Nowadays fiber biphoton sources are nearly as popular as crystal-based ones. They offer a single spatial mode and easy integrability into optical networks. However, fiber sources lack the broad tunability of crystals, which do not require a tunable pump. Here, we report a broadly tunable biphoton source based on a suspended core fiber. This is achieved by introducing pressurized gas into the fibers hollow channels, changing the step index. The mechanism circumvents the need for a tunable pump laser, making this a broadly tunable fiber biphoton source with a convenient tuning mechanism, comparable to crystals. We report a continuous shift of 0.30 THz/bar of the sidebands, using up to 25 bar of argon.Optical fibers are an ideal platform for the generation of entangled photon pairs (biphotons) via spontaneous four-wave-mixing (FWM), due to their long light-matter interaction length. In particular, solid core fibers offer high effective nonlinearity. However, they typically lack the convenient tuning mechanism present in crystal-based biphoton sources, beside the trivial but costly scheme of tuning the pump wavelength. A limited amount of tuning has been demonstrated by stretching and heating the fiber [1], however, these approaches are limited by fiber damage. Meanwhile, gas filled hollow-core fibers offer broad dispersion tuning, but implementing a biphoton source in these fibers remains a challenging task, due to their low nonlinearity. Here, we combine the high nonlinearity of a solid core fiber with the convenient tuning scheme offered by gas filled fibers, to implement a tunable source of entangled photons. This is achieved by filling the channels surrounding the core of a suspended-core fiber (SCF). SCFs are a class of index-guiding microstructured fibers, where light is guided in a glass core suspended by three glass nano-membranes. SCFs have been used in a variety of applications, ranging from supercontinuum generation [2] to gas absorption spectroscopy [3], or chemical sensing [4].In FWM, two photons of an incident beam (denoted pump) are annihilated and the energy is transferred to two daughter photons (denoted signal and idler) symmetrically spaced around the pump. The signal and idler frequencies ω S , ω I are determined by the * jonas.hammer@mpl.mpg.de
We report non-destructive measurement of the diameter of submicron air-clad waveguides to nanometer precision, based on parametric amplification of a broadband seed signal. Ultrashort pump and seed pulses allow the diameter to be longitudinally resolved.
Four-wave mixing in Ar-filled sub-micron suspended-core fibres is used to generate spectrally tunable entangled photon pairs. A continuous shift of 0.30 THz/bar is measured for the generated sidebands with a coincidence-to-accidental ratio over 104.
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