Ultra-Precise Optical to RF-Based Chip-Scale Refractive Index and Temperature Sensor

Levy Uriel, HUJI, Faculty of Science, Applied Physics Department


Micro-ring resonators (MRR), refractive index, stabilization

Current development stage

TRL3 Experimental proof of concept       


  • Resonance cavities are excellent transducers to convert small variations in the refractive index into measurable spectral shifts
  • Specifically, chip-scale micro-disk and micro-ring resonators (MRR) are widely used due to their miniaturize size, relative ease of design and fabrication, high quality factor and the high degree of control over transfer function.
  • The current techniques have a limited sensitivity and accuracy due to thermal drifts and other noise sources of both the resonance cavity and the interrogating laser.

Our Innovation

  • The researchers developed a novel approach for precise real-time monitoring and sensing of analytes using a chip scale silicon-based device that includes frequency locked cascaded micro ring resonators.
  • Ultra-precise - Sensing ultra-small changes in the refractive index with precision better than 10-8 (an order of magnitude compared with the state of the art).
  • Miniature solution
  • Scalable, fast and robust solution


  • Our approach combines micron scale cascaded high Q MRRs (which is achieved via the local oxidation of silicon (LOCOS) technique) together with two independent lasers that are frequency stabilized to the MRR's resonance peaks. The frequency difference between these two lasers is monitored using their beat frequency enabling the implementation of highly sensitive bio-sensor for short time (seconds) and long time (hours).
  • The cascaded MRRs include a reference MRR, that is not subjected to the presence of the analytes, and a sensing MRR which wavelength variations are monitored. The shift in the resonance frequency is the result of the presence of the analytes.


Figure 1: a) Schematic representation of cascaded MRR's b) Illustration of the spectrum of the reference MRR (in blue) and the sensing MRR (solid green and dashed green). The sensing MRR curve is illustrated with and without the refractive index change.


Figure 2: The platform of LOCOS MRRs a) Illustration of a planar LOCOS low loss wave guide. The green color represents silicon, and orange silicon dioxide. b) Scanning Electron micrograph image of the LOCOS MRR c) LOCOS MRR Measured transmission, representing a resonance line shape with a quality factor of ~100,000.


  • Biosensing
  • Chemical sensing
  • Environmental monitoring, temperature and pressure sensing
  • Lasers’ high precision frequency stabilization
  • Semiconductor manufacturing
  • Atomic and molecular spectroscopy


Contact for more information:

Matt Zarek
Contact ME: