Abstract: The present invention concerns a method for constructing a light coupling system wherein a grating is manufactured on the surface of a multimode waveguide and defines the entrance of the waveguide for an incident light beam, said grating comprising a repetition of patterns. The grating is defined by a set of parameters comprising: •grating period (P), separating two adjacent patterns, •grating depth (d) between the highest and the lowest point of the pattern, •incident angle mean value (?) of the incident light with respect to the waveguide. The method comprises a step of optimization of the set of parameters to obtain an optimized second set of parameters, in order to obtain a transmission efficiency (Ce) of the incident light into said waveguide for the first or the second diffractive order exceeding 35% for unpolarized light, or exceeding 50% for polarized light, at a given wavelength of the incident light.

Abstract: The present invention concerns a method for constructing a light coupling system wherein a grating is manufactured on the surface of a multimode waveguide and defines the entrance of the waveguide for an incident light beam, said grating comprising a repetition of patterns. The grating is defined by a set of parameters comprising: •grating period (P), separating two adjacent patterns, •grating depth (d) between the highest and the lowest point of the pattern, •incident angle mean value (?) of the incident light with respect to the waveguide. The method comprises a step of optimization of the set of parameters to obtain an optimized second set of parameters, in order to obtain a transmission efficiency (Ce) of the incident light into said waveguide for the first or the second diffractive order exceeding 35% for unpolarized light, or exceeding 50% for polarized light, at a given wavelength of the incident light.

Abstract: An optical system (100) comprises a coherent light source (101) and optical elements for directing light from the source to a target (1001). The optical elements include at least one diffusing element (141, 161) arranged to reduce a coherence volume of light from the source and a variable optical property element (151). A control system (1021) controls the variable optical property element such that different speckle patterns are formed over time at the target (1001) with a temporal frequency greater than a temporal resolution of an illumination sensor or an eye (1011) of an observer so that speckle contrast ratio in the observed illumination is reduced. The variable optical property element (151) may be a deformable mirror with a vibrating thin plate or film.

Abstract: An apparatus and method for reducing the visibility of speckle in coherent light comprises propagating the coherent light through a multimode optical waveguide 106 to reduce a coherence length of the coherent light by intermodal dispersion. A vibratable membrane mirror 104 is arranged to reflect the coherent light either before or after passing through the multimode optical fiber further to reduce the coherence length by distributing wave packets across different propagating modes and to erase the modal structure by averaging the distribution of energy across the modes leading to a more uniform illumination. The invention may be used for speckle removal in a laser scanning projector.

Abstract: An apparatus and method for reducing the visibility of speckle in coherent light comprises propagating the coherent light through a multimode optical waveguide 106 to reduce a coherence length of the coherent light by intermodal dispersion. A vibratable membrane mirror 104 is arranged to reflect the coherent light either before or after passing through the multimode optical fibre further to reduce the coherence length by distributing wave packets across different propagating modes and to erase the modal structure by averaging the distribution of energy across the modes leading to a more uniform illumination. The invention may be used for speckle removal in a laser scanning projector.

Abstract: An optical system (100) comprises a coherent light source (101) and optical elements for directing light from the source to a target (1001). The optical elements include at least one diffusing element (141, 161) arranged to reduce a coherence volume of light from the source and a variable optical property element (151). A control system (1021) controls the variable optical property element such that different speckle patterns are formed over time at the target (1001) with a temporal frequency greater than a temporal resolution of an illumination sensor or an eye (1011) of an observer so that speckle contrast ratio in the observed illumination is reduced. The variable optical property element (151) may be a deformable mirror with a vibrating thin plate or film.