Generation of 64-fs L-band stretched pulses from an all-fibre Er-doped laser.

We demonstrate an L-band all-fibre erbium-doped laser mode locked by nonlinear polarisation rotation and working in the stretched-pulse regime. The use of a single segment of gain fibre with appropriate length and dispersion and a Brewster fibre grating optimised for the L band as an in-fibre polariser enables the generation of pulses at 1.59-µm central wavelength, which can be linearly compressed to 64-fs duration. Numerical simulations of the laser model support our experimental findings. Our laser design gives a route towards low-cost and low-complexity fibre-integrated laser sources for applications requiring L-band ultrashort pulses.

Compact linear polarization spectrometer based on radiation mode shaped in-fiber diffraction grating.

We propose a compact linear polarization spectrometer based on the in-fiber polarization-dependent diffraction grating. The beam profile of radiated light of the grating is shaped to be a Gaussian profile to improve the performance of the spectrometer, where the size of the focused light spot is reduced from 44 um to 33 um with the shaped radiation mode of the grating. Based on the experimental results, the proposed spectrometer can achieve 0.05 nm resolution and 115 nm wavelength responding range from 1495 nm to 1610 nm. To verify the performance of the proposed fiber spectrometer, we measure the transmission spectra of an excessively tilted fiber grating, which has a pair of orthogonal polarization transmission spectra. Compared with the traditional measuring method, the proposed fiber spectrometer integrates the polarizing and spectral analyzing functions in the measuring system and achieves the polarization-sensitive spectral analysis, which shows good wavelength consistency and perfect polarization characteristics.

In-fiber single-polarization diffraction grating based on radiant tilted fiber grating.

In this Letter, we propose an in-fiber single-polarization diffraction grating based on a radiant tilted fiber grating (TFG), in which the s-polarization light could be diffracted from the fiber core to free space with the wavelength-dependent diffraction angle. For the first time, we have presented the theoretical model of angular dispersion of a radiant TFG by employing the Fourier optics analysis method. The angular dispersion of the radiant TFG has been numerically characterized in terms of tilt angle, period, and wavelength. In the experiment, we have measured the diffraction angles and angular dispersion of the radiant TFGs with tilt angles of 41°, 45°, and 47° UV-inscribed into single-mode fiber, where the experimental results matched well with the simulation results. The simulation and experimental results have indicated that the diffraction light of radiant TFGs has a linear polarization state with over 0.99 degree of polarization at the tilt angle range from 41° to 47°.

Low-cost temperature- and strain-insensitive twist sensor based on a hybrid fiber grating structure.

We proposed and experimentally demonstrated a temperature- and strain-insensitive twist sensor based on a hybrid fiber grating structure, in which the hybrid grating structure is constructed with a 45°-tilted fiber grating and a chirped fiber Bragg grating UV-inscribed in a single-mode fiber in series. The sensing performance has been evaluated by experimental and numerical analyses, which are in good consistency. The experimental results show that the hybrid-grating-structure-based twist sensor has a maximum twist sensitivity up to 15.037 dB/rad. Moreover, due to the invariability of the fiber birefringence and the state of polarization of the input light, such sensor has intrinsically low temperature and strain sensitivities of 7.86×10-3 dB/°C and 6.7×10-5 dB/µÎµ, corresponding to the maximum twist measurement error resulting from temperature and strain of 5.2×10-4 rad/°C and 4.5×10-6 rad/µÎµ, respectively.

Manipulating surface-related ferromagnetism in modulation-doped topological insulators.

A new class of devices based on topological insulators (TI) can be achieved by the direct engineering of the time-reversal-symmetry (TRS) protected surface states. In the meantime, a variety of interesting phenomena are also expected when additional ferromagnetism is introduced to the original topological order. In this Letter, we report the magnetic responses from the magnetically modulation-doped (Bi(z)Sb(1-z))2Te3/Cr(x)(Bi(y)Sb(1-y))2Te3 bilayer films. By electrically tuning the Fermi level across the Dirac point, we show that the top TI surface carriers can effectively mediate the magnetic impurities and generate robust ferromagnetic order. More importantly, such surface magneto-electric effects can be either enhanced or suppressed, depending on the magnetic interaction range inside the TI heterostructures. The manipulation of surface-related ferromagnetism realized in our modulation-doped TI device is important for the realization of TRS-breaking topological physics, and it may also lead to new applications of TI-based multifunctional heterostructures.