To generate PJs with waveguides and optical fibers, solutions where a sphere is put at the end of a hollow-core optical fiber or to use an optical fiber with a shaped tip have been proposed. Optical fiber tips have several advantages: easy to move, no necessary contact with the sample and the possibility to collect backscattered light. As a result, this technique has the potential to become a major solution in industrial processes and characterization, such as sub-micron laser processing or high-resolution spectral analysis. The ICube laboratory was the first to demonstrate that PJs can be obtained using a multimode optical fiber with a shaped tip for sub-wavelength ablation. However, the photonic jet is due to the part of the power injected on the fundamental mode. The energy on the other modes is lost to the process. Due to mode coupling, this can represent 90% of the injected power when the fiber has too many modes such as 100/140 silica fiber. We can then understand the interest of working with fibers with a lower number of modes. Nevertheless, such fibers have smaller core diameters, which makes it difficult to control the fabrication of the tip. Based on an original technique, the problem has been overcome. Fibers (50/125), (9/125) and (5/125) with microlens fitting just on their cores will be presented is this study. To demonstrate the capacity of these fibers to generate PJs, the performance of beam coming out of fibers having shaped tips has been investigated using a direct imaging technique. The volume of the PJ along the optical axis has been retrieved. The three-dimensional beam reconstruction enables not only to extract the narrow width and length of the PJ, but also to investigate the role of the excitation modes, with the aim to reduce the power spreading around the PJ.

The development of ever higher resolution surface 2,5D reconstruction systems is required for validating microsystem machining processes. Finding an easy, non-contact, quantitative method of characterization with a wide field, is still an issue for the semiconductor industry. Optical profilometry, based on white light interferometry, is one of the relevant methods that can provide such solutions. One of its limitations though is the lateral resolution, which is generally worse than the diffraction limit due to system influences. In 2016, several papers from Wang, Montgomery and Kassamakov showed that by adding a dielectric microsphere of a few micrometers in diameter between the interferometer and the sample, the lateral resolution could be increased by a factor of around 4, up to 100 nm line width. Several interferometric configurations can be used. The Linnik configuration, with a complete reference arm, and a second objective lens and microsphere, is probably the most powerful one due to its ability to compensate all the phase delays and aberrations of the imaging system. Conversely, the Mirau configuration is one of the simpler methods, since the reference arm is located directly within the microscope objective assembly. However, due to the virtual image made by the microsphere and the phase shift introduced in the object arm by the sphere, by default, a mismatch occurs between the imaging plane and the coherence plane. This may affect the profile reconstruction. The selection of the adapted microsphere for this kind of interference objective lens will be discussed both experimentally and theoretically. We will show how this mismatch can be minimized and how the coherence length of the source and the depth of field of the microsphere provide a certain tolerance, leading to a more practical nano-characterization tool.

The iterative recovery of quantitative phase information from measurements of the diffracted intensity or flux of a wavefield, has produced entirely new methods in phase imaging. Collectively these approaches may broadly be described as ‘coherent imaging techniques’. Of the numerous types of coherent imaging methods that have emerged ptychography has proved to be one of the most enduringly successful. Not only does ptychography afford high-quality quantitative sample phase data to be obtained it simultaneously reconstructs the incident complex wavefield eliminating artifacts that can be introduced via an imperfect knowledge of the probe or imaging system. Recently we demonstrated that the incorporation of plasmonic nanostructures into optical ptychography results in a significant improvement in both the amplitude and phase contrast. We termed this technique Plasmon Enhanced Ptychography (PE-ptychography). Further, we observed that depending on the incident wavelength the relative values for the individual components of the complex refractive index vary significantly resulting, at certain wavelengths, in a ‘contrast reversal’ relative to the incident probe. Here we discuss the progress and potential of plasmon-mediated phase contrast bioimaging, exploiting the specific near-surface interactions that occur between the sample and plasmon-resonance structure in order to highlight specific sample features. We find that the combination of quantitative phase imaging and plasmonics enables excellent differentiation between sample components that would otherwise be difficult to resolve. The data points to the possibility of significantly enhancing the sensitivity and specificity of label-free bioimaging with the potential to detect the very earliest stages of disease.