Direct wireless readout of fiber Bragg grating sensors using radio-over-fiber.

Wireless readout of optical fiber sensors is of interest for a variety of applications. In the state of the art, the sensor data are digitized before the wireless transmission. We propose a wireless evaluation scheme for fiber Bragg gratings where the sensor signal is transmitted directly without any processing in a simplified sensor node. The underlying concept is explained in detail and validated experimentally. It is based on radio-over-fiber technology and evaluates not only the magnitude of the received analog electrical sensor signal but also the phase. Additionally, signal correction and signal processing schemes are discussed. A series of experimental measurements indicates not only advantages of the phase evaluation method over the magnitude evaluation method but also approves the general feasibility of the direct interrogation approach for wireless sensing applications. Future subjects of interest involve absolute accuracy considerations and maximum achievable sampling rates.

On the Advantages of Microwave Photonic Interrogation of Fiber-Based Sensors: A Noise Analysis.

Although microwave photonic approaches have been used for fiber sensing applications before, most contributions in the past dealt with evaluating the sensor signal's amplitude. Carrying this topic on, the authors previously presented a scheme for the interrogation of fiber sensors that was based on a fiber Bragg grating's phase response for the electrical signal. However, neither has the measurement setup been analyzed nor have the amplitude and phase-based approaches been compared in detail before. Hence, this paper picks up the previously proposed setup, which relies on an amplitude modulation of the optical signal and investigates for sources of signal degradation, an aspect that has not been considered before. Following the incorporation of the microwave signal, the setup is suitable not only for an amplitude-based evaluation of fiber Bragg gratings but also for a phase-based evaluation. In this context, the signal-to-noise ratios are studied for the conventional amplitude-based evaluation approach and for the recently developed phase-based approach. The findings indicate a strong advantage for the signal-to-noise ratio of the phase response evaluation; an 11 dB improvement at the least has been found for the examined setup. Further studies may investigate the consequences and additional benefits of this approach for radio-over-fiber sensing systems or general performance aspects such as achievable sensitivity and sampling rates.