Two mode squeezing is demonstrated in an optical fiber parametric amplifier, with 10 dB gain and strong coherent seed. The source would improve sensitivity of large signal interferometers, while using standard detectors.
Squeezed states of light enable optical measurements with sensitivity beyond the shot noise limit of detection with classical light. Optical fibers represent a major potential platform for quantum squeezed sensing due to the extremely low loss and perfect single-spatial-mode operation. In this work, we demonstrate two-mode intensity squeezing directly within a commercially available optical fiber, based on a four-wave mixing process. The setup operates in a quasi-continuous-wave mode using 15 ns long pulses and relies on standard laser diode sources, telecommunication electro-optic modulators, and simple photo-detectors. The process is seeded by a coherent signal input, generating bright squeezed output states. Absolute noise reduction by 4 dB below the classical shot-noise limit is detected directly with no post-processing, for output signal and idler pulses of 2.4 × 10 6 photons in average. The results are applicable to quantum interferometry over fiber using simple, readily available components.
Nonlinear interferometers offer a robust platform for quantum sensing beyond the standard quantum limit. Specifically, the generation of high-quality intensity-difference-squeezed (IDS) states provides a distinct advantage by circumventing the need for complex phase-coherent local oscillators. However, practical imperfections such as asymmetric inter-stage transmission and unbalanced detection losses severely degrade the generation of these states. In this work, we analyze IDS state generation within fiber nonlinear interferometers utilizing cascaded parametric amplifiers. Using a single-mode theoretical framework and experimental demonstration, we derive an optimal electronic gain ratio for differential detection to compensate for asymmetric detection-induced noise mismatches, extending achievable squeezing into the high-gain regime. We further analyze system tolerance to inter-stage losses and path delays. Experiments demonstrate that while higher initial parametric gain improves quantum correlations, it amplifies intensity noise and accelerates gain saturation, resulting in optimal squeezing at balanced low-gain configurations. These findings establish a robust framework for the design and optimization of all-fiber quantum sensors.
We demonstrate that single-mode broadband amplified spontaneous parametric downconversion, combined with optical parametric amplification, can be used as a classical source of phase-sensitive cross-correlated beams. We first study the single spatial mode emission and the spectral brightness properties of the parametric fluorescence, produced in periodically poled MgO-doped lithium niobate. Using the same single-pass bulk-crystal configuration for a pulsed optical parametric amplifier, we achieve a gain of approximately 20 dB at an average pump power of 2W, and explain the pulse narrowing observed at the output of both parametric fluorescence and amplification in the regime of high gain. Combining these two nonlinear processes, we measured optical coherence tomography signals with standard InGaAs photodiodes, thus realizing the first classical interferometer based on amplified parametric fluorescence. The results suggest their utility for demonstrating phase-conjugate optical coherence tomography.