[论文解读] Optical Coherence Tomography with a nonlinear interferometer in the high parametric gain regime

Gerard J. Machado, Gaetano Frascella+2 more|arXiv (Cornell University)|Jun 3, 2020

Optical Coherence Tomography Applications参考文献 39被引用 46

一句话总结

这篇论文在高参量增益下的 SU(1,1) 非线性干涉仪中实现了光学相干断层成像（OCT），能够实现高光子通量、标准探测器，并提高对微小损耗的灵敏度。

ABSTRACT

We demonstrate optical coherence tomography based on an SU(1,1) nonlinear interferometer with high-gain parametric down-conversion. For imaging and sensing applications, this scheme promises to outperform previous experiments working at low parametric gain, since higher photon fluxes provide lower integration times for obtaining high-quality images. In this way one can avoid using single-photon detectors or CCD cameras with very high sensitivities, and standard spectrometers can be used instead. Other advantages are: higher sensitivity to small loss and amplification before detection, so that the detected light power considerably exceeds the probing one.

研究动机与目标

• Motivate and demonstrate OCT with a nonlinear interferometer operating at high parametric gain to improve image acquisition speed and sensitivity.
• Show that high-gain operation yields higher photon flux, enabling ordinary detectors while maintaining or improving axial resolution.
• Compare high-gain performance to low-gain regimes, and illustrate both time-domain and Fourier-domain OCT in this architecture.

提出的方法

• Use an SU(1,1) interferometer formed by two passes through a nonlinear crystal pumped by a 532 nm Nd:YAG laser to generate correlated signal and idler photons.
• Operate the system at high parametric gain G (measured G = 1.7 ± 0.2 for the first pass) to achieve large photon flux (≈ 13,000 idler photons per pulse probing the sample and ≈ 4×10^5 signal photons detected per pulse).
• Derive and use the multimode interference visibility V as a function of sample and system reflectivities (Eq. 4 in the paper) and show its nonlinear dependence on r_s and r_i.
• Implement both time-domain OCT and Fourier-domain OCT by scanning phase for fringes or analyzing the spectrum of the output signal, with path-length difference constraints (Eq. 8).
• Provide analytic expressions for the spectrum S(Ω) of the signal photons (Eq. 1) and the Bogoliubov transformations governing the first and second pass through the crystal (S1–S4 in Supplementary Material).
• Demonstrate axial resolution and spectral analysis via Fourier transform of the detected spectrum, yielding an OCT depth profile.

实验结果

研究问题

• RQ1 Does operating an SU(1,1) interferometer in the high parametric gain regime improve OCT performance compared with low-gain regimes?
• RQ2 Can high-gain OCT utilize standard detectors (CCD cameras or spectrometers) while maintaining image quality and sensitivity to small losses?
• RQ3 What is the influence of sample reflectivity on interference visibility in high-gain SU(1,1) OCT, and how does it compare to low-gain behavior?
• RQ4 How can Fourier-domain OCT be realized in this nonlinear interferometer, and what axial resolutions are achievable given the PDC bandwidth?
• RQ5 What are the practical considerations (path-length difference, losses, and spectral resolution) for implementing high-gain OCT in this architecture?

主要发现

• Demonstrated interference visibility up to 90% in high-gain OCT with r_s = 0.6 and varying r_i.
• Found nonlinear dependence of visibility on sample reflectivity, with high gain enhancing sensitivity to small losses.
• In the very high-gain regime, visibility approaches V = 2|r_s|/(|r_s|^2 + |r_i|^2) × |r_i|, and for matched losses (r_s = r_i) visibility equals 1.
• FD-OCT is feasible in this setup, with an axial resolution of approximately 60 μm under the current bandwidth and spectrometer constraints.
• Achieved high photon flux allowing the use of standard detectors (CCD or spectrometer) rather than single-photon detectors, while probing with near-infrared light and detecting in the visible range.
• Provided a practical framework showing that detected power can exceed probing power due to parametric amplification after interaction with the sample.