Abstract
Enabled by the ultrahigh-speed all-optical wavelength-swept mechanism and broadband optical amplification, amplified optical time-stretch optical coherence tomography (AOT-OCT) has recently been demonstrated as a practical alternative to achieve ultrafast A-scan rate of multi-MHz in OCT. With the aim of identifying the optimal scenarios for MHz operation in AOT-OCT, we here present a theoretical framework to evaluate its performance metric. In particular, the analysis discusses the unique features of AOT-OCT, such as its superior coherence length, and the relationship between the optical gain and the A-scan rate. More importantly, we evaluate the sensitivity of AOT-OCT in the MHz regime under the influence of the amplifier noise. Notably, the model shows that AOT-OCT is particularly promising when operated at the A-scan rate well beyond multi-MHz--not trivially achievable by any existing swept-source OCT platform. A sensitivity beyond 90 dB, close to the shot-noise limit, can be maintained in the range of 2 - 10 MHz with an optical net gain of ~10 dB. Experimental measurement also shows excellent agreement with the theoretical prediction. While distributed fiber Raman amplification is mainly considered in this paper, the theoretical model is generally applicable to any type of amplification schemes. As a result, our analysis serves as a useful tool for further optimization of AOT-OCT system--as a practical alternative to enable MHz OCT operation.
Highlights
Optical coherence tomography (OCT) has proven to be a powerful noninvasive optical bioimaging modality because of its ability to offer label-free tissue tomographic and functional assessments in three-dimensional (3D) without relying on excisional biopsy and histopathology
To exemplify the influence of the coupling ratios on the amplified optical timestretch optical coherence tomography (AOT-OCT) sensitivity and signal-to-noise ratio (SNR), we here assume that the two couplers have the same coupling ratios, i.e. C1 = C2 and evaluate the sensitivity such AOT-OCT system running at an A-scan rate of 5 MHz based on
Concluding remarks We have presented a theoretical model to evaluate the performance of an AOT-OCT system, in the multi-MHz A-scan rate regime
Summary
Optical coherence tomography (OCT) has proven to be a powerful noninvasive optical bioimaging modality because of its ability to offer label-free tissue tomographic and functional assessments in three-dimensional (3D) without relying on excisional biopsy and histopathology. We have demonstrated a practical time-stretch OCT modality, called amplified optical timestretch OCT (AOT-OCT) which achieves tissue bioimaging with a record high sensitivity above 80 dB at an A-scan rate as high as 7.14 MHz [22]. We note that a recent work demonstrated the potential of a high-speed wavelength-stepped laser for MHz AOT [24] It showed that such novel laser design based on intracavity pulse stretching and compression using specialty GVD engineering can achieve a swept rate of 9 MHz. Further improvement of the AOT-OCT performance requires in-depth understanding of the roles of key determining parameters in the system. We anticipate that the present study could provide a comprehensive insight for designing a robust AOT-OCT system as a practical SS-OCT alternative running in the MHz regime
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