When designing a laser scanning picoprojector, one has to deal with important aspects that do not strictly involve design of hardware and software. We have identified two issues that play a decisive role in the final specifications of a laser scanning picoprojector: the characteristics of the optical displaying system and color management. Regarding the optical system, we have studied the diameter requirements of the laser beam emitted from a picoprojector from the point of view of image quality. Resolution is assessed by calculating the image modulation produced by a projected laser spot over a range of projection distances and image sizes. We also show that a suitable election of the RGB wavelengths increases the lumens-per-watt ratio and thereby improves efficiency of a laser-based picoprojector.
Laser scanning picoprojectors present a new challenge in the field of laser safety with methods of calculating accessible emission limits still in their infancy. We present a laser safety analysis and a calculation of an example picoprojector. We show that, due to its scanning operation, a picoprojector should be considered an extended laser source, and we also show that a picoprojector with two separate one-axis microelectromechanical systems mirrors offers a higher safe power limit than a projector with a single scanning mirror. Finally, a safety analysis is done under conditions of mirror failure. We show that, if the projector fails to scan in just one of the axes, the ocular hazard rises sharply, highlighting the need for a fail-safe system to be built into laser scanning picoprojectors.
In this letter we present a novel study about the combination of four laser wavelengths in order to maximize both color gamut and efficacy to produce the color white. Firstly, an analytic method to calculate efficacy as function of both four laser wavelengths and four laser powers is derived. Secondly we provide a new way to present the results by providing the diagram efficacy vs color gamut area that summarizes the performance of any wavelength combination for projection purposes. The results indicate that the maximal efficacy for the D65 white is only achievable by using a suitable combination of both laser power ratios and wavelengths.
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