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Accepted papers to appear in an upcoming issue

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Extinction ratio and resonant wavelength tuning using three dimensions of silica microresonators

Lei Shi, Song Zhu, Yang Liu, xinbiao xu, and Xinliang Zhang

Doc ID: 269140 Received 24 Jun 2016; Accepted 13 Aug 2016; Posted 17 Aug 2016  View: PDF

Abstract: In this paper, a multidimensional tuning method of the silica microcapillary resonator (MCR) is proposed and demonstrated (i.e., the extinction ratio (ER) as well as the resonant wavelength can be individually controlled). An ER tuning range of up to 17 dB and a maximum tuning sensitivity of 0.3 dB/μm are realized due to the tapered profile of the silica optical microfiber (MF) when the MF is adjusted along its axial direction. Compared to direct tuning of coupling gap, this way could lower the requirement for the resolution of displacement stage to ~μm. When the MF is adjusted along the axial direction of the silica microcapillary, a resonance shift of 3.06 nm and a maximum tuning sensitivity of 0.01 nm/μm are achieved. This way avoids an applied external field to control the silica microresonators. Moreover, when air is replaced by ethanol and water in the core of the silica microcapillary, the maximum resonance shift of 5.22 nm is also achieved to further enlarge the resonance tuning range. Our method fully takes advantage of the unique structure of the MCR to separately and easily tune its key parameters and may broaden its applications in optical signal processing and sensing.

Improved optical enhancement using double-width plasmonic gratings with nanogaps

Joseph Herzog, Ahmad Darweesh, and Stephen Bauman

Doc ID: 269491 Received 30 Jun 2016; Accepted 09 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: Plasmonic grating structures have been shown effective at increasing near-field optical enhancement. A double-width plasmonic grating design is introduced, where each period has two alternating metal widths separated by a nanogap. With this new design, analysis has shown that plasmonic resonances couple between each metal section, resulting in even greater optical enhancement compared with single-width gratings. The geometry that gives the greatest optical enhancement has been determined with a computational model. This work demonstrates that the increased enhancement is due to hybridized modes that couple between the two grating segments.

Measuring the fractional topological charge of a vortex light beam by dynamic angular double slits

Pei Zhang, Jing Zhu, Dongzhi Fu, Dongxu Chen, Rui-feng Liu, Yingnan Zhou, Hong Gao, and fuli li

Doc ID: 269178 Received 28 Jun 2016; Accepted 06 Aug 2016; Posted 09 Aug 2016  View: PDF

Abstract: Vortex beams with fractional topological charge (FTC) have many special characters, such as its intensity pattern possess a radial opening (low-intensity gap) on the annular intensity ring surrounding the dark singular point and its states is a superposition state of the basis of integer OAM states. Because of those characters, the fractional vortex beams have some novel applications on the areas of guiding and transporting particles, optical sorting, anisotropic edge enhancement, investigating high-dimensional entanglement of orbital angular momentum (OAM) states and so on. One of the obstacles for the above applications is the difficulty of precisely determining the FTC of the fractional vortex beams. We find that when a vortex beam with a fractional topological charge illuminates a dynamic angular double slits (ADS), the far-field interference patterns which include the information of the FTC of the beam at the angular bisector direction of the ADS vary periodically. Based on this property, a simple dynamic ADS device combining the method of fitting the experimental data can be use to precisely measure the FTC of a vortex light beam which has an error less than 5%.

Unveiling Stability of Multiple Filamentation Caused by Axial-Symmetry Breaking of Polarization

Hui-Tian Wang, Si-Min Li, Zhi-Cheng Ren, Ling-Jun Kong, Sheng-Xia Qian, Chenghou Tu, and Yongnan Li

Doc ID: 264250 Received 29 Apr 2016; Accepted 06 Aug 2016; Posted 10 Aug 2016  View: PDF

Abstract: Femtosecond laser filamentation is generally initialized from unpredictable symmetry breaking caused by random noise, making it be hardly controlled. However, it is always anticipated for stable and controllable filamentation. We presented and demonstrated an idea that hybridly polarized vector fields with the axial-symmetry broken polarization, which associate with a pair of orthogonally linearly polarized vortices carrying the opposite-handed orbital angular momenta, could achieve the controllable and robust multiple filamentation. Here our motivation is to unveil the underlying physics behind such controllable and robust multiple filamentation. The symmetry breaking should be firstly actively controllable and should then be able to effectively inhibit the random noise. The robust multiple filamentation is inseparable from the fact that the phases between the multiple filaments are always locked. In contrast, the uncontrollable multiple filamentation accompanies always with the loss of phase, i.e., the multiple filaments become incoherent each other. Our results maybe offer a suggestion for achieving the controllable and robust multiple filamentation in other systems.

Communications using Optical Vortex

Jian Wang

Doc ID: 264787 Received 16 May 2016; Accepted 04 Aug 2016; Posted 05 Aug 2016  View: PDF

Abstract: Communications using Optical Vortex

Experimental performance evaluation of quadrature amplitude modulation signal transmission in a silicon microring

Chengcheng Gui and Jian Wang

Doc ID: 266576 Received 18 May 2016; Accepted 20 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: We comprehensively characterize the transmission performance of m-ary quadrature amplitude modulation (m-QAM) signals through a silicon microring resonator in the experiment. Using orthogonal frequency-division multiplexing based on offset QAM (OFDM/OQAM) which is modulated with m-QAM modulations, we demonstrate low-penalty data transmission of OFDM/OQAM 64-QAM, 128-QAM, 256-QAM and 512-QAM signals in a silicon microring resonator. The observed optical signal-to-noise ratio (OSNR) penalties are 1.7 dB for 64-QAM, 1.7 dB for 128-QAM, 3.1 dB for 256-QAM at a bit-error rate (BER) of 2e-3 and 3.3 dB for 512-QAM at a BER of 2e-2. The performance degradation due to the wavelength detuning from the microring resonance is evaluated, showing a wavelength range of ~0.48 nm with BER below 2e-3. Moreover, we demonstrate data transmission of 191.2-Gbit/s simultaneous 8 wavelength channel OFDM/OQAM 256-QAM signals in a silicon microring resonator, achieving OSNR penalties less than 2 dB at a BER of 2e-2.

Multilayer black phosphorus as saturable absorber for Er:Lu₂O₃ laser at ~ 3 μm

Tao Li, Mingqi Fan, Shengzhi Zhao, Guiqiu Li, Xiaochun Gao, Kejian Yang, Dechun Li, and Christian Kraenkel

Doc ID: 269206 Received 24 Jun 2016; Accepted 20 Jul 2016; Posted 22 Jul 2016  View: PDF

Abstract: Multilayer black phosphorus (BP) nanoplatelets of different thicknesses were prepared by the liquid phase exfoliation method and deposited onto YAG substrates to form saturable absorbers (SAs). These were characterized with respect to their thickness-dependent saturable absorption properties at 3 μm. The BP-SAs were employed in a passively Q-switched Er:Lu₂O₃ laser at 2.84 μm. By using BP exfoliated in different solvents, stable pulses as short as 359 ns were generated at an average output power of up to 755 mW. The repetition rate in the experiment was 107 kHz, corresponding to a pulse energy of 7.1 μJ. These results prove that BP-SAs have a great potential for the generation of ultrashort pulses in the mid-IR range.

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