Three-Port Dual-Wavelength-Band Grating Coupler for WDM-PON Applications

Grating coupling is a widely adopted strategy for coupling light into optical waveguides. While this versatile approach benefits both fabrication and alignment, grating couplers are particularly sensitive to both wavelength and polarization. These drawbacks hinder its application in integrated wavelength-division-multiplexing passive optical network (WDM-PON) transceivers, where widely separated wavelength bands are utilized for upstream and downstream signals. In this letter, we propose a three-port grating coupler that enables polarization-independent receiving for the downstream signal from fiber and single-polarized coupling of the upstream signal from chip. Dual-wavelength-band operation is obtained by adding an output port to couple upstream wavelength on existing polarization-splitting grating coupler for downstream wavelength. Peak coupling efficiencies of -2.93 dB and -3.50 dB are achieved for 1266 nm and 1481 nm respectively. This grating coupler design can be adopted in transceivers for fiber-to-the-home (FTTH) networks.