We propose and demonstrate a microwave photonic communication system with tunable wireless multi-waveband based on pulse shaping, direct detection, and multi-wavelength optical comb. Duo to the parameter configuration and RF- photonics modulation, the number of the flat channels output from a multi-wavelength optical comb can be up to 21. In the near terminal unit of the communication system, four adjacent optical sources output from the multi-wavelength optical comb can be obtained. One of the four optical sources is modulated by a RF vector signal with the frequency of 5 GHz. A single sideband optical signal can be obtained from the modulated signal by pulse shaping via a Gaussian optical filter. The single sideband optical signal and the other three optical sources are coupled into a standard single-mode fiber with 50 km, and then reach the remote terminal unit of the communication system, in which the wireless carriers with the frequency of 5 GHz, 25 GHz, 45 GHz, and 65 GHz can be obtained via a photoelectric direct detector. These multi- carriers can be employed for wireless transmission between the mobile terminal and the remote terminal unit; in addition, three pure optical sources utilized for the uplink can be obtained in the meantime.
A simple fiber-optic relative humidity sensor based on cellulose acetate butyrate (CAB) and Fresnel reflection is proposed and investigated theoretically and experimentally. The sensing system is only composed of one light source, three optical couplers, two photo-detectors and two fiber sensing ends. The operation principle is based on relative Fresnel reflection and water-absorption characteristic of the CAB which simultaneously contains hydrophilic and hydrophobic groups. The water absorption process will lead to variation of the CAB’s refractive index or permittivity. It has to be noted that the double-channel system can effectively eliminate the intensity fluctuation of the light source and the influence of the environment. In this paper, the relative humidity environments approximately ranging from 10 % to 100% are generated and measured both in the humidification and dehumidification processes, which shows a good repeatability and reveals a very good fitting feature with a high value of R2 above 0.99. It is of reflection type and can be simply extend to be a multi-point-monitoring system. The sensing system is of cost- effective, simple operation and high precision.
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