A. Sizmann

Propagation of quantum properties of sub-picosecond solitons in a fiber

We present new results on photon number squeezing of spectrally filtered solitons in fibers. The impact of frequency low-, high-, and bandpass filtering on noise reduction has been measured as a function of fiber length for 130-fs pulses close to the soliton energy. For short fibers our results agree qualitatively with theoretical predictions. For longer fibers, however, the measured squeezing increases to an unexpectedly large value. Filtering out the long-wavelength components of strongly Raman-shifted, higher energy pulses squeezed the directly detected photocurrent fluctuations down to 3.8+/-0,2 dB (59%) below the shot noise level. The measured noise reductions are broadband from 5 to 90 MHz.

V The Optical Kerr Effect and Quantum Optics in Fibers

Publisher Summary This chapter reviews the experiments for quantum optics in fibers by studying the effect of the nonlinear optical Kerr interaction and stimulated Raman scattering on the quantum properties of light in silica fibers. The chapter outlines the basic characteristics of the optical Kerr effect. The chapter discusses the essential properties of optical solitons, thermal noise sources in fibers, and the quadrature squeezing in fibers using self-phase modulation (SPM). Recent progress includes the use of cross-phase modulation (XPM) for quadrature squeezing. The chapter describes the quantum nondemolition (QND) measurements in fibers, where XPM is used to achieve quantum entanglement of two modes or two pulses. New squeezing mechanisms are also discussed in the chapter. The nonlinear Kerr effect is the basic underlying squeezing mechanism. The perspectives emerging from these experiments, including the potential impact on all-optical signal processing, are discussed in the chapter.

Bulk Er:Yb:glass soliton femtosecond laser

Summary form only given. A bulk solid state Er:glass laser can combine the advantages of existing Er:fiber lasers, i.e. femtosecond pulses, with pulse-width tunability and low phase noise. Moreover, the combination of low-cost glass and pumping-by a relatively low-power diode laser is competitive to other bulk gain materials, e.g. Cr:YAG crystals using a pump power of several Watts, working at the eyesafe and telecommunications wavelength around 1.5 gin. However, the shortest pulses reported for a bulk Er:glass laser were limited to 2.5 ps. To overcome the limitation to the picosecond regime we increased the intracavity self-phase modulation in order to achieve soliton modelocking. This was realized by the insertion of an additional Kerr medium in the focal region of the resonator.

Fibre-optic photon-number squeezing in the normal group-velocity dispersion regime

Abstract The nonlinear optical Kerr effect, acting on optical pulses in fibres, creates spectral sidebands and noise correlations between these sidebands. The reduction of photon-number fluctuations of these pulses below the shot-noise limit by spectral filtering is well established in the anomalous dispersion regime which allows for soliton formation. Here it is demonstrated that a significant quantum-noise reduction with spectral filtering can also be reached for pulses in the normal dispersion regime. The filter function was optimized and the power dependence of the noise reduction was investigated. The best squeezing result is (1.2 ± 0.2) dB (corresponding to (2.6 ± 0.7) dB inferred for 100% detection efficiency).

Soliton backaction-evading measurement using spectral filtering

We report on a backaction-evading (BAE) measurement of the photon number of fiber-optical solitons operating in the quantum regime. We employ a recently proposed different detection scheme based on spectral filtering of colliding optical solitons. The measurements of the BAE criteria demonstrate significant quantum state preparation and transfer of the input signal to the signal and probe outputs exiting the apparatus, displaying the quantum-nondemolition behavior of the experiment.

Quantum Solitons in Optical Fibres: Basic Requisites for Experimental Quantum Communication

Continuous variable quantum entanglement emerges from nonlinear interactions of: fibre optical solitons in combination with some linear operation. We describe the detection and characterization of bright EPR-entanglement and QND-entanglement produced in this way and discuss the prospects of bright-beam-based quantum communication.

Photon-Number Noise of Spectrally Filtered Optical Solitons

Fundamental optical solitons in fibers are stationary objects if described within the framework of classical electrodynamics. Quantum optical solitons, however, have uncertainties associated with their position, momentum, phase and amplitude. These uncertainties become mutually correlated, broaden or contract as the quantum soliton propagates. Thus, the fundamental quantum soliton is not a stationary object during propagation [1]–[4].

Conditional measurement of the photon number optical pulse collision

Summary form only given. The optical Kerr effect of fibers produced unique nonclassical correlations through intensity-dependent phase shifts in a variety of quadrature-amplitude squeezing and quantum-nondemolition (QND) experiments. Later, a new squeezing mechanism was observed with spectral filtering of fiber-optical pulses. Our novel QND approach applies spectral filtering to two interacting pulses in order to obtain a QND readout that is immune to phase noise. In a pulse collision the spectral separation between the center frequencies of the pulses is transiently enhanced, with the spectral shift of one (meter) pulse depending on the photon number of the other (signal) pulse. Thus photon-number fluctuations of one pulse are transferred to frequency fluctuations of the other pulse which are directly detectable after a spectral filter. The maximum frequency shift occurs in the center of the collision, where the pulses are well separated in frequency space, even if there is a spectral overlap before the collision.

Quantum Correlations of Colliding Soltions

Soliton collisions in a WDM transmission system produce power and phase correlations among the interacting channels. The quantum limits of the cross-phase-modulation-induced coupling of solitons were intensively investigated in theory and in experiment, however, only in terms of number-phase correlations. A recent multi-mode analysis of propagating solitons and of the soliton collisions shows intra- and inter-pulse photon-number correlations. This analysis provides new insights into the quantum structure of solitons, into the back-action evading detection of the photon number and into a mechanism of intensity modulation cross-talk in WDM transmission systems in the presence of spectral filters.

Investigation of strongly photon-number squeezed solitons from an asymmetric fiber Sagnac interferometer

Summary form only given. Recently a new scheme was proposed and reported to reduce the quantum uncertainty of solitons below that of a coherent state by propagating them through a nonlinear fiber interferometer with an asymmetric splitting ratio. We investigated the optimum parameters of this promising scheme for quantum soliton generation, experimentally as well as theoretically.