Optical time-domain reflectometry of discrete fiber Raman amplifiers

Optical time-domain reflectometry is proposed and demonstrated as a means to characterize the signal power evolution in discrete fiber Raman amplifiers. Up to /spl sim/20-dB-gain amplifiers have been characterized comprising different fibers, under copropagating and counterpropagating signal-pump configurations, and under saturated and unsaturated conditions. The results demonstrate the flexibility of this simple and useful amplifier characterization technique. Simulations show good agreement with experimental results, and sustain the reliability of the technique.     

Dual wavelength-swept fibre ring laser for wavelength-dependent pump-probe measurements

A dual wavelength-swept laser is experimentally demonstrated using two Fabry-Perot tunable filters in a single fibre ring cavity. The laser emits two wavelengths that can be swept simulaneously or one at a time. The source can be used to conduct wavelength dependent pump- probe experiments and eliminates the need for multiple lasers.     

Spectrally stable Er-fiber laser for application in phase-sensitive optical time-domain reflectometry

A high degree of frequency stability in an Er-fiber laser with the Fabry-Perot configuration was achieved using a long (25-km) optical-feedback loop. The frequency-drift rate was determined to be <1 MHz/min by observing temporal fringes in an unbalanced Mach-Zehnder interferometer. Instantaneous linewidth measured with a delayed self-heterodyne interferometer was less than the 3-kHz resolution limit. The laser was utilized in an optical time-domain reflectometry experiment to detect and locate a time-varying phase perturbation applied to an optical fiber.     

Optical time-domain reflectometer with a semiconductor laser amplifier

An optical time-domain reflectometer (OTDR) using a semiconductor laser as an optical pulse generator and as a back-scattered optical signal amplifier is reported. It is found that the detectable one-way loss of the apparatus is improved by 4.5 dB compared with the conventional OTDR using direct detection.     

基于相位光时域反射的光纤分布式声波传感研究

文中提出了一种光纤分布式声波传感方案。作用在传感光纤上的声波信号导致后向瑞利散射光的相位变化,将含有声波信息的后向瑞利散射信号注入到迈克尔逊干涉仪,并采用相位载波解调算法解调出相位信息。实验中采用压电拉伸器模拟声波振动,分布式声波传感系统实现了10 m的空间分辨率以及平坦的频响。     

Advances in phase-sensitive optical time-domain reflectometry

Phase-sensitive optical time-domain reflectometry (Φ-OTDR) has attracted numerous attention due to its superior per-formance in detecting the weak perturbations...     

Optical time-domain reflectometry (OTDR) of diameter modulations insingle mode fibers

The influence of several types of diameter variations on the attenuation and on the optical time-domain reflectometry (OTDR) traces of specially prepared depressed cladding SM (single-mode) fibers is experimentally investigated. Depressed-cladding SM fibers have been prepared by the low-pressure plasma-induced chemical vapor deposition (PCVD) process. The core consists of GeO₂-doped SiO₂ and the cladding region of fluorine-doped silica. During drawing, the diameter of the fiber is controlled within ±0.3 μm for slow perturbations by adjusting the drawing speed (Anritsu M501A). Variations of the core diameter have been accomplished by changing the set point of the fiber diameter control. Core diameter changes give rise to steps or deviations in slope of the OTDR power trace of about 0.3 dB/μm. No indication of additional attenuation due to axial fiber parameter variations has been found up to core diameter changes of 12 μm/m, despite severe distortions of the OTDR traces     

High-efficiency, single-longitudinal-mode ring fibre laser

A novel single-longitudinal-mode erbium-doped ring fibre laser is proposed and demonstrated experimentally. It combines a narrow-linewidth fibre Bragg grating (FBG) with several Mach-Zehnder mode filters (MZF) to obtain a single-frequency emission. It yields a power conversion efficiency of 16%. It is shown that the sidemodes are suppressed when one inserts the series of MZFs inside the cavity. At 1547 nm, the output power measures over 15 dBm, with a sidemode suppression ratio of 50 dB and a linewidth of no more than 7 kHz.     

Optical differential amplification in nonlinear fibre ring resonator

The theoretical basis and analytical expressions for the operation of a nonlinear fibre ring resonator as an optical differential amplifier are reported.<>     

Stabilisation of modelocking in fibre ring laser through pulsebunching

Bunching of equally spaced pulses is reported to be the most stable mode of operation in a passively modelocked fibre ring laser. The ring includes dispersion management, which results in the absence of strict pulse energy quantisation, giving pulse bunching a better immunity to environmental perturbation     

154 GHz polarisation-maintaining dispersion-managed activelymodelocked fibre ring laser

Optical pulses with a repetition rate of 154 GHz are generated directly from a polarisation-maintaining dispersion-managed fibre ring laser using fourth-order FM modelocking. External chirp compensation of the laser output yields transform-limited Gaussian pulses with 1.1 ps duration corresponding to a duty cycle of <0.2     

Optical fibre up-taper back-reflector for laser transmitterevaluation

Evaluation of reflection effects on semiconductor laser transmitters is complicated by multipath interference, which causes degradations in bit-error-rate and is independent of laser isolation. The authors have constructed a variable back-reflector utilising optical fibre up-tapers, which eliminates multipath interference effects by reducing spurious reflection levels to below -50 dB. Reflection levels of -50 dB to -16.5 dB into the laser cavity are possible. Results of measurements of reflection effects on several multilongitudinal mode 1.3 μm lasers operating at 1.7 Gbit/s are shown     

Long-range 1.5 ?m OTDR in a single-mode fibre using A D2 gas-in-glass laser (100 km) or a semiconductor laser (60 km)

We have observed Rayleigh backscatter in a single-mode fibre in optical time domain refiectometry at 1.56 ?m wavelength to a range of 100 km using a D2 gas-in-glass laser, and to 60 km at 1.53 ?m using an injection laser. The low-noise receiver used an InGaAs PIN photodiode and a FET-input operational amplifier with averaging of 1000 times to provide signal/noise enhancement.     

Self-starting additive pulse mode-locked erbium fibre ring laser

Nonlinear polarisation rotation has been used to additive pulse mode-lock (APM) a single loop erbium fibre ring laser. The system is fully self-starting without triggering and has been made to produce single pulses of 452 fs duration per round trip time.<>     

Multiwavelength-switchable SOA-fibre ring laser using sampled Hi-Bi fibre grating

A novel multiwavelength-switchable laser based on a semiconductor optical amplifier (SOA) within a fibre ring cavity with a sampled high-birefringence fibre grating is proposed. Four channels with 0.8 nm spacing have been generated at room temperature and switched to other channels with 0.4 nm wavelength-shift by adjusting an inserted polariser. The laser can be used in hierarchical cross-connect WDM networks employing an interleaved waveband concept.     

Widely tunable narrow linewidth erbium doped fibre ring laser

An erbium doped fibre ring laser enabling singlemode operation over a continuous wavelength tuning range of 44 nm (1528 nm-1572 nm) with laser linewidths of less than 10 kHz is reported.<>     

Travelling-wave erbium fibre ring laser with 60 kHz linewidth

Operation of an erbium-doped-phospho-alumino-silicate-fibre ring laser in a unidirectional travelling-wave configuration enables narrow linewidth, single frequency emission to be obtained at a wavelength of 1.555 mu m. A 60 kHz linewidth has been measured.<>     

Ultrastable harmonically and regeneratively modelockedpolarisation-maintaining erbium fibre ring laser

The authors report the operation of a harmonically and regeneratively modelocked erbium fibre ring laser at 1.55 μm for the first time. Harmonic regenerative modelocking was achieved by feeding back the harmonic longitudinal beat signal which was detected with a high speed photodetector and a high Q dielectric filter. The repetition rate was 10 GHz and the soliton effect shortened-the pulse width from 7.0 to 2.7 ps     

Tunability of erbium-doped fibre ring laser based on bending loss of active fibre

A single frequency depressed-cladding erbium-doped fibre ring laser which can be tuned by exploiting the fibre bending losses has been proposed and experimentally demonstrated. A tunability range of about 44 nm, between 1491 and 1535 nm, has been measured. A saturable absorber formed by an unpumped erbium-doped fibre has been employed to guarantee single frequency operation     

Optical transmission experiment at 1.12 Gbit/s using a graded-index fibre with a length of 1.652 km

The letter describes the transmission of an optical p.c.m. signal with a pulse rate of 1.12 Gbit/s by using a graded-index fibre with a length of 1.652 km and a c.w. semiconductor laser as transmitter. We studied the dependence of the dispersion on the laser wavelength and on the coupling arrangement between laser and fibre. For estimating the material dispersion, we analysed the dynamic spectral behaviour of the laser.