Photonic Crystal Waveguide Devices Research Articles

Semi‐Supervised Learning Leveraging Denoising Diffusion Probabilistic Models for the Characterization of Nanophotonic Devices

AbstractAlbeit the recent successful demonstrations of nanophotonic device designs leveraging data‐driven supervised learning methods, several challenges still remain. One of the primary constraints of these methods is their computational cost because they require a massive amount of highly time‐consuming full‐wave electromagnetic simulations. In this study, semi‐supervised learning methods are implemented to avoid this issue. Photonic crystal waveguide devices, which offer interesting light‐matter interactions such as the slow‐light effect and the filtering effect, are employed to validate the methodologies. To utilize unlabeled data within this framework, a novel deep generative model, the denoising diffusion probabilistic model is introduced. Next, a pseudo‐labeling process is introduced to assign synthetic labels to the unlabeled data. The performance of a semi‐supervised learning method is compared with a supervised learning scheme, demonstrating that the performance of the neural network can be enhanced without additional numerical calculations. This method holds extensive potential to elevate the efficiency of designing and characterizing future nanophotonic devices.

Midinfrared Refractive-index Sensor with High Sensitivity Based on an Optimized Photonic Crystal Coupled-cavity Waveguide

A photonic crystal coupled-cavity waveguide created on silicon-on-insulator is designed to act as a refractive-index-sensing device at midinfrared wavelengths around 4 μm. To realize high sensitivity, effort is made to engineer the structural parameters to obtain strong modal confinement, which can enhance the interaction between the resonance modes and the analyzed sample. By adjusting some parameters, including the shape of the cavity, the width of the coupling cavity, and the size of the surrounding dielectric columns, a high-sensitivity refractive-index sensor based on the optimized photonic crystal coupled-cavity waveguide is proposed, and a sensitivity of approximately 2620 nm/RIU obtained. When an analyte is measured in the range of 1.0–1.4, the sensor can always maintain a high sensitivity of greater than 2400 nm/RIU. This work demonstrates the viability of high-sensitivity photonic crystal waveguide devices in the midinfrared band.

Proposal for high efficiently 1×4 power splitter based on photonic crystal waveguides

We proposed a new kind of 1×4 optical power splitter composed of one input photonic crystal (PC) waveguide (PCW) and two PC branches with a triangular lattice of air holes. By employing the coupling between a defect region and one input, four output PCWs, the input power can be efficiently split into four output ports. The total transmittance as high as 99.4% at the wavelength 1550 nm is achieved. By modifying two holes at junction area, the input power can be almost evenly split into four parts with a bandwidth larger than 80 nm. It provides a new method and a compact model to split input power into multiple output ports in PCW devices and may find practical applications in future photonic integrated circuits.

SPECTRAL-DOMAIN FORMULATION OF PILLAR-TYPE PHOTONIC CRYSTAL WAVEGUIDE DEVICES OF INFINITE EXTENT

This paper presents a novel formulation for the modeling of electromagnetic wave propagation in pillar-type photonic crystal waveguide devices. The structure under consideration is formed in an infinitely extended pillar-type photonic crystal and the wave propagation is controlled by removing some cylinders from the original periodic structure. The structure is considered as cascade connections of straight waveguides, and the input/output properties of the devices are obtained using an analysis method of multilayer structure. Each layer includes periodic circular cylinder array with defects, and the transfer-matrix is obtained by using a spectral-domain approach based on the recursive transition-matrix algorithm with the lattice sums technique and the pseudo-periodic Fourier transform.

Numerical Analysis of Two-Dimensional Photonic Crystal Waveguide Devices Using Periodic Boundary Conditions

This paper presents a formulation of two-dimensional photonic crystal waveguide devices formed by circular cylinders. The device structures are considered as cascade connections of straight waveguides. Decomposing the structure into layers of the cylinder arrays, the input/output properties of the devices are obtained using an analysis method of multilayer structure. We introduce periodic boundary conditions in the direction perpendicular to the wave propagation, and the Floquet-modes of each layer are calculated by the Fourier series expansion method with the help of the recursive transition-matrix algorithm. Then, the input/output properties of the devices are obtained by recursive calculation of scattering matrix with each layer. The presented formulation is validated by numerical experiments by comparing with the previous works.

Dispersion-controlled slow light in photonic crystal waveguides

Slow light with a markedly low group velocity is a promising solution for optical buffering and advanced time-domain optical signal processing. It is also anticipated to enhance linear and nonlinear effects and so miniaturize functional photonic devices because slow light compresses optical energy in space. Photonic crystal waveguide devices generate on-chip slow light at room temperature with a wide bandwidth and low dispersion suitable for short pulse transmission. This paper first explains the delay-bandwidth product, fractional delay, and tunability as crucial criteria for buffering capacity of slow light devices. Then the paper describes experimental observations of slow light pulse, exhibiting their record high values. It also demonstrates the nonlinear enhancement based on slow light pulse transmission.

Novel structures of simplified photonic crystal waveguides

A conventional photonic crystal waveguide (PCWG) has been fabricated by constructing a large bulk of periodical rods (or holes) and omitting those on the desired optical paths. Thus the PCWG device usually occupies large area because of too many unnecessary rods/holes. In this paper, a simplified PCWG structure is described, which needs only three layers of rods on each side of the optical paths, to implement an ultra-compact optoelectronic device. Extra rods are eliminated. It is shown that the performance of the simplified PCWG is almost identical to that of the conventional one. The respective frequency responses of the transmission characteristics are analyzed by a finite-difference time-domain (FDTD) method and compared.

Experimental demonstration of prism coupling of infrared waves into planar photonic crystal waveguide devices

We demonstrate an efficient prism coupling method to couple nonplanar infrared waves into a 2-D planar photonic-crystal (PhC) device, such as a PhC waveguide (PhCW). A coupling efficiency of 31.1% is obtained experimentally. Results from finite-difference time-domain (FDTD) modeling are shown to closely match the results measured in a fabricated sample.

High transmission and single-mode operation in low-index-contrast photonic crystal waveguide devices

We investigate photonic crystal films made of low-index glass materials. Polarization-sensitive waveguiding and single-mode operation (with losses as low as 1.7 dB/mm) have been observed in wide multimode photonic crystal waveguides after propagation of some millimeters. Furthermore, single-mode operation and transmission as high as about 50% per bend has been observed experimentally in low-index photonic crystal waveguide bends.

Planar photonic crystal waveguide devices for integrated optics

The concept of photonic crystal waveguides and related device applications in integrated optics are discussed, as well as some of the fabrication technology required to realise these structures in practise. Photonic crystal waveguides interact with light on a wavelength scale, which leads to a novel class of miniaturised devices that display designer dispersion.

Separation of photonic crystal waveguides modes using femtosecond time-of-flight

We demonstrate that ultrabroadband ultrashort-pulse white light supercontinua can be used to track the group velocity of photons in optical waveguides using a Kerr gate technique. Results on silicon nitride slab waveguides show both polarization birefringence and multimode dispersion, which vanish at critical wavelengths. When photonic crystals are embedded in the waveguides, the higher order modes are excited within the band-gap region, demonstrating the need to control their dispersion to make effective use of photonic crystal waveguide devices.

Experimental investigation of photonic crystal waveguide devices and line-defect waveguide bends

Photonic crystal waveguide devices incorporating line-defect waveguide bends have been fabricated. In this paper we present preliminary experimental analysis of these structures. Although evidence of photonic band-gap effects are observed in the spectra, transmission efficiency was found to be extremely low due to significant up-scattering losses from the holes. In order to quantify this loss mechanism, a detailed experimental and theoretical analysis of scattering effects in regular photonic crystal waveguide devices with band gaps at visible wavelength is presented. Field profiles in line defect structures are analysed using a FDTD (finite difference time domain) method.