Tunable multi-wavelength fiber ring laser based on a Hi-Bi fiber loop mirror

A novel tunable multi-wavelength fiber ring laser based on semiconductor optical amplifier (SOA) is proposed by using a high-birefringence (Hi-Bi) fiber loop mirror (FLM) as wavelength filter. With this configuration, the wavelength spacing of this laser can be varied by using the different lengths of Hi-Bi fiber. 8 wavelengths spacing on 450 GHz are experimentally obtained with more than 25-dB signal-to-noise ratio (SNR) for each channel using 1.28-m Hi-Bi fiber in Hi-Bi FLM. The output power variation between different channels is measured to be less than 5.9 dB. The linewidth of each channel is compressed from 0.347 to 0.186 nm by 1.5-m unpumped erbium-doped fiber (EDF). Meanwhile, 17 wavelengths spacing on ITU-gird (100 GHz) are also obtained with 5.9-m Hi-Bi fiber in Hi-Bi FLM. All these channels can be tuned together over 0.4 nm.     

Suppression of mode competition in fiber lasers by using a saturable absorber and a fiber ring

An erbium-doped fiber (EDF) laser was configured with a fiber grating, a fiber ring resonator, and a saturable absorber by using un-pumped EDF as mode selection element. The laser showed single mode operation with a narrow linewidth of 5 kHz. The mode selection mechanisms of the un-pumped EDF and the ring resonator are theoretically and experimentally analyzed.     

Compensating large PMD by a fiber grating

In this paper, the first- and second-order polarization mode dispersion (PMD) with the amount of 132.994-ps differential group-delay (DGD) and maximum 476.129-ps/nm second-order PMD can be compensated by a two-stages PMD compensator at a 40-Gb/s optical fiber communication system. The first stage has one free degree that is used for first order and high orders PMD compensations by rotating the state of     

Multi-wavelength fiber ring laser based on a chirped moiré fiber grating and a semiconductor optical amplifier

A simple and cost-effective multi-wavelength fiber ring laser based on a chirped Moiré fiber grating (CMFG) and a semiconductor optical amplifier (SOA) is proposed.Stable triple-wavelength lasing oscillations at room temperature are experimentally demonstrated.The measured optical signal-to-noise ratio (SNR) reaches the highest value of 50 dB and the power fluctuation of each wavelength is less than 0.2 dB within a 1-h period.To serve as a wavelength selective element,the CMFG possesses excellent comb-like ...     

Generation of a hollow laser beam by a multimode fiber

A simple method to generate a hollow laser beam by multimode fiber is reported.A dark hollow laser beam is generated from a multimode fiber and the dependence of the output beam profile on the incident angle of laser beam is analyzed.The results show that this hollow laser beam can be used to trap and guide cold atoms.     

Multi-wavelength fiber source based on double-pass superfluorescent fiber source and a reflection Mach-Zehnder filter

A spectrum-sliced multi-wavelength fiber source (SS-MWFS) based on double-pass superfluorescent fiber source (SFS) with a reflection Mach-Zehnder filter (RMZF) as the reflected comb filter is demonstrated. With backward pumped configuration, MWFS with 50 wavelength channels of extinction ratio (ER) of 16.7 dB is obtained over the almost total C-band gain region. Total output power of the MWFS is 16.2 mW which shows that a power of about 0.3 mW of per channel is achieved. The SS-MWFS with forward pumped configuration is also discussed for comparing. The backward pumped configuration can provide a larger output power while only a little smaller ER than that of the forward pumped configuration.     

Three-channel dual-wavelength fiber laser based on a digital micromirror-device processor and photonic crystal fiber

A stable three-channel dual-wavelength fiber ring laser is proposed and experimentally demonstrated. The digital micromirror-device(DMD) processor can select and recirculate any dual waveband from the gain spectrum of the erbium-doped fiber at each channel. The uniform and stable dual-wavelength oscillation is obtained by a highly nonlinear photonic crystal fiber, which causes two degenerate the four-wave-mixing processes. By loading different reproducibility diffraction gratings on the optoelectronic DMD processor, the laser can be operated stably in a three-channel dual-wavelength scheme at room temperature. The power fluctuation of each laser channel is less than ～0.02 d B.     

Bragg scattering in a positive β4 fiber

The phase-matching curves for the four-wave mixing effect of Bragg scattering in two fibers with opposite sign β(4) dispersion coefficients have been measured experimentally. The measured phase-matching curves are in good agreement with theoretical expectations, and their dependence on several key parameters has been determined.     

A self-seeded fiber laser incorporated with a fiber Bragg grating external cavity semiconductor laser

A self-seeded fiber laser incorporated with a fiber Bragg grating external cavity semiconductor laser (FBG-ECL) and a Mach-Zehnder interferometer (MZI) were reported in this paper. The MZI provided a Q-switching with response time in the order of micro-seconds. The FBG-ECL provided narrow pulses as seeds to shorten the Q-switched pulses. Experimentally, pulse width of 0.8 μs was measured, which was one fifth of the pulse width without self-seeding.     

Ultrasonic wave scattering in a fiber reinforced composite

I.IntroductionWiththerapiddevelopmentoffiberreinforeedcompositematerials,muchattcntionhasbeenpaidtothecva1uationofthefiber/matrixinterfaces[1-51wheredefectSmayemergeafterlongusageofthecomposites.Foraweakenedinterface,twostiffnessconstantsareusuallyin-tfoducedtomodc1theboundaryconditionsforthestressesanddisNacementsatbothsidesandtheyareclose1yrclatedtotheultrasonicattenuationduetoscattering['].However,sofarnopublishedrcportsarcavai1ab1e.Whitemadeadetailedinvestigationofsoundwavescatteringatac…     

Transverse-mode controlling of a large-mode-area multimode fiber laser

Coiling technique is used to control the transverse mode of a large-mode-area(LMA)multimode fiber laser.By winding the fiber to a coil with different radius,high-order modes of a multimode fiber laser are suppressed one by one and finally 15.4-W single-transverse-mode output is achieved when the coil radius is 20 mm.It is found that as the coil radius decreases,the beam quality of a multimode fiber laser gets better but the slope efficiency drops for higher-order modes are discriminated.During the experiment,as the coil radius of multimode fiber changes,output characteristic of the laser has been measured.Meanwhile, the mode loss of different modes is calculated theoretically.It is proved that the experimental measured results fit well with the theoretically calculated results.     

Tm–Ho codoped fiber based all fiber amplification of a gain-switched 2 μm fiber laser

A Tm–Ho codoped fiber amplifier system is built. And, amplification of a gain-switched Tm–Ho codoped fiber laser is investigated. Average output of 300 mW is obtained at repetition rate of tens of kHz with an amplification gain bigger than 11 dB. And, pulse amplification efficiency of resonantly pumped Tm–Ho codoped single clad fiber is comparable with 793 nm pumped Tm-doped double clad fiber. The maximal pulse energy generated is about 13.1 μJ, corresponding to a peak power of 282 W at 20 kHz. During the amplification process, gain-switching, partially modulated gain-switched mode-locking and 100% modulated gain-switched mode-locking are observed sequentially. At gain-switching mode, the laser output enjoys a narrow linewidth of 0.31 nm, while at gain-switched mode-locking mode, the spectral linewidth broadens to 0.6 nm.     

Coherent combining of fiber lasers using a ring coupled cavity and?single-mode fiber filtering

Coherent combining of two fiber lasers has been experimentally demonstrated by using a ring coupled cavity and single-mode fiber filtering technique. Their phases are primarily synchronized due to mutual injection coupling introduced by a common ring coupled cavity, and efficient phase locking is realized by utilizing a single-mode feedback fiber to filter the far-field pattern. The detailed experimental investigations indicate that the stability of phase locking can be improved significantly by this spatial filtering technique, and the far-field intensity distribution can be manipulated by controlling the position of the filtering fiber.     

Simple air-gap fiber Fabry–Perot interferometers based on a fiber endface with Sn-microsphere overlay

This study presents a simple, cost-effective and sensitive air-gap fiber Fabry–Perot interferometer (AG-PPFI) which is based on a metal Tin (Sn)-overlaying fiber technique. An extremely small drop of metallic Sn was heated and then melted to shrink into a microsphere owing to the cohesion of the material. When a fiber was inserted into the melting Sn microsphere, an air gap was naturally formed between the fiber endface and the metal Sn during the cooling process. By carefully controlling the reaction time, various air-gaps can be formed as the Fabry–Perot interferometric cavities for the proposed AG-PPFIs. Measurements reveal that a smaller length of air-gap and heavier mass of Sn-microsphere are associated with higher sensitivity of temperature, but the former is dominated. A best temperature sensitivity of wavelength shift with +4.3 nm/°C is achieved when the air-gap is about 5 μm with mass of Sn-microsphere of about 10 μg. The variation of the wavelength shift is equivalent to sensitivity for a change in the cavity length of +14.83 nm/°C.     

Wavelength switching in a mixed structure of a long-period and a Bragg fiber gratings

We built a numerical model for evaluating the coupling processes of a mixed structure of a Bragg fiber grat-ing and a long-period grating. From the numerical results, we not only confirmed the wavelength switchingphenomena observed in previously reported experiments, but also discovered a new coupling mechanism,which generated the reflection of a signal with its wavelength longer than the Bragg wavelength. Thedependencies of the wavelength switching behaviors on various parameters of the mixed grating structure     

Dynamics of dark-bright vector solitons in a birefringent fiber

Coupled dark-bright vector solitons are considered in a birefringent fiber,and their dynamics are studied by the variational approach.The stationary states are analyzed,and it is found that their intensity distribution depends strictly on the ratio of the group-velocity delay strength to the effective total energy. Finally,the propagation of the coupled dark-bright vector solitons is investigated by the numerical method.     

High power, high energy nanosecond pulsed fiber amplifier with a 20-μm-core fiber

We report on a master-oscillator fiber power amplifier (MOPA) system with a core diameter of only 20 μm and 6-m-long Yb³⁺-doped large mode area (LMA) double-clad fiber. Actively Q-switched Nd:YVO₄ laser is used as a seed source of light pluses. The system works at the repetition rate from 40 to 100 kHz. Up to 77 W of amplified radiation with the pulse duration of 17.8 ns at the wavelength of 1064 nm and repetition rate of 40 kHz are generated, corresponding to pulse energy of 1.9 mJ and the slope efficiency of 73.5%. In reported literatures, the 77 W is the highest average power with a 20-μm-core LMA fiber to our knowledge. The stimulate Brillouin scattering (SBS) is observed and investigated.     

Static sensitivity calculation of a novel fiber optic biosensor

A novel structure of fiber optic biosensor and its principle are introduced.The sample is detected in microchannels of several microns diameter in fiber optic biosensors.The relation between the optic fiber tapered angle and the fluorescence incident angle is calculated in signal receiving part.As the sensor is a zero-order system,calculating formula of the static sensitivity is derived.When ZnSe nano-crystalline cluster is used for marking the molecules,the static sensitivity for fiber optic biosensors is calculated. At the same time,the relation between the static sensitivity and the ratio of exciting wavelength to fluorescence wavelength is presented.     

Tunable fiber ring laser employing a Sagnac interferometric filter

Erbium-doped fiber lasers operating in the 1550-nm com-munication window have important applications in wave-length division multiplexing (WDM) communications,true-time-delay (TTD) control of microwave phase-arrayantenna (PAA) systems, and fiber sensors[1-3] .Amongdifferent types of fiber lasers, unidirectional traveling-wave ring laser has the advantages of eliminating backscattering and spatial hole-burning effects, and there-fore has been intensively investigated recently. Opticalfilters…     

High power low-order modes operation of a multimode fiber laser

Coiling technique is used to suppress high-order modes of a large mode area (LMA) double clad multimode fiber.Output powers and beam quality factors M~2 are measured under two different coiling radii.217 W with M~2 of 2.96 can be obtained for coiling radius of 165 mm and 160 W with M2 of 1.38 for 52 mm.The corresponding slope efficiencies are 60% and 48%.With smaller coiling radius,the brightness is 3.4 times as high as that of the larger one.