Combined reflector and DOE couple light into or out of optical circuit

It is sometimes necessary to couple light into or out of a silicon (Si) optical circuit (for example, from a laser diode or into a fiber or waveguide) in a no-coplanar manner, usually in a direction perpendicular to the plane of the optical circuit.

Dec 1st, 2009
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It is sometimes necessary to couple light into or out of a silicon (Si) optical circuit (for example, from a laser diode or into a fiber or waveguide) in a no-coplanar manner, usually in a direction perpendicular to the plane of the optical circuit. This is conventionally done with a 45° microprism and a separate lens (left). Researchers at National Central University (Jhong-li, Taiwan) and National Dong Hwa University (Hualien, Taiwan) have simplified this arrangement by combining an integrated Si 45° microreflector with a focusing diffractive optical element (DOE) etched on the surface of the microreflector (right).

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The angled Si reflector is 216 µm high and is fabricated by anisotropic wet etching. The DOE has a focal length of 150 µm and is created by dry etching, with a minimum 0.71 µm linewidth; a final gold plating increases reflection efficiency. The DOE has an elliptical off-axis design to compensate for astigmatism, producing a 15-µm-diameter spot at best focus and a 20-µm-or-less spot throughout a 600 µm focal depth. Both the reflector and DOE can be monolithically integrated using standard lithographic techniques. Contact Mount-Learn Wu at mlwu@dop.ncu.edu.tw.

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