Forward and backward grating-assisted directional couplers in silicon for wavelength-division multiplexing tunable add-drop applications

A novel tunable optical add-drop multiplexer based on a silicon forward or backward directional coupler is proposed. This device enables one wavelength channel or a small band of channels to be inserted into or extracted from a wavelenghth-division multiplexing (WDM) signal with the capability that the wavelength for which this occurs can be varied utilizing injection current variation. For the backward coupling configuration, an adjacent sidelobe level rejection of - 7.5 dB, coupling efficiency of 96.13%, and a 3-dB bandwidth of 0.174 nm with central wavelength at 1549.93 nm are simulated. Wavelength tunability of 169.3 nm (forward coupling) or 0.78 nm (backward coupling) result from our simulations, corresponding to a voltage-induced refractive index change Delta n of 0.0021. The forward coupling configuration provides a somewhat wider 3-dB bandwidth and more extensive tuning capability. (C) 2006 Society of Photo-Optical Instrumentation Engineers.