The theory of reducing speckles in a laser projector with a very long multimode fiber

• Datum: 2020
• Hauptverfasser: Лапчук, А. С., Горбов, І. В., Пригун, О. В., Морозов, Є. М., Клюєва, Т. Ю., Бородін, Ю. О.
• Format: Artikel
• Sprache: Ukrainian
• Veröffentlicht: Інститут проблем реєстрації інформації НАН України 2020
• Schlagworte: laser projector; speckles; noise; laser speckles; speckle suppression; multimode optical fiber; optical waveguide
• Online Zugang: http://drsp.ipri.kiev.ua/article/view/225901
• Назва журналу: Data Recording, Storage & Processing

A mathematical model of the mechanism of speckles reduction by a passive long multimode optical fiber is developed. It is assumed that there is no modes transformation in the fiber, and that its length is long enough to decorrelate the parts of the beam with a difference in propagation angles relative to the axis, much less than the angular resolution of the eye. The model utilizes the fact that multimode optical fiber decorrelates laser radiation only in the radial direction of propagation perpendicular to the axis of the optical fiber and does not decorrelate the light propagating in different azimuthal directions. That is, the decorrelation is one-dimensional with circular symmetry. It is shown that due to the 1D-dimension nature of the method, the speckles reduction coefficient increases slowly, only as the square root of the ratio of the numerical apertures of the projector lens and the eye. Therefore, it is impossible by the method to reduce the speckle level below the contrast sensitivity of the human eye. To increase the efficiency of speckle reduction, a method modification is required, which should allow to use the azimuthal direction of sub-beam that create image. Fig.: 7. Refs: 17 titles.