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At Lenovo at their Tech World on May 27th 2015 showed a Laser Beam Scanning (LBS) projector integrated into a cell phone prototype (to be clear, a prototype and not a product). White there has been no announcement of the maker of the LBS projector, there is no doubt that is made by STM as I will show below (to give credit where it is due, this was first shown on a blog by Paul Anderson focused on Microvision )
The comparison at left is base on video by Lenovo that included an exploded views of the projector and pictures of STM’s 720p projector from an article from Picoprojector-info.com on Jan 18, 2013. I have drawn lines comparing various elements such as the size and placement of connectors and other components, the size and placement of the 3 major I.C.’s, and even the silk screen “STM” in the same place on both the Lenovo video and the STM article’s photo (circled in yellow).
While there are some minor differences, there are so many direct matches that there can be no doubt that Lenovo is using STM.
The next interesting to consider is how this design compares to the LBS design of Microvision and Sony in the Celluon projector. The Lenovo video shows the projector as being about 34mm by 26mm by 5mm thick. To check this I took the a photo from the Picoprojector.com
article and was able to fit the light engine and electronic into a 34mm by 26mm rectangle arranged as they are in the Lenovo video (yet one more verification that it is STM). I then took a picture I took of the Celluon board to the same scale and show the same 34x26mm rectangle on it. The STM optics plus electronics are 1/4 the area and 1/5th the volume (STM is 5mm thick versus Microvision/Sony’s 7mm).
The Microvision/Sony is has probably about double the lumens/brightness of the STM module due to have two green and two red lasers and I have not had a chance to compare the image quality. Taking out the extra two lasers would make the Microvision/Sony engine optics/heat-sinking smaller by about 25% and have a smaller impact on the board space, but this would still leave them over 3X bigger than STM. The obvious next question is why.
One reason is that the STM either has a simpler electronics design or is more integrated and/or some combination thereof. In particular the Microvision/Sony design requires an external DRAM (large rectangular chip in the Microvision/Sony). STM probably still needs DRAM, but it is likely integrated into one of their chips.
There are not a lot of details on the STM optics (developed by bTendo of Israel before being acquired by STM). But what we do know is STM uses separate simpler and smaller horizontal and vertical mirrors versus Microvision significantly larger and more complex single mirror assembly. Comparing the photos above, the Microvision mirror assembly alone is almost as big as STM’s entire optical engine with lasers. The Microvision mirror assembly has a lot of parts other than the MEMs mirror including some very strong magnets. Generally the optical path of the Microvision engine requires a lot of space to enter and exit the Microvision mirror from the “right” directions.
On the right I have captured two frames from the Lenovo video showing the optics from two directions. What you should notice is that the mirror assembly is perpendicular to the incoming laser light. There appears to be a block of optics (pointed to by the red arrow in the two pictures) that redirects the light down to the first mirror and then returning it to the second mirror. The horizontal scanning mirror is clearly shown in the video but it is not clear (so I took an educated guess) as to the location of the vertical scanning mirror.
Also shown at the right is bTendo patent 8,228,579 showing the path of light for their two scanning mirror design. It does not show the more complex block of optics required to direct the light down to the vertical mirror and then redirect it back down to the horizontal mirror and then out as would be required in the Lenovo design. You might also notice that there is a flat clear glass/plastic output cover shown in the at the 21s point in the video, this is very different from the Microvision/Celluon/Sony design show below.
Shown at left is the Microvision/Celluon beam scanning mirror and the “Exit” Lens. First notices the size and complexity of the scanning mirror assembly with magnets and coils. You can see the single round mirror with its horizontal hinge (green arrow) and the vertical hinge (yellow arrow) on the larger oval yoke. The single mirror/pivot point causes an inherently bow-tied image. You can see how distorted the mirror looks through the Exit Lens (see red arrow); this is caused by the exit lens correcting for the bow-tie effect. This significant corrective lens is also a likely source of chroma aberrations in the final image.
All the above does not mean that the Leveno/STM is going to be a successful product. I have not had a chance to evaluated the Lenovo projector and I still have serious reservations about any embedded projector succeeding in a cell phone (I outlined my reasons in an August 2013 article and I think they still hold true). Being less than 1/5th the volume of the Microvision/Sony design is necessary but I don’t think is sufficient.
This comparison only shows that the STM design is much smaller than Microvisions and Microvision has only made relatively small incremental progress in size since the ShowWX announced in 2009) and Sony so far has not improved on it much, at least so far.