Illumination decisively influences the contrast in microscopic imaging, especially for phase objects or transparent objects. So far, the integration of defined illumination conditions has often been neglected in ultra-compact imaging demonstrations. Addressing this limitation, we introduce the concept and fabrication of a 3D-printed miniaturized Rheinberg illumination system that enables simultaneous dark- and bright-field microscopic imaging. The system fabricated by two-photon lithography makes use of a stained photoresist to generate a color-filtering sub-aperture. This sub-aperture enables spectral separation of light with different illumination angles within and outside an observation microscope objective's numerical aperture, creating dark- and bright-field conditions at different wavelength bands. The sub-millimeter illumination system is integrated directly on an optical multimode fiber tip and on the surface of a micro-LED, to realize ultra-compact, easy-to-integrate illumination solutions. We present single-shot combined dark- and bright-field microscopic imaging experiments with 3D-printed phase objects, as well as static and dynamic biological samples in a microfluidic environment. Our miniaturized, dual-mode microscopic illumination system thus enables single-shot imaging of transparent, dynamic biological systems and promises to benefit illumination and imaging capabilities in confined spaces such as microfluidic channels in life science research.
The development of two-photon direct laser writing has enabled the fabrication of three-dimensional micro-optical components with sub-micron resolution and complex geometries. We adopted a hybrid rapid prototyping approach for the realization of a fiber-optic spectroscopic micro-assembly operating in the visible range from 400 to 690 nm. The system is composed of several individually fabricated optical elements, collimating and focusing refractive micro-lenses, a diffractive grating, and mechanical alignment housing, assembled onto the facet of a multimode optical fiber. The approach differs from monolithic fabrication strategies by combining separately fabricated elements into a micro-assembly, allowing each component to be optimized for both function, resolution, and throughput. The diffractive grating was realized with a 690-nm period to increase spectral separation across the first diffraction order in the visible. Optical components were modeled using ray-tracing simulations to evaluate dispersion and focus characteristics within the limited assembly volume. Fabrication employed multiple photoresists with differing voxel resolutions to match the feature requirements of each optical and mechanical element. The assembled probe was calibrated using monochromatic light-emitting diode (LED) sources and evaluated under broadband illumination and fluorescence standards. The measured spectra showed agreement with modeled performance and confirmed dispersion across the designed wavelength range. This hybrid prototyping approach demonstrates the rapid prototyping utility of combining refractive and diffractive elements within a modular micro-assembly for compact diagnostic and sensing applications.
Mode-division multiplexing (MDM) increases the optical throughput by encoding data into different orthogonal fiber modes for parallel transmission of information. We conceptualize and demonstrate a compact micro-optical system that allows selective excitation of the LP11 mode of a few-mode fiber (FMF) using two single-mode fibers (SMFs). The system consists of micro-optical elements that redirect and reshape the output LP01 mode of each SMF to spatially match the LP11 modal lobe profile, featuring a three-fold fiber connector. Manufacturing by two-photon lithography (TPL) ensures high-precision sub-micron alignment, and high optical surface quality. Unlike approaches relying on explicit phase manipulation, this work focuses on demonstrating spatial (intensity-based) mode shaping to approximate the LP11 modal field. Phase-controlled excitation is not implemented in the present study. We present experiments suggesting a coupling efficiency of 49% for our realized prototype. Compared with other state-of-the-art approaches, our new configuration offers a platform that is robust and easy-to-integrate, promising to advance future interferometric and phase-tuning applications.
This study demonstrates the fabrication and characterization of an aperiodic diffractive intraocular lens (IOL) prototype based on the Devil's staircase function, using two-photon polymerization (2PP). The surface profile was quantified using an optical profilometer. Through-focus modulation transfer function (TF-MTF) and the area under the modulation transfer function (MTFa) were measured on a custom optical bench. Optical simulations were performed to model the expected performance. The fabricated prototype shows that the aperiodic stepwise profile is reproduced with micron-level lateral accuracy (average base-width deviation <6.55 mu m) and submicron step-height accuracy (step height error: <20 nm) across the 6-mm optical zone. The measured TF-MTF and MTFa match the predicted trifocal optical performance, exhibiting distinct focal peaks at far (0.0 D), intermediate (+1.75 D), and near (+3.6 D). These findings demonstrate the promising potential of 2PP for the rapid and precise prototyping of aperiodic diffractive IOL designs.
