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An LED is used for input of the photocoupler. On the other hand, various devices are used for output.
A phototransistor is a detector. Darlington type is also available.
There are products using photodiodes as light-receiving devices, output products such as logic, products with high-current output for gate-drive driving of IGBT and MOSFET, and high-function products such as isolation amplifiers.
A photothyristor or a phototriac is used for output. They are mainly used for control of AC line.
Photorelay (MOSFET output)
The photovoltaic array (photodiode array) drives the gate of the MOSFET to turn the output ON/OFF. By this operation, it can be used as a relay switch of MOSFET output.