Dispersion-mediated conjugate suppression for high speed optical computing OCT imaging
Wenxin ZHANG, Chengming WANG, Zhenyu CHEN, Bin HE, Zhangwei HU and Ping XUE*
Department of Physics, Tsinghua University, Beijing, 100084, China
Abstract
We will illustrate that optical computing optical coherence tomography with proper dispersion imbalance may achieve ~2 times higher resolution and restrain the conjugate signal without any data processing at imaging speed of 5M-A-scans per second.
For all imaging techniques such as optical coherence tomography (OCT) [1], fast imaging speed is always of high demand. Optical computing OCT (OC2T) has achieved ultrahigh speed for real time 3D imaging without post data processing, but its spatial resolution is lowered down due to an imperfect Fourier transformation in the optical computing process. In this talk, we will illustrate the theory of OC2T and prove that the dispersion imbalance between reference arm and sample arm may be introduced to improve the resolution. Furthermore, this novel OC2T technique can also enable a conjugate restrained OCT imaging without any data processing, achieving ~2 times higher resolution than typical OC2T. At an imaging speed of as high as 5M-A-scans per second, the dispersion imbalance OC2T has strong ability of restraining the conjugate signal with a conjugate signal rejection ratio of 2.6
The optical design of the OC2T [2] is shown in Fig.1. An MZM (JDS Uniphase, OC-192, bandwidth of 10GHz) is used to modulate the light. The modulation function is generated by an arbitrary waveform generator (AWG, Keysight, M8195A, bandwidth of 40GHz). An envelope detector is used to acquire the envelope of high frequency signal to form OCT image.
To describe how much the conjugate signal is restrained, we may define conjugate signal rejection ratio CRR=the amplitude of signal /the amplitude of conjugate, which is [3]: CRR=(1+16 a3L4βL4 / c4γ4)1/4, where, γ=(2ln2)1/2λ02/(cπΔλ) is the bandwidth of the light λ0 in angular frequency and Δλ the FWHM bandwidth in wavelength. a is a constant and a*t the modulation frequency of the MZM at the time t. L, βL, c are the fiber length, group-velocity dispersion and speed of light, respectively. Real time conjugate suppression for high speed optical computing OCT imaging is show in Fig. 2.
Larger suppression can be achieved with larger L. However, L has an upper limit for a fixed optical computing speed, which is, by now, 150km to achieve CRR=35 with optical computing speed of 5M-A-scans/s and duty circle of 80%.
Our technique demonstrates, for the first time, the real time conjugate suppression without post-processing at imaging speed of as high as 5M-A-scans per second, the fastest speed up to now to our knowledge.
REFERENCES
[1] D. Huang, et al, “Optical coherence tomography” Science 254, 1178, (1991).
[2] X. Zhang, et al, “Optical computing for optical coherence tomography” Sci. Rep. 6, 37286, (2016).
[3] W. Zhang, et al, “Optical computing optical coherence tomography with conjugate suppression by dispersion” Opt. Lett., 44(8): 2077, (2019).
Speaker
Ping XUE
Department of Physics, Tsinghua University
China
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