Silicon Photonic Spectrometer for Accurate Peak Detection Using the Vernier Effect and Time-Domain Multiplexing

We present a silicon-on-insulator spectrometer for wavelength peak detection operating in a 20-nm wavelength band around 1550 nm with an average accuracy of 12 pm. The silicon photonic integrated circuit occupies a footprint of 250 × 700 μm² and is composed of a passive-arrayed waveguide grating (AWG) and an array of thermo-optic Mach-Zehnder interferometer switches. The AWG multiplexes multiple inputs and outputs with a vernier design that shifts the spectral response of the different inputs. In this demonstration, we use five output channels and four input channels, with a 4.0-nm channel spacing and 5.0-nm channel spacing, respectively. The responses to the different inputs are disentangled at the outputs by time-multiplexing the inputs with the switches. We demonstrate a more than tenfold improvement in peak detection accuracy using the Vernier effect, from nm range using a single input to picometers range using the four inputs.