New solutions are required for short-range optical transmission without lithography due to the complex and inflexible manufacturing processes. Glass is an excellent material for optical applications. Still, few microprocessing technologies are available, which are limited in precision and design freedom. A new glass micromachining process called Laser Induced Deep Etching (LIDE) can accurately machine many types of glass without generating micro-cracks, introducing stress, or causing other damage. This study uses LIDE to produce carrier substrates out of glass for integrated optical systems. Due to its transmission characteristics and refractive index, it also functions as optical cladding for integrated polymer optical waveguides. U-shaped cavities are etched into the glass and filled using the doctor-blade technologie with conventional liquid optical polymers, which are then globally cured. This novel manufacturing method is called LDB (LIDE-Doctor-blade). Optical waveguiding in the visible to near-infrared wavelength range is possible by the higher refractive index of the cured polymer. The waveguide is embedded in a near-surface cavity, with no additional upper cladding other than air to the environment, created by a combination of subtractive and additive manufacturing processes. The exposed area can affect transmission quality, and this study purposely exploits this by applying fluids with different properties, such as refractive index and viscosity. Changes in intensity are analyzed and evaluated to demonstrate a sensory function.
Rotative printing technologies are an approach to manufacturing polymer optical waveguides with high throughput for applications such as electro-optical circuit boards (EOCB) or smart packaging. Processes presumably originating in graphical applications apply defined amounts of polymer onto a polymer substrate. Unlike graphical printing, the use of these processes to manufacture functional waveguides underlies different requirements regarding material transfer, structure of the printed polymer, and multi-layer stacking of functional layers. This work applies the manufacturing processes gravure printing and flexographic printing to realize waveguide cores onto PMMA substrates. Therefore, a modular printing machine with high positional accuracy between multiple printed layers is used. The waveguides are further cladded with another PMMA substrate using thermal lamination. The processes are evaluated according to waveguide geometry and optical parameters. Material transfer per layer, resulting geometrical quality, and aspect ratio of the waveguides are compared regarding their manufacturing process. Functional tests are conducted as optical attenuation measurements to evaluate the waveguide's macro range performance. Using these results, the potentials of each process for an upcoming production of fully-printed cladded waveguides are determined and showcased.
Printing optical waveguides is an approach to the high volume implementation of optical data transmission in conventional electronic systems. Flexographic printing enables the manufacturing of circular segment-shaped polymer waveguides on planar substrates, which show great potential as economic Gbit/s-capable short-range networks. This work describes a process chain to manufacture and integrate a printed optical data transmission path in conventional printed circuit boards (PCB). This sequence of processes gives an outlook on up-scaling utilizing printed optical waveguides to mass manufacturing. Since the significant challenge in integration is achieving sufficient optical coupling, geometrical tolerances are investigated using raytracing simulation. Relevant degrees of freedom of the laser diode and waveguide are varied and validated by measuring alignment profiles. As a result, the mechanical interface provided by the PCB is presented and validated by confocal measurements. An innovative pick and place tool assembles the separated flexible waveguide to realize a demonstration system. As a validation, Fast Ethernet data transmission is presented over a flexible optical connection. In further steps, a miniaturization of the system is the goal to achieve a standardized system for applications like galvanic isolation.
While glass is an ideal material for optics, only a few microprocessing technologies are available. These technologies are usually limited regarding precision and freedom of design. A novel glass micromachining process is Laser Induced Deep Etching (LIDE). Without generating micro-cracks, introducing stress or other damages, it offers the possibility to precisely machine many types of glass. A broad range of features such as high-aspect ratio through holes, cutouts and slits in glass are available. In this work, LIDE is used to produce glass carrier substrates for integrated optical systems. Due to transmission characteristics and refractive index, the glass can be used as optical cladding for integrated polymer optical waveguides (refractive indices < 1.45). Cavities in glass, which can have different cross-sections e.g. u- or v-shaped, are filled with photoactive material by a doctor blade and function as an optical waveguide core. An additional approach examined in this work is the integration of optical fiber into v-shaped cavities. The system uses bare die laser diodes as transmitters and photo diodes as receivers bonded in front of the waveguide. LIDE technology allows to passively align the manufactured optical waveguide in front of the light source and detector due to mechanical features in the carrier substrate itself, eliminating the need for time-consuming and complex active alignment processes. This paper shows geometrical characteristics of waveguides and cavities, with a particular focus on surface roughness and subsequent filling ratio of the optical waveguide. Furthermore, the relative intensity distribution in the waveguide is presented and analyzed.
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