I believe the problem with optical chips is the limitation presented by the wavelength of light: 400 nm (violet) to 750 nm (red). The transistor size on current integrated circuits is typically 7 nm; IBM have manufactured ones as small as 2 nm. Those sorts of dimensions are only accessible to soft X-ray photons with an energy of around 160 eV or higher. Therefore, optical chips that depend on visible frequency light would have a low gate density compared to electronic chips. There was research being done on optical holographic storage. Given a typical laser wavelength of 500 nm or so, the density achieved corresponded to 10^12 bits (1 Terabit) per cubic centimetre - last time I looked into it, anyhow. I'm not sure what the typical read and write access times were. However, I think SSDs can beat that technology in most respects apart perhaps from power requirements. Data centres appear to be moving toward SSDs from HDDs. I can stand to be corrected on my analysis.
