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All-silicon substrateless waveguides have become a leading contender for terahertz device integration owing to their broad operating bandwidth and exceptional efficiency. However, without metallic confinement, these unshielded waveguides are susceptible to evanescent coupling, requiring that waveguides be placed sparsely to resist unwanted interactions. This sparsity remains a critical obstacle to compact devices and integrated systems. To counter this, we demonstrate substrateless extreme skin-depth waveguides, utilizing a self-supporting anisotropic cladding that markedly reduces the evanescent field penetration into the surrounding cladding, and hence, suppresses cross coupling between waveguides. Here, we achieve 20-dB cross-talk suppression across the WR3.4 band, 220–330 GHz, a 40% fractional bandwidth, with less than 0.5 free-space wavelength separations and coupling lengths exceeding ten free-space wavelengths. In addition, we exploit the low bending loss of this waveguide to realize an efficient and simply designable power divider to realize arbitrary extinction ratios between 1:1 and 10:1. Integrable with existing all-silicon devices, we foresee these techniques enabling the dense integration of terahertz systems with substrateless silicon waveguides.

We extend the operation bandwidth of substrateless all-silicon waveguides beyond the single-mode region. This requires a suitably broadband port-access scheme, as well as careful management of undesired higher order modes. It is found that a length of two-conductor waveguide serves both purposes. In this way, we experimentally demonstrate broadband power transfer between dielectric waveguides and numerically investigate suppression of higher order modes. This 3-D solid-metal two-conductor waveguide shows promise as a package-external terahertz port, to address the 40% relative-bandwidth bottleneck that is currently imposed by hollow metallic waveguides. This represents a step toward efficient handheld terahertz systems that fully exploit the broad available spectrum.

Nondestructive evaluation is one of the key envisaged applications for terahertz technology due to nonionizing energy levels and the ability to penetrate many optically opaque materials. Conventional terahertz imaging systems typically rely on raster scanning the target with a moving transceiver, or make use of goniometric beam manipulation schemes. As an alternative, we propose the use of a Risley-prism, essentially a cascaded pair of independently rotating prisms, to function as a simple beam-steering mechanism. When deployed in conjunction with an aspheric, telecentric objective, the Risley-prism allows for scanning a focused terahertz beam in two dimensions. We utilize 3D-printed cyclic olefin copolymer, a low-loss and low-dispersion polymer, to minimize material loss and facilitate the construction of these bulk optics. Owing to true time delay, our imaging system operates over 220–330 GHz, making use of this bandwidth for resolving depth features and hidden objects. We achieve a spatial resolution of 0.419 lp/mm over a circular scanning region 27.8 mm in diameter. The proposed Risley-prism imaging system offers a simple solution to the complicated problem of broadband and high resolution imaging, and hence, is readily amenable to widespread adoption and commercial applications.

Terahertz technology is largely dependent upon planar on-chip antennas that radiate downwards through the substrate, and so an effective means to interface these antennas with integrated waveguides is an attractive prospect. We present a viable methodology for backside coupling between a terahertz oscillator chip and a broadband all-intrinsic-silicon dielectric waveguide. Our investigation employs resonant tunneling diodes as compact two-terminal electronic terahertz oscillators, and terahertz waves are observed from 270 GHz to 404 GHz. The fact that this power is accessed via a curved length of silicon waveguide validates successful backside coupling.

The arrayed waveguide grating (AWG) is a versatile and scalable passive photonic multiplexer that sees widespread usage. However, the necessity of a waveguide array engenders large device size, and gratings invariably commute finite power into undesired diffraction orders. Here, we demonstrate AWG-like functionality without a grating or waveguide array, yielding benefits to compactness, bandwidth, and efficiency. To this end, we exploit optical tunneling from a dielectric waveguide to an adjacent slab in order to realize a slab-confined frequency-scanning beam, which is manipulated using in-slab beamforming techniques that we have developed in order to separate distinct frequency bands. In this way, we devise an all-intrinsic-silicon integrated $4 \times 1$ frequency-division terahertz multiplexer, which is shown to support aggregate data rates up to 48 Gbit/s with an on–off-keying modulation scheme, operating in the vicinity of 350 GHz. Our investigation targets the terahertz range, to provide a critical missing building block for future high-volume wireless communications networks.

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.

We demonstrate a terahertz flat lens based on tri-layer metasurfaces allowing for broadband linear polarization conversion, where the phase can be tuned through a full 2π range by tailoring the geometry of the subwavelength resonators. The lens functionality is realized by arranging these resonators to create a parabolic spatial phase profile. The fabricated 124-μm-thick device is characterized by scanning the beam profile and cross section, showing diffraction-limited focusing and ∼68% overall efficiency at the operating frequency of 400 GHz. This device has potential for applications in terahertz imaging and communications, as well as beam control in general.