Hybrid squeezing of solitonic resonant radiation in photonic crystal fibers

We report the existence of a kind of squeezing in photonic crystal fibers which is conceptually intermediate between four-wave-mixing-induced squeezing in which all the participant waves are monochromatic waves, and self-phase-modulation-induced squeezing for a single pulse in a coherent state. This hybrid squeezing occurs when an arbitrary short soliton emits quasimonochromatic resonant radiation near a zero-group-velocity-dispersion point of the fiber. Photons around the resonant frequency become strongly correlated due to the presence of the classical soliton, and a reduction of the quantum noise below the shot-noise level is predicted.

Figure 1

Squeezing spectrum in various conditions and parameters. (a) Noise spectrum $S\left({\delta }_0\right)$ versus propagation distance $z$ for fixed value of the local oscillator phase $\Phi =1.8$. (b) Noise spectrum $S\left({\delta }_0\right)$ versus $\Phi$ for fixed value of propagation distance $z=0.28$. The green dotted and red solid curves in panels (a) and (b) correspond, respectively, to the soliton wave numbers $q=0.5$ and $q=0.25$. The black straight lines in panels (a) and (b) represent the shot-noise level. (c) Contour plot of ($S-1$) showing the $z$ evolution of the noise spectrum at various noise frequencies $\omega$. Parameters used in (c): $\Phi =1.8$, $q=0.25$. Other parameters used in panels (a), (b) and (c): ${\alpha }_3=-0.2$; all other HOD coefficients vanish; integration time $T=10$; with these parameters the resonant radiation frequency ${\delta }_0\simeq -2.7$. (d) GVD of the PCF used in this work. At the soliton wavelength (${\lambda }_{\mathrm{S}}=1.2$ $\mu$m), ${\alpha }_3\simeq -0.2$.

Figure 2

Schematic of the proposed experimental verification. A pump laser provides optical pulses that propagate through the PCF as solitons. The generated resonant radiation (RR) is isolated with a spectral filter (SF) and coupled into an optical cavity. A photodiode at one cavity output in combination with a spectrum analyzer can be used to measure the noise spectrum around the RR frequency ${\delta }_0$. Tuning the cavity provides access to the quantum fluctuations at any field quadrature.