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Accepted papers to appear in an upcoming issue

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Decaying evolution dynamics of the double-pulse mode-locking

Guomei Wang, GuangWei Chen, Wenlei Li, Chao Zeng, and Huiran Yang

Doc ID: 328885 Received 24 Apr 2018; Accepted 18 Jun 2018; Posted 21 Jun 2018  View: PDF

Abstract: Taking advantage of the dispersive Fourier-transform (DFT) technique, the decaying evolution processes of double-pulse mode-locking in a single-walled carbon nanotube (SWNT) based Er-doped fiber laser are demonstrated in detail for the first time, to our knowledge. The decaying dynamics of double-pulse mode-locking state are analyzed in both the spectral and temporal domains. We reveal that there are two different evolutionary types of both pulses in one cluster during the decaying processes of double-pulse mode-locking state: disappearing simultaneously and vanishing one by one. In addition, the spectral evolution patterns of the special double-pulse state (i.e., bound state) are extremely distinct at different down-rate of the pump power.

Chirped coupled ridge waveguide quantum cascade laser arrays with very stable single lobe far-filed pattern

yue zhao, jinchuan zhang, chuanwei liu, Ning Zhuo, Shenqiang Zhai, lijun wang, Junqi Liu, Shuman Liu, Liu Fengqi, and Zhanguo Wang

Doc ID: 326528 Received 22 Mar 2018; Accepted 13 Jun 2018; Posted 15 Jun 2018  View: PDF

Abstract: Power scaling in broad area quantum cascade laser (QCL) always leads to the deterioration of the beam quality with an emission of multiple lobes far-field pattern. In this letter, we demonstrated a coupled ridge waveguide QCL arrays consisting of five elements with chirped geometry. In-phase mode operation is secured by managing supermode loss by properly designed geometries of ridges. Single-lobe lateral far-field with a nearly diffraction limited beam pattern was obtained in the whole current dynamic range. The fabrication of the device used the wet and dry etching method and the regrowth technique of the InP: Fe insulation layer and InP: Si waveguide layer. Such a structure has a potential to optimize the beam quality of the recently reported high power broad area QCL with reduced cascade number.

Orthogonally polarized single-longitudinal-mode operation in a dual-wavelength monolithic Nd:YAG laser at 1319 nm and 1338 nm

Yung-Fu Chen, H. P. Cheng, Yu Cheng Liu, T. L. Huang, and H. C. Liang

Doc ID: 325827 Received 14 Mar 2018; Accepted 13 Jun 2018; Posted 13 Jun 2018  View: PDF

Abstract: The single-longitudinal-mode operation with single-wavelength emission at 1319 nm and dual-wavelength emission at 1319 and 1338 nm are realized respectively by utilizing two types of coating specification for monolithic Nd:YAG lasers. Each longitudinal mode consists of two orthogonally polarized modes. Experimental results reveal that the frequency splitting between two orthogonal polarizations can be tuned by changing the external mechanical force applied on the Nd:YAG crystal. The beat frequency can be linearly varied from 181.3 MHz to 1.64 GHz. The beat frequencies between two orthogonally polarized modes at 1319 nm and 1338 nm are found to be very close and its difference can be changed from 4.5 MHz to 19.9 MHz by increasing the external mechanical force from 1.6 N to 15 N.

Generation of 84-fs pulses from a mode-locked Tm:CNNGG disordered garnet crystal laser

Zhongben Pan, Yicheng Wang, Yongguang Zhao, Hualei Yuan, Xiaojun Dai, Huaqiang Cai, Ji Bae, Sun Young Choi, Fabian Rotermund, Xavier Mateos, Josep Maria Serres, Pavel Loiko, Uwe Griebner, and Valentin Petrov

Doc ID: 327797 Received 06 Apr 2018; Accepted 08 Jun 2018; Posted 13 Jun 2018  View: PDF

Abstract: A mode-locked laser based on a single-walled carbon nanotube saturable absorber (SWCNT-SA) is demonstrated, operating at a central wavelength of 2018 nm using a Tm:CNNGG disordered crystal as active laser medium. Transform-limited 84-fs pulses are generated with an average output power of 22 mW at a repetition rate of ~90 MHz. A maximum output power of 98 mW is obtained at a slightly longer pulse duration of 114 fs.

Temperature dependence of the ionization coefficients of InAlAs and AlGaAs digital alloys

Yuan Yuan, Jiyuan Zheng, Yaohua Tan, Yiwei Peng, Ann-Kathryn Rockwell, Seth Bank, Avik Ghosh, and Joe Campbell

Doc ID: 328509 Received 17 Apr 2018; Accepted 08 Jun 2018; Posted 13 Jun 2018  View: PDF

Abstract: Digital alloy In0.52Al0.48As avalanche photodiodes exhibit lower excess noise than those fabricated from random alloys. This paper compares the temperature dependence, from 203 K to 3 K, of the impact ionization characteristics of In0.52Al0.48As and Al0.74Ga0.26As digital and random alloys. These results provide insight into the low excess noise exhibited by some digital alloy materials, and these materials can even obtain lower excess noise at low temperature.

Graphene-decorated microfiber knot as broadband resonator for ultrahigh repetition rate pulse fiber lasers

Meng Liu, Rui Tang, Aiping Luo, Wen-Cheng Xu, and Zhi-Chao Luo

Doc ID: 331700 Received 17 May 2018; Accepted 07 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: Searching for ultrahigh repetition rate pulse with hundreds of GHz order is still a challenging task in ultrafast laser community. Recently, high-quality silicon/silica-based resonators were exploited to generate high repetition rate pulse based on the filter-driven four-wave mixing (FD-FWM) effect in fiber lasers. However, silicon/silica-based resonators have some drawbacks, such as single waveband operation and low coupling efficiency between the fiber and silicon/silica-based resonators. To overcome the drawbacks, herein we proposed an all-fiber broadband resonator by depositing the graphene onto a microfiber knot. As the proof-of-concept experiments, the graphene-deposited broadband microfiber knot resonator (MKR) was applied to Er- and Yb-doped fiber lasers operating at two different wavebands, respectively, to efficiently generate hundreds of GHz repetition rate pulses. Such a graphene-deposited broadband MKR would open some new applications in ultrafast laser technology, broadband optical frequency comb generation and other related fields of photonics.

High-efficiency broadband polarization-independent superscatterer using conformal metasurfaces

He-Xiu XU, Shiwei Tang, Chen Sun, Lianlin Li, Haiwen Liu, Xinmi Yang, fang yuan, and Yunming Sun

Doc ID: 327059 Received 28 Mar 2018; Accepted 07 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic (EM) wave control. However, studies have mainly focused on physics and the design of metasurfaces on planar plates, which does not satisfy the current requirement of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface wrapping over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing high-performance multifunctional optoelectronic devices equipped on a moderately curved platform.

Directly modulated quantum dot lasers on Si with milliamp threshold and high temperature stability

Yating Wan, Daisuke Inoue, Daehwan Jung, Justin Norman, Chen Shang, Arthur Gossard, and John Bowers

Doc ID: 328267 Received 13 Apr 2018; Accepted 06 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: Microring lasers feature ultra-low thresholds and inherent wavelength-division multiplexing (WDM) functionalities, offering an attractive approach to miniaturize photonics in a compact area. Here, we present static and dynamic properties of microring quantum-dot (QD) lasers grown directly on exact (001) GaP/Si. Emission near 1.3 µm with few unique modes in spectrally distant locations enable effectively a single-mode operation. High temperature stability with T0 ~103 K has been achieved with a low threshold of 3 mA and a 3dB bandwidth of 6.5 GHz. The directly modulated microring laser, monolithically integrated on a silicon substrate, can incur minimal real estate cost while offering full photonic functionality.

Room Temperature Optical Mass Sensor with an Artificial Molecular Structure Based on Surface Plasmon Optomechanics

Jian Liu and Ka-Di Zhu

Doc ID: 328537 Received 17 Apr 2018; Accepted 05 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: We propose an optical weighing technique with a sensitivity down to singleatom through the coupling between surface plasmon and suspended graphene nanoribbon resonator. The mass is determined via thevibrational frequency shift on the probe absorption spectrum while the atomattaches to the nanoribbon surface. We provide methods to separate out thesignals of the ultralow frequency vibrational mode from strong Rayleighbackground firstly based the quantum coupling. Owing to the spectralenhancement by the use of surface plasmon and due to ultralight mass of the nanoribbon, the methods result in a narrow linewidth (~GHz) and ultrahigh sensitivity(~30yg). Benefited from the low noises in the couplingsystem, our optical mass sensor can be achieved at room temperature and ultrahigh time resolution.

Femtosecond laser-induced periodic surface structures on lithium niobate crystal benefiting from sample heating

Qiang Li, Qiang Wu, Yanan Li, Chunling Zhang, Zixi Jia, Jianghong Yao, Jun Sun, and Jingjun Xu

Doc ID: 322686 Received 07 Feb 2018; Accepted 05 Jun 2018; Posted 07 Jun 2018  View: PDF

Abstract: Periodic surface structures were fabricated by irradiating lithium niobate (LN) crystals with femtosecond laser pulses at sample temperatures ranging from 28-800 ℃. Carrier density and conductivity of the samples were increased via heating LN, which inhibited coulomb explosion to obtain a uniform periodic surface structure. The periodic surface structures cover an area of 8 × 8 mm², and have an average spacing of 174 nm. Meanwhile, the absorption of processed sample is about 70 % in the spectral range of 400-1000 nm, which is one order of magnitude higher than that of pure LN. Fabrication of periodic surface structures on heating LN with femtosecond laser pulses provides a possibility to generate nanogratings or nanostructures on wide-bandgap transparent crystals.

Engineering the Emission of Laser Arrays to Nullify the Jamming from Passive Obstacles

Constantinos Valagiannopoulos and Vassilios Kovanis

Doc ID: 312268 Received 30 Oct 2017; Accepted 29 May 2018; Posted 01 Jun 2018  View: PDF

Abstract: Non-Hermitian characteristics accompany any photonic device incorporating spatial domains of gain and loss. In this work, an one-dimensional beamforming array playing the role of the active part gets disturbed from the scattering losses produced by an obstacle in its vicinity. It is found that the placement of the radiating elements leading to perfect beam-shaping, is practically not affected by the presence of that jammer. A trial-and-error inverse technique of identifying the features of the obstacle is presented based on the difference between the beam target pattern and actual one. Such a difference is an analytic function of the position, size and texture of the object empowering the designer to find the feeding fields for the lasers giving a perfect beamforming. In this way, an optimal beam-shaping equilibrium gets re-established by effectively cloaking the object and nullifying its jamming effect.

Bismuth nanosheets as a Q-switcher for a mid-infrared erbium-doped SrF₂ laser

Jie Liu, Huang Hao, Feng Zhang, Zhen Zhang, Jing Liu, Han Zhang, and Liangbi Su

Doc ID: 327857 Received 06 Apr 2018; Accepted 26 May 2018; Posted 30 May 2018  View: PDF

Abstract: Bismuth nanosheets (Bi-NSs) were successfully prepared and employed as saturable absorber to generate a diode-pumped dual-wavelength Er3+:SrF₂ laser in the mid-infrared region. Q-switched pulses with a maximum output power of 0.226 W were obtained at an absorbed pump power of 1.97 W. A repetition rate of 56.20 kHz and a minimum pulse duration of 980 ns were achieved. To the best of our knowledge, we present the first application of Bi-NSs in a mid-infrared all-solid-state laser. The results prove that Bi-NSs have potential application as an optical modulator in mid-infrared photonic devices or as a mode-locker and Q-switcher.

Polarization oscillating beams constructed by co-propagating optical Frozen waves

Peng Li, Dongjing Wu, yi zhang, Sheng Liu, Yu Li, Shuxia Qi, and Jianlin Zhao

Doc ID: 326558 Received 21 Mar 2018; Accepted 24 May 2018; Posted 24 May 2018  View: PDF

Abstract: Polarization standing waves, commonly formed by a pair of coherent counter-propagating light waves with orthogonal polarizations, oscillate its state of polarization (SoP) periodically within a wavelength interval, offering conceptual and practical interests referring to the light-matter interactions such as nonreciprocal magnetoelectric effect, and impressive applications in optical imaging, sensing and chirality detection. Here, by analogy with the SoP oscillation of the polarization standing wave, we propose a class of polarization oscillating beams that longitudinally vary the SoPs within centimeters spatial interval by conceptually quoting the stationary feature of Frozen wave. We experimentally implement several polarization oscillating beams with different polarization order via the superposition of two co-propagating optical Frozen waves with and pre-shaped longitudinal intensity patterns and transverse phase structures, using a 4f Fourier filtering system combined with computer generated holograms. These polarization oscillating beams could further develop the applications of optical standing wave in optical manipulation, light guiding of atoms, polarization-sensitive sensing, etc.

Vertically standing PtSe2 film: a novel saturable absorber for passively mode-locked Nd:LuVO4 laser

Li Tao, Xiaowen Huang, Junshan He, Yajun Lou, Longhui Zeng, Yonghui Li, hui long, Jingbo Li, Ling Zhang, and Yuen Tsang

Doc ID: 328540 Received 17 Apr 2018; Accepted 22 May 2018; Posted 24 May 2018  View: PDF

Abstract: The novel vertically standing PtSe2 film on transparent quartz was prepared by selenization of platinum film deposited by magnetron sputtering method, and a Nd:LuVO4 passively mode-locked solid-state laser was realized by using the fabricated PtSe2 film as saturable absorber. X-ray diffraction (XRD) pattern and Raman spectrum of the film indicate its good crystallinity with a layered structure. The thickness of PtSe2 film is measured to be 24 nm according to the cross-section height profile of the atomic force microscope (AFM) image. High resolution transmission electron microscopy (HRTEM) images clearly demonstrat its vertically standing structure with an interlayer distance of 0.54 nm along the c-axis direction. The modulation depth (ΔT) and saturable fluence (Φs) of PtSe2 film are measured to be 12.6 % and 17.1 μJ/cm2, respectively. The obtained mode-locked laser spectrum has a central wavelength of 1066.573 nm with a 3dB bandwidth of 0.106 nm. The transform limited pulse width of the mode-locked laser was calculated to be 15.8 ps. A maximum average output power of 180 mW with a working repetition rate of 61.3 MHz is obtained. To the best of our knowledge, it is the first time to report generation of ultrafast mode-locked laser pulses by using the novel layered PtSe2 as a saturable absorber.

Robust and Accurate Terahertz Time-Domain Spectroscopic Ellipsometry

Xuequan Chen, Edward Parrott, Zhe Huang, Hau Ping Chan, and Emma Pickwell-MacPherson

Doc ID: 328820 Received 20 Apr 2018; Accepted 21 May 2018; Posted 24 May 2018  View: PDF

Abstract: In this work we show how fiber-based terahertz systems can be robustly configured for accurate THz ellipsometry. To this end, we explain how our algorithms can be successfully applied to achieve accurate spectroscopic ellipsometry with a high tolerance on the imperfect polarizer extinction ratio and the pulse-shift errors. Highly accurate characterization of transparent, absorptive and conductive samples comprehensively demonstrate the versatility of our algorithms. The improved accuracy we achieve is a fundamental breakthrough for reflection-based measurements and overcomes the hurdle of phase uncertainty.

Intermodal Four Wave Mixing in Silicon waveguides

Stefano Signorini, mattia Mancinelli, Massimo Borghi, Martino Bernard, Mher Ghulinyan, Georg Pucker, and Lorenzo Pavesi

Doc ID: 319640 Received 06 Feb 2018; Accepted 10 May 2018; Posted 15 May 2018  View: PDF

Abstract: In this work, we report the modeling and the experimental demonstration of intermodal spontaneous as well as stimulated four wave mixing (FWM) in silicon waveguides. In intermodal FWM, the phase matching condition is achieved by exploiting the chromatic dispersion of the optical modes in a multimode waveguide. Since both the energy and the wavevectors have to be conserved in the FWM process, this leads to a wide tunability of the generated photon wavelength allowing to achieve a large spectral conversion. We measured several waveguides which differ by their widths and demonstrate large signal generation spanning from the pump wavelength (1550 nm) down to 1202 nm. A suited set-up evidences that the different waves propagated indeed on different order modes, which supports the modeling. Despite we observed a reduced efficiency with respect to intramodal FWM due to the decreased modal overlap, we were able to show a maximum spectral distance between the Signal and Idler of 979.6 nm, with a 1550 nm pump. Our measurements suggest the intermodal FWM as a viable mean for large wavelength conversion and heralded photon sources.

Integrated (de)multiplexer for OAM fiber communications

Zhenwei Xie, She Gao, Ting Lei, Shengfei Feng, Yan Zhang, Fan Li, Jianbo Zhang, Zhaohui Li, and Xiaocong Yuan

Doc ID: 321270 Received 01 Feb 2018; Accepted 09 May 2018; Posted 09 May 2018  View: PDF

Abstract: Quickly increasing data transfer loads requires an urgent revolution in current optical communications. Orbital angular momentum (OAM) multiplexing is a potential candidate with its ability to considerably enhance the capacity of communications. However, the lack of a compact, efficient, and integrated OAM (de)multiplexer prevents it from being widely applied. By attaching vortex gratings onto the facets of a few-mode fiber, we demonstrate one such integrated fiber-based OAM (de)multiplexer. A vortex grating fabricated on the fiber facet enables the direct multiplexing of OAM states at one port and the demultiplexing of OAM states at the other port. The measured bit error rate of the carrier signal after propagating through a 5-km few-mode fiber confirms the validity and effectiveness of the proposed approach. The scheme offers advantages in future high-capacity OAM communications based on optical fiber.

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