Megahertz all-optical swept-source optical coherence tomography based on broadband amplified optical time-stretch

Abstract

We demonstrate all-optical ultrahigh-speed swept-source optical coherence tomography (OCT) based on amplified optical time-stretch (AOT). Such an inertia-free wavelength-swept mechanism, via group velocity dispersion, enables us to realize OCT with an A-scan rate well above MHz. More importantly, the key significance of AOT-OCT is its simultaneous broadband Raman amplification during the time-stretch process-greatly enhancing the detection sensitivity compared with prior attempts to apply optical time-stretch to OCT. Here, we report on an AOT-OCT system which is operated at an A-scan rate of 7.14 MHz, a superior roll-off performance (>2 mm/dB), a record-high sensitivity of time-stretch-based OCT (>80 dB) with a broadband gain bandwidth of 80 nm, which results in an axial resolution of ∼15 μm. Our AOT-OCT system is thus able to, for the first time to the best of our knowledge, perform time-stretch-based OCT of biological tissue in vivo. It represents a major step forward in utilizing AOT as an alternative for achieving practical MHz OCT, without any long-term mechanical stability concerns as in typical swept-source OCT or bypassing the speed limitation of the image sensor employed in spectral-domain OCT.

Ultrahigh-speed optical coherence tomography utilizing all-optical 40 MHz swept-source

“…2(a). Without any calibrations, 12 the temporal swept waveform (short dot line) dramatically shows a good agreement with the spectrum (solid line) captured by an optical spectrum analyzer, as shown in Fig. 2(b).…”

“…Xu et al demonstrated amplified optical timestretch and all-fiber breathing laser-based all-optical ultrahigh-speed SS-OCT at an A-scan rate of 7.14 and 11.5 MHz, respectively. 12,13 However, the effective A-scan rate of the former was only 1.2 MHz due to the averaging processes and the spectral shape of the latter swept-source was far away from the Gaussian shape as required for OCT imaging. Park et al…”

“…It is worthwhile to mention that all imaging is implemented without any averaging 12 of the consecutive A-scan signal. As shown in Fig.…”

High-speed OCT light sources and systems [Invited]

“…Due to high losses, the stretched output needs to be amplified, which increases noise considerably due to the low input power [105]. Raman co-amplification can be used, at the price of increased system complexity [106]. Ironically, the disadvantages of this technology are more severe for slower sweep rates, since more stretching leads to longer fiber and more loss.…”

28 MHz swept source at 10 μm for ultrafast quantitative phase imaging

“…By leveraging a dispersive element, such as the optical fiber and linearly chirped fiber Bragg grating with large group-velocity dispersion (GVD), it spreads the wavelengths of the pulsed lightwave in the time domain. Although successfully applied in the areas such as time-stretch microscope [15], ultrafast spectroscope [17], and optical coherence tomography (OCT) [18][19][20][21][22], it is largely under-explored as ultrastable swept sources, particularly in terms of sweeping bandwidth and stability. In this regard, recently several works have devoted to the speed improvement of the swept source through optical time-stretch technique, particularly in the wavelength windows of 800 nm [23,24] and 1550 nm [25,26].…”