Optical heterodyne detection, also known as optical beating spectroscopy, refers to a technique used for detecting and analyzing the signals in optical communication systems. Some synonyms for this term include heterodyne detection, light beating spectroscopy, and optical beat detection. Other similar terms include opto-electronic mixing, optical frequency mixing, and optical phase locking. These terms all refer to the process of combining two or more signals to produce a new signal with a lower frequency, which can then be more easily analyzed or detected. Overall, these synonyms all describe the same basic concept of using optical signals to detect and analyze information in a variety of applications.