The research, led by scientists from Sapienza University of Rome and other European institutions, utilized Fiber Optic Reflectance Spectroscopy (FORS) and Terahertz Time-Domain Spectroscopy (THz-TDS) to analyze intact potato leaves of the Agata cultivar. By measuring spectral signatures at specific points on the leaves, the team was able to distinguish between healthy tissue, early-stage infection at two days post-inoculation, and advanced necrosis at four days post-inoculation. The key finding is that both techniques reveal physiological and structural changes in the leaf tissue that precede the visible appearance of chlorotic or brown lesions, which typically emerge around the fourth day after infection.

Fiber Optic Reflectance Spectroscopy operates in the visible to near-infrared range, capturing how light reflects off the leaf surface. This method is highly sensitive to the concentration of photosynthetic pigments such as chlorophyll and carotenoids, as well as the internal cellular structure of the leaf. In healthy leaves, the reflectance spectrum shows a characteristic “red edge,” a sharp transition from low reflectance in the red region to high reflectance in the near-infrared. The study found that this red edge position shifts to lower wavelengths as the infection progresses, indicating a decline in chlorophyll content and photosynthetic efficiency. Even at the pre-symptomatic stage of two days post-inoculation, the red edge position shifted significantly compared to healthy controls, providing an early optical marker of stress.

Terahertz Time-Domain Spectroscopy probes the leaf in a different frequency range, from 0.1 to 6 terahertz, which is sensitive to low-frequency molecular vibrations and intermolecular interactions, particularly those involving water. Since liquid water strongly absorbs terahertz radiation, this technique is often used to assess hydration status in plant tissues. The researchers observed that healthy potato leaves exhibit a linear increase in absorbance with frequency, driven primarily by their high water content. However, in leaves infected with P. infestans, the terahertz absorbance profile changed dramatically. At two days post-inoculation, the absorbance at 1.0 terahertz decreased significantly compared to healthy tissue, a change that was statistically distinct despite the lack of visible symptoms. This suggests that the pathogen induces early perturbations in water distribution or cellular integrity that are detectable through terahertz sensing.

As the infection advanced to the necrotic stage at four days post-inoculation, the terahertz spectra revealed even more profound alterations. The absorbance curves for necrotic tissue crossed those of healthy tissue, with higher absorbance at lower frequencies and lower absorbance at higher frequencies. Additionally, a broad absorption band centered around 0.66 terahertz emerged in the necrotic samples, with an amplitude an order of magnitude larger than in healthy leaves. The researchers hypothesize that this band may be associated with the accumulation of flavonoids, such as anthocyanins, which are stress-response pigments produced by the plant during infection. While the exact molecular origin of this band requires further biochemical validation, its presence provides a distinct spectral fingerprint for advanced tissue degradation.

The study highlights the complementary nature of these two spectroscopic methods. FORS provides insights into the biochemical and physiological status of the leaf, such as pigment degradation and photosynthetic stress, while THz-TDS offers information on structural changes and water dynamics. By combining data from both techniques, the researchers were able to create a multiscale assessment of the plant’s health. A principal component analysis of the full spectral datasets confirmed that the three conditions—healthy, early infected, and necrotic—occupy distinct regions in the spectral space, even without using class labels during the analysis. This robust separation suggests that the combined approach could form the basis for automated diagnostic tools capable of classifying disease stages with high accuracy.

The implications for crop management are significant. Current Integrated Pest Management systems prioritize preventive measures and monitoring over reliance on pesticide applications, but effective monitoring requires early detection. The ability to diagnose P. infestans infection before visible symptoms appear allows for targeted and timely interventions, potentially reducing the need for broad-spectrum fungicide treatments. This aligns with the goals of precision agriculture, where data-driven decisions aim to optimize resource use and minimize environmental impact. The non-invasive nature of the spectroscopic techniques means that plants can be monitored repeatedly over time without causing damage, enabling the tracking of disease progression in real-time.

However, the researchers acknowledge several limitations and future directions for the work. The study was conducted on a single potato cultivar under controlled laboratory conditions, and the sample size was limited to three plants per condition. While the spectral changes were consistent across the measured locations, the findings need to be validated across multiple cultivars with varying levels of resistance to the pathogen. Furthermore, the transition from laboratory transmission measurements to field applications presents technical challenges. Field operation would require a reflection configuration rather than transmission, and the instrument would need to account for atmospheric water vapor absorption over longer path lengths. The researchers note that the diagnostic spectral features identified in this study lie in frequency intervals between atmospheric water vapor lines, which is promising for field deployment, but further engineering is required to develop portable, robust systems.

Future research will focus on extending the measurements to multiple commercial cultivars and establishing a dose-response relationship between pathogen load and spectral descriptors. By pairing spectroscopic acquisitions with molecular quantification of the pathogen, such as quantitative PCR, scientists can refine the diagnostic models and improve their predictive power. Additionally, the integration of machine learning algorithms with the spectral data could enhance the ability to classify disease stages and predict progression. The development of a comprehensive terahertz spectral database of compounds involved in pathogenesis will also facilitate accurate interpretation of the signals. These steps are crucial for translating the laboratory findings into practical tools for farmers and plant pathologists.

Ultimately, this work underscores the potential of advanced optical technologies to transform plant disease management. By leveraging the unique sensitivities of visible-near-infrared and terahertz spectroscopy, researchers can uncover hidden physiological changes that precede visible disease symptoms. This early warning capability is essential for protecting crop yields and ensuring food security in the face of climate change and evolving pathogen pressures. As the technology matures and becomes more accessible, it could become a standard component of precision agriculture toolkits, enabling a shift from reactive to proactive crop protection strategies.

Subject of Research: Non-invasive spectroscopic detection of early Phytophthora infestans infection in potato leaves

Article Title: Combined Fibre Optic Reflectance and Terahertz Spectroscopies for the early, non-invasive diagnosis of Phytophthora infestans infection in Solanum tuberosum

Article References: Moffa, C., Beccaccioli, M., Fratini, R. S., Extermann, J., Neri, L., Bertazza, G., Felici, A. C., Reverberi, M., & Petrarca, M. (2026). Combined Fibre Optic Reflectance and Terahertz Spectroscopies for the early, non-invasive diagnosis of Phytophthora infestans infection in Solanum tuberosum. Results in Optics, Article 101186. https://doi.org/10.1016/j.rio.2026.101186

Image Credits: AI Generated

DOI: 10.1016/j.rio.2026.101186

Keywords: potato late blight, terahertz spectroscopy, fiber optic reflectance, plant pathology, precision agriculture, non-invasive diagnosis, Phytophthora infestans, crop monitoring, spectral analysis, early detection, Combined, Fibre

The circulator is one of the oldest and most useful pieces of non-reciprocal optics. In its classic form, a circulator is a three-port device: light entering port one exits at port two, light entering port two exits at port three, and light entering port three exits at port one. In fibre-optic systems, this unidirectional routing is what allows a single fibre to carry traffic in both directions, or allows a transmitter and a receiver to share the same fibre facet, without the powerful outgoing signal leaking into, and blinding, the sensitive detector on the receiving path. Conventional circulators achieve this asymmetry using magneto-optic materials such as yttrium iron garnet, whose interaction with light changes depending on the direction of an applied magnetic field. The physics works beautifully, but the hardware does not scale: magnets, garnet crystals and precision-aligned optical assemblies are large, expensive, and impossible to integrate onto a silicon photonic chip.

The new device sidesteps magneto-optics entirely by exploiting the electro-optic effect in thin-film lithium niobate, a material platform in which a nanometre-scale crystalline film of lithium niobate is bonded to an insulating substrate and patterned into waveguides. Lithium niobate possesses one of the strongest Pockels coefficients of any practical optical material, meaning that an applied electric field changes the refractive index seen by light travelling through it essentially instantaneously. By engineering the phase and magnitude of radio-frequency modulation signals applied to travelling-wave electrodes alongside the optical waveguides, the researchers create an interference condition that is asymmetric in time: light propagating in one direction accumulates a modulation-induced phase shift that routes it toward one output, while light propagating in the opposite direction experiences the modulation differently and is routed, or blocked, accordingly. Because the Pockels effect is inherently non-reciprocal in this dynamically driven configuration, the device achieves genuine non-reciprocal routing without any magnetic material.

The performance numbers reported in the study place the device squarely in the territory of practical deployment rather than laboratory curiosity. Peak isolation of 37 decibels means that fewer than one part in roughly five thousand of the reverse-propagating light survives the journey — more than enough to protect a coherent receiver from the far stronger signal launched in the opposite direction along the same fibre. Equally important is the breadth of the transmission window. Optical networks operate across finely divided wavelength channels, and a circulator that works only at a single narrow wavelength would need to be replicated or retuned for each channel. The broad bandwidth demonstrated here means the same chip can serve the densely wavelength-multiplexed traffic that defines modern long-haul and data-centre interconnects.

The system-level demonstration is arguably the headline result. Rather than characterising the chip in isolation, the researchers connected it into a fibre transmission link and pushed bidirectional traffic through a single standard single-mode fibre at 800 gigabits per second of standard throughput. This is the regime in which commercial optical transceivers live, and the fact that the integrated circulator survived the test — supporting full-duplex communication without degrading the signals in either direction — suggests a clear path from the laboratory bench toward the network equipment rack. A circulator of this kind could allow a single fibre pair to do the work of two, or allow transceivers to pack transmit and receive functions onto shared optical infrastructure with less spare capacity held in reserve.

Thin-film lithium niobate has been on a remarkable run over the past several years. The platform combines the ultra-low optical loss and strong electro-optic response of bulk lithium niobate with the compactness and fabrication scalability of chip-based photonics. Researchers have used it to build modulators with bandwidths exceeding one hundred gigahertz, frequency comb sources, quantum photonic circuits, and high-performance filters. What has often been missing from the toolbox, however, is non-reciprocity. Passive integrated photonics built on silicon or silicon nitride is fundamentally reciprocal: light travels through the same component identically in either direction, which is a direct consequence of the linearity and time-independence of the underlying physics. Lasers on optical chips therefore remain vulnerable to back-reflections, and full-duplex links have required external, discrete circulators — exactly the kind of bulky component that integrated photonics was invented to eliminate.

The electro-optic approach demonstrated here changes that calculus by making non-reciprocity a matter of circuit design rather than materials sourcing. Because the circulator is built with the same lithographic processes and electrode structures used for lithium niobate modulators, it can in principle be co-fabricated on the same chip as the high-speed modulators, switches and filters that already exist on the platform. A complete transceiver front end — laser-coupled modulator on the transmit path, circulator sharing the fibre, and coherent receiver on the return path — could then live on a single lithographic die. The authors’ demonstration of standard 800G throughput through single-mode fibre speaks directly to the engineering requirements of that vision, since it shows the device operating with the modulation formats, channel counts and power levels that real systems actually use.

The implications extend beyond telecommunications. Data-centre interconnects are consuming fibre and transceiver capacity at a pace that strains both supply chains and power budgets, and any component that lets one fibre carry two directions of traffic efficiently translates directly into infrastructure savings. In fibre-to-the-home networks, circulators are already standard equipment for sharing fibre between downstream and upstream signals; an integrated, magnet-free version could shrink the optical line terminals at the heart of those networks. Coherent transceivers, sensing systems such as fibre-optic distributed acoustic sensors, and free-space laser communication terminals all rely on separating transmitted and received light, and all would benefit from a compact, low-loss, broadband circulator that integrates with the rest of the photonic circuit.

There remain, as with any first demonstration, engineering questions on the road to volume manufacturing. Insertion loss, the fraction of signal power sacrificed in passing through the device, must be minimised so that network link budgets can absorb the circulator without shortening reach. The radio-frequency drive electronics consume power and add complexity, and the modulation scheme must be stabilised against temperature drift and fabrication variation across large wafers. Scalability of the fabrication process — yields, wafer-scale uniformity, and packaging of the optical fibre interfaces — will determine whether the device makes the leap from the laboratory to the production line. Yet the platform’s rapid commercial maturation, with thin-film lithium niobate foundry services now offered by multiple suppliers, gives the field reason for optimism that these are problems of engineering refinement rather than fundamental physics.

The broader significance of the work lies in what it says about the direction of photonics as a discipline. For half a century, the non-reciprocal components at the heart of optical networks have been the last holdouts against integration, stubbornly magnetic, bulky and discrete while everything around them shrank onto chips. By demonstrating a high-isolation, broadband circulator with genuine system-level throughput on thin-film lithium niobate, the researchers have shown that even this last holdout can be brought into the integrated fold. If the technology follows the trajectory of the platform’s modulators — from laboratory record to commercial product in a handful of years — the optical circulator may soon be as unremarkable a fixture inside a transceiver as the amplifier and the modulator, quietly enabling the two-way flow of data over the single strands of glass that carry the world’s information.

Subject of Research: Integrated electro-optic circulator on thin-film lithium niobate for bidirectional optical fibre transmission

Article Title: Integrated electro-optic circulator on thin-film lithium niobate for bidirectional optical fibre transmission

Article References: St-Arnault, C., Laperle, C., Kita, D. M., Reimer, C., & Plant, D. V. (2026). Integrated electro-optic circulator on thin-film lithium niobate for bidirectional optical fibre transmission. Nature Photonics. https://doi.org/10.1038/s41566-026-02008-9

Image Credits: AI Generated

DOI: 10.1038/s41566-026-02008-9

Keywords: Integrated, electro-optic, circulator, thin-film, lithium, niobate, bidirectional, optical, fibre, transmission, scientific research