AN OPTICAL BI-PHASE MODULATOR FOR MILLIMETER-WAVE SUBCARRIER SYSTEMS

This paper proposes a novel optical modulator for a millimeter wave (M MW) subcarrier optic link. The modulator enables the bi-phase modulati on of MMW subcarriers. It simplifies the optic link by unifying such f unctions as IF modulation, up-convertion to MMW, and optical modulatio n, which are separately equipped in a conventional system. A simple mo del of a Mach-Zehnder external optical modulator (EOM) is used to illu strate how bi-phase modulation of millimeter wave (MMW) subcarriers ca n be accomplished by switching the EOM bias with a binary data signal. Experimental results are presented to confirm predictions. A wideband communications test system employing the EOM as a bi-phase modulator and utilizing spread spectrum modulation (1.3 mu m optical wavelength, 40 GHz subcarrier, 100 MHz chip rate, 10 MHz data rate) was developed . Bit error rate (BER) characleristics of an optical link that include s the proposed modulator are presented and compared with ideal perform ance and simulated predictions. Degradation of the BER characteristics from the simulation was less than 1 dB at a BER of 10(-6). A frequenc y doubling subcarrier bi-phase modulator is also described.