No abstract

No abstract

Round-trip nonlinear phase-shift of an input signal due to optically induced thermal effects and saturable index change in a low intensity resonant reflective vertical cavity semiconductor (quantum wells) saturable absorber (VCSSA) is investigated theoretically for 2R (reamplification and re-shaping) regeneration. Calculations are carried out for a high contrast switching system to find the optimum value of parameters such as energy time filling factor (FF) of the input pump signal, top mirror reflectivity (R t ) of the Fabry-Pérot cavity and wavelength detuning from the low intensity resonant wavelength of the Fabry-Pérot cavity. It is observed that the optimum contrasts are almost the same for a wavelength tuning range as large as 8 nm around the low intensity resonance wavelength of the InGaAs/InP quantum-wells-based VCSSA with R t of 0.72 and FF of 0.10. The simulation shows that the required average input power is minimal for high contrast 2R regeneration when operated in the short wavelength side.

An all-solid-state, gain-switched, green laser is developed using a side diode-array pumped Nd:YAG laser and a KTiOPO(4) (KTP) crystal as an intracavity frequency doubler. The effect of nonlinear coupling on the pulse width of the fundamental is studied and is found to be in good agreement with the experimental measurement. In this preliminary experiment, a peak power of 40 W at 532 nm corresponding to a pulse width of 409 ns is obtained for an average pump power of 2 W. Compared to a Q-switched laser, it is simple and does not require a high voltage RF driver or saturable absorbers in its operation. The laser may be useful where relatively longer nanosecond pulses are required such as eye surgery, micromachining, and underwater communication.

The phase response of a commercial saturable absorber based on semiconductor quantum wells embedded in a resonant cavity is investigated. The nonlinear absorption change is accompanied by a variation of the spectral phase characteristic. Also, a nonlinear change in the refractive index of the material, induced by the modified carrier density, produces a weak shift in the resonant wavelength of the cavity. These effects can be exploited to realize an optically-controllable phase shifter. Simulations based on a nonlinear model are also carried out in order to investigate the effect of the various cavity parameters and phase response of the device under different operating conditions. The results from this characterization and numerical analysis show that such device can have the potential for practical applications in telecom systems, including dynamic dispersion compensation, tunable nonlinear effects compensation, and nonlinear signal processing and all-optical regeneration of phase-modulated optical signals.