Photonic Crystal Nanocavity Research Articles

Detection of ionized air using a photonic-crystal nanocavity excited by broadband light from a superluminescent diode.

It has been shown that silicon photonic crystal nanocavities excited by spectrally narrow light can be used to detect ionized air. Here, to increase the range of possible applications of nanocavity-based sensing, the use of broadband light is considered. We find that the use of a superluminescent diode (SLD) as an excitation source enables a more reproducible detection of ionized air. When our photonic-crystal nanocavity is exposed to ionized air, carriers are transferred to the cavity and the light emission from the cavity decreases due to free carrier absorption. Owing to the broadband light source, the resonance wavelength shifts caused by the carriers in this system (for example, due to temperature fluctuations) do not influence the emission intensity. SLD-excited cavities could be useful to determine the density of ions in air quantitatively.

Crosstalk-free all-optical switching enabled by Fano resonance in a multi-mode photonic crystal nanocavity.

We demonstrate all-optical switching using a multi-mode membranized photonic crystal nanocavity exploiting the free-carrier induced dispersion in InP and the sharp asymmetric lineshape of Fano resonances. A multi-mode cavity is designed to sustain two spatially overlapping modes with a spectral spacing of 18 nm. The measured transmission spectrum of the fabricated device shows multiple asymmetric Fano resonances as predicted by optical simulations. The capabilities of the device are benchmarked by comparing a wavelength conversion from 1538.2 nm to 1565.2 nm with a single-mode wavelength conversion at 1566.2 nm on the same device. The results show an improvement in signal quality with a 5.6 dB power penalty reduction at the receiver as well as in energy efficiency with a reduction of the pump power from 534 fJ/bit to 445 fJ/bit.

Giant Enhancement of Nonlinear Harmonic Generation in a Silicon Topological Photonic Crystal Nanocavity Chain

AbstractStrongly enhanced third‐harmonic generation (THG) by the topological localization of an edge mode in a Su‐Schrieffer‐Heeger (SSH) chain of silicon photonic crystal nanocavities is demonstrated. The edge mode of the nanocavity chain not only naturally inherits resonant properties of the single nanocavity, but also exhibits the topological feature with mode robustness extending well beyond individual nanocavity. By engineering the SSH nanocavities with alternating strong and weak coupling strengths on a silicon slab, the edge mode formation that entails a strong THG signal similar to that obtained from a single nanocavity is observed, which both show three orders of magnitude enhancement compared with that in a trivial SSH structure. The results indicate that the photonic crystal nanocavity chain can provide a promising on‐chip platform for topology‐driven nonlinear photonics.

Spontaneous Symmetry Breaking in a Coherently Driven Nanophotonic Bose-Hubbard Dimer.

We report on the first experimental observation of spontaneous mirror symmetry breaking (SSB) in coherently driven-dissipative coupled optical cavities. SSB is observed as the breaking of the spatial or mirror Z_{2} symmetry between two symmetrically pumped and evanescently coupled photonic crystal nanocavities, and manifests itself as random intensity localization in one of the two cavities. We show that, in a system featuring repulsive boson interactions (U>0), the observation of a pure pitchfork bifurcation requires negative photon hopping energies (J<0), which we have realized in our photonic crystal molecule. SSB is observed over a wide range of the two-dimensional parameter space of driving intensity and detuning, where we also find a region that exhibits bistable symmetric behavior. Our results pave the way for the experimental study of limit cycles and deterministic chaos arising from SSB, as well as the study of nonclassical photon correlations close to SSB transitions.

Direct observation of zero modes in a non-Hermitian optical nanocavity array

Zero modes are symmetry protected ones whose energy eigenvalues have zero real parts. In Hermitian arrays, they arise as a consequence of the sublattice symmetry, implying that they are dark modes. In non-Hermitian systems that naturally emerge in gain/loss optical cavities, particle-hole symmetry prevails instead; the resulting zero modes are no longer dark but feature &#x03C0;/2 phase jumps between adjacent cavities. Here, we report on the direct observation of zero modes in a non-Hermitian three coupled photonic crystal nanocavities array containing quantum wells. Unlike the Hermitian counterparts, the observation of non-Hermitian zero modes upon single pump spot illumination requires vanishing sublattice detuning, and they can be identified through far-field imaging and spectral filtering of the photoluminescence at selected pump locations. We explain the zero-mode coalescence as a parity-time phase transition for small coupling. These zero modes are robust against coupling disorder and can be used for laser mode engineering and photonic computing.

Imaginary couplings in non-Hermitian coupled-mode theory: Effects on exceptional points of optical resonators

Exceptional point (EP) degeneracies in coupled cavities with gain and loss provide on-chip photonic devices with unconventional features and performance. However, such systems with realistic structures often miss the exact EPs even in simulation, and the mechanism of this EP disruption has yet to be thoroughly identified. Here, we extend the coupled-mode theory of one-dimensional non-Hermitian resonator arrays to study the effects of the imaginary part of the inter-cavity coupling, which is a second-order term and attributed to material amplification, absorption, and radiation. By taking an appropriate gauge for the model, we clarify that the imaginary coupling components have a symmetric form in the effective Hamiltonian and hence represent non-Hermiticity. These additional factors can lift the gain- and loss-based EP degeneracies. However, they are proportional to the sum of the imaginary permittivities for involved cavity pairs. Thus, when the amplification and absorption of adjacent cavities are balanced, their contribution to the imaginary coupling is canceled, and the EP singularity can be restored. Radiation-induced imaginary couplings measure the change in net radiation loss by the interference between cavity modes. Their impact on the EP can also be counteracted by small cavity resonance detuning even in loss-biased cases. We show and analyze eligible simulation examples based on photonic crystal nanocavities, and highlight design of an ideal EP degeneracy that is protected by generalized PT symmetry and induced by radiation.

Semiclassical bifurcations and quantum trajectories: a case study of the open Bose–Hubbard dimer

We consider the open two-site Bose–Hubbard dimer, a well-known quantum mechanical model that has been realised recently for photons in two coupled photonic crystal nanocavities. The system is described by a Lindblad master equation which, for large numbers of photons, gives rise to a limiting semiclassical model in the form of a four-dimensional vector field. From the situation where both sites trap the same amount of photons under symmetric pumping, one encounters a transition that involves symmetry breaking, the creation of periodic oscillations and multistability as the pump strength is increased. We show that the associated one-parameter bifurcation diagram of the semiclassical model captures the essence of statistical properties of computed quantum trajectories as the pump strength is increased. Even for small numbers of photons, the fingerprint of the semiclassical bifurcations can be recognised reliably in observables of quantum trajectories.

Chaotic switching in driven-dissipative Bose-Hubbard dimers: When a flip bifurcation meets a T-point in $ \mathbb{R}^4 $

&lt;p style='text-indent:20px;'&gt;The Bose-Hubbard dimer model is a celebrated fundamental quantum mechanical model that accounts for the dynamics of bosons at two interacting sites. It has been realized experimentally by two coupled, driven and lossy photonic crystal nanocavities, which are optical devices that operate with only a few hundred photons due to their extremely small size. Our work focuses on characterizing the different dynamics that arise in the semiclassical approximation of such driven-dissipative photonic Bose-Hubbard dimers. Mathematically, this system is a four-dimensional autonomous vector field that describes two specific coupled oscillators, where both the amplitude and the phase are important. We perform a bifurcation analysis of this system to identify regions of different behavior as the pump power &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ f $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; and the detuning &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ \delta $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt; of the driving signal are varied, for the case of fixed positive coupling. The bifurcation diagram in the &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ (f, \delta) $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;-plane is organized by two points of codimension-two bifurcations——a &lt;inline-formula&gt;&lt;tex-math id="M5"&gt;\begin{document}$ \mathbb{Z}_2 $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;-equivariant homoclinic flip bifurcation and a Bykov T-point——and provides a roadmap for the observable dynamics, including different types of chaotic behavior. To illustrate the overall structure and different accumulation processes of bifurcation curves and associated regions, our bifurcation analysis is complemented by the computation of kneading invariants and of maximum Lyapunov exponents in the &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ (f, \delta) $\end{document}&lt;/tex-math&gt;&lt;/inline-formula&gt;-plane. The bifurcation diagram displays a menagerie of dynamical behavior and offers insights into the theory of global bifurcations in a four-dimensional phase space, including novel bifurcation phenomena such as degenerate singular heteroclinic cycles.&lt;/p&gt;

Electrically controlled on-demand photon transfer between high-Q photonic crystal nanocavities on a silicon chip

Optical buffer memories, which do not rely on an intermediate conversion between optical and electrical signals, can be used to realize optical networks with low latency and low energy consumption. Photonic-crystal nanocavities can confine photons in a very small region for a long time, and thus may be used as core components of such optical buffer memories. However, a scalable method for on-demand photon transfer between nanocavities is required. Here we demonstrate a photonics–electronics integration solution that realizes electrical control of a coupled ultrahigh-quality-factor nanocavity system on a silicon chip. In this system, the photons confined in one of the two storage nanocavities can be transferred to the other storage nanocavity by applying a voltage pulse to the control cavity. A transfer efficiency of 76% and a cavity photon lifetime of 1.3 ns after the transfer are achieved. Researchers demonstrate the transfer of photons from one storage nanocavity into another by applying a voltage pulse. A transfer efficiency of 76% is achieved.

Dispersive coupling between MoSe2 and an integrated zero-dimensional nanocavity

Establishing a coherent interaction between a material resonance and an optical cavity is a necessary first step to study semiconductor quantum optics. Here we report on the signature of a coherent interaction between a two-dimensional excitonic transition in monolayer MoSe2 and a zero-dimensional, ultra-low mode volume (V m ∼ 2(λ/n)3) on-chip photonic crystal nanocavity. This coherent interaction manifests as a dispersive shift of the cavity transmission spectrum, when the exciton-cavity detuning is decreased via temperature tuning. The exciton-cavity coupling is estimated to be ≈6.5 meV, with a cooperativity of ≈4.0 at 80 K, showing our material system is on the verge of strong coupling. The small mode-volume of the resonator is instrumental in reaching the strongly nonlinear regime, while on-chip cavities will help create a scalable quantum photonic platform.

Exciting Magnetic Dipole Mode of Split-Ring Plasmonic Nano-Resonator by Photonic Crystal Nanocavity.

On-chip exciting electric modes in individual plasmonic nanostructures are realized widely; nevertheless, the excitation of their magnetic counterparts is seldom reported. Here, we propose a highly efficient on-chip excitation approach of the magnetic dipole mode of an individual split-ring resonator (SRR) by integrating it onto a photonic crystal nanocavity (PCNC). A high excitation efficiency of up to 58% is realized through the resonant coupling between the modes of the SRR and PCNC. A further fine adjustment of the excited magnetic dipole mode is demonstrated by tuning the relative position and twist angle between the SRR and PCNC. Finally, a structure with a photonic crystal waveguide side-coupled with the hybrid SRR–PCNC is illustrated, which could excite the magnetic dipole mode with an in-plane coupling geometry and potentially facilitate the future device application. Our result may open a way for developing chip-integrated photonic devices employing a magnetic field component in the optical field.

LED pumped Raman laser: Towards the design of an on-chip all-silicon laser

Design of an on-chip silicon Raman laser is proposed based on a slotted photonic crystal nanocavity. The slot has been considered to be filled with the silicon nanocrystal material having ultra-high Raman gain coefficient, which has further been fortified by the tight spatio-temporal optical confinement inside the nanocavity. Consequently, the threshold power as required for the lasing is miniaturized substantially, and a light emitting diode (LED) suffices for optical pumping. The LED is amenable for integration on the same platform as of the silicon nanocrystal embedded slotted photonic crystal nanocavity exploiting the efficient electroluminescence of the silicon nanocrystal material. The coupled mode equations for stimulated Raman scattering interactions, which govern the evolution of the pump and the Stokes photons, have been solved using a novel self-consistent algorithm to analyze the characteristics of the proposed laser. A lasing threshold-power, as small as, 5 μW has been achieved. Moreover, small-signal frequency response of the proposed LED pumped laser has also been evaluated in steady-state condition, and a modulation bandwidth as high as ∼1.6 GHz has been demonstrated which is almost two orders of magnitude higher than that of the conventional Raman lasers.

Topological hybrid nanocavity for coupling phase transition

Topological photonic nanocavity provides a robust platform for realizing nano-photonic devices and studying light–matter interaction. Here, a topological photonic-plasmonic hybrid nanocavity, assembling a topological photonic crystal (PhC) nanocavity with a plasmonic nano-antenna, is proposed to have an ultra-high figure of merit Q/V of , which is two orders higher than that of the bare topological PhC nanocavity. The single-atom cooperativity parameter is improved by over 60 times due to the large enhancement of Q/V, which makes the coupling between light and a single emitter enter a strong coupling region in topological photonic realm for the first time. Meanwhile, strong coupling and weak coupling can be easily switched in the topological hybrid system by tuning the structure dimension of plasmonic nano-antennas. This work provides a robust platform to control coupling phase transition between light and a single emitter, which has great potential in topological lasers, quantum optics and quantum information.

Design considerations of III-nitride-based two-dimensional photonic crystal cavities with crystallographically induced disorder

We present a study on the improvement of quality factors (Q-factors) of III-nitride-based two-dimensional photonic crystal (2D-PhC) nanocavities. Although III-nitride-based 2D-PhC cavities have been studied for long time, they typically show relatively low experimental Q-factors due to disorders inevitably introduced during the fabrication processes. In order to realize high-Q-factors, it is necessary to introduce cavities that are tolerant to disorder. We numerically reproduce the experimental found disorder in simulations, and discuss the influence of disorder on Q-factors of several types of cavities. We demonstrate the suitability of these cavities for the realization of high-Q-factors, and show which structures have the largest tolerance for disorders.

Spontaneous Emission Enhancement of CdSe Quantum Dots Embedded in a Two-dimensional Photonic Crystal L3 Nanocavity

Two-dimensional photonic crystal nanocavities were designed to tailor cavity quantum electrodynamics. Enhancing the spontaneous emission of low-quality factor nanocavity with embedded CdSe quantum dots (QDs) emitters is the aim of this study. Low concentration layer of CdSe QDs was sandwiched between two layers of Si2 N3 membrane using plasma-enhanced chemical vapor deposition. The modification rate in spontaneous emission of L3 nanocavity up to 2.3-fold has been observed at 629.5 nm in compare to bare cavities. High field confinement in the sub-wavelength regime became an interest field for quantum electrodynamics applications and good platform to study light matter interactions.

Determination of Nonlinear Optical Efficiencies of Ultrahigh-Q Photonic Crystal Nanocavities with Structural Imperfections

Determination of Nonlinear Optical Efficiencies of Ultrahigh-<i>Q</i> Photonic Crystal Nanocavities with Structural Imperfections

Photon blockade in a coupled double quantum dot—nonlinear optomechanical system

We propose a scheme to generate strongly sub-Poissonian light via photon blockade in a photonic crystal nanocavity embedded with a χ (2) nonlinear material and two interacting quantum dots (QD). The second- order correlation function at zero time delay g (2)(0) in our scheme can be reduced to g (2)(0) ∼ 10−3 by a large χ (2) nonlinearity and by optimizing the QD and optical cavity detuning. Our proposal provides a highly tunable and efficient method for single photon source on demand which has potential applications in solid state based quantum information processing.

High-Q 1D rod-based nanocavities.

We report an analysis of one-dimensional rod-based photonic crystal nanocavities. These cavities offer opportunities for dielectric materials which lack a matching low-refractive index substrate or are limited in under-etching possibilities to create slab-based PhC cavities. They offer high theoretical Q-values exceeding 106 for transverse magnetic polarized modes with modal volumes below 2.5(λ/n)3. For practical implementations, we propose embedding these structures in a low-refractive index polymer. An analysis of intentionally introduced variations in a rod diameter reveals which design directions should be followed in order to create cavities that are most robust for fabrication-induced variations.

Detection of hemoglobin in blood and urine glucose level samples using a graphene-coated SPR based biosensor

In this paper, we have presented a design and simulation of a graphene-coated surface plasmon resonance (SPR) based biosensor for targeting specific biological components. We have explicitly shown the detection of the hemoglobin level in blood samples and the glucose concentration level in urine samples by using the finite element method (FEM) based numerical simulation. In the blood component, the 0.001 refractive index increment causes a 6.1025 g/l hemoglobin (HB) level increment, which has been detected using this SPR based sensor with 200 deg/RIU angular sensitivity. Moreover, we have also detected the presence or absence of diabetes using the glucose concentration level in urine samples with this SPR sensor. Therefore, the novelty of this paper is detecting the blood hemoglobin level and glucose concentration levels in urine samples more accurately than the previously proposed whispering gallery mode (WGM) and photonic crystal nanocavity based optical sensors.

1.2-µm-band ultrahigh-Q photonic crystal nanocavities and their potential for Raman silicon lasers

Nanocavity devices based on silicon that can operate in the 1.2-µm band would be beneficial for several applications. We fabricate fifteen cavities with resonance wavelengths between 1.20 and 1.23 µm. Experimental quality (Q) factors larger than one million are obtained and the average Q values are lower for shorter wavelengths. Furthermore, we observe continuous-wave operation of a Raman silicon laser with an excitation wavelength of 1.20 µm and a Raman laser wavelength of 1.28 µm. The Q values of the nanocavity modes used to confine the excitation light and the Raman scattered light are about half of those for our Raman silicon laser operating in the 1.55-µm band. Nevertheless, this device exhibits an input-output characteristic with a clear laser threshold. Finally, we consider the effect of the higher scattering probability at shorter wavelengths on the Raman laser performance in the 1.2-µm band.