Hacker News Reader

Comment by denton-scratch | Hacker News Reader

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?

View on HN

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.

Reply on news.ycombinator.com