Optical Directional Coupler Research Articles

An excellent super-polarization-independent optical directional coupler based on dual-core photonic crystal fibre with a bandwidth of 390 nm

In this work, a novel structure of dual-core photonic crystal fibre (PCF) is proposed to realize the super-polarization-independent optical directional coupler, based on the feasibility of optical fibre manufacturing process and the need of practical application into account. The introduced fluorine-doped elliptical cores with a rotation angle of 45 degrees successfully realize the super-polarization-independent coupling performance within the effective wavelength range of 1230–1620 nm, with a difference in coupling ratios between two polarized lights of less than 0.004%. In other words, it counteracts the negative effects of the introduction of dual cores on the structure’s symmetry. This greatly reduces the difference in coupling ratio between the two polarization states and effectively eliminates the polarization-dependence of the dual-core PCF. In addition, when compared to traditional elliptical air holes, the solid elliptical structure offers greater ease of control, making manufacturing less challenging. Consequently, this innovative structure is poised for widespread adoption in today’s optical communication networks.

Triple Micro Optical Multiple Asymmetric Ring Resonator Performance Analysis as Optical Filter

The present article implements the modelling of triple asymmetrical optical micro ring resonator (TAOMRR) in z-domain and the waveguide spacing is designed using Finite Difference Time Domain (FDTD) methodology. The formulation of the transmission function is prepared in z-domain utilizing the delay line signal processing technique. The developed configuration is scrutinized by evaluating the frequency response analysis as well as various important characteristics that are dispersion, group delay, and finesse using MATLAB software. The efficacy of the proposed methodology is tested using OptiFDTD software and it is found that the results of both MATLAB and OptiFDTD are in very nearby settlement. The field analysis of propagated wave inside the microring resonator is shown. The specific gap for various optical directional couplers is also determined using OptiFDTD in this article. The proposed technique is very useful for modeling and analyzing of different configurations of micro optical asymmetric ring resonator which found great application in the field of optical filters as well as optical sensors.

Harnessing XPM effects in non-linear directional couplers for 4-bit gray code conversion and even parity verification

Abstract The all-optical switching phenomena in the non-linear directional coupler using cross-phase modulation (XPM) effect have been proposed. It is designed to generate an all-optical XOR functionality, considering the XOR logic gates as a basic module the design and analysis of an efficient all-optical 4-bit binary to gray code converter and 4-bit even parity checker circuit is proposed. The design methodology includes the switching of a weak continuous-wave (CW) signal, which is controlled by the combination of two controlled pump signals. In this paper, mathematical analysis of the coupled mode theory associated with optical directional couplers has been discussed. The switching characteristics of XPM effect based All-optical directional couplers have been examined for appropriate values of the controlled pump signals. Appropriate values of extinction ratio and corresponding controlled pump signal levels are investigated for an efficient generation of XOR logic gates. Further, the detailed analysis of layout generation and design aspects of All-optical 4-bit binary to gray code converter and 4-bit even parity checker circuits have been carried out. The proposed methodology is verified by the appropriate simulation results, which include the transmittivity, extinction ratio (Xratio) curve variation and dynamic time domain plot associated with proposed units.

The Optimal Operating Point for Linearizing an Integrated Optical Lithium Niobate Directional Coupler Modulator

The influence of an operating point on the linearity of an integrated optical lithium niobate directional coupler modulator was studied. It was found that the optimal setting for the position of an operating point for suppressing the third-order intermodulation distortion depended on the power of the high-frequency modulation signal. Thus, despite the simple design of the device, the directional coupler modulator requires a complex algorithm for setting an operating point to achieve a high linearity of operation. An active system for setting an operating point based on the low-frequency pilot signal and zeroing its third harmonic was used to demonstrate the possibility of linearization when the amplitude of the modulation signal changes. The use of an operating point control system became possible after limiting the drift of the operating point by etching the dielectric buffer layer in the interelectrode gap. The results obtained look promising for high-performance analog optical links.

Effect of Temperature and Material Dispersion on the Performance of Single Mode Optical Fibers Directional Coupler

Effect of Temperature and Material Dispersion on the Performance of Single Mode Optical Fibers Directional Coupler

An Optical Measuring Transducer for a Micro-Opto-Electro-Mechanical Micro-g Accelerometer Based on the Optical Tunneling Effect

Micro-opto-electro-mechanical (MOEM) accelerometers that can measure small accelerations are attracting growing attention thanks to their considerable advantages—such as high sensitivity and immunity to electromagnetic noise—over their rivals. In this treatise, we analyze 12 schemes of MOEM-accelerometers, which include a spring mass and a tunneling-effect-based optical sensing system containing an optical directional coupler consisting of a fixed and a movable waveguide separated by an air gap. The movable waveguide can perform linear and angular movement. In addition, the waveguides can lie in single or different planes. Under acceleration, the schemes feature the following changes to the optical system: gap, coupling length, overlapping area between the movable and fixed waveguides. The schemes with altering coupling lengths feature the lowest sensitivity, yet possess a virtually unlimited dynamic range, which makes them comparable to capacitive transducers. The sensitivity of the scheme depends on the coupling length and amounts to 11.25 × 103 m−1 for a coupling length of 44 μm and 30 × 103 m−1 for a coupling length of 15 μm. The schemes with changing overlapping areas possess moderate sensitivity (1.25 × 106 m−1). The highest sensitivity (above 6.25 × 106 m−1) belongs to the schemes with an altering gap between the waveguides.

Quantum Projectors Implemented With Optical Directional Couplers in Ion-Exchanged Glasses

Ion-exchanged glass as a platform for quantum photonics is proposed. Quantum projectors are implemented with integrated optical directional couplers fabricated by ion-exchange K <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^+$</tex-math></inline-formula> /Na <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^+$</tex-math></inline-formula> in soda-lime glass. We consider devices composed of concatenated directional couplers which implement <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N$</tex-math></inline-formula> -dimensional quantum projective measurements, and concomitantly the production of 1-qudit states. The fundamental units of these devices are 2 × 2 directional couplers that are experimentally studied in order to obtain, through an optical characterization, empiric relationships between fabrication and optical parameters of such couplers. Likewise, a two-dimensional quantum projector is demonstrated so that projective measurements are obtained for the states of bases <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> (diagonal) and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> (circular).

Reconfigurable electro-optical logic gates using a 2-layer multilayer perceptron

In this work, we aim to use the optical amplifiers, directional couplers and phase modulators to build the electro-optical gates. Thanks to the 2-layer-multilayer-perceptron structure, the inversion of matrix is performed to obtain the coupling ratio of the directional couplers and the phase delay of the phase modulators. The electro-optical OR, AND, XOR, NAND, NOR and XNOR gates are demonstrated. Moreover, we not only study the results under the ideal condition of device, but also discuss the imperfect situation with 1% error of fabrication or operation to study the tolerance of this system. Through our simulation results, the visibility of the gate output can be higher than 0.83. The gates can be fabricated in a silicon-based chip to develop the integrated optics computing system.

Analysis of the behavior of an all-optical not logic gate in a photonic crystal directional coupler / Análise do comportamento de uma porta lógica not totalmente óptica em um acoplador direcional de cristal fotônico

In the present work, an optical directional coupler (ODC) based on two-dimensional (2-D) photonic crystal (PhC) was analyzed and proposed, through the methods of plane wave expansion (PWE) and finite-difference time-domain (FDTD), which were used with the purpose of analyzing the behavior of a new all-optical NOT logic gate and the electric field distribution in the coupler for linear (bar), non-linear (cross) states and the control signal. The simulation results in OptiFDTD software show that the proposed crystal structure is a strong candidate for use in ultrafast photonic integrated circuits (PICs), being highly advantageous with excellent transmission performance and simple design.

Stable hybrid plasmonic directional coupler based on an embedded silver nanostructure waveguide.

In this paper, a stable hybrid plasmonic optical directional coupler based on an embedded silver nanostructure that can offer a power transfer up to 95% is presented. This optimum power transfer is obtained at an outer edge-to-edge separation of 0.58 µm between the two waveguides. The obtained propagation loss is as low as 0.0863 dB/µm. The electric field distributions of the symmetric and antisymmetric modes of the coupler are compared, and the transmission characteristics are studied in detail using the finite element method. The performances of the directional coupler have been further characterized in terms of excess loss, coupling degree, and directionality. The shortest coupling length at which the maximum power coupling occurs is obtained as 2.488 µm. The proposed compact directional coupler features good field confinement and low propagation loss, which opens the door for many device applications in photonic-integrated circuits and optoelectronic industries.

The Method of Lines Analysis of TE Mode Propagation in Silica based Optical Directional Couplers

Optical directional couplers fabricated using planar light wave circuit (PLC) technology are versatile tools in integrated photonics devices. They have the advantages of small size, high consistency, ability for high volume production, and excellent possibility to be integrated with electronics circuits. Optical waveguide couplers are mainly utilized as power dividers, optical switches, and wavelength division multiplexers/de-multiplexers (WDM). A number of methods have been used to analyze directional couplers, such as coupled mode theory (CMT), the beam propagation method (BPM), the method of lines (MoL), finite-difference methods (FDM), and finite element methods (FEM). Among these numerical approaches, MoL is the simplest method to analyze mode propagation inside directional couplers because it has the advantages of very fast convergence and accurate solutions for one-dimensional structures. The objective of this study was to analyze the propagation of TE modes in optical directional couplers by using MoL. The parameters used, i.e. waveguide width, refractive index, and wavelength, were taken from the characteristics of silica-on-silicon directional couplers that were used in fabrication. MoL is considered a special finite-difference method, which discretizes a one- or two-dimensional wave equation in the transverse direction and uses an analytical solution for the propagation directions. Basically, MoL is a semi analytical numerical method with the advantages of numerical stability, computational efficiency, and calculation time reduction. Further, we explored the possibility of using directional couplers as optical switching devices.

Robust Light Coupling in a Quadratically Bent Directional Coupler

Bending the axis of an optical directional coupler can result in phase mismatch between the evanescently coupled waveguides. Using a quadratic bending profile, we realize the phase mismatch with a sign flip scheme for robust light coupling between the waveguides. We derive an analytical solution for the coupling scheme and show its robustness against parameter variations. Beam propagation method solution of the scalar wave equation verifies the two-level analysis and the device robustness.

Modeling and performance analysis of single fiber ring incorporated with fiber Bragg grating

The mathematical model of an optical ring resonator (RR) configuration using a single directional optical coupler (DOC) with a uniform fiber Bragg grating (FBG) incorporated and an RR configuration using two DOCs with an FBG incorporated is developed in the Z-domain. The developed mathematical model is used for the evaluation of transmission response. Spectral characteristics in terms of peak transmittance, resonant frequency, and free spectral range are determined for a single fiber ring configuration using two DOCs with an FBG incorporated. The results are found to be in very close agreement with measured values. The transmission characteristic of the single waveguide structure comprising a ring of length 2 mm enclosing a Bragg grating is analyzed. By properly optimizing the grating reflectivity and power coupling ratios of the coupler, a narrow full width at half maximum of 4.72 GHz that is around 78 times sharper than the normal FBG resonance is obtained. Further narrowing of the spectral width is achieved by increasing the RR length. The grating lengths are chosen judiciously to minimize the side peaks. The group delay and dispersion characteristics are addressed.

Quantum statistical signature of $ {\cal P}{\cal T} $PT symmetry breaking.

In multiparticle quantum interference, bosons show rather generally the tendency to bunch together, while fermions cannot. This behavior, which is rooted in the different statistics of the particles, results in a higher coincidence rate $ P $P for fermions than for bosons, i.e., $ {P^{(\rm bos)}} \lt {P^{(\rm ferm)}} $P(bos)<P(ferm). However, in lossy systems, such a general rule can be violated because bosons can avoid lossy regions. Here it is shown that, in a rather general optical system showing passive parity-time ($ {\cal P}{\cal T} $PT) symmetry, at the $ {\cal P}{\cal T} $PT symmetry breaking phase transition point, the coincidence probabilities for bosons and fermions are equalized, while in the broken $ {\cal P}{\cal T} $PT phase, the reversal $ {P^{(\rm bos)}} \gt {P^{(\rm ferm)}} $P(bos)>P(ferm) is observed. Such effect is exemplified by considering the passive $ {\cal P}{\cal T} $PT-symmetric optical directional coupler.

LiTaO3 Directional Coupler Switch with Enhanced Extinction Ratio and Low Insertion Loss

A novel design of optical directional coupler switch with S-bend waveguides on LiTaO3 platform has been designed with R-Soft CAD tool and the same is simulated by Beam propagation method (BPM) for light propagation analysis. The simulation results of the optical directional coupler (ODC) switch is reported. We observed that the directional coupler (DC) switch has lower insertion losses and higher extinction ratios for a certain values that are discussed in the paper. This was studied by variation in waveguide parameters such as, wavelength, waveguide gap, and length of the device. Simulation results designate that the switching efficiency for TE and TM modes with extinction ratio about 3dB when the waveguide gap is 3.5μm for both the polarization modes and insertion loss is 13dB with same waveguide gap in TE mode and 16dB in TM mode at 1550nm wavelength.

Optical properties of plasmonic components based on a nanoscale three-dimensional plasmonic waveguide

In this paper, the properties of five kinds of passive nanoscale optical devices (including directional coupler, waveguide ring resonator, add-drop filter, nano light focusing device, and Mach–Zehnder interferometer, etc.) based on a new nanoscale three-dimensional plasmonic waveguide the authors proposed previously are presented. For the proposed nanoscale optical directional coupler, the coupling length does not show monotonic increase with the increase of edge-to-edge distance between two waveguides, and thus there exists an optimal edge-to-edge distance of around 0.1 μm with a minimum coupling length of about 2.7 μm and high coupling efficiency of 93.4%. And the waveguide ring resonator with a very small ring radius of 1.1 μm and a separate gap of 80 nm features an extinction ratio as small as 2.9%, with large free spectral range of 194 nm, and a bandwidth of 24 nm. Moreover, an add-drop filter with the same ring radius of 1.1 μm and a separate gap of 80 nm features a 24.4% extinction ratio. The optical properties of the devices are numerically investigated by the finite-difference time-domain simulation method. These excellent properties make them have great potential in nanophotonic integrated circuits.

Hollow Fiber Coupler Sensor.

We present a bi-conical optical directional coupler composed of solid and hollow core fibers. Through an evanescent wave coupling mechanism, the detection of liquid refractive index and its temperature are demonstrated. The experimental results illustrated that the sensor offers a sensitivity of volts per refractive index units (V/RIU) for refractive indices ranging from to with a resolution of refractive index units (RIU).

Optimization of a liquid refractive index sensor based on an integrated optic slot-waveguide directional coupler

An integrated optic silica slot-waveguide directional coupler is investigated here for its ability to measure the refractive index (n) of a liquid biochemical species. The geometrical dimensions of the directional coupler are optimized so that the output power of the directional coupler is linear when refractive index of the liquid species changes from 1.33 to 1.38. The best geometrical dimensions achieved here from a simulation with the beam propagation method (BPM) were a waveguide width of 6um, a gap of 2um, a slot-widht of 0.5um, and a channel length of 2,000um. The proposed directional coupler type of biochemical sensor changes its output power linearly from 2 to 24% when the refractive index of the liquid species varies from 1.33 to 1.38.

A Lithium-Niobate Waveguide Directional Coupler for Switchable Mode Multiplexing

We propose a lithium-niobate optical waveguide asymmetric directional coupler for the realization of an electro-optically switchable mode (de)multiplexer. Our typical fabricated coupler, designed for (de)multiplexing the LP01 and the LP11a mode, provides a switching efficiency higher than 90% and the operation wavelength can be tuned over a wide range of ~240 nm by varying the driving voltage between −23 and +20 V. Our proposed switchable mode multiplexer could find applications as a wavelength-selective mode switch or a reconfigurable mode add-drop (de)multiplexer for mode-division-multiplexing networks.

Topological whispering gallery modes in two-dimensional photonic crystal cavities

Utilizing the robust transport properties of the topological photonic crystal interface, we experimentally realize two-dimensional topological photonic crystal cavities, where discrete whispering gallery modes can propagate unidirectionally along the cavity circumference. Different from traditional cavities, these topological whispering galley modes are insensitive to cavity shapes. Our microwave demonstration has a good agreement with numerical simulations. Using pure dielectrics, by scaling down to the optical wavelength, an optical directional coupler based on the same topological photonic crystal scheme is also proposed. We here show that topological photonics can provide more novel designs for optical devices.