Cavity-waveguide Systems Research Articles

Phase‐Coupling‐Induced Far‐Field Modulation between Nontrivial and Trivial Modes in Cavity–Waveguide Systems

Photonic crystal (PhC) can be accurately designed to generate nontrivial and trivial modes, that is, edge states (ES)/corner states (CS) and cavity modes, respectively. The coupled cavity–waveguide system designed by PhC provides a chip‐scale platform to manipulate electromagnetic (EM) waves that is usually based on near‐field coupling between nontrivial and trivial modes. However, the far‐field interaction between nontrivial and trivial modes for manipulating EM waves has not attracted wide attention yet. Herein this article, the coupled cavity–waveguide systems, which consist of two separated CS cavities (interacting with single/multiple trivial cavity/cavities) coupled by means of an ES waveguide, are designed to robustly tune the transmission properties of EM waves by modulating the phase coupling between CS cavities. As proof‐of‐principle examples, single‐, dual‐, and triple‐electromagnetically‐induced‐transparency‐like (EIT‐like) phenomena with tunable transmission spectra are theoretically and numerically demonstrated by controlling the distance (generated phase accumulation) between the CS cavities. In addition, the robustness in generating EIT‐like transmission characteristics is also demonstrated due to the robustness of the CS cavities. The unique cavity–waveguide systems with unprecedented capability in robustly tuning the transmission spectra of EM waves can be extended to design other high‐performance devices with potential applications in sensing, detecting, and information processing.

Enhanced sensing of optomechanically induced nonlinearity by linewidth suppression and optical bistability in cavity-waveguide systems.

We study the enhanced sensing of optomechanically induced nonlinearity (OMIN) in a cavity-waveguide coupled system. The Hamiltonian of the system is anti-PT symmetric, with the two involved cavities being dissipatively coupled via the waveguide. The anti-PT symmetry may break down when a weak waveguide-mediated coherent coupling is introduced. However, we find a strong bistable response of the cavity intensity to the OMIN near the cavity resonance, benefiting from linewidth suppression caused by the vacuum induced coherence. The joint effect of optical bistability and the linewidth suppression is inaccessible by the anti-PT symmetric system involving only dissipative coupling. Due to that, the sensitivity measured by an enhancement factor is greatly enhanced by two orders of magnitude compared to that for the anti-PT symmetric model. Moreover, the enhancement factor shows resistance to a reasonably large cavity decay and robustness to fluctuations in the cavity-waveguide detuning. Based on the integrated optomechanical cavity-waveguide systems, the scheme can be used for sensing different physical quantities related to the single-photon coupling strength and has potential applications in high-precision measurements with systems involving Kerr-type nonlinearity.

Manipulating electromagnetic waves in a cavity-waveguide system with nontrivial and trivial modes.

The coupled cavity-waveguide approach provides a flexible platform to design integrated photonic devices that are widely applied in optical communications and information processing. Topological photonic crystals that can excite the nontrivial edge state (ES) and corner state (CS) have an unprecedented capability to manipulate electromagnetic (EM) waves, leading to a variety of unusual functionalities that are impossible to achieve with conventional cavity-waveguide systems. In this Letter, two-dimensional photonic crystals consisting of an ES waveguide, a CS cavity, and a trivial cavity are proposed as a means to robustly control the transmission characteristics of electromagnetic waves. As a proof-of-principle example, the analog of electromagnetically induced transparency (EIT) that is tolerated in disorders due to the robustness of the CS is numerically demonstrated. In addition, the analog of multi-EIT is also verified by introducing a trivial cavity with two degenerate orthogonal modes. This unique approach for robustly manipulating EM waves may open an avenue to the design of high-performance filters, modulators, and on-chip processors.

Simulation study on active control of electromagnetically induced transparency analogue in coupled photonic crystal nanobeam cavity-waveguide systems integrated with graphene.

We proposed and numerically investigated a coupled photonic crystal nanobeam (PCN) cavity-waveguide system which is composed of a bus waveguide and two one-dimensional PCN cavities, acting as bright and dark mode cavities, to achieve a distinct electromagnetically induced transparency analogue (EIT-like) effect by changing the near-field coupling strength between two cavities. By further integrating with graphene on top of the dark mode cavity, the three-dimensional finite-difference time-domain simulation results show that the generated EIT-like transparency window can be actively tuned and a complete on-to-off modulation of the EIT-like effect is realized by electrically tuning the graphene's Fermi level without reoptimizing or refabricating the structure. Theoretical analysis based on the coupled mode theory is then conducted and the results are highly consistent with the numerical results. In addition, we demonstrated that the group delay of the system can also be actively modulated by changing the Fermi level of graphene, achieving a well-controlled slow light effect. Our proposed coupled PCN cavity-waveguide system, combining the merits of PCN cavity and graphene in a single device, may provide a new platform for applications in chip-integrated slow light devices, tunable switches, optical modulators and high-sensitive sensors.

Hybrid Toffoli gates with dipole-induced transparency effect in series and parallel cavity-waveguide systems

We propose two feasible schemes for realizing hybrid Toffoli gates with dipole-induced transparency (DIT) effect in series and parallel cavity-waveguide systems. The gate operations are accomplished by encoding information on flying photon and dipole emitter evanescently coupled to the microcavity, and the spatial as well as polarization states of photon will be flipped conditional on the quantum states of dipole emitters. The schemes could be physically realized in one step and straightforwardly extended to realize the N-qubit Toffoli gate, which greatly simplifies the experimental implementation of Toffoli gate and promises a much higher fidelity compared to those based on elementary gate decomposition. Benefiting from DIT effect, the schemes can be achievable without requirement of strong coupling condition of cavity-waveguide system, and they are insensitive to experimental noises, imperfections and the phase delay of adjacent microcavities, which may be feasible with present accessible technology.

Theory and Limits of On-Demand Single-Photon Sources Using Plasmonic Resonators: A Quantized Quasinormal Mode Approach

Quantum emitters coupled to plasmonic resonators are known to allow enhanced broadband Purcell factors, and such systems have been recently suggested as possible candidates for on-demand single photon sources, with fast operation speeds. However, a true single photon source has strict requirements of high efficiency (brightness) and quantum indistinguishability of the emitted photons, which can be quantified through two-photon interference experiments. To help address this problem, we employ and extend a recently developed quantized quasinormal mode approach, which rigorously quantizes arbitrarily lossy open system modes, to compute the key parameters that accurately quantify the figures of merit for plasmon-based single photon sources. We also present a quantized input-output theory to quantify the radiative and nonradiative quantum efficiencies. We exemplify the theory using a nanoplasmonic dimer resonator made up of two gold nanorods, which yields large Purcell factors and good radiative output beta factors. Considering an optically pulsed excitation scheme, we explore the key roles of pulse duration and pure dephasing on the single photon properties, and show that ultrashort pulses (sub-ps) are generally required for such structures, even for low temperature operation. We also quantify the role of the nonradiative beta factor both for single photon and two-photon emission processes. Our general approach can be applied to a wide variety of plasmon systems, including metal-dielectrics, and cavity-waveguide systems, without recourse to phenomenological quantization schemes.

Calculation, normalization, and perturbation of quasinormal modes in coupled cavity-waveguide systems.

We show how one can use a nonlocal boundary condition, which is compatible with standard frequency domain methods, for numerical calculation of quasinormal modes in optical cavities coupled to waveguides. In addition, we extend the definition of the quasinormal mode norm by use of the theory of divergent series to provide a framework for modeling of optical phenomena in such coupled cavity-waveguide systems. As example applications, we calculate the Purcell factor and study perturbative changes in the complex resonance frequency of a photonic crystal cavity coupled to a defect waveguide.

“Transfer matrix” method for direct and indirect coupling of cascaded cavities in resonator-waveguide systems

Using formalism similar to the transfer matrix, we analyze the problem of direct and indirect coupling of cascaded cavities in resonator-waveguide systems based on the temporal coupled-mode theory. The recurrence relations between modes supported by the cascaded cavities are established by using transfer matrix technique. By setting two auxiliary cavities as the start and termination conditions, the optical properties of the cascaded cavity system can be obtained, especially convenient to get the transmission properties. We validate our method by comparing its prediction with the finite-difference time-domain method in a channel drop filter system in photonic crystals and obtaining excellent agreement between the two. The new analytical method provides a powerful tool to design and analyze complex cavity-waveguide systems.

Optimal switching using coherent control

We introduce a general framework for the analysis of coherent control in coupled optical cavity-waveguide systems. Within this framework, we use an analytically solvable model, which is validated by independent numerical calculations, to investigate switching in a micro cavity and demonstrate that the switching time, in general, is not limited by the cavity lifetime. Therefore, the total energy required for switching is a more relevant figure of merit than the switching speed, and for a particular two-pulse switching scheme we use calculus of variations to optimize the switching in terms of input energy.

Erratum: Dipole Induced Transparency in Drop-Filter Cavity-Waveguide Systems [Phys. Rev. Lett.96, 153601 (2006)

Erratum: Dipole Induced Transparency in Drop-Filter Cavity-Waveguide Systems [Phys. Rev. Lett.<b>96</b>, 153601 (2006)

Coupled cavity polaritons for switching and slow light applications

We derive the frequency response of a chain of weakly coupled cavities, loaded with three-level quantum systems; one transition of the quantum state is entangled with the cavity mode, and the other one is driven by an external field not related to any cavity mode. In a system composed of photonic crystals and quantum states, we can exploit two quantum optical effects: the first due to a totally destructive interference between an incoming field and the field radiated by a dipole in a cavity in Purcell regime, known as “dipole-induced reflectivity” (DIR) reminiscent of the “dipole-induced transparency” reported by Waks et al. [E. Waks, J. Vuckovic, Dipole induced transparency in Drop-Filter Cavity-Waveguide Systems, Phys. Rev. Lett. 96 (2006) 153601], and the “electromagnetic-induced transparency” (EIT) in a quantum state. We demonstrate that it is possible to design tunable flat response filters using external fields with different Rabi frequency values, and furnish the design guidelines for tunable delay lines with very large bandwidth.

Dipole Induced Transparency in Drop-Filter Cavity-Waveguide Systems

We show that a waveguide that is normally opaque due to interaction with a drop-filter cavity can be made transparent when the drop filter is also coupled to a dipole, even when the vacuum Rabi frequency of the dipole is much less than the cavity decay rate. The condition for transparency is simply achieving large Purcell factors. We describe how this effect can be useful for designing quantum repeaters for long distance quantum communication.