Fiber-optic millimeter-wave downlink system using 60 GHz-band external modulation

In this paper, a fiber-optic millimeter-wave (mm-wave) downlink system usin g 60 GHz-band external modulation is investigated. We prepare the fiber-opt ic 60 GHz-band mm-wave downlink testbed, It consists of an optical modulati on section with a mm-wave signal generator, an optical single sideband (SSB ) filter, a standard single-mode fiber (SMF), an optical detection section with a 60 GHz-band radio transmitter and a 60 GHz-band radio receiver. To m odulate the laser output with 60 GHz-band mm-wave signals directly, a speci ally designed electro-absorption modulator with high efficiency at around 6 0 GHz is used. The use of this modulator makes the simpler system configura tion possible. Using the downlink testbed, the 5 m-long free space propagat ion of subcarrier multiplexed 156 Mb/s-DPSK 60 GHz-band mm-wave signals rec overed by optical direct detection is successfully demonstrated. The transm ission of the mm-wave signals over 85 km-long standard SMF is also successf ully demonstrated, using an optical SSB filtering technique to overcome the fiber dispersion. The BER of 10(-9) is achievable at the optical received power of -7.0 dBm.