Optical parametric oscillator

It converts an input laser wave (called "pump") with frequency

The first optical parametric oscillator was demonstrated by Joseph A. Giordmaine and Robert C. Miller in 1965,[2] five years after the invention of the laser, at Bell Labs.

In the nonlinear optical crystal, the pump, signal and idler waves overlap.

Thus, in steady-state operation, the amplitude of the resonated wave is determined by the condition that this gain equals the (constant) loss.

The photon conversion efficiency, the number of output photons per unit time in the output signal or idler wave relative to number of pump photons incident per unit time into the OPO can be high, in the range of tens of percent.

Typical threshold pump power is between tens of milliwatts to several watts, depending on losses of the resonator, the frequencies of the interacting light, the intensity in the nonlinear material, and its nonlinearity.

If the idler wave is given from the outside along with the pump beam, then the process is called difference frequency generation (DFG).

This is a more efficient process than optical parametric oscillation, and in principle can be thresholdless.

If the nonlinear optical crystal cannot be phase-matched, quasi-phase-matching (QPM) can be employed.

An important feature of the OPO is the coherence and the spectral width of the generated radiation.

Many demonstrations of quantum information protocols for continuous variables were realized using OPOs.

[8] It turns out that the phases of the twin beams are quantum correlated as well, leading to entanglement, theoretically predicted in 1988.

[11] Above threshold, the pump beam depletion makes it sensitive to the quantum phenomena happening inside the crystal.

[14] Not only intensity and phase of the twin beams share quantum correlations, but also do their spatial modes.

[15] This feature could be used to enhance signal to noise ratio in image systems and hence surpass the standard quantum limit (or the shot noise limit) for imaging.

[16] The OPO is being employed nowadays as a source of squeezed light tuned to atomic transitions, in order to study how the atoms interact with squeezed light.

[17] It has also recently been demonstrated that a degenerate OPO can be used as an all-optical quantum random number generator that does not require post processing.