  Continuous-wave (cw) squeezed states of light have applications in sensing,
metrology and secure communication. In recent decades their efficient
generation has been based on parametric down-conversion, which requires pumping
by externally generated pump light of twice the optical frequency. Currently,
there is immense effort in miniaturizing squeezed-light sources for
chip-integration. Designs that require just a single input wavelength are
favored since they offer an easier realization. Here we report the first
observation of cw squeezed states generated by self-phase modulation caused by
subsequent up and down conversions. The wavelengths of input light and of
balanced homodyne detection are identical, and 1550 nm in our case. At sideband
frequencies around 1.075 GHz, a nonclassical noise reduction of (2.4 +/- 0.1)
dB is observed. The setup uses a second-order nonlinear crystal, but no
externally generated light of twice the frequency. Our experiment is not
miniaturized, but might open a route towards simplified chip-integrated
realizations.
