short-wave infrared integrated spectrometers in GaSb/silicon waveguide circuits

Research Area: Mid IR silicon photonics

Main Researcher: Muhammad Muneeb

Although Silicon photonics was originally conceived for telecommunication and data communication it is also emerging as potential integration platform for a broader wavelength range. For spectroscopic sensing moving to short/mid-infrared wavelength region is very attractive as the characteristic absorption lines of molecules of interest become much stronger at longer wavelengths, thereby increasing the sensitivity of the sensing system. The silicon integration platform can potentially be used to realize this functionality in a compact and low-cost fashion. Basic passive components like low loss waveguides and high efficiency grating couplers have been realized on silicon-on-insulator covering the wavelength range of 2-2.5 um. Single-mode waveguide losses in the short-wave infrared below 0.6 dB/cm are reported and -3.8 dB coupling efficiency from a standard single-mode fiber to an SOI waveguide at 2.1 μm has been realized experimentally.

Measured transmission spectrum of short-wave grating couplers (Left) SOI Waveguide loss (Right)

Silicon-on-insulator (SOI) based spectrometers have been realized for a wide operational wavelength range, both planar concave grating (PCG, also known as echelle grating) and arrayed waveguide grating (AWG) spectrometer designs. These passive wavelength demultiplexers are combined with GaInAsSb photodiodes. These photodiodes are heterogeneously integrated on SOI with benzocyclobutene (DVS-BCB) as an adhesive bonding layer. The uniformity of the photodiode characteristics and high processing yield, indicate a robust fabrication process. Good performance of the miniature spectrometers over the 1500nm – 2300 nm wavelength range has been demonstrated which paves the way to on-chip absorption spectroscopy in this wavelength range.

Measured transmission spectrum of different spectrometers (Left) Microscope image of spectrometers with integrated detectors (Right)

Silicon is optically transparent up to 8μm, which allows to extend the wavelength range of operation of the SOI platform even further but at longer wavelengths buried silicon dioxide starts absorbing heavily. To access how far in wavelength SOI platform can be extended we realized high performance dispersive spectrometers based on both planar concave grating (PCG, also known as echelle grating) and arrayed waveguide grating (AWG). Waveguide losses at around 3.8 um wavelength range are below -6 dB/cm while spectrometers have excess loss better than -3 dB and crosstalk level around -20 dB.

Measured waveguide losses (Left) Measured transmission spectrum of an AWG based spectrometer

Other people involved:

• Nannicha Hattasan
• Dorian Sanchez
• Muhammad Muneeb

PhD thesises