Effect of Two-Photon Laser Lithography Parameters on the Characteristics of Fabricated Features

Two-photon laser lithography has become one of the most promising additive manufacturing techniques on the micron scale and is applied, e.g., in fields of micro-optics and -robotics as well as optical and mechanical metamaterials. Here, we report on the feasibility, limits and general benefits of this method to fabricate material measures for the calibration of industrial optical topography measuring devices. Since calibration procedures are essential in the scientific and industrial application of those measuring instruments, appropriate material measures are highly required. In contrast to traditional manufacturing technologies, we show that two-photon laser lithography allows a highly resolved fabrication of multiple, almost arbitrary standardized calibration geometries on a micron length scale. Hereby, all structures are fabricated on only one single substrate, therefore enabling a mapping of a broad range of metrological characteristics for topography characterization. The most required calibration geometries are manufactured and analyzed regarding their aging behavior, their quality improvement by a post-UV development and the resolution limits within the manufacturing as well as the calibration process. Thus, the general industrial and scientific relevance of manufacturing material measures with two-photon laser lithography is demonstrated.

Novel cycles: humid air cycle systems

Laser-based micro- and nano-fabrication of photonic structures

6 - Laser-based micro- and nano-fabrication of photonic structures

ABSTRACTHigh quality templates of three-dimensional photonic crystals were fabricated in photoresist SU-8 using femtosecond laser lithography. The templates have woodpile and spiral architectures, which are widely expected to yield spectrally wide and robust photonic band gaps. Their optical characterization reveals fundamental and higher-order photonic stop-gaps in the infrared wavelength range of 2.0–8.0 μm. These templates are mechanically stable, nearly free of shrinkage-related deformations, and can be used for subsequent infiltration by optically active or high refractive index materials.

The development of the two-photon laser lithography technique for the fabrication of optical elements with characteristic dimensions of a few microns is an important goal. Here, two-photon laser lithography is used to produce micro-optical waveguides from OrmoComp® hybrid photoresist. The waveguides are optically isolated from a substrate and are connected to total internal reflection prism adapters for coupling optical radiation in and out of them. The transmission spectra of the entire input adapter–waveguide–output adapter structure are calculated and measured and it is shown that the transmission coefficient in the few-mode regime is 20–40% in the spectral range of 700–1650 nm. According to calculations, the main mechanism of losses in such a structure is determined by strong scattering in the region of joint between the conical part of the adapter and the waveguide caused by the complex structure of the optical field, as well as by the violation of the total internal reflection regime in the prisms due to the large angular aperture of the focused radiation beam. It is shown that the Goos–Hänchen effect has to be taken into account in the design of the coupling elements.

In this work we develop the concept of miniature Otto configuration. The distinctive feature of the proposed prism configuration is an operation for normal angle of incidence. Polymer microprisms with size of several tens of microns were fabricated by two-photon laser lithography on a surface of one-dimensional photonic crystal. The performance of the prisms was studied in the case of the Bloch surface waves excitation. Design of the prism and its optimal geometrical parameters were obtained from results of calculations. Bloch surface waves excitation with the microprisms was observed by the leakage radiation microscopy. The dependence of coupling efficiency on the angle of incidence was studied. Proposed prism configuration is easily compatible with fibers and is very appealing alternative to diffraction grating coupling for future applications.

Fabrication of active fluorescent microstructures with given parameters is an important task of integrated optics. One of the most efficient methods of fabrication of such microstructures is two-photon laser lithography. However, most polymers used in this technology have a relatively low quantum yield of fluorescence. In this work, the properties of microcavity structures obtained by the indicated method from hybrid polymers with addition of various dyes have been studied. The possibility of formation of high-quality microstructures from activated polymers, conservation of their luminescent properties after polymerization under intense laser irradiation, and reduction of the exposure of two-photon laser lithography by two orders of magnitude in the presence of Coumarin-1 dye has been demonstrated. The nonlinear optical microscopy study has shown that the spatial distribution of scattered fluorescence in microcavity structures based on the polymer with the dye corresponds to the excitation of cavity modes or whispering gallery modes.

The development and optimization of methods for creating functional elements of micron and sub-micron sizes for photonic integrated circuits is one of the main tasks of nanophotonics. Two-photon laser lithography is actively developing now to form three-dimensional structures with subwave resolution. Results of this development are reported and it is shown that the use of optimized lithography schemes, the spatial filtering of laser beam used, and the introduction of laser dyes into polymer lead to the formation of optically homogeneous high-quality bulk microstructures with characteristic features down to 300 nm with necessary functional properties. The capabilities of optimized two-photon laser lithography are demonstrated by examples of ring microcavities and optical waveguides with prism input/output adapters located above a substrate. Optical losses upon the coupling of 405-nm radiation into a waveguide using a printed prism adapter was no more than 1.25 dB.

We present an approach to produce plasmonic lithographic patterns with an extended circular dichroism response from the ultraviolet to the near infrared. We analyzed the optical chirality changes of the functionalized Ag nanospheres at every stage: from the chiral ligands to the patterned structures. The molecular chirality from the ligands is wavelength shifted and extended from the ultraviolet to visible after functionalization of the synthesized Ag nanoparticles in solution. New red shifted plasmon peaks appear in assembled metallic nanoparticles. Here we show that predefined optical properties of individual particles are also extended. Therefore, once the patterns are fabricated the optical activity is preserved and extended to the near infrared via induced collective plasmon modes.

An integrated polymer microtoroid resonator system fabricated using single-step, two-photon polymerization laser lithography is reported. The integrated microtoroid-waveguide system includes an integrated coupling waveguide for ease of optical coupling and has a quality factor of 16,000. We further demonstrate a nested double-spiral waveguide that allows higher spatial density of data, akin to a macroscopic form of space-division multiplexing. Experimental characterization reveals good transmission properties in the double-spiral waveguide device. In addition, the waveguides are demonstrated to support 30 Gb/s nonreturn-to-zero and 28 Gb/s pulse amplitude modulation 4 high-speed data.

N-type single-channel junctionless nanowire transistor (JNT) is fabricated on silicon-on-insulator substrate by the two-photon femtosecond laser lithography. The electrical properties of the device are investigated at room and low temperatures. At room temperature, the JNT demonstrates good performance, such as positive threshold voltage, subthreshold swing of 156 mV/dec, and on/off current ratio larger than 105. At low temperatures below 100 K, current oscillations are clearly observed in the initial stage of the conduction, resulting from the quantum confinement effects. In addition, the single channel device exhibits large low field electron mobility of ∼900 cm2 V−1 s−1 at the temperature of 100 K, which has been resulted from the bulk electron transport and incomplete ionization of impurities.

We review our recent results towards the development of a turnkey 3D laser printer, based on self-Q-switched microchip Nd:YAG lasers, with reproducible sub-100nm resolution, and with large-scale (cm) and fast-speed (cm/sec) capability at micron resolution. First of all, we report on line fabrication with 70nm lateral, and 150nm longitudinal resolutions without significant shrinking. This is due to the tight focusing with green visible wavelength, large numerical aperture, and excellent resin properties. Secondly, we report on two-photon sensitive photoacid generators that lead to efficient 3D microfabrication with epoxy SU-8 resin. Thirdly, we demonstrate high-speed microfabrication of large scale, millimeter size, scaffolds and cemtimeter height needle with high repetition rate (130Khz), and high average power (1W) amplified microchip laser. Finally we demonstrate the two-photon induced cross-linking of antibodies to determine the type of red blood cells in microfluidic channels.

A light-driven micro-motor has been fabricated by two-photon absorption laser lithography. The light-driven micro-motor generates optical torque due to momentum change when the incident light is refracted. Earlier scopes have reported a single-stage micro-motor, whereas in this study, we introduce a multi-stage approach of the micro-motor to increase torque and power of the motor. The single-stage and two-stage micro-motor was designed and fabricated. The micro-motor was made as an isosceles right triangle. A beam-concentration unit and a micro-motor in ion-exchanged water were placed on the stage of microscope. 200 mW laser power at 650 nm wavelength was used as a power source of the motor.

We discuss and describe the development of an origination process for planar free-form micro-optical elements from a given optical design. The targeted masters serve as origination structures for a roll-to-roll mass fabrication process. Specifically targeted are complex, optically smooth, surface relief structures with variable structure heights in the range of 1-20 µm, with typical lateral sizes of more than 5 µm. The area of the targeted masters is in the range of 1cm2. The main part of the paper is devoted to the description of a self-developed grayscale laser direct-write platform enabling one- and two-photon absorption lithography, also in combination on one and the same sample. In the following, we describe both methods and show that both lead to excellent structural quality of surface micro-relief structures. As a showcase of what the system can do in principle, we designed and fabricated free-form micro-optical elements to project light from an LED as a defined light pattern onto a wall. The proper optical functionality of the fabricated element was shown within a demonstrator setup.