The Light Control And Its Applications Based On Acousto-optic Interaction In Optical Fibers

The improvement on optical fiber communication systems (OFCS) depends on the development of the optical signal processing devices. Because of its easy integration with the OFCS, all-fiber devices play an irreplaceable role in the OFCS. Among all the all-fiber devices, all-fiber acousto-optic tunable devices are of advantages for convenient tunable characteristics and relatively simple structures, and therefore they are of great significance in practical applications.In this dissertation, the basic principle of all-fiber acousto-optic tunable filter (AOTF) was introduced. Based on the acousto-optic interaction in optical fibers, the fiber winding acousto-optic tunable filter (FWAOTF), acousto-optic tunable add/drop channel couplers and acousto-optic tunable Maher-Zehnder interferometer were experimentally constructed and investigated, respectively. The main contents of the thesis are presented as follows:1. In Chapter one, we introduced the state-of-art progress on the all-fiber optical components in general, which was followed by the current development of the all-fiber AOTF.2. In Chapter two, the principle of AOTF was firstly introduced briefly. Then we introduced the structure, the working principle and the production process of the acoustic transducer, which is the key component of a practical AOTF. At last, we experimentally measured the tunability of an AOTF fabricated by ourselves.3. In Chapter three, we first analyzed the key factors that could influence the coupling efficiency of an AOTF, and then introduced the possible methods to improve the coupling efficiency of the AOTF. Based on which, we proposed and proved a FWAOTF based on a cuneal acoustic transducer. It was demonstrated that FWAOTF is not only of increased coupling efficiency, but also of broad tunability of the coupling efficiency and the resonant wavelength. More impressive feature of FWAOTF is that it is agility in the application. A coarse comb-like transmission spectrum was realized with the FWAOTF in the experiment, which could be useful in the CWDM system.4. In Chapter four, we introduced the all-fiber add/drop channel coupler based on two parallel long period fiber gratings. To realize the fast spectral tunability for the common all-fiber add/drop channel coupler, a tunable add/drop coupler based on an AOTF and a tapered fiber was proposed and fabricated. We demonstrated that this coupler can not only realize energy transfer between the two fibers, but also has faster tunability of the coupling efficiency and the resonant wavelength. Yet this structure can’t maintain the unique insertion loss because there is mismatching on the propagation constants of the cladding modes between the AOTF and the tapered fiber. A new tunable add/drop coupler based on two parallel AOTFs was proposed and testified. It was demonstrated that the new add/drop channel coupler can work well, more importantly, the transmission spectrum of the drop channel is of relatively uniform insertion loss at any resonant wavelength within the working spectrum.5. In Chapter five, AOTF was introduced into Maher-Zehnder interferometer. After introducing the basic principle and the fabrication procedure of all-fiber Maher-Zehnder interferometer, we designed an all-fiber acousto-optic tunable Maher-Zehnder interferometer by cascading an AOTF and a tapered fiber. It could generate the interference spectrum. The tunabilities of the isolation and the central wavelength of the interference spectrum could be controlled by adjusting the power and the frequency of the radio frequency signal, respectively.6. Finally in Chapter six, the work was summarized. The limitations of our work and the further research plan were presented.