Lasers, and specifically solid-state diode lasers are sources of highly monochromatic light with already pre-collimated beams. In this regard, the laser finds application in metrology, imaging illumination as well as high-brightness wide color-gamut image projection. The lasers are coherent light sources, when such a beam is transmitted through or reflected from optical surfaces (for example lenses, prisms, mirrors, and so forth) a laser-speckle pattern is observed.
The laser speckle is a distribution of random high-brightness and low-brightness illumination regions that is the opposite of uniform illumination. In multiple cases, laser speckle is an unwanted phenomenon that degrades illumination quality (by introducing light intensity “noise”) and thus image quality as well, see on the right.
In metrology and imaging, laser speckles can introduce artifacts that interfere with the resolution and/or measurement accuracy, whereas in image projection, if no mitigation measures are taken the perceived image is “grainy” and unpleasant to many viewers. Conventionally, multiple statistically independent speckle patterns can be superimposed either simultaneously or time-sequentially which will leverage integration over time.
Existing methods employ rotating ground glass diffusers in the time-sequential domain. Alternatively, high frequency oscillating reflective diffuser can be used for similar endeavor. However, both of these methods involve utilization of mechanical components, which introduced mechanical complexity, take up space and increase weight. While some existing methods can tolerate this approach, others cannot – specifically micro projection units are ill-suited for bulky mechanical solutions. There exists some methods that employs an oscillating mirror that can be implemented as a mems device which can reach reasonably small footprint. However, the reflective mode of operation might introduce additional optical path length negatively impacting overall footprint. EuroLCDs and Lightspace Technologies can offer patented solution without mechanical components based on liquid crystal technology. Liquid crystal despeckler element or number of elements based on polymer free cholesteric crystal can be installed in optical path to greatly reduce laser speckles.
Single liquid crystal diffuser element is periodically switched between transparent and diffuse state, that removes speckles, see on right.
On top of diffuser attached a basic sheet of paper (acting as a passive diffuser). A green (532 nm) laser pointer beam is expanded using Edmund Optics beam expander to cover a larger circle and illuminate the diffuser element.
In the case driver is put to transparent mode – keeping the diffuser element substantially transparent all the time – scattering occurs only on the “passive diffuser”. In the case driver is put to diffuse mode – keeping the diffuser element substantially diffuse the whole time. Images were taken with a Nikon D800 digital SLR camera with 60 mm MACRO lens. Both cases taken with identical camera settings: Exposure: 1/20 s, Aperture: F/13, ISO-250, Exposure bias: +0.3.
Double elements in counterphase can ensure continuous operation when one element is switched to transparent state. Both elements are bounded with optical clear adhesive in one monobloc. All internal and external anti-reflective coatings can be tuned for maximum transmittance of specific wavelength.
Active area can be from 0.7” to 19”.
For operation high voltage driver is needed.
For more information – please refer to the website:
LCD Product unit and manufacturing plant
Ventspils High Technology Park 2, Ventspils, LV -3602, Latvia
Tel: (+371) 63 600 300
Ziedleju 1, Marupe, LV-2167, Latvia
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