Which of the following modulation types is commonly used in opto-electronics?

The correct answer is amplitude modulation. In opto-electronics, amplitude modulation is frequently utilized due to its effectiveness in altering the intensity of a light source to convey information. This modulation technique involves varying the amplitude of the optical signal in relation to the input signal, which allows for the encoding of data such as audio or video signals.

Amplitude modulation is advantageous in optical communications as it can be easily implemented with light-emitting diodes (LEDs) and laser diodes, which can rapidly adjust their illumination levels. This ability to manipulate light intensity is fundamental in optical fiber communications, where data is transmitted through changes in the optical signal's strength.

While pulse modulation and digital modulation are also used in various contexts within opto-electronics, amplitude modulation remains a staple due to its simplicity and effectiveness in a wide range of applications. Constant modulation is not typically recognized as a standard modulation type in opto-electronics, as it does not involve any variation in the signal to carry information.