An Ultra-Compact Wavelength Diplexer Engineered by Subwavelength Grating

With the assistance of subwavelength grating (SWG), an ultra-compact multimode interference (MMI)based diplexer is proposed. A certain number of SWG pitches are implemented in the middle of the MMI section, which can engineer the effective refractive index for the modes and, therefore, tune the beat length. With proper tailoring of the grating parameters, the beat lengths of the two wavelengths can be reduced as well as the device length, which has to match several odd or even times of beat lengths of both wavelengths. As a result, the proposed wavelength diplexer is 43.4 μm in length, which is only ~30% of its conventional counterpart. It also displays a wide 1-dB bandwidth of ~150 nm around the wavelength of 1310 and ~120 nm around the wavelength of 1550 nm. The insertion losses are less than 0.1 dB for the two operating wavelengths while the extinction ratios are both better than 20 dB.