The development of terahertz (THz) technology exploiting untapped bandwidth is essential for sensing and communications in 6G and beyond. Instrumentation systems for evaluating the performances of THz devices are of increasing interest. Currently, THz device testing with electronics-based vector network analyzers (VNAs) requires a series of frequency extender pairs to cover all individual bands in the THz range. This increases system complexity and cost. Here, we report on an ultrawideband (UWB) photonic THz source, which will enable simpler and cost-effective THz device testing. The source employs a modified unitraveling-carrier photodiode (MUTC-PD) operating from 100 to 600 GHz. The InP-based MUTC-PD is hybrid-integrated with a UWB high-resistivity Si waveguide interface to efficiently couple the optically generated THz waves to the device under test. By utilizing a UWB THz power detector, a waveguide-based scalar transmission measurement system is demonstrated, a crucial step toward a future waveguide-based photonic VNA.

We present a single-element all-dielectric horn antenna for mmWave-THz applications that eliminates conductor loss while supporting hybrid integration. The antenna is excited by a dielectric-rod waveguide (DRW) feed, enabling seamless interfacing to on-chip or packaged sources as well as standard rectangular-waveguide front ends. An index-matched slot-waveguide termination (SWT) is introduced at the silicon-cyclic olefin copolymer (COC) interface to realize an antireflection interface. Numerical analysis validates reflections below -10 dB across 180-400 GHz and below -40 dB at 275 GHz. The SWT launch is expanded by a linear dielectric flare and collimated by an integrated lens, yielding a high-directivity aperture. The combined structure achieves a gain of 21 dBi at 180 GHz and increases up to 29 dBi at 400 GHz with clean E-plane patterns. The material stack and geometry are compatible with additive manufacturing and precision polymer molding, offering a scalable, low-cost path to compact, high-efficiency antennas for next-generation mmWave/THz links and sensing.

We demonstrate an on-chip wavelength monitoring system comprising micro-optical thin-film filters and photodiodes integrated with a hybrid InP/polymer tunable laser, enabling continuous wavelength tuning and measurement over a 0.5-THz range.

This work investigates the development of composite feedstocks as a preliminary step toward additive manufacturing of RF and terahertz (THz) optical components. Semiconductor nanoparticles are incorporated into a high-density polyethylene (HDPE) matrix with the objective of tailoring the effective refractive index of future waveguide and optical structures. The study focuses on feedstock formulation and compounding strategies aimed at achieving homogeneous particle dispersion and suitable processability for subsequent filament extrusion and fused filament fabrication (FFF). The structural characteristics and dielectric properties of the resulting composites are analyzed as key indicators of their suitability for THz applications. Ongoing work is directed toward filament fabrication and the experimental evaluation of refractive index, transmission, and loss in the terahertz range using frequency-domain spectroscopy, to assess their potential as low-loss optical materials.

Filtering microwave signals is a central functionality in radio communication systems. Filter reconfigurability in the central frequency and passband width are highly desirable improvements which are enabled by integrated microwave photonics. In this paper we provide a comprehensive tutorial on the development of integrated microwave photonic filter systems. This involves a wide range of topics, spanning from photonic waveguide and chip design and fabrication to hybrid assembly and packaging, driving electronics and system modeling and characterization. All these aspects are thoroughly explained and illustrated by numerous examples.

Terahertz (THz) and millimeter-wave (mmW) spectroscopy provide non-ionizing, label-free access to the electromagnetic response of a wide range of materials, enabling applications in quality control, biomedical diagnostics, and non-destructive evaluation. Conventional free-space THz spectroscopy, however, often suffers from limited interaction length and reduced sensitivity when the sample is thin, spatially localized, available only in small volume, or incompatible with beam-based fixtures. In this work, we present an integrated, non-contact approach for broadband material-property extraction based on the evanescent field of a low-loss high-resistivity silicon dielectric waveguide. The material under test (MUT) is placed in the cladding region, where it perturbs the guided-mode propagation constant and attenuation. By measuring the complex transmission through a reference waveguide and a waveguide loaded with the MUT and by combining these data with mode simulations and a perturbation-based inversion, we extract the complex permittivity over a continuous frequency band. The approach leverages an evanescent-field-based non-destructive method, a compact measurement setup, and feasibility to rescale toward higher frequencies for broadband material screening in the mmW to THz range.

This work presents the first realization of a photonics-based two-dimensional (2D) array architecture concept that combines a three-dimensional (3D) dielectric rod waveguide (DRW) antenna with a $4 \times 4 \text{InP}$-based photodiode (PD) array. Simulations demonstrate that the proposed approach supports 2D beam-steering at carrier frequencies of at least up to 210 GHz. Preliminary characterization results of the monolithically integrated $4 \times 4 \text{InP}$ PD array, which incorporates semiconductor optical amplifiers (SOAs), confirm wideband THz generation. Furthermore, the proposed architecture mitigates microscale assembly challenges through a novel alignment concept for chiplevel integration. This paves the way towards broadband THz sources for next-generation communication systems.

Test equipment in the millimeter and Terahertz range relies on coaxial or rectangular metal waveguide technologies to connect to RF test probes, which then use planar transmission lines to interface with the devices under test. Dielectric waveguide technology in silicon is an alternative that has been shown to provide broadband contact-less interconnects as well as key functionalities to unlock continuous measurements across the millimeter-wave and Terahertz ranges.

We present a stability analysis of a microwave photonic multi-carrier radio frequency (RF) generator operating across the Ka, Q, and V bands. The system, developed under the ESA-funded THORMUX project (Tunable Photonic RF Demultiplexer for Broadband Satellites), targeting the realization of a 4-channel photonic MUX/DEMUX with dynamic tunability in both center frequency and bandwidth, addressing the growing demand for fully reconfigurable RF front-ends in next-generation satellite payloads. A central feature of the system is its realization using hybrid integration technology on a photonic integrated circuit (PIC) based in low-loss Si3N4 TriPleX (R) platform, offering substantial advantages in size, weight, and power (SWaP) for space applications. Each channel employs an optically generated local oscillator based on heterodyning two tunable lasers, with a total of five lasers integrated together in the chip. This work investigates key challenges related to frequency stability as the system scales to multiple channels, focusing on frequency allocation and thermal effects. We demonstrate best-case frequency drifts below +/- 25 MHz in a free- running regime over a 24-hour measurement period. Using infrared imaging, we characterize the thermal emission of the integrated lasers to correlate heat distribution with RF frequency drift. We further propose design optimizations to improve scalability and thermal management, which directly impact long-term frequency stability and overall system performance.

We unveil a groundbreaking empirical modeling approach for designing band-pass laser filters-based on cascaded Mach-Zehnder Interferometer (MZI) networks. Unlike traditional theoretical frameworks, our model overcomes inherent simplifications by integrating a genetic algorithm for fine-tuning, directly enabling the design of photonicchip compatible lasers with independently tunable free spectral range (FSR) and emission frequency. This innovation, meticulously validated within Lumerical INTERCONNECT, delivers functional resonant optical circuits exhibiting excellent signal-to-noise ratio (SNR). This work provides analytical tools and insights for engineering advanced photonic integrated laser, poised to contribute next-generation optical communication, quantum computing, and high-precision sensing systems.

We demonstrate a Bessel beamformer based on multimode interference (MMI) for the terahertz (THz) wave range. Unlike traditional Bessel beam generation methods, which often rely on bulky free-space optical setups, our approach leverages a 3D-printed cyclic-olefin-copolymer (COC) MMI structure fed from a dielectric waveguide (DW) with a lambda/4 slot-waveguide termination (SWT) that provides an index-matched interface for low reflection. Based on this interface and the low losses of the constituent materials, the beamformer achieves a measured transmission efficiency of 93.9% at 275 GHz, with a propagating distance of 20 mm ( similar to 20 lambda ). Even at an extended distance of 35mm ( similar to 35 lambda ), the beam maintains a 50% efficiency. This approach addresses key limitations of existing free-space methods, offering a workable guided-wave approach to launch a THz Bessel beam.

Photonic Integrated Circuits (PICs) are essential components in modern optical systems, yet their testing often relies on manual adjustments that account for up to 28% of total manufacturing costs. This work presents a novel approach by implementing the RF-DETR architecture to automate the optical characterization process. Utilizing a curated dataset of 4,000 images, the model achieved an Average Precision (AP(50)) exceeding 0.95 and a peak Average Recall of 0.84 for identifying lensed fibers, waveguide facets, and PICs. Experimental results demonstrate an average inference speed of 2.90 FPS, which enables a stable closed-loop response when integrated with PI H-811.12 miniature hexapods for sub-micrometer alignment. These findings justify the potential of Vision Transformer-based frameworks to replace human visual estimation with automated detection, significantly reducing testing cycles and enabling high-throughput production for next-generation optical technologies.

The advancement of terahertz technology is impeded by a lack of viable options for dynamic reconfigurability in compact systems with fixed low‐loss interconnect. To address this absence, we bring conductive walls into proximity with an unclad microscale silicon waveguide core and thereby supply additional boundary conditions to manipulate guided waves through evanescent interaction. This is analogous to a fiber squeezer, in which a dielectric waveguide's dispersion is manipulated via enclosing walls, but in this case, a crucial distinction is that there is no physical contact whatsoever. Analytical and numerical investigations of this phenomenon show that the presence of the conductive walls increases the cutoff frequency and alters the dispersion profile of the waveguide. We implement proof‐of‐concept demonstrations that exploit this effect to realize mechanically tunable terahertz filters of two types: a high‐pass filter and a resonant notch, operating at ∼300 GHz. This experimental demonstration utilizes a featureless straight dielectric waveguide, and the desired frequency‐selective behavior is implemented contactlessly, and hence reversibly, having made no modification to the waveguide core. The capability for on‐demand dispersion tuning of low‐loss terahertz waveguides holds the potential to realize a broad range of practical reconfigurable systems to support diverse applications of terahertz waves.

Abstract In this work, we propose interconnection structures for substrateless all-silicon dielectric waveguides, a platform for terahertz (THz) hybrid integration that currently relies on traditional tapered interfaces. We demonstrate two dielectric waveguide-to-waveguide interconnect approaches: a truncated termination and a quarter-wave-matched (QWM) slot termination. Both designs maintain a confined coupling point, enabling consistent coupling. Experimental results show maximum interconnection coupling losses of 5 dB $5\,\mathrm{dB}$ 5 d B and 2.5 dB $2.5\,\mathrm{dB}$ 2.5 d B for the truncated and QWM-slot terminations, respectively, across the 220–330 GHz band. The QWM-slot transmission coefficient remains above minus 3 dB $-3\,\mathrm{dB}$ − 3 d B with a misalignment tolerance up to 100 mu m $100\,\mu\mathrm{m}$ 100 μ m , representing a 2.5 times $2.5\times$ 2.5 × improvement over the truncated design. Offset characterization along three axes reveals smooth decoupling behavior over a 1 mm range, validating the potential for broadband, contactless interconnects between dielectric waveguide interfaces. These results establish a compact THz interconnect concept with substantially relaxed translational alignment tolerances, making it well-suited for deployment in scalable 6G multi-chip arrays and THz sensing modules.

There is a need to increase the physical robustness of substrateless silicon waveguides for terahertz systems. One recently demonstrated approach involves the exploitation of multimode effects to produce field nulls at specific desired edge-locations, enabling strong support beams without disturbing guided waves. However, these effects are frequency-dependent, and if several such supporting structures are deployed in series, i.e. to enhance device strength, then this frequency dependence will become more severe. In this work, we explore this tradeoff between bandwidth and physical robustness that is mediated by the number of multimode support structures that suspend a silicon waveguide core. It is found experimentally that, whilst a two-support waveguide exhibits ∼31% bandwidth, this reduces to 20% if six structures are used.

There is a need for compact low-cost near-field terahertz systems. To this end, we numerically demonstrate that subwavelength-size all-dielectric slot dipoles are capable of near-field sensing, as the presence of a target detunes the matching condition, and this effect can be observed in the antenna’s return spectrum. This holds potential to miniaturize and simplify terahertz near-field sensor devices.

There is a need for compact, broadband, efficient radiators for terahertz integrated circuits, to serve as feed for large- aperture quasioptics, or as antenna elements in phased arrays. We present a condensed, subwavelength progressive transition between a terahertz microscale dielectric waveguide and a dielectric slot radiating aperture. The result is an endfire point-source radiator spanning > 2.2/1 , from <185 GHz to 410 GHz, which is fabricated in a single etch step from a high-resistivity float-zone intrinsic silicon wafer. The radiation phase center deviates by just sim 500mu*m across the operation bandwidth-less than one free-space wave- length.

Millimeter-wave (MMW) and Terahertz (THz) sources and receivers are essential in a wide range of applications, from high-resolution radar to spectroscopy, as well as high-capacity wireless links. Current efforts are directed towards their integration, benefiting from their small form factor. However, due to the wide bandwidth available at these frequencies, the challenges that need be addressed include increasing the operating bandwidth to use the available spectrum as well as to increase the total radiated power. Two key factors play a role in this, the intrinsic limitation of the components (i.e. limited f(max)) and the inefficient on-chip radiation. In this work we address how dielectric structures can help improve radiation efficiency.