A method for transmitting optical signals over multiple channels is provided, the method including: coding tributaries of data to be transmitted; firstly rearranging the coded tributaries, thereby scrambling the data among the coded tributaries and outputting rearranged coded tributaries; modulating optical carriers with data from one of the coded tributaries, creating modulated optical signals; transmitting the modulated optical signals; spatially multiplexing the modulated optical signals into spatially multiplexed channels; converting the spatially multiplexed optical signals into individual optical signals; receiving the individual optical signals through the multiple channels; demodulating the individual optical signals into electrical signals; decoding the electrical signals into decoded tributaries; and secondly rearranging the decoded of tributaries to recover the tributaries of data before step, wherein, a number of tributaries of data is equal to or more than two and is less than or equal to a number of the multiple channels.