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Thanks to the readership of this blog, I now have my “press credentials” for CES. If there is something in the Pico Projector field in particular or displays in general you hear of at CES you would like to see me try and cover, drop a line to email@example.com.
I also want to let you know what I am working on and give you, the readers, a chance to help guide what I write about.
On the week before CES, I plan on putting out my “Cynics Guide to CES Demos.” I plan it to be a bit tong-in-cheek as the tile would suggest, but hope it will also be informative. For example, “The worse the image quality of the display, the less cloths they put on the female model in the picture they show.”
I’m working on a technical piece explaining why laser illuminated panel (LCOS and DLP) projectors are focus free with lasers. It seems to go against what even highly technical people believe from dealing with non-laser light with cameras and projectors that need focusing.
Have you noticed that the newer WVGA (848×480) and SXGA (1280×800) DLP® projector’s pixels look funny? All the pixels are turned at 45 degrees in what TI call’s “Diamond Pixels.” This was done to try and make the DLP light engines thinner (it will take a while and some pictures to explain why) but it hurts the resolution and causes some strange artifacts (I will show what happens in some pictures).
I know there has been a lot on Laser Beam Scanning (LBS) on the blog as of late. It was a “hot topic” with Microvision’s “false soothsayer” comment coming out. I do have a lot more information the many problems with LBS that they don’t want you to know. The next subject about be on the resolution and flicker problems associated with LBS.
I plan and have an article on why lasers are the key to high volume embedded pico projectors and to continue the “use model” series.
I’m also planning on a series of article discussing the efficiency and size issues with the various pico projector technologies including LCOS, DLP and Lasers but this is going to take some time to write.
If you want to give feedback, ask for one of the above to come out sooner, and/or ask for particular topics, please either comment below or email firstname.lastname@example.org.
Explain laser speckle in some detail, and current methods of addressing the problem. Also, I know that the size of the light source is one thing that affects the need to focus. LED’s are a fairly small light source. But, the projectors that use them are aren’t focus free like a laser source. Why?
I did plan on getting to speckle as part of the “laser series.” Speckle is caused by the coherence of laser light meaning that the waves going out are all in phase with each other (see picture of sunlight, monochromatic LED light, and laser light). When laser light hits a surface it reflects back on itself and constructively/additively and destructively/subtractively interferes/mixes with itself and since the surfaced is not perfect, there are spots (see for example this link). In a projector system the speckle happens in two places, on the display screen and on the retina of the observer’s eye.
Lasers are not totally perfect and don’t put out a single wavelength. As the bandwidth (range of frequencies) widens, each wavelength is incoherent with the others and so the speckle goes down. Frequency double lasers have a very narrow bandwidth on the order of 0.1 nanometers. Usually the frequency doubling crystal is tuned to one very narrow frequency so only lets out a small rangle of wavelengths. There are some companies such as Epicrystal’s in Finland have figure out how to broaden the spectrum when frequency doubling, I think on the order of 0.5 nanometers. Direct diode diode lasers put out a wider range of wavelengths, on the order of 2 nanometers, or about 20 times wider than the typical DPSS/frequency-doubled laser. There still is visible speckle but it is reduce enough that simpler despeckling techniques can be used.
Despeckling comes down to breaking up the coherence. The simplest method is the take the laser light spread it slightly and run it through variable depth glass that is spinning or a vibrating mirror. The light is going through different depths of glass or different mirror gyrations at different times and this will change how it interferes with itself when it hits the screen. There are many variations on this idea. You can also run the light through devices that don’t physically move but change their optical characteristics by and electric field. Despecking narrow bandwidth laser light is a very tough problem and one of the reasons why the wider spectrum direct diode lasers are so desirable.
As far as focus goes, it really will take some time and some figures to explain, but I will try and give a quick answer for now. People think that a “lens is something you have to focus” but that is because they are not used to using them with light that has the optical properties of laser light.
LED light spreads out in all directions (Lambertian). To get the light onto the projection screen you need a lens to “collect” the light that is spreading after is is modulated by the microdisplay and focus it. What “focusing” is all about it collecting the spreading light from a point on the microdisplay and making it come back to roughly the same point on the screen. Laser light on the other hand is all going in parallel lines. If you know something about photography, laser light has essentially “infinite f-number.” F-number can also be express as an angle of the cone of light coming from the light source and since laser light has almost no spread, it it’s f-number is near infinity. Even after the laser light is spread and despeckled in a laser projector it will still have very high f-number. High f-number light is not spreading out much and so does not need much in the way of focusing. With cameras they talk “hyperfocal focusing” where you use a high f-number aperture setting and a wide angle lens and everything becomes acceptably in-focus from a short distance from the camera to infinity. With laser pico projectors, they normally have wide angle lenses and since the laser light itself is high f-number the lens can be very small and the projected image is hyperfocal such that it will be in-focus from a short distance away from the projector to infinity.
I probably fractured more than a few technical terms above. Hopefully it gives you some idea of what is going on. I don’t know how much you know about optics or photography so I don’t know if the above will make sense or not, please let me know.
Karl, thanks for a great blog. I think many things will change in the coming year in the pico-projector business. Microvision will (hopefully) finally go bankrupt and we will see some new players in the business. As they say “Technology Never Sleeps”. I wish you a Happy New Year and Good Luck with your blog for 2012.
Thanks for the positive feedback.
Microvision is IMO between a rock and hard place. If investors understood the real state of their technology and the state of the direct green lasers they probably would not invest. They need investors to believe an “alternate reality” in or to raise money to survive. They have “cried wolf” (or as in the movie UP! “squirrel”) so many times, its crazy that anyone believes them anymore. I also believe they use the green laser availability as a scape goat. First they did this with the “synthetic” green laser. Microvision talked about how they would be so great and efficient and that it would be cost effective when it was available and then the ShowWX came out and it had extremely poor efficiency (much worse than the LED based LCOS and DLP projectors) and host of other problems.
Now they are repeating the same game with Direct Green Lasers. They have to have people believe that the DGL are going to be in high volume low cost production much sooner than is realistic. Furthermore they have built this whole illusion to their investors that direct green lasers are their ONLY problem which it is clearly not. Laser beam scanning has a number of technology problems, but Microvision has successfully misdirected people to focusing only on the green laser issues because it is a “temporal problem” (one that will go away with time) and they gloss-over/ignore/deny a raft of other major problems with LBS.
The big negative issue for the pico projector industry is that they are about to “burn a ~$500m hole in the ground” in the area of pico projectors. With some of that money they have convince a fair number of people that LBS is the best/only approach to pico projectors which is untrue. LBS is an “easy sell” to people that don’t really understand all the technical problems involved. If it was so easy, they wouldn’t have spent nearly $500M jut to get it to work as badly as it does today. A large share of Microvision’s patents are directed to fixing all the myriad of problems with LBS, and each of these “fixes” cost money, power, and hurts image quality in some way.
I’m with you on technology never sleeping. I believe there were eventually be a very large embedded pico projector market that will be using green lasers. Realistically from where the direct green lasers are at, it will probably be in 2014 or beyond which may be forever away to Microvision, but really is just around the corner for companies to ramp production for a high volume product.
There are also some interesting frequency doubled laser developments from multiple companies for making highly efficient and very bright projectors for media players and even ultra efficient televisions (for emerging markets where power is at a big premium). These lasers are getting very efficient and bright but are too slow switching for LBS, but could be ideal for use with panels (LCOS and DLP). These frequency double lasers are probably going to be too big and expensive for high volume embedded cell phones, but will be more efficient and cost effective at high (greater than 100 lumen) brightness.
…These lasers are getting very efficient and bright but are too slow switching for LBS, but could be ideal for use with panels (LCOS and DLP)…
not quite true.
As with Corning and OSRAM’s frequency doubled lasers, to make them fast switching, before them, it appears that the Epicrystal lasers end up being much less efficient (by a factor of 2 or more) and much less bright (60mW versus over 100mW for some of the DPSS laser and there are DPSS green lasers that can be over 1000mW). Also at $45 per 10K, they are much more more expensive. So what is “not quite true?”
The stated price at the link for the Epicrytal laser is $45 at 10,000 pieces for a 60mW which would support a roughly 10 lumen LBS projector. An then you have to add the red and blue laser. You can get red, green, and blue LEDs to support 10 lumens for about $5 and a set of RGB LEDs to support more than 100 lumens with panels for around $15. A set of RGB LEDs to support over 100 lumens cost about When the cell phone makers want the whole projector to cost less than $30 and have well more than 10 lumens, it is hard to see how this spins up the market.
so to whom are you referring to when you speak about…There are also some interesting frequency doubled laser developments from multiple companies…?
i know about spectralus and epicrytsals. do you happen to know the wpe of the spectralus green laser they are offering?
btw i would assume a 1000 mw DPSS laser is pretty useless for a pico projector…;)
Answering Chris’s responses on lasers:
I see you found that Spetralus had about 12% WPE at 532nm about a year or so ago. I believe they have better results now.
C2C and their joint venture with QP lasers has recently announced laser with >20% WPE see: C2C is http://c2clink.com/mGreen-500.htm at over 500mW. This laser is also very small for its light output.
I don’t know if Epicrystals has not given a WPE number that I am aware of, so there is some speculation on my part based on similar devices from Osram and Corning. Note both OSRAM and Corning spent many times what the startup Epicrytals has spent developing their lasers. I know that the other high speed switching frequency double lasers where in the 5% to 6% range.
By the way, there are similar issues with respect to direct diode lasers. Beam scanning lasers requires “single mode” lasers that don’t “hop” because the hopping turns into intensity/color variations in the beam scanning process thus making a noisy image. “Multi-mode” laser’s “hopping” gets averaged out with laser illuminated panel projectors and has has the major benefit of reducing speckle. It is also much easier to make multi-mode lasers so they will end up being cheaper.
wpe for spectralus is available
12%. don’t know about the wpe of the epicrystal green laser.
is spectralus saying anything about price?
…Laser beam scanning has a number of technology problems…
Lcos technology certainly has its own stack of problems…;)
thats a quote from a sec filing Himax released:
… We believe end products utilizing LCOS technology could potentially be a large market. LCOS technology, however, is at a relatively early stage of commercialization and has a relatively immature supply chain. Furthermore, producing LCOS products at acceptable yields has proven difficult. Therefore we cannot assure you that there will be market acceptance of these LCOS products, or that our strategic alliance with 3M or Wingtech Group will be successful.
No doubt, there are issues for LCOS as well and Himax’s boilerplate lists many of them. Himax was using “analog LCOS” which added a number of problems and is proving to be a dead end for field sequential color. By many reports, they have given up as they couldn’t get their analog field sequential color to work reliably. Syndiant went with a digital field sequential color approach that has many advantages both in manufacturing, color, reliability, and light throughput.
The supply chain immaturity is still an issue. Syndiant has spent well less than 1/10th of what Microvision has spent. The biggest thing keeping LCOS back is the investment in volume manufacturing technology. I think LCOS today cost more than double what it will will eventually cost for a given size device due to the lack of investment in manufacturing. LCOS’s biggest advantage is in making small pixels and it is held back in fully utilizing this advantage due to the availability of green lasers. This appears to be changing for frequency doubled lasers in the near term for larger projectors, but will be a few years for direct green diode lasers in the longer term.
thx for all your replies.
i have another question to you since you have mentioned that the biggest advantage of Lcos is in making small pixels. i don’t know whether you are in a position to reveal such information or are bound by NDA. is syndiant going to offer a 720p display solution without increasing the svga panel size in the near future ? say CES…;)
I can’t get into all the details but Syndiant’s current 720P has a 0.37 inch diagonal and is 7.2mm tall. Syndiant has an SVGA (800×600) panel that has a 0.21″ diagonal that is 7mm tall and one that has a 0.37″ SVGA that is 9mm tall. The 720P is shorter because it has a 16-by-9 aspect ratio (HD) and the periphery is smaller.
The current 720P is a “tweener” in that it is small enough to embedded in a early market product but is bigger to collect light from LEDs. We were basically in a wait and see on direct diode lasers to make the panel smaller. The mirrors/pixels are bigger than they have to be to work better with LEDs. There really is nothing keeping LCOS from going below 6mm high for a 720P other than a light source, ala lasers, that will give enough light throughput. With LCOS smaller is also much cheaper as the cost to make is pretty close to being proportional to the area of the device so a linear reduction by “N” in diagonal can result in N-squared reduction in cost to make.