Sep 15, 2015

Designing Irregular Light

posted by Bryon Moyer

Light_image.pngSynopsys recently announced their latest update to their LightTools optical design suite, which we’ve looked at before. The… um… focus (sorry) of this release appears to be on irregular light patterns and behavior.

Any of us who dissected a flashlight as a kid likely understands that the light beam is round because the the “lens” (that cheap piece of flat plastic) is round that reflector thingy in the back is round.

So what if you want something that’s not round? What if you want something irregular, even organic? Tools have been able to handle that, but they require that you set up thousands of parameters to get it to work.

What Synopsys has done with this release is allow users to abstract those parameters to a few higher-level ones, like specifying the light source and the desired illumination pattern. The latter, of course, if it’s a complicated shape, can still be complex to define, but apparently it’s far easier – and more intuitive – than what has been required to date.

Because you can specify any shape under the sun, these are referred to as “freeform optics.” The lenses can end up with some strange shapes, but the good news is that the tools calculate the shapes from the specified higher-level characteristics.

The lenses and reflectors we’re mostly used to are smooth and continuous. But that’s not been the case for a particular class of light, originating with headlamps on cars. Their design challenge is to create a bright spot on the road and illuminate signs and other features – and wild animals – without blinding oncoming traffic.

So faceted reflectors have been used in this application. Instead of being continuously curved, you can think of these reflectors as being piecewise curved: except at the facet transitions, each point is on a flat surface. The shapes, angles, and positioning of the facets are what determine where the light goes.

So the driver’s side headlamp cuts off the top of the beam to limit how much it hits an oncoming driver. The passenger side light, however, is allowed to shine higher since there are no oncoming drivers on that side, while there are street signs. Such lights are also used for streetlights and architectural lighting, both situations where you might want to control the placement of light.

The latest LightTools release allows designers to specify the desired light spread for different facets and have the tool design the reflector.

Meanwhile, it turns out that phosphors used in LEDs have temperature-dependent properties. The latest LightTools now models that behavior so that lighting can be designed to deliver as promised across temperature.

And finally, while many common materials have scattering properties that LightTools understands already, they’ve now added the ability to specify custom scattering – useful for new, proprietary materials. The custom scattering algorithm is compiled into a DLL, so performance is not significantly diminished from scattering algorithms that the tool supports natively.

You can find more in their announcement.


(Image courtesy Synopsys)

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Sep 10, 2015

The Internet of Lightbulbs

posted by Bryon Moyer

iStock_000016897113_Small.jpgBased on a solution just announced by CSR (now part of Qualcomm), you can outfit your new building with lights – and your network will be in place.

OK, they’re not positioning it to replace your Ethernet plant, perhaps, but it could become part of the network. They do this by making each LED lightbulb fixture also a Bluetooth mesh node. In case you missed the news early last year and are objecting that Bluetooth doesn’t have a meshing feature, you’re right – the standard doesn’t. CSR has overlaid the capability in a proprietary offering.

The lighting solution they’re announcing now provides both Bluetooth beacons – supported by the standard – and meshing. They set up and manage the beacons using the mesh; once up and running, the beacons operate independently of the mesh.

But this does raise some questions – especially as Greenpeak founder and CEO Cees Links questioned Bluetooth mesh latency in a conversation we had at Imec’s ITF in Brussels early this summer. The point being that, you might be able to create a mesh, but would it have characteristics that make it useful? Apparently folks tried to mesh WiFi at some point… and that has not become a thing. A reasonable question…

So I asked CSR for some more detail on their latency. And this resulted in a broader explanation of how they handle meshing.

They do what they call “flood meshing” instead of routed meshing. In other words, they start a message going and it follows all routes until a time-to-live flag expires, indicating that a particular trajectory has involved too many hops and should just stop. Presumably, at least one route will take the message to its intended receiver. Nodes keep track of messages they’ve received so that the flood doesn’t reverse.

This is actually more nuanced than it sounds. For power reduction purposes, each node in the mesh wakes up occasionally to see if there’s any message. This means that, at any given time, some number of the nodes in the mesh will be asleep and miss the message. So this flood doesn’t actually cover all nodes – just the ones that happen to be awake at the right time.

To increase the likelihood that nodes can pick up the message and run with it, each node advertises the message on 3 channels 6 times. You can ask for an acknowledgment, but it’s not required. The design of the mesh and the specific timing have to balance the likelihood of at least one node listening at any given time against the power required to listen. Obviously, the denser the network, the better your chances of your message propagating.

A network is protected by an overall network key, keeping networks from leaking information into each other (presumably). A network is also a virtual entity overlying the specific devices – meaning that an individual light bulb, in this case, could participate in more than one network.

And as to that original latency question, best-case single-hop latency is around 15 ms. From a quick check on my part, this doesn’t seem too different from Zigbee. They’re a bit hard to compare directly, since Zigbee uses routed meshing, and may need to request a route before sending a message – which adds to the latency for such instances (routing tables presumably make that necessary only for new destinations). But delivery in the range of 15-100 ms or so doesn’t seem unreasonable for either one.

You can read more about their lighting solution, done in conjunction with SK Telecom, in their announcement.

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Sep 08, 2015

Nanoimprint for Photonics

posted by Bryon Moyer

EVG_SmartNIL_Full_Area_UV_Nanoimprint_Lithography_Wafer_red.jpgWe’ve talked about photonics before and we’ve talked about nanoimprint lithography (NIL) before. Creating silicon photonics features requires masking, which requires lithography, and so it might not be a surprise to hear that all different kinds of lithography techniques – including NIL – were being explored for photonics.

Which is how I went into a discussion with EV Group at Semicon West. But that’s not what the story is at all. This is not about patterning resists to pattern silicon for silicon photonics – this is about building photonics structures directly out of… various other non-silicon materials, using imprint as a direct patterning approach.

I can’t help but think about NIL as if it were printing vinyl albums. Which are black. (Except a few novelty ones.) Even if printing resist, any resist I remember seeing way back in my fab days was distinctly not transparent. So picturing these materials as conduits for light is something my brain, well, resists.

But it’s apparently true: many of the materials available to be imprinted happen to be transparent (at suitable wavelengths). So you can build the conduits right on the surface of the wafer – no further etching required.

EVG notes that there are a number of high-volume apps for NIL these days:

  • Polarizers
  • Patterns for extracting more energy out of LEDs
  • Biotech (they can’t say specifically what)
  • And… one more big one coming that they also couldn’t talk specifically about.

Meanwhile, they’ve also teamed with Leti in a so-called INSPIRE program to further develop techniques and applications for NIL. You can find more about this in their announcement.


(Image courtesy EV Group)

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