Based on restricted interferences mechanism in a 1x2 MMI beam splitter, we theoretically investigate and experimentally demonstrate an ultra-compact MMI-based demultiplexer for the NIR/MIR wavelengths of 1.55 μm and 2 μm. The device is fabricated on 340 nm SOI platform, with a footprint of 293x6 μm2. It exhibits extremely low insertion losses of 0.14 dB and 1.2 dB at the wavelengths of 1.55 μm and 2 μm, respectively, with contrasts of approximately 20 dB for both wavelengths, and a cross-talk of 18.83 dB.