At the SID Mobile Display conference in San Diego this week, we caught up with JongHyeong Song, principle engineer at the Samsung SOM business group. Over dinner he shared with us the latest iteration of their spatial optical modulator based pico-projector shown at the conference this week. He actually had two versions of the laser-illuminated device, one operating at 7.5 lumens, and 5% speckle, the other at 10 lumens and 10% speckle. Part of his motive in showing the units was to show-off new speckle suppression technology developed by the group, and to determine just how much speckle is acceptable in a hand held display.

Steve Sechrist
Senior Analyst and Editor

Song fired up the battery powered units right there in the restaurant and we moved to the wall to take a look at the images, and more importantly, how the two differed. One interesting point, even if you’ve never seen speckle from a laser illuminated display before when looking at the two images side-by-side, you don’t have to have it explained to you–the artifact became self evident in this kind of "good" vs. "better" comparison.

Microvision, another vendor using lasers for illumination, defines speckle as, "An effect of laser light hitting a surface, where the reflection back to an observer appears as incoherent light that sparkles." (See Mobile Display Report August-08 p.6.) It also seems to be much more evident on darker display surfaces.

Speckle on Samsung’s 10% model was noticeable (much more than the other display) and it was hard to imagine that just 5% speckle separated the two. Exactly how Samsung measures speckle was not explained, however. The off-white wall may have played a factor in the display quality, plus the light from the setting sun that came into the restaurant (see photo).

Microvision was also at the SID event with their "PicoP" pico projector that looked a bit smaller than the Samsung prototype models. The next day Song brought his device over to the Microvision booth to compare images. This was a simple ad hoc viewing, and it was hard to get a clear comparison of the two, since even the screen surfaces were different. Brightness of the two did appear about the same, however.

Both Samsung displays were VGA compared to the Microvision WVGA scanner, but Song assured us that they could easily scale up to HD resolution if required. The SOM technology uses a MEMS-based linear modulator coupled to a mechanical scan mirror to sweep a line of light, creating an image. It is the same concept employed in Sony and Evans & Sutherlands GxL laser display system and Kodak’s GEMS system, but with some differences (to be covered in our subscription newsletters). As a result, the SOM technology can support VGA and WVGA at the same time, with no change to the chip. "We simply change the scan rotation angle," explained Song.

Unlike Samsung, who went on record as putting a lot of effort in decreasing speckle, the Microvision approach is to let the customer decide if the trade-off of speckle for a large (really) mobile display from an embedded pico projector is acceptable. They may be right, and the Microvision and Samsung units could be "good enough" to sell in the market as is–but there are other issues like power, and cost that still need to be addressed. (Song told us their latest unit reached power levels of 1.7W to as low as 1.5W with a target of sub-1W by 2010 launch time.)

But while looking over the display images at the restaurant during that lovely San Diego sunset, inside guests at the only other table were not enjoying the view but rather noticeably distracted by two display "gear heads" projecting images on the wall from a pair of hand held devices. What an interesting time to be alive…