Doctoral Thesis: Terahertz wave-molecule interactions via CMOS chips: From comb gas sensor with absolute specificity to ultra-stable, miniaturized clock

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Event Speaker: 

Cheng Wang

Event Location: 

36-462

Event Date/Time: 

Monday, October 28, 2019 - 3:00pm

Abstract:

Polar gaseous molecules generate unique rotational spectrum, under the excitation of electromagnetic wave within millimeter wave & sub-terahertz regime. The frequency and absorption intensity of rotational spectral lines are directly linked onto the micro-scale molecular structure. They serve as an indicator or "finger-print" of molecules. Thus, rotational spectrometer with absolute specificity is promising for complicated gas mixture analysis (e.g. human exhaled breath and industrial gas leakage). To utilize this magnificent property, a Dual-Frequency-Comb spectrometer is proposed and implemented. Broadband (220~320 GHz), fast scanning (20X) and highly sensitive (ppm-level w/o pre-concentration) gas analysis is accomplished by not only intelligent spectrometer architecture embracing parallelism, but also multi-functional, highly-efficient integrated circuit on CMOS. Furthermore, the rotational spectral line with quality factor of ~10^6 is also an ultra-stable quantum system for frequency reference. Subsequently, a new technology, chip-scale molecular clock (CSMC) locking on to 231.061 GHz rotational spectral line of Carbonyl Sulfide (OCS) molecules is demonstrated, which shows  "atomic-clock" level stability, miniaturization, low cost and low DC power, due to  full-electronic implementation on 65nm CMOS. Two CSMC prototypes have been demonstrated: The first CSMC prototype locking onto fundamental dispersion curve, built on a frequency-shift-keying (FSK) spectral line probing scheme, exhibits a measured Allan deviation of 3.8e-10 with an averaging time of tau=10^3 s. Next, an updated CSMC prototype adopting high order dispersion curve locking technology effectively increases the clock stability by 8X and 9X for short (tau=1~s) and long-term (tau=10^3 s), respectively. The CSMCs will benefit time/phase synchronization for future high-speed wireless access network, precise navigation and very long baseline interferometry in seismology.
 
Thesis Supervisor: Prof. Ruonan Han