Questions on Laser Beam Steering/Scanning

Based on my comments on the state of green lasers, a recent Microvision 8-K and blog talking about “false soothsayers” talking about green lasers, I am getting a lot of questions about laser beam steering/scanning (also known as laser flying spot scanning and several other names.    I’m going to try and start this page for answering those questions rather than having them mixed up into all the various comments on the blog.

10 comments

  1. Hi!

    I`m a Norwegian student, working on my final report on my degree. I was wondering if you could help me with a few questions regarding green lasers. I have very little experience with lasers, and I`m working on a project where I`m suggesting to use laser light in stead of LED light. I`m going to use green light, and a class between 2 and 3B. So, my questions are:
    – What type of lasers produces the least heat?
    – And do you think it`s possible to embed this without cooling, when it`s suppose to work for an hour?

    Thank you for your time!

    With best regards
    Hege

    1. Hege,

      There is insufficient information to really answer your question. You did not say how you were going to be using the LEDs/Lasers. Is this for general lighting or for a projector for example?

      The laser safety classification is based on how the laser light is used. If you are sending a tight bean (like a laser pointer) you can have a lot less total light than if you spread the light out.

      For general lighting today, a green laser is very inefficient compare to say LEDs. Whether you need cooling or not depends on a lot of factors including the ambient temperature and how big a heat sink you have.

      Lasers are most useful in application were the light has to be very concentrated (high f-number and low etendue).

      I hope this helps,
      Karl

  2. Hi Karl,

    I am working on designing an all-in-one portable video conferencing device for small groups. It is smartphone-controlled and include a cam, speakers, microphones and a projector.

    We use a projector so that we can get rid of the screen and be able to provide decent small group video conferencing experience whatever the place, as long as there is a wall nearby.

    So the requirements for the projector are :
    – an image that is at least 21 inches big and bright enough for typical workspace lighting
    – a cooling system that is almost silent

    LBS seemed to be the most suitable technology but Microvision told me they can’t go further than 30 lumens and I am afraid that doesn’t look good in normal lighting even for a small image size.

    If our project is validated, we should start shipping on fall 2018. Should I give up on LBS ? What technology would you recommend ? Who can provide me with that technology ?

    Best regards,
    Cherif

    1. These are some of the classic issues with pico projectors. I would definitely forget about LBS for a decently lit room. Forget all the marketing garbage, lumens are lumens whether they are lasers or not.

      A well lit room (but no window with direct sun) as about 30 to 100 lumens per square foot (https://www.kguttag.com/2011/12/09/being-usefull-part-2-ambient-light/). A 21 inch diagonal image in 16:9 format is about 1.36 square feet. So you could have on the wall about 40 to 140 lumens on the wall you are competing with. For “barely readable” text you want 2:1 contrast and for decent colors I would want about 8 to 1. So this puts you at about 400 to 1000 lumens for the projector (multiplying the ambient lumens by about 8). You might compromise and go with something in the 400 to 500 range and then say if the room is bright you get a smaller image. Also note that projector companies fudge their Lumen numbers so you probably want a “650 to 800 lumen” projector to get a “real” 500 lumens.

      I have not done a study of how loud the various projectors are. The amount of noise will depend on their cooling design and what they spent on the fans. But anything in the 500 lumen range is going to have to have fan(s).

      You would have to be crazy to even consider LBS for a well lit room. The only projector technology that would seem to fit your requirements would be using DLP. There are a number of DLP “pico” projectors that might work such as the AAXA P700 (http://www.aaxatech.com/products/p700pro_pico_projector.html). I can tell you want most people have figured out is that a large tablet or thin laptop computer (that will cost less than a 500+ lumen projector). will work better in more situations. You don’t have to worry about having a good wall/screen to project on or the ambient light in a room. I would recommend you try with some various brightness projectors and a large tablet and/or laptop computer.

      Let me know if this helps,
      Karl

        1. I remember Casio being the first to introduce laser-hybrid, but didn’t remember/know appotronics invented it. Laser hybrid (blue lasers stimulating phosphors for green and sometimes blue and/or red but usually red is done with LEDs) lets you burst through the 1000 lumen barrier to get 2000 to 3000 lumens in a relatively slim (or not) form factor.

          But as best I know, a laser hybrid is going to require a PLUG or a very large external battery pack (i.e. takes too much power for a small battery). There is a gap between the ~500 to 700 lumen LED with battery and the several thousand lumen hybrids. While the hybrids are efficient in terms of lumens per Watt, they have a lot of lumens and thus a lot of Watts. There are less expensive hybrid projectors that are thicker or you have the slim ones (most from Casio) that are more expensive (in the $1000+ range). Those slim Casio designs were aimed at the “road warrior” market where a person wants a projector in their backpack/briefcase; the goal is to be no bigger in x and y than a pad of paper and a thin as possible. The Casio’s often thinner than even the ~500+ lumen LED based projectors with battery, but bigger in total volume (i.e. form factor is better).

          So it comes down to your market requirements. Are you willing to require a plug? Does the form factor and cost of say a thin Casio meet your needs? You have to watch that you are not spiraling away from a a solution. Look at a flat panel for the same size and weight and what it would cost (about 1/10th that of the Casio hybrid/laser thin projector and lower in weight and several times thinner).

          Karl

  3. Hi Karl,
    Thanks for the great blog! My understanding is that DLP works by flipping a tiny mirror between discreet on and off states. Would it be possible to have a large micro-mirror array with elements that could move continuously? I could imagine a high frame rate projector projecting onto such an array, synchronized so that the image presented depends on the angle from which it is viewed. The result would be similar to a micro-lens array based light field display, but it should be able to achieve higher spatial resolution. Has this been done before? Or are there some problems I am overlooking?

    Thanks,
    Ryan

    1. I’m not sure totally what you are getting at, but there have been companies that have tried a single mirror that is “analog” of sorts (follow a Lissajous pattern). It would be exceeding difficult to build and control and array of analog moving mirrors.

  4. Hi,

    Could you do a review of Voga V phone with laser projector.
    Bought one and have been using it for almost a week now. I’ve owned several dlp home theater projectors and Samsung Galaxy 1 and 2. Voga V was my first laser projector and had to say I was really disappointed with the projection quality; it is much brighter and colors more vibrant but with speckles and what not Beam 2’s 800×480 resolution looks better to my eye (no sparkling speckles and blurriness) and I think it shows more details in dark areas.

    I’ve tried to accept Voga V’s projection for what it is but can’t seem to get over the bad quality, different surfaces seem to yield different results: Bathroom tiles giving the best result, in second place comes my bedroom ceiling with very uneven texture, that seems to eliminate the sparkling effect and most of the speckles too. Still no way to get real feeling of sharp 720p projection which I’m quite sure I would get if the projector was dlp instead of laser.

    Enough of me rambling, I would greatly appreciate your professional opinions about this new wave of smartphones with “720p” laser projectors, their weaknesses and strong points.

    Timo

    1. Timo,

      I thought about buying a Voga V to review, but I didn’t see it being worth the time and expense. I have already reviewed the Celluon in detail including a teardown. I did see the MOVI (the same as a Voga V) at CES, and it did seem to have more speckle. The Celluon used the larger Sony engine with 5 lasers and some optics that seemed aimed at reducing speckle. I suspect to make the engine smaller and less expensive, they went back to 3 lasers and without the speckle reduction optics.

      As I have written many times, Microvision (the laser scanner in the Voga V and Celluon) lies about their resolution. By any objective measure, the resolution is half (in both X and Y) or less what they claim. I have gone into this in many articles on how Microvision’s scan process works and why it is physically impossible to for them to have the claimed resolution in addition to measuring it. They also have a huge amount of 30hz flicker due to the interlaced scanning process.

      For the record, the best way to reduce flicker is to vibrate the screen. You can take a cheap disposable toothbrush vibrator or old cell phone vibrator and attached it to the screen and let it run. The random vibrations will break up the speckle (a more sophisticated version of this is what Dolby uses in their laser Cinemas).

      This gets to the fundamental problem with all pico projectors, that of having a convenient screen. If you have to carry the screen around with you (and one with a vibrator) then why not just carry a tablet computer? The fundamental problem with pico projectors remains that you need a screen, a place for the screen, a place for the projector, and a place that is fairly dark. Too many times one or more of these conditions can’t be met, and so it is “undependable” whereas a tablet computer will work in all but the brightest conditions.

      I hear that there is a market for pico projectors in parts of China and the rest of Asia driven by an indoor home use model, but I have not verified this. A laser projector offers no advantage in this use case as an LED projector is going to be less expensive, much brighter, and with better overall image quality.

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