| Abstract [eng] |
Characterization and optimization of actively mode-locked fiber laser source operating at 1570 nm wavelength Giedrius Dubosas The aim of this work is to investigate the performance of an actively mode-locked fiber laser source operating at 1570 nm wavelength and the pulse generation characteristics by varying the active modulation frequency, modulation depth and spectral filtering. Fiber laser circuit with an Erbium-doped active fiber and a fiber electro-optic modulator was assembled. Active fiber was pumped through both ends using 976 nm continuous wave laser diodes with single-mode fiber outputs. The electro-optic modulator was controlled using sinusoidal or pulsed RF signal with fixed repetition rate. The investigation of a fiber laser source for active mode-locking showed that the pulse generation in a fiber optic circuit is strongly influenced both by the parameters of the modulated signal, and by the characteristics of the fiber circuit. The stability of the generated pulses was mainly influenced by the control signal noise of the modulator used in the experiment, but was also affected by inaccurate choice of modulation frequency or modulator opening voltages. The stability of the pulses is additionally strongly influenced by laser pumping. It has been found that the stability of the generated pulses improves with increasing gain, at least in the range of pump power levels used in this experiment. A study with two filter configurations has also shown that the use of a narrowband filter in the fiber circuit results in a significant reduction in the spectral width of the generated pulses, even below the filter bandwidth. The control of the repetition rate of the pulses generated by an actively mode-locked fiber laser source has been investigated. It was determined that the energy of the generated pulses changes inversely with the repetition rate. It was also observed that the measured average power is only marginally dependent on the modulation frequency used and remains almost the same when changing the repetition rate. The study also investigated the dependence of the width of the generated pulses on the pulse repetition rate. It was found that the width of the pulses increases with increasing pulse repetition rate and that, as a result, the peak power of the pulses is not exactly inversely proportional to the pulse repetition rate. |
