Speckle in laser imagery: efficient methods of quantification and minimization

Martinsen, R.; Kennedy, Keegan; Radl, Andrew J.

doi:10.1109/leos.1999.813629

Cited by 6 publications

(3 citation statements)

References 4 publications

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“…Pictures were taken for each laser source separately from a uniformly illuminated screen. After applying a low-pass filter to the pictures, speckle contrasts were calculated [16] .…”

Section: Resultsmentioning

confidence: 99%

Future prospects of high-end laser projectors

Janssens

Malfait

2009

SPIE Proceedings

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During the last years, a trend to replace commonly used short arc lamps in projection systems with alternative light sources is seen. Next to LEDs for low light output products, lasers try to enter the projection area and have the ambition to infiltrate from low (picoprojection) towards high light output systems (digital cinema).One of the benefits of lasers is their narrow spectral bandwidth. As a consequence, the display can have a very large colour gamut, if the lasers are carefully selected. Another benefit is the very low intrinsic étendue of the source. One can imagine using less complex, more efficient, smaller but more powerful optical systems. This not only for scanning projectors, but also for 2D light valve based projectors (LCOS, LCD, DLP). In addition, the limited lifetime of lamps has serious impact on a system's cost of ownership, and puts light source reliability/lifetime high on the list of priorities for future developments. For this reason, Barco entered the European FP6-project OSIRIS, in a subtask where a 300 lm laser projector demonstrator has to be developed and evaluated.So far, we found out that next to obvious challenges such as laser cost and laser power, the most critical issue regarding image quality is speckle interference which counteracts the beneficial nature of the light source. This phenomenon is a direct consequence of the coherent nature of a laser and cannot be solved as easily as is often claimed. We will describe laser speckle in the context of laser projection and the theoretical limits of several reduction techniques. This leads to guidelines which can make laser projection worth considering.

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“…Pictures were taken for each laser source separately from a uniformly illuminated screen. After applying a low-pass filter to the pictures, speckle contrasts were calculated [16] .…”

Section: Resultsmentioning

confidence: 99%

Future prospects of high-end laser projectors

Janssens

Malfait

2009

SPIE Proceedings

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“…Additionally, wavelength diversity and-or vibration of large core multi-mode optical fiber used to couple the laser sources can also be utilized. 2,3,4…”

Section: Speckle Mitigation In Traditional Projection Display Archite...mentioning

confidence: 99%

Speckle mitigation techniques for laser point scanned displays in head-up display applications

McDonald

Mermillod²

2023

Advances in Display Technologies XIII

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Laser source displays offer wide color gamut and deep color saturation. However, they also suffer from speckle due to their coherent wave-front interaction with surface roughness or imperfections from any component in the optical chain of the display. Speckle can be offensive to the viewer as it gives the displayed image a noticeable "shimmer" or grainy appearance. For an expanded beam, flood illumination display such as those using a Spatial Light modulator (SLM), there exist methods to minimize this speckle to where it is not noticeable to the viewer. However, a laser scanned display is a different situation as the image is generated by a single flying spot and speckle strategy relying on mitigation of flood illumination imaging cannot be efficiently used. Static components such as close packed microlens arrays used in the diffuser optical plane in a typical Head Up Display (HUD) layout are a good compromise and do a reasonable job mitigating speckle. However, the microlens size must be closely matched to the laser beam spot size to minimize other artifacts such as Moiré pattern in the image. Despite being a good countermeasure against speckle, in high magnification HUD systems, the microlens array structure can be viewed in the image and can sometimes be perceived as "pixelization". We propose utilizing discrete step index motion of a close packed microlens array to both double the perceived image resolution and mitigate speckle.

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“…Image scanning can potentially lead to high image resolution. However, the high spatial and temporal coherence of laser light creates speckle patterns that can in some cases severely degrade the image quality, thus requiring the use of speckle reduction techniques [22]- [24].…”

Section: A Increasing the Source Luminancementioning

confidence: 99%

Design Methodology for High Brightness Projectors

Fournier

Rolland

2008

J. Display Technol.

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The low luminance levels of light-emitting diodes (LEDs) compared to arc lamps make it difficult to design high-brightness LED-based projectors. Besides, the specificities of LEDs do not always allow using the same design schemes as with arc lamp-based projection displays. This paper performs a taxonomy of the techniques that can be used to increase the brightness of LED-based projection displays. We show that, in étendue-limited systems, the perceived brightness depends on the system étendue limit, the efficiency of the light engine, and the source luminance. The ability to improve each of these parameters depends on the design constraints. The system étendue limit can be increased at the expense of bulkier, more complex, and more expensive designs. The light engine efficiency can be increased by using free-form shape components adapted to the shapes and the emission patterns of the considered LEDs. The apparent source luminance can be increased at the expense of the flux by either recycling light or restricting the light collection to a smaller étendue with higher average luminance. Luminance can also be increased by using multiple color primaries (spatial multiplexing) or pulsed LEDs (temporal multiplexing). Finally, we review how light recycling can be implemented to convert polarization without increasing étendue.

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Speckle in laser imagery: efficient methods of quantification and minimization

Cited by 6 publications

References 4 publications

Future prospects of high-end laser projectors

Future prospects of high-end laser projectors

Speckle mitigation techniques for laser point scanned displays in head-up display applications

Design Methodology for High Brightness Projectors

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