Twin-photon techniques for fiber measurements

Characterization of single-mode optical fibers requires a basis for time, wavelength and polarization.Parametric downconversion in non-linear crystals naturally provide pairs of photons extremelyhighly correlated in time, energy (thus wavelength) and polarization. It is thus tempting to exploresuch photon pairs for fiber and fiber device characterization. Historically, entangled photon pairswhere first used in delicate tests of quantum mechanics [1]. Indeed, their correlation is higher thanclassically possible! However, nowaday photon pair sources can be made cheap and compact enoughto offer practical alternatives for many of the traditional measurement schemes. In addition photonpairs provide entirely new possibilities and open the door to new developments in metrology. Thepurpose of this contribution is first to present some concrete proposals and results along the abovelines, and next to draw the attention of the audience to these rather revolutionary new combinationsof quantum optics and communication.