Zonglin Liu

High power 1018 nm ytterbium doped fiber laser with an output power of 309 W

In this letter, we report on a high power 1018 nm ytterbium doped fiber laser. The unwanted gain near 1030 nm is suppressed by appropriately selecting the specifications of YDF. A record output power of 309 W is obtained, with an efficiency of 71%.

Mid-IR supercontinuum generation in Tm/Ho codoped fiber amplifier

We demonstrate all-fiber-integrated mid-IR supercontinuum generation in a Tm/Ho codoped fiber amplifier, where the codoped fiber is both nonlinear and a gain medium. The observed supercontinuum spectrum ranges from 1760 to 2600 nm and has an extremely high spectral flatness, with a 3 dB bandwidth ~635 nm (from 1845 to 2480 nm). In the Tm/Ho codoped fiber, as well as the nonlinear optical processes, the Tm3+ and Ho3+ ions also play important roles in mid-IR supercontinuum generation. The 3F4–3H6 transition for Tm3+ radiates a laser in the 1.8–2.1 μm spectral region, the 5I7–5I8 transition for Ho3+ radiates a laser around 2.1 μm and the 3H4–3H5 transition for Tm3+ radiates a laser in the 2.2–2.5 μm spectral region. All of these energy level transitions contribute towards supercontinuum generation.

Passive Coherent Polarization Beam Combination of a Four-Fiber Amplifier Array

We present what we believe to be a new architecture for coherent beam combination of a fiber amplifier array. Four polarization-maintained fiber amplifiers are passively coherent polarization beam combined by using an optical feedback in a ring cavity. Experimental results verify that the architecture is robust and effective. The combining efficiency of the whole system can be as high as 91%, and the phase noise can be suppressed effectively. We believe that the configuration presented in this paper is a promising approach for high-power laser combination without degrading the beam quality of the coherently combined beam.

Iteration Interleaving--Based SIMD Lane Partition

The efficacy of single instruction, multiple data (SIMD) architectures is limited when handling divergent control flows. This circumstance results in SIMD fragments using only a subset of the available lanes. We propose an iteration interleaving--based SIMD lane partition (IISLP) architecture that interleaves the execution of consecutive iterations and dynamically partitions SIMD lanes into branch paths with comparable execution time. The benefits are twofold: SIMD fragments under divergent branches can execute in parallel, and the pathology of fragment starvation can also be well eliminated. Our experiments show that IISLP doubles the performance of a baseline mechanism and provides a speedup of 28% versus instruction shuffle.

Gain-switched thulium-doped fiber laser with ultra-wide tuning range

We demonstrate an all-fiber gain-switched thulium-doped fiber laser (TDFL) producing nanosecond pulses with variable wavelength in the 2 μm waveband. The laser features tunable operation in an ultra-wide spectral region of 1765 – 2055 nm (24 THz). The nearly 300 nm tunability doubles the record tuning range of existing gain-switched fiber lasers, and to the best of our knowledge, presents the broadest tuning range that has been reported for a monolithic pulsed rare earth doped fiber laser to date. The TDFL can operate at a repetition rate of 5 – 100 kHz with a pulse width as short as ~200 ns. A modest compromise in the tuning range allows pulse width reduction to sub-100 ns.

Achieving Memory Access Equalization Via Round-Trip Routing Latency Prediction in 3D Many-Core NoCs

3D many-core NoCs are emerging architectures for future high-performance single chips due to its integration of many processor cores and memories by stacking multiple layers. In such architecture, because processor cores and memories reside in different locations (center, corner, edge, etc.), memory accesses behave differently due to their different communication distances, and the performance (latency) gap of different memory accesses becomes larger as the network size is scaled up. This phenomenon may lead to very high latencies suffered from by some memory accesses, thus degrading the system performance. To achieve high performance, it is crucial to reduce the number of memory accesses with very high latencies. However, this should be done with care since shortening the latency of one memory access can worsen the latency of another as a result of shared network resources. Therefore, the goal should focus on narrowing the latency difference of memory accesses. In the paper, we address the goal by proposing to prioritize the memory access packets based on predicting the round-trip routing latencies of memory accesses. The communication distance and the number of the occupied items in the buffers in the remaining routing path are used to predict the round-trip latency of a memory access. The predicted round-trip routing latency is used as the base to arbitrate the memory access packets so that the memory access with potential high latency can be transferred as early and fast as possible, thus equalizing the memory access latencies as much as possible. Experiments with varied network sizes and packet injection rates prove that our approach can achieve the goal of memory access equalization and outperforms the classic round-robin arbitration in terms of maximum latency, average latency, and LSD1. In the experiments, the maximum improvement of the maximum latency, the average latency and the LSD are 80%, 14%, and 45% respectively.

Average Spreading of Apertured Laser Beams With Beam Distortions In Non-Kolmogorov Turbulence

Abstract RMS beam width of an apertured laser beam with beam distortions in non-Kolmogorov turbulence is derived with the help of statistical optics methods and extended Huygens-Fresnel principle. Variations of the beam width of an apertured beam with amplitude modulations and phase fluctuations propagating in non-Kolmogorov turbulence are studied in detail. Numerical examples reveal that the beam width mainly depends on the phase fluctuations and the truncations as well as the exponent value, the inner- and outer-scale parameters of the non-Kolmogorov turbulence. It is shown that phase fluctuations can vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the inner- and outer-scale parameters. It is interesting to find that the effects of the phase fluctuations are negligible as long as the phase fluctuations are controlled under a certain level, i.e., a > 0.03 for the situation considered in the paper. Thus, there exists a phase fluctuation tolerance, which is meaningful for practical applications.