1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Small Reflective Projector LCD

  1. Oct 27, 2016 #1

    I need some assistance on a current project I'm working on.

    Here is some basic background information:
    I am currently trying to use a "makeshift" SLM, spatial light modulator, to impose a diffraction pattern so that when I shine a laser on it, the beam is diffracted into a donut shape which I will then use for STED microscopy. That is the basic premise.

    What I have so far:
    -Matlab code that creates a diffraction pattern, based on resolution, that will in turn create a donut shaped beam for ionization when a laser hits the diffraction pattern
    -A makeshift SLM that was built by someone else in my group by using an old projector. Steps were followed in a research paper to use the projector as an SLM

    What I am trying to do:
    -Run the code on my computer and generate a diffraction patter. Then, using a video cable, display the image on the pc screen onto the lcd
    -Next shine a laser on the lcd in order to create the donut shaped beam
    -Apply the beam to a diamond sample to run my groups experiment

    What I'm stuck on:
    -I have no way of knowing whether or not the image I have on my computer is being sent through the cable and causing the LCD to align itself in a way that will simulate the diffraction pattern.
    I've tried using a low powered laser to shine on the LCD but it seems as though the crystals never change no matter what image I display on the computer

    Basically I want to know how I can effectively test the reflective LCD to see if it's indeed trying to display the image from the PC.

    Do I need to polarize the laser before it hits the LCD? Do I need a more powerful laser?

    I am stuck at the moment and any help would be appreciated.

    I have information on the reflective LCD being used if need be. I can also take pictures of the set-up tomorrow for reference

    Thank you

    [ Mod Note: will try this thread in General Physics ]
    Last edited by a moderator: Oct 30, 2016
  2. jcsd
  3. Nov 3, 2016 #2


    User Avatar
    Science Advisor

    Here is an http://www.lxdinc.com/faq/difference_between_reflective_and_transreflective [Broken]of the three types of LCD displays and their construction. Hopefully it has enough information for you to get a visual indication of what, if anything, is on the display.
    Last edited by a moderator: May 8, 2017
  4. Nov 3, 2016 #3

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    I have a small amount of experience with this type of device.

    Can you simply place a linear polarizer over the SLM and view the pixel array directly to verify that the elements are being controlled as you expect?

    Can you program a 'test pattern'(say, an array of stripes) or otherwise verify the device works?
  5. Nov 7, 2016 #4
    Hello thank you for all your responses.

    I have been late in my responses because my phone recently broke and it had all the information of my project on it. I am still waiting for my new phone so I can recollect the data and take new pictures
  6. Nov 7, 2016 #5
    I did have pictures of the set-up which would have probably made everything more clear, along with information on the LCD. Unfortunately my phone had that information and it broke, so I have to wait until I get a new phone to replace the data.

    Basically this SLM was built years ago and was just given to me. I have no idea how they built it or the process, all I have is the end product. It's basically the motherboard of the projector with 4 different DVI cable inputs. There are two separate boards actually, and there's a data ribbon attaching them. We're able to power the board with a power supply we built (we know this because when we turn on the specific voltages needed there are indicator LED's on the circuitboard that lead my group to believe it's being powered.

    I know it all sounds very confusing but I'll try to get the pictures ASAP
  7. Nov 7, 2016 #6
    This is what I have been trying to do I believe. We have patterns already generated from the Matlab code. What I do is display that image, fullscreen, on the computer screen, then use DVI cables to connect it to the projectors DVI inputs and 'test' the LCD with a laser to see if anything has changed. I put on projector mode from the computer so I know that the image is supposed to be duplicated.

    There's no discernible difference in the layout of the pixels that are reflected when I illuminate it with the laser. For example I'll have the pattern on the screen, output it with projector mode, then shine a laser on the small LCD and it reflects an orderly grid of pixels on the wall. Then I'll test with other patterns, I'll test with different pictures, I'll test it by taking off the LCD and it's pattern stays exactly the same everytime.

    I don't know if maybe the laser is too narrow, or if the set-up is even correct in the first place where the LCD is changing according to the displayed image
  8. Nov 7, 2016 #7
    I would think the easiest way to see if the LCD is doing anything would be to place it over a light table or similar between crossed sheets of Polaroid. (I.e. A polarimeter) These are common tools and someone around the building may already have one hidden in the back of a cabinet. You'll probably need a magnifier to see the pixels, so try it in a low mag field microscope. Failing that, try changing large blocks of pixels the same way so the blocks are big enough for you to see.
  9. Nov 7, 2016 #8
    Oops, sorry. My last post is too much like post 4. Sorry for wasting everyone's time.
  10. Nov 7, 2016 #9
    No worries, all ideas are appreciated. Everything helps to be honest, I have different perspectives on what I can do now.

    So do you know what that pattern is after I illuminate it with a laser?
  11. Nov 8, 2016 #10

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    Wait- you haven't expanded the laser beam? It should illuminate nearly the entire LCD.
  12. Nov 8, 2016 #11
    No I haven't. The other problem is that the dount shaped pattern needs to be very small, it is being projected onto a small diamond sample -- it needs to be in the range of microns.

    How would I go about expanding the beam and then ensuring the size of the pattern? Is the size completely dependent on the code I have to create the diffraction patterns?
  13. Nov 9, 2016 #12

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    Ah- now I understand why nothing is happening. Expand the beam with a spatial filter + plano-convex lens enough to barely cover the LCD array. Then use optics to focus the diffracted beam down as needed- sounds like you may need to use a microscope objective.

    I'm somewhat concerned that you are working alone on this, since nobody in your group is providing basic assistance...?
  14. Nov 9, 2016 #13
    Wow this sounds promising. Thank you.

    Well Im an undergrad graduating next year. I joined my professors team and they obviously want me to learn so they gave me a project under the guidance of another group member. He's helped, as well as others, along the way in a lot of ways. In fact a lot of the results has been a product of his work. However they have their own independent sections of work they need to do so I really need to figure out how to at least do this. They weren't sure either but thats probably because this wasnt their primary task. I have a full schedule also so its pretty difficult to even get hours in at the lab
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted