Ultracompact, Scalable and Flexible Multi-Order Mode Converter for TE0/TE1 Dual-Mode Input

Different from conventional converters only converting one given mode to a single desired one, we here propose a multi-order conversion scheme for TE₀/TE₁ dual-mode input by exploiting asymmetric multimode interference (AMMI) and beam shaping, where an inverse-tapered subwavelength gratings array (ITSWGA) is sandwiched between two AMMI waveguides, followed by asymmetric tapers, respectively. For input TE₀/TE₁ mode, it is divided into two modal components by the ITSWGA and then excites p-th and q-th (p ≠ q, p = 1, 2 & q = 2, 3) modes in two AMMI waveguides via self-imaging effect, where followed tapers can further amend the phase differences of modal components for target modes via beam shaping. Thus, p-th and q-th modes can be obtained in dual-output channels simultaneously, for both input TE₀ and TE₁ modes. Results show that the bandwidth can be enlarged to 90 nm (the worst-case: p = 2 & q = 3) for crosstalk < −10 dB and conversion efficiency >80%, in an ultracompact length of only 8.7 μm, for the dual-mode input. Significantly, the dual-output channels can be flexibly combined into a single-output channel by tapers to form an MZI-like structure, which can convert TE₀ to TE_0+i mode and TE₁ to TE_1+i mode (i = 2, 4 and 6) simultaneously, realizing dual-order conversions in a single structure, and results of the best-case (i = 2) are conversion efficiency = 97.1% (98%), insertion loss = 0.32 dB (0.53 dB), and crosstalk = −16.89 dB (−19.72 dB) @ 1.55 μm for TE₀-to-TE₂ (TE₁-to-TE₃) conversion, within a length of 12.23 μm.