Diffractive Micro-optics Research Articles

Diffractive microoptics in porous silicon oxide by grayscale lithography

We demonstrate focusing as well as imaging using diffractive microoptics, manufactured by two-photon polymerization grayscale lithography (2GL), that have been 3D printed into porous silicon oxide. While typical doublet lens systems require support structures that hold the lenses in place, our optics are held by the porous media itself, decreasing both the fabrication time and design constraints while increasing the optically active area. Compared to the typical two-photon polymerization fabrication process, 2GL offers better shape accuracy while simultaneously increasing throughput. To showcase 2GL manufactured optics in porous media, we fabricate singlet diffractive lenses with a diameter of 500 µm and numerical apertures of up to 0.6. We measure the intensity distribution in the focal plane, and along the optical axis. Furthermore, we design and fabricate a doublet lens system for imaging purposes with a diameter of 600 µm and thinner than 60 µm. We examine the imaging performance with a USAF 1951 resolution test chart and determine the resolution to be 287 lp/mm. 3D printing in porous SiO2 thus holds great promise for future complex and unconventional microoptical solutions.

Two-photon polymerization of silica glass diffractive micro-optics with minimal lateral shrinkage.

Three-dimensional printing enables the fabrication of silica glass optics with complex structures. However, shrinkage remains a significant obstacle to high-precision 3D printing of glass optics. Here we 3D-printed Dammann gratings (DGs) with low lateral shrinkage (<4%) using a two-photon polymerization (2PP) technique. The process consists of two steps: patterning two-photon polymerizable glass slurry with a 515 nm femtosecond laser to form desired structures and debinding/sintering the structures into transparent and dense silica glass. The sintered structures exhibited distinct shrinkage rates in the lateral against longitudinal directions. As the aspect ratio of the structures increased, the lateral shrinkage decreased, while the longitudinal shrinkage increased. Specifically, the structure with an aspect ratio of approximately 60 achieved a minimal lateral shrinkage of 1.1%, the corresponding longitudinal shrinkage was 61.7%. The printed DGs with a surface roughness below 20 nm demonstrated good beam-shaping performance. The presented technique opens up possibilities for rapid prototyping of silica diffractive optical elements.

Phase-type diffractive micro-optics elements in sulfur-based polymeric glass by femtosecond laser direct writing.

Sulfur-based polymeric glasses are promising alternative low-cost IR materials due to their profoundly high IR transparency. In this Letter, femtosecond-laser-induced refractive index change (RIC) was investigated in one typical sulfur-based polymeric glass material, poly(S-r-DIB), for the first time, to the best of our knowledge. The RIC in the laser-engineered region was quantitively characterized, which laid a foundation for phase-type optical element design. By the integration of RIC traces, embedded phase-type micro-optics elements, including Fresnel zone plates, and a Dammann grating were fabricated in bulk poly(S-r-DIB) polymeric glass substrate via the femtosecond laser direct writing technique. The imaging and beam shaping performance were demoed in the near-infrared (NIR) region.

Spatial beam intensity shaping using phase masks on single-mode optical fibers fabricated by femtosecond direct laser writing

Submicrometer dielectric phase masks allow for the realization of the miniaturization of high-quality optical elements. In this Letter we demonstrate spatial intensity beam shaping using phase masks attached to optical single-mode fibers. The phase masks are directly fabricated onto the end facet of optical fibers using femtosecond two-photon direct laser writing, achieving, therefore, submicrometer alignment accuracy. We observe high-quality intensity patterns and find excellent agreement with simulations. Our results prove that 3D printing of diffractive micro-optics can achieve sufficient performance to enable compact devices.

Micro-optics and lithography simulation are key enabling technologies for shadow printing lithography in mask aligners

Abstract Mask aligners are lithographic tools used to transfer a pattern of microstructures by shadow printing lithography onto a planar wafer. Contact lithography allows us to print large mask fields with sub-micron resolution, but requires frequent mask cleaning. Thus, contact lithography is used for small series of wafer production. Proximity lithography, where the mask is located at a distance of typically 30–100 μm above the wafer, provides a resolution of approximately 3–5 μm, limited by diffraction effects. Proximity lithography in mask aligners is a very cost-efficient method widely used in semiconductor, packaging and MEMS manufacturing industry for high-volume production. Micro-optics plays a key role in improving the performance of shadow printing lithography in mask aligners. Refractive or diffractive micro-optics allows us to efficiently collect the light from the light source and to precisely shape the illumination light (customized illumination). Optical proximity correction and phase shift mask technology allow us to influence the diffraction effects in the aerial image and to enhance resolution and critical dimension. The paper describes the status and future trends of shadow printing lithography in mask aligners and the decisive role of micro-optics as key enabling technology.

Protein-based soft micro-optics fabricated by femtosecond laser direct writing

In this work, we report a novel soft diffractive micro-optics, called ‘microscale kinoform phase-type lens (micro-KPL)’, which is fabricated by femtosecond laser direct writing (FsLDW) using bovine serum albumin (BSA) as building blocks and flexible polydimethylsiloxane (PDMS) slices as substrates. By carefully optimizing various process parameters of FsLDW (e.g., average laser power density, scanning step, exposure time on a single point and protein concentration), the as-formed protein micro-KPLs exhibit excellent surface quality, well-defined three-dimensional (3D) geometry and distinctive optical properties, even in relatively harsh operation environments (for instance, in strong acid or base). Laser shaping, imaging and other optical performances can be easily achieved. More importantly, micro-KPLs also have unique flexible and stretchable properties as well as good biocompatibility and biodegradability. Therefore, such protein hydrogel-based micro-optics may have great potential applications, such as in flexible and stretchable photonics and optics, soft integrated optical microsystems and bioimplantable devices. Scientists have used direct laser writing to fabricate flexible and biocompatible optical elements from a protein hydrogel. Yun-Lu Sun and co-workers from Jilin University in China and Pohang University of Science and Technology in Korea say that the miniature optical components produced using this approach could be useful for use in photonic implants or as stretchable optical devices. They fabricated soft, phase-type diffractive lenses with diameters of 50–100 µm by focusing femtosecond pulses from a Ti:sapphire laser into an aqueous ‘protein ink’ comprising a mixture of bovine serum albumin and the photosensitizer methylene blue. Irradiated regions underwent two-photon polymerization to form a soft protein hydrogel. By moving both the laser beam and the sample, the researchers successfully fabricated a three-dimensional optic featuring the desired series of concentric rings needed to act as a phase-type lens.

Emitting far-field multicolor patterns and characters through plastic diffractive micro-optics elements illuminated by common Gaussian lasers in the visible range

Far-field multicolor patterns and characters are emitted effectively in a relatively wide and deep spatial region by plastic diffractive micro-optics elements (DMOEs), which are illuminated directly by common Gaussian lasers in the visible range. Phase-only DMOEs are composed of a large number of fine step-shaped phase microstructures distributed sequentially over the plastic wafer selected. The initial DMOEs in silicon wafer are fabricated by an innovative technique with a combination of a single-mask ultraviolet photolithography and low-cost and rapid wet KOH etching. The fabricated silicon DMOEs are further converted into a nickel mask by the conventional electrochemical method, and they are finally transferred onto the surface of the plastic wafer through mature hot embossing. Morphological measurements show that the surface roughness of the plastic DMOEs is in the nanometer range, and the feature height of the phase steps in diffractive elements is in the submicrometer scale, which can be designed and adjusted flexibly according to requirements. The dimensions of the DMOEs can be changed from the order of millimeters to centimeters. A large number of pixel phase microstructures with a square microappearance employed to construct the phase-only DMOEs are created by the Gerchberg-Saxton algorithm, according to the target patterns and characters and common Gaussian lasers manipulated by the DMOEs fabricated.

Replicated Diffractive Optics and Micro-Optics

Replication technology has moved into the submicrometer world thanks to recent advances in materials and processes. New commercial applications of diffractive optics and micro-optics have emerged as a result.

Diffractive optics and micro-optics: introduction to the feature issue

This issue of Applied Optics features 16 papers on the fabrication, design, and applications of diffractive optics and micro-optics. A companion issue of the Journal of the Optical Society of America A, guest edited by J. N. Mait and H. P. Herzig, presents papers that emphasize the modeling and design of diffractive and micro-optical components.

Diffractive Optics and Micro-optics

Diffractive Optics and Micro-optics

Diffractive optics and micro-optics: introduction to the feature issue

This issue of Applied Optics features 16 papers related to the fabrication, design, and application of diffractive and micro-optical elements. A companion feature in the Journal of the Optical Society of America A [J. Opt. Soc. Am. A 16(5), 1091 (1999)] includes papers on the modeling of diffractive elements.

Diffractive Optics and Micro-Optics: Modeling, Design, Fabrication, and Applications

Diffractive Optics and Micro-Optics: Modeling, Design, Fabrication, and Applications

Pattern transfer for diffractive and refractive microoptics

Pattern transfer technologies developed for very large and ultra-large scale integrated (VLSI and ULSI) circuit processing can be adapted to fabricate high fidelity microstructures for planar diffractive and refractive optical elements (DOEs and ROEs). Lithographic, dry-etching, and material deposition techniques used to pattern continuous and stepped microoptical surface relief structures in dielectric, metallic, and semiconductor materials are reviewed. Examples are given of multilevel DOEs, analog refractive lenslet arrays, and subwavelength structures.

Diffractive optics and micro-optics: introduction to the feature issue

This issue of Applied Optics features 19 articles related to the fabrication and the design of diffractive and micro-optics as well as their applications. A companion feature in the Journal of the Optical Society of America A includes papers on the modeling of diffractive elements.

An optical backplane demonstrator system based on FET-SEED smart pixel arrays and diffractive lenslet arrays

We have demonstrated a representative portion of an optical backplane using FET-SEED smart pixels and free-space optics to interconnect printed circuit boards (PCB's) in a two board, unidirectional link configuration. 4/spl times/4 arrays of FET-SEED transceivers were designed, fabricated, and packaged all the PCB level, The optical interconnection was constructed using diffractive microoptics, and custom optomechanics. The system was operated in two modes, one showing high data throughput, 100 MBit/sec, and the other demonstrating large connection densities, 2222 channel/cm/sup 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Planar-optic-disk pickup with diffractive micro-optics

An integrated optical-disk pickup with a diffractive planar micro-optic system is proposed. In this device, the beam follows a zigzag optical path inside a glass substrate that is used as a light guide. To fabricate off-axis diffractive optical elements, we have recently developed an electron-beam writing system with a curve-pattern generator. It is demonstrated that a transmission off-axis objective microlens, a reflection twin-focusing beam splitter, and reflection layers were integrated on a glass substrate, and such a diffractive planar micro-optic system exhibited an excellent focusing performance and operated forfocus-error signal detection, as designed.

Refractive-diffractive micro-optics for permutation interconnects

Refractive and diffractive micro-optics are combined in monolithically fabricated array components for free-space permutation interconnects. Such space-variant optical interconnects are, e.g., of major importance for smart pixel architectures, which are proposed for photonic switching applications in telecommunication and data communication and for more general parallel information processing, for example, of images. The advantages of the considered optical concept and an experimental demonstration of a 2-D perfect shuttle interconnect with 8 x 8 optical channels are described. We also discuss the scaling behavior and the alignment and wavelength tolerances of the interconnect system.