Low-Cost Interrogation Unit for Wavelength-Coded Fiber Sensors


Beck, M.; Kiesel, P.; Schmidt, O.; Johnson, N. M. Low-Cost Interrogation Unit for Wavelength-Coded Fiber Sensors. accepted for publication in IEEE TRANSACTIONS and JOURNALS (2009)


We have developed a low-cost, compact, and fast wavelength detector suitable for the read-out of many kinds of optical sensors that are based on optical wavelength shifts caused by an external stimulus, e.g., temperature, strain, stress, acceleration, bio-coating, or chemical environment. Examples are Fiber Bragg Grating (FBG) sensors, laser cavity sensors, micro-sphere or micro-ring based sensors as well as photonic crystal sensors. The wavelength monitor we present is capable of resolving sub pm wavelength changes. A photosensor array or position detector element is coated with a linear variable filter, which converts the wavelength information of the incident light into a spatial intensity distribution on the detector. Differential read-out of two adjacent elements of the photosensor array or the position detector is used to determine the centroid of this distribution. A wavelength change of the incident light is detected as a shift of the centroid of the distribution. The performance of this wavelength detector was tested with a wavelength tunable light source. We have demonstrated that our device is capable of detecting wavelength changes as small as ~0.1 pm. The readout speed of our wavelength shift detector exceeds 5 kHz and is currently only limited by the amplifier bandwidth, faster read-out appears to be possible. The performance of this interrogation method has been tested for the case of temperature and strain sensors based on Fiber Bragg Gratings (FBG)

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