A Spot-Size Converter With Concatenated Up- and Down-Tapers Followed by a Thin Slab-Waveguide

A new version of spot-size converter (SSC) 227 μm in length that consists of a horizontal linear up-taper, a vertical down-taper, and a thin slab-waveguide in cascade in a silicon-on-insulator (SOI) substrate for coupling between a single-mode fiber and a silicon-wire waveguide was fabricated and characterized. The sputtering deposition employed in the fabrication was much simpler and more reliable in comparison with that of the prior SSC. The measured coupling losses per port between the fiber and the waveguide for a two-port module chip 2.8 mm in length are 2.6 and 3.4 dB, respectively, for the E
₁₁
^y
and E
₁₁
^x
modes at the optical wavelength of 1.55 μm. The new SSC structure is planar, small in size, robust, much easier to fabricate, and has thus demonstrated its viable potential for manufacturing.