Broadband Optical Couplers Research Articles

Design of enhanced broadband optical couplers for long-infrared quantum well infrared photodetectors

Design of enhanced broadband optical couplers for long-infrared quantum well infrared photodetectors

Ultra-Broadband, Fabrication Tolerant Optical Coupler for Arbitrary Splitting Ratio Using Particle Swarm Optimization Algorithm

This work presents a design approach of multi-segment directional couplers with ultra-broadband flat spectra and benign fabrication tolerance on the silicon nitride platform. Using particle swarm optimization, we optimize design parameters of multiple coupling regions and asymmetric decoupling regions in the multi-segment couplers, and synthesize optimized structures for the intended power splitting ratio over optical telecommunication O, S, E, and C bands. To efficiently model the device with many structural parameters, each part of the fundamental structure is separately modelled by the most efficient method, including effective index method, coupled mode theory, and transfer matrix method to construct the high-dimensional design space. By choosing a proper evaluation function, the optimized couplers achieve flat spectra with less than ±2% fluctuation over ∼300 nm spectrum for 50%/50%,30%/70% and 10%/90% splitting ratios, which is well verified by 3D FDTD. We also discuss performance degradation caused by fabrication variations and offer a general strategy to enhance fabrication tolerance for the broadband optical couplers with asymmetric decoupling regions.

Low-Loss and Broadband Optical Coupler Based on Lensed-Top Vertically Curved Silicon Waveguide

The high-performance silicon optical coupler is one of the significant functional devices, which will be required to enable mass commercialization of silicon photonic integrated circuits (Si-PICs). In this work, we investigated the bending shapes for each device length and have successfully fabricated a very low-loss and broadband 5- $\mu \text{m}$ -beam-spot surface optical coupler based on a lensed-top vertically curved silicon waveguide by adjusting the dose conditions used in the ion implantation process. The fabricated device showed a coupling loss of 2.4 dB, which included a waveguide loss of approximately 0.5 dB and a 0.5-dB-loss bandwidth of more than 220 nm for the transverse electric polarization in the 1.55- $\mu \text{m}$ wavelength band. This coupling device will greatly contribute to the progress in the development of Si-PICs using the coarse wavelength division multiplexing technique.

Geometrical structure, multifractal spectra and localized optical modes of aperiodic Vogel spirals

We present a numerical study of the structural properties, photonic density of states and bandedge modes of Vogel spiral arrays of dielectric cylinders in air. Specifically, we systematically investigate different types of Vogel spirals obtained by the modulation of the divergence angle parameter above and below the golden angle value (≈137.507°). We found that these arrays exhibit large fluctuations in the distribution of neighboring particles characterized by multifractal singularity spectra and pair correlation functions that can be tuned between amorphous and random structures. We also show that the rich structural complexity of Vogel spirals results in a multifractal photonic mode density and isotropic bandedge modes with distinctive spatial localization character. Vogel spiral structures offer the opportunity to create novel photonic devices that leverage radially localized and isotropic bandedge modes to enhance light-matter coupling, such as optical sensors, light sources, concentrators, and broadband optical couplers.

광자결정 광섬유기반 광신호 분배기 개발

A broadband optical coupler with a broad bandwidth of 1000 nm based on a photonic crystal fiber (PCF) is investigated. The PCF has 6 layers of air hole structures and a diameter of . The PCF-based coupler is fabricated by using a fused biconical tapering method based on heating and elongation processes. Changing temperature and an elongation length can control the bandwidth and the bandedge wavelength of the PCF-based broadband coupler. The diameter of the fused region in the PCF-based coupler was measured to be . The fabricated PCF-based coupler has a nearly-flat coupling ration of 3-dB in a broad bandwidth of 1000 nm, which is wider than that of the previously reported PCF-based coupler and that of the single-modefiber-based coupler. Since the resolution of optical coherence tomography system is proportional to the bandwidths of both an optical light sources and an interferometer, the fabricated PCF-based broadband optical coupler has a great potential for realization of a broadband interferogram.

Broad-band optical coupler based on evanescent-field coupling between three parallel long-period fiber gratings

We propose a broad-band 3/spl times/3 optical coupler based on the principle of evanescent-field coupling between three parallel identical long-period fiber gratings. In particular, we demonstrate experimentally the situation where light is launched into one fiber and coupled equally to the other two fibers. The effects of changing the surrounding refractive index and introducing an offset distance between the gratings on the transmission characteristics of the coupler are investigated. Using three identical 35-mm-long gratings, we find that the peak coupling efficiency increases by 9 and 14 dB, as the surrounding refractive index and the offset distance increase from 1.0 to 1.440 and from 0 to 50 mm, respectively. The side-lobe suppression ratio varies between 16.0 and 23.0 dB. We achieve a total power conversion efficiency of 85% at the resonance wavelength with a surrounding refractive index of 1.420 and an offset distance of 50 mm.