Micro-optical Components Research Articles

Creating Tunable Micro-Optical Components via Photopolymerization 3D Printing Combined with Polymer-Dispersed Liquid Crystals.

Based on additive manufacturing via photopolymerization, this study combines polymer-dispersed liquid crystal (PDLC) technology with 3D printing technology to produce tunable micro-optical components with switchable diffraction or focusing characteristics. The diffraction grating and Fresnel zone plate are the research targets. Their structures are designed and simulated to achieve expected optical functions. A liquid crystal display (LCD) 3D printer is used to produce structures on transparent conductive substrates. The printed structures are filled with PDLCs and covered with transparent conductive substrates to achieve tunable functions. The proposed configurations are implemented and verified. The experimental results show that the diffraction efficiency of the 0th order increases from 15% to 50% for the diffraction grating and the focusing spot intensity decreases from 74% to 12% after the application of an electric field. These results demonstrate the feasibility of the proposed tunable optical component configurations.

Orthogonal hologram memory extending from visible to UV mediated with TaOx/TiO2:Ag heterojunctions.

The photon-energy conversion covering the full spectral wave band is crucial for detecting and storing information. Schottky junctions in nanoscale such as TiO2:Ag enable multicolor photochromism and information storage in the visible region. However, the photoelectrons from the UV-excited semiconductor cause the loss of information. It has become a big challenge to the data memory of Schottky junctions extending from the visible to UV band. Herein, we construct a stacked heterojunction structure of TaOx/TiO2:Ag as a full wave band holographic memory. Coherent green laser beams are utilized to inscribe a Fourier transform hologram, followed by burning a computer-generated hologram in a focused UV laser spot array. The holographic array based on UV photothermal effect presents high refractive index modulation in the stacked layered oxide film. Meanwhile, the excellent UV protection of TaOx/TiO2 heterojunctions makes it possible to fully preserve previously written Fourier transform holographic data. Information cross talk between the two kinds of holograms is almost inhibited. This work provides a bright way for high-density data storage, wideband optical detection, and advanced manufacturing of micro-optical components.

Femtosecond Laser Fabrication of Gradient Index Micro-Optics in Chalcogenide Glass

Gradient refractive index (GRIN) lenses have been widely used for many applications. However, the traditional manufacturing methods of GRIN lenses are very time-consuming and only suitable for macro-scale operations. In addition, those methods do not have the ability to produce other GRIN optical components with complex refractive index profiles like aspheric or freeform components. We report here an approach to produce GRIN micro-optical components in chalcogenide glass based on a direct laser writing technique. Using this approach, we are able to locally modulate the refractive index of the glass subtrates and create an arbitrary refractive index profile. To prove the flexibility of the method for the production of GRIN micro-optics, we fabricated GRIN micro-lenses and a micro-Fresnel axicon (Fraxicon). The optical properties of micro-lenses can be controlled by varying the writing parameters or the substrate thickness. As a result, the working distance of the micro-lenses can extend from 0 to more than 1000 μm. Also, the micro-Fraxicon exhibits the ability to convert a Gaussian beam to a Bessel-like beam which concentrates the mid-infrared light into an approximately 1200 μm long confinement zone.

Advanced visual components inspired by animal eyes.

Artificial vision systems pervade our daily lives as a foremost sensing apparatus in various digital technologies, from smartphones to autonomous cars and robotics. The broad range of applications for conventional vision systems requires facile adaptation under extreme and dynamic visual environments. However, these current needs have complicated individual visual components for high-quality image acquisition and processing, which indeed leads to a decline in efficiency in the overall system. Here, we review recent advancements in visual components for high-performance visual processing based on strategies of biological eyes that execute diverse imaging functionalities and sophisticated visual processes with simple and concise ocular structures. This review first covers the structures and functions of biological eyes (i.e., single-lens eyes and compound eyes), which contain micro-optic components and nanophotonic structures. After that, we focus on their inspirations in imaging optics/photonics, light-trapping and filtering components, and retinomorphic devices. We discuss the remaining challenges and notable biological structures waiting to be implemented.

Beam shaping elements for single photon sources based on 3D printed micro-optics

Multiple researchers have explored the use of 3D printed micro-optical components as interfaces to quantum point emitters by considering different designs and configurations. Typically, these designs involve parametric structures optimized in combination with idealized point source models following the principles of imaging optics. In this work, we propose a different approach based on the use of well-known numerical routines developed in the field of illumination optics. We compare the obtained design to reference parametric 3D printed based interfaces, which have been used in the context of 3D printed micro-optical interfaces to single photon sources.

On-chip light sheet illumination for nanoparticle tracking in microfluidic channels.

A simple and inexpensive method is presented to efficiently integrate light sheet illumination in a microfluidic chip for dark-field microscopic tracking and sizing of nanoparticles. The basic idea is to insert an optical fiber inside a polydimethylsiloxane (PDMS) elastomer microfluidic chip and use it as a cylindrical lens. The optical fiber is in this case no longer seen as only an optical waveguide but as a ready-made micro-optical component that is inexpensive and easy to source. Upon insertion, the optical fiber stretches the PDMS microchannel walls, which has two effects. The first effect is to tone down the intrinsic ripples in the PDMS that would otherwise create inhomogeneities in the light sheet illumination. The second effect is to remove any obliqueness of the channel wall and constrain it to be strictly perpendicular to the propagation of the illumination, avoiding the formation of a prismatic diopter. Through calculations, numerical simulations and measurements, we show that the optimal configuration consists in creating a slowly converging light sheet so that its axial thickness is almost uniform along the tracked area. The corresponding thickness was estimated at 12 μm, or 10 times the depth of field of the optical system. This leads to an at least six-fold increase in the signal-to-noise ratio compared to the case without the cylindrical lens. This original light-sheet configuration is used to track and size spherical gold nanoparticles with diameters of 80 nm and 50 nm.

Advances in fabrication of micro-optical components by femtosecond laser with etching technology

Advances in fabrication of micro-optical components by femtosecond laser with etching technology

Effects of high-power laser radiation on polymers for 3D printing micro-optics

3D printing has become a widely used technique for manufacturing micro-optical components for sensing, measurements, biomedical and quantum technologies. Hence, knowing the maximum usable power or damage thresholds of 3D-printed micro-optics becomes crucial. Here we present a first study of the damage threshold values of the IP-S photoresist under high-power cw-, fs-, and ns-pulsed laser radiation with wavelengths in the NIR range. We also study the differences between visual evaluation using bright-field microscopy, DIC-microscopy, and beam-profile damage detection. Finally, we present several application-inspired use cases of 3D printed fiber micro-optics, reaching 10.5 W output power of cw-radiation at 915 nm and 4.5 W and 550 fs pulsed operation at 1040 nm.

A 3D-Printed Micro-Optofluidic Chamber for Fluid Characterization and Microparticle Velocity Detection.

This work proposes a multi-objective polydimethylsiloxane (PDMS) micro-optofluidic (MoF) device suitably designed and manufactured through a 3D-printed-based master-slave approach. It exploits optical detection techniques to characterize immiscible fluids or microparticles in suspension inside a compartment specifically designed at the core of the device referred to as the MoF chamber. In addition, we show our novel, fast, and cost-effective methodology, dual-slit particle signal velocimetry (DPSV), for fluids and microparticle velocity detection. Different from the standard state-of-the-art approaches, the methodology focuses on signal processing rather than image processing. This alternative has several advantages, including the ability to circumvent the requirement of complex and extensive setups and cost reduction. Additionally, its rapid processing speed allows for real-time sample manipulations in ongoing image-based analyses. For our specific design, optical signals have been detected from the micro-optics components placed in two slots designed ad hoc in the device. To show the devices' multipurpose capabilities, the device has been tested with fluids of various colors and densities and the inclusion of synthetic microparticles. Additionally, several experiments have been conducted to prove the effectiveness of the DPSV approach in estimating microparticle velocities. A digital particle image velocimetry (DPIV)-based approach has been used as a baseline against which the outcomes of our methods have been evaluated. The combination of the suitability of the micro-optical components for integration, along with the MoF chamber device and the DPSV approach, demonstrates a proof of concept towards the challenge of real-time total-on-chip analysis.

Numerical analysis of micro-optics based single photon sources via a combined physical optics and rigorous simulations approach.

The use of 3D printed micro-optical components has enabled the miniaturization of various optical systems, including those based on single photon sources. However, in order to enhance their usability and performance, it is crucial to gain insights into the physical effects influencing these systems via computational approaches. As there is no universal numerical method which can be efficiently applied in all cases, combining different techniques becomes essential to reduce modeling and simulation effort. In this work, we investigate the integration of diverse numerical techniques to simulate and analyze optical systems consisting of single photon sources and 3D printed micro-optical components. By leveraging these tools, we primarily focus in evaluating the impact of different far-field spatial distributions and the underlying physical phenomena on the overall performance of a compound micro-optical system via the direct evaluation of a fiber in-coupling efficiency integral expression.

All-polarization-maintaining dual-comb fiber laser with mechanically shared cavity configuration and micro-optic component

An all-polarization-maintaining dual-comb fiber laser with a mechanical shared-cavity configuration was demonstrated. The laser cavity configuration was simplified and downsized using the micro-optic component of a saturable absorber mirror and a wavelength-division multiplexer. A high relative frequency stability was achieved with an Allan deviation of 0.02 Hz. Further, the all-polarization-maintained fiber-based configuration facilitated an integrated phase noise of the relative beat note between dual-frequency combs of 378 rad (10 Hz−1 kHz) and 9.0 rad (100 Hz−1 MHz). The simple, compact, and robust dual-comb fiber laser yielded highly mutually coherent dual-optical frequency combs without active servo control, and significantly simplified dual-comb spectroscopy.

An automated optical inspection (AOI) platform for three-dimensional (3D) defects detection on glass micro-optical components (GMOC)

With the widespread deployment of wavelength division multiplexing (WDM), optical transceivers increasingly use many glass micro-optical components (GMOC). Visual inspection of these GMOCs is a critical manufacturing step to ensure quality and reliability. However, manual inspection is often labor-intensive and time-consuming due to the transparent nature of glass components and the small, randomly located defects in three dimensions. Although automated optical inspection (AOI) exists, it has not yet been able to provide the desired level of accuracy and efficiency.This paper reports the development of an AOI platform for 3D defect detection on GMOCs. The platform incorporates 3D video acquisition and a novel two-stage neural network machine-learning algorithm. It includes a robotic arm for moving parts in 3D, a camera with an illumination module for video acquisition, and a video streaming processing unit with a machine vision algorithm for real-time defect detection on a production line. The robotic arm enables multi-perspective video capture of a test sample without refocusing. The two-stage machine learning network uses a modified YOLOv4 architecture with color channel separation (CCS) convolution, an image quality evaluation (IQE) module, and a frame fusion module to integrate the single frame detection results. This network can process multi-perspective video streams in real-time for defects detection in a coarse-to-fine manner. The AOI platform was trained with only 30 samples and achieved promising performances with a recall rate of 1, a detection accuracy of 97%, and an inspection time of 48 s per part.

Demonstration of a Single-Mode Expanded-Beam Connectorized Module for Photonic Integrated Circuits

We present the optical and mechanical designs of an optically-pluggable package for photonic integrated circuits (PICs). Using off-the-shelf micro-optical components, low-loss (∼2 dB) expanded-beam connection between an edge-coupled SiN-based PIC and standard optical fiber is demonstrated. High reproducibility of coupling efficiency is demonstrated over up to 80 mating/de-mating cycles.

Laser-Induced Fabrication of Micro-Optics on Bioresorbable Calcium Phosphate Glass for Implantable Devices.

In this study, a single-step nanosecond laser-induced generation of micro-optical features is demonstrated on an antibacterial bioresorbable Cu-doped calcium phosphate glass. The inverse Marangoni flow of the laser-generated melt is exploited for the fabrication of microlens arrays and diffraction gratings. The process is realized in a matter of few seconds and, by optimizing the laser parameters, micro-optical features with a smooth surface are obtained showing a good optical quality. The tunability of the microlens' dimensions is achieved by varying the laser power, allowing the obtaining of multi-focal microlenses that are of great interest for three-dimensional (3D) imaging. Furthermore, the microlens' shape can be tuned between hyperboloid and spherical. The fabricated microlenses exhibited good focusing and imaging performance and the variable focal lengths were measured experimentally, showing good agreement with the calculated values. The diffraction gratings obtained by this method showed the typical periodic pattern with a first-order efficiency of about 5.1%. Finally, the dissolution characteristics of the fabricated micropatterns were studied in a phosphate-buffered saline solution (PBS, pH = 7.4) demonstrating the bioresorbability of the micro-optical components. This study offers a new approach for the fabrication of micro-optics on bioresorbable glass, which could enable the manufacturing of new implantable optical sensing components for biomedical applications.

Calcination-Enhanced Laser-Induced Damage Threshold of 3D Micro-Optics Made with Laser Multi-Photon Lithography

Laser Direct Writing (LDW), also known as 3D multi-photon laser lithography of resins, is a promising technique for fabricating complex free-form elements, including micro-optical functional components. Regular organic or hybrid (organic–inorganic) resins are often used, with the latter exhibiting better optical characteristics, as well as having the option to be heat-treated into inorganic glass-like structures particularly useful for resilient micro-optics. This work is a continuation of our SZ2080™ calcination development of micro-optics, specifically studying the Laser-Induced Damage Threshold (LIDT). Such sol–gel-derived glass 3D micro-structures, particularly those that undergo heat treatment, have not been well-characterized in this respect. In this pilot study, we investigated the LIDT using the Series-on-One (S-on-1) protocol of functional micro-lenses produced via LDW and subsequently calcinated. Our results demonstrate that the LIDT can be significantly increased, even multiple times, by this approach, thus enhancing the resilience and usefulness of these free-form micro-optics. This work represents the first investigation in terms of LIDT into the impact of calcination on LDW-produced, sol–gel-derived glass micro-structures and provides important insights for the development of robust micro-optical devices.

Design and Realization of Polymeric Waveguide/Microring Structures for Telecommunication Domain.

Polymer-based micro-optical components are very important for applications in optical communication. In this study, we theoretically investigated the coupling of polymeric waveguide and microring structures and experimentally demonstrated an efficient fabrication method to realize these structures on demand. First, the structures were designed and simulated using the FDTD method. The optical mode and loss in the coupling structures were calculated, thereby giving the optimal distance for optical mode coupling between two rib waveguide structures or for optical mode coupling in a microring resonance structure. Simulations results then guided us in the fabrication of the desired ring resonance microstructures using a robust and flexible direct laser writing technique. The entire optical system was thus designed and manufactured on a flat base plate so that it could be easily integrated in optical circuits.

Wear of mold surfaces: Interfacial adhesion in precision glass molding

Micro-optical components, such as glass-based microlens arrays, have become essential in applications relying on advanced optical systems such as 3D displays, optical fiber coupling, and unmanned vehicles. Precision glass molding (PGM) has emerged as a promising method for fabricating optical components based on the formability of glasses beyond their glass transition temperature (Tg), while adhesion wear strength and mechanism of mold-glass interfaces remain major obstacles. This paper aims to explore the adhesion wear mechanisms between mold surfaces and optical glass D-FK95 in PGM. The applicability of WC molds with coatings of Ta–C, AlCrN, and AlTiN was investigated respectively considering their thermodynamic properties and surface energy characteristics. The study identified three adhesion wear mechanisms in the open-air atmosphere with WO3 oxidation on mold surfaces and four adhesion mechanisms featured by scattered distribution, island aggregation, dispersed flow, and planar coverage in an inert atmosphere. It was also found that when the temperature was close to Tg, the WC-glass adhesion force was negligible. The adhesion stress increased to 0.80 MPa with an increase in the applied temperature and pressure. With coating, however, the adhesion stress reduced significantly to 0.03 MPa. The study also concluded that when paired with the D-FK95 glass, the WC mold coated with Ta–C provides the best anti-adhesive performance in comparison to those with AlCrN and AlTiN coatings.

Special Section Guest Editorial: Microendoscopy

The <i>Journal of Optical Microsystems</i> is a Gold Open Access journal that publishes cutting-edge research in all aspects of optical and photonic microsystems, from materials and fabrication of micro-optical and photonic components, through assembly and packaging, to systems and applications. Open access fees will be waived for all submissions through 2023.

Advanced Technologies in the Fabrication of a Micro-Optical Light Splitter

In microfluidics, it is important to confine and transport light as close as possible to the sample by guiding it into a small volume of the microfluidic channel, acquiring the emitted/transmitted radiation. A challenge in this context is the miniaturization of the optical components and their integration into the microfluidic device. Among all of the optical components, a particular role is played by the beam splitter, an important optical device capable of splitting light into several paths. In this paper, a micro-splitter is designed and realized by exploiting low-cost technologies. The micro-splitter consists of a micro-mirror in-between two micro-waveguides. This component was fabricated in different materials: poly-dimethyl-siloxane (PDMS), poly(methyl methacrylate) (PMMA), and VeroClear RGD810. A 3D printing master–slave fabrication protocol was used with PDMS, a direct 3D printing approach with VeroClear, and a laser cutting procedure with PMMA. The experimental results obtained show the high potential of the proposed fabrication protocols, based on low-cost technologies, for the realization of micro-optical components, which could also be easily integrated with microfluidics systems.

Complex aspherical singlet and doublet microoptics by grayscale 3D printing.

We demonstrate 3D printed aspherical singlet and doublet microoptical components by grayscale lithography and characterize and evaluate their excellent shape accuracy and optical performance. The typical two-photon polymerization (2PP) 3D printing process creates steps in the structure which is undesired for optical surfaces. We utilize two-photon grayscale lithography (2GL) to create step-free lenses. To showcase the 2GL process, the focusing ability of a spherical and aspherical singlet lens are compared. The surface deviations of the aspherical lens are minimized by an iterative design process and no distinct steps can be measured via confocal microscopy. We design, print, and optimize an air-spaced doublet lens with a diameter of 300 µm. After optimization, the residual shape deviation is less than 100 nm for the top lens and 20 nm for the bottom lens of the doublet. We examine the optical performance with an USAF 1951 resolution test chart to find a resolution of 645 lp/mm.