Beam-steering devices are attractive for spatial optical interconnections. Those devices are essential not only for fixed connecting routed optical interconnections, but for flexible connecting routed optical interconnections. The flexible connecting routed optical interconections are more powerful than the conventional fixed connecting routed ones. Structures and characteristics of beam-steering devices, a beam-scanning laser diode and a fringe-shifting laser diode, are reported for those interconnections. Using these lasers, the configurations of several optical interconnections, such as optical buses and optical data switching links as examples of fixed and flexible connecting routed optical interconnections are discussed.

Three efficient designs of Self-Checking (SC) checkers for various 2-rail codes (Self-Checking Two-rail code Checker: SCTC) are described. In the designs, only one type of modules with 2 pairs of inputs and a pair of outputs is used. The module is realized by a 2-level AND-OR circuit, and denoted by N2. Every N2 in a checker needs a set of 4 test patterns (the set is denoted by T) to detect any fault in N2. Firstly, it is shown that any tree (fanout-free) circuit consisting of only N2's is an SCTC if the number of code words is (32n-21) or more. Secondarily, a design which is called a checking design is proposed. For a given 2-rail code and a properly constructed checker, the checking design checks whether T is applied or not to every N2 in the checker. If T is applied, the checker becomes an SCTC. Whether the checking design can construct an SCTC or not is a probability phenomenon mainly due to the number of code words in the given 2-rail code. Therefore, the probability is derived from practical experiments. The probability shows that SCTC's can be constructed by the checking design for most codes. Thirdly, an algorithmic design is proposed for codes consisting of a very few code words. A necessary and sufficient condition for which an SCTC can be constructed for a given code is presented, and the algorithmic design is described. The experimental results show that the algorithmic design can construct SCTC's successfully.