Guided-mode Propagation Analysis Research Articles

1 × 2 Graphene Surface Plasmon Waveguide Beam Splitter Based on Self-Imaging

Based on the principle of self-imaging, a 1 × 2 graphene waveguide beam splitter is proposed in this work, which can split the graphene surface plasmons excited by far-infrared light. The multimode interference process in the graphene waveguide is analyzed by guided-mode propagation analysis (MPA), and then the imaging position is calculated. The simulation results show that the incident beam can be obviously divided into two parts by the self-imaging of the graphene surface plasmon. In addition, the influences of the excited light wavelength, Fermi level, dielectric environment on the transmission efficiency are studied, which provide a reference for the research of graphene waveguide related devices.

Ultrahigh-sensitive multimode interference-based fiber optic liquid-level sensor realized using illuminating zero-order Bessel–Gauss beam

A proposal toward the enhancement in the sensitivity of a multimode interference-based fiber optic liquid-level sensor is explored analytically using a zero-order Bessel–Gauss (BG) beam as the input source. The sensor head consists of a suitable length of no-core fiber (NCF) sandwiched between two specialty high-order mode fibers. The coupling efficiency of various order modes inside the sensor structure is assessed using guided-mode propagation analysis and the performance of the proposed sensor has been benchmarked against the conventional sensor using a Gaussian beam. Furthermore, the study has been corroborated using a finite-difference beam propagation method in Lumerical’s Mode Solutions software to investigate the propagation of the zero-order BG beam inside the sensor structure. Based on the simulation outcomes, the proposed scheme yields a maximum absolute sensitivity of up to 3.551 dB / mm and a sensing resolution of 2.816 × 10 − 3 mm through the choice of an appropriate length of NCF at an operating wavelength of 1.55 μm. Owing to this superior sensing performance, the reported sensing technology expedites an avenue to devise a high-performance fiber optic-level sensor that finds profound implication in different physical, biological, and chemical sensing purposes.

Improved Numerical Calculation of the Single-Mode-No-Core-Single-Mode Fiber Structure Using the Fields Far from Cutoff Approximation

Multimode interferometers based on the single-mode-no-core-single-mode fiber (SNCS) structure have been widely investigated as functional devices and sensors. However, the theoretical support for the sensing mechanism is still imperfect, especially for the cladding refractive index response. In this paper, a modified model of no-core fiber (NCF) based on far from cut-off approximation is proposed to investigate the spectrum characteristic and sensing mechanism of the SNCS structure. Guided-mode propagation analysis (MPA) is used to analyze the self-image effect and spectrum response to the cladding refractive index and temperature. Verified by experiments, the performance of the SNCS structure can be estimated specifically and easily by the proposed method.

A Chalcogenide Multimode Interferometric Temperature Sensor Operating at a Wavelength of $2~\mu\text{m}$

This paper investigated the fabrication of a singlemode-multimode-singlemode fiber structure based on a chalcogenide (As2S3 and AsxS1-x) multimode fiber sandwiched between two standard silica singlemode fibers using a commercial fiber fusion splicer. The temperature dependence of this hybrid fiber structure was investigated and a first proof of concept showed that the hybrid SMS fiber structure has an average experimental temperature sensitivity of circa 84.38 pm/°C over a temperature range of 20 °C~100°C at the wavelength range around $2~\mu \text{m}$ . The measured results show a general agreement with numerical simulations based on a guided-mode propagation analysis method. Our result provides a potential platform for the development of compact, high-optical-quality, and robust sensing devices operating at the midinfrared wavelength range.

Acoustic multimode interference and self-imaging phenomena realized in multimodal phononic crystal waveguides

We report an acoustic multimode interference effect and self-imaging phenomena in an acoustic multimode waveguide system which consists of M parallel phononic crystal waveguides (M-PnCWs). Results show that the self-imaging principle remains applicable for acoustic waveguides just as it does for optical multimode waveguides. To achieve the dispersions and replicas of the input acoustic waves produced along the propagation direction, we performed the finite element method on M-PnCWs, which support M guided modes within the target frequency range. The simulation results show that single images (including direct and mirrored images) and N-fold images (N is an integer) are identified along the propagation direction with asymmetric and symmetric incidence discussed separately. The simulated positions of the replicas agree well with the calculated values that are theoretically decided by self-imaging conditions based on the guided mode propagation analysis. Moreover, the potential applications based on this self-imaging effect for acoustic wavelength de-multiplexing and beam splitting in the acoustic field are also presented.

Study the Coupled-Cavity Waveguides Photonic Crystal Power Splitter

We propose a photonic crystal power splitter that allows the electromagnetic waves with a phase shift of 1800between output signals. The splitter consists of two parallel coupled-cavity waveguides placed in proximity. On the basis of the guided mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam and experimentally demonstrated. The results show that both output paths have the same physical length, the two output signals are synchronized. The splitter is very attractive for splitting high-speed optical signals in integrated optical circuits.

A Three-Channels WDN Based on Multimode Interference Photonic Crystal

A photonic crystal waveguide coupled structure can be constructed by putting three photonic crystal waveguides in parallel and adjacent form. Study the coupling of the approximate solution interference acts and the self-image phenomenon of this multi-mode waveguide system based on the guided mode propagation analysis method, a three-channels multimode interference wavelength division multiplexing is designed. The presented device not only has a high transmission rate, but also has the advantages of multiple wavelength selection and may have potential and practical applications in the field of photonic integrated circuits in future.

An ultra-short double-wavelength optical power splitter for two waveguides operation based on photonic crystal multimode interference

In this paper, we design an ultra-short 1 × 2 1310/1550 nm double-waveguide optical power splitter based on photonic crystal multimode interference. The device can be used to divide the input beam equally for both 1310 nm and 1550 nm at the same time. The total multimode waveguide length of this device is only about 13 μm, which is one 210th of the conventional dielectric counterparts reported. On the basis of the guided-mode propagation analysis method, the self-imaging effect is discussed for the case of symmetric incidence. The finite-difference time-domain method is used to simulate the propagation of the beam in the multimode interference. The results show that the repetitive appearances of single image and twofold image of the input field occur alternatively in this device.

Investigation on Single-Mode–Multimode– Single-Mode Fiber Structure

This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally.

Analysis of the fully destructive interference of overlapping-images in MMI couplers

Based on self-imaging effect and overlapping-imaging properties of multimode interference couplers, the phenomenon of fully destructive interference of overlapping-images in MMI couplers is revealed, for the first time. The condition for overlapping-image fully destructive interference is derived. From the point of view of overlapping-image fully destructive interference, we explain the paired interference and the symmetric interference. The expressions of the positions and number of output images for two especial overlapping-images are also given. We prove that this kind of phenomena exists not only in the paired interference and the symmetric interference by way of an example. The influence of the positional number on the fully destructive interference images is also analyzed. And the guided-mode propagation analysis method is used to confirm the analytical results.

General imaging properties of two-dimensional multimode interference couplers

Based on the guided-mode propagation analysis method and the self-imaging effect, the general imaging properties of the two-dimensional multimode interference coupler (2-D MMI) are generalized and discussed. The general formulas for the positions, intensities, and phases of the self-images, and for image overlap in 2-D MMIs are derived. The numbers, positions, intensities, and phases of the self-images are directly related to the position of the input field and the positional number. The self-imaging properties of 2-D MMIs can be regarded as the interference superposition of two orthogonal one-dimensional self-imaging effects. These results are verified by guided-mode propagation analysis.

Optimal design of N × N silica multimode interference couplers – an improved approach

An improved approach for optimization of N×N silica multimode interference (MMI) couplers is presented in this paper. Using guided-mode propagation analysis, we adjust the width and length of the multimode waveguides in the devices to optimize loss and uniformity. We show that the length of the multimode section can be varied in a well-defined range to find optimal device performance. The range is linked to the propagation constant spacing of fundamental and higher order modes of the multimode waveguide. We apply this approach to optimize the design of a 4×4 silica MMI coupler, and demonstrate that the device width and length must be adjusted simultaneously to achieve both low loss and good uniformity. It is found that optimal performance can be achieved with multiple length/width combinations.

Self-imaging phenomena in multi-mode photonic crystal line-defect waveguides: application to wavelength de-multiplexing

We show that the self-imaging principle still holds true in multimode photonic crystal (PhC) line-defect waveguides just as it does in conventional multi-mode waveguides. To observe the images reproduced by this self-imaging phenomenon, the finite-difference time-domain computation is performed on a multi-mode PhC line-defect waveguide that supports five guided modes. From the computed result, the reproduced images are identified and their positions along the propagation axis are theoretically described by self-imaging conditions which are derived from guided mode propagation analysis. We report a good agreement between the computational simulation and the theoretical description. As a possible application of our work, a photonic crystal 1-to-2 wavelength demultiplexer is designed and its performance is numerically verified. This approach can be extended to novel designs of PhC devices.

Analysis of multimode effects in the free-propagation region of a silicon-on-insulator-based arrayed-waveguide grating demultiplexer.

Multimode effects in the free-propagation regions (FPRs) of an arrayed-waveguide grating (AWG) demultiplexer based on silicon-on-insulator are considered. Some undesired multimode effects, such as the increase of the insertion loss and the cross talk, are studied by use of a method of three-dimensional guided-mode propagation analysis. It is found that the multimode effects for the edge channels are more serious than those for the central channel. For an AWG demultiplexer with a small channel number, the multimode effects can be minimized by choosing appropriate FPR parameters such as the length and the thickness of the FPR. The coupling coefficient between the FPR and an arrayed waveguide is sensitive to the thickness of the FPR.

Optical multi-mode interference devices based on self-imaging: principles and applications

This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers. >