Bias-free telecommunication-compatible plasmonic photoconductive terahertz source (Conference Presentation)

High-power pulsed terahertz radiation sources are highly in demand for time-domain terahertz imaging and spectroscopy systems. A common way to generate pulsed terahertz radiation is exciting a biased ultrafast photoconductor with a femtosecond optical pulse. The photo-generated carriers drift to a terahertz radiating element under the induced bias electric field and a pulsed terahertz radiation is generated. Developing photoconductive terahertz sources operating at telecommunication wavelengths (~1550 nm) is very attractive because of the availability of high-power, narrow-pulse-width, and compact fiber lasers at these wavelengths. However, photoconductors responsive to telecommunication wavelengths often have low resistivity due to their small bandgap energy, resulting in excessive dark current levels under an applied bias voltage. As a result, telecommunication-compatible photoconductive sources experience a premature thermal breakdown under high bias voltages and cannot offer high terahertz radiation powers. To address this limitation, we introduce a new type of telecommunication-compatible photoconductive terahertz source that does not require an externally applied bias voltage and relies on a built-in electric field formed at the interface between the photoconductor and terahertz antenna contact electrodes. By eliminating the bias voltage, the device operates at a zero dark current, enabling a highly reliable operation. We use an array of plasmonic nanoantennas as the terahertz radiating elements to achieve a broad terahertz radiation bandwidth and high optical-to-terahertz conversion efficiency. We demonstrate pulsed terahertz radiation with powers exceeding 100 μW, enabling time-domain terahertz spectroscopy with a 100 dB dynamic range over a 0.1-3 THz bandwidth.