.3 pm/°C. The proposed sensor is low cost, easily fabricated, and may be useful for detection of temperature.

Harnessing the fiber fuse for sensing applications.

A simple refractive index sensor based on a small section of fiber damaged by the fiber fuse is proposed and demonstrated with a sensitivity of 350.58 nm/refractive index unit (RIU). For comparison, a hetero-core structure fiber sensor composed of a short no-core fiber (NCF) sandwiched between two pieces of single-mode fibers is demonstrated with a sensitivity of 157.29 nm/RIU. The fiber fuse technique can allow mass production of sensors by incorporating small sections of the damaged fiber of any type into each device. We believe this is the first application of the periodic damage tracks in optical fibers formed by the fiber fuse.

Conventional and dissipative solitons in a CFBG-based fiber laser mode-locked with a graphene–nanotube mixture

A graphene–nanotube mode-locked tandem fiber laser with a chirped fiber Bragg grating (CFBG) is proposed, for the first time to our best knowledge. This laser is composed of two resonators with opposite net dispersions, and it delivers a conventional soliton (CS) and a dissipative soliton (DS) simultaneously. The CS operated in a net-anomalous-dispersion cavity has a spectral width of ~0.59 nm and a pulse duration of ~5 ps, and the DS is operated in another cavity with a pulse duration of ~15.3 ps. By using a piece of single-mode fiber, the DS can be compressed to ~6.5 ps, while the CS is gradually broadened up to ~9 ps.

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64pm/°C from 200°C to 1000°C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675°C/με. The reasons for realizing the high temperature sensitivity is also discussed.

Simulation analysis of an improved optical triangular-shaped pulse train generator based on quadrupling RF modulation incorporating fiber dispersion-induced power fading

We report an improved approach to generate optical triangular-shaped pulse train using quadrupling RF modulation and fiber dispersion-induced power fading. In the proposal, quadrupling RF modulation (via a dual-parallel Mach–Zehnder modulator) is employed to generate four primary optical sidebands (±2nd and ±6th) in spectrum. Then a piece of single mode fiber is connected as the dispersive media. Because of the power degradation induced by fiber dispersion, the undesired 8th order harmonic in optical intensity can be removed. It is found that when the modulation index is adjusted to a proper value (m=4.438), optical intensity with its expression corresponding to the Fourier expansion of idea triangular-shaped waveform can be found. Since the quadrupling RF modulation technique is employed, repetition rate of the target pulse train is four times of the driving frequency, which makes pulse train generation with higher repetition rate or smaller pulse duration possible.

A High Sensitivity Index Sensor Based on No-Core Fibers

A simple, small-size, compact and high-sensitivity refractive-index sensor composed of a short no-core fiber (NCF) about 20 mm in length sandwiched between two pieces of single-mode fibers is proposed in this paper. The index measurement is experimentally demonstrated with the sensitivity of 7792.85 nm/ RIU in the range from 1.440 to 1.454 and 227.14 nm/ RIU in the range from 1.300 to 1.430. This sensing mechanism is based on the induced multi-mode interfering wavelength shift in the no-core fiber when the reflective index of the fiber outside is changed.

The generation of a broadband, spectrally flat supercontinuum extended to the mid-infrared with the use of conventional passive single-mode fibers and thulium-doped single-mode fibers pumped by 1.55 μm pulses

Flatly broadened supercontinuum (SC) generation spread toward the mid-infrared region is achieved in telecom-grade passive fibers (SMF-28) as well as in single-mode thulium-doped fibers pumped by 1 ns pulses at a wavelength of 1550 nm. Using only a piece of single-mode fiber (SMF) as a nonlinear medium the SC spread from ∼1300 to 2500 nm with an output power of up to 2 W. A spectrum flatness variation below 5 dB in a span of 640 nm (from 1.6 to 2.24 μm) and a corresponding spectral density of ∼1.1 mW nm−1 were obtained. Using a single-mode silica Tm-doped fiber, the SC cut-off wavelength was extended to 2.65 μm. For this case, broadband mid-IR radiation with a <5 dB spectral flatness in the wavelength interval ranging from 1.95 to 2.51 μm (spectral span of 560 nm) was demonstrated. The output average power was over 1 W out of which ∼85% was in a band of >1.9 μm, which is, to the best of our knowledge, the highest average power of an SC generated directly from a single-mode Tm-doped fiber.

Filter-free ultra-wideband doublet pulses generation based on wavelength conversion and fiber dispersion effect

Filter-free ultra-wideband (UWB) doublet pulse generation is experimentally demonstrated in the optical domain based on cross-gain modulation (XGM) in semiconductor optical amplifier (SOA) and UWB-over-fiber technology is implemented by exploiting dispersion-induced pulse broadening effect in single-mode fiber (SMF). In our proposed system, the SOA generates a polarity-inversed Gaussian pulse train with respect to the injected one through the XGM. After a piece of SMF, the bandwidth of polarity-reversed Gaussian pulse broadens due to the induced dispersion. After the combination of the two light waves with a suitable time delay between them, UWB pulse is obtained. The key parameters for UWB pulse, including central frequency, 10dB bandwidth, as well as fractional bandwidth are experimentally obtained with 8GHz, 9.9GHz and 123% respectively. The generated UWB doublet pulse conforms with the UWB definition of Federal Communications Commission (FCC).

Generation of controllable nondiffracting beams using multimode optical fibers

A method of generating nondiffracting beams using multimode optical fibers is reported. When a large-core multimode fiber is spliced onto a piece of single-mode fiber, only linearly polarized (LP0,n) modes are excited inside the multimode fiber segment because of mode orthogonality and on-axis excitation. Since the excited LP0,n modes are actually Bessel fields with different transverse wave vectors truncated by the core of the multimode fiber, the beam exiting the multimode fiber facet can form a variety of readily controllable and nearly nondiffracting optical patterns resulting from interference of apertured Bessel fields.

Miniature fiber-optic high temperature sensor based on a hybrid structured Fabry–Perot interferometer

A miniature Fabry-Perot (FP) interferometric fiber-optic sensor suitable for high-temperature sensing is proposed and demonstrated. The sensor head consists of two FP cavities formed by fusion splicing a short hollow-core fiber and a piece of single-mode fiber at a photonic crystal fiber in series. The reflection spectra of an implemented sensor are measured at several temperatures and analyzed in the spatial frequency domain. The experiment shows that the thermal-optic effect of the cavity material is much more appreciable than its thermal expansion. The temperature measurements up to 1000 degrees C with a step of 50 degrees C confirm that it could be applicable as a high-temperature sensor.

A hetero-core structured fiber optic pH sensor

Novel spectroscopic sensor based on a hetero-core structured fiber optic is described in this paper. The hetero-core structured fiber optic consists of multi mode fibers and a short piece of single mode fiber which was inserted in the multi mode fibers. Phenol red and/or cresol red as pH sensitive dyes were immobilized on the surface of the hetero-core portion by using sol–gel method, and the pH change detection was performed by immersing the hetero-core portion into the solution. In the case that the cresol-red immobilized fiber was immersed in the alkaline and/or acidic solution, the peak wavelength of the propagating loss spectra were about 575 and 545 nm, respectively. These propagating loss spectra were similar to that of the absorbance spectra of the dye solution. In the propagating loss spectra of phenol-red immobilized fiber, these spectra were similar to that of the dye solution. The colorimetric change of the dye in the support matrix was reversible, and the response time of the sensor was within 30 s.

Fiber-grating-based self-matched additive-pulse mode-locked fiber lasers

Fiber-grating-based self-matched additive-pulse mode-locked (APM) fiber lasers were investigated both theoretically and experimentally. With three fiber gratings to form the linearly coupled cavities, such a fiber laser system could generate stable mode-locked output without critical cavity length control. It was shown that the wavelength dependence of the effective penetration length of a fiber grating led to the self-matching of the cavity lengths of the coupled cavities. A millimeter-order cavity-length mismatch could be tolerated. In a similar laser structure using chirped fiber gratings with a designated arrangement of the grating polarities, the APM fiber laser could have the advantages of higher tolerance of cavity-length mismatch and stretched-pulse amplification. After pulse compression with a piece of single-mode fiber, output pulses with full-width at half-maximum pulsewidths of 930 fs were obtained.

A non-linear high temperature fracture mechanics basis for strain range partitioning. (Report): Kitamura, T. and Halford, G. R.NASA Tech. Memo. NASA TM-4133 1989, 14 pp

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.