Blur resolved OCT: full-range interferometric synthetic aperture microscopy through dispersion encoding

Improved dispersion-encoded full-range spectral interferometry for large depth, large inclination and rough samples

In this study, we provide and validate an enhanced dispersion-encoded full-range spectral interferometry that offers improved measurement accuracy for samples characterized by significant depth, inclination, and roughness. Due to the low intensity of the optical signal in these samples, the optical signal is easy to be overwhelmed by the disturbance terms, demanding a more precise phase compensation. To address this issue, the direct current is removed by subtracting the envelope of the interference spectrum, allowing the weak signal near zero optical delay can be identified. Besides, considering the unwrapped phase error caused by the spectrometer aberrations, only the data with good phase continuity are preserved, which improves the accuracy of phase compensation. Using the proposed technique, the depth measurement range of the system is extended from 6 mm to 12 mm, while achieving an axial measurement precision of 2.5µm. In addition, the full-depth images of a ceramic standard step block and a 3D-printed sample are measured. It shows that our system exhibits superior adaptation to complex surfaces compared to the laser line profiler.

Suppression of the conjugate signal for broadband computed imaging via synthetic phase modulation

We present synthetic-phase-modulated interferometric synthetic aperture microscopy (SPM-ISAM), a method to perform 3D object reconstructions from data acquired with confocal broadband interferometric microscopy (BIM) that reconstructs images virtually free of coherent and depth-dependent defocus artifacts. This is achieved by implementing a sinusoidal SPM method in combination with an ISAM reconstruction algorithm that uses relatively low-modulation frequencies compared with acquisition frequencies. A theoretical framework and numerical results are provided here.

Stable complex conjugate artifact removal in OCT using circularly polarized light as reference

In Fourier domain optical coherence tomography (FDOCT), the depth profile is mirrored about the zero delay between the sample and reference optical paths, limiting the imaging depth to half of the entire ranging space and undermining the optimal sensitivity window. We present a new method, to the best of our knowledge, to remove the complex conjugate artifact by using circularly polarized light as reference. Quadrature detection of the complex fringe is achieved by utilizing the intrinsic λ/4 delay between two polarization channels. We use passive broadband polarization optics to control the polarization state of the light in the reference and sample arms and a balanced polarization diversity detection unit to simultaneously detect phase-shifted fringes. We demonstrate a 40 dB artifact suppression ratio with a swept-source optical coherence tomography system. Our proposed method is immune to sample motion and laser phase noise, and imposes no restrictions to the source bandwidth, imaging speed, or computational power. In vivo images of the human finger, as well as the cornea and retina of a non-human primate, were demonstrated.