Multiwavelength optical sensor based on a gradient photonic crystal with a hexagonal plasmonic array

Sensitivity and versatility are characteristics that make a sensor device attractive for wide-spread applications in everyday life. Surface-enhanced Raman spectroscopy (SERS) is capable of providing the highest sensitivity, that of single-molecule detection, and excellent specificity due to its fingerprinting capability. However, conventional SERS substrates must be optimized to operate for a particular excitation wavelength. Here in this work, we achieve for the first time multiwavelength amplification with a hybrid plasmonic/photonic heterostructure integrating a gradient photonic crystal and an Ag nanotriangle array. We demonstrate the detection of ultrathin molecular layers showing a signal amplification for the typical laser wavelengths used in Raman spectroscopy detection. By combining photonics and plasmonics in a single silicon chip, we expand multiwavelength- and spatially-selective ultra-sensitive detection to a wide range of applications from biomedicine to safety.