Towards Arbitrary Time-frequency Mode Squeezing with Self-conjugated Mode Squeezing in Fiber

Optical parametric amplification generates squeezed light in device-specific sets of time-frequency eigenmodes, and it has been widely accepted that detection and utilization of squeezing must comply with this modal constraint. We show that this constraint can be considerably relaxed under the continuous-wave pump and broadband phase-matching approximation, where the modal decomposition is non-unique. Specifically, any time-frequency mode with "self-conjugated" spectral symmetry can approximate a squeezing eigenmode, and partial homodyne detection can herald squeezing in arbitrary time-frequency modes. We demonstrate this using a high-efficiency, low-loss all-fiber source, measuring 4.38 +- 0.11dB and 0.88 +- 0.09 dB squeezing on partially coherent and chaotic self-conjugated modes. Using a bichromatic self-conjugated mode with reduced local-oscillator noise, we achieve 7.50 +- 0.12dB squeezing, which represents the highest level reported for fully guided-wave squeezing sources based on chi(2) and chi(3) nonlinearities.