Terahertz Spectroscope Using CMOS Camera and Dispersive Optics

There is a need to reduce the cost and size of functional terahertz devices, in order to expedite this notoriously underutilized frequency band toward practical applications. Electronic integrated circuits (ICs) are extremely useful to this end, as they provide a means to achieve miniaturization and mass production, leveraging the foundries and techniques that have made digital electronics ubiquitous. Although integration of terahertz systems is expected to diminish performance and functionality, the increased number and availability of devices is likely to compensate for such disadvantages. In this work, we develop a terahertz-range spectroscope that combines a CMOS terahertz camera with custom-machined reflective optics. It is noted that the individual pixels of the camera employ incoherent detection, and hence a single pixel is not able to differentiate distinct frequencies. For this reason, the reflective optics are designed to split a terahertz beam into its constituent frequencies, and target each to a different position on the terahertz camera's focal plane array. The required frequency-scanning functionality is provided by a corrugated reflective optic that operates in a manner similar to a curved diffraction grating. The developed spectroscope is experimentally validated, and its functionality agrees closely with simulation. This work provides a pathway to a new generation of compact, low-cost, all-electronic terahertz spectrometers that employ mass-producible silicon ICs for all active components.