Describe the purpose of an optical isolator.

An optical isolator serves a crucial purpose in laser systems by preventing feedback, which can lead to instability and performance issues. In laser applications, unwanted light that reflects back into the laser cavity can cause fluctuations in the output laser beam and can potentially damage the laser source. By allowing light to pass through in only one direction while blocking any light traveling in the opposite direction, optical isolators help maintain the integrity of the laser's output, ensuring consistent performance and stability. This characteristic is essential in a variety of applications where the reliability of the laser source is critical, such as in telecommunications and medical devices.

The other choices relate to functions that are not primary purposes of optical isolators. While enhancing signal transmission and filtering out unwanted frequencies are important in optical systems, they do not describe the specific function of an optical isolator. Additionally, amplification of laser light pertains to different devices, such as optical amplifiers, rather than to the isolators themselves. Thus, understanding the correct role of an optical isolator is key in both designing and working with laser systems effectively.