Low-Cost Interrogation Unit for Wavelength-Coded Fiber Sensors

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)

Citation

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)