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Accepted papers to appear in an upcoming issue

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Lower the energy consumption in silicon photonic devices and systems

Zhiping Zhou, Bing Yin, Qingzhong Deng, Xinbai Li, and Jishi Cui

Doc ID: 238414 Received 20 Apr 2015; Accepted 23 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: We review the current silicon photonic devices and their performance in connection with the energy consumption. Four classes of critical issues are identified to lower energy consumption in devices and systems: reducing the influence of the thermo-optic effect, increasing the wall-plug efficiency of lasers on silicon, optimizing energy performance of modulators, and enhancing the sensitivity of photodetectors. Major findings are: 1) MZI-based devices can achieve athermal performance without any extra energy consumption while microrings do not have an efficient passive athermal solution; 2) While direct bonded III-V-based Si lasers can meet system power requirement for now, hetero-epitaxial grown III-V QD lasers are very competitive and may be a better option for the future; 3) Resonant modulators are promising for low energy consumption operation even when the power to stabilize their operation is included, especially coupling modulators; 4) Benefiting from high sensitivity and low cost, Ge/Si APD is the most promising photodetector and can be used to effectively reduce the optical link power budget. These analyses and solutions will contribute to further lowering the energy consumption to meet the aggressive energy demands in future systems.

Effect of Packing Density and Packing Geometry on Light Extraction of III-Nitride Light-Emitting Diodes with Microsphere Arrays

Peifen Zhu and Nelson Tansu

Doc ID: 235348 Received 27 Feb 2015; Accepted 17 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: The Finite-Difference Time-Domain (FDTD) method was employed to calculate light extraction efficiency of thin-film flip-chip InGaN/GaN quantum well (QW) LEDs with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays were investigated by focusing on the effect of the packing density, packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having hexagonal and close-packed monolayer microsphere arrays configuration for achieving optimum extraction efficiency, which translated into 3.6 times enhancement in light extraction compared that for planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns were also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.

Mode converter based on dual-core all-solid photonic bandgap fiber

Wang Yuan, Yongjun Zhang, Shanyong Cai, Mingying Lan, Song Yu, and Wanyi Gu

Doc ID: 239689 Received 08 May 2015; Accepted 15 Jun 2015; Posted 19 Jun 2015  View: PDF

Abstract: In this paper, we present a mode selective coupler based on a dual-core all-solid photonic bandgap fiber (ASPBGF). Because of its all solid property, mode converter based on AS-PBGF is easier to splice to other fibers than that based on air-hole photonic crystal fiber (PCF). Mode conversions between LP 01 mode and LP11 mode, between LP01 mode and LP21 mode, between LP01 mode and LP02 mode are obtained at the wavelength λ = 1550 nm. The 3 dB wavelength bandwidth of these mode converters are 47.8 nm, 20.3 nm and 20.3 nm respectively, which is better than that based on conventional air-hole PCF.

Silicon and hybrid silicon photonic devices for intra-datacenter applications: state of the art and perspectives

Andrew Poon, Yu Li, Yu ZHANG, and Lei Zhang

Doc ID: 237213 Received 03 Apr 2015; Accepted 05 Jun 2015; Posted 26 Jun 2015  View: PDF

Abstract: In this review, we give a bird’s eye view of the state of the art of and our perspectives on silicon and hybrid silicon photonic devices for optical interconnects in datacenters. After a brief discussion of the key requirements for intra-datacenter optical interconnects, we propose a wavelength-division multiplexing (WDM)-based optical interconnect for intra-datacenter applications. Following our proposed interconnects configuration, the bulk of the review emphasizes on the recent developments concerning on-chip hybrid silicon microlasers and WDM transmitters, and silicon photonic switch fabrics for intra-datacenters. For hybrid silicon microlasers and WDM transmitters, we outline remaining challenges and key issues towards realizing low power consumption, direct modulation, and integration of multi-wavelength microlaser arrays. For silicon photonic switch fabrics, we review various topologies and configurations of high-port-count N-by-N switch fabrics using Mach-Zehnder interferometers and microring resonators as switch elements, and discuss their prospects towards practical implementations with active reconfiguration. For the microring-based switch fabrics, we review recent developments of active stabilization schemes at the sub-system level. Lastly, we outline several grand challenges and problems for silicon and hybrid silicon photonics to meet for intra-datacenter applications and propose potential solutions.

Quantum dot lasers for silicon photonics

Alan Liu, Arthur Gossard, John Bowers, sudharsanan srinivasan, and Justin Norman

Doc ID: 235818 Received 03 Apr 2015; Accepted 21 May 2015; Posted 04 Jun 2015  View: PDF

Abstract: We review recent advances in the field of quantum dot lasers on silicon. A summary of device performance, reliability, and comparison with similar quantum well lasers grown on silicon will be presented. We consider the possibility of scalable, low SWaP (size, weight, and power) nanolasers grown on silicon enabled by quantum dot active regions.

Modification of wettability of stainless steel by picosecond laser surface microstructuring

Zongjie Bao, Quanzhong Zhao, Yang Zhang, and Cheng-Wei Wang

Doc ID: 233624 Received 03 Feb 2015; Accepted 20 May 2015; Posted 26 May 2015  View: PDF

Abstract: We report on the modification of wettability of stainless steel by picosecond laser surface microstructuring in this paper. Compared with traditional methods, picosecond laser induced surface modification provides a fast and facile method for the surface modification without chemical damage and environmental pollution. After treated by 100 ps laser pulses, microstructures are fabricated on the stainless steel sample surface, contributing to the increasing of contact angle from 88° to 105°, which realizes a transformation from hydrophilicity to hydrophobicity. The morphological features of fabricated microstructures are characterized by scanning electron microscope and optical microscope.

Theoretical investigation on core modes cutoff condition for tapered multi-core fiber

Xuanfeng Zhou, Zilun Chen, Hang Zhou, and Jing Hou

Doc ID: 234093 Received 06 Feb 2015; Accepted 19 May 2015; Posted 22 May 2015  View: PDF

Abstract: Core mode cutoff is a very useful concept not only for a tapered single-core fiber (SCF) but also for a tapered multi-core fiber (MCF) to realize cladding mode transmission. In this paper, cutoff conditions of either core mode for tapered SCFs or super-modes for MCFs are theoretically investigated. Rigorous analytical formulas are derived for the modes of SCF by three-layer waveguide (TLW) model and an approximation formula of cutoff condition is given for the LP01 mode. The super-modes of MCFs are analyses by coupling mode theory and the cutoff condition is calculated by a numerical method. Simulation results show that the in-phase super-mode of MCFs has a similar cutoff condition with that of SCF. Based on this property, a convenient approximate formula is given to estimate the cutoff condition of the in-phase super-mode for tapered MCFs.

Propagation of high power fiber laser with high order mode content

Rumao Tao, Long Huang, Pu Zhou, Lei Si, and Zejin Liu

Doc ID: 235522 Received 03 Mar 2015; Accepted 11 May 2015; Posted 13 May 2015  View: PDF

Abstract: Propagation characteristics of high power fiber laser with high order mode (HOM) content are studied numerically for the first time. The effect of HOM on the propagation property is evaluated by the power in the bucket (PIB) metric. It is shown that PIB is mainly dependent on HOM content rather than the relative phase between fundamental mode and HOM. The PIB in free space is more than 80% when the power in the HOM is controlled to be less than 50% at 5km. The relative phase impacts the peak position and concentration of the far-field intensity distribution. If adaptive optics system is used to correct the peak intensity deviation, the results indicate that there exists an optimization of PIB as relative phase increases. Such effect is weakened when propagating in turbulence. Compared to the laser beams without HOM, laser beams with HOM content are less influenced by the turbulence and can reduce average intensity fluctuation. The results may be useful in design of high power fiber laser system.

73 nJ、109 fs Yb-doped fiber laser at 19 MHz repetition rate in amplifier similariton regime

Yizhou Liu, Yifan Cui, Jian Zhang, Aimin Wang, and Zhigang Zhang

Doc ID: 232649 Received 20 Jan 2015; Accepted 02 Apr 2015; Posted 15 Apr 2015  View: PDF

Abstract: We report femtosecond pulse generation in an amplifier similariton oscillator and a pre-chirped fiber amplifier system. The final output power is 1.4 W fundamental repetition rate is 19.1 MHz after a single state fiber amplifier. The pulse width is 109fs.

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