On-chip Fourier transform spectrometer on silicon-on-sapphire (Conference Presentation)

Abstract

The temperature of earth depends upon the balance between the energy enterring and leaving the planet. The dynamic balance has been broken by the drastical increase of greenhouse gases generated by human activities during the past 150 years. Thus, monitoring of the global emission of greenhouse gases is urgent for human beings. Fourier transform spectroscopy (FTS) in infrared wavelength range is an effective measure for this purpose. An infrared spectrum represents a fingerprint of a material with absorption peaks corresponding to the vibration of the bonds of the atoms making up the material. Because each material is a unique combination of atoms, no two compounds produce the exact same infrared spectrum. Therefore, infrared spectroscopy can result in a positive identification (qualitative analysis) of every kind of materials. In addition, the size of the peaks in the spectrum is a direct indication of the amount of material present. Compared to dispersive optics or filter based spectroscopy approaches, FTS has a few significant advantages, such as high throughput, high signal-to-noise ratio, and high sensitivity. However, the size, weight and free space optics components make FTS a laboratory only instrument demanding extensive human involvement. In this paper, we report a demonstration of an on-chip Fourier transform spectrometer near 3.3 μm wavelength on silicon-on-sapphire. Propagation loss of 5.2 dB/cm has been experimentally demonstrated for strip waveguides. The on-chip FTS comprises an array of Mach–Zehnder interferometers (MZIs) with linearly increased optical path differences. The recovery of the spectrum of an inter-band cascaded laser has been demonstrated.