Small semiconductor lasers have attracted a wide interest in academia owing to their potential as highly integrated components in photonic circuits. Particularly, microdisk lasers exploiting whispering gallery modes have been regarded as a good candidate because of ultrasmall modal volume and low threshold property. To exploit large index difference between gain and surrounding medium, microdisk resonators with an underlying post using undercut etching have been proposed and widely investigated in many previous studies. However, it has been challenging in microdisk laser to operate single mode due to the large number of exsiting whispering gallery modes. Here, we propose and demonstrate a novel subwavelength scale microdisk laser. InGaAsP multi-quantum wells microdisk is self-suspended in air by connecting bridges. The behavior of TE-like whispering gallery modes, which belong to most dominant class of mode in thin disk configuration, is both numerically and experimentally investigated. We highlight that bridge does not only provide mechanical stability, but the number of bridges can be an important factor to improve or suppress wave confinement of whispering gallery modes by protecting or breaking spatial symmetry of mode. Moreover, a suitable choice of bridges increases quality factor by up to 79% comparing to the microdisk resonator without bridges. Using this scheme, we numerically and experimentally investigate mode selectivity and further demonstrate single mode microdisk lasers operating at near-infrared telecommunication wavelength.
We present progress on the experimental observation of exceptional points (EPs) in passive plasmonic nanostructures. The system has EPs which are degeneracies in open wave systems where at least two energy levels and their corresponding eigenstates coalesce. They manifest themselves by the simultaneous degeneracy of both resonant frequencies and its linewidths. We consider a plasmonic system based on a multilayer plasmonic structure with structural offset [1, 2]. The realization of an EP via hybridized modes requires the control of at least two physical parameters. The two parameters used for the above system to reach an EP are the shift between bars and the periodicity.
Mie theory describes how electromagnetic waves scatter at the interface between a homogeneous spherical dielectric particle surrounded by a material of a different optical index. Numerical improvements have allowed studying more complicated geometries with the multipole decomposition of the spherical harmonics. Hence, Mie theory is widely applied in theoretical and applied physics, to enable novel light manipulation, to model Fano resonances, nonlinear optics, or to design dielectric metamaterials. Recently, the anapole state has brought attention to the community as one of the most interesting phenomena. It can be interpreted as a destructive interference in the far field between the fields scattered by the toroidal and electrical dipoles at a given frequency. Such element is therefore transparent to any incoming plane wave. However, things are different if the element is excited in its near field, where it can be excited by an internal source. In this work, we experimentally demonstrate a semiconductor laser based on a single cylindrical resonator suspended in air. An epitaxially grown InGaAsP layer on an InP substrate is patterned by e-beam lithography. We study the shift of the Mie resonance as geometrical parameters are varied, and show how it affects the shift of the lasing frequency. Our investigation of Mie resonances from an active gain medium would is a rich platform to study nontrivial excitation of a complex field and paves the way to designing active devices exploiting Mie theory.
Steering the beam of a wave source has been demonstrated using mechanical and non-mechanical techniques. While mechanical techniques are bulky and slow, non-mechanical techniques rely on breaking the symmetry of the refractive index profile either using asymmetric structure or injecting a non-uniform current. In this contribution, we theoretically and experimentally demonstrated a new type of topological steering of light sources in which the phase offset is provided by Floquet-Bloch phase in periodic structure. It was shown that in periodic structures, there exist singular states in the radiation region of the band diagram that exhibit diverging quality factor. Thus light sources can operate at these states with lower power threshold. The existence of these singular states are topologically protected, and their momentum are very sensitive to any small perturbations, which is used to control the steering angle. By uniformly controlling some parameters in the system, such as a physical dimension or injecting current uniformly, the beam of the light source steers. Our experimental demonstrations open new paradigm in the implementation of light steering with applications in data communications, bio imaging and sensing.
In 1929, von Neumann and Wigner showed that Schrödinger’s equation can have, somewhat surprisingly, bound states above the continuum threshold . These bound states represent the limiting case of quasi-bound states with an infinite lifetime, i.e., resonances that do not decay. It was recently realized that bound states in the continuum (BICs) are intrinsically a wave phenomenon and are thus not restricted to quantum mechanics. Since then, they have been shown to occur in many different fields of wave physics such as acoustics and photonics.
In photonics’ terminology, BICs are eigenmodes of an open system with an infinite radiation quality factor, Qrad. To take advantage of this unique property to design high quality resonant cavities, most investigations have focused on dielectric structures that, unlike their plasmonic counterparts, are not limited by their material quality factor, Qmat [3-5]. To investigate the properties of BICs, various platforms have been used such as 1D gratings , waveguide arrays , and 2D photonic crystal slabs .
In this contribution, we have designed a high quality cavity based on a BIC and harnessed its novel properties to achieve a compact low-threshold nanophotonic laser.
 J. von Neumann and E. Wigner, “On some peculiar discrete eigenvalues” Phys. Z, 465 (1929).
 C. Linton et al., “Embedded trapped modes in water waves and acoustics” Wave Motion 45, 16 (2007).
 D. C. Marinica et al., “Bound states in the continuum in photonics” Phys. Rev. Lett. 100, 183902 (2008).
 Y. Plotnik et al., “Experimental observation of optical bound states in the continuum” Phys. Rev. Lett. 107, 183901 (2011).
 C. W. Hsu et al., “Observation of trapped light within the radiation continuum” Nature 499, 188 (2013).
A budding topic of interest is that of applications in the field of plasmonics which currently range from chemical and biological sensing to enhanced photovoltaics. At the core of these plasmonic devices are resonances that govern their unique function and the ability to manipulate said resonances is crucial to their design. In order to manipulate resonances, we must be able to observe them quantitatively. We describe an effective Hamiltonian formalism to quantitatively study and tailor plasmonic resonances of coupled plasmonic particles at optical frequencies.
Over the past fifteen years, a lot of efforts have been focused on understanding the effective properties of metamaterials . In the last few years, metasurfaces in particular have been widely investigated . Several homogenization methods dedicated to them have been proposed but, due to the topic’s complexity, none have yet to be widely accepted. We considered a specific homogenization method dedicated to metasurfaces, namely Generalized Sheet Transition Conditions (GSTC, ). This method was chosen because it is compatible with retrieval from reflection and transmission coefficients. In this method, metasurfaces are characterized by electric and magnetic susceptibilities. In the literature, retrieved effective parameters have been shown to violate causality around resonances and this has been attributed to spatial dispersion . In order to determine if spatial dispersion is the only source of this phenomenon, we have investigated the statistical properties of estimators that have been put forward for these susceptibilities. We have thus computed the Cramér-Rao lower bounds on the variance of these estimators. We have shown that this bound increases substantially around resonances making retrieval possible only for very high Signal-to-Noise Ratio (SNR, ). Therefore, in experiments, issues arising from spatial dispersion and noise compound and result in non-physical effective parameters. To mitigate this, we have proposed a least-squares estimator for susceptibilities that has a better performance with respect to noise. Sensitivity to noise is particularly acute for low-loss metasurfaces. It often results in required SNRs that are unachievable in practice. The present work is thus relevant to the development of loss-compensated metasurfaces for which the issues posed by retrieval will have to be closely considered for accurate and robust device characterization.