Speckle contrast for superposed speckle patterns created by rotating the orientation of laser polarization

Abstract

For a rough diffuser that fully depolarizes a linearly polarized laser, the speckle contrast of a fully developed speckle image can be reduced from 1 to 0.5 by polarization diversity. This reduction is achieved by rotating an x-polarized laser to the y-polarized orientation to form four independent speckle patterns with equal intensities during the detector exposure time. For the case of arbitrary rotation of the polarization, we derived a generalized speckle contrast formula for the superposed speckle patterns. This formula completes the theory of speckle contrast for the sum of correlated speckle intensities as it relates to polarization diversity.

Compound Speckle Reduction in Laser Imaging Systems by Using a Vibrating Multimode Fiber and a Tracked Moving Flexible DOE Loop

“…For wavelength diversity, the use of laser diode arrays or a broadband laser is usually required to reduce speckles [6]- [8]; this increases the cost and complexity of light sources. The use of polarization diversity to reduce speckles is generally limited because lasers have only two polarization states [9]. Angular diversity is one of the most effective techniques, and speckle reduction can be achieved by a diffractive optical element (DOE), diffuser, multimode fiber, light pipe, etc.…”

Spatial statistics of superposition of two uncorrelated speckle patterns with polarization diversity

“…It has been reported that the superposition of independent speckle patterns reduces the contrast of the superposed speckle pattern [16]. Manipulation of the contrast can also be achieved, if polarization diversity is introduced to the case of superposition of correlated speckle patterns [17]. Superposition of uncorrelated speckle patterns has been reported to be useful for polarization sensing through a scattering medium [18].…”

Speckle reduction using phase plate array and lens array

“…Speckle is a drawback of laser display for it can downgrade the image quality greatly. To solve this problem, numerous methods have been proposed, such as: using a deformable mirror 3 or a scanning mirror 4,5 to realize angle diversity; using a broad-area vertical-cavity surface-emitting laser 6 or random lasers 7 to realize wavelength diversity; using a staircase element 8 or a refractive steppers 9 to realize optical path difference; rotating independent speckle patterns 10 or a magneto-optical disk 11 to realize polarization diversity; using a light pipe 12 or a multimode optical fiber bundle 13 to realize time averaging and so on. J. I. Trisnadi firstly proposed the speckle reduction method using Hadamard phase diffuser 14,15 .…”