Abstract-A surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs/GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22-ps fullwidth at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz.

Liquefying gallium shows a huge reversible optical nonlinearity which is compatible with waveguide technology and promises to be a breakthrough in broadband, light by light modulation at milliwatt operating power levels and frequency band spanning up to several hundred kilohertz.

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Using a nonlinear cavity element, a liquefying gallium mirror, we demonstrate stable, self-starting, passive Q-switching of both erbium and ytterbium fiber laser cavities operating at wavelengths of 1550 and 1030 nm, respectively. The performance at 1550 nm is shown to be equivalent to that achieved with a state of the art semiconductor saturable absorber designed to work at this wavelength. The results highlight the suitability of this tremendously broadband, inexpensive nonlinear medium for a wide range of passive Q-switch applications.

The gallium/silica interface optical nonlinearity associated with a light-induced structural phase transition from a-gallium to a more reflective, more metallic phase shows an exceptionally broadband spectral response. It allows 40% deep nanosecond/microsecond cross-wavelength intensity modulation between signals at 1.3 and 1.55aem.