Experimental retroreflectors with very wide field of view

This paper reports the development of novel retroreflectors for use in free-space optical communication systems. It will be important for the retroreflectors to have a very wide field of view to make such systems practicable and affordable. Comer cube retroreflectors present a practical means of meeting the requirement for a wide field of view, but require use of materials with very high refractive index. Practical measurements on initial samples of high index corner cubes have shown encouraging optical performance. The measured results approximately confirm predictions of the variation of reflection efficiency with the angle of incidence. Retroreflectors based on graded-index, spherical (GRIN-sphere) lenses potentially offer an alternative with valuable technical advantages over the use of high-index corner cubes, if such lenses can be fabricated with a suitable combination of optical quality, size and relative aperture. The key property of GRIN-sphere lenses is that they can in principle suppress the most problematic feature of sphere lenses, that is, their strong spherical aberration. Predictions for practical graded-index sphere lens structures show valuable potential for improvement compared to uniform sphere lenses, including diffraction limited optical performance over significant fractions of the lens aperture.