Search

The excessive emulation of the human visual system and the lack of connection between chromatic data and distortion have been the major bottlenecks in developing image quality assessment. To address this issue, we develop a new no-reference (NR) image quality assessment (IQA) metric that accounts for the impact of pre-attention and spatial dependency on the perceived quality of distorted images. The resulting model, dubbed the Pre-attention and Spatial-dependency driven Quality Assessment (PSQA) predictor, introduces the pre-attention theory to emulate early phase visual perception by refining luminance-channel data. Chromatic data are also processed concurrently by transforming images from RGB to the perceptually optimized SCIELAB color space. Considering that the gray-tone spatial dependency matrix conveys important texture properties that are closely related to visual quality, this matrix, as a mathematical solution for subsequent visual process emulation, is calculated along with its statistical features on both gray and color channels. To clarify the influence of different regression procedures on model output, support vector regression and AdaBoosting Back Propagation (BP) neural networks are adopted separately to train the prediction models. We thoroughly evaluated PSQA on four public image quality databases: LIVE, TID2013, CSIQ, and VCL. The experimental results show that PSQA delivers highly competitive performance compared with top-rank NR and full-reference IQA metrics.

We experimentally demonstrate a passively mode-locking thulium-doped fiber laser based on the combination of the nonlinear polarization rotation (NPR) and the semiconductor saturable absorber mirror (SESAM). In contrast to SESAM mode-locking merely, the fiber lasers based on NPR working together with SESAM have more advantages. By using two mode-locking mechanisms, the nonlinear effect can be enhanced tremendously; then, the threshold of high-order harmonic mode-locking (HML) pulse trains can be decreased, and the pulses width can be compressed. The shapes of the pulses can also be reshaped better, and the HML pulse trains stability can be improved. The high repetition rate of 1.78 GHz is obtained by both NPR and SESAM in the experiment. Because of the variation of the gain-and-loss distribution in the cavity, the output wavelength of mode-locking fiber laser can be tuned from 1839 to 1890 nm, and the multiwavelength HML is also observed in the experiment.

A multi-wavelength Brillouin erbium-doped fiber laser sensor is proposed and investigated experimentally. It is a linear laser cavity multi-wavelength fiber laser, formed by fixing two high-reflectivity Sangac loop mirrors at both ends. We investigate the laser system output characteristics and test the sensor performance for different temperature. Temperature/humidity and reliable linear-cavity fiber laser sensing operation were successfully achieved. Experimental results show that the temperature sensitivity is $$27.15$$ MHz/ °C and the measurement error caused by frequency drift is about $$\pm 0. 2 8 5$$ °C.

The transmission performance of orbital angular momentum(OAM) beam and Gaussian beam in atmospheric turbulent channel was studied and compared experimentally. The beam spreading, pointing error, power jitter and bit error rate of the two beams were measured respectively, the OAM beam loaded with modulated signals and the Gaussian beam were as carrier. The experimental results show that in the atmospheric turbulence channel, compared with Gaussian beam, beam spreading ratio of the OAM beams reduces by 10.5%, variance of power jitter falls 0.13, dispersion circle diameter of the pointing error decreases by 30.4%, and more focused on the distribution of the center of the beam axis. The lowest detection sensitivity of the OAM beam carrier system reaches −28.97 dBm, which improved 2.5 dB compared with that of Gaussian beam. The experimental results verify that OAM beam is less affected by turbulence than Gaussian beam in atmospheric turbulence channel, and the deterioration of beam quality of OAM beam is much less than Gaussian beam with the increase of turbulence intensity. The results of the experiment provide a reference for the development and application of free space laser communication in atmospheric turbulent channel.

We develop a full-reference (FR) video quality assessment framework that integrates analysis of space–time slices (STSs) with frame-based image quality measurement (IQA) to form a high-performance video quality predictor. The approach first arranges the reference and test video sequences into a space–time slice representation. To more comprehensively characterize space–time distortions, a collection of distortion-aware maps are computed on each reference–test video pair. These reference-distorted maps are then processed using a standard image quality model, such as peak signal-to-noise ratio (PSNR) or Structural Similarity (SSIM). A simple learned pooling strategy is used to combine the multiple IQA outputs to generate a final video quality score. This leads to an algorithm called Space–TimeSlice PSNR (STS-PSNR), which we thoroughly tested on three publicly available video quality assessment databases and found it to deliver significantly elevated performance relative to state-of-the-art video quality models. Source code for STS-PSNR is freely available at: http://live.ece.utexas.edu/research/Quality/STS-PSNR_release.zip .

We integrally demonstrate 2 μm mode-locked pulses performances in all-fiber net anomalous dispersion cavity. Stable mode-locking operations with the center wavelength around 1950-1980 nm can be achieved by using the nonlinear polarization rotation structure and properly designing the dispersion management component. Conventional soliton is firstly obtained with a total anomalous dispersion cavity. Due to the contribution of commercial ultra-high numerical aperture fibers, net dispersion is reduced to -0.077 ps2. So that stretched pulse with 19.4 nm optical bandwidth is obtained and the de-chirped pulse-width can reach 312 fs using extra-cavity compression. Under pump power greater than 890 mW, stretched pulse can evolve into noise-like pulse with 41.3 nm bandwidth. The envelope and peak of such broadband pulse can be compressed with up to 2.2 ps and 145 fs, respectively. The single pulse energy of largely chirped stretched and noise-like pulse can reach 1.785 nJ and 1.53 nJ, respectively. Furthermore, extra-cavity compression can also contribute to a significant increase of peak power.

A simple approach to generate stable microwave signals by heterodyning pump light and Stokes lasing light from a dual-wavelength Brillouin fiber laser is proposed and demonstrated. A 10-km-long single mode fiber is used as the Brillouin gain medium, and an ultranarrow linewidth distributed feedback laser is used as Brillouin pump, while a 4-m-long unpumped polarization maintaining erbium-doped fiber and subring cavity suppress unwanted side modes. A 10.7 GHz microwave signal is detected by photodetector and the signal linewidth is about 300 kHz. Signal to noise ratio of the microwave signal is about 50 dB. The power and frequency of microwave signal is highly stable, with almost no fluctuations over the test period. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1513–1516, 2014

A multiwavelength tunable fiber laser operating at 1.9 µm is demonstrated. A 4 m long Tm-doped single-mode fiber is pumped by a 1.57 µm fiber laser. A Sagnac fiber loop is used in the fiber laser cavity as a tunable filter, and the fiber loop consists of a 3-dB coupler, a polarization controller (PC), and a segment of polarization-maintaining fiber. Adjusting the PC state and pump power, multiwavelength laser with wavelength spacing of 2.5 nm 1895–1915 nm is observed. The number of output wavelength can be tuned precisely from one to four by adjusting the PC state. The 3-dB linewidth and side-mode suppression ratio are 0.045 nm and 45 dB, respectively. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:401–403, 2015

We propose an all-fiber source at 3.8 μm with a high Tm-doped fiber as the gain medium pumped by a 1565-nm high-power fiber laser. With a laser diode at 1565 nm amplified by a high power erbium-doped fiber amplifier injecting into a segment of Tm-doped fiber, a fiber laser at 3.8 μm generates. Simultaneously, a second-order laser at 1.9 μm (dual-frequency of 3.8 μm) can be observed clearly. The laser has a threshold pump power of ∼300 mW and generates more than 176 mW continuous-wave output power with 1560 mW pump power. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:848–850, 2014

A novel linear multiwavelength Brillouin-erbium fiber laser based on a nonlinear fiber amplified loop is demonstrated. The nonlinear fiber amplified loop induces wavelength-dependent cavity loss and it provides flexibility on controlling the amount of light reflected and transmitted into and out of the laser's cavity. At the Brillouin pump (BP) power of 25 mW and the 980 nm pump power of 200 mW, 21 output channels with 0.08 nm channel spacing are achieved. We realize the tunable output of multiwavelength through adjusting the polarization controller and the BP wavelength. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1741–1743, 2013