Finite element modeling of coupling characteristics of directional coupler for multiplexer and de-multiplexer application

Numerical simulation of directional coupler that is based on the finite element method was conducted using the COMSOL Multiphysics software. The distributions of electric field and power flow of light propagates in two cores of directional coupler were analyzed. The results showed the dependencies of coupling length and maximum transfer power between cores on the cores separation and the wavelength, the characteristic of a subwavelength directional coupler can be used for photonic integrated circuits. Asymmetric directional coupler was also designed by changing in the device dimension, as the core width. The variation of coupling length with the core width were analysed. It was found that the power switching between cores is reduced when introducing a small difference in the one core width of directional coupler, followed by increased coupling length. At the same time, the coupling length can be decreased efficiently by increasing the difference in one core width; therefore, a directional coupler with large core width is more convenient to reduce the power switching between cores than the smaller core width. This study is useful for determining the coupling characteristics between the cores that may be used as a platform for future photonic integrated circuits in optical communication systems.

Optical Power Splitter Based on Single Mode Directional Coupler Waveguide Using SnO2 Nanomaterial

Optical power splitter based on waveguide had been simulated numerically using Finite Difference Beam Propagation Method (FDBPM). Proposed waveguide was designed in the form of simple directional coupler waveguide. The waveguide was contained SnO2 nanomaterial as film or the guide part and the other supporting material as cladding with lower refractive index such as flint glasses. The waveguide used 2 μm of width to establish single-mode waveguide. The structure of waveguide is divided into three parts such as input, coupling and output part. While the waveguide was modified with angle in input and output parts to avoid coupling between waveguides. Furthermore, the proposed waveguide was analysed by varying the angle and coupling length. The analysed result shows that the waveguide has best performance in angle of 0.5 degrees and coupling length of 300 μm when the propagation loss was around 0.53%. Using the parameter, the output distribution percentage of waveguide approached 55%:44.5%. This performance indicated that the proposed waveguide can be used as optical power splitter. The application is very useful for optical telecommunication networking development.

Reduction in Crosstalk Using Uniform Germanium Strips for Dense Integration of Photonic Waveguides

The requirement of low crosstalk between the neighboring waveguides should be considered essentially, in order to achieve the compact photonic integrated circuit (PIC), which includes photonic waveguides. Literature shows that the lower crosstalk can be realized by using the silicon-on-insulator (SOI) based waveguide, having an appropriate separation between them. The current work is focused on reducing the waveguide separation to further improve the photonic integration over the PICs. This has been achieved by inserting the germanium strips between the photonic waveguides. The investigations of the impact of variations in heights and widths of germanium strip have demonstrated that the crosstalk can be reduced by a significant amount, which provides noteworthy improvement in coupling length. The maximum coupling lengths of 81578 µm, 67099 µm, and 66810 µm have been achieved at their respective end-to-end separations of 300 nm, 250 nm, and 200 nm, and their corresponding minimum crosstalk values have been noted as -29.40 dB, -27.71 dB, and − 27.70 dB. Moreover, the analysis to realize the coupling length for Ge-strip, have been compared with the Si-, and SiN-strips. The approach presented in the current work can be utilized for the design of many compact photonic applications, such as polarization splitter, integrated photonic switches, etc.

Flow coupling between active and passive fluids across water–oil interfaces

Active fluid droplets surrounded by oil can spontaneously develop circulatory flows. However, the dynamics of the surrounding oil and their influence on the active fluid remain poorly understood. To investigate interactions between the active fluid and the passive oil across their interface, kinesin-driven microtubule-based active fluid droplets were immersed in oil and compressed into a cylinder-like shape. The droplet geometry supported intradroplet circulatory flows, but the circulation was suppressed when the thickness of the oil layer surrounding the droplet decreased. Experiments with tracers and network structure analyses and continuum models based on the dynamics of self-elongating rods demonstrated that the flow transition resulted from flow coupling across the interface between active fluid and oil, with a millimeter–scale coupling length. In addition, two novel millifluidic devices were developed that could trigger and suppress intradroplet circulatory flows in real time: one by changing the thickness of the surrounding oil layer and the other by locally deforming the droplet. This work highlights the role of interfacial dynamics in the active fluid droplet system and shows that circulatory flows within droplets can be affected by millimeter–scale flow coupling across the interface between the active fluid and the oil.

Design of Nanoscale Hybrid Insulator-metal-insulator Plasmonic Waveguide

Optical properties of the fundamental hybrid mode of hybrid insulator-metal-insulator plasmonic waveguide (HIMIPW), consists of insulator-metal-insulator sandwiched between two dielectric waveguides, have been investigated to achieve the relatively high propagation length and large normalized intensity at 1.55 µm working wavelength. The main aim of the current work is to settle the issues of high power loss and size of waveguide dimension. The optimum waveguide dimension of 0.2 µm × 0.02 µm has been obtained propagation length around 289.26 µm. The normalized intensity in the low-index region of the HIMIPW has been achieved around 67.50 , due to the electric field enhancement in this region. It is beneficial for the design of bio-sensing, optical manipulations, etc. The electric field intensity has been attained highest values at wavelength 1.55 µm for the optimum dimension of the HIMIPW ( = 0.2 µm, and ), due to highly localized surface plasmon resonance at the metal-dielectric interfaces. The investigation of the coupling length between the two identical parallel HIMIPWs with a separation distance has been done. Further to improve the coupling length, a metallic strip has been inserted between them, keeping the separation distance unchanged. The higher coupling length leads to lower crosstalk between two parallel hybrid plasmonic waveguides, which can be highly useful to achieve the larger integration over the photonic chip.

A Novel Gold Film-Coated V-Shape Dual-Core Photonic Crystal Fiber Polarization Beam Splitter Covering the E + S + C + L + U Band

In this paper, a novel gold film-coated V-shape dual-core photonic crystal fiber (V-DC-PCF) polarization beam splitter (PBS) based on surface plasmon resonance effect is proposed. The coupling lengths of the X-polarization (X-pol) and Y-polarization (Y-pol) and the corresponding coupling length ratio of the proposed V-DC-PCF PBS without gold film and with gold film are compared. The fiber structure parameters and thickness of the gold film are optimized through investigating their effects on the coupling lengths and coupling length ratio. As the propagation length increases, the normalized output powers of the X-pol and Y-pol of the proposed V-DC-PCF PBS at the three wavelengths 1.610, 1.631, and 1.650 μm are demonstrated. The relationships between the extinction ratio (ER), insertion loss (IL) and wavelength for the three splitting lengths (SLs) 188, 185, and 182 μm are investigated. Finally, it is demonstrated that for the proposed V-DC-PCF PBS, the optimal SL is 188 μm, the ILs of the X-pol and Y-pol are less than 0.22 dB, and the splitting bandwidth (SB) can cover the E + S + C + L + U band. The proposed V-DC-PCF PBS has the ultra-short SL, ultra-wide SB, and ultra-low IL, so it is expected to have important applications in the laser, sensing, and dense wavelength division multiplexing systems.

Polarization Beam Splitter Based on Si3N4/SiO2 Horizontal Slot Waveguides for On-Chip High-Power Applications

In this paper, we propose an Si3N4/SiO2 horizontal-slot-waveguide-based polarization beam splitter (PBS) with low nonlinearity for on-chip high-power systems. The coupling length ratio between the quasi-TE and quasi-TM modes (LTE/LTM) was optimized to 2 for an efficient polarization splitting. For the single-slot design, the coupling length of the PBS was 281.5 μm, while the extinction ratios (ER) of the quasi-TM and quasi-TE modes were 23.9 dB and 20.8 dB, respectively. Compared to PBS based on the Si3N4 strip waveguide, the coupling length became 22.6% shorter. The proposed PBSs also had a relatively good fabrication tolerance for an ER of >20 dB. For the multi-slot design, the coupling length of the PBS was 290.3 μm, while the corresponding ER of the two polarizations were 24.0 dB and 21.0 dB, respectively. Furthermore, we investigated the tradeoff between the ER and coupling length for the optimized PBSs with single slot or multiple slots.