Ultra-compact monolithically-integrated silicon single-microring spectrometer breaking the free-spectral-range limitation

Abstract Highly-integrated spectrometers with performance excellence are extremely desired for various applications, such as consumer electronics and unmanned aerial vehicles. In this paper, an ultra-compact monolithically-integrated single-microring spectrometer on silicon is proposed and realized with a high resolution as well as a broad working window. In particular, an innovative scheme of utilizing the free spectral range (FSR) dispersion for a single-microring and strategically inducing resonant peaks red-shift more than twice of the FSR is proposed for the first time. In this way, the working window of the single-microring is significantly extended far beyond the FSR limitation with the assistance of intelligent algorithm. Moreover, the single-microring is realized with a high-Q factor by introducing ultra-low-loss broadened optical waveguides designed with modified-Euler curves, resulting in ultra-narrow-linewidth responses and ultra-high-resolution spectrum measurement. The monolithically-integrated silicon single-microring spectrometer is experimentally demonstrated with a resolution as high as 0.02 nm in a broad working window of 66 nm (which is >15 times larger than the microring's FSR). Besides, the present on-chip spectrometer is fabricated with standard processes for silicon photonics, showing an ultra-compact footprint of 370×110 μm2, which is the smallest monolithically-integrated spectrometer with the highest channel-to-footprint ratio (8.3×104 mm−2) to date. The present spectrometer is expected to be very attractive for realizing low-cost portable sensing modules and lab-on-a-chip systems because of the performance excellence, the footprint compactness and the integration density.