Holograms Can’t be Too Thin

We’ve seen the 3D phone fad come and go, with devices like the Evo 3D, that used a parallax barrier to achieve autostereoscopy (that is, 3D viewing without glasses). These displays aren’t holograms, they are just showing your eyes two different images like a 3D movie or a stereopticon. However, researchers from Australia and China are hoping to change that. They’ve developed a nano-hologram (their term) that is about 1000 times thinner than a human hair. You can see a video about the invention, below.

Conventional holograms modulate the phase of light to give the illusion of three-dimensional depth. But to generate the required phase shifts, those holograms need to be as thick as the optical wavelengths involved. The researchers claim the holograms are “simple” to make, but that depends on what you compare it to. You need some exotic materials, vacuum deposition gear, and a laser that can do femtosecond-long pulses.

The research team has broken this thickness limit with a 25 nanometer hologram. Their technique relies on a topological insulator material a novel quantum material that holds a low refractive index in the surface layer but a much higher refractive index in the bulk of the material. This forms an intrinsic optical resonant cavity which can enhance the phase shifts and makes holography possible.

The next step is to develop a rigid thin film to overlay an LCD screen. The current version has pixels at least ten times too large to be practical for that application, so that’s another hurdle to overcome.

We’ve seen screens that shoot 3D images on movies like Star Wars for years. This isn’t it yet, but it is the next step. Imagine a phone, a wrist watch, or a contact lens that could generate a holographic image. Or a garbage-can-sized robot.

If your resources don’t stretch to the creation of real holograms, you can always create something that almost looks like one.

28 thoughts on “Holograms Can’t be Too Thin

    1. That video is deceptive.

      It’s not going to be a lifelike hologram that is visible to users at any angle or distance, rather, it’ll be a dynamic version of those holographic stickers from childhood that the author alluded to (holographic photography). The end result will be a 3D display which can provide a limited optical illusion of an object extending beyond the frame of the display, that can be viewed from a wider range of angles and is animated.

      What about colors though?

        1. Yes it does and they are wrong, at very best a screen can give a sense of depth within its display area.

          In addition they have not at any point created a dynamic holo-pixel that can be turned on or off by an electric signal their pixels are changed through laser ablation. This is purely a new media for creating a static hologram.

  1. I wonder if there is something here that can help the semiconductor industry. The first think I thought of was solid immersion lenses and maybe the materials here could provide an improvement.

    I also wonder if the industry could use this in testing and FA of chips to enhance the techniques involving IR lasers that are used today.

    1. IR? Semiconductor photolithography have (AFAIK) always used UV with current systems using 192nm DUV (Deep UV) while the next generation soon to be production ready is 13.5nm EUV (Extreme UV).

      1. Silicon is transparent to IR and the photons can stimulate the junctions. FA stands for failure analysis. Say a chip fails a test after fab and you want to know why. One technique involves using IR lasers (since silicon is transparent to IR) to stimulate junctions in the material instead of using electricity. I was wondering if this holographic technique could provide a finer focus onto smaller features in the chips.

        I don’t know if this holographic technique could benefit lithography. I don’t know if it can help get around the diffraction limit.

        1. Mea culpa. Shouldn’t reply when too tired to read and understand correctly :P

          Interesting question BTW, sadly don’t know enough to even begin to reason about it.

  2. I am seriously irritated by that video. Released by an university, it looks just as if it was produced by one of those viral video outlets that combine wild speculation with clickbait style headlines. “Screen size would become irrelevant. Information could be displayed outside of the device,” in the context of the technology they describe is, plain and simple, a lie.

  3. This is my personal fact check based on my knowledge, so some things might by wrong or actual research might by further developed than I know of.

    Written statements in that videos:

    0:15 “You don’t need 3D glasses to see it.”
    True, just like with every other type of white light / reflection hologram.

    0:17 “It overcomes size barriers faced by computer generated holograms.”
    Mostly untrue. If making the display thinner than 1µm is your goal, than it’s true. But that is actually a secondary if not ternary problem. Others are much more importanded than that.

    0:22 “And gets us to having 3D holograms in everyday devices.”
    Assertion. Can’t say how true that actually is.

    0:27 “The screen size would become irrelevant.”
    Untrue (absolut bullshit). See following explanation.

    0:29 “Information could be displayed outside the device.”
    Untrue (nearly absolut bullshit). See following explanation.

    0:33 “The next stage would be to develop a rigid thin film – ”
    Probably true, since I can’t check, because I’m not affiliated with the researcher.

    0:37 “that can be laid on an LCD screen to enable display.”
    Half true, since the ability of displaying a hologram on an LCD relies mostly on the pixelsize of said LCD. The developed layer on top of the LCD can make the display thinner, but is not needed for all types of LCD (depends on the type of the LCD).

    0:42-0:45 “We are now closer to a science fiction world, where hologramsare part of our every day.”
    Irrelevant. Every day that people think about how to create holograms brings us closer to that “science fiction world”. Marketing cant.

    0:47 “The possibilities are endless.”
    Irrelevant. Totally marketing cant.

    First. How does a hologram work from an observers perspektive?
    Imagene a small white spot on a dark canvas. Light hits the spot and is scattered. The reflected light propagates outwards as a sphere with increasing radius carrying phase and amplitude information. All human visible information of an object is transfered through such spheres of light. In our example a human eye can focus an that bright spot. Through training (learning) a human knows at what distance the spot he/she focuses on is relative to the eye (focus is one important depth cue if don’t want to to feel seek, which is a short coming of current consumer grad 3D displays).
    All an observer can see are these spheres. Or discribed as rays: divergend light rays. So all a hologram has to do is recreate those spheres / divergend rays of light. And as people might gues at this point: That’s the actual hard part!

    But holograms on film excist for multiple decades now. However these have fringes smaller than the used wavelength. So to recreate these you need pixels smaller than the wavelength of the used light (450nm for blue light and a size of lambda/2 if you want your hologram to recreat the wave fronts for the entire half sphere in front of the display). Creating an LCD with these pixel sizes is actually technically possible and was done in the past. However an object or a surface part of an object recreated by a hologram can only be seen inside the cone created by the display surface and your eye. That’s the absolut bullshit part of that marketing video. The size of the display matters, because the display is the window to the recreation the hologram produces.
    But why is the hologram only recreating the parts that are inside this cone?
    Well it’s fairly easy if you think about it. To see something light needs to reach your eye. But where is this light coming from? From the display! This light is created inside it and needs to go through the surface of said display to reach your eye. Since normal LCD can’t create light in front the LCD / outside the LCD only parts inside said cone can be recreate through such a display.
    The only technology I know of, that can create light in front of it (visible at an angle of 90 or more degrees to the “display”), is a focused high power laser beam, which creates spheres of plasma, which produces light. However this technology is neither portable, since high power laser aren’t small just like high power energy sources, neither is it a good idea from a safety perspective to shoot high power laser from a handheld device around.

    Why do I comment “Untrue (NEARLY absolut bullshit)” on the videos claim “Information could be displayed outside the device.”?
    Well this sentence and the nice computer generated images are creating the impression that the display is capable of somehow creating something in front of the display, which can be seen outside the region occupied by the display (said cone). Which is cleary wrong as discribte above.
    Than why do I say “nearly”?
    Because It’s technically true, that “information could be displayed outside the device”. Objects can be recrated everywhere inside said cone. And that cone starts at the observer’s eye, which are obviously outside the device. So this information can be made to appear outside the device, while in truth it’s generated inside the display. So whether you want that statement to be true or wrong depends on what that “information” means to you. If that information is a recreated object, which is made to appear in front or behind the device, than that statement is true. If that information is the light leaving the display encoded with a specific phase and amplitude, than that statement is wrong, because that light is allways created inside the display.

    Well, that’s the reason why I hate these kind of computer generated images. Current technology just can’t recreate the impression these videos create.
    HOWEVER I can understand why ALL producers of holographic use these kind of “tricks”, because none holographic displays just can’t recreate the impression such a display would create. And this video is cleary made for a normal display, not a holographic one. If this video would show how a true holographic display would look like, filmed with a normal camera and display on a normal display it would look like a window for objects purely behind the display and would look extremly off, because object in front of the display would be clipped to the visible surface area of the holographic display. Object in front of such a display would appear and disappear, when they pass through said cone.

    Why don’t we have holographic displays, if all I said till this point is that this technology can be produced today?
    Well it’s true that a display with pixels small enough could be produced today. However these wouldn’t be of usable total size. For a small smart watch this might be ok, but even for a smart phone these displays would be to small much less a laptop screen or big entertainment tv. Displays of usable size can’t be reliable produced with such small pixel sizes. And even if that would be solved, there’s allready the next problem:
    Imagine a small display of 10x10cm² with a pixel size of 250nm. Well that would be 40,000 pixels just allong one direction or 1,600,000,000 pixels or 1.6 billion pixels in total! As a comparison a 4K display (4096×2160) has only 8.8 million pixels. For all of these pixels you need to compute the pixel value (1.6 tera flops, if each pixel would only require one floating point operation), probably temporarily store the pixel value (4.8 giga byte for a single frame at one byte per rgb channel) and transfer and refresh each pixel on that display (1152 giga bits per second at 30 frames per second and one byte per rgb channel). And now imagine how many pixels / flops / ram / bandwidth you would need for a normal tv!
    So unless you find and excessively use every trick you can think of to reduce that requirement it’s impossible to produce a holographic display with todays technology. However there are tricks and compromises, which actually allows one to buy a holographic display today (if you got enough money). For one example of such a requirement reducing trick is to recreate the hologram only where it is needed – being the pupil of the observer – instead of the full half sphere in front of the display (whether something like that deserves to be called a “hologram” or even “true hologram” is up to you).

    Why is this development still a step further to consumer available holographic displays, even if that video is utter marketing bullshit?
    Well if you think about the efficiency of current LCD technology, than they all suck. They need light of defined polarization to be able to switch light on and off. That is done by a polarizer on unpolarized light, meaning half the genereated light is absorbed in that polarizer. And then you can only modulate the amplitude. Other types of displays can modulate the phase of the propagating light, but these were thick to achieve the needed phase shift. The researcher work can change that now and produce thinner devices. However this would be phase modulation only. Ideal for a holographic display would be both phase and amplitude modulation.

      1. Yep, that’s what I talked about, when I said “the only technology, being able to create light in front of it”. These “Fairy Lights” seem to be a good step to the right direction. However even if they are “safe to touch” (as long nothing goes wrong), there is still the concern about eye safety. An intensity / energy “safe to touch” is still enough to blind you.

  4. The fake gimmickry I keep seeing from dishonest marketing sheisters really annoys me. This is what a screenshot from that video looks like before and after cropping out the fake crap:

    And worse, that large menu hovering over the tiny watch display is just too much. Most 3D display companies have been guilty of this fakery.

    1. Viewing a hologram is like looking through a window, where the window is the size of the phone (or watch) display. It is important for 3D content to not extend anything through the display that would get cropped at the edges. With a true hologram this would be even worse. They only way to view that scene in the screenshot above is straight down, where you will see only building roofs, not sides.

      1. Thank you for recreating how a real hologram would look like in that given example.
        Yes the surface of the display is like a window. However your statement about “the only way to view that scene is from above straight down” is wrong, as your corrected image clearly shows. You can look at it at a slight angle. But you can’t look at it at 90 degrees to the surface normal, because your your viewing windows gets smaller when look at from the side. At 90 degrees you can’t see the surface anymore and therefor no hologram.

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