  We report the generation of squeezed vacuum states of light at 1550 nm with a
broadband quantum noise reduction of up to 4.8 dB ranging from 5 MHz to 1.2 GHz
sideband frequency. We used a custom-designed 2.6 mm long biconvex
periodically-poled potassium titanyl phosphate (PPKTP) crystal. It featured
reflectively coated end surfaces, 2.26 GHz of linewidth and generated the
squeezing via optical parametric amplification. Two homodyne detectors with
different quantum efficiencies and bandwidths were used to characterize the
non-classical noise suppression. We measured squeezing values of up to 4.8 dB
from 5 to 100 MHz and up to 3 dB from 100 MHz to 1.2 GHz. The squeezed vacuum
measurements were limited by detection loss. We propose an improved detection
scheme to measure up to 10 dB squeezing over 1 GHz. Our results of GHz
bandwidth squeezed light generation provide new prospects for high-speed
quantum key distribution.
