Abstract
We demonstrate an application of gray scale electron beam lithography (EBL) for the fabrication of polymer waveguides and grating output couplers with depth variable features, using the SU-8 resist. The technique is mainly applicable for multi-level binary profile, where groove depths of the structure are controlled by choosing a proper exposure dose. Unlike reactive ion etching which is limited by the lag effect, the gray scale EBL allows free combination of groove widths and depths. Shrinking effect which is critical in polymer couplers' writing is taken into account and can be compensated. For better fabrication feasibility, the grating couplers can be simultaneously produced with waveguides with no inter-step alignment required. Therefore, this is a promising technique in manufacturing grating output couplers for polymer based waveguides with high performance in terms of mode matching/confinement and coupling efficiency.
Highlights
Microscale optical devices for “Lab‐on‐a‐chip” (LOC) appli‐ cation, like waveguides and micro‐cavities, using polymer materials, have been intensively developed due to favorable optical properties, flexible morphology and low material cost [1]‐[3]
We demonstrate an application of gray scale electron beam lithography (EBL) for the fabrication of polymer waveguides and grating output couplers with depth variable features, using the SU-8 resist
This provides cer‐ tain freedom to write grooves with arbitrary depths and widths, which can help improving the coupling efficiency and mode confinement [11]. This is an obvious advantage in comparison with reactive ion etching (RIE) process which leads to the lag effect deteriorating the performance of a final device [12]
Summary
Microscale optical devices for “Lab‐on‐a‐chip” (LOC) appli‐ cation, like waveguides and micro‐cavities, using polymer materials, have been intensively developed due to favorable optical properties, flexible morphology and low material cost [1]‐[3]. With gray scale EBL, it can be avoided by using variable exposure dose This provides cer‐ tain freedom to write grooves with arbitrary depths and widths, which can help improving the coupling efficiency and mode confinement [11]. This is an obvious advantage in comparison with reactive ion etching (RIE) process which leads to the lag effect deteriorating the performance of a final device [12]. This technique is promising to give 3D polymer grating out‐ put couplers with modulated groove depth and high cou‐ pling efficiency
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