RINP 485 No of Pages 4, Model 5G 30 December 2016 Results in Physics xxx (2016) xxx–xxx Contents lists available at ScienceDirect Results in Physics journal homepage: www.journals.elsevier.com/results-in-physics New surface plasmon polariton waveguide based on GaN nanowires Jun Zhu a,b,c,⇑, Zhengjie Xu b, Wenju Xu b, Fu Deli b, Shuxiang Song b 10 2 13 14 15 16 17 18 19 20 21 22 23 24 a Guangxi Key Lab of Multi-source Information Mining & Security, Guangxi Normal University, Guilin 541004, China College of Electronic Engineering, Guangxi Normal University, Guilin 541004, China c Guangxi Key Laboratory of Automatic Detecting Technology and Instruments, Guilin University of Electronic Technology, Guilin 541004, China b a r t i c l e i n f o Article history: Received 22 November 2016 Received in revised form 19 December 2016 Accepted 19 December 2016 Available online xxxx Keywords: Random laser Surface plasmon polariton Feedback mechanism Low threshold Subwavelength constraints a b s t r a c t Lasers are nowadays widely used in industry, in hospitals and in many devices that we have at home Random laser development is challenging given its high threshold and low integration Surface plasmon polariton (SPP) can improve random laser characteristics because of its ability to control diffraction In this study, we establish a random laser structural model with silicon-based parcel GaN nanowires The GaN nanowire gain and enhanced surface plasmon increase population inversion level Our laser model is based on random particle scattering feedback mechanism, nanowire use, and surface plasmon enhancement effect, which causes stochastic laser emergence Analysis shows that the SPP mode and nanowire waveguides coupled in the dielectric layer of low refractive index can store light energy like a capacitor under low refractive index clearance The waveguide mode field area and limiting factors show that the modeled laser can achieve sub-wavelength constraints of the output light field We also investigate emergent laser performance for a more limited light field capacity and lower threshold Ó 2016 The Author Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Introduction 42 Random laser is an unconventional laser with a feedback mechanism based on random scattering [1,2] This feedback mechanism is completely different from that of traditional lasers with mirror reflection [3–5] This unique feedback mechanism is very useful for lasers without effective reflection components, such as UV and X-ray lasers [6] H Cao and team from Northwestern University proposed the use of ZnO powder-based lasers [7–9] They were also the first to observe coupling between random laser modes and random system interaction between intrinsic modes The low manufacturing cost, flexibility, special wavelength, and substrate compatibility of random laser make its use beneficial Random laser is a reliable and cost-efficient identification method in the field of search and rescue and machine vision [10,11] Xiaoyang Zhu and team reported the very low laser threshold and high quality factor of nanowire wavelength tunable lasers [12,13] However, the current developed random laser still has a high threshold and low integration The application of surface plasmon in improving diffraction limitations has been investigated Surface plasmon polariton (SPP) is a surface electromagnetic wave that spreads in the interface between two media instead of the dielectric constant 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 ⇑ Corresponding author at: College of Electronic Engineering, Guangxi Normal University, Guilin 541004, China E-mail address: zhujun1985810@sohu.com (J Zhu) [14] The surface pattern of SPP tightly restricts light in the interface At the same time, it is far smaller than the wavelength of free space in the space dimension, which is no longer restricted to the diffraction limit Therefore, SPP enables laser device miniaturization and integration [3,12,15] Based on this background, this study establish random laser structural model with silicon-based parcel GaN nanowires The laser model is based on random particle scattering feedback mechanism, nanowires, and surface plasmon enhancement effect, which causes stochastic laser emergence 62 Physical model and theoretical analysis 71 Structural model of GaN nanowires 72 Fig shows the structural model of the random laser established with silicon parcel GaN nanowires The model has a bottom silicon layer, a GaN nanowire package, a second MgF2 dielectric layer, and a third Au layer Incident light from the silicon surface with a vertical angle incident to the MgF2 dielectric layer is concentrated in the electric field between the gold layer and GaN nanowires Light is pumped along the angle of incidence, activating metal on the sides of the silicon surface to produce electronic and photonic resonance A laser is formed on both ends of the nanowires because the gain of GaN nanowires and SPP enhancement will increase population invasion level GaN nanowires grown by MOCVD technology have good optical properties when 73 http://dx.doi.org/10.1016/j.rinp.2016.12.019 2211-3797/Ó 2016 The Author Published by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Zhu J et al New surface plasmon polariton waveguide based on GaN nanowires Results Phys (2016), http://dx.doi.org/ 10.1016/j.rinp.2016.12.019 63 64 65 66 67 68 69 70 74 75 76 77 78 79 80 81 82 83 84 RINP 485 No of Pages 4, Model 5G 30 December 2016 J Zhu et al / Results in Physics xxx (2016) xxx–xxx Fig 1 is Silicon; is GaN nanowires; is MgF2 dielectric layer; is Au metal layer;5 is incident light; is pump light; is laser The model has a bottom silicon layer, a GaN nanowire package, a second MgF2 dielectric layer, and a third Au layer Incident light from the silicon surface with a vertical angle incident to the MgF2 dielectric layer is concentrated in the electric field between the gold layer and GaN nanowires Mathematical analysis of model 93 The effective mode field area Aeff of the waveguide mode is as follows: 94 Z Z Aeff ¼ 2 Z Z jEj2 dxdy = jEj4 dxdy ð1Þ where E is the electric field The mode field area of diffraction limit A0 is defined as follows: A0 ¼ k =4 Fig Text system of experiment 85 86 87 88 89 90 91 92 combined with plasma, providing a wide band gap range The MgF2 dielectric layer prevents metal oxidation and focuses light to within the nanowire vicinity The laser stochastically emerges from the ends of the nanowires through random particle scattering feedback mechanism and SPP enhancement effect The structural model is not only useful for effective reflection element laser manufacture, but also provides an effective light source for small areas of photonic circuits and optoelectronic integration ð2Þ Limiting factor C is defined as the ratio of electric field energy and total energy of the waveguide in the GaN nanowires The characteristics Q and laser threshold gth are further investigated based on waveguide mode characteristics and optical resonator cognition The laser optical resonator is assessed by the quality factor Q Stronger photon microcavity ability is associated with higher quality factor A low pump value is required to activate the laser The pump value is expressed as follows: Q ¼ 2p f e Pd ; ð3Þ Fig Electric field distribution Please cite this article in press as: Zhu J et al New surface plasmon polariton waveguide based on GaN nanowires Results Phys (2016), http://dx.doi.org/ 10.1016/j.rinp.2016.12.019 95 96 98 99 100 101 103 104 105 106 107 108 109 110 111 112 114 RINP 485 No of Pages 4, Model 5G 30 December 2016 J Zhu et al / Results in Physics xxx (2016) xxx–xxx Fig Surface plasmon waveguide mode features: (a) the effective refractive index; (b) transmission loss; (c) the normalized mode field area; (d) limiting factors Fig Laser characteristics (a) contrast fig of too sample’s input power and output power relationship; (b) emission spectra of the four corresponding dot in fig (a) P1, P2, P3, P4 115 117 e ẳ n0 hfV; 4ị 118 120 de dn n0 À t Pd ¼ À ¼ À :hfV ¼ e sR :hfV; dt dt sR ð5Þ 121 123 124 125 126 127 128 Q ¼ 2pf sR L ¼ 2p f : d:c ð6Þ where f is the intracavity frequency of the light field, e is the total energy of intracavity storage, Pd is the energy loss per unit time, n0 is the photon number density inside the cavity at the moment t = 0, h is the Planck constant, V is the cavity volume, n is the photon number density inside the cavity, sR is the time constant, d is the cavity loss, and L is the cavity length We only consider the resonator mirror loss and disregard other cavity losses Moreover, the laser threshold gain is affected by GaN cavity length L and end surface reflectance R End reflectivity R is defined as follows: R ¼ ðneff 1ị=neff ỵ 1ị 7ị Gain threshold is expressed as follows: g th ẳ k0 aeff ỵ ln1=Rị=Lị=Cneff =nwire ị: 129 130 131 132 133 135 136 ð8Þ In formula (8), the first transmission loss on the right side of equation aeff includes the metal and radiation loss associated with nanowire coupling The second transmission loss includes cavity Please cite this article in press as: Zhu J et al New surface plasmon polariton waveguide based on GaN nanowires Results Phys (2016), http://dx.doi.org/ 10.1016/j.rinp.2016.12.019 137 139 140 141 142 RINP 485 No of Pages 4, Model 5G 30 December 2016 143 144 145 146 147 J Zhu et al / Results in Physics xxx (2016) xxx–xxx mirror loss The internal absorption and scattering losses of the nanowires are disregarded Therefore, k0 is the wave number in a vacuum, k0 ¼ 2p=k; nwire is the refractive index of gain medium nanowires, and the scaling factor neff =nwire is the enhanced part mode of the refractive index 148 Simulation and experiment 149 Experimental system 150 Fig shows the experimental system design The experiment is conducted at room temperature with thrice the frequency by Nd: YAG laser in ns The pump samples of the experimental system have an impulse of 10 Hz, wavelength of 355 nm, and beam radius of approximately 20 lm along a specific direction of incidence to the experimental samples The radiation laser passing through a cylindrical lens and the CCD receiving object passing straight through an objective are simultaneously detected by a spectrometer 151 152 153 154 155 156 157 158 Moreover, the laser has higher light field capacity limit and lower threshold 201 Conclusion 203 A variety of nano-laser light sources have been developed in recent years, with applications in optical interconnection, biological detection, medical treatment, nanometer lithography, and data storage Although different applications require different working conditions and different volumes, laser development is taking a more miniaturized direction Therefore, we introduce a new type of laser and analyze its features based on the SPP waveguide theory We obtain ideal waveguide mode features, high quality factors, and low threshold limit by adjusting waveguide design parameters Thus, our nanometer laser has a higher light field capacity limit and lower threshold 204 Uncited reference 215 [16] 159 Electrical field analysis 160 190 The design model of the electric field distribution is shown in Figs 2(e) and 3(a)À(d) Fig 3(c) shows the normalized electric field distribution represented by the horizontal and vertical dashed lines The device widths are 600 nm and 500 nm The bottom silicon layer thickness is 200 nm The GaN nanowire diameter is 80 nm, and the MgF2 dielectric layer thickness is 50 nm The Au metal layer thickness is 140 nm Fig shows that the device design strongly localizes light characteristics, which significantly enhances the electric field of the middle MgF2 layer This phenomenon is caused by the combination of surface plasmon waveguide, SPP mode, and nanowire waveguide mode coupled with the low refractive index of the air gap layer Similar to capacitors, low refractive gaps store light energy Most of the light field is limited in the low refractive index of the air gap to form a highly localized enhancement effect, therefore obtaining laser emission in the subwavelength constraints The electric field energy is mainly distributed between the nanowires and MgF2 Therefore, we analyze the effects of MgF2 thickness MF and nanowire radius r on waveguide mode characteristics GaN nanowire radius r values are set as 50, 60, 70, and 80 nm The simulation results are shown in Fig 4.When r is fixed, the effective refraction stably oscillates, as shown in Fig When MF is fixed, the effective refractive index increases as nanowire radius increases This result is caused by expanding the highly refractive medium area Therefore, the refractive index also increases The limiting factor also increases as MF and r increase Fig 4(c) shows that when nanowire radius is fixed, increasing MgF2 thickness will increase the normalized mode field area The normalized mode field area is approximately 0.02, as shown in Fig 3(c) and (d).The limiting factor is 0.25 Therefore, the model obtains an output light field with deep subwavelength constraints 191 Laser characteristic analysis 192 The pump intensity is set at 1.0 MW/cm2.The structures with and without the nanowire waveguide are analyzed, as shown in Fig The fold point (threshold) is approximately0.5 MW/cm2 and 0.6 MW/cm2, as shown in Fig 5(a) The line width’s peak value is less than 0.35 nm (laser mode), as depicted in Fig 5(b) More peak values appear in the spectrum as the pump intensity increases The number of peak values increases with area Therefore, the waveguide structure design realizes a coherent random laser and the localization of GaN nanowire waveguide is improved 161 162 163 164 165 166 167 168 169 170 171 172 173 174 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Anisotropy-assisted non-scattering coherent absorption of surface plasmon- polaritons Ann Phys 2016;528(7– 8):537–42 [12] Yang F, Tian H Surface plasmon polaritons mode conversion via a coupled plasmonic system... metal whiskers by surface plasmon polariton excitation MRS Adv 2016;1(12):1–6 [14] Wu JJ, Lin HE, Yang TJ, et al Open waveguide based on low frequency spoof surface plasmon polaritons J Electromagn... numerical investigation of surface plasmon waveguides Opt Commun 2017;382:132–7 [7] Kumar G, Sarswat PK Interaction of surface plasmon polaritons with nanomaterials In: Reviews in plasmonics 2015 Springer