Not clear to me where the novelty is in this... people have been doing similar stuff for ages, and the performance of the optics here leaves a bit to be desired as well.
Sure we can mass produce these, but we can also mass produce wafer-scale lenses, and in any serious application, a normal metamaterial lens would justify the higher cost with its performance
> In this study, we present a simplified method for fabricating visible Fresnel zone plate (FZP) planar lenses, a type of diffractive optical element, using an i-line stepper and a special photoresist (color resist) that only necessitates coating, exposure, and development, eliminating the need for etching or other post-processing steps.
That's just modern science no? The low hanging fruit has mostly been picked so advances are smaller and smaller, but we're doing more and more of them in parallel so the total advancement speed is still greater.
Seems like simpler fabrication but not sure why they can't just make a master and then stamp/pattern these at scale like how gratings are manufactured.
you definitely can and people definitely do this. There are arguments that stamp patterning is better suited for optics as well - specifically point defects seem to be less deleterious and that the feature shapes (not sizes) are more readily done via stamps. However, typically a lot of semiconductor manufacturing is viewed from an electronics perspective today, where stamping is definitely considered an inferior process.
It's a really smart idea to try to leverage the inherent scalability of semiconductor photonics. I think the use of a linear optical resonator to amplify a weak optical nonlinearity is quite genius, and something the relatively small nonlinear photonics community has been trying to do forever. That they showed this kind of 'all-optical-ish' nonlinearity on a relatively mature process in a foundry is nothing to scoff at, and likely one of the biggest results in semiconductor photonics in a while. At the single device level I think it makes so much sense, but what concerns me in general is how well this scales from a few perspectives:
1. resonators and device-to-device variance: in general it's pretty hard to get these resonant effects to line up with each other from a production POV, especially with large arrays. Silicon photonics has come far, but I don't think it has approached the level of uniformity as electronics. They have demonstrated some level of electro-optic tunability, which is the traditional solution, but they still need to leverage that for their nonlinear effects too.
2. area and space: the 'minimum' trace size of these planar photonics circuits is still quite large (~200 nm minimum feature size typically for these waveguides). This is essentially due to a minimum size needed to confine light within a waveguide which depends generally on the waveguide's refractive index and target wavelength. These are currently all integrated on a planar manner, so each channel becomes quite large, especially if now you also need a relatively large ring resonator, which in this case is at least ~100 micrometers or so in diameter
3. the combination of 1 and 2: high device-to-device variation, along with a large planar footprint means that these things are quite expensive and difficult to manufacture, without some kind of miniaturization benefit that you would typically get with electronics (at least not yet). This effect appears to be more than the sum of 1 + 2.
The planar footprint can be relatively easy be mitigated by just using a mirror and sending the next layer back to the same plane a few nanometers higher?
It is a solution to increase density, but this introduces significant integration complexity in addition to just increasing the overall cost. I think if this optical analog computer takes off, this kind of routing will likely be necessary
light speed isn't really all that good when you remember that information in your electrical circuit is traveling as fast (if not faster) than light in the medium in this case. Sounds good in marketing, but the key here is bandwidth, not 'speed'
Layman here. Isn't the big speed penalty in digital electronics the clock speed of the transistors changing state? Not the actual signal going down the wire from gate to gate?
certainly -- not necessarily the raw velocity of light, but the ability to augment other properties of light to increase the bandwidth.
Is it correct then to say that augmenting the other properties of light increases overall information density/capacity of light as a medium? whereas with electricity we only have 2D: amplitude & freq?
Information in an electric circuit travels along that circuit at ~0.9c. The physical light pulses that are running through the optical waveguides are more or less traveling at around ~c/n, where n is the refractive index of the material (in this case silicon, so n ~ 3.5).
the actual optical "packet" of information is traveling slower than the electric "packet". The key here is that the electric packet can a few bits, while the photonic packet in theory has a much larger bandwidth.
It's actually more confusing IMHO, because these graphs overload the radial dimension to show probability as "distance from the origin". You have to multiply that by the radial function to get an actual probability distribution, which kinda/sorta looks like these pictures but not really.
Really the harmonics are best understood as something like "wave height on the surface of a sphere". They tell you how the electrons (or whatever) are going to distribute themselves radially, not where they're going in 3D space.
Also FWIW: the much harder thing to grok here (at least it was for me), and that no one tries to tackle, is why the "l" number corresponds directly to angular momentum. In particular "l==0" doesn't look like there's any rotation going on at all.
Simply speaking, "l" describes the number of nodes. In the same sense that a particle in a box with sin(nx) wave function has more nodes the higher energy (or momentum) state it is in.
As for why l==0 has no rotation going on at all, one would say that this should be expected. Qualitatively, the symmetric sphere does not change with rotation, so how would we tell if it is rotating or not? And perhaps the next step is controversial, but if there is no way to tell, maybe there is no dependence? This is a similar argument to why the electric field of an infinite plane is constant with respect to distance from it.
you are correct. The Schrödinger equation for the hydrogen atoms in spherical coordinates demonstrates separability which allows you to separate the radial and angular coordinates. The radial term, which is most interesting due to the 1/r potential is typically a Laguerre polynomial. The angular term is 'free' from any potential is typically a spherical harmonic.
The spherical harmonics in general are typically derived as part of the solution to the Laplace equation in spherical coordinates. A bit of a semantic point (though perhaps the distinction is important) though, since the Laplace equation's angular dependence is identical to that of the Schrödinger equation for the hydrogen atom.
I'm not sure I understand. My knives are razor sharp (I keep a Shapton 1000 and 4000 on my counter along with a strop, my daily driver is a carbon steel I have to wipe down every time I cut a vegetable). They sail through the onion, but the sliced-up onion still splays out to both sides when I make the horizontal cut, and if you watch cooks doing it, it happens there too. What harm am I doing to the structure of the onion by doing it in the "wrong order"? They're the same cuts. The difference seems to be that in my order, the onion stays more stationary.
Don't get me wrong, I'm sure there's a reason everyone is doing it this way, because it's kind of clearly more annoying than the way I'm doing it?
the vertical cuts do not significantly the internal structure of the onion as each individual cut I make does not entirely sever the connection between the thin vertical slices I'm making. This means that I can do a lot of these, and not worry about harming the overall structural integrity. Then I make a single horizontal cut which does harm the overall structural integrity. This is not intrinsic to the horizontal cut itself, but the fact that I have both horizontal and vertical cuts.
If I start with the horizontal cut, again I do not signficantly harm the structural integrity of the onion. However, each subsequent vertical cut I make is now going to individually compromise the integrity of the onion.
With a sufficiently sharp knife, the single horizontal cut at the end does not really pose a significant danger overall.
This all being said I almost never do the horizontal cut out of pure laziness, and instead prefer to just do angled vertical cuts analogous to the video. They're never perfect but fine enough for me...
I still don't get why you need the horizontal cut at all. The diagram at the bottom of the blog post shows how unnecessary it is when you do the vertical cuts at a narrow range of angles like that (which I have been doing for a while now).
The point of Kenji's method (really, all radial-ish methods, but radial is strictly worse) is that you don't have to do the horizontal slice. If you slice vertically, you do --- you can see it for yourself, if you don't the dice from the edges of the onion are almost twice as big as the diece from the center.
Sure we can mass produce these, but we can also mass produce wafer-scale lenses, and in any serious application, a normal metamaterial lens would justify the higher cost with its performance
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