Prototyping micro-optical components with integrated out-of-plane coupling structures using deep lithography with protons

Abstract

We present Deep Lithography with Protons (DLP) as a rapid prototyping technology to fabricate waveguidebased micro-optical components with monolithically integrated 45 • micro-mirrors acting as out-of-plane couplers, splitting the optical signal in 3 separated paths. For the first time, two different proton beam sizes are used during one irradiation and a 20µm collimating aperture is chosen to accurately define the out-of-plane coupling structures. We fully optimized the DLP process for this 20µm proton beam and we measured the surface roughness (R q =27.5nm) and the flatness (R t =3.17µm) of the realized components. Finally, we experimentally measured the optical transmission efficiency of the micro-optical splitter component. The results are in excellent agreement with non-sequential ray-tracing simulations performed for the design.Above that, we present a pluggable out-of-plane coupler incorporating a single micro-mirror for the 90 • coupling of light to or from polymer multimode waveguides integrated on a printed circuit board (PCB). This millimeter-sized mass-reproducible component can then be readily inserted into laser ablated cavities. Nonsequential ray-tracing simulations are performed to predict the optical performance of the component, showing coupling efficiencies up to 78%. These results are then experimentally verified using piezo-motorized positioning equipment with submicron accuracy in a multimode fiber-to-fiber coupling scheme, showing coupling efficiencies up to 56%. The fabricated coupling components are suitable for low-cost mass production since our micro-optical prototyping technology is compatible with standard replication techniques, such as hot embossing and injection molding, has been shown before.

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Deep proton writing: a rapid prototyping polymer micro-fabrication tool for micro-optical modules

“…Our concept differs from most approaches since we propose a pluggable out-of-planning coupling component [24] instead of writing the micro-mirrors directly in the waveguides. We believe such components can be easily mass-replicated from a master prototype.…”

“…With this proton beam size, an error in the position of the beam will be more pronounced and the signal-to-noise ratio of the measured proton current will be significantly smaller than with our standard 140 µm proton beam (as the proton current is 49 times smaller to obtain an equal proton fluence). Nevertheless, we succeeded in creating very high quality surface profiles even with this aperture [24]. In figure 5, the resulting local surface RMS roughness (R q ) and peak-to-valley flatness (R t ) are given.…”

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“…By measuring the rim of the micro-holes with an optical profiler we find a standard deviation on the hole positions below 0.8-µm (limited by the measurement apparatus). We measured an average in-line coupling loss over the complete 2D array of only 0.06-dB in the telecom C and L bands, with a maximum coupling loss of 0.15-dB (Van Erps et al, 2006a). The histogram of the connector losses over the whole array is shown in the right-hand side of Figure 10.…”

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