Design And Applications Of Rectangular Ptical Filter Based On Stimulated Rillouin Scattering

Tunable narrowband optical filter has various applications in fieldssuch as ultra-dense wavelength division multiplex, optical orthogonalfrequency division multiplexing, microwave photonics, etc. Theseapplication situations need optical filters with small in-band ripples andsteep edges. Some existing solutions include special designed fiber Bragggate, cascaded Fabry-Perot cavity, cascaded micro-ring resonator, etc. Forall these technologies, to achieve rectangular transmission profile is still abig challenge.In order to meet this challenge, this thesis presents a novel activeoptical filter, based on the accumulation of Brillouin gain spectrums frommulti-pumps. To reduce the in-band ripples, a feedback compensationprocess is proposed. This process can adjust the pump lines with thefeedback information of last measured gain spectrum. After several timesfeedback process, a rectangular active filter can be achieved.This thesis will first discuss the feasibility of the active optical filtertechnology and the necessity of the feedback compensation process, bysome theoretical research and numerical simulation. Then someexperiments will be performed to verify the technology. By improving theexperimental scheme continually, we solved important problems in theexperiment, such as the measurement of Brillouin gain profile, thesensitivity of feedback process, the spectrum asymmetry of doublesideband modulation, etc. Finally we achieved a series of active opticalfilters with bandwidth from40MHz up to1.5GHz. The resolution of bandwidth controlling is20MHz. The in-band ripple of1GHz bandwidth isless than0.8dB, and the shape factor is0.84. The experiment results meetthe requirements of flat top and steep edge. And to our knowledge, this isthe first optical filter whose transmission profile is so close to an idealrectangle.