Based on the optical orthogonal codes, a method for constructing irregular LDPC (low-density
parity check) codes was presented. These LDPC codes are quasi-cyclic codes and can be encoded with low
complexity with a linear relationship to code length. These codes haveTanner graphs free of 4-cycles. They
performwellwith the sum-product iterative decoding. Comparedwith random codes and regularLDPC codes
based on the optical orthogonal codes with similar parameters, they have decoding performance gains
respectively about 0.3 and 0.15 dB when bit error rate is 10-5.