Optical Fibre-Based Humidity Sensor for Harsh Environments


Electronics - Sensors & Instrumentation
Electronics - Lasers, Optics & Photonics
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United Kingdom


This optical fibre sensor has been developed in cooperation with an industrial collaborator that has an application requiring a sensor capable of measuring humidity in a harsh waste water treatment environment.  The sensor employs a Fibre Bragg Grating (FBG) which acts as the basis of the Relative Humidity (RH) sensor design and the humidity sensing concept exploits the strain effect induced in a FBG through the swelling of a thin layer of applied polymer coating. The swelling of the polymer coating, arising from the absorption of moisture, changes the Bragg wavelength of the FBG, where this can be calibrated to give a direct indication of the humidity level.


Compared to the electrical humidity sensors commercially available, the optical humidity sensor has shown key technological advantages which is highlighted below:

  • Immunity to electromagnetic (EM) interference
  • Wide sensing range
  • Consistent, reproducible performance
  • Insensitive to chemical attacks
  • Can be used in hazardous or explosive environments
  • Small size and light weight
  • Multiplexing: allowing for simultaneous measurement of multi-points and multi-parameters using one single length of an optical fibre.
  • Suitable for monitoring both small and large-scale structures/materials to provide a profile of the moisture/temperature pattern required.

Recent trials with a waste water treatment application have verified the performance of the device in this exceedingly harsh environment.


The technology can be used in water and waste water treatment, security, food industry, healthcare, telecommunication, biotechnology, aerospace, energy sector (oil and gas energy), smart home, etc.  Although this sensor can be used in many applications where an electrical humidity sensor may be employed, it demonstrates superior performance over an electrical humidity sensor were the environment is harsh, may contain corrosive vapours and gases, water and potentially where the environment may be explosive or electrical power might lead to fire, and where safety is of critical importance.

Market Trends & Opportunities

According to market reports, the global photonic sensor market is predicted to have a quantum shift over the next few years. This surge in demand can be attributed to factors such as innovation in the field of fibre optics and expanding the spectral use of sensors in varied industries. The growth of the Fibre Bragg grating (FBG) sensors is one of the most exciting developments in the field of fibre optic sensors in recent years. Compared with conventional fibre-optic sensors, FBG sensors have a number of distinguishing advantages, which makes it a popular choice among many industries. The researcher team have explored this technology extensively to produce a number of FBG-based sensors, including humidity and temperature sensors, which have been recognized by a number of industrial sectors.  As the volume of this sensor type expands it is expected that the cost of manufacture will continue ot fall bringing in more application opportunities which have hitherto not been accessible.


Most commercial humidity sensors on the market are unsuitable for the harsh environments intended for the FBG humidity sensor and therefore the FBG humidity sensor creates new opportunities for applications that have so far been difficult or impossible to address with currently available technology and products.

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