| Abstract | In optical fiber communication systems using direct detection, the code sequence used has
to be unipolar. Most of the existing codes for conventional Code-Division Multiple-Access
(CDMA) are bipolar. This results in studying a new class of address codes for using in optical
CDMA. Such codes are called Optical Orthogonal Codes (OOC). Since the codes were proposed
in 1989, it has been given considerable attention. A number of code constructions were published.
A good code construction is the one that can construct code with various choices of length and
weight, and gives maximum number of codewords. The maximum number of possible codewords
for a given length, weight, auto- and cross- correlation constraints (i.e., n,w,A.0 ,A.c) can be
calculated by the Johnson bound. The OOC with maximum number of codewords is called an
optimal code. Among the given construction in the past, there are good constructions of (n,w,1,1)
and (n,w,2,1). The (n,w,2,2)-00C have more codewords than them. However, the optimal
construction of (n,w,2,2)-00C that exists is not clear and has a lot of restriction on length and
weight. This research clarifies the construction. Then it gives more method for (n,w,2,2)-00C's
construction based on various techniques. One of these methods is optimal. |