Applications Of Fiber Gratings In Microwave Photonics

Microwave photonics is an interdisciplinary area, which combines the advantages of microwave technology and optical communication. Processing the microwave signals with photonic techniques has many advantages, such as low cost, high bandwidth, immunity to electromagnetic interference ect. The fiber Bragg grating(FBG) is a key component for the applications in microwave photonics, for its diversity of the spectrum and flexibility. It can be used in radio over fiber technology, microwave/millimeter-wave generation, phased-array radar and photonics signal processing, etc. In this thesis, the applications of FBGs in microwave photonics are studied:A low-cost method for improving RoF performances by using a phase-shift fiber Bragg grating is proposed. The fiber grating with an ultra-narrow bandwidth is implemented as an optical filter, to suppress the optical carrier of the double-sideband signal. Experimental results show that 17 dB improvement of the RoF link gain and noise figure can be achieved after the carrier suppression. The spur-free dynamic range can also be significantly improved. As a result, the RF gain response is flat with fluctuation less than 2dB ranging from 4 GHz to 14 GHz.A novel system configuration is introduced for optical generation of 60GHz millimeter wave, which is realized through Brillouin-erbium fiber laser and a fiber Bragg grating. The nth-order Stokes wave is generated in the Brillouin-erbium fiber laser, and filtered out by the fiber Bragg grating. The microwave/mm-wave is generated by the mixing of the nth-order Stokes wave and the pump power on the high-speed photodetector.60GHz millimeter wave is generated without any microwave generator.A novel tunable ultra-wideband bandpass filter with narrow notched band is proposed based on a phase-shift fiber Bragg grating. The proposed filter ranges from 3.1 to 10.6 GHz with the center frequency of narrow notched band located at about 5.5 GHz. The rejection loss is more than 25 dB at the dip of the notched band. It can avoid interference that occurs with IEEE 802.11a radio signals significantly. Instantaneous microwave frequency measurement based on frequency-to-power mapping is proposed and demonstrated by using the transmission spectrum of a FBG. The microwave frequency can be estimated by measuring the microwave power difference when the carrier located at the different positions of the FBG. The entire system was significantly simplified and cost-effective since only a FBG was used. Microwave frequency measurement with improved measurement range and resolution is realized. In addition, the optical phase modulator has smaller insertion loss, and can be worked without the bias circuit, so the system is more stable by using an optical phase modulator than Mach-Zehnder intensity modulator.