Photonic Crystal Waveguide Research Articles

Dynamics of matter-wave quantum emitters in a structured vacuum

The characteristics of spontaneous emission can be strongly modified by the mode structure of the vacuum. In waveguide quantum-electrodynamics based on photonic crystals, this modification is exploited to engineer atom-photon interactions near a band edge, but the physics of coupling to an entire band has not yet been explored in experiments. Using ultracold atoms in an optical lattice, we study the decay dynamics of matter-wave quantum emitters coupled to a single band of an effective photonic crystal waveguide structure with tunable characteristics. Depending on the ratio between vacuum coupling and bandwidth, we observe a transition from irreversible decay to fully oscillatory dynamics linked to the interplay of matter-wave bound states near the band edges, whose spatial structure we characterize. Our results shed light on the emergence of coherence in an open quantum system in a controllable environment, and are of relevance for the understanding of vacuum-induced decay phenomena in photonic systems.

Photonic crystal waveguide for second harmonic generation: exact solution

We provide the exact solution of the dispersion equation for a waveguided semiconductor structure with a photonic crystal core that provides the efficient second harmonic generation in the visible range. The comparison of the results with an approximate solution shows good agreement.

Chiral topological photonics with an embedded quantum emitter

Topological photonic interfaces support topologically nontrivial optical modes with helical character. When combined with an embedded quantum emitter that has a circularly polarized transition dipole moment, a chiral quantum optical interface is formed due to spin-momentum locking. Here, we experimentally realize such an interface by integrating semiconductor quantum dots into a valley-Hall topological photonic crystal waveguide. We harness the robust waveguide transport to create a ring resonator that supports helical modes. Chiral coupling of quantum dot transitions, with directional contrast as high as 75%, is demonstrated. The interface also supports a topologically trivial mode, comparison with which allows us to clearly demonstrate the protection afforded by topology to the nontrivial mode.

Dielectric resonator antenna fed by photonic crystal waveguide based on silicon-on-glass technology

Terahertz (THz) antennas can be used for high-speed indoor wireless communications. The antennas must have a wide bandwidth, high gain, and low loss. In this study, a dielectric resonator antenna fed by the photonic crystal (PC) waveguide based on a newly developed silicon-on-glass technology is proposed and analyzed. The PC waveguide is designed by float-zone silicon that can help propagation guided modes with low loss. Coupling matching between waveguide and antenna, and also between the antenna and free space can be analyzed by coupling mode theory. The reflection loss at the interface between the components is minimized using three matching air holes. The proposed compact antenna operates at 325 GHz with about 5.2% bandwidth. The end-fire antenna is introduced with a high gain of about 12 dBi, low loss, and sidelobe levels of −11 and −8.8 dB in the E- and H-planes. The high efficiency of over 97% in the entire antenna operational bandwidth is achieved. The platform is used for THz communications at the high data rate.

A photonic crystal sensor array side-coupled to a linear waveguide with enhanced bandwidth

We report a photonic crystal (PhC) sensor array consisting of six nanocavities which are side-coupled to a linear PhC waveguide. The design approach to cavities is based on rotating functional holes and changing their radius. Based on traditional linear waveguide, we also design a PhC waveguide with enhanced bandwidth by adjusting the holes on both sides of the central linear defect to weaken the Bragg reflector effect. With 3-D finite-difference time-domain (FDTD) method, the Q value and RI sensitivities for each sensor unit are adjusted from 3.67×105 to 5.41×106 and from 264 nm/RUI to 332 nm/RIU, respectively. Moreover, the free spectral range (FSR) values between every two adjacent sensing units are relatively larger enough compared with structures proposed previously. Accordingly, it provides the possibility to realize the integrated sensing and excellent sensing properties more effectively.

Coupling of light and mechanics in a photonic crystal waveguide

Observations of thermally driven transverse vibration of a photonic crystal waveguide (PCW) are reported. The PCW consists of two parallel nanobeams whose width is modulated symmetrically with a spatial period of 370 nm about a 240-nm vacuum gap between the beams. The resulting dielectric structure has a band gap (i.e., a photonic crystal stop band) with band edges in the near infrared that provide a regime for transduction of nanobeam motion to phase and amplitude modulation of an optical guided mode. This regime is in contrast to more conventional optomechanical coupling by way of moving end mirrors in resonant optical cavities. Models are developed and validated for this optomechanical mechanism in a PCW for probe frequencies far from and near to the dielectric band edge (i.e., stop band edge). The large optomechanical coupling strength predicted should make possible measurements with an imprecision below that at the standard quantum limit and well into the backaction-dominated regime. Since our PCW has been designed for near-field atom trapping, this research provides a foundation for evaluating possible deleterious effects of thermal motion on optical atomic traps near the surfaces of PCWs. Longer-term goals are to achieve strong atom-mediated links between individual phonons of vibration and single photons propagating in the guided modes (GMs) of the PCW, thereby enabling optomechanics at the quantum level with atoms, photons, and phonons. The experiments and models reported here provide a basis for assessing such goals.

Reconfigurable slow light in phase change photonic crystal waveguide

Experimental demonstration of light propagation with ultralow group velocity, i.e., slow light, allows for revolutionary solutions for time-domain processing and buffering of optical signals. It can spatially compress optical energy, which lessens the device footprint and enhances linear and nonlinear optical effects. Photonic crystal waveguides (PCWs) are appealing for producing slow light since they can be on-chip integrated and operated under room temperature. However, most PCW slow-light devices are restricted to the narrow spectral range of material resonance, leading to a small delay-bandwidth product, which restricts the maximum data rate, operation frequency, and storage capacity. Furthermore, the lack of broadly tunable slow light hinders practical applications in tunable photonic devices. We propose a reconfigurable slow-light device using a PCW based on a prototypical chalcogenide glass, Ge2Sb2Te5 (GST225) to solve the problems. We find that the operating wavelength of the slow light within the structure can be reversibly switched between 3575 and 4905 nm by changing the structural state of GST225 between amorphous and crystalline ones. The corresponding average group indices are 40.8 and 54.4, respectively. We experimentally illustrate that the reversible phase transition of GST225 between amorphous and crystalline ones can be realized in nanoseconds. Our proof of concept may provide a platform for actively engineering slow light that might otherwise be difficult to obtain in photonic systems. We expect it to improve the device performance in the fields of nonlinearity and sensing.

Dispersion engineering of W2 steeple-house-defect waveguide photonic crystal

An epitome for dispersion and buffering in a photonic crystal was set forth. Slots in the form of a line of contacted steeple-houses are implanted in a two-line photonic crystal waveguide (2LPCW) to form an irregular slot of steeple-house defect PCW (SDPCW) to realize bandwidth expanding and a significant regulator for group delay (GD), group velocity dispersion (GVD) and group delay dispersion (GDD) effects. The SDPCW was compared with other types of defects reported in this study and in the literature previously, we fulfilled the highest favorable value of buffering capacity about 210.256 bits. Furthermore, low GDD is achieved in the range from 1ps2to 10ps2 for 1 mm delay line length. The SDPCW may be appropriate for the workable application, which has a utility in coupling enhancement between the cavities as it was observed from the field distribution detected over confined spatial light along the propagation path for enhancing the transmission bandwidth, buffering properties and outstanding tolerance to fabrication errors. Moreover, stopping and/or slowing the light has an excessive advantage in the store of quantum states of light for an adequately long time to make quantum operations. Besides, the SDPCW achieved high electro-optical (EO) sensitivity about 244.42 nm/RIU. Thus, the proposed SDPCW can be used for enhancing the interaction between light and the sensing medium.

Silicon Photonic Crystal Modulators for High-Speed Transmission and Wavelength Division Multiplexing

For next-era optical interconnects in data centers, development of compact, energy-efficient, low-cost, and high-speed optical transceivers are required, for which high-performance external modulators in silicon photonics will be key components. We present a silicon photonic crystal waveguide slow light Mach-Zehnder modulator suitable for this purpose. The enhancement in the modulation efficiency via the slow light effect reduces the halfwave voltage-length product VπL, maintaining a wide working spectrum over 15 nm. The frequency response of the slow light modulator is constricted by an electrooptic phase mismatch between slow light and RF signals. In this study, this was dramatically improved by matching the phase using meanderline electrodes that delay RF signals. The cutoff frequency was experimentally evaluated to be 32-38 GHz. Using this device, we demonstrated high-speed modulation, including 64-Gbps on-off keying, 100-Gbps pulse amplitude modulation, and 50-Gbps/ch wavelength division multiplexing in 170-200-μm- long devices.

Hybrid demultiplexer for mode and dense wavelength division multiplexing based on photonic crystal and nanowire waveguides

We propose a hybrid demultiplexer for mode and dense wavelength division multiplexing (DWDM) based on photonic crystal (PhC) and nanowire waveguides. The designed demultiplexer consists of DWDM module using PhC cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential and mode division multiplexing module constructing of asymmetric directional coupler using nanowire waveguides. The performance parameters of the demultiplexer are analysed by two-dimensional finite-difference time-domain method. The results show that the fundamental transverse electric (TE0) modes and first-order TE (TE1) modes of 1573.0 and 1572.2 nm can be demultiplexed simultaneously. The insertion loss is smaller than 0.6 dB, and the crosstalk is smaller than −18.6 dB. Besides, the demultiplexer has a large free spectral range up to 250 nm, which can almost cover the whole range of DWDM system.

Nanowire-assisted microcavity in a photonic crystal waveguide and the enabled high-efficiency optical frequency conversions

We report an indium phosphide nanowire (NW)-induced cavity in a silicon planar photonic crystal (PPC) waveguide to improve the light–NW coupling. The integration of NW shifts the transmission band of the PPC waveguide into the mode gap of the bare waveguide, which gives rise to a microcavity located on the NW section. Resonant modes with Q factors exceeding 10 3 are obtained. Leveraging on the high density of the electric field in the microcavity, the light–NW interaction is enhanced strongly for efficient nonlinear frequency conversion. Second-harmonic generation and sum-frequency generation in the NW are realized with a continuous-wave pump laser in a power level of tens of microwatts, showing a cavity-enhancement factor of 112. The hybrid integration structure of NW-PPC waveguide and the self-formed microcavity not only opens a simple strategy to effectively enhance light–NW interactions, but also provides a compact platform to construct NW-based on-chip active devices.

Theory of intrinsic propagation losses in topological edge states of planar photonic crystals

Using a semi-analytic guided-mode expansion technique, we present theory and analysis of intrinsic propagation losses for topological photonic crystal slab waveguide structures with modified honeycomb lattices of circular or triangular holes. Although conventional photonic crystal waveguide structures, such as the W1 waveguide, have been designed to have lossless propagation modes, they are prone to disorder-induced losses and backscattering. Topological structures have been proposed to help mitigate this effect as their photonic edge states may allow for topological protection. However, the intrinsic propagation losses of these structures are not well understood and the concept of the light line can become blurred. For four example topological edge state structures, photonic band diagrams, loss parameters, and electromagnetic fields of the guided modes are computed. Two of these structures, based on armchair edge states, are found to have significant intrinsic losses for modes inside the photonic band gap, more than 100 dB/cm, which is comparable to or larger than typical disorder-induced losses using slow-light modes in conventional photonic crystal waveguides, while the other two structures, using the valley Hall effect and inversion symmetry, are found to have a good bandwidth for exploiting lossless propagation modes below the light line.

Thermo-Optic Beam Scanner Employing Silicon Photonic Crystal Slow-Light Waveguides

Optical beam scanning is a widely utilized function in optical systems and a compact nonmechanical solid-state device has long been anticipated. Here, we have studied such a device consisting of photonic crystal slow-light waveguides and switch trees, fabricated by a Si photonics process, employing a bespoke prism lens for beam collimation. Further in this study, we particularly demonstrated the operation of the device only by the thermo-optic (TO) tuning of its components, at a fixed wavelength of light. A spot beam of ~0.1° divergence, was scanned in two dimensions, in the angular range of 40° × 8.8° and average power consumption of <; 0.7 W. Neglecting some disordered beams caused by the non-uniformity of the fabricated device, the estimated number of resolution points was 400 × 32 = 12,800, which required a significant effort in the device fabrication and calibration, utilizing optical-phased arrays, if the same performance was targeted.

Apparatus for High-Precision Angle-Resolved Reflection Spectroscopy in the Mid-Infrared Region.

Fourier transform (FT) spectroscopy is a versatile technique for studying the infrared (IR) optical response of solid-, liquid-, and gas-phase samples. In standard Fourier transform infrared (FT-IR) spectrometers, a light beam passing through a Michelson interferometer is focused onto a sample with condenser optics. This design enables us to examine relatively small samples, but the large solid angle of the focused infrared beam makes it difficult to analyze angle-dependent characteristics. Here, we design and construct a high-precision angle-resolved reflection setup compatible with a commercial FT-IR spectrometer. Our setup converts the focused beam into an achromatically collimated beam with an angle dispersion as high as 0.25°. The setup also permits us to scan the incident angle over ∼8° across zero (normal incidence). The beam diameter can be reduced to ∼1 mm, which is limited by the sensitivity of an HgCdTe detector. The small-footprint apparatus is easily installed in an FT-IR sample compartment. As a demonstration of the capability of our reflection setup, we measure the angle-dependent mid-infrared reflectance of two-dimensional photonic crystal slabs and determine the in-plane dispersion relation in the vicinity of the Γ point in momentum space. We observe the formation of photonic Dirac cones, i.e., linear dispersions with an accidental degeneracy at Γ, in an ideally designed sample. Our apparatus is useful for characterizing various systems that have a strong in-plane anisotropy, including photonic crystal waveguides, plasmonic metasurfaces, and molecular crystalline films.

Design and optimization of Y-Junction and T-Junction splitters using photonic crystal

We proposed a high transmission Y-Junction and T-Junction 1x2 power splitters based on two Dimensional photonic crystal waveguide with lattice consisting of air holes. The 1x2 power splitters is made of silicon rods with the refractive index n 1 = 3 . 46 which are perforated in air with refractive index n 2 = 1. The defects are formed by adding additional glass rods at its bends, and by increasing rods radius nearer to the propagation path. Plane wave expansion solver method is used for calculating the photonic band gap. The Resulted optical properties are obtained by using Opti-FDTD simulation at a wavelength λ = 1900 nm, a wave which was used to calculate the Poynting vector z as well as the magnetic and electric field. The Comparison of results for Y and T-Junction shows that the T-Junction has improved Electric and Magnetic Fields better than Y-Junction.

All‐optical logic inverter for large‐scale integration in silicon photonic circuits

A new device architecture of an all-optical logic inverter (AOLI) has been proposed in this study. The AOLI functions based on stimulated Raman scattering (SRS) in silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW). The operating power and footprint size of the proposed device have significantly been scaled down to ∼1.5 mW and ∼ 8.5 × 42 μ m 2 , respectively, by combining the benefits of giant SRS gain of silicon nanocrystal and ultra-high spatio-temporal confinement of the SPCW. Cascadability of the proposed AOLI has been investigated using the maximum product criterion of the noise margin. The successful operation of the AOLI has been demonstrated for the repetition rate of the pulses as high as 100 Gbps. Finally, tolerance of performance of the design under different types of fabrication imperfections has also been calculated to establish its sustainability in a practical scenario.

One-dimensional photonic crystal waveguide based on SOI platform for transverse magnetic polarization-maintaining devices

In this letter, a TM-polarization C-band pass one-dimensional photonic crystal strip waveguide (1D-PCSW) is presented. The waveguide structure is based on a silicon-on-insulator platform which is easy to realize using standard CMOS technology. The numerical study is conducted via 3D-finite element method (FEM). The transmittance and polarization extinction ratio (PER) is enhanced by optimizing the geometric parameters of the device. As a result, a TM polarized light can travel in the waveguide with ~2 dB loss for all C-band telecommunication wavelength window whereas the TE polarized light suffers a high transmission loss of &gt;30 dB. As a result, a PER of ~28.5 dB can be obtained for the whole C-band wavelengths range. The total length of the proposed device is around 8.4 µm long including 1 µm silicon strip waveguide segment on both ends. Based on our study presented in this paper, several photonic devices can be realized where strict polarization filtering is required. Full Text: PDF ReferencesB. Wang, S. Blaize, R.S-Montiel, "Nanoscale plasmonic TM-pass polarizer integrated on silicon photonics", Nanoscale, 11, 20685 (2019). CrossRef D. Dai, J.E. Bowers, "Silicon-based on-chip multiplexing technologies and devices for Peta-bit optical interconnects", Nanophotonics, 3, 283 (2014). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "Optical elements based on silicon photonics", Computer Optics, 43, 1079 (2019). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "Compact design of a polarization beam splitter based on silicon-on-insulator platform", Laser Physics, 28, 116202 (2018). CrossRef M.A. Butt, S.N. Khonina, N.L. Kazanskiy, "A T-shaped 1 × 8 balanced optical power splitter based on 90° bend asymmetric vertical slot waveguides", Laser Physics, 29, 046207 (2019). CrossRef Q. Wang, S.-T. Ho, "Ultracompact TM-Pass Silicon Nanophotonic Waveguide Polarizer and Design", IEEE Photonics J., 2, 49 (2010). CrossRef C.-H. Chen, L. Pang, C.-H. Tsai, U. Levy, Y. Fainman, "Compact and integrated TM-pass waveguide polarizer", Opt. Express, 13, 5347 (2005). CrossRef S. Yuan, Y. Wang, Q. Huang, J. Xia, J. Yu, "Ultracompact TM-pass/TE-reflected integrated polarizer based on a hybrid plasmonic waveguide for silicon photonics", in 11th International Conference on Group IV Photonics (GFP) (IEEE, 2014), pp. 183-184. CrossRef X. Guan, P. Chen, S. Chen, P. Xu, Y. Shi, D. Dai, "Low-loss ultracompact transverse-magnetic-pass polarizer with a silicon subwavelength grating waveguide", Opt. Lett., 39, 4514 (2014). CrossRef A.E.- S. Abd-Elkader, M.F. O. Hameed, N.F. Areed, H.E.-D. Mostafa, and S.S. Obayya, "Ultracompact AZO-based TE-pass and TM-pass hybrid plasmonic polarizers", J.Opt. Soc. Am. B., 36, 652 (2019). CrossRef J. Li et al., "Photonic Crystal Waveguide Electro-Optic Modulator With a Wide Bandwidth", Journal of Lightwave Technology, 31, 1601-1607 (2013). CrossRef N. Skivesen et al., "Photonic-crystal waveguide biosensor", Optics Express, 15, 3169-3176 (2007). CrossRef S. Lin, J. Hu, L. Kimerling, K. Crozier, "Design of nanoslotted photonic crystal waveguide cavities for single nanoparticle trapping and detection", Optics Letters, 34, 3451-3453 (2009). CrossRef T. Liu, A.R. Zakharian, M. Fallahi, J.V. Moloney, M. Mansuripur, "Design of a compact photonic-crystal-based polarizing beam splitter", IEEE Photonics Technology Letters, 17, 1435-1437 (2005). CrossRef R. K. Sinha, Y. Kalra, "Design of optical waveguide polarizer using photonic band gap", Optics Express, 14, 10790 (2006). CrossRef

Interaction-Induced Transparency for Strong-Coupling Polaritons.

The propagation of light in strongly coupled atomic media takes place through the formation of polaritons-hybrid quasiparticles resulting from a superposition of an atomic and a photonic excitation. Here we consider the propagation under the condition of electromagnetically induced transparency and show that a novel many-body phenomenon can appear due to strong, dissipative interactions between the polaritons. Upon increasing the photon-pump strength, we find a first-order transition between an opaque phase with strongly broadened polaritons and a transparent phase where a long-lived polariton branch with highly tunable occupation emerges. Across this nonequilibrium phase transition, the transparency window is reconstructed via nonlinear interference effects induced by the dissipative polariton interactions. Our predictions are based on a systematic diagrammatic expansion of the nonequilibrium Dyson equations which can be controlled, even in the nonperturbative regime of large single-atom cooperativities, provided the polariton interactions are sufficiently long-ranged. Such a regime can be reached in photonic crystal waveguides thanks to the tunability of interactions, allowing us to observe the interaction-induced transparency transition even at low polariton densities.

Lifetimes and Quantum Efficiencies of Quantum Dots Deterministically Positioned in Photonic‐Crystal Waveguides

AbstractInterfacing single emitters and photonic nanostructures enables modifying their emission properties, such as enhancing individual decay rates or controlling the emission direction. To achieve full control, the single emitter must be positioned in the nanostructures deterministically. Here, spectroscopy is used to gain spectral and spatial information about individual quantum dots (QD) in order to position each emitter in a predetermined location in a unit cell of a photonic‐crystal waveguide (PhCW). Depending on the spatial and spectral positioning within the structured nanophotonic mode, the quantum dot emission is observed to either be suppressed or enhanced. These results represent an important step towards unlocking the full potential of nanophotonic systems and will be crucial to the creation of complex multi‐emitter quantum photonic circuits.

Analysis of Unidirectional Coupling in Topological Valley Photonic Crystal Waveguides

Valley photonic crystal is a typical strategy of topological photonics with promising applications for novel integrated waveguides. The valley pseudospin provides an intrinsic paradigm to implement unidirectional coupling with robustly optical transport. But the key issue on the analysis of unidirectional coupling based on topological modes is lack of deep understanding on valley photonic crystals. In this work, we systematically study the mechanism and performance of unidirectional coupling between valley photonic crystal waveguides and chiral dipole emitters. Forming by two topologically-distinct valley photonic crystals, there are two types of valley-interface waveguides, i.e. bearded stack with glide-plane symmetry and zigzag stack with inversion symmetry. Analytical derivation shows that the Stokes parameters of topological eigenmodes can predict the directionality in the above two types of valley-interface waveguides, which is also confirmed by full-wave simulations. The strategy of bearded valley-interface waveguide can be easier to achieve high efficiency of unidirectional coupling than the zigzag case, and can relax the bias error of frequency and source location. It is also proved that the topological-protected unidirectional coupling supports robust transport against sharp-bending interface. Finally, we give a brief summary and perspective in the development of topological integrated photonics. This work gives a deterministic guidance on chiral light-matter interaction based on topological photonics, as well as shows the outlook of topological integrated photonics.