Sensor for Absorption Spectroscopy

Sensor with compact serpentine-like WG to maximize absorption/area. A heater whose current is modulated is present in the dithering block aiming to mitigate potential reflections from the sensing area

The sensor is a device which provides an output whose optical power is related to the absorption of a given substance in proximity of the photonic integrated circuit (PIC) sensing area.

The source-to-PIC input coupling is done through spot-size converters. The sensor’s principle is based on the absorption of light in a long waveguide (WG) through the interaction of a substance with the evanescent field of the guided light in the WG. The power is measured with and without substance (possibly in a dual beam configuration) and, from their ratio, substance characteristics e.g. content percentage can be extracted. In the configuration proposed, a serpentine-like WG with no upper cladding is used as sensing path. A dithering block is added to average potential reflections coming from the sensing area by modulating the current of the heater present in the dithering block.

For deployment in applications requiring miniaturized sensors.


  • Compatible with free-space coupled light sources with modal area ~ 8 µm2 (4.7 x 1.7 µm2) near 3.4 µm
  • Broadband
  • Length and light overlap can be tuned to achieve a given absorption strength

On going

  • Improving insertion loss performance

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