Use of Longer Soliton Pulses to Reduce Raman Noise in Fibre Squeezing

A source of quantum noise in a non-linear optical medium is the coupling of photons with thermal phonons, called the Raman effect. This noise source sets the lower limit of squeezing in the polarisation variables for ultrashort pulses. Increasing the soliton pulse width reduces the coupling between photons and phonons by decreasing the overlap of the pulse spectrum and the Raman frequency response, which is specific to the medium. We investigate the dependence of squeezing on the soliton pulse width, to determine if improvements in squeezing result from longer pulses. We numerically solve a stochastic nonlinear Schrodinger equation with extra nonlinear terms for Raman effect (derived within the truncated Wigner approach), for a 3M FS-PM 7811 silica fibre using the pde solver XMDS 2.0. Computational efficiency was improved by use of a single-Lorentzian approximation for the Raman gain profile. Results show that squeezing can be improved for longer pulse widths. However, there is a tradeoff between the Raman effects and the classical phase noise due to guided acoustic wave Brillouin scattering.A source of quantum noise in a non-linear optical medium is the coupling of photons with thermal phonons, called the Raman effect. This noise source sets the lower limit of squeezing in the polarisation variables for ultrashort pulses. Increasing the soliton pulse width reduces the coupling between photons and phonons by decreasing the overlap of the pulse spectrum and the Raman frequency response, which is specific to the medium. We investigate the dependence of squeezing on the soliton pulse width, to determine if improvements in squeezing result from longer pulses. We numerically solve a stochastic nonlinear Schrodinger equation with extra nonlinear terms for Raman effect (derived within the truncated Wigner approach), for a 3M FS-PM 7811 silica fibre using the pde solver XMDS 2.0. Computational efficiency was improved by use of a single-Lorentzian approximation for the Raman gain profile. Results show that squeezing can be improved for longer pulse widths. However, there is a tradeoff between the Raman effects and the classical phase noise due to guided acoustic wave Brillouin scattering.

Aug 1, 20110 citations

Numerical Simulations on Quantum Noise Squeezing for Soliton-like Pulses in Optical Fiber

Arseny A. Sorokin, Nikolay I. Salnikov, Anna N. Kosareva +2 more

Generation of light with nonclassical properties, such as squeezed light, has gathered a lot of attention because of possible uses in such areas as quantum state engineering, quantum imaging, continuous variable quantum computing, and detection of gravitational waves. Squeezed light is generally produced by transporting light through a nonlinear medium. One such media is Kerr-nonlinear optical fibres. We aim to find the parameters for a fibre polarization squeezing setup by studying the dependencies of quantum noise suppression on the duration of the pulse and the input power. This is performed by modeling the light field propagation using the split-step Fourier method to numerically solve the stochastic nonlinear Schrödinger equation obtained by using the Wigner representation. This equation includes such physical effects as damping, quantum loss noise, dispersion, Kerr and Raman nonlinearities, and stochastic Raman noise.Generation of light with nonclassical properties, such as squeezed light, has gathered a lot of attention because of possible uses in such areas as quantum state engineering, quantum imaging, continuous variable quantum computing, and detection of gravitational waves. Squeezed light is generally produced by transporting light through a nonlinear medium. One such media is Kerr-nonlinear optical fibres. We aim to find the parameters for a fibre polarization squeezing setup by studying the dependencies of quantum noise suppression on the duration of the pulse and the input power. This is performed by modeling the light field propagation using the split-step Fourier method to numerically solve the stochastic nonlinear Schrödinger equation obtained by using the Wigner representation. This equation includes such physical effects as damping, quantum loss noise, dispersion, Kerr and Raman nonlinearities, and stochastic Raman noise.

International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD)Sep 12, 20220 citations

Optical Squeezing of Light in Photonic Crystal Fibres

M. Tacey

This thesis presents a comprehensive numerical investigation of polarisation squeezing in photonic crystal fibre. Squeezing is the reduction of quantum noise in one variable beyond the Heisenberg limit at the expense of increased noise in the conjugate. The greater confinement of light that is possible in photonic crystal fibres leads to a greater effective nonlinearity, which promises to yield greater quantum squeezing than is possible in standard optical fibre. There are two dominant noise sources that limit the degree of polarisation squeezing. Raman noise is the interaction of photons with phonons in the fibre medium the degree of which is characteristic of the fibre medium and scales inversely with pulse width. And guided acoustic wave Brillouin scattering is due to thermally excited mechanical eigenmodes which scales with fibre length. The larger nonlinearity of photonic crystal fibres allows shorter fibre lengths with larger pulse widths providing a means to significantly reduce the dominant noise sources and obtain polarisation squeezing beyond that of ordinary silica fibre. This thesis presents an extensive quantum treatment using the truncated Wigner method that includes loss, a non-instantaneous Raman response, excess phase-noise, second- and third- order dispersion and self-steepening to identify the physical factors that limit current photonic crystal fibre squeezing experiments and demonstrate the optimal parameters to obtain the best squeezing.This thesis presents a comprehensive numerical investigation of polarisation squeezing in photonic crystal fibre. Squeezing is the reduction of quantum noise in one variable beyond the Heisenberg limit at the expense of increased noise in the conjugate. The greater confinement of light that is possible in photonic crystal fibres leads to a greater effective nonlinearity, which promises to yield greater quantum squeezing than is possible in standard optical fibre. There are two dominant noise sources that limit the degree of polarisation squeezing. Raman noise is the interaction of photons with phonons in the fibre medium the degree of which is characteristic of the fibre medium and scales inversely with pulse width. And guided acoustic wave Brillouin scattering is due to thermally excited mechanical eigenmodes which scales with fibre length. The larger nonlinearity of photonic crystal fibres allows shorter fibre lengths with larger pulse widths providing a means to significantly reduce the dominant noise sources and obtain polarisation squeezing beyond that of ordinary silica fibre. This thesis presents an extensive quantum treatment using the truncated Wigner method that includes loss, a non-instantaneous Raman response, excess phase-noise, second- and third- order dispersion and self-steepening to identify the physical factors that limit current photonic crystal fibre squeezing experiments and demonstrate the optimal parameters to obtain the best squeezing.

Jan 1, 20130 citations

Quantum Dynamics and Polarisation Squeezing of Ultrashort Pulses in Optical Fibre

Joel Frederick Corney, P. D. Drummond, J. Heersink +3 more

Comparing stochastic simulations and experimental measurements, we study the quantum dynamics of polarisation squeezing in optical fibres. Squeezing of -6.8 dB is measured, with Raman effects limiting squeezing for higher pulse energies and longer fibres. Depolarising GAWBS phase-noise adversely affects squeezing at low pulse energies. Third-order dispersion is also accounted for in the simulations, and this has an effect on pulses with more than the soliton energy. We theoretically determine the optimal pulse energy and fibre length for the best squeezing.Comparing stochastic simulations and experimental measurements, we study the quantum dynamics of polarisation squeezing in optical fibres. Squeezing of -6.8 dB is measured, with Raman effects limiting squeezing for higher pulse energies and longer fibres. Depolarising GAWBS phase-noise adversely affects squeezing at low pulse energies. Third-order dispersion is also accounted for in the simulations, and this has an effect on pulses with more than the soliton energy. We theoretically determine the optimal pulse energy and fibre length for the best squeezing.

Quantum-Atom Optics Downunder (QAO)Jan 1, 20070 citations

Simulations and experiments on polarization squeezing in optical fiber

Joel Frederick Corney, J. Heersink, Ruifang Dong +4 more

We investigate polarization squeezing of ultrashort pulses in optical fiber, over a wide range of input energies and fiber lengths. Comparisons are made between experimental data and quantum dynamical simulations to find good quantitative agreement. The numerical calculations, performed using both truncated Wigner and exact $+P$ phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonon variables. The simulations reveal that excess phase noise, such as from depolarizing guided acoustic wave Brillouin scattering, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fiber lengths. We also calculate the optimum fiber length for maximum squeezing.We investigate polarization squeezing of ultrashort pulses in optical fiber, over a wide range of input energies and fiber lengths. Comparisons are made between experimental data and quantum dynamical simulations to find good quantitative agreement. The numerical calculations, performed using both truncated Wigner and exact $+P$ phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonon variables. The simulations reveal that excess phase noise, such as from depolarizing guided acoustic wave Brillouin scattering, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fiber lengths. We also calculate the optimum fiber length for maximum squeezing.

arXiv:0807.2502Physical Review AAug 19, 200870 citations

Squeezed solitons: quantum and thermal noise effects

Robert M. Shelby, M. Rosenbluh, P. D. Drummond +1 more

Optical solitons are pulses that propagate in optical fibers without temporal or spectral distortion, owing to balancing of the second-order dispersion of the refractive index by nonlinear self-phase modulation induced by the intensity-dependent refractive index. Classically, this stationary distortion-free propagation only requires the proper choice of pulse width and shape for a given pulse energy. However, quantum fluctuations do not undergo stationary propagation but rather evolve due to dispersion and self-phase modulation. As a soliton pulse propagates, zero-point or vacuum noise associated with the pulse evolves into squeezed noise. Vacuum fluctuations are responsible for the fundamental detector noise floor known as the shot noise limit. Reduction of the noise in the detection of squeezed soliton pulses has achieved a noise level 34% below this limit. In optical fibers, thermal fluctuation of the refractive index limit the noise reduction that can be achieved by adding phase fluctuations in excess of the vacuum noise. At low frequencies thermal noise originates from local structural dynamics of fused silica which produces a 1/f power spectrum and from guided acoustic wage Brillouin scattering which modulates the refractive index at frequencies characteristic of the fiber structure. The bandwidth of these fluctuations is ~2 GHz; and for soliton pulses with spectral bandwidth much >2 GHz, we have shown that this noise can be made insignificant. For very short pulses, however, noise from Raman scattering must be considered. Recent calculations incorporating this noise mechanism are compared with experiment.Optical solitons are pulses that propagate in optical fibers without temporal or spectral distortion, owing to balancing of the second-order dispersion of the refractive index by nonlinear self-phase modulation induced by the intensity-dependent refractive index. Classically, this stationary distortion-free propagation only requires the proper choice of pulse width and shape for a given pulse energy. However, quantum fluctuations do not undergo stationary propagation but rather evolve due to dispersion and self-phase modulation. As a soliton pulse propagates, zero-point or vacuum noise associated with the pulse evolves into squeezed noise. Vacuum fluctuations are responsible for the fundamental detector noise floor known as the shot noise limit. Reduction of the noise in the detection of squeezed soliton pulses has achieved a noise level 34% below this limit. In optical fibers, thermal fluctuation of the refractive index limit the noise reduction that can be achieved by adding phase fluctuations in excess of the vacuum noise. At low frequencies thermal noise originates from local structural dynamics of fused silica which produces a 1/f power spectrum and from guided acoustic wage Brillouin scattering which modulates the refractive index at frequencies characteristic of the fiber structure. The bandwidth of these fluctuations is ~2 GHz; and for soliton pulses with spectral bandwidth much >2 GHz, we have shown that this noise can be made insignificant. For very short pulses, however, noise from Raman scattering must be considered. Recent calculations incorporating this noise mechanism are compared with experiment.

Annual Meeting Optical Society of AmericaJan 1, 19910 citations

+P

phase-space methods, include nonlinear and stochastic Raman effects, through coupling to phonon variables. The simulations reveal that excess phase noise, such as from depolarizing guided acoustic wave Brillouin scattering, affects squeezing at low input energies, while Raman effects cause a marked deterioration of squeezing at higher energies and longer fiber lengths. We also calculate the optimum fiber length for maximum squeezing.