RP Photonics logo
RP Photonics
Encyclopedia
Technical consulting services on lasers, nonlinear optics, fiber optics etc.
Profit from the knowledge and experience of a top expert!
Powerful simulation and design software.
Make computer models in order to get a comprehensive understanding of your devices!
Success comes from understanding – be it in science or in industrial development.
The famous Encyclopedia of Laser Physics and Technology – available online for free!
The ideal place for finding suppliers for many photonics products.
Advertisers: Make sure to have your products displayed here!
… combined with a great Buyer's Guide!
VLib part of the
Virtual
Library

Modulation Depth

<<<  |  >>>

Definition: a relative modulation amplitude, or (for a saturable absorber) the maximum change in absorption

German: Modulationstiefe

Units: dimensionless or %

How to cite the article; suggest additional literature

When a quantity such as the transmission of an optical modulator is sinusoidally modulated, the modulation depth can be defined as the modulation amplitude (i.e. one-half of the peak-to-peak changes) divided by the mean value. A modulation depth of 100% thus corresponds to a situation where the minimum value of the modulated quantity is zero, and the maximum is twice the mean value.

modulation depth

Figure 1: A signal with a modulation depth of 50%. Here, the modulation amplitude is half the mean value.

In the context of saturable absorbers, the modulation depth is the maximum change in absorption (or reflectivity) which can be induced by incident light with a given wavelength. This is an important design parameter in passively mode-locked lasers. A large modulation depth leads to strong pulse shaping by the saturable absorber, which can lead to a short pulse duration and reliable self-starting, but also to Q-switching instabilities.

See also: saturable absorbers, semiconductor saturable absorber mirrors

If you like this article, share it with your friends and colleagues, e.g. via social media:

arrow