I got asked a series of questions by reader “me_wwwing” after the article Laser with LCOS is Focus Free — Yes Really! that I am answering in this post because I thought they would be of general interest.  I did have to edit a few of the questions for clarity but tried to keep the intent as best I could and I have re-ordered the questions to put what I think are the more interesting questions first.   For background for the reader I need to add that from prior questions and comments, I know me_wwwing to be a fan of Microvision’s laser beam scanning (LBS) so that may color some of the questions and the answers.

Q1. Does Syndiant need to use the same lasers as MVIS [Microvision laser beam scanning (LBS)]?

The simple answer is that LCOS panels can use any of the lasers that LBS can use and can use lasers that LBS cannot use.   LBS puts constraints on both Diode Pump Solid State Lasers (DPSS also known as “synthetic” or “frequency doubled) and for direct diode lasers (DGL).

Answer Part 1: DPSS Green Lasers

First, Syndiant makes the LCOS microdisplays and not the entire optical engine.     A panel (LCOS or DLP) optical engine has a wider selection of lasers that it can use both for direct green lasers as well as DPSS green lasers.   So the quick answer is that it can use any of the lasers that a LBS system can use plus it can use laser types and variation that LBS cannot use.

With DPSS green lasers, panels could use the less expensive to make and much more electrically efficient (generally about 2X the efficiency) slower switching lasers.  The slower switching frequency doubled lasers are capable of greater than 12% wall plug efficiency (WPE) with the desirable 532nm wavelength green.   About the best the fast switching frequency double green lasers ever got to was about 6% WPE.

The slower switching DPSS greens are capable of going to very high brightness; they can be over 10 times brighter than today’s Direct Green Diode Lasers (DGL).   Their electrical to lumen efficiency is over 3X the best DGLs today.   And their cost is lower than DGLs.   But the drawbacks to DPSS greens include the size and the small spectral bandwidth that causes higher speckle.

Answer Part 2: Direct Green Diode Lasers (DGL)

It turns out that there are different kinds of direct-diode lasers as well.  Most notably there are “single mode” and “multi-mode” lasers.

LCOS or DLP can use either the single-mode or multi-mode lasers, but lasers LBS can only use single-mode lasers.   Multi-mode lasers change wavelength, phase, and/or optical polarity somewhat randomly.  The rate of mode changing would look like noise in a LBS scanning process so it is unusable in an LBS system, but in a panel (LCOS or DLP) system the hopping simply gets average out as it is faster than the eye can detect.

Since changing wavelength and phase reduces speckle, multimode lasers have less speckle.  It turns out that lasers naturally want to mode hop, so it is easier (cheaper) to make multimode lasers, multimode lasers are more electrically efficient and multi-mode lasers can be made much brighter/more powerful (in fact, as they make the laser cavity bigger to make lasers more powerful it is hard to keep them from mode hopping).  So panel based projectors have a significant advantage in being able to use multi-mode lasers.

Historically, traditional laser uses such as telecom and interferometry, needed single mode lasers.   But the same coherent light for these applications is what causes speckle, so for panel based projectors you want “poor quality” lasers with less coherency and thus speckle.

Q2. How big is Syndiant Controller?

The Syndiant’s 720p ASIC is currently 9mm X 9mm in its current package, but could be put in a significantly smaller package by reducing the pin count for an embedded cell phone.  The current package has a lot of extra pins for supporting a mix of applications that make it bigger.

Q3. What are the dimensions of Syndiant’s PCB?  The new one or the old one to have a starting point.

Syndiant sells the panel and the driver ASIC and not a PCB per say.  Single SYA1231 ASIC for their 720p is currently 9mm x 9mm includes frame buffer memory and ARM CPU and can be put in a smaller package for embedded applications.    So there really isn’t much in the way of board space for the new Syndiant 720p controller.  Basically, it is just one small chip 9mm X 9mm chip and not a “PCB” per say.

Syndiant’s single small ASIC compares extremely favorably to the Microvision 720p board which has 2 custom ASICS (one about ~11mm x 11mm and the other ~10mm x 10mm)  and an Altera FPGA (~6mm x 6mm)  on it.  There is also a 4th I.C. on their board which is an Intersil laser driver (5mm x 5mm).   The  picture below is from www.technogytell.com with my notes added it:

Totalling up the area of Microvision’s two ASICs and FGPA, Syndiant’s current control ASIC takes about 1/3rd the area and 1/3rd the ICs of Microvision’s 3 chip controller.   Also just looking at all the power conversion circuitry required in the Microvision “720p” board suggests that it needs a lot of different voltages with some significant power requirements and all this adds cost, board space, and power.

Q4. What size diagonal lens (encased) does Syndiant’s displays need to cover the diagonal of the display?  A length too would be nice. old specs are ok to start with [assuming laser illumination]

The diagonal of the “active display” of the older SYL2010 was 0.21”.  It had a 5.4 micron (10^-6 meter)  pixel such that an 800 pixel high display was 4.3mm.   The lens would need to be a bit thicker than this diagonal.  For a small high volume product the lens would be cut to a more rectangular than circular shape to reduce height.   So the lens could be about 6 mm thick.   The SSTDC SEE100 prototype engine http://www.picoprojector-info.com/laseno-see100-module-photo  engine’s lens with its barrel was non-optimized (circular) and was about 8mm thick and 8mm long.  An optimize rectangular-cut lens could have been about 5mm tall.

There is nothing keeping LCOS with laser illumination from going below 5 micron pitch (they will eventually get to around 3 micron and perhaps less) for its pixels.   At about 5 microns the active display for a 720p would be about 3.6mm tall.  A rectangular cut lens would then be about 4.5mm to 5mm tall or a round lens would be about 7mm tall.

Q5. Does the dichroic color combiner lens need to cover the surface of the Vibrating Despeckle unit [the answer addresses the broader question of the light combining system for LCOS and LBS]?

No, the light is not significantly spread out before the dichroic color combiners in an LCOS system.  Also the alignment of the dichroic mirrors/filters and the lasers is non-critical in an LCOS or DLP optical engine.

In should note, however that the alignment of the lasers and the dichroic combiners is very critical in an LBS design.  You should note in this teardown picture (picture taken from a laserpointerforums) that I have labeled the two ball shaped optics (pointed to in magenta) used to aligned the red and blue lasers and then glued into place.   The need to critically align the lasers adds cost and quality issues into to the manufacturing process.

 

Q6. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power. 

It is helpful to break the power into two part, the panel and controller electronics and then the illumination and optics.   For low lumen (less than 30 lumen) projectors, the power of the display and its control is a significant part of the overall power (and less so at higher brightnesses).

The Syndiant LCOS display and ASIC for the WVGA or SVGA will usually consumed about 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

With lasers the efficiency depends heavily on the lasers used and is dominated by the green laser efficiency which is pretty poor with today’s DGLs.   With today’s DGL efficiencies, LEDs will produce more lumens per Watt, but this will change in the future as lasers improve.   I fully expect to see eventually over 30 lumens per Watt with DGL and LCOS because today with the current DGL, they would be doing well to get 3 to 5 lumens per Watt .

Q7. What would be the lumen output from Syndiant’s displays using the new lasers that Microvision will use [this question was edited for clarity].

This is not a simple question as the spec’s on the lasers and how they can be driven have not been finalized.   I’m pretty sure the lasers that Microvision was using “lab prototype” lasers at CES that were being “over driven.”  The best I can answer right now is to give some insight into the lumens per watt that can be expected as the lasers are perfected.

To begin with, the optical throughput for a laser/LCOS engine should be in the 30% to 40% range where for LBS the optical throughput is reported to be in the 55% to 60% range.   But note, this is the part of the system were LBS looks best in terms of efficiency, but this does not tell the whole story.

Where LBS looses in terms of efficiency is in the drive and control of the laser and the MEM’s mirror.    The Microvision MEM’s mirror alone (not including the ASICs and FPGA’s) at WVGA has been reported to take about 0.4 Watts.   Syndiant’s new 720p LCOS Microdisplay and ASIC combined will take less than that.   Then you have all the power of the 2 ASIC’s and the FPGA that the Microvision 720p board requires.    So LCOS starts with a big lead in terms of power just in power of the display and control.

Then we have biggest power wasters for LBS, that of having to analog modulate the laser drive power.   First you have the fact that each pixel in the laser beam scanning process must be analog modulated at very high speed and high speed analog modulation wastes power.

Additionally, most people are not aware that the laser beam also has to be modulated due to the varying speed of the laser sweep.   If you think about it the laser beam horizontal sweep has to accelerate from zero to the maximum speed at the center of the screen and then decelerate to stop at the far side before returning.  To make a solid image appear uniform, the laser drive has to be constantly varying (for a “solid white” image the drive approximates a sine wave).  See such as the Microvision White Paper (a figure from which is copied below) and the excerpt (copied below) from the Microvision patent application”Apparatus and Method for Interpolating the Intensities of Scanned Pixels“:

Q7. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power.

The LCOS display and ASIC for the WVGA or SVGA will usually consume less than ess than 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 2X to 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

Q8. Which VGA display panel is best suited for the cell phone market?

I don’t know that there is a “best.”  Right now about the only reasonably high volume embedded panel is the color filter LCOS one by Himax that is used in cell phones for the India and China market.   The performance of these engines is too poor to be used in “first world” markets.   I think many of them are also less than VGA resolution.   They are typically about 5 to 10 lumens with pretty poor color and contrast and use very cheap but relatively large optics.

Personally, I don’t see a big “first world” need for a VGA or WVGA display.   Why bother projecting an image that lower in resolution than the cell phone’s display?   I think the big market will be to projector resolutions that are at least 720p

Q9. Does Syndiant plan on building the Light Engine?

I can’t comment on Syndiant’s future plans, but Syndiant’s business model has been to be a panel supplier.    There are very large number of good optical engine companies in the world so I don’t know why Syndiant would want to change.

Q10. Is Syndiant depending on someone else to make the Light Engine and Syndiant only sell the display panel?

Syndiant makes the panel and for use by many companies.   This allows different companies to make different products aimed at different markets.

Q11. Does Syndiant’s displays need a Vibrating Despeckle unit with DGLs?

It depends on the DGLs.  With the multimode DGLs you can drive them in such a way as to induce more mode-hopping to reduce speckle.   I would expect the there will not be despeckling required with volume production DGLs.

Q12. Does the light coming off the Vibrating Despeckle unit need to cover the homoginizer [a reference to the 3 year old SSTDC optical engine that used a vibrating despeckler]?

In the old SSTDC design with a vibrating despeckler, the light was partly spread before going to the despeckling mirror but not as large as the homoginizer.

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