High‐Resolution and Broad‐Band On‐Chip Optical Spectrometer Beyond 1.55 µm

Abstract The 2‐µm band, covering the eye‐safe wavelength range and various gas absorption spectra, holds high significance for various applications such as gas sensing, biomedicine, and lidar. This paper proposes and demonstrates a silicon photonic spectrometer beyond 1.55 µm (extending to 2‐µm), featuring a high resolution and a wide bandwidth as well as a compact size. A high‐Q racetrack micro‐ring resonator with modified‐Euler‐bends is introduced for significantly enhancing the spectral resolution. Additionally, cascaded (AEM) resonators are incorporated to achieve maximized free spectral range (FSR), while Vernier effect existing in cascaded AEM resonators is utilized to further expand the operational bandwidth. Experimentally, the study performs the measurement of several representative spectra, including single‐/dual‐peak spectra as well as a gas absorption spectrum, demonstrating a high resolution of <30 pm and a broad working bandwidth as large as 230 nm in the 2‐µm band, while the footprint is less than 0.34 mm 2 . The present on‐chip 2‐µm‐band spectrometer achieves a high resolution, broad working bandwidth, compact footprint, showing the highest bandwidth‐to‐resolution ratio among various short‐wave infrared (SWIR) and mid‐infrared (MIR) dispersive spectrometers on silicon reported to date, showing great potential for the applications like gas monitoring, wearable biosensors, etc.