What does the term 'optical gain' refer to in opto-electronics?

The term 'optical gain' pertains specifically to the increase in optical power that is achieved through amplification processes in opto-electronic devices. This phenomenon is critical in various applications, such as lasers and optical amplifiers, where the goal is to boost the strength of an optical signal.

In practical terms, when light passes through a medium that has been excited (for example, a gain medium in a laser), it can emerge with greater intensity than when it entered. This amplification can result from stimulated emission, where incoming photons stimulate the release of additional photons, effectively increasing the overall optical power.

In contrast, the other options refer to different concepts. The ratio of light output to electrical input describes efficiency rather than the process of gaining power. Loss of light intensity during transmission relates to attenuation rather than amplification, and the amount of light scattered refers to how light is diffused rather than enhanced. Thus, the concept of optical gain is fundamentally linked to the amplification of light, making it an essential principle in the field of opto-electronics.