A 10 Gb/s optical heterodyne detection experiment using a 23 GHz bandwidth balanced receiver

A 0.5-30-GHz GaAs MESFET monolithic distributed amplifier using coplanar waveguides and a wideband InGaAs twin p-i-n photodiode was fabricated. A wideband balanced optical receiver was fabricated by connecting these devices using the solder bump flip-chip technique to reduce parasitic inductance and capacitance. A 10-Gb/s optical continuous-phase frequency shift keying (CPFSK) heterodyne detection experiment was conducted using the balanced optical receiver. A multielectrode 1.55- mu m distributed feedback laser diode (DFB-LD) was directly modulated with a 10-Gb/s NRZ signal. The 10-Gb/s modulation signal was multiplexed with a 5-Gb/s RZ fixed pattern having a delay of several bits. the LD frequency modulation bandwidth was 12 GHz, and the modulation index was 0.52. The modulation signal was combined with a local oscillator light, and the combined signals were detected with the receiver. The IF center frequency was 13 GHz. The IF signal was demodulated by a differential detector. The demodulated eye pattern was degraded by the frequency bandwidth limitation of the mixer used in this experiment and the optical receiver frequency response. A wideband mixer and improved optical receiver packaging are needed.<>