Flat lenses made of nanostructures transform tiny cameras and projectors | Hacker News Reader

Flat lenses made of nanostructures transform tiny cameras and projectors

spectrum.ieee.org

113 pointslutrinus24 comments

Speaking of Fresnel lenses, one of the coolest applications is a plastic "wide-angle lens" sticker that you could affix to your car's rear window (https://www.amazon.de/-/en/WIDE-ANGLE-WINDOW-FRESNEL-OPTICAL...) to increase the field of view. Their popularity has dropped since the advent of "back-up cameras" however.

Be careful with this, you can start a fire with fresnel lenses at the right angle in direct sun...

This reminded of salt grain size cameras

https://engineering.princeton.edu/news/2021/11/29/researcher...

https://light.princeton.edu/publication/neural-nano-optics/

Therre's a diagram in TFA, comparing the construction of a conventional lens with a metalens.

The diagram shows two labelled parts that I didn't understand:

a) Glass plate with bandpass filter

b) Near-infrared contact image sensor

The legend doesn't say, but I suspect the diagrams show a distance sensor, not a camera. So I assume the infrared lasers have been omitted from the diagram. Also, I'd quite like to know a bit more about the optical bandpass filter. I suppose any "transparent" material is effectively a bandpass filter; this one presumably passes near-infrared, so is it like the dark-red plastic filter on a TV remote?

Why's the sensor called a "contact" image sensor?

Optical bandpass filters are used to fine-tune the bandwidth of the sensor, as most sensors actually have pretty wide bandwidths. Typical silicon sensors have sensitivity extending well into the IR, which can confuse people when their pictures show lights they can't see. This can totally be made using something like the dark-red filter on the TV remote (reversed, it'd block red so appear blue), but fancier ones will use thin-film coatings to achieve steeper roll-offs. I don't see how meta-lenses are supposed to achieve this effect. They may use absorbing substrate, or may add a backside coating.

Contact image sensors are image sensors designed to be slapped right up against something. They're used in scanners and surface inspection sensors. No clue how this relates to meta-lenses.

I suspect it's just a bad diagram. Their barrel design is impossible to manufacture.

Source: Optical engineer.

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10...

https://en.wikipedia.org/wiki/Contact_image_sensor

> They may use absorbing substrate, or may add a backside coating.

Yup, since the optic is planar it can integrate with backend coating processes

> Contact image sensors ... No clue how this relates to meta-lenses.

I'm also not sure how "contact" got into the copy

> I suspect it's just a bad diagram. Their barrel design is impossible to manufacture.

Yea, the barrels end up looking like more traditional barrels

Source: Metalenz CTO

Neat, thanks for the reply! Impressive tech you've got.

The key is this statement buried in the paper.

   The process starts by illuminating a scene with a monochromatic light source—a 
   laser.

What that means is that this only works with monochromatic light. The focal distance would be different for each wavelength. That's why it's useful for laser range finding. You would need to illuminate with several different lasers to get a "full color" image, and likely have multiple lenses... although some are tunable.

So it's not gonna work for standard glasses, current VR or anything else like that.

When will we get thick spectacles in impressively thin format?

Thin, frenzel-free VR goggles in the future then?

Seems like one of the obvious applications. I wonder why it isn't mentioned. Is there a technical limitation that make it impractical? Size maybe, the lens shown in the article are all tiny and I guess lens that would be practical for AR/VR would be really expensive.

> Is there a technical limitation that make it impractical?

Yes. Diffractive optics (which includes meta-lenses) have significant wavelength dependence. Visible light is 400-700nm, which are different by about a factor of 2. This means blue light will focus almost twice as far away as red light does.

The neat bit is this is actually the reverse of how refractive optics behave, which means you can use both together and cancel out a significant portion of chromatic aberration. If we can scale up the manufacturing (and ideally apply them to curved surfaces) they could improve performance and reduce complexity and weight of VR/AR optics.

Will this work for spectacles?

Not right now. Sounds like they are working on lenses that could one day work with colored light for cameras. Maybe after that, they could be used for specials?

This article describes how nano metalenses work and what they can be used for.

Spoiler alert: they can't be used to replace your smartphone's camera lenses yet, but can be used for IR distance sensors used on drones and soon, polarization sensors that will be able to tell materials apart and even detect cracks in concrete.

> polarization sensors that will be able to tell materials apart

Video of Gavin Smith explaining polarization with a neat mechanical/visual demonstration: https://youtu.be/9SAzxlF57mc?feature=shared&t=128

Not sure if he ever made the camera.

I wonder if this has applications for sensing in self-driving cars.

AI-equipped cars with a real sense of feeling in their tires. It’ll be like the sensation of touch for them. Everything they run over, they will feel. Make them learn that animals feel gross to touch. Make them feel remorse for running over a human. Boom! Self-driving safety solved!

This opens the door to kinky AI

Yeah that’s exactly what we need.

An AI that calls us “daddy”

That can’t possibly go wrong. Nope.

Door already wide open: https://www.reuters.com/technology/ai-chatbot-company-replik...

> feeling in their tires.

Ignoring the rest...

I feel like this would be much easier to accomplish with acoustic sensors and wheel/suspension telemetry, given that an attentive human driver can sort of "feel" the road surface already.

One step closer to a tricorder.

can you make an optical camo with this?

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