A True Optoelectronic Spectrum Analyzer for Millimeter Waves With Hz Resolution

We present an architecture for millimeter-wave spectrum analyzers with Hz resolution and precision based on heterodyne down-conversion using ErAs:InGaAs photoconductive mixers driven by a tunable ultra-narrow linewidth continuous-wave (CW) photonic local oscillator. Unlike previous optoelectronic or electronic architectures, there is no requirement for an external electronic spectrum analyzer or any frequency extenders, keeping the system less complex and less expensive. We demonstrate the architecture for a frequency range that surpasses the E-band range by 10 GHz, i.e. from 50 to 90 GHz, but it is easily extendable to frequencies beyond 300 GHz or to frequencies as low as 25 GHz. A minimum power of 300 fW at 72 GHz was detected when using a resolution bandwidth of 1 Hz.