Traditional underwater polarization imaging methods can only provide clear degree of polarization (DOP) and intensity images of the object but cannot provide images of the polarization state of the object. This paper proposes a method to extract clear object information from turbid water in all four Stokes parameter (I, Q, U, and V) channels by using the full Stokes camera, enabling clear polarization state image reconstruction. The method utilizes multiple images from different angles to construct a low-rank and sparse matrix. Then, by decomposing this matrix into sparse and low-rank components, clear Q, U, and V images (i.e., the full polarization state) can be obtained. Unlike traditional methods that assume the circularly polarized component (V component) to be zero, this method retains V channel information, allowing for circular polarization component measurement. The study successfully reconstructed clear underwater images of samples with inhomogeneous DOP distribution and obtained the clear polarization states of polarizers and fish in the turbid water. The results show that the proposed method can visualize and analyze the object’s polarization state quantitatively with high accuracy in turbid water for the first time, potentially extending the applicability of polarization underwater imaging in ocean exploration.

Optical coherence tomography (OCT) is a noninvasive optical imaging technique that can generate cross-sectional images of the turbid samples, enabling the visualization of 3D microanatomy with high resolution (1 to $20\mu \mathrm{m}$).¹ To provide additional contrast when imaging birefringent sample, polarization-sensitive OCT (PS-OCT) has been developed to characterize anisotropic biological structures, such as tendon, muscle, collagen, and nerve fiber bundles.^{2 – 11} The initial PS-OCT was based on free-space setup since the bulk air-spaced optical components permit precise control over the polarization state of light in the sample and reference arms.^{2 – 4,10 – 12} Compared with the free-space setup, fiber-based interferometers offer distinct advantages in terms of system alignment and handling, desirable for clinical translations. However, because the optical fiber can introduce complex changes in the polarization state of the light, the fiber-based implementation of the PS-OCT is still practically challenging. In the previous studies, polarization-maintaining (PM) fiber that supports the propagation of two orthogonal polarization modes with high isolation was utilized to develop the fiber-based PS-OCT.^{5 – 9,13} Although the two polarization modes of the incident light can be preserved in the PM fiber during their propagation, the phase delay between them is difficult to control since multiple factors, e.g., fiber length, environmental temperature, and strain variations, can cause unpredictable changes in phase. Any disturbance in the PM fiber can induce a change in the output polarization state. This challenge generates a strict requirement for the stability of the system’s working environment, thus difficult to achieve in practical applications, especially in clinical translations.

To achieve accurate selection and synchronous imaging of blood vessels and lymph, a speckle spectrum contrast method (SSC) based on spectral-domain optical coherence tomography (SD-OCT) is proposed in this Letter. In this method, the time-lapse optical coherence tomography (OCT) intensity signal is transformed to the Fourier frequency domain. By analyzing the frequency spectrum of the time-lapse OCT intensity signal, a parameter called SSC signal, which represents the ratio of different intervals of the high frequency to the low frequency, is utilized to extract and contrast different types of the vessels in the biological tissues. In the SSC spectrum, the SSC signals of the static tissue, lymphatic vessels, and vascular vessels can be separated in three different frequency intervals, enabling differentiation and synchronous imaging of the lymphatic-vascular vessels. A mouse ear was used to demonstrate the feasibility and efficiency of this method. By using the SSC signal as the imaging parameter, the lymphatic and blood vessels of the mouse ear are differentiated and visualized simultaneously. This study shows the feasibility of the three-dimensional (3D) synchronous angio-lymphography based on the SSC method, which provides a tool to improve the understanding for disease research and treatment.

Significance: Cerebral blood flow (CBF) regulation at neurovascular coupling (NVC) plays an important role in normal brain functioning to support oxygen delivery to activating neurons. Therefore, studying the mechanisms of CBF adjustment is crucial for the improved understanding of brain activity. Aim: We investigated the temporal profile of hemodynamic signal change in mouse cortex caused by neural activation and its variation over cortical depth. Approach: Following the cranial window surgery, intrinsic optical signal imaging (IOSI) was used to spatially locate the activated region in mouse cortex during whisker stimulation. Optical microangiography (OMAG), the functional extension of optical coherence tomography, was applied to image the activated and control regions identified by IOSI. Temporal profiles of hemodynamic response signals obtained by IOSI and OMAG were compared, and OMAG signal was analyzed over cortical layers. Results: Our results showed that the hemodynamic response to neural activity revealed by blood flow change signal signal through IOSI is slower than that observed by OMAG signal. OMAG also indicated the laminar variation of the response over cortical depth, showing the largest response in cortical layer IV. Conclusions: Overall, we demonstrated the development and application of dual-modality imaging system composed of IOSI and OMAG, which may have potential to enable the future investigations of depth-resolved CBF and to provide the insights of hemodynamic events associated with the NVC.

Optical coherence tomography (OCT) is a fast, noninvasive, high-resolution optical imaging technique for cross-sectional and volumetric imaging by detecting the interferometric signal to measure the echo delay of backscattered light. Since its first introduction by Huang et al.,¹ it has become an indispensable imaging tool for diagnosing and evaluating many eye diseases in the field of ophthalmology.^{2 – 5} In recent years, research in dermatology and cardiovascular fields has also received increasing attention.^{6 – 9} With the development of OCT technology in recent decades, various functional imaging methods, such as optical coherence tomography angiography (OCTA), polarization-sensitive OCT (PS-OCT), and optical coherence elastography, have been gradually developed.^{10 – 15} Among them, OCTA is a microvascular imaging tool with three-dimensional visualization and high spatial resolution that does not require exogenous contrast agents. The blood flow image is obtained by capturing the dynamic signal among multiple scans at the same imaging position. This functional imaging modality has been widely used in preclinical procedures and clinical diagnoses. Several algorithms can be used for OCTA to extract blood flow signals, such as the phase-based variance method,¹⁶ the split-spectrum amplitude-decorrelation angiography method,¹⁷ and the complex-based optical micro-angiography (OMAG) method.¹⁸ However, the functional imaging modality of OCTA suffers from random fluctuations of noise and speckles inherent in the imaging system.¹⁹ These undesirable artifacts can generate a false appearance of blood flow and may lead to incorrect interpretation and quantification of OCTA images.