Comb generator

Lore & Background

The comb generator derives its name from the visual pattern of its output on a spectrum analyzer, which resembles the teeth of a comb. Internally, an optical comb generator is a resonant electro-optic modulator capable of generating hundreds of sidebands with a total span of at least 3 terahertz, limited by the optical dispersion of the lithium niobate crystal, and a frequency spacing of 17 GHz. Other constructions can be based on erbium-doped fiber lasers or Ti-sapphire lasers, often in combination with carrier envelope offset control.

Reader's Guide

Comb generators are most commonly used in broadband frequency synthesizers, where the high-frequency signals act as stable references correlated to lower-energy references; the outputs can be used directly or to synchronize phase-locked loop oscillators. They may also be used to generate a complete set of substitution channels for testing, each carrying the same baseband audio and video signal.

In RFI testing of consumer electronics, the comb generator's output serves as simulated RF emissions, providing a stable broadband noise source with repeatable output. It is also used during compliance testing to various government requirements for products such as medical devices (FDA), military electronics (MIL-STD-461), commercial avionics (Federal Aviation Administration), and digital electronics (Federal Communications Commission) in the USA. An optical comb generator can be used as a generator of terahertz radiation.