Optical-fiber source of polarization-entangled photons in the 1550 nm telecom band

We present a fiber-based source of polarization-entangled photons that is well suited for quantum communication applications in the 1550 nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal and idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal and idler photons yields biphoton interference with visibility greater than 90%, while no interference is observed in direct detection of either signal or idler photons. All four Bell states can be prepared with our setup and we demonstrate violations of the Clauser-Horne-Shimony-Holt form of Bell's inequality by up to 10 standard deviations of measurement uncertainty.     

Soliton squeezing in microstructure fiber

We demonstrate, for the first time to our knowledge, the generation of squeezed light by means of soliton self-phase modulation in microstructure fiber. We observe and characterize the formation of solitons in the microstructure fiber at 1550 nm. A maximum squeezing of 2.7 dB is observed, corresponding to 4.0 dB after correcting for detection losses. The dependence of this quantum-noise reduction on various system parameters is studied in detail. Features of the microstructure fiber can be exploited for generation of low-energy continuous-variable entangled pulses for use in all-fiber teleportation experiments.     

Resonant optical interactions with molecules confined in photonic band-gap fibers

We investigate resonant nonlinear optical interactions and demonstrate induced transparency in acetylene molecules in a hollow-core photonic-band-gap fiber at 1.5 mum. The induced spectral transmission window is used to demonstrate slow-light effects, and we show that the observed broadening of the spectral features is due to collisions of the molecules with the inner walls of the fiber core. Our results illustrate that such fibers can be used to facilitate strong coherent light-matter interactions even when the optical response of the individual molecules is weak.     

Storage and long-distance distribution of telecommunications-band polarization entanglement generated in an optical fiber

We demonstrate storage of polarization-entangled photons for 125 micros, a record storage time to date, in a 25-km-long fiber spool, using a telecommunications-band fiber-based source of entanglement. With this source we also demonstrate distribution of polarization entanglement over 50 km by separating the two photons of an entangled pair and transmitting them individually over separate 25-km fibers. The measured two-photon fringe visibilities were 82% in the storage experiment and 86% in the distribution experiment. Preservation of polarization entanglement over such long-distance transmission demonstrates the viability of all-fiber sources for use in quantum memories and quantum logic gates.     

Fiber optical parametric oscillator for sub-50 fs pulse generation: optimization of fiber length

We demonstrate generation of 48fs pulses with linear chirp using a short (27mm) fiber optical parametric oscillator (FOPO), which is synchronously pumped by a mode-locked ytterbium-doped fiber laser. We also study the pulse quality for both the short- and long-wavelength operation where the fiber length inside of the oscillator varies from 17 to 61mm. The optimal pulse duration is observed only in the short-wavelength operation. Furthermore, we model the FOPO system as a single-pass parametric amplifier including dispersive pulse broadening and walk-off between the pump and output. The optimal condition arises from the minimization of the walk-off and dispersion. When walk-off is large, the parametric amplification process is most efficient over some reduced effective fiber length, leading to an upper limit in the amount of the observed pulse broadening.