Photonic Crystal Waveguide Research Articles

Giant anomalous self-steepening and temporal soliton compression in silicon photonic crystal waveguides

Self-steepening (SS) is enhanced by slow-light effects in photonic crystal waveguides (PhCWs), with coefficients as large as hundreds of femtoseconds, and it plays an important role in temporally compressed solitons with narrow widths. Here, we investigate the soliton evolution in silicon PhCWs through experiments and numerical simulations; the simulated results agree well with the experimental measurements and help in revealing the physical mechanism of high-order soliton evolution. The dual opposite effects of giant anomalous SS on temporal soliton compression are demonstrated for the first time, i.e., the SS weakens or improves the compression competing with the effects of third-order dispersion (TOD) through two different physical mechanisms. It is also found that SS flattens or steepens the pulse leading edge depending on the strength of the positive TOD perturbation. These results promote the understanding of high-order solitons and can help with the design of suitable dispersion engineered silicon waveguides for superior on-chip temporal pulse compression for optical interconnects, data processing, and microwave photonics.

Mach–Zehnder modulator based on a tapered waveguide and carrier plasma dispersion in photonic crystal: publisher’s note

This publisher’s note corrects the author listing of J. Opt. Technol.88, 242 (2021).JOTEE41070-976210.1364/JOT.88.000242

Observation of Ultrashort Laser Pulse Evolution in a Silicon Photonic Crystal Waveguide

Using the sum frequency generation cross-correlation frequency-resolved optical gating (SFG-XFROG) measurement setup, we observed the soliton evolution of low energy pulse in an Si photonic crystal waveguide, and it exhibited the pulse broadening, blue shift, and evident pulse acceleration. The soliton evolution was also investigated by nonlinear Schrödinger equation (NLSE) modelling simulation, and the simulated results agreed well with the experimental measurements. The effects of waveguide length on the pulse evolution were analyzed; the results showed that the pulse width changed periodically with increasing waveguide length. The results further the understanding of the ultra-fast nonlinear dynamics of solitons in silicon waveguides, and are helpful to soliton-based functional elements on CMOS-compatible platforms.

Random singlet phase of cold atoms coupled to a photonic crystal waveguide

Systems consisting of cold atoms trapped near photonic crystal waveguides have recently emerged as an exciting platform for quantum atom-light interfaces. Such a system enables realization of tunable long-range interactions between internal states of atoms (spins), mediated by guided photons. Currently, experimental platforms are still limited by low filling fractions, where the atom number is much smaller than the number of sites at which atoms can potentially be trapped. Here, we show that this regime in fact enables interesting many-body quantum phenomena, which are typically associated with short-range disordered systems. As an example, we show how the system can realize the so-called ``random singlet phase'' (RSP), in which all atoms pair into entangled singlets, but the pairing occurs over a distribution of ranges as opposed to nearest neighbors. We use a renormalization group method to obtain the distribution of spin entanglement in the RSP, and show how this state can be approximately reached via adiabatic evolution from the ground state of a noninteracting Hamiltonian. We also discuss how experimentally this RSP can be observed. We anticipate that this work will accelerate the route toward the exploration of strongly correlated matter in atom-nanophotonics interfaces, by avoiding the requirement of perfectly filled lattices.

Space-time-domain observation of high-speed optical beam scanning in a thermo-optic Si photonic crystal slow-light beam scanner.

We developed a thermo-optically controlled nonmechanical optical beam scanner using a Si photonic crystal slow-light waveguide with a diffraction grating to achieve on-chip light detection and ranging (LIDAR). This Letter applies pre-emphasis signals to the thermo-optic control, and the cutoff frequency increases to 500 kHz. Observing the beam scanning in the space-time domain showed that the turn-on and turn-off times of the scanner for a rectangular drive voltage were 10 µs and reduced to 2.7 µs when the pre-emphasis signals were optimized. This new, to the best of our knowledge, result enables a frame rate of 29 fps for 12,800 resolution points in LIDAR.

Dynamic modulation of slow light rainbow trapping and releasing in a tapered waveguide based on low-symmetric photonic crystals

We propose a numerical investigation of slow light rainbow trapping and releasing in a tapered photonic crystal waveguide which is formed by linearly modifying the structural parameters in low-symmetric photonic crystals. Through dispersion analysis and numerical simulations, the electromagnetic waves of different frequencies in a normalized bandwith of ~5% can be trapped at different positions, as called “rainbow trapping”. Moreover, the tapered photonic crystal waveguide is created on polystyrene subtract, of which refractive index can be adjusted by tuning the external voltage based on electro-optic effect. Therefore, when the applied voltage is properly modulated, the trapped wave will be captured in different positions even released. The structure has broad application prospects in optical switch, wavelength-division multiplexing, and other optical communication devices.

Structure and dispersion of exciton-trion-polaritons in two-dimensional materials: Experiments and theory

The nature of trions and their interaction with light has remained a puzzle. The composition and dispersion of polaritons involving trions provide insights into this puzzle. Trions and excitons in doped two-dimensional (2D) materials are not independent excitations but are strongly coupled as a result of Coulomb interactions. When excitons in doped 2D materials are also strongly coupled with light inside an optical waveguide, the resulting polariton states are coherent superpositions of exciton, trion, and photon states. We realize these exciton-trion-polaritons by coupling an electron-doped monolayer of 2D material ${\mathrm{MoSe}}_{2}$ to the optical mode in a photonic crystal waveguide. Our theoretical model, based on a many-body description of these polaritons, reproduces the measured polariton energy band dispersion and Rabi splittings with excellent accuracy. Our work sheds light on the structure of trion states in 2D materials and also on the indirect mechanism by which they interact with light.

Ultrahigh-efficiency Enhanced Four-wave-mixing in Si-Ge-Graphene Photonic Crystal Waveguide

Background: All-optical processing has a huge superiority in speed and efficiency than traditional optical-electrical-optical signal processing. Four-wave-mixing is an important nonlinear parametric process to achieve all-optical processing. Objective: We proposed the photonic crystal waveguide to enhance the conversion efficiency of four-wave-mixing significantly in practical application. Results: We demonstrated a waveguide composed of silicon with mono-layer graphene-coated as core and Si-Ge distributed periodically on both sides as cladding. By the introduction of the slow light effect of Si-Ge photonic crystal and the localization effect of graphene, the conversion efficiency of four-wave-mixing had enhanced dramatically. Results:: The conversion efficiency can be increased by 16dB compared with a silicon waveguide. The maximum efficiency as high as -9.1dB can be achieved in the Si-Ge-Graphene photonic crystal waveguide (SGG-PhCWG). The propagation loss can be decreased to 0.032dB/cm. Conclusion:: Numerical results of the proposed SGG-PhCWG matched well with nonlinear coupled- mode theory. This configuration offered a new physical mechanism and solution for alloptical signal processing and high-efficiency nonlinear nanoscale devices.

Theoretical model of gain calculation of active photonic-crystal microcavity waveguide

In this paper, we propose an active photonic-crystal microcavity waveguide with two-level atom-doped-dielectric slab as background material, and derive the model for signal gain calculation and analyze its gain characteristics. The analytical results show that the structure can generate high gain in a short length because of the efficient utilization of pump power in the microcavity. The proposed waveguide will be promising for the development of an active integrated photonic system.

Focusing characteristics of graded photonic crystal waveguide lens based on interference lithography

Using multi-beam interferometry, a photonic structure with a graded intensity distribution is designed and obtained experimentally. Based on the structure, we choose different exposure thresholds and background materials to design a graded photonic crystal (GPC) lens with a graded air hole diameter. The transmission and focusing characteristics of the GPC lens with bismuth silicate crystal (BSO) and polymethyl methacrylate (PMMA) as background materials are investigated in the visible-light band. Comparatively speaking, the graded photonic crystal lens of BSO with a large refractive index had better performance. In addition, the focal intensity does not decrease significantly with increasing the angle of incidence. The focus point intensity remains above 93% of parallel incidence for both lenses.

Band-Gap Solitons in Nonlinear Photonic Crystal Waveguides and Their Application for Functional All-Optical Logic Gating

This review paper summarizes our previous findings regarding propagation characteristics of band-gap temporal solitons in photonic crystal waveguides with Kerr-type nonlinearity and a realization of functional and easily scalable all-optical NOT, AND and NAND logic gates. The proposed structure consists of a planar air-hole type photonic crystal in crystalline silicon as the nonlinear background material. A main advantage of proposing the gap-soliton as a signal carrier is that, by operating in the true time-domain, the temporal soliton maintains a stable pulse envelope during each logical operation. Hence, multiple concatenated all-optical logic gates can be easily realized paving the way to multiple-input ultrafast full-optical digital signal processing. In the suggested setup, due to the gap-soliton features, there is no need to amplify the output signal after each operation which can be directly used as a new input signal for another logical operation. The efficiency of the proposed logic gates as well as their scalability is validated using our original rigorous theoretical formalism confirmed by full-wave computational electromagnetics.

Surface-Enhanced Infrared Absorption Spectroscopic Chalcogenide Waveguide Sensor Using a Silver Island Film.

A surface-enhanced infrared absorption spectroscopic chalcogenide waveguide sensor based on the silver island film was proposed for the first time to enhance the sensing performance in both liquid and gas phases. The chalcogenide waveguide sensor was fabricated by the lift-off and oblique angle deposition methods. The surface morphology of the silver island film with different thicknesses was characterized. The absorption of ethanol (liquid) at a wavelength of 1654 nm and that of methane (gas) at 3291 nm were measured using the fabricated chalcogenide waveguide sensor. The chalcogenide waveguide sensor integrated with the 1.8 nm-thick silver island film revealed the best sensing performance. With an acceptable increased waveguide loss resulting from the fabrication of the film, the absorbance enhancement factors for ethanol and methane were experimentally obtained to be >1.5 and >2.3, respectively. The 1σ limit of detection of methane for the sensor integrated with the 1.8 nm-thick silver island film was ∼4.11% for an averaging time of 0.2 s. The mathematic relation between the absorbance enhancement factor and the waveguide loss was derived for sensing performance improvement. Also, the proposed rectangular waveguide sensor provides an idea for the design of a sensor-on-a-chip instead of other waveguide sensors with a high requirement of fabrication accuracy, for example, a slot waveguide or a photonic crystal waveguide.

Analyzing two-dimensional tunable photonic crystal waveguides for communication band optical filter applications

Analyzing two-dimensional tunable photonic crystal waveguides for communication band optical filter applications

Infinitely many multipulse solitons of different symmetry types in the nonlinear Schrödinger equation with quartic dispersion

We show that the generalized nonlinear Schr\"odinger equation (GNLSE) with quartic dispersion supports infinitely many multipulse solitons for a wide parameter range of the dispersion terms. These solitons exist through the balance between the quartic and quadratic dispersions with the Kerr nonlinearity, and they come in infinite families with different signatures. A traveling wave ansatz, where the optical pulse does not undergo a change in shape while propagating, allows us to transform the GNLSE into a fourth-order nonlinear Hamiltonian ordinary differential equation with two reversibilities. Studying families of connecting orbits with different symmetry properties of this reduced system, connecting equilibria to themselves or to periodic solutions, provides the key to understanding the overall structure of solitons of the GNLSE. Integrating a perturbation of them as solutions of the GNLSE suggests that some of these solitons may be observable experimentally in photonic crystal waveguides over several dispersion lengths.

Wideband switch enhanced by photonic crystal waveguide with graphene nanosheet heater

A compact wideband optical switch assisted by graphene nanosheet heater is demonstrated by shifting the bandedge of the photonic crystal waveguides (PhCWG) through current-induced heating. The high heating efficiency of graphene and the high light-matter interactions in slow-light PhCWG are combined to enhance the heating efficiency and extinction ratio. The extinction ratio is increased from 15 dB to 22 dB and the tuning bandwidth is up to 20 nm with only 28 K temperature change. Our measurements match well with simulation results, suggesting an effective way for CMOS compatible chip-scale integrated graphene microheater switch.

Design of New Convex Lens Shaped Y Splitter for better Optical Communication

This Paper describes, a photonic crystal waveguide based a Y-splitter. The outcomes of this Y-splitter are fixed by mechanisms of plane wave augmentation and Finite Difference Time Domain (FDTD). A lattice structure of hexagon shape is chosen as a basis for the formation of waveguide structure for the designing of Y-splitter. Subsequently, the calculation of power in transverse magnetic mode in equivalent the power calculated of the dual output ports of the proposed device.; the proposed device design of the splitter dispenses moderately greater transmission efficiency. This is affirmed by the simulation results obtained from the work done. The splitting ratio for both the halves was almost at 46%, and the aggregate radiation loss was confirmed to be almost 8 % for each output port. Therefore, the suggested Y-splitter is estimated as a better and more efficient as compare to basic splitter and ASS modified splitter.

Tunable optical isolator using Graphene-photonic crystal-based hybrid system

In this article, an optical isolator is designed and simulated based on a hybrid configuration of the photonic crystal (PhC) and graphene. The PhC membrane is a hexagonal lattice of air holes arranged in a nonlinear silicon substrate. To provide a nonreciprocal transmission (optical isolator), breaking the symmetry of the light propagation path (the forth and back routes) is an essential condition. Here, the asymmetrical round trip of the light propagation and the Kerr-nonlinear effect are employed to obtain asymmetric propagation. The isolator structure includes a PhC waveguide that asymmetrically side-coupled to a specific embedded cavity. Then, to attain a tunable asymmetric transmission, a Nano-layer of graphene is located on the top of the mentioned PhC configuration. By altering the chemical potential of graphene one can control the isolation rate, frequency, and bandwidth of offered structure and thus possess a tunable optical isolator. The simulation results show that a 0.5 nm frequency shift can attain by the graphene chemical potential alterations from 0.45 eV to 0.65 eV in which it is suitable for Dense Wavelength Division Multiplexing (DWDM) communication and integrated optical circuits. Furthermore, as another advantage, a high forward normalized transmission (0.6) has resulted in a large average isolation rate of 32.5 dB due to low losses of the proposed structure.

Significance of Bloch impedance over wave impedance in photonic crystal waveguides

The impedance of a medium carrying electromagnetic waves had been one of the important metrics for designing devices. However, the conclusions of wave impedance in periodic media like photonic crystal (PhC) waveguides fail to describe different wave propagation phenomena. Instead, Bloch impedance fits more appropriately in such a case. However, the existing definition of Bloch impedance by Boscolo et al. [J. Lightwave Technol. 20, 304 (2002)JLTEDG0733-872410.1109/50.983245] is also unable to encounter some typical characteristics of wave propagation. This work brings out these discrepancies by providing a detailed comparison between the wave impedance, and the said Bloch impedance in rods-in-air-type and holes-in-dielectric-type PhC (hole-type) structures. The theoretical analysis shows that the nature of wave propagation in a rods-in-air-type PhC waveguide can be successfully described by this Bloch impedance in the whole band, whereas the wave impedance fails in it at and beyond the point of transition (from positive to negative) in group velocity. Conversely, this Bloch impedance is unable to characterize the wave propagation at the point of transition in group velocity within a hole-type PhC. Thereby, a procedural change in the calculation of Bloch impedance is proposed, and the supremacy of this proposed calculation over existing ones has been established for both the types of PhC waveguides. Moreover, the unexplored odd mode of the hole-type PhC waveguide has also been examined along with its even band in order to signify the importance of Bloch impedance over wave impedance.

Slow light-based refractive index sensor in single mode photonic crystal waveguide

Here, a slow light-based refractive index sensor has been presented in a hole-type 2D hexagonal lattice photonic crystal waveguide by insertion of only four defect holes inside the channel. The width of the channel has been optimized to provide single mode operation and large free spectral range. Also, the performance of the sensor with and without introducing the central cavity inside the channel have been regarded for different radii of defects. The proposed sensor presents the highest sensitivity and detection range of 126 nm/RIU and 1–2.2, respectively for the detection based on band edge shift. The defects inside the channel have been introduced to obtain high Q-factor by defect radii tailoring. The highest average Q-factor and sensitivity of 1570 and 249.5 have been obtained for defect hole with radius of rc = 0.34a. The study has been carried out by plane wave expansion and finite difference time domain analysis. There is a good agreement between the results and the study proves the effect of slow light on the enhancement of light-matter interaction and sensitivity. The proposed structures can find potential applications in gas or liquid detection in medical and biochemical fields.

Photonic Crystal Based Bio-Sensor Detection in Nanophotonic Structure Using FEM Method

Background & Objective: In this article, a nano-cell coupled 2D photonic crystal waveguide bio- detection platform is proposed for the detection of organic liquids such as water, ethanol, glycerol, benzene and bromine for different refractive indices (n). Methods: The detection characteristics are analyzed and obtained for the band diagram, before and after change of radius (r) as well as after the injection of liquids into the heart of the nanostructure cell at the resonant wavelength (λ res). Also, we extracted variations from the power flow norm (P) to the resonance and the transmission (T) for each material. This nanostructure for different (n) materials used, gives (P) at different levels to the resonance. This explains the importance of the refractive index parameter (n) which plays a crucial role in the detection of materials. Results & Conclusion: The proposed biosensor enables the detection of liquids. This is shown through the numerical results obtained. These results give a good observation of the different behavior of the signal in the presence of the liquids used which depend on their refractive indices 'n'. This parameter 'n' is very important for detection when it varies from material to material. The proposed biosensor can be used in several research areas, particularly in medical and environmental applications.