We present a full description of the design and fabrication of a compact laterally tapered spotsize converter (SSC) that provides both low-loss coupling and large fabrication tolerances. The SSC is based on a laterally tapered waveguide with a narrow core width that can be fabricated simply by using the usual fabrication process. We discuss the design concept of the SSC in detail and provide a simple design procedure with which to obtain the optimum SSC design parameters. We also investigate the fiber misalignment tolerance and mode field diameter of the SSC and confirm that it is suitable for integration with large-scale optical devices. Furthermore, we examine the performance of the SSC for higher refractive index difference (Delta) of 2.0% and 2.5% with a smaller bending radius. We fabricated the 2-mm-long SSC using 1.5%-, 2.0%-, and 2.5%-Delta silica-based planar lightwave circuits. This enabled us to reduce the single-mode fiber coupling loss to 0.4 dB at a single waveguide junction with a low polarization-dependent loss of 0.05 dB regardless of the Delta; values, while providing a core width fabrication tolerance of ±0.3 µm and an endface position tolerance of ±0.2 mm.
© 2004 IEEE
Takayuki Mizuno, Tsutomu Kitoh, Mikitaka Itoh, Takashi Saida, Tomohiro Shibata, and Yoshinori Hibino, "Optical Spotsize Converter Using Narrow Laterally Tapered Waveguide for Planar Lightwave Circuits," J. Lightwave Technol. 22, 833- (2004)