Optical interconnections are expected to alleviate the “interconnection bottleneck” in developments of large-scale computing and switching systems using high-density and -speed synchronous parallel optical transmissions. Intra-and inter-module skew control, DC-coupled and error-free transmission, and compact, low-power, reliable and inexpensive modules are main technical issues. A monolithically integrated low-threshold, efficient and uniform LD array is a key device. This paper reviews summary of recent work on optical interconnections and our developed compact 200-Mbit/s/ch 10-ch optical interconnections we developed by using single-mode fiber and 3-mA-threshold current 1.3 μm LD arrays.