Ultra-Compact Lab-on-Chip CMOS Photonics Sensor

  • Osama H. Al Mrayat

Student thesis: Master's Thesis


Recently, there has been a significant demand for low-cost, highly-sensitive, ultra-compact optical gas sensors that can be deployed in diverse applications, including chemical and biomedical analysis, environmental monitoring, industry and food processing. Gas sensors can be realized through different sensing mechanisms: electrical, thermal, and optical. Integrated optical sensors have superior advantages, including greater sensitivity, wider dynamic range, and immunity to electromagnetic interference. It also allows for a chip-scale implementation of complex and multiplexed sensing platforms, and by far, mass fabrication. Silicon photonics provides cost-effective and ultra-compact sensitive sensing structures with the potential of electronics and photonics integration on the same platform. It also enables implementation of inexpensive and large-scale sensor arrays. To leverage the significant developments in silicon photonics, and to benefit from the well-established microelectronic fabrication infrastructure exploited by the electronic industry, in this thesis we propose a low power SOI photonic integrated circuit for gas sensing applications. It incorporates high quality-factor (high-Q) Vernier-cascaded micro ring resonators combined with a low-resolution spectral element. The proposed chip enables spatial separation of different wavelength channels of an optical signal. The design includes both passive components (e.g. micro-ring resonators) and active components such as waveguide germanium photo-detectors, and a superluminescent diode (SLD) to provide a broadband light source. The sensing structure is based on two-cascaded micro-ring resonators with different free spectral ranges (FSRs) with a difference of (Δ___ = 0.32 nm) to excite the Vernier-effect, which extends the dynamic range as well as improves both sensitivity and detection limit. The Vernier effect also eliminates the need for an external bulky and expensive spectrum analyzer, and therefore enables both the portability and low-cost features of the sensor. Moreover, an on-chip spectrometer is implemented using a planar echelle grating; it has 8-channels with a 5nm channel spacing (8 × 5__) as well as a linear dispersion of 1.4 μm/__ and an effective crosstalk level as good as − 29 __. This configuration enables a detection limit of 689 × 10__ __ (Refractive Index Unit) and a sensitivity of 7257 __/__ . The photonic gas sensor has an overall footprint 2 × 3.2__; it was designed based on a nanophotonic SOI material platform, and fabricated through the IME CMOS fabrication facility. However, due to the unavailability of the chip at the time of writing this thesis, this research only discusses the design, modelling, and numerical assessment of the proposed sensor.
Date of AwardMay 2015
Original languageAmerican English
SupervisorMahmoud Rasras (Supervisor)


  • Gas sensors
  • chemical analysis
  • biomedical analysis
  • environmental monitoring
  • sensing mechanisms
  • optical sensors
  • sensor arrays
  • silicon photonics
  • gas sensing applications.

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