We employ aligned two-photon lithography (A2PL®), to push high precision alignment tasks from the photonic packaging step towards the fabrication process in a one step process. Combined with Two-Photon Grayscale Lithography (2GL®), this approach enables direct fabrication of micro-optical elements onto devices, enhancing functionality with highest surface quality and shape fidelity at high throughput. We demonstrate automated 3D alignment using customer-ready detection algorithms, to fabricate micro-optical elements attached to various topographies and material platforms with exceptional accuracy below 100 nm. We showcase micro-optical elements aligned to fiber tips, photonic edge couplers, and photonic grating couplers to demonstrate the validity of A2PL for improved coupling losses and beam quality.
KEYWORDS: Printing, Two photon polymerization, Standards development, 3D microstructuring, Microfluidics, Microfabrication, In vivo imaging, Biomedical applications, Artificial intelligence, Tissue engineering
Herein, we demonstrate the translation of Two-Photon Grayscale Lithography (2GL®), as well as Aligned 2-Photon Lithography (A2PL®), to biomedical applications. Specifically, we will present a novel workflow of aligned two-photon polymerization (2PP) microfabrication for 3D cell assays and perfusion inside microfluidic devices. For completeness, we also reveal how 2GL® can be applied to artificial intelligence (AI) generated topographies for enhanced and scalable 2.5D cell culturing. The versatility offered by both aligned and 2GL® printing holds great promise for various applications in biotechnology, tissue engineering, and microfluidics, creating new opportunities for innovation within established biomedical and pharmaceutical industries.
We present a novel photonic structure on the end-face of a polarization-maintaining single-mode optical fiber for broadband vector beam generation, specifically radially and azimuthally polarized beams and modes. The structure, micro-3D printed using 2-photon lithography, is sub-mm long, and features a unique design comprising complex sequential sections. Our unprecedented design enables spatial control over light's intensity profile and polarization at the optical fiber’s output, with potential significant implications for fields such as optical communications, optical trapping, microscopy, and material processing.
We present recent advancements in two-photon grayscale lithography (2GL®). In contrast to one-photon grayscale lithography, for 2GL®, the exposed volume pixel is strongly confined to the vicinity of the laser focus allowing for a truly 3-dimensional dose control with very high spatial resolution. Discrete and accurate steps as well as essentially continuous topographies can be printed with increased throughput, on any substrate, and without the need for additional lithography steps or mask fabrication. We update on throughput and quality levels of the method. As demonstrators we fabricate and characterize a variety of microoptics and other benchmark structures.
Bessel beams (BBs) were first introduced by Durnin in 1987 and have a transverse intensity distribution dictated by the Bessel function. BBs are characterized by their diffraction-free propagation and self-healing nature. The family of BBs is categorized into two sets - zeroth-order Bessel beams (ZOBBs) with narrow high-intensity center and high-order Bessel beams (HOBBs) with phase singularity and dark center. HOBBs are vortex beams as they carry orbital angular momentum (OAM). Several approaches to generate BBs have been devised; some of them include transforming a narrow annular beam with a lens, using an axicon, or using spatial light modulators. Nevertheless, these techniques involve space-consuming and expensive table-top diffractive optical elements. In recent years, the on-fiber generation of BBs has gained prominence as it offers miniaturized optical probes that can find exciting applications in different fields, ranging from bio-imaging to communications. Here, we present on-fiber 3D printed complex photonic structures that convert the Gaussian-like mode from single-mode fibers into BBs of various orders. Remarkably, we report for the first time the generation of HOBBs from optical fibers. Our technique is inspired by Durnin's approach of generating BBs due to the transformation of an annular beam through a lens. Our novel design has three sections; the first and second sections contain photonic crystal waveguides that convert the input Gaussian-like mode into an annular beam of arbitrary radius and width, which is then transformed into BBs with the help of a micro-lens. To generate HOBBs, we also integrated a spiral phase plate in the stacked structure. We compared the experimentally generated BB parameters with what predicted from theory and found an excellent match. For HOBBs, we performed modal decomposition to confirm the existence of OAM. Overall, we showcase the results of various BBs with orders up to 20.
We present recent advancements in two-photon grayscale lithography (2GL®). In contrast to one-photon grayscale lithography, for 2GL®, the exposed volume pixel is strongly confined to the vicinity of the laser focus allowing for a truly 3-dimensional dose control with very high spatial resolution. Discrete and accurate steps, as well as essentially continuous topographies, can be printed with increased throughput, on any substrate, and without the need for additional lithography steps or mask fabrication. We update on throughput and quality levels of the method. As demonstrators, we fabricate and characterize optics masters for replication technologies like nanoimprint lithography.
The conventional way of generating Bessel beams (BBs) is based on axicon and other diffractive optical elements such as light modulators. These methods involve space-consuming optics. To overcome this limitation, over the past years, efforts were made to create BBs using miniaturized optics and generation of BBs directly from optical fibers. We propose a novel photonic structure 3D micro-printed on the end-face of an optical fiber, generating BBs of various orders. With our approach, we report for the first time the generation of high-order BBs from optical fibers. The results showcase Bessel beams ranging from orders zero- to 20.
Photonic crystal fibers (PCF) have revolutionized the field of optical fibers. Their unique properties, as endlessly single-mode operation, high birefringence, and hollow-core optical guidance, are enabled and controlled by their hole-array geometry. Thanks to these properties, optical waveguides based on geometrically unbound PCF designs could be exploited to realize miniaturized complex devices which implement advanced photonic operations. However, arbitrary PCF geometries are difficult or even impossible to produce using current PCF fabrication methods. Here, we show how to fabricate optical waveguide segments with PCF designs by 3D microprinting and how the combination of these segments can realize complex photonic devices.
Optical tweezers based on single optical fibers are typically fabricated with methods that grant only limited design flexibility in the trapping geometry. Here, we present a novel hybrid micro-optical structure 3D printed in a single step on a standard single-mode optical fiber, to create an ultra-compact fiber tweezer. The structure is made of stacked refractive, reflective, and waveguiding optical elements. Our approach allows an easy and independent tuning of trapping parameters as the numerical aperture and the working distance of the optical trap. We experimentally illustrate the 3D trapping capabilities of the proposed fiber optical tweezers.
The miniaturization of optical fiber polarization beam splitters (PBS) is highly desired, especially in optical communications. Here, we demonstrate the first-ever PBS based on Photonic Crystal Fibers (PCFs). The device is enabled by high-resolution 3D printing based on two-photon lithography, a method that grants unprecedented design flexibility to realize PCF segments with arbitrary geometries.
The PCF-PBS is composed of three segments, for a total length of 210 µm, and is directly printed in a single step on a single-mode fiber. The PCF-PBS has an extinction ratio greater than 10 dB on a 100 nm bandwidth centered at around 1550 nm.
We exploit the strong field enhancement offered by vertical gold nanocones resonating at 1 THz to induce THz field-driven electron emission. The nanocones are fabricated via an advanced 3D printing technique on a photopolymer and are successively gold coated. We demonstrate the clear advantage offered by nanocones featuring a monopolar resonance at THz frequencies with respect to traditional non-resonant tips via numerical modelling, THz far-field characterization, and the analysis of electron-induced argon gas fluorescence. Finally, we show that a further degree of optimization is enabled by tailoring the collective response of the nanocones when arranged in an array geometry.
We present a novel design for a Stimulated Raman Scattering (SRS) microscope based on a dual beam femtosecond laser in combination with spectral shaping through a fast and narrowband Acousto Optical Tunable Filter. This configuration allows the measurement of broad SRS spectra, all the way from fingerprint region to CH stretch region without any modification of the optical setup. High spectral resolution over a broad spectral region allows label-free quantitative imaging of biological samples. We will show the application of our SRS system to a quantitative study of lipid droplets in colon Cancer Stem Cells.
We show a dynamic counterpropagating optical trapping scheme based on a single low-NA objective and two right-angle prism mirrors µ-3D printed on a glass coverslip.
Multiple beams are created with a Spatial Light Modulator and redirected to face each other by the mirrors. The key advantages of this approach are the simple alignment, the long working distance that allows trapping of large samples, the straightforward compatibility with other advanced microscopies and the intrinsic side-view of the trapped object. We demonstrate the viability of our approach by performing trapping and 3D manipulation of dielectric beads and cells.
We propose a dual step µ-3D printing (two-photon lithography) strategy, which is the 3D version of the classic lithography etching-mask strategy, to achieve selective gold metallization for the realization of reflective micro-optics. We apply this strategy to obtain right-angle prism micro-mirrors used to create dynamic counterpropagating optical traps for biological samples in a holographic optical trapping setup with a single low-NA objective. We print the prisms on standard glass coverslips to create integrated optical trapping chips. We show the automatization of alignment between prisms and masks by a computer vision software.
In the last three decades, optical trapping techniques were heavily employed for contactless trapping and manipulation of biological samples. Dual-beam laser traps (DBLT) proved their convenience and became widely used as biophysical tool once a simplified experimental setup was proposed. This simplification was achieved by replacing the two objectives with optical fibers to deliver the two counter-propagating laser beams. However, fiber alignment can be inconvenient, time consuming and requires a lot of practice. Here, we present a novel way to overcome these issues by combining reconfigurable diffractive optical elements (DOE) and two photon lithography (2PL), using a single low NA objective. A single laser beam is divided into several beams by displaying a DOE on a spatial light modulator (SLM). This allows us to dynamically reconfigure the number of the beams, their shape, and relative 3D alignment. Furthermore, we use 3D printed micro-mirrors to direct the laser beams against each other and obtain a DBLT. The micro-mirrors were fabricated on top of a coverslip, by means of 2PL. Our preliminary results show the ability to trap dielectric and biological samples and their full 3D manipulation in a DBLT configuration. The ability to use DOEs to set the number of beams and their shape allow this technique to be coupled with novel forms of microscopy.
Graded index (GRIN) lens-based microendoscopes are widely used to perform two-photon fluorescence microscopy in deep (> 1 mm) regions of highly scattering biological tissue, such as the mammalian brain. However, GRIN microendoscopes are limited by intrinsic aberrations which severely restrict the usable field-of-view (FOV). The effect of aberrations is particularly relevant in ultrathin (diameter < 500 μm) microendoscopes which allow a less invasive insertion of the optical probe into the brain tissue but which are characterized by relatively small imaging FOV. Currently, there are limited commercially available solutions to correct aberrations in these ultrathin microendoscopes because of the difficulty in fabricating corrective optics at the small spatial scale corresponding to the microendoscope diameter. Here, we report the development and application of a new approach to correct aberrations in GRIN microendoscopes using microfabricated polymeric lenses. Corrective optical elements were first designed using optical simulation software, then fabricated by two-photon lithography, and finally coupled with the GRIN lens to generate aberration-corrected microendoscopic probes. The method that we developed was applied to several types of GRIN lenses that differed in length and diameter, and corrected microendoscopes had up to 9 folds larger FOV compared to uncorrected probes. We put corrected microendoscopes to the test by performing high-resolution functional imaging of hundreds of hippocampal or thalamic cells expressing genetically encoded fluorescent indicators in the mouse brain in vivo.
Two-photon lithography based 3D Direct Laser Writing (DLW) has shown its unique potential as a method to fabricate and integrate miniaturized optical elements which can parallel the function of bulk optical elements used in large scale systems [1]. Up to now, this fabrication method has been mainly used to obtain reflective, refractive and diffractive optical elements. The difficulty on using and controlling printable materials with intrinsic birefringence in 3D DLW has so far prevented the scaling down of polarization retarders elements. Here we present the DLW fabrication of a miniaturized Fresnel Rhomb, which is a prism in which the light gets reflected two times with a precise incidence angle to have a 90 degrees phase shift between the p and s polarization components, thus acting as a quarter-waveplate. Being not based on an intrinsically birefringent material, this optical element features a very broadband behavior covering a band exceeding 300 nm. To demonstrate the direct integration and flexibility provided by this method we have printed a miniaturized optical assembly consisting of the Fresnel Rhomb and a collimating micro lens on a polarization maintaining optical fiber so as to obtain a miniaturized on-fiber broadband source of pure circularly polarized light. This structure could find application to create a remote ultra compact probe in circular dichroism and Raman Optical Activity spectroscopies but could also be used as a phase retarder for other integrated applications, where control of the polarization on small scales is needed.
[1] Dietrich, P. I., Blaicher, M., Reuter, I., Billah, M., Hoose, T., Hofmann, A., et al. (2018). In situ 3D nanoprinting of free-form coupling elements for hybrid photonic integration. Nature Photonics, 1–9. http://doi.org/10.1038/s41566-018-0133-4
To avoid the unwanted non-resonant background contribution induced by cross-phase modulation (XPM) in Stimulated Raman Scattering (SRS) microscopy [1], the collection of forward transmitted signal is normally done with a microscope objective having a numerical aperture (NA) higher than the objective used for excitation. However, while high NA microscope objectives are usually bulky and expensive, because a complex design is needed to achieve good optical imaging performances, only a capability to collimate highly divergent beams is needed for forward detection of signal in SRS microscopy. Additionally, because high NA microscope objectives have a short working distance and are bulky, their use as forward collecting optical element is not compatible with tightly closed top-stage incubators, as used in live-cell experiments.
Here we show the use of a high NA 3D printed ultra-thin optical lens, composed of micro-reflective and -refractive elements, to replace commercial high NA microscope objectives for forward collection of signal in Stimulated Raman Scattering microscopy.
The lens is fabricated on a 170µm thick coverslip with direct laser writing based on Two-Photon Lithography with a commercial system (Nanoscribe) and using the proprietary IP-S photoresist. It has a thickness of 300 µm and a diameter of 1 cm. Thanks to its compactness, this optical element can easily fit inside top-stage microscope incubators. The resulting NA of this catadioptric condenser lens is 1.2 when working in water immersion. We show the complete removal of the non-resonant XPM contribution from SRS spectra of incubated cells.
[1] Ji-Xin Cheng, Xiaoliang Sunney Xie, Coherent Raman scattering microscopy, CRC press, 2016.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.