25 March 1996 All-silicon waveguides and bulk-etched alignment structures on (110) silicon for integrated micro-opto-mechanical systems
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Abstract
We present the first large-area, all-silicon rib waveguides and fiber guiding U-grooves fabricated on (110) silicon substrates. Waveguide rib structures with a height of 6.7 micrometers and widths of 5, 10, and 15 micrometer are RIE etched into lightly doped epitaxial silicon layers deposited on heavily doped silicon substrates. Fiber-guiding U-grooves with unique corner compensation structures are anisotropically etched by a 35 wt% KOH solution at 70 degrees C, with and without ultrasonic agitation of the etching solution. Devices fabricated without ultrasonic agitation have a U-groove bottom surface roughness (Ra) of 5606 angstrom, while devices with ultrasonic agitation have a surface roughness (Ra) of 341 angstrom. Ultrasonic etching improves the surface roughness of the U-groove bottoms by a factor of 16.4. We found that the variation of U-groove etch depth is grater than 1 micrometer across the wafer, even with ultrasonic agitation of the etchant. Examination of the waveguide modal structure indicates that devices with 6.7 micrometer tall and 10 micrometer wide rib structures propagate only one waveguide mode at 1550 nm. The total loss of the straight waveguides was as low as 4.88 dB, and the propagation loss was estimated to be 1.68 dB. These loss values indicate waveguide end-faces fabricated by anisotropic etching of (110) silicon do not need to be polished.
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Steven W. Smith, Mehran Mehregany, Francis L. Merat, David A. Smith, "All-silicon waveguides and bulk-etched alignment structures on (110) silicon for integrated micro-opto-mechanical systems", Proc. SPIE 2686, Integrated Optics and Microstructures III, (25 March 1996); doi: 10.1117/12.236136; https://doi.org/10.1117/12.236136
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