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Abstract

We present the observation of optical fields carrying squeezed vacuum states at sideband frequencies from 10 Hz to above 35 MHz. The field was generated with type-I optical parametric oscillation below threshold at 1064 nm. A coherent, unbalanced classical modulation field at 40 MHz enabled the generation of error signals for stable phase control of the squeezed vacuum field with respect to a strong local oscillator. Broadband squeezing of approximately −4 dB was measured with balanced homodyne detection. The spectrum of the squeezed field allows a quantum noise reduction of ground-based gravitational wave detectors over their full detection band, regardless of whether homodyne readout or radio-frequency heterodyne readout is used.