An integrated optical displacement sensor based on a reflective Mach–Zehnder interferometer (MZI) was developed. The sensor features a low-loss autocollimation measurement head fabricated using a 62.5-μm gradient index fiber as lens, which separates the incoming and reflected light. The mounting of the lenses and the fiber coupling were performed using a passive alignment assembly technology. Using a 3 × 3 directional coupler (DC), the direction of the phase shift can be resolved. The measurement head exhibits low losses compared to a conventional DC to separate the reflected light. A measurement range of 225 μm could be achieved in good agreement with the expected 230 μm. The results show a good agreement between simulation and measurements. Using basic measurement electronics, movements of 2 nm can be resolved, while a resolution of <1 nm is expected using optimized measurement equipment.
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.
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 .
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 PCB's 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 PCB's 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.
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