Simultaneous Upconversion Of Several Channels In MM-Wave Subearrier Transmission Systems for Wireless LANs at 60 GHz

Simultaneous upconversion of several channels in nzm-wave subcarrier transmission systems is proposed. The technique is advanta,geous for optical backbones of wireless LANs at 60 GHz with numerous base stations. Low cross-talk was obtained in experiments. Introduction For future mobile broadband communiication systems or wireless LANs millimeter-wave (mm-wave) fiber links are increasingly considered as attractive solutions for signal distribution to the base stations. In recent years, different concepts have been proposed. Heterodyne techniques using two lasers need complex circuitry for suppressing phase noise. Resonantly modulated [ 11 or mode-locked [2] lasers are other solutions for optical generation of mm-waves, where dual-mode devices [3] are preferable. In [4] two correlated subcarriers were generated by externally modulating a single laser diode and suppressing the carrier, resulting in detection of twice the modulation frequency. Furthermore, direct signal modulation of a laser diode and upconversion of the signal by an external modulator has been demonstrated 151. All techniques discussed so far concentrate on the generation of mm-wave subcarriers of a single channel. However, for a coinmunication system at 60 GHz 161 we propose upconversion of many baseband signals simultaneously with a single external modulator using a dense wavelength division mulliplex (WDM) system. The upconverted signals can easily have different subcarrier frequencies being required for a frequency division multiplexed (FDM) communication system. Furthermore, we propose the use of a phase inodulator and simple dispersion management instead of a IClach-Zehnder intensity modulator. This results in a 6-dB-imlprovement of the signal dletected [7]. Hence, the system proposed is well-suited for efficient upconversion of many downlink signals in a communication system at mm-wave frequencies. System Concept The concept for simultaneous upconversion of many subcarriers with a single external modulator is shown in Fig. 1. Basically, a dense wavelength division multiplexed (WDM) system is used for multiplexing many carriers at different waveliengths into a fiber bus. These signals are generated by laser diodes being available at well-defined emission wavelengths for dense WDM systems. Each laser with its emission wavelength is assigned to a certain base station and is modulat.ed with the corresponding datas in the baseband or at an intermediate frequency. By choosing different intermediate frequencies for different