A 100-channel near-infrared SOI waveguide microspectrometer:: Design and fabrication challenges

We present recent advances in the development of a waveguide micro spectrometer chip with high spectral resolution in the near-infrared part of the spectrum. The microspectrometer is designed for a high index contrast silicon-on-insulator (SOI) platform, where high number of spectral channels can be obtained with high spectral resolution in a compact device. We present a 100-channel SOI microspectrometer with designed spectral resolution of similar to 0.08 nm at 1.5 mu m wavelength and about 8x8 mm(2) in size. A number of critical design issues are discussed, including design of deep-etched tapers near the Rowland circle required for high-resolution performance as well as coupling between closely spaced waveguides. Device fabrication process is discussed in detail, including two-step e-beam patterning and two-level ICP etches, the focus being on achieving deep and smooth vertical etches in silicon with controllable sub-micron waveguide widths and gaps. The potentially available spectral range of the microspectrometer is limited by the transparency of silicon, extending from the band edge of Si at 1.107 mu m to the onset of lattice phonon absorption band near 5 mu m. Such compact high-resolution multi-channel integrated microspectrometers are promising for a variety of applications, including spectroscopy, telecommunications, optical interconnects, environmental and bio-sensing.