Until photonic processors become cheap, and then it’s a keccak-256 ASIC. Silicon wafers at 90nm quality are already quite cheap, but actually, a photonic waveguide can be made out of doped glass or grown on any substrate. Also, the 3D integration possibilities are nearly endless. If there was a real economic demand for these processors, the cost would go to nearly zero. If you can figure out an actual hash with just…
Photonic chips for analog matrix processing are already being commercialized.
The underlying platform, CMOS Silicon Photonics is commercial already (in every data center) and produced in high volume.
Heavyhash can be constructed such that the Keccak hashes comprise a minimal amount of the work.
Quoting from the BIP:
"Below is a conceptual representation of a 3D-packaged oPoW mining chip. Note that the majority of the real estate and cost comes from the photonic die and the laser, with only a small digital SHA3 die needed (as opposed to a conventional miner of the same cost, which would have many copies of this die running in parallel)."