摘要
New designs are proposed for 2×2 electro-optical switching in the 1.3–12μm wavelength range.Directional couplers are analyzed using a two-dimensional effective-index approximation.It is shown that three or four side-coupled Si or Ge channel waveguides can provide complete crossbar broad-spectrum switching when the central waveguides are injected with electrons and holes to modify the waveguides’core index by an amountΔn+iΔk.The four-waveguide device is found to have a required active length L that is 50%shorter than L for the three-waveguide switch.A rule ofΔβL>28 for 3w andΔβL>14 for 4w is deduced to promise insertion loss<1.5 dB and crosstalk<−15 dB at the bar state.At an injection ofΔNe=ΔNh=5×10^(17)cm^(−3),the predicted L decreased from∼2 to∼0.5 mm asλincreased from 1.32 to 12μm.Because of Ge’s largeΔk,the Ge bar loss is high in 4w but is acceptable in 3w.
