We present a polarization-maintaining PANDA ring-core fiber (PM-PRCF) characterized by the combination of a ring-core structure with two stress-applying rods. This special fiber design separates the adjacent modes and avoids the cutoff of the higher-order modes, which is a common problem in elliptical core polarization-maintaining few-mode fibers. Using a high-contrast index ring and stress-induced birefringence, the PM-PRCF features support for 10 vector modes, with effective refractive index separations from their adjacent modes >10?4. Broadband performance is investigated subsequently over a wide wavelength range from 1500 to 1630 nm. The proposed fiber is targeted at applications in space-division multiplexing while eliminating the complex multiple-input multiple-output signal processing.

The time-delay signature (TDS) of chaos output in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) subject to fiber Bragg grating (FBG) feedback is investigated experimentally. Autocorrelation function (ACF) and mutual information (MI) are used for quantitatively identifying the TDS of chaos. For various bias currents, the TDS evolution with the feedback strength is different, as the FBG provides wavelength-selective feedback. Furthermore, based on the TDS map of the FBG feedback VCSEL (FBGF-VCSEL) in the parameter space of feedback strength and bias current, the optimal TDS suppression regions, where the dominant polarization mode of FBGF-VCSEL locates at the edge of the main lobe of FBG reflection spectrum, have been determined. Finally, for comparative purpose, the TDS of chaos in mirror feedback VCSEL (MF-VCSEL) also has been presented, and the results show that an FBGF-VCSEL possesses better TDS suppression performance than an MF-VCSEL.(XDJK2016D060).

In this work, we study the photonic band of cumulative Fibonacci lattices, of which the structure is composed of all generated units in a Fibonacci sequence. The results are compared with distributed Bragg reflector (DBR) structures with the same numbers of layers. Photonic bandgaps are found at two characteristic frequencies, symmetrically separated from the central bandgap in the DBR counterpart. Field amplitude and phase distribution in the Fibonacci lattice indicates an interferential origin of the bandgaps. Fourier transform on the refractive index profile is carried out, and the result confirms a determinate long-range periodicity that agrees well with the photonic band structure.Province of China (Q2015002).

We propose theoretically and verify experimentally a method of combining a q-plate and a spiral phase plate to generate arbitrary vector vortex beams on a hybrid-order Poincaré sphere. We demonstrate that a vector vortex beam can be decomposed into a vector beam and a vortex, whereby the generation can be realized by sequentially using a q-plate and a spiral phase plate. The generated vector beam, vortex, and vector vortex beam are verified and show good agreement with the prediction. Another advantage that should be pointed out is that the spiral phase plate and q-plate are both fabricated on silica substrates, suggesting the potential possibility to integrate the two structures on a single plate. Based on a compact method of transmissive-type transformation, our scheme may have potential applications in future integrated optical devices.

In this work, TeO0.7 thin films were prepared by the reactive magnetron-controlling sputtering method. Complex gray-scale patterns were successfully fabricated on TeO0.7 thin films through the laser direct writing method. The structural origin of TeO0.7 thin film was investigated for gray-scale pattern formation. It is found that multiple gray-scale levels are dependent on the “virtual” bandgap energy of TeO0.7 thin films. The bandgap energy changes lead to refractive index and reflectivity difference. Thus, gray-scale tones can be formed. By accurately controlling laser energy, various “virtual” bandgaps can be generated in TeO0.7 thin films, and colorful gray-scale levels can be formed. Experimental results indicate that TeO0.7 thin film can be used as micro/nano image writing material.

Through anisotropic Ag overgrowth on the surface of Au nanobipyramids (AuNBPs), high-purity and sizecontrolled Ag nanorods (Au/AgNRs) are obtained by a simplified purification process. The diameters of the Au/AgNRs are determined by the size of the as-prepared AuNBPs, and the lengths of the Au/AgNRs are tunableusing different amounts of Ag precursor in the growth solution. Surface-enhanced Raman scattering (SERS) studies using Rhodamine-6G (R6G) as a test molecule indicate that the Au/AgNRs have excellent sensing potential. The tunable optical properties and strong electromagnetic effect of the Au/AgNRs, along with their superior SERSsignal enhancement, show that Au/AgNRs are promising for further applications in plasmon sensing and biomolecular detection.of Nanjing Institute of Technology (CKJB201411, QKJB201409, YKJ201538); Qing Lan Project and Priority Academic Program Development of Jiangsu Higher Education Institutions.

Two-dimensional (2D) graphite carbon nitride (g-C3N4) nanosheets have been successfully used as a saturable absorber (SA) in a passively Q-switched Nd:LLF laser at 1.3 μm for the first time, to the best of our knowledge. Under an incident pump power of 9.97 W, the shortest pulse duration of 275 ns was acquired with output power of 0.96 W and pulse repetition rate of 154 kHz, resulting in a pulse energy of 6.2 μJ. In addition, the saturable absorption behaviors of zero-dimensional 12 nm g-C3N4 nanoparticles (g-C3N4-NPs) and three-dimensional ordered mesoporous g-C3N4 (mpg-C3N4) were also observed, although their morphology and structure were quite different from 2D g-C3N4. The experimental results introduce the potential application of g-C3N4 nanomaterials as SAs in Q-switched lasers.

We have experimentally studied the mode-locking dynamics of a polarization-maintaining figure-of-eight laser which has a semiconductor optical amplifier as gain medium. Self-starting mode-locking at the fundamental repetition rate of 18 MHz is obtained at the lasing threshold, and further increasing the bias current leads to the progressive emission of additional optical pulses in each round trip and eventually to mode-locked emission at increasingly high harmonics of the fundamental repetition rate, up to 2.45 GHz. The intensity autocorrelation of the amplified mode-locked pulses has a full width at half-maximum duration of 382 fs, which corresponds to a pulse duration of 247 fs.

We show how quantum entangled biphoton states can be used to realize ghost scattering, a nonlocal scheme to obtain scattering information of an unknown object through the correlation measurement of the scattering photons in two different optical paths. We present a framework to describe the biphoton ghost scattering process from the T-matrix formula of the scattering theory. We find the scattering information of a test object can be retrieved from either the test arm or the reference arm. By adjusting the biphoton states, the ghost scattering patterns may be varied from the scattering pattern of the object in the test arm to the object in the reference arm.

By simultaneously employing both an electro-optic modulator and carbon nanotube saturable absorber (CNT-SA) in a dual-loss modulator, a subnanosecond single mode-locking pulse underneath a Q-switched envelope with high peak power was generated from a doubly Q-switched and mode-locked (QML) Nd:Lu0.15Y0.85VO4 laser at 1.06 μm for the first time, to our knowledge. CNTs with different wall structures—single-walled CNTs (SWCNTs), double-walled CNTs (DWCNTs), and multi-walled CNTs (MWCNTs)—were used as SAs in the experiment to investigate the single mode-locking pulse characteristics. At pump power of 10.72 W, the maximum peak power of 1.312 MW was obtained with the DWCNT.

We demonstrate that ferroferric-oxide (Fe3O4) nanoparticles exhibit nonlinear saturable absorption property at 1.55 μm, and fabricate two filmy saturable absorbers by embedding the nanoparticles into a polyvinyl alcohol (PVA) film or polyimide (PI) film separately. In the Fe3O4-PVA (Fe3O4-PI) Q-switched fiber laser, the pulse repetition rate increases from 8.5 kHz (5.5 kHz) to 28 kHz (49 kHz) and the pulse duration decreases from 23.5 μs (47 μs) to 6 μs (3.5 μs) by varying the pump power from 25 mW (23 mW) to 150 mW (650 mW). Experiment results indicate that PI-based saturable absorbers can afford larger powers than PVA-based saturable absorbers, which can be attributed to the higher fusion point of the PI film. The Fe3O4-PI saturable absorber exhibits features of high damage threshold, low cost, and good flexibility, which could be applied in fields of near-infrared pulse generation and frequency conversions.