Fabrication of Polymer Waveguides by Laser Ablation Using a 355 nm Wavelength Nd:YAG Laser

Abstract

-The demand for optical waveguides integrated into Printed Circuit Boards (PCBs) is increasing as the limitations of copper interconnects are being reached. Optical polymer materials offer a good solution due to their relatively low cost and compatibility with traditional PCB manufacturing processes. Laser ablation is one method of manufacture, for which excimer lasers have been used, butUV Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) lasersare an attractive alternative due to their widespread use within the PCB industry for drilling vias. In this paper, 355nm, 60ns pulse length UV Nd:YAG laser ablation of Truemode™ acrylate-based optical polymer was investigated. The UV Nd:YAG laser was found to be able to ablate the polymer efficiently and the effects of laser ablation power and pulse repetition frequency (PRF) on depth of ablation were studied and used to determine optimum settings. Multimode optical waveguides were fabricated to demonstrate the process and optical loss measurements were carried out. These measurements demonstrated that the structures were able to transmit light at the data communications wavelength of 850 nm (NIR), but further work is required to reduce the level of loss.The use of UV Nd:YAG as a possible alternative to excimer for laser micromachining would facilitate the rapid deployment of the optical technology within the PCB industry.

Experiment and Prediction of Ablation Depth in Excimer Laser Micromachining of Optical Polymer Waveguides

“…e refractive indices were measured at 850 nm wavelength, which is the same wavelength at which the optical propagation loss is measured for polymer waveguides. Figure 2 shows the key fabrication phases employed in patterning a single layer optical waveguide (single-or mutimode), similar to what is reported in [19]. To summarise, the FR4 base substrate was decontaminated from debris by cleaning in water (or methanol) and was allowed to get fully dry in an oven.…”

Multi-criteria optimization in CO2 laser ablation of multimode polymer waveguides

“…It was coupled to a 10 m 50/125, numerical aperture NA¼0.2, step index multimode fibre for launching light into the waveguides. This procedure is detailed in [6].…”

“…To ameliorate this, femto-second lasers have been proposed and trialled, but this has not progressed faster enough. Furthermore, UV Nd:YAG laser, being a high-power industrial laser used to create vias between layers of the circuit boards, has been demonstrated [3,6] for patterning multimode waveguides in certain optical polymers.…”

Laser Ablation for Polymer Waveguide Fabrication

“…A single layer of waveguide fabrication is common as this is currently enough to provide the data rate requirements for OI, but a multilayer waveguide has also been demonstrated [Hendrickx, et al, 2007a[Hendrickx, et al, , 2007bMatsuoka, et al, 2010]. Multimode waveguides are also common; dimensions such as 20 µm × 20 µm, 30 µm × 30 µm, 35 µm × 35 µm, 45 µm × 45 µm, 50 µm × 50 µm, 50 µm × 20 µm, 70 µm × 70 µm, 75 µm × 75 µm, 85 µm × 100 µm have already been reported [Albrecht, et al, 2005;Bamiedakis, et al, 2007;Dangel, et al, 2004;Immonen, et al, 2005Immonen, et al, , 2007Liang, et al, 2008;Tooley, et al, 2001;Van Steenberge, et al, 2004;Zakariyah, 2009, Zakariyah, et al, 2011. Two or more adjacent waveguides with a pitch of 250 µm [Albrecht, et al, 2005;Horst, 2009;Hwang, et al, 2010;Kim, et al, 2007;Van Steenberge, et al, 2004] is preferred as it is the pitch used for Vertical Cavity Surface Emitting Lasers (VCSEL) and photodector arrays, but other pitch sizes such as 80 µm [Dangel, et al, 2007], 100 µm [Dangel, et al, 2004] and 125 µm [Matsuoka, et al, 2010;Van Steenberge, et al, 2006] www.intechopen.com relatively short, loss due to multimode is acceptable and that alignment between various optical components would be relaxed.…”

“…Furthermore, waveguides can be 'crossed' at 90 degree (Figure 10) or other shapes may be desired. While excimer laser ablated waveguides is favoured, UV Nd:YAG (λ = 355 nm) [Van Steenberge, et al, 2004;Zakariyah, et al, 2011] and 10.6 µm CO 2 [Zakariyah, 2010] have been demonstrated as promising candidates especially for mass production at a low-cost. …”