Ultracompact silicon-based wavelength diplexer for 155/2 μm using subwavelength gratings

An ultracompact silicon-based wavelength diplexer assisted by subwavelength grating (SWG) couplers is proposed for wavelengths of 1.55 and 2 μm. The embedded SWGs with the narrowed strip wires enable significantly reduced beat lengths for both wavelengths. Additionally, the use of symmetric directional couplers results in tuning of the required structural dimensions for further enhancing the device performance. As a result, the present device has a total length of only ∼13.9 μm, showing a nearly 20-fold reduction compared with the previous counterpart, and provides a high contrast (C) of 27.5 (24.7) dB, a low insertion loss (IL) of 0.14 (0.80) dB, and a low reflection loss of −30.9(−27.6) dB for a wavelength of 1.55 (2.0) μm. Its bandwidth of C>15 dB and IL<1.2 dB exceeds 100 nm for both wavelengths. In addition, fabrication tolerances are analyzed, and the modal field evolution is presented.