A novel vertical directional coupler switch with a switching-operation-induced section and an extinction-ratio-enhanced section is proposed. Switching operation is achieved by changing the refractive indexes of both cores in the switching-operation-induced section, and an improvement of extinction ratios larger than 30 dB for both cross and bar states is achieved by controlling the asymmetry of the refractive indexes of two cores in the extinction-ratio-enhanced section without changing the refractive index of the inner-cladding layer between the two waveguides. The required refractive indexes for the cores in the switching-operation-induced and extinction-ratio-enhanced sections are calculated for various thickness of the inner-cladding layer.
Sung-Chan Cho, Byung-Min Jung, Boo-Gyoun Kim, Hyun Ha Hong, and Ali Shakouri, "A Novel Vertical Directional Coupler Switch With Switching-Operation-Induced Section and Extinction-Ratio-Enhanced Section," J. Lightwave Technol. 20, 1773- (2002)