The term "optical grating" is synonym with diffraction grating or multiple slit. Optical gratings are periodical structures for diffraction of light. Such structures are originated e.g. by means of laser-interference-lithography. Two dimensional modulated grating structures can be realized by multiple exposure between which the sample will be revolved. By tilting the substrate prismatic respectively sawtooth-like structural forms can be achieved. Diffraction gratings can be used for energy efficiency improvements of thin-film PV-cells and organic PV-cells by lengthening the light paths within the PV-layer. Also polarizer films (nanowire grid polarizers) and transparent electrodes (metal mesh surfaces) can be realised with nano linear-structures.