For signals to be switched, up to what frequency can be used?

For signals to be passed through the switch between the output terminals in a photorelay, the degree of damage on their waveform quality varies depending on the performances of C_OFF, the output capacitance when the photorelay is OFF, and R_ON, the resistance between the output terminals when the photorelay is ON (ON-state resistance). Products in a product series with these R_ON and C_OFF being small can even handle GHz signals. They can also be used for tester applications.