Slow-light Structure Research Articles

Slow light structure implementation to improve Fano response of optical waveguide as a refractive index sensing

Optical sensor based on the coupled cavity is an interesting topic because these types of sensors have higher Figure of merit (FOM) and sensitivity in comparison to other types of sensors. In this paper, a novel refractive sensor based on the coupled cavity by using T-stub and grating transmission line is suggested. The T-stub interaction with the cavity and coupled line make two capacitances and the Fano-shape of the transmission appeared. The grating as a slow light structure enhanced the transmission and Q-factor of the proposed coupled waveguide sensor by controlling the phase in the transmission line. The proposed sensor is modified to have dual-band characteristics as a Fano form at 1286 and 1629 nm (233 and 184 THz respectively) and for this aim, the T-Stub and the grating structure play the main role. This sensor is used to check the materials with refractive index in the range of 1–1.5 and the maximum sensitivity and FOM are obtained at 1730 nm/RIU and 728 RIU−1, respectively. The full wave method of FIT (Finite Integrated Technique) as a time domain method is utilized for analyzing this sensor.

Inverse design of slow light devices at telecommunication band based on metamaterials using a deep learning attempt

Slow light devices have important applications in many fields such as optical communication, optical storage, optical signal shaping and synchronization. Although a variety of high-performance slow light devices can be purchased in the market, it is still a worthwhile research topic to design slow light devices according to specific wavelengths and requirements. Here we employ machine learning method to inverse design electromagnetically induced transparency (EIT) based slow light devices in communication band using metal–dielectric hybrid metamaterials. Three characteristic points of transmittance as well as the group refractive index and bandwidth are chosen as input parameters. By replacing the complex fully connected layer with a one-dimensional convolutional neural network (1DCNN) layer to optimize the fully connected network, the proposed model can break the limitation of passive modulation and find the best slow light structure parameters. The slow light parameters could reach a bandwidth of 38.71 nm and average group refractive index of 10.51. In addition, the model can predict hybrid metamaterial structure parameters of slow light devices in the communication band from 1400 nm to 1600 nm. By combining active and passive modulation technologies, our proposed method improves the adjustment range of design parameters of slow light devices. The procedure can be potentially applied in the design of other nano optical devices.

Slow light generation by using one-dimensional photonic crystals for quantum memory applications

In this study, an efficient and compact optical device for slowing light in corrugated photonic crystals with different corrugation patterns are discussed. The proposed structure shows relatively large group delay with wide bandwidth and approximately zero group velocity dispersion in near-infrared region. Also, due to the zero group velocity dispersion applied on transmitted pulse, high quality pulse can be obtained by using this approach. For comparison, three different photonic crystal structures containing triangular, sinusoidal and graded sinusoidal corrugation patterns were investigated. The group index as much as 5 with the bandwidth about 50 nm is achieved in the sinusoidal corrugated photonic crystal with 8 μm length. This slow-light structure is very promising for application in quantum memories.

Conical Swiss Roll Metamaterial Application for Slow-Light Waveguides

The framework for designing and fabricating a slow-light waveguide structure with conical Swiss roll metamaterial core at Terahertz frequencies has been carried out in this article. In the earliest work, theoretical backgrounds based on Maxwell’s equations have been developed for anisotropic single-negative permeability slab waveguides and anisotropic metamaterial slab waveguides. Subsequently, simulation results fulfilled by the MATLAB programming tool verify extremely low group velocities in the aforementioned slab waveguides in the Terahertz regime frequency. A volumetric conical Swiss roll metamaterial has been proposed as a practical achievement for slow-light waveguides. Dispersion characteristics of the electromagnetic waves in the proposed conical Swiss roll metamaterial have been investigated using the CST simulation tool in Terahertz frequencies. Furthermore, a 2-D dispersion diagram fulfilled by CST and MATLAB validates highly electromagnetic field concentration as well as the presence of backward waves in the conical Swiss roll configuration.

Phase-coupled plasmon-induced transparency and slow light in graphene stub detuning structures

Tunable phase-coupled plasmon-induced transparency (PIT) and slow light are investigated theoretically and numerically by cascading two stub resonators with a certain distance along the graphene bus waveguide. The theoretical model is analyzed by the coupled mode theory and transfer matrix method. The transmission and slow light effects in the transparent window can be tailored not only by changing the detuning of the two stub resonators but also by adjusting the separation distance L or chemical potential between the two stubs. In addition, multiple PITs and slow light are proposed and simulated with a triple-stub structure. By the numerical simulation, a conclusion is drawn that the added phase coupling can trap the SPPs in the waveguide with longer time, resulting in the slow wave effect more obviously than that with only the detuning coupled method. The proposed slow light structure will pave another way towards dynamic controlling slow light in the terahertz and mid-infrared regimes.

Slow Light Investigation on Power Consumption of Lithium Niobate Phc Switch Based on Linear Electro-Optic Effect

AbstractIn this work, an optical switch based on electro-optic effect is reported. We used defect mode in two-dimensional photonic crystal made of Lithium Niobate. Under an applied voltage of 3 V, a refractive index change of −0.0702 is obtained which has led to a transmittance contrast about 60% for the ON state and a high extinction ratio of about 20 dB. Moreover, Slow light structure performance is investigated to optimize proposed optic switch. Due to elliptic shape of holes, the applied voltage is decreased to 0.5 V. Also, a refractive index change decrease around −0.0481, a transmittance contrast increase 65 %, and an extinction ratio increase by 5 dB have been observed. We used plan wave expansion and finite difference time domain methods to analyze the structures performances. It is seen that a defect mode shift about 40 nm and a switching length of 6.48 μm are obtained with drive voltage of 3 V for simple structure and only 0.5 V for slow light structure.

Tunable slow light based on detuned coupling between graphene nanoribbon and square ring splitting modes

We proposed and numerically investigated a newly slow light structure with graphene doublet detuned coupling effect. The novelty and uniqueness of the proposed structure is that the bandwidth and group index can be enhanced simultaneously by changing the length or chemical potential of the nanoribbon resonator. The maximum group index can attain to 131 at $$\mu_{c}$$ = 0.145 eV with the bandwidth of 0.85 THz. By means of the standing wave distribution of square ring splitting modes, the group indices can be enhanced at one window and suppressed at another by adjusting the coupling position of nanoribbon. The proposed structure would have potential prospect in realizing plasmonic filter, optical nonlinearity, optical buffering and storage devices at terahertz frequencies.

Mid-Infrared Slow Light Engineering and Tuning in 1-D Grating Waveguide

The design, fabrication, and characterization of 1-D grating waveguide as slow light structure working in mid-infrared (MIR) region are demonstrated for the first time. The effects of various structural parameters on slow light properties are investigated through theoretical analysis, simulation and experimental verification, providing guidance on slow light engineering in 1-D grating waveguide. By adjusting structural parameters, average group indices of 9.4–15.5 with bandwidths of 23–66 nm and normalized delay-bandwidth products of 0.093–0.164 are obtained. Thermo-optic tuning is also demonstrated with π phase shift and group index tuning from 23 to 33 at the wavelength of 3.9024 μm by applying 1.4 mA current. The proposed tunable 1-D grating slow light waveguide provides a promising platform for various MIR applications such as on-chip absorption-based biochemical sensors, tunable optical buffers, and thermo-optic modulators.

Comments on “Simultaneous measurement of angular velocities of two vertical directions in a slow-light structure”

Abstract A recent paper by Gu and Liu reported a fiber double-ring resonator gyroscope that can simultaneously measure rotation in two orthogonal axes, with a sensitivity predicted to be 35 times larger than that of an interferometric fiber optic gyroscope (IFOG). Because the two rings have different lengths, the gyroscope could not be biased properly, and the authors remark that as a result, its sensitivity to a small rotation rate is reduced. We stress that this sensor actually responds quadratically to a small applied rotation rate, and that it is therefore essentially insensitive to a small rotation rate. We point out that it could easily be biased properly and this major issue is eliminated by using two rings with nominally equal lengths. We also show that in general, and unlike claimed, this sensor does not measure rotation on orthogonal axes independently. This cross-sensitivity between axes worsens significantly when the sensor is properly biased, and it is then much too strong for inertial navigation of aircraft. A conceptual method that might reduce this cross-sensitivity is suggested. A simple physical argument is also presented to explain why this gyroscope was entirely expected to be more sensitive than an IFOG, and shows that as a result of algebraic errors, the predicted factor of 35 is actually only at most 11.

Analysis of Kerr nonlinearity enhancement in silicon nitride waveguides using one-dimensional slow light structure

A corrugated based slow-light silicon nitride waveguide is studied numerically to enhance Kerr nonlinearity by increasing the group index of the waveguide at the band edge. The structure is optimized taking into account the limitations existing in CMOS-compatible platforms. Bandwidth limitations of the structure are investigated at different wavelengths for various slow-down factors. Finite size realizations of the structure are studied using transfer matrix method to obtain the desired transmission and group velocity at the band edge. Optical loss corresponding to slow-light effect is modeled, and the limitations imposed by the slow-light loss on the nonlinear phase shift saturation are considered. It is shown that by employing slow-down factor of 3, the nonlinear phase shift is improved by a factor of 5. Also, in comparison with a straight waveguide, shorter corrugated waveguides (up to nine times) can provide the same accumulated nonlinear phase shift.

Magnetic-field-dependent slow light in strontium atom-cavity system

Realizing and controlling a long-lived slow light is of fundamental importance in physics and may find applications in quantum router and quantum information processing. In this work, we propose a feasible scheme to realize the slow light in a strontium atom-cavity system, in which the value of group delay can be continuously adjusted within a range of different Zeeman splittings and vacuum Rabi frequencies by varying the applied static magnetic field and the atom number instead of a strong coherent field. In our scheme, the major limitations of the slow-light structure, namely, dispersion and loss, can be effectively resolved, and so our scheme may help to achieve the practical application of slow light relevant to the optical communication network.

Optimal interfacing with coupled-cavities slow-light waveguides: mimicking periodic structures with a compact device.

We present a design for optimal interfacing (I/O coupling) with slow-light structures consisting of coupled cavities. The I/O couplers are based on adding a small set of cavities with varying coupling coefficients at edges of the coupled cavities waveguide in order to match its impedance with that of the I/O waveguides. I/O efficiencies exceeding 99.9% are shown to be possible over a bandwidth which is larger than 50% of that of the coupled cavities waveguide. Consequently, the reflections at the edges of the slow-light structure are practically eliminated. We discuss the properties of the perfectly impedance matched slow-light structure as an effective (super-structure) cavity and study the impact of the number of cavities comprising the I/O coupler. We also consider in details the impact of errors and disorder in the I/O coupling sections.

Method proposing a slow light ring resonator structure coupled with a metal-dielectric-metal waveguide system based on plasmonic induced transparency.

We demonstrate the analogue of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) plasmonic waveguide. Plasmonic induced transparency is a method similar to EIT. In this paper, a plasmonic MDM waveguide is proposed by using an ellipse shaped side-coupled ring resonator and simulated by finite difference time domain. Plasmonics as a new field of chip-scale technology is an interesting substrate, which is used to propose and numerically investigate a novel MDM structure. The aforementioned framework is a 2×2 plasmonic ring resonator, employing gold as a metal and polymethyl methacrylate as a dielectric. Simulations show that a transparent window is located at 1550 nm and signal wavelength is assumed to be 860 nm, which is the phenomenon of plasmonic induced transparency. The velocity of the plasmonic mode can be considerably slowed while propagating along the MDM bends. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends. This plasmonic waveguide system may find important applications for multichannel plasmonic filters, nano-scale optical switching, delay time devices, and slow-light devices in highly integrated optical circuits and networks. In comparison with our previous theoretical work based on circular shaped ring resonators, it is shown that ellipse shaped ring resonators demonstrate better specifications with a slow down factor estimated to be more than 30.

Slow light engineering in a photonic crystal slab waveguide through optofluidic infiltration and geometric modulation

In this paper, a new type of flat-band slow light structure with high group index (n g) and large normalized delay-bandwidth product (NDBP) in a silicon on insulator (SOI) based photonic crystal (PC) slab waveguide with a triangular lattice of circular holes is demonstrated. The dispersion engineering is performed by infiltrating optical fluids with different refractive indices n f in the first row and shifting the second row of air holes adjacent to the PC waveguide (PCW) in the longitudinal direction. In the optimized case, a high NDBP of 0.32 with a group index of 54.55 and a bandwidth of 9.13 nm could be obtained. Furthermore, an ultra-low group velocity dispersion (GVD) in the range of 10–20 s2/m is achieved in all of the structures. These results are obtained by numerical simulations based on three-dimensional (3D) plane wave expansion (PWE) method.

Simultaneous measurement of angular velocities of two vertical directions in a slow-light structure

Abstract A dual-axis optical velocity sensor comprising an asymmetrical double-ring slow-light structure (ADRSLS) coupled by a 3 × 3 coupler is presented. The phase difference caused by the ADRSLS between the counter-propagating waves is derived and discussed. We design and built the experimental system and successfully realize the simultaneous measurement of angular velocities of two vertical directions. The maximum sensitivity of the slow light gyroscope in our case is about 35 times higher than that of an interferometric fiber optic gyroscope (IFOG).

Thermal nonlinear effect in high Q factor silicon-on-insulator microring resonator

In this paper, all–optical switching in silicon-on-insulator (SOI) serially coupled ring resonator based on thermal nonlinear effect is proposed. The radii of the silicon microring resonator are 10μm. In experiment, firstly measured by single pump injection technology with vertical coupling surface grating coupler method, the highest notch of serially coupled ring resonator is 17dB. The strong transverse light-confinement nature of the resonator induces nonlinear optical response with low pump power. Thermal nonlinear effect is achieved by controlling the power of the continuous-wave (CW) pump with very low tuning threshold (0.33nm). And the slop of resonant wavelength as a function of injected pump is 220pm/mw. Secondly, switching time measured by two pump injection technology is 3.01μs and 1.03μs, respectively. Which could be used in integrated photonic communication circuits based optical logic and slow-light structure.

Rotation sensing with Er3+-doped active ring resonator slow light structure

An optical gyroscope, which is constituted by Er3+-doped active ring resonator (EDARR) slow light structure, is presented for the first time. The principle of improving the sensitivity of the detection of angular velocity is analysed in detail. The expression of the rotation phase difference of EDARR between the counter-propagating waves is derived and discussed. At the resonant frequency, the phase shift difference has the maximum value when the light power in the cavity is far greater than the input light power. We designed an experimental scheme of Er3+-doped active ring resonator slow light system. Two additional bias phases ϕb = ±π/2 were introduced in the optical path, by recording the light intensity difference and I0 at the resonant frequency , the input angular velocity can be obtained. The slow light structure based on EDARR can enhance the sensitivity of the detection of the angular velocity by three orders of magnitude.

Angular Velocity Sensing Based on Double-Ring Slow-Light Structure

An optical gyroscope comprising a double-ring slow-light structure (DRSLS) coupled by a $3 \times 3$ coupler is presented. A technique for improving the sensitivity of the detection of the angular velocity is analyzed in detail. The expression for the rotation phase difference of the DRSLS between the counter-propagating waves is derived and discussed. In our experiment, a Y-waveguide integrated phase modulator is used as the light beam splitter and combiner. After applying a square wave to the modulator, the best sensitivity of the system is obtained, and the complexity of the signal detection is greatly reduced.

Dynamically tunable slow light based on plasmon induced transparency in disk resonators coupled MDM waveguide system

Ultrafast and low-power dynamically tunable single channel and multichannel slow light based on plasmon induced transparencies (PITs) in disk resonators coupled to a metal-dielectric-metal (MDM) waveguide system with a nonlinear optical Kerr medium is investigated both numerically and analytically. A coupled-mode theory (CMT) is introduced to analyze this dynamically tunable single channel slow light structure. Multichannel slow light is realized in this plasmonic waveguide structure based on a bright–dark mode coupling mechanism. In order to reduce the pump intensity and obtain ultrafast response time, the traditional nonlinear Kerr material is replaced by monolayer graphene. It is found that the magnitude of the single PIT window can be controlled between 0.08 and 0.48, while the corresponding group index is controlled between 14.5 and 2.0 by dynamically decreasing pump intensity from 11.7 to 4.4 MW cm−2. Moreover, the phase shift multiplication effect is found in this structure. This work paves a new way towards the realization of highly integrated optical circuits and networks, especially for wavelength-selective, all-optical storage and nonlinear devices.

Slow light structure with enhanced delay–bandwidth product

In this study, we propose a special type of slow light photonic crystal (PC) waveguide structure to achieve slow light with an improved delay and bandwidth product (DBP). The waveguide is based on a triangular lattice PC with a line defect imposed by changing the radii and locations of the holes lying along the waveguide centerline. By altering the locations of these central holes, group indices ranging approximately from 25 to 40 are obtained over frequency intervals, attaining a nearly constant group index. It is also observed that the group index spectrum has an S-like shape under certain circumstances. The manipulations of structural parameters easily allow attaining higher or lower group indices. For special configurations, normalized DBPs can be enhanced up to a value of 0.554. According to the best of the authors’ knowledge, this value is the highest value achieved with PC waveguide structures, and this value is achieved without using any special optimization methods such as topology optimization. Group velocity dispersion values of various configurations are minimized to enable proper optical pulse propagation.