Combination of micro-scanning mirrors and multi-mode fibers for speckle reduction in high lumen laser projector applications

Abstract

In high lumen laser projectors, it is required to use laser diodes coupled to multi-mode fibers (MMFs) to obtain a high power illumination module. In this paper, we have fabricated an electromagnetic micro-scanning mirror (EM-MSM), and we have firstly demonstrated a speckle reduction method by the combination of the EM-MSM and the MMF. With the help of a condenser lens, laser beams modulated and reflected from the EM-MSM are coupled into the MMF within its acceptance angle. Because the fast scanning behavior of the EM-MSM results in the phase modulation and mode coupling among the MMF guided modes, the light intensity field distributions at the exit aperture of the MMF are changing. During the charge-coupled device (CCD) integration time, the random speckle patterns are integrated and homogenized by the CCD camera, and hence speckle is reduced. By driving the EM-MSM in raster scan, the lowest compound speckle contrast ratio at 0.0794 is obtained, where the EM-MSM half scanning angles are 0.4 ° and the optical power loss is lower than 4.5%. The demonstrated technique is compact and can endure the high power of the laser module; thus, it has a promising potential in high lumen laser projector applications.

Laser speckle reduction utilized by lens vibration for laser projection applications

“…The plane which contains both the projection lens and the CCD camera is located 1 m from the the screen. The integration time of the CCD camera was set to be 50 msec to mimic the response time of the human eye [20], while the camera lens had a focal length of 50 mm and the F-number was 11 [1]. The resulting output image was an 8-bit grayscale image.…”

“…Compared to the previously mentioned light sources, there are many advantages to using lasers as a light source: they have a smaller divergence angle, a wider color gamut, higher brightness, and a longer lifetime versus traditional sources [1]. Laser projectors have shown to be capable of a wide variety of applications that are seen frequently in day-to-day life, such as: conference rooms [2], home theaters [3], cinemas [4], and pico-projectors [5].…”

“…So, if the power of the laser source is increased this mean that the power density of the laser beam will be increased, this unfortunately can destroy the mirrors. Based on this, the author in [1] designed a large size 2D MEMS mirror with diameter 6.5 mm instead of 2 mm in [18].…”

Spatial coherence research and passive speckle suppression for edge-emitting broad-area semiconductor lasers

“…These methods can be classified as polarization diversity, wavelength diversity and angular diversity. The most prevalent method is creating independent speckle patterns at different times by moving scattering optical elements, such as the diffuser [8,9], diffraction optical elements [10,11], multimode fiber (MMF) [12,13], multimode fiber bundle [14] or projection screen [15,16], or by using active phase modulating components, such as a spatial light modulator [17], deformable mirror [18], electromagnetic micro-scanning mirror [19] or ultrasonic grating [20]. However, these methods require moving devices or expensive modulators, which introduce additional power consumption and make the projection system hard to implement.…”

A Large-Size MEMS Scanning Mirror for Speckle Reduction Application

“…Solid-state lasers can provide wider color gamut, longer lifetime, and higher brightness and contrast of images compared to light emitting diodes (LEDs), a popular light source for projection displays [ 1 ]. Laser display technology plays a significant role in our life, and can be applied in various fields such as movie theatres, home televisions and conference rooms.…”