Mode hops are often provoked by external influences as laser case temperature, length drifts of the laser resonator, injection current and optical feedback. And as a matter of fact, mode hops often result from attempts to tune the wavelength of a laser. Let’s see here the two main causes behind laser mode hopping: temperature and injection current. Temperature The laser cavity can support many different wavelengths or longitudinal modes. In laser diodes, these modes are separated by typically 10 to…

Mode hopping is characterized by a stochastic exchange of power between two longitudinal modes of a laser, inducing a high-level intensity noise in the laser’s output. You can read more about why is laser mode hopping so bad for many applications in a previous article. We will review here why laser mode hopping occurs in semiconductor lasers. The mode wavelengths and the gain peak wavelength depend on the laser’s temperature: the mode wavelengths shift with temperature at about typically 0.06 nm/°C, while…

Semiconductor lasers have found widespread use in fiberoptic communications, entertainment (videodisc and compact disc players), merchandising (bar-code scanners), and in the scientific field as well (spectroscopy) thanks to their variety of wavelengths, compact size, low price and ease of control. Unfortunately some applications require a minimum degree of stability of wavelength that is not always met by semiconductor lasers, especially when mode hopping occurs. Before reviewing why laser mode hopping is so bad, let’s remember what mode hopping refers to….