Reverse proton exchange waveguides in periodically poled lithium niobate enable efficient frequency conversion of optical signals at powers down to the single-photon level. One can show that sum- and difference-frequency generation allows one to translate the wavelength of a quantum state of light while preserving all quantum information (like phase coherence and photon statistics, for example), in a process called Quantum Frequency Conversion. QFC offers a way by which hybrid quantum systems with components operating at very different wavelengths can be created.
QPM based on periodically poled ferroelectrics have enjoyed widespread use due to the ability to engineer a device for a particular nonlinear interaction of interest. Random duty cycle errors are inherent in production of QPM gratings by periodic poling as domains spread out slightly unevenly from poling electrodes. We have imaged domain disorder in our own PPLN devices (a) to quantify their severity: a histogram of domain size in a typical device is shown in (b).
Ultrashort pulses are regularly used to study ultrafast phenomena in all types of materials. Temporal imaging can be used to measure ultrafast waveforms in a single shot. It is a waveform manipulation technique that enables the expansion, compression, and even Fourier transforming of an input field in time while preserving the fidelity of the overall profile. Like any spatial imaging system, such as a camera or microscope, the performance of the entire system is highly dependent on the quality of its lens.