Speckle noise reduction in the laser mini-projector by vibrating diffuser

Pan, Jui-Wen; Shih, Chi Hao

doi:10.1088/2040-8986/aa608d

Cited by 13 publications

(9 citation statements)

References 10 publications

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“…It is well known that the measurement conditions have a significant impact on measuring the SCR, thus the measurement conditions used correspond to the human eye perception. In order to ensure an accurate SCR value, the parameters used in this work agree with the previously reported work in [15,17,19,22,26] to measure the SCR in a handheld laser projector such as pico-projector. The pixel size of the CCD camera is 5.2 um×5.2 um with a resolution of 1280×1024 pixels.…”

Section: Speckle Reduction Characterizationsupporting

confidence: 56%

“…It can, therefore, be shown that a minimum SCR ranging from 0.035 to 0.04 can be achieved by employing two green lasers and two-dimensional vibration of lenses. The SCR can be further reduced to be under 4% by using optical diffusers or even a combination of them [17], but this will be on the expense of the optical efficiency of the illumination system [19]. For example, in [22], the minimum SCR achieved was from 2.81% to 4.60% with optical efficiency from 34 to 43% by using pairs of high divergence angle diffusers under vibration'.…”

Section: Optimization Of Operating Frequenciesmentioning

confidence: 99%

“…Due to the benefits associated with laser projection, multiple techniques have been implemented to take advantage of these speckle reduction methods. They include but are not limited to, the use of micro-electro-mechanical systems (MEMS) scanning mirrors [15,16], deformable mirrors [17], diffractive optical elements [18], and vibrating diffusers [19]. Although these techniques effectively suppress speckle noise, they can be unattractive to manufacturers due to a high cost and/or degree of complexity, as well as reduced optical and electrical efficiency [18].…”

Section: Introductionmentioning

confidence: 99%

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Speckle reduction by employing two green lasers and two-dimensional vibration of lenses

Mohamed

Kashak

et al. 2019

Eng. Res. Express

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A method of speckle reduction suitable for use in a laser projector was proposed in the paper. Speckle contrast ratio (SCR) reduction was achieved by combining wavelength diversity and angular diversity methods. First, wavelength diversity was demonstrated by the use of two green laser sources (a 520 nm laser diode (LD) and a 532 nm diode-pumped solid-state (DPSS) laser) at a power ratio of 4:1. Second, angular diversity was achieved via the vibration of two lenses in two orthogonal directions placed directly after the laser source. The vibrating lenses are small and do not require changes to the beam path of the laser source, allowing for more compact projector designs. The frequency of vibration of these lenses was optimized to minimize the SCR in the output image. A SCR of less than 4% was achieved without the use of optical diffusers, which significantly reduces optical losses. Optical transmission could be further increased with the optimization of optical coatings on the lenses. This result shows great promise for applications such as laser pico-projectors within the realm of heads-up displays (HUDs) and mobile devices.

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Section: Speckle Reduction Characterizationsupporting

confidence: 56%

Section: Optimization Of Operating Frequenciesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Speckle reduction by employing two green lasers and two-dimensional vibration of lenses

Mohamed

Kashak

et al. 2019

Eng. Res. Express

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“…The second diffuser is removed from the Pico LASER projector design used in the speckle testing experiments to make it more compact in size. Two diffusers are used in Type 3 for comparison with previous studies [7,20]. The divergence angles of the circular distribution diffusers are 5 degrees (5X5), 10 degrees (10X10) and 30 degrees (30X30) and the divergence angles of the elliptical distribution diffusers are 5 degrees and 30 degrees (5X30), 10 degrees and 50 degrees (10X50), and 20 degrees and 80 degrees (20X80), described as the angle of the full width at half maximum (FWHM) of the bidirectional transmittance distribution function (BTDF) in the X and Y directions.…”

Section: Speckle Reduction By a Deformable Mirror With Different Diffmentioning

confidence: 99%

Speckle reduction using deformable mirrors with diffusers in a laser pico-projector

2017

Self Cite

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We propose a design for speckle reduction in a laser pico-projector adopting diffusers and deformable mirrors. This research focuses on speckle noise suppression by changing the angle of divergence of the diffuser. Moreover, the speckle contrast value can be further reduced by the addition of a deformable mirror. The speckle reduction ability obtained using diffusers with different divergence angles is compared. Three types of diffuser designs are compared in the experiments. For Type 1 which uses a circular symmetric diffuser the speckle contrast value can be decreased to 0.0264. For Type 2, the speckle contrast value can be reduced to 0.0267 because of the inclusion of an elliptical distribution diffuser. With Type 3 which includes a combination of the circular distribution diffuser and elliptical distribution diffuser, the speckle contrast value can be reduced to 0.0236. For all three types, the speckle contrast value is lower than 0.05. Under this speckle value, the speckle phenomenon is invisible to the human eye.

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“…The coherence can be reduced by using moving, rotating or vibrating optical elements (e.g. diffusers [5][6][7], diffractive optical elements [8], micromirrors [9], multimode fibers or fiber bundles [10]), screen vibration [11], use of broadband lasers [12], multiwavelength illumination (e.g. mode hop of laser diode) [13], etc.…”

Section: Introductionmentioning

confidence: 99%

Homogenization with coherent light illuminated beam shaping diffusers for vision applications: spatial resolution limited by speckle pattern

Kondász

Hopp

Smausz

2018

J. Eur. Opt. Soc.-Rapid Publ.

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Background: Homogenizing properties of beam shaping diffusers illuminated with coherent laser light was studied with special regard on their use in vision applications. Experimental: Two diffusers projecting circular pattern at different scattering angles (Thorlabs Engineered Diffuser™) were illuminated with different spatial intensity distribution (elliptical Gaussian, nearly flat-top and granular multimode fiber output, respectively) collimated beams. Results: The intensity distribution measured at high angular resolution with a CMOS sensor revealed the granular (speckle) pattern of the projected light having contrast of nearly 1. The smallest speckle size (highest speckle density) could be obtained at the largest aperture size using nearly flat-top and multimode fiber illumination. Conclusion: As an important measure of the homogeneity for vision applications the apparent local contrast was calculated as the function of the spatial averaging. Although, the homogeneity requirements depend on the actual application, the usability of such diffusers in combination with coherent light sources is in general strongly limited in megapixel resolution imaging applications, unless time-varying speckle averaging methods can be applied.

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Speckle noise reduction in the laser mini-projector by vibrating diffuser

Cited by 13 publications

References 10 publications

Speckle reduction by employing two green lasers and two-dimensional vibration of lenses

Speckle reduction by employing two green lasers and two-dimensional vibration of lenses

Speckle reduction using deformable mirrors with diffusers in a laser pico-projector

Homogenization with coherent light illuminated beam shaping diffusers for vision applications: spatial resolution limited by speckle pattern

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