4 ms·

Chip-scale blue light phased array

59 points by WaitWaitWha 6y ago

cryptonector 6y ago
Solid state LIDAR?
ISL 6y ago
Very cool. OSA press-release here: https://www.osa.org/en-us/about_osa/newsroom/news_releases/2020/chip-based_device_opens_new_doors_for_augmented_re/ https://www.osa.org/en-us/about_osa/newsroom/news_releases/2...
phkahler 6y ago
>> Large-scale integration of this platform paves the way for fully reconfigurable chip-scale three-dimensional volumetric light projection across the entire visible range. That's what I thought. Do this a wafer-scale and you have a fully holographic display. Curious how they phase synchronize so many light emitters but the full paper looks like $$
- ambicapter 6y ago
  When you say holographic display do you mean, projected in thin air? How would that even work?
  - sp332 6y ago
    No, like a normal hologram, but this one can be animated by changing the light coming from it. https://en.m.wikipedia.org/wiki/Holography#How_it_works https://en.m.wikipedia.org/wiki/Holography#How_it_works
- hwillis 6y ago
  > Curious how they phase synchronize so many light emitters but the full paper looks like $$ I sent a request on their researchgate: https://www.researchgate.net/publication/339277200_Chip-scale_Blue_Light_Phased_Array https://www.researchgate.net/publication/339277200_Chip-scal... There's only a single light emitter, a fiber laser that feeds the device. That's split in treelike fashion. At each branching part, there's an optical resonator that ensures light is fed evenly to each branch. Each branch has its own phase delay, which requires a bit of software tuning to account for variations.
mysterEFrank 6y ago
Awesome, this could enable cheap high-resolution 3D displays
madengr 6y ago
With an aperiodic spacing, I wonder how high the grating lobes are? The paper is paywalled.
- mNovak 6y ago
  Being aperiodic should mean there's no well defined grating lobes. Basically each emitter pair has a different spacing and thus different grating lobe location, so across the whole array they get smeared out to an even sidelobe level. But yes, wondering what the mainlobe contrast is.. it's also >lambda spacing so the efficiency is probably poor.
hwillis 6y ago
This is quite a cool paper. I haven't read the full thing yet, but any talk of displays is EXTREMELY premature. This isn't even one pixel- it's steerable in only one direction. In order to steer in two directions, you'd need to stack up hundreds of these. That would give you a pixel... one that's at least a millimeter wide, or 10x wider than a color block on the screen I'm typing this into. Certainly it would be incredibly expensive to make an entire display out of this. It's even pretty premature for lidar- for safety reasons lidar is in the infrared, usually around 1 micron wavelength, which makes a big difference in terms of manufacturability and price. One of the biggest problems for solid state lidar is the beamwidth, which can be a couple degrees or even >10 degrees in some cases. This is .17 degrees, which is a fantastic result, but still quite large compared to conventional lidar. Top end lidar has angular resolution below .1 degrees and you can integrate data over time to find edges as sharp as the beamspot, which can give you some really insane precision. If we used this system, the intense blur over the spot would require deconvolution and strongly limit precision. Back of the envelope math: at .75 m (2.5'), .17 degrees between pixels would give you ~2.25 mm pixel pitch. Even at that distance, the blurring will be intense- the middle picture here[1] is semi-accurate. Obviously fidelity wasn't the goal and this doesn't represent the limits of the technology! Don't give up hope. Just expect to see someone demonstrate something that exceeds the requirement for fidelity before it actually gets made into a consumer product. This paper has similar results to an MIT paper[2], but with 3x higher wavelength. Naturally, 3x higher wavelength way more than 3x harder. This device is also smaller- the MIT device is ~1 mm by .1 mm vs. ~1 mm by ~10 nm. That's mostly due to the fact that the MIT device can steer in two directions- the first direction works with phase shifters just like this device, but the second direction works by heating up the emitters so that they change size (genius). The device here basically just pipes laser light out through the side of the wafer, which syncs up excellently with the MIT approach. MIT used very long (500 micron) antennas that have a thin-thick-thin wavy pattern[3]; at each wide part (IIRC) refraction causes light to escape at a particular angle. Changing the length of the wide parts changes the resonance of the light inside and therefor the angle light escapes at, and that's how they did beamforming. Normally this would require atomically-perfect manufacturing, but the long antenna averages errors out (although you still end up with just under 1 degree of beamwidth). With a suitable intermediate layer you might be able to plug this work into the MIT antennas and get full steering without needing to stack arrays. This is all way better than current commercial solid state lidars, which mostly use rectangular patch antennas to project lasers. The optical properties of those systems are really bad. It's a shame there isn't more money in research like this, because it's necessary to make that final jump. [1]: https://en.wikipedia.org/wiki/Gaussian_blur#/media/File:Cappadocia_Gaussian_Blur.svg https://en.wikipedia.org/wiki/Gaussian_blur#/media/File:Capp... [2]: https://www.researchgate.net/publication/320235900_Coherent_solid-state_LIDAR_with_silicon_photonic_optical_phased_arrays https://www.researchgate.net/publication/320235900_Coherent_... [3]: https://spectrum.ieee.org/image/Mjc5NjU5MA.jpeg https://spectrum.ieee.org/image/Mjc5NjU5MA.jpeg

59 points by WaitWaitWha 6y ago

Solid state LIDAR?

ISL 6y ago

Very cool. OSA press-release here: https://www.osa.org/en-us/about_osa/newsroom/news_releases/2020/chip-based_device_opens_new_doors_for_augmented_re/ https://www.osa.org/en-us/about_osa/newsroom/news_releases/2...

phkahler 6y ago

>> Large-scale integration of this platform paves the way for fully reconfigurable chip-scale three-dimensional volumetric light projection across the entire visible range. That's what I thought. Do this a wafer-scale and you have a fully holographic display. Curious how they phase synchronize so many light emitters but the full paper looks like $$

ambicapter 6y ago
When you say holographic display do you mean, projected in thin air? How would that even work?
- sp332 6y ago
  No, like a normal hologram, but this one can be animated by changing the light coming from it. https://en.m.wikipedia.org/wiki/Holography#How_it_works https://en.m.wikipedia.org/wiki/Holography#How_it_works
hwillis 6y ago
> Curious how they phase synchronize so many light emitters but the full paper looks like $$ I sent a request on their researchgate: https://www.researchgate.net/publication/339277200_Chip-scale_Blue_Light_Phased_Array https://www.researchgate.net/publication/339277200_Chip-scal... There's only a single light emitter, a fiber laser that feeds the device. That's split in treelike fashion. At each branching part, there's an optical resonator that ensures light is fed evenly to each branch. Each branch has its own phase delay, which requires a bit of software tuning to account for variations.

mysterEFrank 6y ago

Awesome, this could enable cheap high-resolution 3D displays

madengr 6y ago

With an aperiodic spacing, I wonder how high the grating lobes are? The paper is paywalled.

mNovak 6y ago
Being aperiodic should mean there's no well defined grating lobes. Basically each emitter pair has a different spacing and thus different grating lobe location, so across the whole array they get smeared out to an even sidelobe level. But yes, wondering what the mainlobe contrast is.. it's also >lambda spacing so the efficiency is probably poor.

hwillis 6y ago

This is quite a cool paper. I haven't read the full thing yet, but any talk of displays is EXTREMELY premature. This isn't even one pixel- it's steerable in only one direction. In order to steer in two directions, you'd need to stack up hundreds of these. That would give you a pixel... one that's at least a millimeter wide, or 10x wider than a color block on the screen I'm typing this into. Certainly it would be incredibly expensive to make an entire display out of this. It's even pretty premature for lidar- for safety reasons lidar is in the infrared, usually around 1 micron wavelength, which makes a big difference in terms of manufacturability and price. One of the biggest problems for solid state lidar is the beamwidth, which can be a couple degrees or even >10 degrees in some cases. This is .17 degrees, which is a fantastic result, but still quite large compared to conventional lidar. Top end lidar has angular resolution below .1 degrees and you can integrate data over time to find edges as sharp as the beamspot, which can give you some really insane precision. If we used this system, the intense blur over the spot would require deconvolution and strongly limit precision. Back of the envelope math: at .75 m (2.5'), .17 degrees between pixels would give you ~2.25 mm pixel pitch. Even at that distance, the blurring will be intense- the middle picture here[1] is semi-accurate. Obviously fidelity wasn't the goal and this doesn't represent the limits of the technology! Don't give up hope. Just expect to see someone demonstrate something that exceeds the requirement for fidelity before it actually gets made into a consumer product. This paper has similar results to an MIT paper[2], but with 3x higher wavelength. Naturally, 3x higher wavelength way more than 3x harder. This device is also smaller- the MIT device is ~1 mm by .1 mm vs. ~1 mm by ~10 nm. That's mostly due to the fact that the MIT device can steer in two directions- the first direction works with phase shifters just like this device, but the second direction works by heating up the emitters so that they change size (genius). The device here basically just pipes laser light out through the side of the wafer, which syncs up excellently with the MIT approach. MIT used very long (500 micron) antennas that have a thin-thick-thin wavy pattern[3]; at each wide part (IIRC) refraction causes light to escape at a particular angle. Changing the length of the wide parts changes the resonance of the light inside and therefor the angle light escapes at, and that's how they did beamforming. Normally this would require atomically-perfect manufacturing, but the long antenna averages errors out (although you still end up with just under 1 degree of beamwidth). With a suitable intermediate layer you might be able to plug this work into the MIT antennas and get full steering without needing to stack arrays. This is all way better than current commercial solid state lidars, which mostly use rectangular patch antennas to project lasers. The optical properties of those systems are really bad. It's a shame there isn't more money in research like this, because it's necessary to make that final jump. [1]: https://en.wikipedia.org/wiki/Gaussian_blur#/media/File:Cappadocia_Gaussian_Blur.svg https://en.wikipedia.org/wiki/Gaussian_blur#/media/File:Capp... [2]: https://www.researchgate.net/publication/320235900_Coherent_solid-state_LIDAR_with_silicon_photonic_optical_phased_arrays https://www.researchgate.net/publication/320235900_Coherent_... [3]: https://spectrum.ieee.org/image/Mjc5NjU5MA.jpeg https://spectrum.ieee.org/image/Mjc5NjU5MA.jpeg