We report the first observation of optical bistability in a rare-earth doped single-mode fibre laser. Hysteresis has been obtained in the lasing characteristic of an Er3+-doped fibre laser operating at 1.54µm using the mechanism of saturable absorption
Resonance properties of the all-fiber ring cavity filled with nonlinear material - saturable rare-earth-doped fiber are analyzed and experimentally investigated. Unlike the earlier investigated erbium-doped fiber at 1550nm where the optical absorption photo-induced change (saturation) is observed only, the ytterbium-doped fiber at 1064nm demonstrates the saturation of the refractive index mainly. For this configuration we report experimental observation of the optical bistability and hysteresis in the transmitted output light at the 10mW-scale incident light power. The experimental results are in qualitative agreement with the theoretical analysis that takes into account the saturation of both parameters: the optical absorption and the refractive index of the doped fiber. The reported results seem promising for applications in high-sensitivity interferometric configurations at 1064nm operation wavelength.
Optical bistability derived from the negative nonlinear absorption effect was investigated in 470 ppm erbium-doped fibers using a 1.5 µm laser diode. Optical bistability was observed in a laser intensity range of 0.3 W/cm2 to 2.5 kW/cm2 at a fiber length of 6 m. The transmitted laser intensity (I out), propagating through the fiber, decreased exponentially in accordance with the well-known exponential law. However, the amplitude of the optical bistability (ΔI out) increased logarithmically as the fiber length was increased. It was clarified that ΔI out was proportional to the product of exp (-L) and log (L) as a function of the fiber length (L). The optical bistability can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.
The authors investigate the optical bistability in an L-band dual-wavelength erbium-doped fiber (EDF) laser with overlapping cavities. The bistable input-output hysteresis behavior of the two lasing wavelengths evolves in antiphase. The bistable region is tens of milliwatts wide. The bistability is essentially due to the homogeneous saturable absorption of EDF. The cross-gain saturation causes the bistabilities of the two lasing lines to evolve in antiphase with respect to each other. The gain clamping effect helps to widen the bistable region, which may be controlled by the cavity loss and by the EDF length.
The dependence of the negative nonlinear absorption effect at 1.5μm on the sample temperature, the modulation frequency and the sample length were investigated in glasses containing amounts higher than 20mol% Er3+. Reversed-phase waveforms were observed in the temperature range -260-600°C and at modulation frequencies from 1kHz to 10GHz in an erbium-doped phosphate glass. With increasing temperature, the amplitude of the reversed-phase waveforms decreases exponentially according to two separate steps. Optical bistability in the transmitted laser was observed in the range of incident laser intensity of 30μW/cm2-2.4mW/cm2. The transmitted laser intensity propagating through the glass decreased exponentially according to the well-known exponential law. However, the amplitude of the optical bistability increased logarithmically as the sample length was increased. The negative nonlinear absorption effect can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.
We report on the experimental demonstration of stable all-optical switching between two steady state values of optical bistability from a laser diode end-pumped quasi-three-level Tm,Ho:LLF laser in the 2 μm spectral region. The width of the hysteresis cycle and jump power values can be efficiently controlled by changing the length of the cavity, which is very important to adjust and optimize the optical switching process. The all-optical bistable switching effect is realized by only adding short positive and negative trigger pulses to the pump light. This is, to our knowledge, the first observation of all-optical bistable switching in a rare earth doped solid state laser.