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Surface-related synergistic nonlinear optical enhancement of graphene/CdS nanohybrids under single pulse laser irradiation

Baohua Zhu, Fangfang Wang, Guixia Wang, and Yuzong Gu

Doc ID: 335482 Received 21 Jun 2018; Accepted 17 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: Surface states is very important for altering the nonlinear optical (NLO) properties of graphene. To investigate the correlation between surface structure and the synergistic NLO response in graphene-based nanocomposites, we attached CdS nanocrystals on the surface of graphene (G) and prepared G/CdS nanohybrids (NHs) consisting of various oxygen-containing functional groups via chemical method. The NLO absorption and NLO refraction of G/CdS NHs under single pulse laser irradiation are enhanced 17.5 times with the concentration decrease of surface oxygen-containing groups, which might be attributed to the local field effects and synergetic effects stemming from charge transfer between the two components. But the optical nonlinearity is decreased with further concentration decrease, which might arise from sp2 fragments interconnection and surface defects in NHs. The NLO absorption transformation from two-photon absorption to saturable absorption with oxygen decrease is observed, and intensity-related NLO absorption and refraction in NHs are also discussed. Meanwhile, the G/CdS NHs exhibit superior NLO properties, implying the potential applications of this NHs material in NLO devices.

Phase-modulation nested structure optical fields for extending optical filament

Hui-Tian Wang, Jia-Qi Lv, Ping-Ping Li, Dan Wang, Chenghou Tu, and Yongnan Li

Doc ID: 339912 Received 18 Jul 2018; Accepted 17 Oct 2018; Posted 18 Oct 2018  View: PDF

Abstract: Extending the propagation length of femtosecond laser filamentation has always been expected since the needs in practical application. Here we achieve experimentally and theoretically great extending of single filament in BK7 glass by using phase modulated nested structure optical fields. The function for realizing the arising of filamentation and following energy replenishment are assembled in one nested optical field. The common path generating system insures the stability of generated filaments while the adjustable parameters provide the possibility to find the longest high-quality filament under the constraint of finite input power. Beside the significance of continuous replenishment has been discussed and the potential of generating more extended filament has been predicted.

Embedded whispering-gallery mode microsphere resonator in a tapered hollow annular core fiber

Jiawei Wang, Xiaobei Zhang, Ming Yan, Lei Yang, Fengyu Hou, Wen Sun, Xiaotong Zhang, Libo Yuan, Hai Xiao, and Tingyun Wang

Doc ID: 344719 Received 31 Aug 2018; Accepted 13 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We propose and demonstrate a tapered hollow annular core fiber (HACF) coupler for excitation of whispering-gallery modes (WGMs) of an embedded microsphere resonator. The coupler is simply fabricated by fusing splicing a segment of HACF with the single mode fiber (SMF), and then improved by tapering the splicing joint to reduce the cone-apex angle. Therefore, the coupling efficiency from the SMF to HACF is enhanced to excite various WGMs via evanescent field coupling. Normal positive, negative symmetrical Lorentzian and asymmetric Fano line shapes can be obtained by varying the resonator size and location. Another interesting phenomenon is observed that a higher Q-factor mode in a lower Q-factor mode has a contrast as high as 58. Temperature sensing with good stability is also demonstrated. This embedded WGM microsphere resonator in the tapered HACF is expected to promote the environmental adaptability in the practical application due to its simplify and robustness.

High efficient generation of tunable ellipse perfect vector beams

CHENLIANG CHANG, LIN Li, Caojin Yuan, Shaoteng Feng, Shouping Nie, Hui-Tian Wang, Jianping Ding, and Zhi-Cheng Ren

Doc ID: 335066 Received 13 Jun 2018; Accepted 12 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: We present a method of generating and shaping ellipse perfect vector beams (EPVB) with prescribed ellipse intensity profile and continuously variant linear polarization state. The scheme is based on the coaxial superposition of two orthogonally polarized ellipse laser beams of controllable phase vortex serving as base vector components. The phase-only CGH is specifically designed by means of a modified iteration algorithm involving complex amplitude constraint, which is able to generate EPVB with high diffraction efficiency in the vector optical field generator. We also discuss and demonstrate the simultaneous shaping of multiple EPVBs with independent tunable ellipticity and polarization vortex in both of transversal (2D) and axial (3D) focusing structures, proving potentials in a variety of polarization-mediated applications such as trapping and transportation of particles in a more complex geometry circumstances.

High Efficiency Solid–liquid Hybrid-state Quantum Dot Light-emitting Diodes

Jiasheng Li, Yong Tang, Zongtao Li, Longshi Rao, Xinrui Ding, and Binhai Yu

Doc ID: 341874 Received 08 Aug 2018; Accepted 10 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: Quantum dots (QDs) can achieve high quantum yields (QYs) close to unity in liquid solutions, whereas they exhibit a decreased conversion efficiency after being integrated into solid-state polymer matrices for light-emitting diode (LED) devices, which is called as the host matrix effect. In this study, we propose a solid–liquid hybrid-state QD-LED to solve this issue. The ethylene-terminated PDMS (ethylene-PDMS) is used to establish a solid-state cross-linked network, whereas the methyl-terminated PDMS (methyl-PDMS) is used in its liquid state. From a macroscopic level, the cured solid–liquid hybrid-state PDMS (SLHP) composites reach a solid state, which is stable and flexible to be used in LED devices. Compared with LEDs using conventional QD/solid PDMS (SP) composites at equal color conversion efficiency (CCE) ranging from 40% to 60%, the luminous flux of LEDs with QD/SLHP composites are increased by 13.0% using an optimized methyl-PDMS concentration of 85 wt%. As a result, high efficiency QD-LEDs using QDs as the only color convertor with luminous efficacy of 89.6 lm/W (0.19 A) were achieved, which show a working stability comparable with that using conventional solid-state structures at a harsh condition. Consequently, the novel approach shows great potential for achieving high efficiency and high stability QD-LEDs, which is also compatible with current structures that used in illumination and display applications.

Resonance-assisted light-control-light characteristics of SnS₂ on microfiber knot resonator with fast response

Huihui Lu, zhongmin wang, zhijin huang, jun tao, hanqing xiong, Wentao Qiu, Heyuan Guan, Huazhuo Dong, Jiangli Dong, Wenguo Zhu, JianHui Yu, Yongchun Zhong, Yunhan Luo, Jun Zhang, and zhe chen

Doc ID: 347500 Received 04 Oct 2018; Accepted 08 Oct 2018; Posted 12 Oct 2018  View: PDF

Abstract: An all optical light-control-light functionality with a structure of microfiber knot resonator (MKR) coated with tin disulfide (SnS₂) nanosheets is experimentally demonstrated. The evanescent light in the MKR (with a resonance Q of ~ 59,000 and an extinction ratio (ER) of ~ 26 dB) is exploited to enhance light matter interaction by coating a two dimensional material SnS₂ nanosheet onto it. Thanks to the enhanced light-matter interaction and the strong absorption property of SnS₂, the transmitted optical power can be tuned quasi linearly with an external violet pump light power where a transmitted optical power variation rate ΔT with respect to violet light power of ~ 0.22 dB/mW is obtained. In addition, the MKR structure possessing multiple resonances enables a direct experimental demonstration of the relationship between resonance properties (such as Q and ER etc) and the obtained ΔT variation rate with respect to violet light power. It verifies experimentally that a higher resonance Q and a larger ER can lead to a higher ΔT variation rate. In terms of the operating speed, this device runs as fast as ~ 3.2 ms. This kind of all optical light-control-light functional structure may find applications in future all optical circuitry and hand held fiber sensors etc.

Low-power nonlinear enhanced electromagnetic transmission of a subwavelength metallic aperture

yunsheng guo, saiyu liu, ke bi, ming lei, and ji zhou

Doc ID: 341078 Received 31 Jul 2018; Accepted 08 Oct 2018; Posted 10 Oct 2018  View: PDF

Abstract: When a dielectric meta-atom is placed into a subwavelength metallic aperture, 20-fold enhanced electromagnetic transmission through the aperture is realized at the meta-atom’s resonant frequency. Additionally, when the incident electromagnetic power increases, thermal energy gathered by the meta-atom, which is converted from electromagnetic losses, can cause the meta-atom’s temperature to increase. Because of the high temperature coefficient of the meta-atom’s resonant frequency, this temperature increase causes a blue shift in the transmission peak. Therefore, this frequency-dependent enhanced electromagnetic transmission even produces a nonlinear effect at low incident powers. Over an incident power range from 0 to 20 dBm, measured and simulated spectra near the meta-atom’s resonant frequency both show distinctly nonlinear transmission.

Electro-thermally tunable reflective colors in a self-organized cholesteric helical superstructure

Wei Lee, Po-Chang Wu, Guan-Wei Wu, Ivan Timofeev, and Victor Zyryanov

Doc ID: 340395 Received 25 Jul 2018; Accepted 30 Sep 2018; Posted 02 Oct 2018  View: PDF

Abstract: We propose to dynamically control the reflective color of a cholesteric liquid crystal (CLC) by electrically tuning the center wavelength (λc) of the bandgap. The CLC, sandwiched in a planar-aligned cell with indium-tin-oxide electrodes, possesses negative dielectric anisotropy and thermo-responsive spectral properties. The helix in the Grandjean planar state subject to a vertically applied voltage should be undisturbed in that the long molecular axis is initially perpendicular to the direction of the electric field. Surprisingly, when the frequency of the applied voltage is higher than a critical value, λc of the CLC cell varies as a function of the voltage. The underlying mechanism is the voltage-induced temperature change through dielectric heating in the frequency regime of pseudo-dielectric relaxation, attributable to the finite conductance of the electrode layers. The driving voltage enabling the tuning of λc in the entire visible spectrum is as low as 12 Vrms in a 5-μm-thick cell at a frequency of 2 MHz. The proposed CLC cell exhibiting a broad electrically tunable spectral range from near infrared to ultraviolet holds great promise for developing tunable photonic devices such as multicolor reflectors, filters, and sensors.

Bound states in the continuum and high-Q resonances supported by a dielectric ridge on a slab waveguide

Evgeni Bezus, Dmitry Bykov, and Leonid Doskolovich

Doc ID: 337954 Received 05 Jul 2018; Accepted 20 Sep 2018; Posted 20 Sep 2018  View: PDF

Abstract: We investigate the diffraction of guided modes of a dielectric slab waveguide on a simple integrated structure consisting of a single dielectric ridge on the surface of the waveguide. Numerical simulations based on aperiodic rigorous coupled-wave analysis demonstrate the existence of sharp resonant features and bound states in the continuum (BICs) in the reflectance and the transmittance spectra occurring at oblique incidence of a TE-polarized guided mode on the ridge. Using the effective index method, we explain the resonances by the excitation of the cross-polarized modes of the ridge. The formation of the BICs is confirmed using a theoretical model based on the coupled-wave theory. The model suggests that the BICs occur due to coupling of quasi-TE and quasi-TM modes of the structure. Simple analytical expressions for the angle of incidence and the ridge width predicting the location of the BICs are obtained. The existence of high-Q resonances and BICs makes the considered integrated structure promising for filtering, sensing, transformation of optical signals, and enhancing nonlinear light-matter interactions.

Coupling Strategies for Silicon Photonics Integrated Chips

Cosimo Lacava, Riccardo Marchetti, Lee Carroll, Kamil Gradkowski, and Paolo Minzioni

Doc ID: 338163 Received 06 Jul 2018; Accepted 18 Sep 2018; Posted 20 Sep 2018  View: PDF

Abstract: In the last 20 years, silicon photonics has revolutionized the field of integrated optics, providing a novel and powerful platform to build mass-producible optical circuits. One of the most attractive peculiarity of silicon photonics is its ability to supply extremely small optical components, whose typical dimensions are order of magnitude smaller than optical fiber devices. This dimension discrepancy makes the design of fiber-to chip interfaces extremely challenging and, over the years, has stimulated an incredibly large amount of research efforts in the field. Fiber-to-Silicon photonic chip interfaces can be broadly divided into two big categories: in-plane and out-of-plane couplers. Devices falling in the first category typically offer high coupling efficiency, large coupling bandwidth (in wavelength) and no polarization dependence, but they require relatively complex fabrication procedures and do not allow for wafer-scale testing.Conversely, out-of-plane device offer lower efficiency, limited bandwidth and are typically polarization dependent. However they are compatible with high-volume fabrication processes, and allow on-wafer accessing any part of the optical circuit. In this paper we review the current state of the art of optical couplers, aiming to give to the reader a comprehensive and broad view of the field, identifying advantages and disadvantages of each solution proposed.As fiber-to-chip couplers are inherently related to packaging technologies, and the co-design of optical packages has become essential, we also review in this document the main solutions currently used to package and assemble optical fibers with Silicon-photonic integrated circuits.

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