Photonic Crystal Waveguide Research Articles

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.

Analyzing dispersion properties of photonic crystal waveguides with hole and ring like lattice by introducing systematic shift and twist

Analyzing dispersion properties of photonic crystal waveguides with hole and ring like lattice by introducing systematic shift and twist

Fidelity of time-bin-entangled multiphoton states from a quantum emitter

We devise a mathematical framework for assessing the fidelity of multi-photon entangled states generated by a single solid-state quantum emitter, such as a quantum dot or a nitrogen-vacancy center. Within this formalism, we theoretically study the role of imperfections present in real systems on the generation of time-bin encoded Greenberger-Horne-Zeilinger and one-dimensional cluster states. We consider both fundamental limitations, such as the effect of phonon-induced dephasing, interaction with the nuclear spin bath, and second-order emissions, as well as technological imperfections, such as branching effects, non-perfect filtering, and photon losses. In a companion paper, we consider a particular physical implementation based on a quantum dot emitter embedded in a photonic crystal waveguide and apply our theoretical formalism to assess the fidelities achievable with current technologies.

Waveguide-QED platform for synthetic quantum matter

An exciting frontier in quantum information science is the realization and control of complex quantum many-body systems. The hybrid nanophotonic system with cold atoms has emerged as a paradigmatic platform for realizing long-range spin models from the bottom up, exploiting their modal geometry and group dispersion for tailored interactions. An important challenge is the physical limitation imposed by the photonic bath, constraining the types of local Hamiltonians that decompose the available physical models and restricting the spatial dimensions to that of the dielectric media. However, at the nanoscopic scale, atom-field interaction inherently accompanies significant driven-dissipative quantum forces that may be tamed as a new form of a mediator for controlling the atomic internal states. Here we formulate a quantum optics toolbox for constructing universal quantum matter with individual atoms in the vicinity of one-dimensional photonic crystal waveguides. The enabling platform synthesizes analog quantum materials of universal 2-local Hamiltonian graphs mediated by phononic superfluids of the trapped atoms. We generalize our microscopic theory of an analog universal quantum simulator to the development of dynamical gauge fields. In the spirit of gauge theories, we investigate emergent lattice models of arbitrary graphs, for which strongly coupled $\mathrm{SU}(n)$ excitations are driven by an underlying multibody interaction. As a minimal model in the infrared, we explore the realization of an archetypical strong-coupling quantum field theory, the $\mathrm{SU}(n)$ Wess-Zumino-Witten model, and discuss a diagnostic tool to map the conformal data of the field theory to the static and dynamical correlators of the fluctuating photons in the guided mode.

Slow Light Tuning in Annular Slotted Photonic Crystal Waveguide with Incoming Polymer

An advanced post-processing scheme of reconfigurable dielectric infiltration into an annular slotted photonic crystal waveguide (ASPhCW) is proposed in this paper. Ionic liquids have had prominent effects in enhancing the optical properties of photonic crystals, especially in the aspect of tuning the transmission rate and velocity through optical materials. Using the two-dimensional plane wave expansion method, the flat band dispersion of the slow light is obtained and the tuning of the operating wavelength of the crystal could be realized by incoming polymer technology. The operating wavelength tuning range could be as large as 459.27nm and the group index could be tuned as high as 44.8 with a near zero group velocity dispersion. Using this method, a high group index equaling 45 with the bandwidth equaling 11.3nm and the normalized delay bandwidth product (NDBP) equaling 0.25 is realized. This incoming polymer technology provides an effective method of getting flat band of slow light flexibly and makes it possible to offer longer delay and low group velocity after fabrication.

Exciton–polaritons in GaAs-based slab waveguide photonic crystals

We report the observation of bandgaps for low loss exciton–polaritons propagating outside the light cone in GaAs-based planar waveguides patterned into two-dimensional photonic crystals. By etching square lattice arrays of shallow holes into the uppermost layer of our structure, we open gaps on the order of 10 meV in the photonic mode dispersion, whose size and light–matter composition can be tuned by proximity to the strongly coupled exciton resonance. We demonstrate gaps ranging from almost fully photonic to highly excitonic. Opening a gap in the exciton-dominated part of the polariton spectrum is a promising first step toward the realization of quantum-Hall-like states arising from topologically nontrivial hybridization of excitons and photons.

Study of a hexagonal lattice defect photonic crystal waveguide slow wave structure for G-band traveling wave tube

A defect photonic crystal waveguide (DPCW) slow wave structure (SWS) for G-band traveling wave tube (TWT) is proposed. This DPCW SWS is arrayed in hexagonal lattice with the center defect cells. The TWT based on DPCW SWS operates at 16 kV beam voltage and 120 mA beam current with a 0.6 T focusing magnetic field. A saturated output power of 22.3W, corresponding to a gain of 36.5 dB, is achieved with an input power of 5 mW. The output power is over 10W in a 30 GHz bandwidth. Stable output signal can be achieved without attenuator or sever which shows that the proposed DPCW SWS can depress the oscillation and harmonic in nature. A DPCW SWS sample was fabricated by computer control (CNC) milling, and the measured results show great agreement with the simulation results.

Optical spin sorting chain.

Transverse spin angular momentum of light is a key concept in recent nanophotonics to realize unidirectional light transport in waveguides by spin-momentum locking. Herein we theoretically propose subwavelength nanoparticle chain waveguides that efficiently sort optical spins with engineerable spin density distributions. By arranging high-refractive-index nanospheres or nanodisks of different sizes in a zigzag manner, directional optical spin propagation is realized. The origin of efficient spin transport is revealed by analyzing the dispersion relation and spin angular momentum density distributions, being attributed to guided modes that possess transverse spin angular momenta. In contrast to conventional waveguides, the proposed asymmetric waveguide can spatially separate up- and down-spins and locate one parity inside and the other outside the structure. Moreover, robustness against bending the waveguide and its application as an optical spin sorter are presented. Compared to previous reports on spatial engineering of local spins in photonic crystal waveguides, we achieved miniaturization of the entire footprint down to the subwavelength scale.

Polymer Photonic Crystal Waveguides Generated by Femtosecond Laser

AbstractFemtosecond laser‐based fabrication of integrated photonic crystal waveguides inside of a transparent polymer is reported. In general, the fabrication of waveguides based on femtosecond laser‐induced positive refractive index modifications is feasible. However, in transparent polymers their performance is limited since only minor refractive index changes can be achieved with this technique. These restrictions can be circumvented by generating hexagonal “photonic lattice like” waveguides, which consist of negative refractive index modifications in the cladding, enabling light confinement in the unirradiated core. A comprehensive study on the fabrication of this new class of polymer waveguide is performed as well as a characterization of its numerical aperture, mode field diameter, and attenuation. In addition, integration of Bragg gratings based on positive and negative refractive index modulations within the waveguide's core is studied. Moreover, we highlight that polymer photonic crystal waveguides are compatible with common femtosecond laser‐based internal structuring processes, enabling the creation of monolithic optofluidic devices, which is demonstrated by the fabrication of a Fabry–Pérot interferometer.

Spin-momentum locked interface modes based on transverse resonance and Zak phase in finite thickness dielectric slabs

The field of topological photonics has made great strides in the past decade with many new designs based on bandgap and band inversion structures that provide robust, unidirectional, and reflection-free propagation of energy. The topological invariant or Chern number of a metamaterial guarantees the existence of topologically protected edge modes. However, its mathematical application to real systems is not always straightforward and can be greatly simplified by reducing the dimensional complexity of the problem by the calculation of a Zak phase that determines the topological phase in just one dimension. This work explores two methods of creating interface modes with finite height dielectric slabs: (1) transverse resonance through variable edge truncation of a photonic crystal (PhC) or cell sliding and (2) a uni-axial topological phase by means of scaling the internal features of a unit cell. The proposed metamaterial devices use the same C4v symmetric unit cell structure on both sides of the interface and are finite in all three dimensions, allowing for easy fabrication, excitation, and implementation in real-world applications. The all-dielectric design also enables an easy transition to and from conventional PhC waveguides and lends itself well to operation in frequencies spanning across the microwave and optical spectrum without concerns of additional metallic losses in the THz region.

Inverse-Designed Photonic Crystal Circuits for Optical Beam Steering

The ability of photonic crystal waveguides (PCWs) to confine and slow down light makes them an ideal component to enhance the performance of various photonic devices, such as optical modulators or sensors. However, the integration of PCWs in photonic applications poses design challenges, most notably, engineering the PCW mode dispersion and creating efficient coupling devices. Here, we solve these challenges with photonic inverse design, and experimentally demonstrate a slow-light PCW optical phased array (OPA) with a wide steering range. Even and odd mode PCWs are engineered for a group index of 25, over a bandwidth of 20nm and 12nm, respectively. Additionally, for both PCW designs, we create strip waveguide couplers and free-space vertical couplers. Finally, also relying on inverse design, the radiative losses of the PCW are engineered, allowing us to construct OPAs with a 20° steering range in a 20nm bandwidth.

Performance reduction and discrepancies between supported and suspended 1D photonic-crystal/photonic-wire with medium extended microcavity length

We report the performance of silicon-on-insulator medium-length extended microcavity (3 to 4.5 μm long) one-dimensional photonic crystal waveguide. Quality-factor (Q-factor) values ranging from 2000 to 37,000 were observed. The waveguides/wire were fabricated using an inductively coupled plasma reactive ion etching with SF6 and C4F8 gasses. Optical transmission of the design is heavily influenced by the surface roughness of the waveguide wall. We achieved a good free spectral range control for resonance frequency separations in between 39 and 65 nm. Supported and suspended microcavity structures for the case of a medium-length extended microcavity were compared. We observed an inferior performance in terms of the optical transmission and Q-factor in the latter. We have selected 4-μm microcavity length for comparison. The suspended structure was obtained by utilizing the wet etching technique on the same device. A high Q-factor value of ∼26,000 was observed in one of the resonances excited for cladding-layer supported extended microcavity. However, the Q-factor was reduced to ∼17,000 after removing the silica cladding beneath the silicon waveguide core.

Slow Light Rainbow Trapping in a Uniformly Magnetized Gyromagnetic Photonic Crystal Waveguide

We present a hybrid gyromagnetic photonic crystal (GPC) waveguide composed of different GPC waveguide segments possessing various cylinder radii and waveguide widths but biased by a uniform external magnetic field. We demonstrate in frequency and time domains that based on the strong coupling of two counter-propagating topologically protected one-way edge states, the intriguing slow light rainbow trapping (SLRT) of electromagnetic (EM) waves can be achieved, that is, EM waves of different frequencies can be slowed down and trapped at different positions without cross talk and overlap. More importantly, due to the existence of one-way edge states, external EM waves can be non-reciprocally coupled to the SLRT waveguide channel, although the incident position of the EM wave is far away from the waveguide channel. Besides, the frequency range of the slow light states can also be easily regulated by tuning the intensity of an external magnetic field, which is very beneficial to solve the contradiction between slow light and broad bandwidth. Our results can be applied to the design of high-performance photonic devices, such as an optical buffer, optical switch, and optical filter.

Two-dimensional anisotropic non-Hermitian Lieb lattice

We study an anisotropic two-dimensional non-Hermitian Lieb lattice, where the staggered gain and loss present in the horizontal and vertical directions, respectively. The intra-cell nonreciprocal coupling generates magnetic flux enclosed in the unit cell of the Lieb lattice and creates nontrivial topology. The active and dissipative topological edge states are along the horizontal and vertical directions, respectively. The two-dimensional non-Hermitian Lieb lattice also supports passive topological corner state. At appropriate magnetic flux, the non-Hermiticity can alter the corner state from one corner to the opposite corner as the non-Hermiticity increases. The gapless phase of the Lieb lattice is characterized by different configurations of exceptional points in the Brillouin zone. The topology of the anisotropic non-Hermitian Lieb lattices can be verified in many experimental platforms including the optical waveguide lattices, photonic crystals, and electronic circuits.

Photon Hall effect in two-dimensional photonic crystal waveguide

The finding of Photon Hall effect (PHE) on metal surface is an important progress in photonics, but it will be more practical if PHE can be realized in line-type waveguide. In this paper, we suggested a way to realize PHE in two-dimensional photonic crystal (PC) waveguide. Numerical simulation results show that the propagating direction and strength of light in the PC waveguide can be controlled by the polarization state of incident light. Different from the PHE on metal surface, the PHE in PC waveguide can be driven not only by circularly polarized light, but also by linearly polarized light. The PHE in PC waveguide can be attributed to the interference of the two component waves excited by the incident light.

Si photonic crystal slow-light waveguides optimized through informatics technology.

We modeled the photonic bands of SiO2-cladded Si lattice-shifted photonic crystal waveguides via machine learning and found a structure that generates low-dispersion slow light with a group index of approximately 20 in the full C-band at telecom wavelengths. The normalized delay-bandwidth product is as large as 0.45, which is close to the theoretical upper limit. The transition structure between this waveguide and a Si-channel waveguide was designed using an evolutional optimization, and a C-band average loss of 0.116 dB/transition was calculated. These results prove the possibility of further enhancing the versatility of slow light.

Pure-quartic solitons and their generalizations—Theory and experiments

Solitons are wave packets that can propagate without changing shape by balancing nonlinear effects with the effects of dispersion. In photonics, they have underpinned numerous applications, ranging from telecommunications and spectroscopy to ultrashort pulse generation. Although traditionally the dominant dispersion type has been quadratic dispersion, experimental and theoretical research in recent years has shown that high-order, even dispersion enriches the phenomenon and may lead to novel applications. In this Tutorial, which is aimed both at soliton novices and at experienced researchers, we review the exciting developments in this burgeoning area, which includes pure-quartic solitons and their generalizations. We include theory, numerics, and experimental results, covering both fundamental aspects and applications. The theory covers the relevant equations and the intuition to make sense of the results. We discuss experiments in silicon photonic crystal waveguides and in a fiber laser and assess the promises in additional platforms. We hope that this Tutorial will encourage our colleagues to join in the investigation of this exciting and promising field.

Midinfrared Refractive-index Sensor with High Sensitivity Based on an Optimized Photonic Crystal Coupled-cavity Waveguide

A photonic crystal coupled-cavity waveguide created on silicon-on-insulator is designed to act as a refractive-index-sensing device at midinfrared wavelengths around 4 μm. To realize high sensitivity, effort is made to engineer the structural parameters to obtain strong modal confinement, which can enhance the interaction between the resonance modes and the analyzed sample. By adjusting some parameters, including the shape of the cavity, the width of the coupling cavity, and the size of the surrounding dielectric columns, a high-sensitivity refractive-index sensor based on the optimized photonic crystal coupled-cavity waveguide is proposed, and a sensitivity of approximately 2620 nm/RIU obtained. When an analyte is measured in the range of 1.0–1.4, the sensor can always maintain a high sensitivity of greater than 2400 nm/RIU. This work demonstrates the viability of high-sensitivity photonic crystal waveguide devices in the midinfrared band.

Influence of medium column type on edge states in all-media topological photonic crystals

We have constructed photonic crystals (PCs) of a standard honeycomb lattice composed of solid dielectric columns, hollow dielectric columns, and composite dielectric columns and studied the influence of their dielectric constant and filling ratio on the topological boundary states. The optical quantum spin Hall effect is realized by compressing and stretching the standard honeycomb lattice. In the waveguide structure with sharp bends, cavity, and disorder, the electromagnetic (EM) wave is transmitted unidirectionally and robustly, which verifies the transmission characteristics of the topological edge states. In addition, by replacing several solid dielectric columns near the junction of PCs with different topological states with composite dielectric columns, disturbance is introduced to the edge states, and the influence of the relative effective permittivity of the composite dielectric columns on the edge states is studied. It is found that the EM wave in the gap between the upper boundary state and the lower boundary state cannot be transmitted, and with the increase of the relative effective permittivity of the composite dielectric columns, the gap becomes larger and larger, and the position of the gap gradually moves down. Based on this, a photonic crystal (PC) waveguide structure that has higher transmission efficiency, robust unidirectionality, and higher optical localization performance, is designed. It has more potential development in filters, optical switches, optical communication systems, and semiconductor technology.

Utilization of slow light enhancement of four-wave mixing within a silicon photonic crystal for microwave frequency measurement purposes

We report the demonstration of an instantaneous frequency measurement system based on the four-wave mixing (FWM) effect in short dispersion engineered slow-light silicon photonic crystal waveguides for RF frequency measurement purposes within a range of 10 MHz to 80 GHz. Three nonlinear media were investigated including 3 mm ridge waveguide, 80 µm nanowire, and 80 µm photonic crystal (PhC). The system size could thus be decreased, and as a result system integration would become possible. We have shown that the optical power required to excite FWM is low enough to remove any need for optical amplification, and hence the system noise floor will be kept low. Issues due to the amplifier saturation will also be resolved this way. As a result, no noise reduction system, like lock-in amplification, would be required. A better system latency will also be achieved accordingly. The system dynamic range would also be improved in two ways. First, due to the low noise floor, and second, because of removing any optical amplifier that possibly could become saturated at higher power levels. All three media behaviors were simulated by the split step Fourier method, and the results showed that the best medium to be used is PhC.