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Modulation properties of solitary and optically injected phased-array semiconductor lasers

Nianqiang Li, Hadi Susanto, Ben Cemlyn, Ian Henning, and Michael Adams

Doc ID: 328119 Received 12 Apr 2018; Accepted 17 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: We study modulation properties of two-element phased-array semiconductor lasers that can be described by coupled mode theory. We consider four different waveguide structures and modulate the array either in phase or out of phase within the phase-locked regions, guided by stability diagrams obtained from direct numerical simulations. Specifically, we find that out-of-phase modulation allows for bandwidth enhancement if the waveguide structure is properly chosen; for example for a combination of index antiguiding and gain-guiding, the achievable modulation bandwidth in the case of out-of-phase modulation could be much higher than the one when they are modulated in phase. Proper array design of the coupling, controllable in terms of the laser separation and the frequency offset between the two lasers is shown to be beneficial to slightly improve the bandwidth but not the resonance frequency, while the inclusion of the frequency offset leads to the appearance of double peak response curves. For comparison, we explore the case of only modulating one element of the phased array, and find that double peak response curves are found. To improve the resonance frequency and the modulation bandwidth, we introduce simultaneous external injection into the phased array and modulate the phased array or its master light within the injection locking region. We observe a significant improvement of the modulation properties, and in some cases, by modulating the amplitude of the master light before injection, the resulting 3-dB bandwidths could be enhanced up to 160 GHz. Such a record bandwidth for phased-array modulation could pave the way for various applications, notably optical communications that require high-speed integrated photonic devices.

Passively Q-switched fs-laser-written thulium waveguide laser based on evanescent field interaction with carbon nanotubes

Esrom Kifle, Pavel Loiko, Javier Vazquez de Aldana, Carolina Romero, Airan Rodenas, Sun Young Choi, Ji Eun Bae, Fabian Rotermund, Viktor Zakharov, Andrei Veniaminov, Magdalena Aguilo, Francesc Diaz, Uwe Griebner, Valentin Petrov, and Xavier Mateos

Doc ID: 336536 Received 29 Jun 2018; Accepted 17 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: Surface channel waveguides (WGs) were fabricated in a monoclinic Tm3+:KLu(WO4)2 crystal by femtosecond direct laser writing (fs-DLW). The WGs consisted of a half-ring cladding with a diameter of 50 and 60 µm located just beneath the crystal surface. They were characterized by confocal laser microscopy and µ-Raman spectroscopy, indicating a reduced crystallinity and stress-induced birefringence of the WG cladding. In the continuous-wave mode, under Ti:Sapphire laser pumping at 802 nm, the maximum output power reached 171.1 mW at 1847.4 nm corresponding to a slope efficiency η of 37.8% for the 60 µm diameter WG. The WG propagation loss was 0.7±0.3 dB/cm. The top surface of the WGs was spin-coated by a PMMA film containing randomly-oriented (spaghetti-like) arc-discharge single-walled carbon nanotubes serving as a saturable absorber based on evanescent field coupling. Stable passively Q-switched (PQS) operation was achieved. The PQS 60 µm diameter WG laser generated a record output power of 150 mW at 1846.8 nm with η = 34.6%. The conversion efficiency with respect to the CW mode was 87.6%. The best pulse characteristics (energy / duration) were 105.6 nJ / 98 ns at a repetition rate of 1.42 MHz.

Mid-infrared high-Q germanium nanocavity

Tinghui Xiao, Ziqiang Zhao, Wen Zhou, Mitsuru Takenaka, Hon Tsang, Zhenzhou Cheng, and Keisuke Goda

Doc ID: 328993 Received 23 Apr 2018; Accepted 16 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: Mid-infrared (MIR) integrated photonics has attracted broad interest due to its promising applications in biochemical sensing, environmental monitoring, disease diagnosis, and optical communication. Among MIR integration platforms, germanium-based platforms hold many excellent properties, such as wide transparency windows, high refractive indices, and high nonlinear coefficients, but the development of MIR germanium photonic devices is still in its infancy. Specifically, MIR high-Q germanium resonators with comparable or even superior performance to their silicon counterparts remain unprecedented. Here we experimentally demonstrate an MIR germanium nanocavity with a Q factor of ~18,000, the highest-to-date of reported nanocavities across all MIR integration platforms. This is achieved through a combination of feasible theoretical design, Smart-Cut methods for wafer development, and optimized device fabrication processes. Our nanocavity, with its high Q factor and ultrasmall mode volume, opens new avenues for on-chip applications in the whole fingerprint spectral region (2 - 15 µm).

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.

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.

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