Investigation of speckle suppression beyond human eye sensitivity by using a passive multimode fiber and a multimode fiber bundle

Abstract

A method of speckle suppression without any active device is expected for pico-projectors. The effectiveness of the passive method of speckle reduction using a single multimode fiber and a multimode fiber bundle was actually measured and theoretically analyzed. The dependences of the speckle contrast and speckle suppression coefficient on the parameters of multimode fiber and projection systems were investigated. Our results shown that the efficiency of speckle suppression was limited because only the radial direction of the objective lens aperture was used. An improvement using both of the radial and azimuthal directions of the objective lens aperture is required.

Теорія Зменшення Спеклів У Лазерному Проекторі Дуже Довгим Багатомодовим Волокном

“…Передбачалося, що метод може бути використаний в лазерному проекторі для зменшення контрасту спеклів на екрані нижче контрастної чутливості людського ока [13]. Однак нами було показано [14,15], що лазерний пучок світла, який вийшов з дальнього кінця хвилевода має в перетині області когерентності у вигляді вузьких кілець у просторі кутів поширення (в просторовій площині Фур'є лазерного пучка). І тому цей метод є 1D-метод, що робить для нього неможливим досягнення зменшення спеклів нижче контрастної чутливістю людського ока.…”

Spatial coherence research and passive speckle suppression for edge-emitting broad-area semiconductor lasers

“…In recent years, passive speckle suppression methods have attracted much attention. These methods do not need moving elements or much time to suppress speckle [21][22][23][24][25][26][27][28], so they are suitable for high-speed imaging and easy to implement. These methods are based on phase delay [21][22][23][24][25][26] or orthometric phase modulation [27,28] to weaken the spatial coherence of the laser.…”

“…These methods do not need moving elements or much time to suppress speckle [21][22][23][24][25][26][27][28], so they are suitable for high-speed imaging and easy to implement. These methods are based on phase delay [21][22][23][24][25][26] or orthometric phase modulation [27,28] to weaken the spatial coherence of the laser. Mode dispersion in MMF is often used to produce partially coherent beams [22][23][24], but more than 10 m of MMF (0.22 NA) is needed to suppress the speckle contrast below 10% for a 0.5 nm 1 e −1 bandwidth laser [22].…”

“…These methods are based on phase delay [21][22][23][24][25][26] or orthometric phase modulation [27,28] to weaken the spatial coherence of the laser. Mode dispersion in MMF is often used to produce partially coherent beams [22][23][24], but more than 10 m of MMF (0.22 NA) is needed to suppress the speckle contrast below 10% for a 0.5 nm 1 e −1 bandwidth laser [22]. In a practical laser projection system, the MMF needs to be coiled at a radius of more than 20 cm to reduce the bending loss [29].…”

Coherent Matrix-Based Approach for Evaluation of First-Order Speckle Intensity Statistics and Its Application for Speckle Suppression

“…In laser imaging systems, a diffractive optical element [11]- [16], a long multimode fiber/fiber bundle [17], [18], or an optical retardation element [19] is usually used to obtain many subbeams and suppress speckle noise. For example, a moving DOE [11] or the switching of DOE structures [12] can be used to generate decorrelated diffraction sub-beams.…”