Compact spectrometer based on a disordered photonic chip

Light scattering in disordered media has been studied extensively due to its prevalence in natural and artificial systems. In photonics most of the research has focused on understanding and mitigating the effects of scattering, which are often detrimental. For certain applications, however, intentionally introducing disorder can actually improve device performance, as in photovoltaics. Here, we demonstrate a spectrometer based on multiple light scattering in a silicon-on-insulator chip featuring a random structure. The probe signal diffuses through the chip generating wavelength-dependent speckle patterns, which are detected and used to recover the input spectrum after calibration. A spectral resolution of 0.75 nm at a wavelength of 1,500 nm in a 25-mu m-radius structure is achieved. Such a compact, high-resolution spectrometer is well suited for lab-on-a-chip spectroscopy applications.