Comment by danpalmer
4 days ago
This sounds impressive, but this bit stood out to me:
> This process works by sending a tiny bit of the optical signal to a photodiode that measures how much optical power is there.
It seems that the benefit of the approach in general is to keep compute in optics, because crossing the optical to electrical boundary takes too long. But then in the middle of their described process is a boundary transition.
How is this so different to the CMOS/CCD boundary? Is a photodiode that much quicker to activate that it doesn't matter?
I'm sure you'll get a better answer eventually but yes photodiodes are widely available that have sub-nanosecond response time, and the output could potentially be used in its raw analog form do whatever modulation they are describing.
Edit: Turbo encabulator description from the paper linked at the bottom:
>To realize a programmable coherent optical activation function, we developed a resonant electro-optical nonlinearity (Fig. 1(iii)). This device directs a fraction of the incident optical power ∣b∣2 into a photodiode by programming the phase shift θ in an MZI. The photodiode is electrically connected to a p–n-doped resonant microring modulator, and the resultant photocurrent (or photovoltage) detunes the resonance by either injecting (or deplet-ing) carriers from the waveguide.
... and a couple of notes on the observed latency later in the paper
>We experimentally characterized the computational latency of the NOFU in this mode, finding that the response time for carrier injection was shorter than 100 ps and that 75 μA of photocurrent was sufficient to detune the resonator by a linewidth, corresponding to a static power dissipation of 60 μW.
>As our architecture computes entirely in the optical domain and is integrated onto a single photonic circuit, inference latency is limited only by the optical time of flight through the chip