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In electronics, analog signal processing/computation suffers from parasitic capacitance which leads to slew rate—which is the maximum rate of voltage change allowed, so handling super-high frequency becomes impossible.

Is this still true for optical signal processing/computation, such as optical (frequency) mixer or optical frequency multiplier? If so, what would be the physics behind?

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    \$\begingroup\$ You might want to ask this question on Physics.SE... \$\endgroup\$ – Dave Tweed Nov 13 '15 at 18:19
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    \$\begingroup\$ You still need to convert between optical end electrical and there lies the problem. \$\endgroup\$ – user59864 Nov 13 '15 at 18:35
  • \$\begingroup\$ Isn't light an electro-magnetic wave? Speed of light (in material) is still affected by dielectric material E0 and magnetic permeability mu0. So there is still an equivalent slew rate. \$\endgroup\$ – MarkU Nov 13 '15 at 20:30
  • \$\begingroup\$ @MarkU I don't think that slew rate and propagation speed are directly related. \$\endgroup\$ – JimmyB Nov 13 '15 at 20:47
  • \$\begingroup\$ @hannobinder True, slew rate and propagation speed are different effects, but slew rate is directly related to capacitance. I don't see how light could avoid the dielectric material's effect on the wave's electric field. \$\endgroup\$ – MarkU Nov 13 '15 at 20:56
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Your question includes both the conversion (since you speak of processing) and light propagation. Conversion involves electronics, as @Nasha mentions, and thus is directly impacted by the slew rate.

Light propagation speed is reduced (with respect to that in vacuum) by the refractive index of the material. The physics causing the finite slew rate is also also causing the fact that the refractive index of the material is always greater than 1.

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