ABSTRACT
The compact and straightforward construction of a pico-projector using an original method for speckle suppression via a simple 1D diffractive optical element (DOE) structure on a loop of flexible film with tracked motion is demonstrated. The 1D-DOE structure is based on binary pseudorandom sequences. The method requires very little energy and space and can decrease speckle noise to levels below the detection sensitivity of the human eye. Large speckle suppression coefficients and low speckle contrasts are obtained for blue, green, and red lasers. Speckle suppression efficiency will be further significantly improved by optimization of the DOE structure and film material.
ABSTRACT
We present the first general theoretical description of speckle suppression efficiency based on an active diffractive optical element (DOE). The approach is based on spectral analysis of diffracted beams and a coherent matrix. Analytical formulae are obtained for the dispersion of speckle suppression efficiency using different DOE structures and different DOE activation methods. We show that a one-sided 2D DOE structure has smaller speckle suppression range than a two-sided 1D DOE structure. Both DOE structures have sufficient speckle suppression range to suppress low-order speckles in the entire visible range, but only the two-sided 1D DOE can suppress higher-order speckles. We also show that a linear shift 2D DOE in a laser projector with a large numerical aperture has higher effective speckle suppression efficiency than the method using switching or step-wise shift DOE structures. The generalized theoretical models elucidate the mechanism and practical realization of speckle suppression.
