Markus Michler

Mass production of planar polymer waveguides and their applications

The increasing demand for planar polymer optical waveguides integrated into electrical printed circuit boards (PCB) calls for mass production capabilities: Hence, appropriate materials, systems, assembly concepts and production technologies become vital, in order to guarantee a high reproducibility and quality of the waveguides. The manufacturing and assembly costs have to be kept on a low level, while the integration of the highly sensible waveguides into the rough environment of PCBs with their cheap and non-ideal substrates is a particular challenge. The present paper describes an assembly and manufacturing technology for electro-optical circuit boards which meets these requirements. First, the manufacturing and characterization of multimode polymer waveguides is presented and the process for layer deposition and structuring is described. Specific attention is given to the reproducibility of these processes ensuring the high optical quality of the waveguides. Additionally, some problems arising from the integration of the waveguides into the PCBs are discussed. Second, various light coupling concepts are presented. In particular, a novel mirror element based on parabolic reflectors is described. The optical design was calculated analytically and optimized using computer simulations. The mirror element was fabricated using injection molding in a reproducible manner at high quantities and lowest cost. To allow for a wider tolerance in the subsequent assembly steps our novel electro-optical transceivers concept facilitates the use of conventional SMD- placement machines for mounting which makes the process very cost effective. This concept was demonstrated successfully and is also described within the third section. In the last part the practical use of this building set is illustrated with different successfully realized applications in the field of ICT and optical sensor technology.

Passively aligned multichannel fiber-pigtailing of planar integrated optical waveguides

Abstract. A silicon device to simplify the coupling of multiple single-mode fibers to embedded single-mode waveguides has been developed. The silicon device features alignment structures that enable a passive alignment of fibers to integrated waveguides. For passive alignment, precisely machined V-grooves on a silicon device are used and the planar lightwave circuit board features high-precision structures acting as a mechanical stop. The approach has been tested for up to eight fiber-to-waveguide connections. The alignment approach, the design, and the fabrication of the silicon device as well as the assembly process are presented. The characterization of the fiber-to-waveguide link reveals total coupling losses of (0.45±0.20  dB) per coupling interface, which is significantly lower than the values reported in earlier works. Subsequent climate tests reveal that the coupling losses remain stable during thermal cycling but increases significantly during an 85°C/85 Rh-test. All applied fabrication and bonding steps have been performed using standard MOEMS fabrication and packaging processes.

Influence of temperature and environment on the laser damage threshold of ion-beam sputtered anti-reflective coatings at 355 nm wavelength

In this investigation the influence of the local environment on the laser damage threshold of anti-reflective coatings is reported. For this purpose, HfO2 / SiO2 anti-reflective coatings were deposited on fused silica substrates using an ionbeam sputter system. Laser damage threshold measurements were performed using two test procedures, S-on-1 and Ron- 1, at 355 nm for temperatures ranging from room temperature up to 250 °C and in different atmospheres. The two test procedures had comparable LIDT results with a possible pre-conditioning effect evidenced by a broadening of the transition range of the R-on-1 measured samples. It was found that samples measured in normal atmospheric air showed superior laser resistance compared to samples measured under nitrogen purge or in dry air. Samples measured in normal atmospheric air also showed a temperature dependence with an improved laser resistance at 25 °C. No temperature dependence was observed for samples measured under nitrogen purge or in dry air. In this paper, literature showing similar effects is reviewed and the influence of a water epilayer on the coating as a possible cause for the observed results is discussed.

Measurement of the thermo-optical effect of integrated waveguides

Thermo-optical switches are widely used in integrated optics and various types of integrated optical structures have been reported in literature. These structures include, but are not limited to Mach-Zehnder-Interferometer (MZI) switches and digital optical switches. The thermo-optical effect depends on the refractive index, the polarizability and the density of a material. The polarizability effect can often be neglected and the change of refractive index is dominated by a density change due to the thermal expansion of the material. We report herein a new method to measure the thermo-optical effect of waveguides directly, using integrated MZIs fabricated in polymer waveguide technology. Common methods rely on macroscopic samples, but the properties can differ significantly for micro-structured waveguides. Using a floodlight halogen rod lamp and metal-shields, we realized a radiation heater with a trapezoidal-shaped heating pattern. While the heating occurred from the bottom side, a thermocouple was placed on top of the sample. By dynamically measuring the temperature and the corresponding output-power of the MZI, the temperature difference between constructive and destructive interference can be determined. Multiple measurements of different sample MZIs exhibit an average thermo-optical coefficient (TOC) of 1.6 ∗ 10-4 1/K .

Investigation of the ageing effects exhibited by AR coatings exposed to ultraviolet laser irradiation

Optical coatings used in ultraviolet applications are often exposed to harsh environments operating at elevated temperatures. In order to study the impact of the ageing effects optical coatings experience at various operating temperatures, an ultraviolet laser-induced degradation test system has been developed. It allows for flexible use in both a long-term stability test bench as well as in an LIDT measurement system. This work contains the preliminary results of optical degradation tests at 355 nm performed on anti-reflective coatings. As a subsequent step, the LIDT of the samples were measured using a Q-Switched Nd:YAG laser operating at 1064nm.

Comparative study of the laser damage threshold and optical characteristics of Ta2O5 - SiO2 multilayers deposited using various methods

Manufacturing processes from the private and academic sectors were used to deposit anti-reflective and high-reflective coatings composed of Ta2O5 - SiO2 multilayers. Used deposition techniques included three Ion Assisted Deposition (IAD) systems and an Ion Beam Sputtering (IBS) system. Coatings were performed on fused silica (Corning 7980) substrates polished by two different suppliers. LIDT Measurements were performed using a Q-Switched Nd:YAG laser operating at 1064nm. The paper presents a comparison of the coatings in terms of laser damage threshold values, optical properties and surface quality.