We theoretically suggest and experimentally demonstrate a broadband composite optical rotator that is capable of rotating the polarization plane of a linearly-polarized light at any chosen angle. The device is composed of an even number of half-wave plates rotated at specific angles with respect to their fast-polarization axes. The frequency bandwidth of the polarization rotator in principal increases with the number of half-wave plates. Here we experimentally examine the performance of rotators composed of two, four, six, eight and ten half-wave plates.

We propose a novel optical parametric amplification scheme which combines quasi-phase-matching with a composite pulse approach that involves crystal segments of specific lengths. The presented scheme highly increases the robustness of the frequency conversion against variations of the nonlinear coupling and of the pump, idler or signal wavelengths and has therefore the potential to enhance high amplification and broadband operation. Simulations examples applied to LiNbO3 are given. PACS numbers:

A simple scheme for a broadband polarization rotator with tunable rotation angle is proposed and verified experimentally. The rotator consists of only three wave-plates, one of which is a full-wave plate. The robust approach inspired by the composite pulses analogy allows to compensate the wave-plate dispersion in large extent.

It is shown that cascaded nonlinear optical frequency conversion over an intermediate wavelength subjected to dissipation behaves similarly to population transfer via a decaying state in a three-state non-Hermitian quantum system. The intermediate dissipation leads to a fixed phase relationship between the input signal wave and the wave at the target frequency, what finally stabilizes both waves preventing any spatial oscillation of their powers. The cascaded conversion acts as a stable wave splitter between the input and target waves, the latter being nearly immune to power fluctuations of the pumps. A case of a simultaneous cascade of the sum frequency generation (SFG) and the difference frequency generation (DFG) processes is discussed as an example and a possible implementation based on aperiodically engineered quasi-phase-matching in lithium niobate is proposed.

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