Optical coherence tomography in Optics Express [Invited]

3D CNN-based fingerprint anti-spoofing through optical coherence tomography

Optical coherence tomography (OCT) is a noninvasive high-resolution imaging technology that can accurately acquire the internal characteristics of tissues within a few millimeters. Using OCT technology, the internal fingerprint structure, which is consistent with external fingerprints and sweat glands, can be collected, leading to high anti-spoofing capabilities. In this paper, an OCT fingerprint anti-spoofing method based on a 3D convolutional neural network (CNN) is proposed, considering the spatial continuity of 3D biometrics in fingertips. Experiments were conducted on self-built and public datasets to test the feasibility of the proposed anti-spoofing method. The anti-spoofing strategy using a 3D CNN achieved the best results compared with classic networks.

Accessing depth-resolved high spatial frequency content from the optical coherence tomography signal

Optical coherence tomography (OCT) is a rapidly evolving technology with a broad range of applications, including biomedical imaging and diagnosis. Conventional intensity-based OCT provides depth-resolved imaging with a typical resolution and sensitivity to structural alterations of about 5–10 microns. It would be desirable for functional biological imaging to detect smaller features in tissues due to the nature of pathological processes. In this article, we perform the analysis of the spatial frequency content of the OCT signal based on scattering theory. We demonstrate that the OCT signal, even at limited spectral bandwidth, contains information about high spatial frequencies present in the object which relates to the small, sub-wavelength size structures. Experimental single frame imaging of phantoms with well-known sub-micron internal structures confirms the theory. Examples of visualization of the nanoscale structural changes within mesenchymal stem cells (MSC), which are invisible using conventional OCT, are also shown. Presented results provide a theoretical and experimental basis for the extraction of high spatial frequency information to substantially improve the sensitivity of OCT to structural alterations at clinically relevant depths.

Structural similarity assessment of an optical coherence tomographic image enhanced using the wavelet transform technique

We report on the quality assessment of an optical coherence tomography (OCT) image. A set of recent digital filters are used for denoising the interferometric signals. It is found that when a combination of continuous wavelet transform (WT) decomposition and the WT denoising techniques is imposed on raw signals, the highest signal-to-noise ratio of 17.8 can be reached. The structural similarity (SSIM) index is eventually employed to evaluate the modality of the reconstructed OCT image. Further, we found out that a SSIM value of about 0.95 can be reached, independent of the method used for envelope extraction.

High-dynamic-range areal profilometry using an imaging, dispersion-encoded low-coherence interferometer

This work presents the design and characterization of an approach for areal surface profilometry with sub-nm axial resolution. The developed approach is based on a low-coherence interferometer enhanced by an dispersive element to control the axial resolution and measurement range. Optical path differences are detected by an imaging spectrometer where equalization wavelengths are determined as a basis for fitting spectra. This enables the acquisition of surface profiles with a length of up to 1.5 mm without mechanical scanning where a minimal resolution of 0.1 nm in an axial measurement range of nearly 80 µm was achieved. The resolution calculation was based on the standard deviation of measured feature heights. In addition to the system design, its capabilities are demonstrated on samples such as height standards.

Ghost optical coherence tomography

We demonstrate experimentally ghost optical coherence tomography using a broadband incoherent supercontinuum light source with shot-to-shot random spectral fluctuations. The technique is based on ghost imaging in the spectral domain where the object is the spectral interference pattern generated from an optical coherence tomography interferometer in which a physical sample is placed. The axial profile of the sample is obtained from the Fourier transform of the correlation between the spectrally resolved intensity fluctuations of the supercontinuum and the integrated signal measured at the output of the interferometer. The results are in excellent agreement with measurements obtained from a conventional optical coherence tomography system.

Review on Retrospective Procedures to Correct Retinal Motion Artefacts in OCT Imaging

Motion artefacts from involuntary changes in eye fixation remain a major imaging issue in optical coherence tomography (OCT). This paper reviews the state-of-the-art of retrospective procedures to correct retinal motion and axial eye motion artefacts in OCT imaging. Following an overview of motion induced artefacts and correction strategies, a chronological survey of retrospective approaches since the introduction of OCT until the current days is presented. Pre-processing, registration, and validation techniques are described. The review finishes by discussing the limitations of the current techniques and the challenges to be tackled in future developments.

Raman soliton at 2 μm in picosecond pumped supercontinuum by a weak CW trigger

Injecting a weak narrow-linewidth CW trigger to control the picosecond pulse pumped supercontinuum (SC) generation in a highly nonlinear dispersion shifted fiber (HNL-DSF), the Raman soliton at 2 μm is experimentally observed. We demonstrate that the cascaded four-wave mixing (FWM) caused by the weak CW trigger accelerates soliton fission and collision, and the large red-shift by the Raman effect in fibers induces obvious Raman soliton occurring in the long wavelength range of SC. A reduced effect on spectral modification on the SC spectrum at higher pump powers is also observed in the experiment. Simulations of the spectral evolution and spectrogram are carried out to verify the experimental observation. Both experiment and simulation results show the SC characteristics in the mid-infrared region can be greatly improved by the triggering effect.

20th anniversary review articles: concluding a year of celebration

Editor-in-Chief Andrew M. Weiner summarizes the full list of invited review and perspective articles for Optics Express's 20th Anniversary celebration, completing the year of special content.