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Polarization-multiplexed, dual-comb all-fiber mode-locked laser

xin zhao, Li ting, Ya Liu, Qian Li, and Zheng Zheng

Doc ID: 328118 Received 13 Apr 2018; Accepted 08 Jul 2018; Posted 11 Jul 2018  View: PDF

Abstract: Mode-locked fiber lasers that can simultaneously generate two asynchronous ultrashort pulse trains could play an attractive role as the alternative light sources for low-complexity dual-comb metrology applications. While a few multiplexing schemes to realize such lasers had been proposed and demonstrated, here we investigate the lasing characteristics of a passively mode-locked fiber laser with a finite amount of intracavity birefringence. By introducing a section of polarization-maintaining (PM) fiber into the otherwise-non-PM-single-mode cavity, dual asynchronous pulses with nearly orthogonal states of polarization are generated. With hundreds of Hz repetition rate difference, the pulses have well-overlapped spectra and show typical features of polarization-locked vector solitons. It is demonstrated that under anomalous or net normal dispersion regime, either dual vector solitons or dual dissipative vector solitons can be generated, respectively. Such polarization-multiplexed single single-cavity dual-comb lasers could further find applications in various applications in need of simple dual-comb system solutions.

Solitons in fractional Schrödinger equation with PT-symmetric lattice potential

Xiankun Yao and Xueming Liu

Doc ID: 334753 Received 11 Jun 2018; Accepted 08 Jul 2018; Posted 11 Jul 2018  View: PDF

Abstract: We investigate the properties of spatial solitons in fractional Schrödinger equation (FSE) with PT-symmetric lattice potential supported by focusing Kerr nonlinearity. Both one- and two-dimensional solitons can stably propagate in PT-symmetric lattices under noise perturbations. The domains of stability for both one- and two-dimensional solitons strongly depend on the gain/loss strength of the lattice. In spatial domain, the solitons are rigidly modulated by lattice potential for the weak diffraction in FSE systems. In the inverse space, due to the periodicity of lattices, the spectra of solitons experience sharp peaks when the values of wavenumbers are even. The transverse power flows induced by the imaginary part of the lattice are also investigated, which can preserve the internal energy balances within the solitons.

Nonlinear optical properties of WSe2 and MoSe2 films and their applications in ultrafast photonics

Wen Liu, Mengli liu, Hainian Han, SHAOBO FANG, Hao Teng, Ming Lei, and Zhiyi Wei

Doc ID: 330890 Received 08 May 2018; Accepted 08 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: Transition metal dichalcogenides (TMDs) are successfully applied in ultrafast photonics for their photoelectric properties. However, in previous work, how to improve the modulation depth of TMDs-based saturable absorber (SA) has been a challenging issue. In this paper, WSe2 and MoSe2 SAs are fabricated with the chemical vapor deposition method. Compared with previous experiments, the modulation depth of WSe2 and MoSe2 SAs are effectively increased to 31.25% and 25.69%, respectively. The all-fiber passively Q-switched erbium doped fiber lasers based on WSe2 and MoSe2 SAs are demonstrated. The signal-to-noise ratio of those lasers are measured to be 72 dB and 57 dB, respectively. Results indicate that the proposed WSe2 and MoSe2 SAs are efficient photonic devices to realize stable fiber lasers.

Self-Q-switched and wavelength tunable WS2-based passively Q-switched Er:Y2O3 ceramic lasers

Xiaofeng Guan, jiawei wang, yuzhao zhang, Bin Xu, Zhengqian Luo, Huiying XU, Zhiping Cai, Xiaodong Xu, Jian Zhang, and Jun Xu

Doc ID: 337975 Received 05 Jul 2018; Accepted 08 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We report on diode-pumped Er:Y2O3 ceramic lasers at about 2.7 μm in tunable continues-wave, self Q-switching and WS2-based passively Q-switching regimes. For stable self Q-switched operation, the maximum output power reaches 106.6 mW under an absorbed power of 2.71 W. The shortest pulse width is measured to be about 1.39 μs at repetition rate of 26.7 kHz at maximum output. Using a spin-coated WS2 as saturable absorber, passively Q-switched Er:Y2O3 ceramic laser is also realized with a maximum average output power of 3.5 mW, for the first time to the best of our knowledge. The shortest pulse width reduces to 0.72 μs at corresponding repetition rate of 29.4 kHz, which leads to a pulse energy of 7.92 μJ and a peak power of 11.0 W. By inserting an undoped YAG thin plate as F-P etalon, for the passive Q-switching, wavelength tunings are also demonstrated at around 2710 nm, 2717 nm, 2727 nm and 2740 nm.

Enhancing Plasmonic Trapping with Perfect Radially Polarized Beam

xianyou wang, Yuquan Zhang, yanmeng dai, Changjun Min, and Xiaocong Yuan

Doc ID: 328577 Received 17 Apr 2018; Accepted 04 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Strong plasmonic focal spot, excited by radially polarized light on a smooth thin metallic film, has been widely applied to trap various micro- and nano-sized objects. However, the direct transmission part of incident light leads to the scattering force exerted on trapped particles, which seriously affects the stability of the plasmonic trap. Here we employ a novel perfect radially polarized beam to solve this problem. Both theoretical and experimental results verify that such beam could strongly suppress the directly transmitted light and enhance the plasmonic trapping stiffness. The present work opens up new opportunities for a variety of researches requiring stable manipulations of particles.

Review of fast methods for computer-generated holography (Invited)

Peter Tsang, Ting-Chung Poon, and Yumo Wu

Doc ID: 331162 Received 08 May 2018; Accepted 02 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Computer-generated holography (CGH) is a technique for converting a three-dimensional (3-D) object scene into a two-dimensional (2-D), complex-valued hologram. One of the major bottlenecks of CGH is the intensive computation that is involved in the hologram generation process. To overcoming this problem, numerous research works have been conducted with the aim of reducing arithmetic operations involved in CGH. In this paper, we shall review a number of fast CGH methods that have been developed in the past decade. While each method has its own strength and weakness, trading off conflicting issues such as computation efficiency and memory requirement, they also exhibit potential grounds of synergy. We hope that this paper will bring out the essence of each method, as well as providing some insight on how different methods may crossover into better ones.

Widely tunable 2.3 µm III-V-on-silicon Vernier lasers for broadband spectroscopic sensing

Ruijun Wang, Stephan Sprengel, Anton Vasiliev, Gerhard Boehm, Joris Van Campenhout, Guy Lepage, Peter Verheyen, Roel G. Baets, Markus Amann, and Gunther Roelkens

Doc ID: 332254 Received 23 May 2018; Accepted 02 Jul 2018; Posted 06 Jul 2018  View: PDF

Abstract: Heterogeneously integrating III-V materials on silicon photonic integrated circuits has emerged as a promising approach to make advanced laser sources for optical communication and sensing applications. Tunable semiconductor lasers operating in the 2-2.5 µm are of great interest for industrial and medical applications since many gases (e.g., CO2, CO, CH4) and bio-molecules (such as blood glucose) have strong absorption features in this wavelength region. The development of integrated tunable laser sources in this wavelength range enables low-cost and miniature spectroscopic sensors. Here we report heterogeneously integrated widely tunable III-V-on-silicon Vernier lasers using two silicon micro-ring resonators as the wavelength tuning components. The laser has a wavelength tuning range of more than 40 nm near 2.35 µm. By combing two lasers with different distributed Bragg reflectors, a tuning range of more than 70 nm is achieved. Over the whole tuning range, the side mode suppression ratio (SMSR) is higher than 35 dB. As a proof-of-principle, this III-V-on-silicon Vernier laser is used to measure the absorption lines of CO. The measurement results match very well with the HITRAN database and indicate that this laser is suitable for broadband spectroscopy.

Parity-Time symmetry breaking transitions without exceptional points in dissipative photonic systems

Yogesh Joglekar and Andrew Harter

Doc ID: 314689 Received 11 Jan 2018; Accepted 28 Jun 2018; Posted 02 Jul 2018  View: PDF

Abstract: Over the past decade, parity-time ($\mathcal{PT}$)-symmetric Hamiltonians have been experimentally realized in classical, optical settings with balanced gain and loss, or in quantum systems with localized loss. In both realizations, the $\mathcal{PT}$-symmetry breaking transition occurs at the exceptional point of the non-Hermitian Hamiltonian, where its eigenvalues and the corresponding eigenvectors both coincide. Here, we show that, in lossy systems, the $\mathcal{PT}$ transition is a robust phenomenon that broadly occurs without an attendant exceptional point. With experimentally realizable quantum models in mind, we investigate dimer and trimer waveguide configurations with one lossy waveguide. We validate the tight-binding model results by using the beam propagation method analysis. Our results pave a robust way toward studying interplay between $\mathcal{PT}$ transitions and quantum effects in dissipative photonic configurations.

Saturated absorption of different layered Bi2Se3 films in resonance zone

Juna Zhang, Tian Jiang, Tong Zhou, Hao Ouyang, chenxi zhang, Xin Zheng, zhenyu wang, and Xiang'ai Cheng

Doc ID: 330805 Received 17 May 2018; Accepted 22 Jun 2018; Posted 26 Jun 2018  View: PDF

Abstract: Here, we used micro P-scan method to investigate the saturated absorption (SA) of different layered Bi2Se3 continuous films. Through resonance excitation, firstly, we studied the influence of the second surface state (2nd SS) on saturated absorption. The 2nd SS resonance excitation (~2.07 eV) brought a four orders larger free carrier cross section than usual which can be used to locate the 2nd SS. At a same time, we found the fast relaxation process of the massless Dirac electrons is much shorter than electrons in bulk states, which means Bi2Se3 saturable absorber can achieve high speed response when working in the 2nd SS resonance zone. Moreover, the 2nd SS excitation resonance would reduce the saturation intensity. Secondly, we studied the effect of the layers on the saturated absorption properties of materials. The results showed that the saturation intensity was positive correlated to the layers, the same as the modulation depth. And the thicker the Bi2Se3 film was, the less influence of the 2nd SS it would get. This work demonstrated that, using Bi2Se3 as saturable absorber, through changing the layers or excitation wavelength, a controllable saturated absorption could be achieved.

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.

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.

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.

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.

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.

Anomalous transport of light at the phase transition to localization: Strong dependence with incident angle

Ernesto Jimenez Villar, Mario Cesar Xavier, Niklaus Wetter, Valdeci junior, Weliton Martins, Gilberto de Sa, Gabriel Basso, Francisco Marques, and Viktor Ermakov

Doc ID: 326761 Received 26 Mar 2018; Accepted 05 Jun 2018; Posted 09 Jul 2018  View: PDF

Abstract: Disordered optical media have seen a growing interest in recent year due their potentials applications in solar collectors, random lasers, light confinement and other advance photonic functions. This paper studies the transport of light for different incidence angles in a strongly disordered optical medium composed by core-shell TiO2@Silica nanoparticles suspended in ethanol solution. A decrease of optical conductance and an increase of absorption near the input border are reported when the incidence angle increases. The specular reflection, measured for the photons that enter the sample, is lower than the effective internal reflection undergone by the coherently backscattered photons in the exact opposite direction, indicating a non-reciprocal propagation of light. This study represents a novel approach in order to understand the complex physics involved at the phase transition to localization.

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.

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