Low loss single-mode optical waveguides with large cross-section in standard epitaxial silicon

Low Loss All-Silicon Single Mode Optical Waveguide with Small Cross-Section

“…Equation (1) proves that, despite relatively high losses ¢¬ in the highly doped substrate, the attenuation of slab waveguides can be reduced proportionally to 1=H 3 for large layer thickness H, and to ¢n 3=2 for large doping level N. So, combining large values of H to very high-doped substrates, simple SOS structures may indeed yield relatively low loss waveguides. Following these lines, losses as low as 1.5 dB/cm at ¶ˆ1:3 mm and ¶ˆ1:55 mm have been achieved [6] in n/n 1 silicon single-mode 16-mm wide rib waveguides, with epilayer thickness of 20 mm and substrate doping level of about 10 1 19 cm ¡3 . Thus, it is possible to determine two ways to reduce the propagation losses: to use a thicker core layer on normally doped substrates or to increase the substrate doping at a very high level.…”

“…Finally, in order Low Loss All-Silicon Single Mode Optical Waveguide to verify the coupling e ciency numerical evaluation of the overlap integral was performed between the mode distribution of the waveguide (the 8 £ 8 mm 2 one) and a standard single-mode ® ber with a mode ® eld diameter of 6 mm: the minimum value of coupling losses was 0.9 dB. Similar analysis carried on the larger waveguide (20 £ 16 mm 2 ) proposed by Splett and Petermann [6] provides a value of about 6.5 dB. This section can be concluded recapitulating some basic consideration.…”

“…These waveguides suOE ered considerable losses because of the absorption of the optical wave penetrating in the substrate. More recently, it has been shown [6] that for a su ciently large waveguide layer thickness …H ¾ ¶ †, and for a high doping level in the substrate N, the losses ¬ for the fundamental slab mode are given by…”

“…Theoretical and experimental results show that under certain condition, the con® nement eOE ect prevails and the net result is a global reduction of the waveguide propagation losses. It should be noted, however, that substrates with a very high doping level are di cult to obtain and therefore a Low Loss All-Silicon Single Mode Optical Waveguide reduction of the propagation losses can be obtained reasonably only by recurring to thicker epitaxial layers ( ¶ 20 mm) [6], at expenses of the coupling e ciency to singlemode optical ® bers. Moreover, the realization of very thick epitaxial layer is timeconsuming, expensive, and often incompatible with standard microelectronic processes.…”

<title>Integrated optoelectronic waveguide detectors in SiGe for optical communications</title>

“…Some waveguide concepts require special growth or diffusion techniques [2,13,14], other waveguide concepts are based on an index step in the vertical direction of commercially available materials, which is due to the incorporated layers, i.e. epitaxial silicon with different doping levels in the substrate and epi-layer [15], or Silicon-On-Insulator (SOl) [16]. The waveguides considered here are of both types, MBFrgrown SiGe-layers and commercially available Silicon-On-Insulator (SOT).…”