| Popis: |
A low-loss and compact TM-pass polarizer on silicon is proposed using an asymmetrical directional coupler (ADC) consisted of a silicon wire waveguide and a sub-wavelength-grating (SWG) waveguide. To reduce the reflection loss and improve the extinction ratio (ER), tapered structure and sharp bending are introduced at the input and output port of the SWG waveguide, respectively. The TE input-mode is coupled into the SWG waveguide through the ADC, and then filtered out and absorbed by the Chromium wires located at two sides of the end of the bending. By properly selecting the structure parameters, the TM mode is cut-off in the SWG waveguide and thus directly passes through the silicon wire waveguide. Results show that a compact device length of 9.6μm with an ER of 18.3 dB and insertion loss of 0.16 dB is obtained at the wavelength of 1.55μm. To further improve the performance of the device, a cascaded scheme is constructed and analyzed. The total device length of the scheme is 40μm with an operating bandwidth of ~62nm for ensuring ER> 30dB. Similar concepts can also be used to produce a TE-pass polarizer by simply constructing a vertical ADC. |
