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.

We present an ultra-broadband and inexpensive photonic spectrum analyzer (PSA) for wireless signals with a frequency coverage from the microwave range till deep into the terahertz range. The difference frequency of two continuous-wave laser diodes works as the local oscillator frequency and a photoconductive antenna downconverts a signal under test with the aid of the optical local oscillator. With this approach we achieve a frequency coverage from less than 25 GHz to more than 1.25 THz, mostly limited by the tuning range of the lasers. No component of our spectrum analyzer needs to be interchanged in order to achieve the full tuning range, which makes our spectrum analyzer a fraction of the cost of an electronic spectrum analyzer that requires several extension modules for covering a similar frequency range. The system offers a minimum resolution bandwidth of 1.2 MHz at a displayed average noise level (DANL) as low as -113.8 dBm/Hz at 100 GHz or as low as -88.2 dBm/Hz at 1050 GHz.

We introduce a new scheme for the detection of terahertz pulses based on the frequency selective optoelectronic downconversion of its individual modes with a continous-wave (CW) ErAs:InGaAs photoconductive antenna (PCA) driven by a comb-based CW photonic signal. The detection scheme can be used as metrology tool for the analysis of the fundamental resolution and stability limits of terahertz pulses and the mode-locked-lasers (MLLs) that drives them, as well as an ultra-high-resolution measurement technique for terahertz components or gas spectroscopy. We demonstrate both applications by measuring the linewidth of two frequency components of the particular terahertz pulse analyzed here (one at 75 GHz and one at 340 GHz) and by measuring a very narrowband filter between 70 and 80 GHz. The main advantage of this technique with respect to other terahertz pulse detection schemes is its capability of performing ultrahigh-resolution measurements without the need of unpractically long scanning ranges or synchronization of two MLLs.

Signals in the terahertz range are mainly wireless, waveguide-bound or on-chip signals. To measure their spectral power, linewidth and harmonics, usually spectrum analyzers are used. Here we present a photonic spectrum analyzer for waveguide-bound signals for the frequency range from 450 GHz to 1.05 THz with the possibility to extend its operation to onchip signals. Therefore, a photonically generated local oscillator frequency is used to downconvert the signal under test within a photoconductor. A Vivaldi antenna feeds the signal from a dielectric waveguide to the photoconductor. This allows the measurement of any signal that can be transported via a dielectric waveguide. We show details on the transition from a rectangular metallic hollow waveguide to a dielectric waveguide and spectral measurements of a rectangular metallic hollow waveguide source. The same transition can also be used to attach metallic waveguide-coupled ground-source-ground probes in order to characterize on-chip sources.

We present a novel technique for the detection terahertz pulses generated by femtosecond lasers. It features a Hz-level resolution and does not require a mechanical delay stage or a second femtosecond laser. It works by opto-electronically downconverting the individual frequency components composing the terahertz pulse. Unlike other techniques, it does not require an external spectrum analyzer or a lock-in amplifier for its implementation, although it can also be implemented using them. We believe this technique is a valuable tool to study the ultimate frequency stability of terahertz pulsed systems and the phase noise of the femtosecond lasers that drives them.