Cover story: Zhang L, Zhang M, Chen TN, Liu DJ, Hong SH et al. Ultrahigh-resolution on-chip spectrometer with silicon photonic resonators. Opto-Electron Adv 5, 210100 (2022).

Spectrometers are of great importance in our scientific research and daily life. However, traditional spectrometers based on free-space optics are usually cumbersome and expensive. Therefore, great efforts have been made to realize on-chip spectrometers. As it is well known, high resolution is highly desired for spectrometers used for microbiology, food monitoring, gas sensing and so on, where fine spectrum identification is required. Recently, Prof. Daoxin Dai’s group from the College of Optical Science and Engineering at Zhejiang University, China, has proposed and demonstrated an ultra-compact and ultrahigh-resolution spectrometer on silicon by using the configuration with an ultra-narrow-band filter and a wideband filter array. In particular, an ultrahigh-Q resonator with Euler bends was introduced to achieve ultra-high-resolution wavelength- selective filtering. Meanwhile, the wideband filter array was used for achieving an extended working window of the on-chip spectrometer. For the demonstrated on-chip spectrometer, the footprint is as compact as 0.35 mm² and the resolution is as high as 0.005 nm, which is the highest for on-chip dispersive spectrometers. The working window is about 10 nm and the ratio between the working window and the resolution is as large ~2000, which is the record for spectrometers with a footprint less than 1 mm². The proposed spectrometer breaks the bottleneck of insufficient resolution of the dispersive chip-level spectrometer. It is expected that the present ultrahigh-resolution on-chip spectrometer plays an important role in environmental monitoring, aerospace and many other fields, especially in the field of spectral analyzing in smart phones.