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UltraBroadBand Optical Parametric Amplifier or Oscillator
 Created: Sunday, 01 March 2009
Potential applications include wavelengthmultiplexing communications and generating reference frequencies.
A concept for an ultrabroadband optical parametric amplifier or oscillator has emerged as a byproduct of a theoretical study in fundamental quantum optics. The study was originally intended to address the question of whether the twophoton temporal correlation function of light [in particular, light produced by spontaneous parametric down conversion (SPDC)] can be considerably narrower than the inverse of the spectral width (bandwidth) of the light. The answer to the question was found to be negative. More specifically, on the basis of the universal integral relations between the quantum twophoton temporal correlation and the classical spectrum of light, it was found that the lower limit of twophoton correlation time is set approximately by the inverse of the bandwidth. The mathematical solution for the minimum twophoton correlation time also provides the minimum relative frequency dispersion of the downconverted light components; in turn, the minimum relative frequency dispersion translates to the maximum bandwidth, which is important for the design of an ultrabroadband optical parametric oscillator or amplifier.
In the study, results of an analysis of the general integral relations were applied in the case of an optically nonlinear, frequencydispersive crystal in which SPDC produces collinear photons. Equations were found for the crystal orientation and pump wavelength, specific for each parametricdown converting crystal, that eliminate the relative frequency dispersion of collinear degenerate (equalfrequency) signal and idler components up to the fourth order in the frequencydetuning parameter, ξ. [The degenerate frequency, ν_{0}, of the signal or idler component is half the pump frequency. If the difference between the signal or pump component and the degenerate frequency is ν (in which case the corresponding difference for the pump or signal component, respectively, is –ν), then ξ ≡ ν/ν_{0}.]As a result of the elimination of the relative frequency dispersion up to fourth order, an optical parametric amplifier consisting of such a crystal at the specified orientation and pumped at the specified wavelength can be designed to exhibit a relatively flat spectraldensityversusfrequency curve over more than an octave (see figure). Conveniently, the octave could be chosen to include two wavelength bands — centered at 1,330 and 1,560 nm — that are used in optical communications. Hence, for example, the amplifier might be useful in a wavelengthmultiplexing communication system using these two wavelength bands. In another potential application, by configuring this amplifier as a modelocked oscillator, one could obtain a selflocked comblike spectrum that could serve as an excellent set of frequency references.
This work was done by Dmitry Strekalov, Andrey Matsko, Anatoliy Savchenkov, and Lute Maleki of Caltech for NASA’s Jet Propulsion Laboratory. For further information, contact This email address is being protected from spambots. You need JavaScript enabled to view it.. NPO41584
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