Abstract This paper reviews the quasi‐phase‐matched (QPM) waveguide nonlinear‐optic device technologies for generation of quantum‐entangled twin photons indispensable for quantum‐information techniques. After a brief introduction to the concept of entanglement, quantum theory analysis of twin‐photon generation (TPG) is outlined to clarify the properties of twin photons. Then, methods for entangled‐photon generation are discussed. Practical design and theoretical performances of LiNbO3 waveguide QPM TPG devices, as well as the fabrication techniques, are described. Finally, experimental demonstrations of polarization‐entangled twin‐photon generation by waveguide Type‐I and Type‐II QPM TPG devices are presented.
Quantum-entangled twin photons are expected to play an important role in future quantum communications and information processing. We propose and demonstrate a Type-I quasi-phase-matched (QPM) nonlinear-optic (NLO) LiNbO3waveguide device for high-efficiency polarization-entangled twin photon generation. The device consists of a Ti:LiNbO3channel waveguide, a ferroelectric domain-inverted grating for Type-I QPM, and a thin-film half-wave plate for polarization conversion at the center of the NLO interaction region. Generation of polarization-entangled twin-photons is demonstrated through quantum interference experiment.