Impact of aberrations and defocusing of the laser projector on the efficiency of reducing speckle noise

• Дата: 2020
• Автори: Kliuieva, T. Yu., Gorbov, I. V., Prygun, A. V.
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: Інститут проблем реєстрації інформації НАН України 2020
• Теми: лазерний проектор; сканування; спекли; аберації; розфокусування; дифракційні елементи; laser projector; aberrations; defocusing; speckle; noise; speckle suppression; diffractive optical element
• Онлайн доступ: http://drsp.ipri.kiev.ua/article/view/211251
• Назва журналу: Data Recording, Storage & Processing

The impact of aberrations and the effect of defocusing on the efficiency of reduction of speckle noise in the system of a laser projector containing a moving diffractive optical element (DOE) is investigated. The effects of aberration and defocusing in the mechanisms of reducing speckle noise in laser projection displays were studied using the Fresnel approximation and the model of thin lenses. The results of the analysis based on the number of diffraction orders that have passed through the optical system are presented. The analysis showed that aberrations should not affect the contrast of the speckles, and the displacement of the screen relative to the image plane (defocus) only leads to re-scaling of the autocorrelation function of the scanning beam, which is equivalent to refocusing the lens to a new screen position. The use of the speckle-noise reduction method when scanning a laser display using Barker code should not require an increase in the resolution of the projection system screen compared to normal values. The resolution is determined exclusively by the requirements to image quality. It is shown that small aberrations change only the phase of the wave-front of the diffraction orders and therefore do not change the number of diffraction orders that illuminate a given area of the screen, and therefore do not change the contrast of the speckles. But larger aberrations cause a reversal of the direction of propagation of the rays that have passed through the lens. The contrast of speckles in the paraxial region of the screen is almost insensitive to aberration, but the contrast of speckles in peripheral areas changes abruptly if the aberrations change the number of diffraction orders that illuminate the area. In the optical circuit with DOE located in front of the optical modulator, the contrast of the speckles is not sensitive to the distance between the optical modulator and DOE, if the optical modulator is illuminated by all diffraction orders. Fig.: 4. Refs: 10 titles.