Phase wavefront perturbation calculation model for spectroscopic refractive index matching of hybrid materials.

A low-cost flexible spectroscopic refractive index matching (SRIM) material with bandpass filtering properties without incidence angle and polarization dependence by randomly dispersing inorganic C a F 2 particles in organic polydimethylsiloxane (PDMS) materials was proposed in our previous study. Since the micron size of the dispersed particles is much larger than the visible wavelength, the calculation based on the commonly used finite-difference time-domain (FDTD) method to simulate light propagation through the SRIM material is too bulky; however, on the other hand, the light tracing method based on Monte Carlo theory in our previous study cannot adequately explain the process. Therefore, a novel approximate calculation model, to the best of our knowledge, based on phase wavefront perturbation is proposed that can well explain the propagation of light through this SRIM sample material and can also be used to approximate the soft scattering of light through composite materials with small refractive index differences, such as translucent ceramics. The model simplifies the complex superposition of wavefront phase disturbances and the calculation of scattered light propagation in space. The scattered and nonscattered light ratios; the light intensity distribution after transmission through the spectroscopic material; and the influence of absorption attenuation of the PDMS organic material on the spectroscopic performance are also considered. The simulation results based on the model are in great agreement with the experimental results. This work is important to further improve the performance of SRIM materials.

Histological classification of atherosclerotic arteries using high-speed confocal Raman microscopy with machine learning.

Confocal Raman microscopy is a useful tool to observe composition and constitution of label-free samples at high spatial resolution. However, accurate characterization of microstructure of tissue and its application in diagnostic imaging are challenging due to weak Raman scattering signal and complex chemical composition of tissue. We have developed a method to improve imaging speed, diffraction efficiency, and spectral resolution of confocal Raman microscopy. In addition to the novel imaging technique, the machine learning method enables confocal Raman microscopy to visualize accurate histology of tissue sections. Here, we have demonstrated the performance of the proposed method by measuring histological classification of atherosclerotic arteries and compared the histological confocal Raman images with the conventional staining method. Our new confocal Raman microscopy enables us to comprehend the structure and biochemical composition of tissue and diagnose the buildup of atherosclerotic plaques in the arterial wall without labeling.

Color tunable Ca8ZnM(PO4)7 (M = Lu/Tb, Lu/Eu, Tb/Eu) phosphors: luminescence, energy transfer and thermal stability studies for n-UV white LEDs.

A series of Tb3+- and Eu3+-doped Ca8ZnLu(PO4)7 (CZLP:Tb3+ and CZLP:Eu3+) as well as Ca8ZnTb(PO4)7:Eu3+ (CZTP:Eu3+) phosphors have been prepared via the traditional high-temperature solid-state reaction. X-ray powder diffraction (XRD) patterns of the as-prepared phosphors indicate that the introduction of Tb3+ or Eu3+ affects neither the phase impurity nor the crystal structure of the CZLP host lattice. The concentration dependent photoluminescence (PL) spectra reveal that even if Lu3+ was fully substituted by the dopants, Tb3+ or Eu3+, the phenomenon of concentration quenching would not occur. Color tunable emissions from green to red can be realized by adjusting the type of doping ion (Tb3+ and Eu3+) and their relative concentration. Furthermore, the energy transfer from Tb3+ to Eu3+ was confirmed and the mechanism was determined to be the dipole-quadrupole interaction. In addition, the quantum efficiencies were found to be 0.61, 0.58 and 0.85 for CZTP, CZTP:0.2Eu3+ and CaZnEu(PO4)7 (CZEP), respectively. As a result, a white light emitting diode (WLED) device was fabricated using the optimal CZTP:0.2Eu3+ yellow phosphor, the BaMgAl10O17:Eu2+ (BAM:Eu2+) blue phosphor and a 370 nm near-ultraviolet (n-UV) chip. The obtained device displays a suitable color rendering index (CRI, ∼81.3) and correlated color temperature (CCT, ∼2634 K) value, indicating its potential application in n-UV LEDs.

Utilization potential of intraluminal optical coherence tomography for the Eustachian tube.

Imaging the Eustachian tube is challenging because of its complex anatomy and limited accessibility. This study fabricated a fiber-based optical coherence tomography (OCT) catheter and investigated its potential for assessing the Eustachian tube anatomy. A customized OCT system and an imaging catheter, termed the Eustachian OCT, were developed for visualizing the Eustachian tube. Three male swine cadaver heads were used to study OCT image acquisition and for subsequent histologic correlation. The imaging catheter was introduced through the nasopharyngeal opening and reached toward the middle ear. The OCT images were acquired from the superior to the nasopharyngeal opening before and after Eustachian tube balloon dilatation. The histological anatomy of the Eustachian tube was compared with corresponding OCT images, The new, Eustachian OCT catheter was successfully inserted in the tubal lumen without damage. Cross-sectional images of the tube were successfully obtained, and the margins of the anatomical structures including cartilage, mucosa lining, and fat could be successfully delineated. After balloon dilatation, the expansion of the cross-sectional area could be identified from the OCT images. Using the OCT technique to assess the Eustachian tube anatomy was shown to be feasible, and the fabricated OCT image catheter was determined to be suitable for Eustachian tube assessment.

Astigmatism-corrected endoscopic imaging probe for optical coherence tomography using soft lithography.

In endoscopic optical coherence tomography, a transparent protective sheath is used to protect the optics and tissue. However, the sheath causes astigmatism, which degrades transverse resolution and signal-to-noise ratio due to the cylindrical lens effect. Generally used methods for correcting this astigmatism are complex, difficult to control precisely, high-cost, and increase the dimensions of the imaging probe. To overcome these problems, we have developed an astigmatism-corrected imaging probe with an epoxy window. The astigmatism is precisely and cost-effectively adjusted controlling the curvature radius of the epoxy window, which is produced by soft lithography. Using the fiber optic fusion splicing, the fabrication process is simple. The fabricated imaging probe is almost monolithic, so its diameter is similar to that of a standard single-mode fiber. We demonstrate its astigmatism-correcting performance using focal spot analysis, imaging micro-beads and a biological sample.

Removal of back-reflection noise at ultrathin imaging probes by the single-core illumination and wide-field detection.

Thin waveguides such as graded-index lenses and fiber bundles are often used as imaging probes for high-resolution endomicroscopes. However, strong back-reflection from the end surfaces of the probes makes it difficult for them to resolve weak contrast objects, especially in the reflectance-mode imaging. Here we propose a method to spatially isolate illumination pathways from detection channels, and demonstrate wide-field reflectance imaging free from back-reflection noise. In the image fiber bundle, we send illumination light through individual core fibers and detect signals from target objects through the other fibers. The transmission matrix of the fiber bundle is measured and used to reconstruct a pixelation-free image. We demonstrated that the proposed imaging method improved 3.2 times on the signal to noise ratio produced by the conventional illumination-detection scheme.

Endoscopic micro-optical coherence tomography with extended depth of focus using a binary phase spatial filter.

Micro-optical coherence tomography (µOCT) is an advanced imaging technique that acquires a three-dimensional microstructure of biological samples with a high spatial resolution, up to 1 µm, by using a broadband light source and a high numerical aperture (NA) lens. As high NA produces a short depth of focus (DOF), extending the DOF is necessary to obtain a reasonable imaging depth. However, due to the complexity of optics and the limited space, it has been challenging to fabricate endoscopic µOCT, which is essential for clinical translation. Here, we report an endoscopic µOCT probe with an extended DOF by using a binary phase spatial filter. The imaging results from latex beads demonstrated that the µOCT probe achieved an axial resolution of 2.49 µm and a lateral resolution of 2.59 µm with a DOF extended by a factor of 2. The feasibility of clinical use was demonstrated by ex vivo imaging of the rabbit iliac artery.

Design and fabrication of an optical probe with a phase filter for extended depth of focus.

The trade-off between spot size and depth of focus (DOF) often limits the performance of optical systems, such as optical coherence tomography and optical tweezers. Although researchers have proposed various methods to extend the DOF in free-space optics, many are difficult to implement in miniaturized optical probes due to space limitations. In this study, we present an optical probe with an extended DOF using a binary phase spatial filter (BPSF). The BPSF pattern was fabricated on the distal tip of an optical probe with a diameter of 1 mm by replica molding soft lithography, which can be easily implemented in a miniaturized optical probe due to its simple configuration. We optimized the BPSF pattern to enhance DOF, spot diameter, and light efficiency. To evaluate the fabricated endoscopic optical probe, we measured the three-dimensional point spread function of the BPSF probe and compared it with a probe without BPSF. The BPSF probe has a spot diameter of 3.56 µm and a DOF of 199.7 µm, while the probe without BPSF has a spot diameter of 3.69 µm and a DOF of 73.9 µm, representing a DOF gain of 2.7. We anticipate that this optical probe can be used in biomedical applications, including optical imaging and optical trapping techniques.