an output signal from the laser is received by the i q modulator which is driven by the binary data source at its i q inputs the laser is thereby modulated by the i q modulator driven by the two binary sequences thereby generating a qpsk constellation as may be implemented in a 40 g dqpsk or 100 g dp qpsk system for example the mzm is driven by a third binary sequence while the other port is grounded when operated according to the present disclosure an 8 qam output is realized more specifically and as those skilled in the art will appreciate a dual drive mzm such as that shown in fig1 a is conventionally designed for intensity modulation only with reduced v u03c0 i e voltage swing required to drive mzm between mass and null in an arrangement according to the present disclosure one port of the mzm is grounded while the other port is driven by a third binary sequence assuming that 0 and 1 are represented by drive voltages v 1 and v 2 to the dual drive mzm we have the following relations is the amplitude ratio between the inner ring and outer ring of the 8_qam constellation operationally this means that the drive voltage or difference between v 1 and v 2 should be v u03c0 2 for initializing this may be easily performed by driving the mzm to v u03c0 first by checking the on off keying eye diagram and then adding a 3 db rf attenuator to the driving path once the drive voltage is set one can then observe the eye diagram of the.