Parametric Oscillators and Amplifiers
Created | Updated Oct 10, 2002
Introduction
As well as harmonic generation and frequency mixing, there is another way of generating new wavelengths of light. This technique is called parametric generation. It too is an example of nonlinear optics.
What is it?
Parametric generation is a method of generating longer wavelength light from shorter1. The exact mechanism for this to occur is a little complex and here a more simple explanation will be used. A laser beam is focused into a crystal with a high X(2) nonlinear susceptibility. An interaction takes place within the crystal, in which the original photon is converted into two photons, whose energies add up to that of the original photon. Parametric generation is sometimes known as photon splitting, for this reason.
How is it done?
As mentioned before, this process requires a laser beam to be focused inside a nonlinear crystal. There are two methods then to generate parametric light. One is to enclose the crystal in mirrors - not unlike a laser cavity. The generated light is made to resonate within the cavity and at one end there is a slightly leaky mirror. This method is called optical parametric oscillation, and the device is an optical parametric oscillator, or OPO.
In very high powered systems, the cavity is not required. There is no oscillation and so the process is called optical parametric amplification, with the device being called an optical parametric amplifier, or OPA.
How are they used?
OPOs and OPAs are used to access longer wavelength light, for which there may not be a suitable laser. The author personally uses an OPO in his laser research to access the region around 1.3 microns, where there is no laser suitable for the application he performs. OPAs are often used in the telecommunications industry to generate light at 1.5 microns, which is used in fibre optic communications.
1Or redder from bluer
