Photonic Integrated Continuous Wave Terahertz Spectrometer with 90 dB Dynamic Range and 4 THz Bandwidth

We present the first photonic integrated terahertz spectrometer that is able to cover the tuning bandwidth of state-of-the-art continuous wave (cw) terahertz (THz) antennas. The dedicated photonic integrated circuit (PIC) based on two widely tunable sampled grating DBR (SG-DBR) lasers allows for the generation of up to 5 THz optical difference frequency for THz spectroscopy. With an integrated phase control, the amplitude and phase of the THz signal are detected without the need for any moving parts such as fiber stretchers or free-space optics. Our experimental evaluation is the first demonstration of 90 dB peak dynamic range and 4 THz bandwidth with a PIC spectrometer. This approach is a milestone towards photonic integrated, compact and economic THz systems for cost-sensitive areas in research and industry.

I. Introduction

Today’s terahertz (THz) spectroscopy systems are still primarily a scientific tool rather than being widely adopted for high-volume industrial use. Here, common available spectrometers lack scalability in footprint and often have too low measurement rates for industrial applications. With continuous wave (cw) THz generation based on optoelectronic photomixing, we overcome these limitations by employing photonic integrated solutions that allow for small footprints and scalable costs. In contrast to time-domain spectroscopy (TDS) systems, which rely on fs-optical pulses and often require variable optical delay lines, all parts of a cw THz system can be implemented as photonic integrated components. Furthermore, with fast tunable semiconductor lasers and optical phase modulation, there is also potential to increase the measurement rate beyond the current state-of-the-art of commercial terahertz spectrometers.