An optical transmitter includes a first encoder, a first interleaver, a second encoder, a mapper, a second interleaver, and a frame generator. The first encoder is configured to encode data using a staircase code to generate first codewords. The first interleaver is configured to interleave the first codewords using convolutional interleaving to spread a transmission order of the first codewords. The second encoder is configured to encode the interleaved first codewords using a second code to generate second codewords. The mapper is configured to map the second codewords to transmit symbols. The second interleaver is configured to interleave the transmit symbols to distribute the transmit symbols between pilot symbols. The frame generator is configured to generate a transmit frame including the interleaved transmit symbols and the pilot symbols.