Dispersion-cancelled biological imaging with quantum-inspired interferometry

Abstract

Quantum information science promises transformative impact over a range of key technologies in computing, communication, and sensing. A prominent example uses entangled photons to overcome the resolution-degrading effects of dispersion in the medical-imaging technology, optical coherence tomography. The quantum solution introduces new challenges: inherently low signal and artifacts, additional unwanted signal features. It has recently been shown that entanglement is not a requirement for automatic dispersion cancellation. Such classical techniques could solve the low-signal problem, however they all still suffer from artifacts. Here, we introduce a method of chirped-pulse interferometry based on shaped laser pulses, and use it to produce artifact-free, high-resolution, dispersion-cancelled images of the internal structure of a biological sample. Our work fulfills one of the promises of quantum technologies: automatic-dispersion-cancellation interferometry in biomedical imaging. It also shows how subtle differences between a quantum technique and its classical analogue may have unforeseen, yet beneficial, consequences.

Intensity-interferometric spectral-domain optical coherence tomography with dispersion cancellation

“…(14) must be replaced by a convolution of the Fourier transform of the ω 0 -dependent quantity Aω 0 1 jμω 0 ω 0 ; ω 0 − ω 0 j 2 and the five termsĉ 0 x,ĉ 1 x, andĉ 2 x in Eq. (14). In this case, it is expected that these five terms are broadened and thus the resolution is reduced.…”

“…This is readily achievable in our technique by use of the real part of the expression given by Eq. (14), because the termsĉ 0 x andĉ 2 x are real and the remaining termsĉ 1 x are purely imaginary. As a result, the signal termĉ 2 x is no longer affected by the adjacent term c 1 x as far as the real part of Eq.…”

“…Such an artifact emerges in Q-OCT [5][6][7] and the related classical OCT [13] as well, and it is readily discriminated from the true OCT signals, e.g., by slightly changing the operating wavelength λ 0 2πc∕ω 0 . In a recent chirped-pulse OCT with dispersion cancellation [14], suppression of all artifacts has been demonstrated experimentally using a specific method associated with the working principle of such an OCT system.…”

“…By exploiting the frequency entanglement associated with the twin-photon pairs, one finds that the cancellation of all even-order dispersions, including groupvelocity dispersion (GVD), is possible, and an improvement by a factor of 2 in longitudinal resolution relative to conventional classical OCT is achievable with Q-OCT. We note, however, that the weak, fragile nature of quantum entangled light hinders the practical use of Q-OCT, especially in biomedical imaging. Instead, a number of attempts stimulated by this technique have been made toward establishing classical OCT with resolution enhancement and dispersion cancellation mimicking those in Q-OCT without cumbersome quantum entanglement [8][9][10][11][12][13][14], albeit with some debate on the classical counterpart of quantum nonlocal dispersion cancellation [15][16][17][18][19][20][21]. Progress in Q-OCT and its classical analogues is summarized in a recent review [22].…”

“…It is important to emphasize that these classical analogues of Q-OCT are not expected to replace the existing OCT techniques, since they need specific apparatuses of considerable complexity to be implemented in practice, such as the nonlinear optical device for generating classical phase-sensitive light in phase-conjugate OCT [8,9] and the optical stretcher and compressor for producing pairs of oppositely chirped ultrashort laser pulses in chirped-pulse OCT [12][13][14]. It is also worth noting that all the dispersion-cancellation OCT techniques proposed so far, be they quantum or classical, are based on time-domain (TD) OCT, where axial measurements are performed by scanning a reference mirror in the setup.…”