字幕表 動画を再生する 英語字幕をプリント You already know that I'm an engineer and I'm really passionate about holography. I believe this will be the technology of the future, and I would love to talk a little bit more about it. When people hear what I do, they usually ask me about Tupac's hologram and I'm really sorry to tell you that this is just an optical illusion, which has nothing to do with true holography. The way it works is that you have a thin sheet of glass that both transmits and reflects light, so when you look into it you see the people standing behind it, as well as Tupac's reflection. I mostly know holography from reading, — research papers, PhD dissertations — and in fact, I wanted to know a bit more about it. So I made a Google search — the most popular thing I guess. And I was shocked to realized that a lot of people who claim that they developed a novel holographic technology were not making holography in the scientific sense. Of course these technologies exist and they are quite impressive, but, for instance, a 3D display is just a 2D image projected onto a cylindrical surface. As you walk around, you have the impression that you are seeing a person from different perspectives but is nonetheless a 2D image. So what is holography? I like to think about holography as playing with light. And you probably heard somewhere that light is a wave. What does it mean for us? I like to imagine the situation by looking at water waves. As you make a ripple, it travels outwards in a circular manner, if you make two ripples at the same time, you can see that these two waves overlap and form a certain pattern. You will soon realize that there will be some places where water doesn't seem to move at all. And in some places we have a large oscillation. A few words for clarification, water waves are quite big and easy to see, however, light is a very small wave, is as small as one hundredth of a human hair, and it oscillates very, very fast, as fast as 500 billion times [per second]. What does this have to do with holography? Imagine that you have an array 1,000 X 1,000 of small slits and you can open and closed them in any way you want. What you can see on the screen is a sample hologram which is just an array of black and white squares. Black means a closed slit and white an open one, Each open slit will create a new small wave and since there's loads of these waves they will overlap in some way and form a pattern on the screen. What we are doing here is we're telling light that it should appear in certain places but not in others. I should say a few words about the hologram generation. As you can guess it's a pretty complex operation, and in fact, about ten years ago, you would need a supercomputer to do the calculation within a reasonable time frame. Now you probably don't realize, but most of you have a super computer at home. And it's called a graphic card. Graphic cards can do operations much faster than processors and do them all in parallel. We said something about holograms — how we generate them — now I'm going to tell you how we display them. First of all you need a source of light which is laser. That laser beam illuminates the micro display and later on we project the image onto the surface, The angle view depends on the type of lens you use, and in fact in my research, we use a simple ball of glass, that gives us a very wide angle but produces a lot of blur in the image. What is blur? This is the ideal image, and I'm going to show you two types of blur, one of them is called defocus; — for instance, it happens when the lens is slightly misplaced from its position — and the other type of blur is called coma and the name comes from the fact that the point seems to have a tail like a comet. But as I have already said, in holography, we design the wave, we tell light how it should behave and in fact we can correct that. In order to do that we use special functions called Zernike Polynomials, and to correct the defocus aberration, we use a Third Zernike Polynomial which looks like that. In fact, every single aberration has a Zernike Polynomial associated with it that corrects it. We need to know an odd proportion to combine the aberrations, and the way I approached the problem is, I used the webcam in order to measure the aberrations. Let's have a look at the results. What you should see here is a grid of points, and as you can see this is quite bad. In the corrected image, in fact most of the points are small and circular. Next one is a page of a text and if you try to read this, you'd probably have a hard time. But in the corrected version, most of the text can be read. Let's proceed to 3D holography and wonder what makes us see things. Imagine you see the tiger, you see it because the sun illuminated it and the scattered rays somehow ended up in your eyes. Imagine we are able to reproduce the same set of rays that the real object would produce. And in that case, you would see a three dimensional tiger behind the display. Now, when I was younger, I was interested in computer graphics and programming, and this added definition is slightly closer to my heart. What you should see here is you take every single point in the image and you focus it at different distances and that's precisely how you create a 3D hologram. How does it look like? At this point I was focusing the camera at different depths, and you can see how different parts of the image go in and out of focus. I have another — —whoops, sorry! — So, what you should see here is that we have different letters at different distances; it should read TEDxWarsaw. This is the experimental set up where we viewed the hologram. With a source of light, which is a laser diode, two lenses expand the beam, and as you look into the micro display, you see a three dimensional object. OK, I'm afraid the video didn't really work, but — what you can see here is that we were moving our viewpoint and in fact, this situation is somehow similar to approaching a platform [while] on a train. The platform itself moves very, very fast, the trees, some distance away, move by a small amount, and the sun in the sky doesn't seem to move at all. And that is precisely what is happening here. You've seen some basic properties of 3D holograms. However, these holograms were pretty simple, and at this point I'm going to show you what a lot of resources and computer power can do. This system can display a 3D image that is 14 centimeters in size and does that in real time, meaning 30 times a second. However, the system is pretty expensive and requires a lot of computers in order to produce the image. However, researchers all over the world are working in order to shrink the system, improve the image quality and make it available for everyone.