We demonstrate an optical orthogonal frequency division multiplex (OOFDM) transmitter using a simple dual-electrode Mach- Zehnder modulator (MZM) to perform tandem single-sideband optical modulation. This allows a doubling of transmission capacity. A commercial optical transmitter card, equipped with an on-board arbitrary waveform generator, is used for the system test. A proof-of-concept transmission experiment is conducted using a fiber-optic re-circulating loop.