A. González-García

Tunable dual-wavelength actively Q-switched Er/Yb double-clad fiber laser

We demonstrate experimentally a dual-wavelength tunable actively Q-switched fiber laser using 3 m of Er3+/Yb3+ co-doped fiber as the gain medium. For wavelength tuning we used a tunable Hi-Bi FBG having two reflection wavelengths separated by 0.4 nm. The laser emits a dual-wavelength signal that is tunable in a range of 11.8 nm. Laser operation can be switched between single and double wavelength emission. The laser operates at repetition rates from 30 to 110 kHz with pulse durations of 280 ns and pulse energies near 0.5 μJ.

Switchable and tuneable multi-wavelength Er-doped fibre ring laser using Sagnac filters

We demonstrate experimentally a simple configuration to perform wavelength-tuning and multi-wavelength operation in a fibre ring laser that is composed of an Erbium-doped fibre and includes a fibre-optic Sagnac interferometer as a spectral filter. We consider three different Sagnac filters including a 3 dB coupler, two wave retarders (WRs) and respectively 7 cm, 1 and 7 m of high birefringence fibre. The transmission spectrum of each filter is sinusoidal with a 70, 6, and 0.85 nm period, and its maxima can be shifted over one period by adjusting the angle of the retarders in the loop. By adjusting the WRs included in the filter and in the laser ring, tuneable single wavelength and several two- or three-wavelength lasing regimes were observed. In particular, fine adjustments of the WRs allow observing two- and three- wavelength operation with wavelength separations well below the homogeneous bandwidth of the gain medium. The stability of these modes of operation however strongly depends on environmental conditions at room temperature.

Multiple noise-like pulsing of a figure-eight fibre laser

In this work we study multiple noise-like pulse generation in a 320?m long passively mode-locked erbium-doped figure-eight fibre laser in the normal net dispersion regime. The nonlinear optical loop mirror (NOLM) that is used as a mode locker operates through polarization asymmetry, which allows us to control its switching power by birefringence adjustments at the NOLM input, using a half-wave retarder (HWR). Over some range of the HWR orientation, a single noise-like pulse is observed in the cavity. Its peak power is adjustable as it remains clamped to the variable switching power, and its duration varies inversely between ?5 and ?22?ps. Beyond the HWR position, corresponding to the longest duration, the pulse splits into several noise-like pulses. These multiple pulses usually present a walkoff, however they can be synchronized through slight birefringence adjustments, although they are not evenly spaced in time. Up to 12 simultaneous noise-like pulses were observed experimentally, with a duration of ?2?ns. Multiple pulsing and synchronization of the pulses are interpreted in terms of mechanisms of interaction between pulses. Multiple pulsing appears to be indirectly related to the peak power limiting effect of the NOLM.

High-order harmonic noise-like pulsing of a passively mode-locked double-clad Er/Yb fibre ring laser

In this paper, we study noise-like pulse generation in a km-long fibre ring laser including a double-clad erbium?ytterbium fibre and passively mode-locked through nonlinear polarization evolution. Although single noise-like pulsing is only observed at moderate pump power, pulse energies as high as 120?nJ are reached in this regime. For higher pump power, the pulse splits into several noise-like pulses, which then rearrange into a stable and periodic pulse train. Harmonic mode locking from the 2nd to the 48th orders is readily obtained. At pump powers close to the damage threshold of the setup, much denser noise-like pulse trains are demonstrated, reaching harmonic orders beyond 1200 and repetition frequencies in excess of a quarter of a GHz. The mechanisms leading to noise-like pulse breaking and stable high-order harmonic mode locking are discussed.

Raman-induced polarization stabilization of vector solitons in circularly birefringent fibers.

Vector soliton propagation in circularly birefringent fibers was studied by perturbation analysis and numerically. The results show that in presence of both Raman self-frequency shift and group velocity difference between circularly polarized components the Raman cross-polarization term causes an energy transfer from the slower to the faster circular component of vector solitons. This effect leads to polarization stabilization of circularly polarized vector solitons.

Critical pump power and cross-section calculation for Yb3+-doped novel inner-clad structures

Rare-earth doped fiber lasers are now considered suitable sources for the 1.0-, 1.5-, and even 2.0-μm regions in a relatively large number of applications. In particular, Yb3+-doped fiber lasers have received strong interest due to its high quantum efficiency, broad tunability, and available high output power. In this work, we present results on a newly developed code for the simulation of the critical power that is required when designing double-clad high-power Yb3+-doped fiber lasers, which are based on novel inner-clad structures. From our results, we can also estimate σep, σel, σap, and σal for the aforementioned free-running laser cavities. Finally, we will formulate our predictions for feasible fiber laser cross sections.

Characterizing the Statistics of a Bunch of Optical Pulses Using a Nonlinear Optical Loop Mirror

We propose in this work a technique for determining the amplitude distribution of a wave packet containing a large number of short optical pulses with different amplitudes. The technique takes advantage of the fast response of the optical Kerr effect in a fiber nonlinear optical loop mirror (NOLM). Under some assumptions, the statistics of the pulses can be determined from the energy transfer characteristic of the packet through the NOLM, which can be measured with a low-frequency detection setup. The statistical distribution is retrieved numerically by approximating the solution of a system of nonlinear algebraic equations using the least squares method. The technique is demonstrated numerically in the case of a packet of solitons.

Compact wavelength-tunable actively Q-switched fiber laser in CW and pulsed operation based on a fiber Bragg grating

We report a double-clad Er/Yb doped fiber tunable laser in continuous wave (CW) and actively Q-switched modes using a fiber Bragg grating (FBG) as wavelength selective in a linear cavity resonator. The laser was tuned in a range from 1532 to 1542 nm for both CW and pulsed modes. The minimum pulse duration was 420 ns at a repetition rate of 120 kHz and ~0.7 W average output power in CW (slope efficiency of ~8%) and 1.03 W average output power in pulse mode (slope efficiency of ~12%).

73-nm tuning of a double-clad Yb3+-doped fiber laser based on a hybrid array

We report on a wide wavelength tuning in a double-clad ytterbium-doped fiber laser. The laser cavity consists of an array of broadband high-reflection fiber Bragg gratings and a bulk grating as the output coupler and wavelength selection element. The proposed fiber laser configuration combines a low intracavity loss of the fiber Bragg grating mirrors with a wide wavelength tuning of the bulk gratings. We demonstrate a >70-nm wavelength tuning range, limited only by the available fiber Bragg gratings.

Laser line wavelength sensor based in a dual-wavelength fiber laser with a Hi-Bi loop Sagnac interferometer

We present an experimental method for straight forward dual wavelength Erbium doped fiber linear cavity laser characterization based in laser line spectrum behavior due to the Hi-Bi FOLM transmission spectrum wavelength displacement by temperature variations in the fiber loop. The laser operation is for a single and dual mode, obtained through the adjustment of the cavity losses by the Sagnac interferometer spectrum wavelength displacement due to the temperature variation of the fiber loop. The method allow determine the laser operation from a single emission line and a two emission lines simultaneously through the Sagnac transmittance spectrum optical power variations measurement due to wavelength spectrum shifting for each laser wavelength generated separately and overlapping these obtained spectrums.