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Magnetic properties of Cu-doped LaMn1-xCuxO3 (x=0.05-0.30) systems are carefully studied in the temperature range of 2–300 K. A visible unexpected drop is observed in the ac susceptibility and the zero-field cooled dc magnetization curves for the dilute x ≤0.10 near 100K, which depends on the measuring frequency and magnetic field. Measurements on frequency dependence of ac susceptibility, observation of magnetic relaxation, and the existence of critical field indicate that the anomaly can be attributed to the domain wall pinning effects. This is directly proven by the results of ball milled nano-sized powder counterparts compared with the bulk materials.

Birefringence of a microstructure fibre with irregular structures is investigated using the finite element method. The birefringence of each sample is statistically analysed, and the relation between the birefringence and the irregular structure of the microstructure fibre is derived. The results indicate that the irregular structure of the symmetrical microstructure fibre result in the birefringence which is more strongly affected by disorder of air holes than the nonuniformity. Moreover, lower birefringence can be obtained with smaller air holes and larger pitch in the fibre structure.

Fibre Bragg gratings (FBGs) are inscribed in homemade microstructured fibres by the standard phase mask method. Enhanced couplings between the forward fundamental mode and backward cladding modes are obtained. The mode coupling and spectral characteristics are investigated experimentally. The cladding mode resonances can be affected by filling active materials into the air holes, which will be useful for the implementation of tunable photonic devices in optical fibre communication and sensing systems.

Enhancing coherent combining efficiency via choosing appropriate lasing wavelength in a Michelson compound cavity based on two 3?dB fibre loop mirrors and one fibre Bragg grating (FBG) has been experimentally demonstrated. The FBG with 4.5% reflectivity is replaced at the cleaved facet with 4% Fresnel reflection. A high coherent combining efficiency of 93.5% is obtained when the FBG with central wavelength at 1559.845?nm is introduced into the cavity, while it is only 90.1% combining efficiency with the FBG at central wavelength 1557.830?nm. In comparison with other reports, the proposed compound-cavity laser has the advantage of needless tuning FBG to obtain the coherent condition, and it is facile to ascertain the seemly wavelength lasing for a Michelson compound cavity.

A dual-wavelength laser system with wideband tunable wavelength spacing and more than 2 W output power is proposed and demonstrated. The operation principle of the laser system is based on the saturation gain characteristic of a cladding-pumped Er3+/Yb3+ co-doped fibre amplifier combining with a wideband tunable fibre laser with flat power spectrum. The tuning range of the wavelength spacing is continuous within a 35 nm spectral range, and the power difference between both lasing wavelengths can be easily adjusted and controlled by a variable optical attenuator. The total output power can approximately keep unchangeable when the wavelength spacing and the power difference between both lasing wavelengths are continuously tuned and changed. The maximum total output power of the laser system is about 2.22 W.

Novel highly birefringent photonic bandgap fibres (PBGFs) are obtained by filling of a high index material in the air holes of total internal reflection birefringent photonic crystal fibres. The effect of the filling high index material on the transmission characteristics has been theoretically investigated. The photonic bandgap has been achieved by using plane-wave method. Moreover, the phase and group modal birefringence have been studied by a full-vector finite-element method. Numerical results show that very high group and phase modal birefringence with magnitude of order of 10−2 and 10−3 has been respectively acquired, which is much higher than those of the non-filled fibres. Furthermore, strong coupling between surface modes and the fundamental modes has been found in the bandgap of the birefringent PBGFs, whose effect on the birefringence and confinement loss has also been discussed.

A passive Q-switched large-mode-area Yb-doped fibre laser is demonstrated using a GaAs wafer as the saturable absorber. A high Yb doping concentration double-clad fibre with a core diameter of 30 μm and a numerical aperture of 0.07 is used to increase the laser gain volume, permitting greater energy storage and higher output power than conventional fibres. The maximum average output power is 7.2 W at 1080 nm wavelength, with the shortest pulse duration of 580 ns and the highest peak power of 161 W when the laser is pumped with a 25 W diode laser operating at 976 nm. The repetition rate increases with the pump power linearly and the highest repetition rate of 77 kHz is obtained in the experiment.

We propose and demonstrate a new concept of stable narrow-line-width and close wavelength spacing dual-wavelength lasing in an Er-doped fibre ring laser (EDFRL) by cleaving the spectrum with a wavelength-selective component in the EDFRL. A fibre loop mirror (FLM) combining with a polarization controller (PC) acts as the cleaver. The cleaver can produce a fine pectinate spectrum. By adjusting the PC, the fine pectinate spectrum can be so changeable that cleaving the spectrum of a fibre Bragg grating (FBG) into two parts. As a result, we obtain the dual-wavelength fibre lasering with a bandwidth of only 0.03 nm and a wavelength spacing of only 0.07 nm. Furthermore, the laser can also perform stable switchable single wavelength or stable different-bandwidth dual-wavelength by carefully adjusting the PC at room temperature.

A polarization-independent all-fibre comb filter with dynamically halved channel spacing is proposed. The filter is based on high-birefringent fibre Sagnac interferometers and its channel spacing can be dynamically halved by turning on an optical switch. A good agreement between the numerical simulation and the experimental results is achieved.

A high-power Er3+/Yb3+-codoped double-cladding all-fibre amplifier was successfully demonstrated and experimentally investigated. The amplifier could be operated with a maximum output power of 2.18 W and 2.11 W at 1541 nm and 1550 nm wavelengths, respectively, when the maximum pump power was 6.07 W. The power conversion efficiency was up to 35.6% and 34.4% at the two wavelengths, respectively. The output power and the gain were greater than 2.00 W and 20.0 dB, respectively, in the wavelength range from 1539 nm to 1565 nm for 20.0 mW input signal power. The gain fluctuation and the noise figure around 1550 nm wavelength were less than 0.3 dB and 6.0 dB, respectively.

Multiwavelength operation of a linear cavity erbium-doped fibre laser (EDFL) is proposed and demonstrated. A 3-dB fibre loop mirror and a high birefringence (HiBi) fibre loop mirror are utilized as the cavity reflectors. By utilizing the wavelength-dependent polarization rotation induced by the HiBi fibre loop mirror and by using a fibre polarizer to control the intracavity polarization state, the polarization states of different wavelengths are diversified. Therefore, the polarization hole burning (PHB) effect has been greatly enhanced and the homogeneous broadening of erbium-doped fibre is suppressed to a large extent. By simply tuning a polarization controller, we experimentally obtained simultaneous lasing of four and five wavelengths with wavelength spacing of ~1.8 nm and less than 2 nm at room temperature, respectively. The repeated scans show that all of these lasers have good stability.

All-fibre high power erbium–ytterbium co-doped double clad fibre lasers are proposed and demonstrated. By using different back-cavity mirrors, the different double clad fibre lasers are constructed. It is experimentally found that the output behaviour of laser can be controlled by a back-cavity mirror. The lower the reflectivity of the back-cavity mirror, the higher the output power and the high the slop efficiency. The maximum output power is about 1.6 W and the slop efficiency is 27.6%.

A tunable Yb-doped double-clad fibre (YDCF) laser by tuning the fibre Bragg grating (FBG) is successfully demonstrated. The FBG was fabricated in the YDCF directly, resulting in low splicing loss and compact configuration. A continuous tuning range of 15.6 nm from 1046.6 nm to 1062.2 nm is achieved. The laser linewidth is smaller than 0.1 nm in the whole tuning range. A maximum output power 117 mW is achieved when the pump power is 332 mW. The laser oscillation is quite stable in the whole operation.

A polarization controlled switchable multiwavelength erbium-doped fibre laser with overlapping cavities is proposed. The wavelengths are specified by two Bragg gratings in polarization-maintaining PANDA fibre. The proposed laser can be designed to be operated in stable four-wavelength or wavelength switching modes only by simple adjustment of two polarization controllers. For wavelength switching, four single-wavelength, six dual-wavelength, and four three-wavelength operations have been obtained. The minimum wavelength spacing is only about 0.4 nm.

A simple actively mode-locked fibre ring laser is proposed and successfully demonstrated to generate switchable dual-wavelength picosecond pulses using a Bragg grating in a polarization-maintaining fibre. The wavelength spacing specified by the grating is only 0.52 nm. The proposed laser can be made to operate in stable dual-wavelength or switch between wavelengths at room temperature, by simple adjustment of a polarization controller.

A novel Yb3+-doped double-clad fibre laser based on a double-clad fibre Bragg grating is presented. The fibre Bragg grating, as the output mirror, has been formed in Yb3+-doped double-clad fibre with the phase-mask method. When the input pump power is 2.8 W, the maximum laser output power is 570 mW, with

A novel Yb3+-doped four-wavelength double clad fibre laser based on a Fabry-Perot filter, and pumped by a 976 nm laser diode is presented. Its output laser wavelengths are 1085, 1090, 1095 and 1010 nm, respectively. The laser exhibits 0.32 nm line-width, 1.5 W laser output power, 40 dB signal-to-noise ratio and 66% slope efficiency.

We study the pulsed laser ablation of wurtzite gallium nitride (GaN) films grown on sapphire, using the femtosecond laser beam at a central wavelength of 800 nm as the source for the high-speed ablation of GaN films. By measuring the backscattered Raman spectrum of ablated samples, the dependence of the ablation depth on laser fluence with one pulse was obtained. The threshold laser fluence for the ablation of GaN films was determined to be about 0.25 J/cm2. Laser ablation depth increases with the increasing laser fluence until the amount of removed material is not further increased. The ablated surface was investigated by an optical surface interference profile meter.

A novel and simple approach of temperature-independent stress and displacement bidirectional sensing tuned by an applied bilateral cantilever beam is proposed and demonstrated. The 3dB bandwidth of fibre gratings is linear with respect to the stress and displacement in the tuning range of 16 nm. The sensing sensitivities of the stress and displacement are 5.76 nm/N and 0.941 nm/mm, respectively.

A novel Yb3+-doped double-clad silica fibre with rectangular inner cladding was designed and developed by using the modified chemical vapour deposition process, solution-doping and optical machining all together. The dimensions of the inner cladding are 100×70 µm, and Yb3+-doped concentration in the core is about 0.24 wt.%. The operation of the fibre laser pumped by inner cladding is reported. The threshold of the laser is 34 mW. When the pump power launched is 141 mW, the laser output is 84 mW at the wavelength 1075.6 nm, and the slope efficiency is 77%.

A novel four-wavelength all-fibre laser based on fibre Bragg gratings is presented. The four wavelengths are 1555.8, 1556.6, 1557.4 and 1558.2 nm, respectively. Each output laser is 1 mW in power. The suppression ratio between adjacent wavelengths is >30 dB. The laser was applied in a wavelength division multiplexing (WDM) system and the 100 km transmission of 1.2 Gb/s nonreturn-to-zero code, 1.2 Gb/s return-to-zero code, 2.5 GHz analogue signal and 5 GHz analogue signal was realized with it.

Starting from our definition of apodization profile functions, we discover the optimal profiles and the characteristics of defined apodization functions in sidelobe suppression. It is shown by numerical analysis that the optimal grating length is 45?mm to compensate for dispersion induced by 100?km fibres and the smoothness of the ripples in time-delay characteristics is related to the defined parameters.

We have measured the power dependence of the photoluminesence spectra from a set of strained InxGa1-xAs/GaAs single quantum wells. The result shows that the excitation power has important effect on the carrier recombination processes. When the power increases from 0.5 to 14 mW, the photoluminescence from the barrier becomes more intense than that from the well and the trapping efficiency decreases. At high excitation level, the ratio of the radiative recombination rate to the nonradiative recombination rate of the barrier increases ten times than that at lower excitation level, while it only doubles for the well.

Moire fibre Bragg gratings are made in a single mode fibre and a polarization-maintaining fibre respectively, using an excimer KrF laser and a phase mask. Two gratings are written at the same location of the optical fibre. The wavelength spacing can be finely tuned from 0 to 1.86 nm by straining the optical fibre during UV illumination.

We propose a simple configuration for dual-wavelength operation in an actively mode-locked fibre ring laser with fibre Bragg gratings. We experimentally demonstrate simultaneously mode-locked operation with two wavelengths at different repetition rates: one is harmonically mode-locked and the other is rational harmonically mode-locked.

A short-cavity Er/Yb-P/Al/Si co-doped fibre grating laser is demonstrated, with a pair of fibre Bragg gratings whose central resonant wavelengths are around 1551 nm and the reflectivities are 10.5 and 15 dB. The threshold value is about 48 mW and the slope efficiency is 1.1%. The signal-to-noise ratio is 59 dB, and the output central wavelength is 1550.94 nm. A peak power of 1.112 mW at a pump power of 80 mW has been achieved.

We have measured the time-resolved photoluminescence spectra of several InxGa1-xAs/GaAs single quantum well samples at 77K. The different temporal behaviors of the photoluminescence (PL) from the GaAs layer and the excitonic emission from the InxGa1-xAs well were obtained. The lifetime for the exciton in the InxGa1-xAs well were determined to be 110-170ps. The trapping efficiency of the well to the carriers was about 80%.