Distributed Sensing

The ability to adjust transmission properties of optical fibers externally was a groundbreaking discovery for optical sensing technology. This distributed sensing is unique to fiber optic sensing technology and allows for measurements over very long distances. In addition to this capability, the optical sensors transmit data using light, not electrical currents, which makes the transfer a stable process and eliminate any need for power supply.

Multiplexed sensor arrays using (a) OTDR and (b) WDM / Bragg grating principles.

Within distributed sensing a technique called wavelength division multiplexing (WDM) can be used. This multiplexing system uses wavelengths that are slightly different from the Bragg wavelengths and allow a wavelength tunable laser to adjust reflectivity (4). As a result of this, temperature or pressure can be influenced. A broadband light source can also be used to create a similar result.

Another common technique is time division multiplexing (TDM). This system uses consistent yet weak reflective gratings along with frequent light pulses. This technique is used with wavelength division multiplexing to dramatically increase the number of channels available.

August 16, 2011

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