The optical design of a laser scanning picoprojector can be separated into discrete tasks. Typically, diode lasers are employed and their highly divergent emission is firstly collimated. Some beam shaping is required since the asymmetric divergence from diode lasers is converted to an elliptical collimated beam. The red, green and blue beams then need to be combined to produce a single beam which can be controlled to present any colour of the available colour gamut. The final step of the process is to direct the combined beam towards a MEMS scan head comprising a single, bi-axis or two, single axis scanning micro-mirrors.
There is currently an impetus to embed picoprojector opto-electro-mechanics into other devices such as mobile telephones and this restricts the 3D volume available for the collimation, beam combination and MEMS scan head. Even for a standalone picoprojector there is an incentive for a compact design.
So along with conventional optical engineering tasks such as lens design, Gaussian beam propagation, tolerancing, laser safety and design for manufacture, there is an additional task of determining the best optical architecture to achieve the goal.
Here we present a design study of a laser scanning picoprojector where the various optical architecture possibilities are presented. A novel solution is presented which has been built as a prototype projector and which offers excellent future miniaturisation possibilities.