energy, single-mode, narrow-linewidth fiber laser source using stimulated Brillouin scattering beam cleanup. Optics Express, Optical Society of America, 2007, 15 (10) Abstract:We propose an original nonlinear beam cleaning fiber laser architecture to obtain high energy pulses with a good beam quality and a narrow linewidth. The output beam of a large core Er:Yb co-doped multimode fiber amplifier (M 2 ~ 6, 220 µJ) is converted into a near diffraction limited beam (M 2 = 1.6) through a stimulated Brillouin scattering injection seeded beam cleanup process. We report in this experiment a multimode to single mode conversion efficiency of 50% while preserving the master oscillator linewidth.

We report on an opto-electronic oscillator (OEO) widely tunable from 2.5 to 5.5 GHz. It is based on an Er,Yb:glass Dual-Frequency Laser operating at 1.53 which naturally provides an electrically-tunable beatnote. Inserted in an optical frequency-locked loop including a long fiber delay line, the laser beatnote reaches a spectral purity comparable to the one obtained with classical fixed frequency OEOs. As the oscillator scheme does not require an RF filter, the tunability is simply achieved by tuning the laser beatnote frequency. A fine optimization of the loop has allowed reaching a -27 dBc/Hz (respectively -108 dBc/Hz) phase noise power spectral density at 10 Hz (respectively 10 kHz) of the carrier with only 100 m optical fiber, this performance being independent of the frequency.Index Terms-Dual-frequency laser, optical frequency-locked loop (OFLL), opto-electronic oscillator.

The generation of optically carried microwave signals is of great interest for a wide range of fields, from long-range transmission of RF to wideband radar signal processing. Among the available generation techniques, the potentialities of optical heterodyning are firmly established. However, it leads to severe constraints in optical phase-locked loop (OPLL) design. In this paper, we report on the realization of a compact and ruggedized Er,Yb:glass OFL at 1.5 11m stabilized with three servo-loops.The principle of our OFL is the same as the one presented in [1]. A linear phase anisotropy is inserted inside the laser cavity in order to lift the polarization eigenstates degeneracy. Adjusting the amount of phase anisotropy allows then the frequency difference between the two orthogonal polarizations to be tuned. Since the two optical oscillators share the same cavity, common first-order frequency fluctuations cancel in the resulting beatnote. The laser cavity (see Fig. la and Fig. Ib) is composed of four elements: the gain medium (co-doped phosphate glass) pumped at 975 nm, the birefringent medium (PLZT ceramics), an uncoated silica etalon (ensuring stable dual frequency operation), and the output coupler (2% transmission). PLZT ceramics and etalon are bonded to glass holders, which are pressed between active medium and output coupler in order to achieve the best mechanical stability possible. Under 1.3 W pump power level, the laser outputs a Gaussian beam with a 60 m W overall output power at 1.53 11m, (more than 30 mW are fiber-coupled). The ouput beam is composed by two cross-polarized optical frequencies. Their frequency difference depends on the voltage applied on PLZT element, varing from 800 MHz to 13 GHz with 650 V. When the two frequencies are projected along the same polarization axis, it results in an optical beatnote which frequency is the frequency difference. This beatnote is detected with a photo diode and this leads to the generation of a microwave electrical signal.

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