Microring resonators (MRRs) are widely used in optical filters due to their compact size, high Q, and narrow linewidth. However, traditional MRR-based high sensitivity sensors suffer from narrow free spectral range (FSR), which limits the number of channels for detecting substances and causes interference with the identification of the center wavelength when the refractive index of analytes changes significantly. In this paper, we propose an ultra-large FSR and high sensitivity filter utilizing subwavelength grating slot microring resonator with inner silicon blocks with different widths, achieving FSR of 95.5 nm and refractive index sensitivity of 743 nm/RIU. And a lab-on-chip system comprised of eight channels-based filters is presented, promoting the development of silicon photonics in the detecting resolution of small refractive index changes of analytes to 3.60×10-4 RIU and multiple analytes simultaneously.
An on-chip optical power splitter is a crucial component for optical signal processing, widely used to implement Mach-Zehnder Interferometer, 1×2 switches, and optical arrays for various photonic integrated circuit (PIC) applications. In this paper, we present a tapered silicon waveguide power splitter with assisted subwavelength gratings (SWGs) that enhances coupling between waveguides and relaxes the critical dimensions requirement of the devices, with a taper tip width of 100 nm. The three-dimensional Finite-Difference-Time-Domain (3D-FDTD) simulation results demonstrate that the splitter has a low loss of only 0.1 dB over an ultra-broad wavelength range from 1200 nm to 1700 nm. The dependence of the performance on geometry variations, including tip width, gap spacing, waveguide width, and thickness of the device layer, is also investigated to illustrate the fabrication tolerance. The power splitter is also proved to be temperature-insensitive. With the advantages of low loss, ultra-broadband, fabrication-tolerant, temperature-insensitive, and relaxed critical dimensions (≥100 nm), the proposed power splitter is a promising practical building block for large-scale PICs.
High efficient photodetectors are of paramount importance in optical communications as the advent of the big data era. The bandwidth-efficiency trade-off of detectors has always been being a limiting problem. We demonstrate here that ultrahigh absorption more than 85% can be achieved at wavelength 1300 nm by only patterning an ultrathin germanium (Ge) slab with a periodic array of air holes, which is about 3 times comparing with that of a uniform Ge slab of the same thickness. The enhanced absorption is mainly attributed to the critical coupling of the guided resonance of the photonic crystal slab. This work paves a way for high-responsivity surface-illuminated photodetection with a patterned ultrathin Ge slab.
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