A cost-efficient and low-complexity optical input/output (I/O) packaging solution is a substantial challenge for volume production of photonic integrated circuits. To address this, metamaterial fiber couplers are an attractive solution for integrated photonic devices especially for optical I/O, interfacing standard optical fibers to photonic chips. They offer the advantages of refractive index engineering to achieve better mode match as well as higher fabrication tolerances. Metamaterial waveguides, as a fundamental building block of these fiber couplers, have attracted tremendous attention in recent years. Here, we report on effective optical return loss control in Si metamaterial waveguide designs to achieve ultra-low reflection loss in CMOS-compatible silicon photonics implemented in a 300 mm production line. Low backscattering is a substantial consideration for a range of applications. Here, a return loss of better than −30 dB is achieved.