Holographic planar lightwave circuit for on-chip spectroscopy

Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties. Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography. Here, we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization. The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer. While maintaining the total device footprint below 2 cm 2 , the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range, over a 148 nm spectral range and 926 channels. This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing. Spectroscopy: on-chip integration An on-chip spectrometer based on digital planar holograms offers a miniature alternative to conventional devices. Developed by three research team in California, USA, the spectrometer uses two computer-designed holograms as high-resolution gratings for separating different wavelengths of light in the spectral bands of 630–694 nm and 766–850 nm. The holograms are made by electron beam lithography and reactive ion etching of a Si/SiO 2 /Si 3 N 4 substrate. The result is a semiconductor spectrometer chip that occupies a footprint of less than 2 cm 2 and boasts a resolution of 0.15 nm and a bandwidth of 148 nm across the red and near-infrared regions. The researchers say that the device’s performance is comparable to much larger conventional instruments and will be a useful component for ‘lab-on-a-chip’ applications such as sensing. They also believe that it should be possible to make even smaller versions with higher performance in the future.