We investigate the electrically controlled light propagation in the metal–dielectric–metal plasmonic waveguide with a sandwiched graphene monolayer. The theoretical and simulation results show that the propagation loss exhibits an obvious peak when the permittivity of graphene approaches an epsilon-near-zero point when adjusting the gate voltage on graphene. The analog of electromagnetically induced transparency(EIT) can be generated by introducing side-coupled stubs into the waveguide. Based on the EIT-like effect, the hybrid plasmonic waveguide with a length of only 1.5 μm can work as a modulator with an extinction ratio of ～15.8 d B, which is 2.3times larger than the case without the stubs. The active modulation of surface plasmon polariton propagation can be further improved by tuning the carrier mobility of graphene. The graphene-supported plasmonic waveguide system could find applications for the nanoscale manipulation of light and chip-integrated modulation.
Light fields with spatially structured states of polarization（SoPs） are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional（3 D） modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.
We propose a low-threshold soliton fiber laser passively mode locked with two different types of film-like saturable absorbers, one of which is fabricated by mixing Bi2Te3 with de-ionized water, as well as polyvinyl alcohol（PVA）, and then evaporating them in a Petri dish, and the other of which is prepared by directly dropping Bi2Te3 solution on the PVA film. Both Bi2Te3–PVA films exhibit outstanding features of low loss, high flexibility, and easy synthesis. By incorporating Bi2Te3–PVA films into fiber lasers, stable single-soliton emissions are obtained at a low pump power of 13 mW. Our results suggest that the Bi2Te3 can work as a promising mode locker for ultrafast lasers,while PVA is an excellent host for fabricating high-performance film-based saturable absorbers.
Dong MaoBiqiang JiangXuetao GanChaojie MaYu ChenChujun ZhaoHan ZhangJianbang ZhengJianlin Zhao
We demonstrate the first achievement of continuous-wave(CW)pumped second harmonic generation(SHG)in few-and monolayer gallium selenide(GaSe)flakes,which are coated on silicon photonic crystal(PC)cavities.Because of ultrahigh second order nonlinearity of the two-dimensional(2D)GaSe and localized resonant mode in the PC cavity,SHG’s pump power is greatly reduced to microwatts.In a nine-layer GaSe coated PC cavity,while the optical power inside the GaSe flake is only 1.5%of that in the silicon PC slab,the SHG in GaSe is more than 650 times stronger than the third harmonic generation in silicon slab,indicating 2D GaSe’s great potentials to strengthen nonlinear processes in silicon photonics.Our study opens up a new view to expand 2D materials’optoelectronic applications in nonlinear regime and chip-integrated active devices.
Polarization oscillating beams, namely, polarization standing waves, commonly formed by a pair of coherent counterpropagating light waves with orthogonal polarizations, oscillate their states of polarization periodically within a wavelength interval, offering conceptual and practical interests in light-matter interactions such as the nonreciprocal magnetoelectric effect, and impressive applications in optical imaging, sensing, and chirality detection. Here, we propose a new class of polarization oscillating beams that longitudinally vary states of polarization with spatial intervals within centimeters via the superposition of two copropagating optical frozen waves with preshaped longitudinal intensity profiles and transverse phase structures. The flexibility and manipulability are demonstrated by creating several polarization oscillating beams with different polarization structures. This work paves a new way to manipulate other waves and may be useful for applications of optical standing waves in optical manipulation, light guiding of atoms, polarization-sensitive sensing, etc.
Optical vortices carrying orbital angular momentum(OAM)have attracted extensive attention in recent decades because of their interesting applications in optical trapping,optical machining,optical communication,quantum information,and optical microscopy.Intriguing effects induced by OAMs,such as angular momentum conversion,spin Hall effect of light(SHEL),and spin– orbital interaction,have also gained increasing interest.In this article,we provide an overview of the modulations of OAMs on the propagation dynamics of scalar and vector fields in free space.First,we introduce the evolution of canonical and noncanonical optical vortices and analyze the modulations by means of local spatial frequency.Second,we review the Pancharatnam–Berry(PB)phases arising from spin–orbital interaction and reveal the control of beam evolution referring to novel behavior such as spindependent splitting and polarization singularity conversion.Finally,we discuss the propagation and focusing properties of azimuthally broken vector vortex beams.
We report a method to tune the second harmonic generation(SHG) frequency of a metallic octamer by employing cylindrical vector beams as the excitation. Our method exploits the ability to spatially match the polarization state of excitations with the fundamental target plasmonic modes, enabling flexible control of the SHG resonant frequency.It is found that SHG of the octamer is enhanced over a broad band(400 nm) by changing the excitation from the linearly polarized Gaussian beam to radially and azimuthally polarized beams. More strikingly, when subjected to an azimuthally polarized beam, the SHG intensity of the octamer becomes 30 times stronger than that for the linearly polarized beam even in the presence of Fano resonance.
