3 ms·

Agreed: how is this a "circuit"? How does the output drive the input of another one of these? It looks like this is just "shine a laser at a material to change

Agreed: how is this a "circuit"? How does the output drive the input of another one of these? It looks like this is just "shine a laser at a material to change it, and then use another laser to detect the difference."

adrian_b 4y ago
You can describe any transistor with the same words as "shine a laser at a material to change it, and then use another laser to detect the difference": "apply a voltage at a device to change it, and then use another voltage to detect the difference (i.e. to detect if a current passes)". This is an optical switch, like a transistor is an electrical switch. An optical switch that is not very efficient, because the transmission is varied only between 100% and 80%, but one that is very fast. It can be used in THz range mixers and oscillators.
- amelius 4y ago
  That's not a good argument. I could say: "Put a voltage over a resistor and use an ammeter to detect the difference" and make a resistor look like a transistor which it clearly isn't.
  - nullish_signal 4y ago
    The comment above yours said "and then ... detect the difference", implying sequential action and a real change of state - not simultaneous action+measure. """Because the laser pulse is so fast, the water can switch states in a matter of picoseconds, which are trillionths of a second.""" Although after reading, I must agree that the time-scale feels quite ridiculous!! (EDIT: RE: "Capacitors can't be logic gates" below - Maybe. But if 1+0=1, and 1+1=2, then surely differentiating 0/1 vs 2 on the output creates an AND gate?) (I am "posting too fast" with 3 posts in the last hour. Sorry :)
    - amelius 4y ago
      > implying sequential action and a real change of state - not simultaneous action+measure. Ok, replace resistor by capacitor :) I.e., run a current through a capacitor, then (some time later) measure the voltage over it. I don't recall anyone actually creating logic gates using capacitors only.
  - adrian_b 4y ago
    Not at all. In the definition of any controlled switch, e.g. transistor, optical switch or any other kind, it is essential that there are two distinct quantities, e.g. voltages or light beams, one that controls the output state and one that provides power to the output circuit. A resistor corresponds to a tinted window, not to an optical switch.
    - amelius 4y ago
      Ok, with that addition, here is another analogy: I have one battery that I use to charge a capacitor. Then I have another battery in my voltmeter, which I use to measure the voltage over the capacitor. How does this make it possible to build logic gates with capacitors? Instead of trying to generalize the principle, why don't you explain how you can make logic gates using the technology of the article? And how can you tie these logic gates together without the signal becoming weaker between input and output?
- dtgriscom 4y ago
  Note that in a transistor, "another voltage to detect the difference" can be used to trigger another transistor, and so on. Until the laser reading the state of water can itself trigger a write in another water "switch", this is just a cute dead-end phenomenon.

adrian_b 4y ago

You can describe any transistor with the same words as "shine a laser at a material to change it, and then use another laser to detect the difference": "apply a voltage at a device to change it, and then use another voltage to detect the difference (i.e. to detect if a current passes)". This is an optical switch, like a transistor is an electrical switch. An optical switch that is not very efficient, because the transmission is varied only between 100% and 80%, but one that is very fast. It can be used in THz range mixers and oscillators.

amelius 4y ago
That's not a good argument. I could say: "Put a voltage over a resistor and use an ammeter to detect the difference" and make a resistor look like a transistor which it clearly isn't.
- nullish_signal 4y ago
  The comment above yours said "and then ... detect the difference", implying sequential action and a real change of state - not simultaneous action+measure. """Because the laser pulse is so fast, the water can switch states in a matter of picoseconds, which are trillionths of a second.""" Although after reading, I must agree that the time-scale feels quite ridiculous!! (EDIT: RE: "Capacitors can't be logic gates" below - Maybe. But if 1+0=1, and 1+1=2, then surely differentiating 0/1 vs 2 on the output creates an AND gate?) (I am "posting too fast" with 3 posts in the last hour. Sorry :)
  - amelius 4y ago
    > implying sequential action and a real change of state - not simultaneous action+measure. Ok, replace resistor by capacitor :) I.e., run a current through a capacitor, then (some time later) measure the voltage over it. I don't recall anyone actually creating logic gates using capacitors only.
- adrian_b 4y ago
  Not at all. In the definition of any controlled switch, e.g. transistor, optical switch or any other kind, it is essential that there are two distinct quantities, e.g. voltages or light beams, one that controls the output state and one that provides power to the output circuit. A resistor corresponds to a tinted window, not to an optical switch.
  - amelius 4y ago
    Ok, with that addition, here is another analogy: I have one battery that I use to charge a capacitor. Then I have another battery in my voltmeter, which I use to measure the voltage over the capacitor. How does this make it possible to build logic gates with capacitors? Instead of trying to generalize the principle, why don't you explain how you can make logic gates using the technology of the article? And how can you tie these logic gates together without the signal becoming weaker between input and output?
dtgriscom 4y ago
Note that in a transistor, "another voltage to detect the difference" can be used to trigger another transistor, and so on. Until the laser reading the state of water can itself trigger a write in another water "switch", this is just a cute dead-end phenomenon.