Photonic neuromorphic computing (using light to do neural-network math) promises big speed/energy wins, but there’s a catch: training has almost always happened in silico. You build a digital model of the chip, train it on a GPU, then transfer the weights to the physical device. That approach:
- Requires an accurate physics model of every component (expensive to build and validate)
- Breaks down when fabrication imperfections make the real chip deviate from the model.
- Doesn’t scale well as circuits get larger and more complex.
What INSPIRE does.
INSPIRE (IN-Situ Physical gRadient dEscent) is a general on-chip training method for photonic integrated circuits. The key mechanism is on-chip synthetic time-reversal holography — essentially exploiting optical reciprocity so that the physical system itself generates the gradient information:
1. Forward pass: light propagates through the circuit carrying your input.








