Moore's law for CMOS computers is still continuing, but its near-future saturation is now being discussed. One of the serious saturations is about its latency. The computation delay for a CMOS transistor is already saturated above 10 ps, which will be problematic when ultralow-latency response is required for broad-band data streams, even with parallelization or pipe-line processing. We regard that optical circuits may serve as ultralow-latency computation circuits if they are small enough and tightly combined with electronic circuits. The former requires nanophotonic devices/circuits and the former requires OE/EO conversion with ultrasmall capacitance.