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Optical AND gate

Discussion in 'Mathematics and Physics' started by neptune, May 18, 2012.

  1. neptune

    neptune Member

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    hi,

    i want to ask would this setup act as AND logic for light rays.
    Above image shows 2 white rays which are made by splitting a single white ray, passing through a intensity reducer such as glass or other elements. a single ray cannot pass through that material but if both shines it will get throuh the material.

    Below image shows one white light and one red light both of which alone cannot pass through that material. now if red light has to pass then it must have white light to assist it, since white light is mixture of all lights, only red light will adds up rest all diminish.

    will this setup work ?
     
  2. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    You have several concepts mixed up in this proposal. There surely are processes that require two photons, but the experiment you describe will not detect such reactions/absorptions.

    You need to read more about measurable aspects of light. Not necessarily at the quantum level, but just at the practical level.

    First, read about "absorbance" (aka, Optical Density) which is:


    Io = intensity of incident beam; I = intensity of transmitted beam. Thus, a filter that reduces the intensity to 10% of the original has an optical density (absorption) of 1.0. You can see that regardless of the optical density of the filter, some photons will pass, until it becomes random...i.e. some measurements will detect a photon; others will not. I don't think you have the equipment for single photon analyses. Beer's Law (Beer-Lambert Law) is a good place to start.

    Your second concept has to do with color. White is not a single wavelength of light. You need to study that aspect too. For the sake of discussion, red can be viewed as a single wavelength. Thus, white light going through something that absorbs only red light and absorbs 99.99% of red light will loose 99.99% of its red component. Now, if you are operating with intensities measured by a few photons, then red + white will yield more photons passing than red alone or white alone. Read about refraction of light and color.

    Regards, John
     
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  3. neptune

    neptune Member

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    hey i am not proposing experiment for single photon. Let me re-phrase my words. when we pass a light through a material which absorbs light then light gets reduced to some degree while passing through that material. now if we choose a minimum value of intensity to be detected at the far end of that material, for Ex- light intensity reduces to say 30% of original value, then we can assume it to be logic '0' then when we pass 2 light rays through that same material then light will get through and will get reduce to say 80% of its original value, that can be said to be logic '1'

    yes i know white is mixture of all frequencies, my question is if we have two separate light beams, one pure red and one white, and if we mix them up then will we get more intensity of red wavelength since red is being added twice, both in red and white beam ?
     
  4. dave

    Dave New Member

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  5. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    No, that is incorrect.

    Assuming the two light beams have the same intensity for the color being absorbed,* then if a filter reduces the incident beam to 30% of its original value (Io) for either single beam, the combined beams will still be reduced to 30% of their initial intensity. Since the initial intensity of the combined beams is 2Io (call it Io'), 0.3X2Io = 0.3XIo' = 0.6XIo.

    John

    *That also applies to different colors or white light when a "neutral density" filter is used. I omitted discussion of neutral density filters for clarity. Also for clarity, ideal behavior is being assumed.
     
  6. neptune

    neptune Member

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    can you clarify what type of filters you are talkimg about here
     
  7. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    Re: What type of filters?

    The same ones you have been talking about. At least, I assumed that your terms, "intensity reducer" and "material that absorbs light" were referring to filters in a general sense. As I alluded to above, there are so called neutral density filters that partially block all wavelengths of light about equally and other filters that contain a substance or substances that absorb light. Some have broad absorptions and are almost like neutral density filters over a limited range of wavelengths, others may have a very sharp absorption band, such as the hypothetical red filter we discussed, and others will show multiple and usually broad absorption bands.

    Interference filters are another type of filter. While such filters are quite common, I think at this point it is important for you to understand in general terms how filters and light interact without getting into the details of how to make a filter. As you said, this is not for practice but for theory.

    John
     
  8. neptune

    neptune Member

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    ok now i only want to discuss white light reducer or attenuator first , when we pass white light through a dark film then say its intensity got reduced by 30% of original 100%. then if we use 2 light source at same spot then we will get 60% intensity of its original 200% so, we can term 60% as logic '1' .
    dark films that i am talking about are used in car windows
     
  9. jpanhalt

    jpanhalt Well-Known Member Most Helpful Member

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    How did you calculate the underlined portion? Please show the work.

    John
     
  10. neptune

    neptune Member

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    I didn't calculated anything, it is just my intuition, like if we are seeing a bright light source from a film its intensity is reduced to say half, but when we double the brightness of that light source then we will see more brighter source behind the film.
    Now instead of using single light source we use 2 light source illuminated in same position ( like over laying each other) and the film will reduce the intensity to half. these 2 light source will be like 2 input of AND gate.
    then logic of AND gate would be, (Io = intensity of the single light source)
    Io + Io = Io
    Io + zero light = 1/2 Io
    zero light + Io = 1/2 Io
    zero light + zero light = zero light
     
  11. steveB

    steveB Well-Known Member Most Helpful Member

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    Neptune, one of the problems with what you are suggesting is that it is basically analog addition in a linear medium, but gates are usually digital and nonlinear devices. In principle, what you are proposing can work as an and-gate, but it is not a robust approach and the approach can not be scaled to multiple gates and full digital logic systems.

    I can make an and gate with 2 dogs, 2 electric shock devices and a microphone with a level threshold that latches a relay. If I shock zero dogs, then they dont bark and the microphone picks up no signal. If I shock one dog only, then that dog barks but the sound is not enough to trip the threshold circuit connected to the microphone. But if I shock two dogs, then the combined loudness from 2 dogs is enough to trip the level circuit.

    Will anyone care about my device? :)

    We can also look at it mathematically. Your linear system behaves like standard addition.

    0+0=0
    0+1=1
    1+0=1
    1+1=2

    Then a level circuit is set at 1.5 to make an and-gate, and 0.5 to make an or gate.

    But, real gates do boolean math automatically.

    0+0=0
    0+1=1
    1+0=1
    1+1=1

    Which is an or-gate

    0 * 0 =0
    0 * 1 =0
    1 * 0 =0
    1 * 1 =1

    which is an and-gate
     
    Last edited: Oct 16, 2014
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  12. JimB

    JimB Super Moderator Most Helpful Member

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    An interesting concept, but the noise would be so bad that the neighbours would soon start complaining. :D

    JimB
     
  13. neptune

    neptune Member

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    why does it matter if its working
    you mean they are not modular, yes there output cannot be used in their own input but they can be input to other gates with different intensity thresh hold, here is how
    Gate 1
    Io + Io = Io
    Io + zero light = 1/2 Io
    zero light + Io = 1/2 Io
    zero light + zero light = zero light
    output of gate 1 would be treated like this
    Io = output Logic '1', 1/2 Io = output logic '0', zero light = output logic '0'
    these will go as input of gate 2

    gate 2 all possible input and output would be like this

    Io + Io = Io
    Io + 1/2 Io = 3/4 Io (vice versa) (1*0=0)
    Io + zero light = 1/2 Io (vice versa)(1*0 =0)
    Zero light + 1/2 Io = 1/4 Io (vice versa) (0*0 =0)
    output of gate 2 would be treated like this
    anything below Io is Logic '0' otherwise '1'

    isn't that amazing that you can build Logic from anything ...sound, heat, water etc. conversely everything has Binary logic

    only if it improves the existing technology

    yes that would be a problem (AND as input to OR gate) but it can be solved by designing each stage to get triggered by different threshold level
     
  14. steveB

    steveB Well-Known Member Most Helpful Member

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    Since the same idea can be done using voltage instead of light, then I would suggest you try to build a system along the lines you are suggesting. Try connecting many stages of logic. You will quickly discover problems with noise margin, glitches and parameter sensitivity, as well as many others. You will then discover the "logic" behind the conventional way to build logic devices based on inherently nonlinear switching devices.
     
    Last edited: Oct 17, 2014
  15. neptune

    neptune Member

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    So in short one can't build digital logic using linear elements

    and here linear element is the intensity reducing material
     
    Last edited: Oct 18, 2014
  16. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Why bother with "the intensity reducing material"? Just shine two lights each of intensity I directly at a detector with a threshold 1.5 x I .
     
  17. neptune

    neptune Member

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    wow ! you are one step ahead of me :D
     

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