Acousto-optic Wavelength-tunable Erbium-doped Fiber Ring Laser

The tunable erbium-doped fiber lasers (EDFLs) as a new type of light source have been extensively studied. EDFLs lasing at 1550 nm are compatible with optical fiber communication systems. EDFLs are attractive light sources for dynamic wavelength assignment and improving the flexibility of the network, and are of high conversion efficiencies, low insertion loss. EDFLs can be applied in various fields such as optical communication systems, optical fiber sensors and spectroscopy. A tunable EDFL, which utilizes an acousto-optic tunable filter (AOTF) as the tuning component, has wide tuning range (covering the C-band range), fast lasing wavelength tuning speeds (in the order of microseconds), and convenient tuning way (no mechanical tuning).The background and current status of research on tunable EDFLs are introduced firstly. Then, the filtering theory of AOTF is analyzed. The transfer function of the multi-stage filter is deduced, and the filtering curves of double and triple-stage filters are obtained, the sidelobe values are calculated. In order to suppress the sidelobes, multi-stage AOTFs by cascading several single-stage filters are investigated experimentally. The sidelobe of double-stage AOTF is measured to be about -19 dB. In further, another AOTF is cascaded, and then a triple-stage filter is obtained. The experimental results show that the sidelobe of this triple-stage device is suppressed to -27 dB,and the bandwidth is narrower.The frequency-shift compensation of polarization-independent quasi-collinear AOTF is analyzed in detail, and the acousto-optic tunable EDFL is designed. Considering the EDF as a homogeneously broadened three-level system, the operation principle of this laser is discussed, and the output characteristics is simulated. Using this polarization-independent AOTF as the tuning component, the tunable fiber ring laser is experimentally demonstrated, and continuous wavelength tuning with a range of 38 nm (1524.7-1562.4nm) is obtained and the compensation of frequency-shift is realized obviously.Finally, a novel design of AOTF, which utilizes double broad-band interdigital transducers to broaden its filtering range, is proposed. And the feasibility of its application in acousto-optic spectrum analyzers is discussed. This work was supported by the National Natural Science Foundation of China"Study on the broad-bandwidth tunable fiber laser with single-longitudinal-mode operation based on integrated AOTF", and the Key Scientific and Technological Project of Tianjin"Study on the polarization-independent multi-stage integrated acousto-optic tunable filter (AOTF)".