Spectrum allocation with wavelength conversion for enhanced spectral efficiency in multi-band elastic optical networks

High-performance optical Kerr switch and efficient wavelength conversion via MC-based microfiber in the mid-infrared region

Spectral broadening via phase modulation is widely employed in high-power laser systems to suppress transverse-stimulated Brillouin scattering and improve beam uniformity.However, non-uniform spectral transmittance and group velocity dispersion can induce frequency modulation-to-amplitude modulation (FM-to-AM), threatening the safety of large-aperture optics.Current monitoring techniques rely on high-speed oscilloscopes and wavelength conversion, thereby increasing the cost and complexity.This study presents a real-time FM-to-AM detection method based on a dual-comparator delayunlocked detection architecture.The system employs a high-speed photodetector, lownoise amplifier, envelope detection, and delay-unlocked dual-comparator.The module reliably measures modulation depths from 1.27% to 19.15% for pulses with a rise time of < 60 ps and a modulation frequency of 20 GHz.This compact, low-cost, and modular design enables robust FM-to-AM monitoring without high-speed oscilloscopes, facilitating realtime feedback and enhancing the operational stability in large-scale laser drivers, while offering scalability for multi-channel deployment in future inertial confinement fusion facilities.

Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have been demonstrated only indoors or over short outdoor distances. Here, by developing channel-fluctuation-independent high-precision manipulation of continuous-variable quantum states, high-accuracy quantum signal acquisition and processing, and high-efficiency free-space acquisition, tracking, and pointing technology, we overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and narrow-linewidth spectral filtering and demonstrate for the first time long-distance free-space quantum key distribution under the asymptotic condition over 7-km inland and 9.6-km maritime atmospheric channels with Gaussian-modulated coherent states. Given that the CVQKD system is naturally compatible with existing ground fiber telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications.

We propose a practical spectral image rendering method for fluorescent objects using a renderer that does not natively support wavelength-shifting transport. For scenes composed of matte fluorescent and non-fluorescent surfaces, the illumination incident on a target fluorescent object is classified into three types: (1) direct illumination from a light source, (2) indirect illumination reflected from other reflective objects, and (3) luminescent illumination emitted from other fluorescent objects. We express the radiance observed on a fluorescent surface as a linear combination of five terms: reflection and fluorescence under direct illumination, reflection and fluorescence under indirect illumination, and reflection induced by luminescent illumination emitted by other fluorescent surfaces. Assuming isotropic emission and single-bounce fluorescence, the fluorescent shading terms reuse the diffuse-reflection shading produced by the renderer, while measured Donaldson matrices provide the wavelength conversion. Mitsuba is used as the underlying conventional rendering system. Experiments conducted with a physically built Cornell Box validate the proposed method through comparisons with direct measurements and an existing fluorescence capable renderer. Finally, we demonstrate an extension to non-planar fluorescent objects via sparse emitter discretization.

Agile and Broadband All-Optical Wavelength Conversion with Multi-Wavelength Lasers

The hybrid multiplexing technique is an essential way to satisfy the rapid growth of optical communication capacity. All-optical wavelength conversion (AOWC), a fundamental function to support the all-optical networks, becomes challenging for hybrid multiplexed signals involving wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM). An AOWC method is presented for hybrid WDM-MDM signals based on a segmented thin-film periodically poled lithium niobate (STFPPLN) waveguide, which has the ability to deal with each mode in a separate segment. By considering three modes (TE0, TE1, and TE2), the STFPPLN waveguide is designed and a difference-frequency generation (DFG) conversion efficiency of -9.67dB with a uniformity variation of 0.37dB throughout the C band is achieved using a 100mW pump in an 11mm long waveguide. The conversion bandwidth is predicted as 87.5nm, which enables 330 WDM-MDM channels (110 wavelengths×3 modes), with the crosstalk suppressed below -50dB.

This tutorial reviews silicon core fibers: a platform that unites fiber optics and silicon photonics. The timing is such that it celebrates a remarkable syzygy: the 60th anniversary of the foundational paper that drove modern fiber communications, the 40th anniversary of silicon photonics, and the 20th anniversary of the first practical silicon core fibers. Included herein is a brief history of silicon core fibers, detailed discussions of the various fabrication methods that have been trialed, and interactions that arise during or following fabrication. The properties and performance of silicon core fibers also are discussed and, where possible, compared with their on-chip counterparts. Particular focus is placed on their potential use in various applications, such as optical modulators, wavelength conversion, amplification, in-fiber junctions and diodes, photovoltaic fibers, and sensors/wearable structures. The tutorial concludes with topics for future exploration and remaining challenges for this technology.

ABSTRACT We report the first successful synthesis and characterization of a new family of high‐entropy rare earth borate ( R n BBO) single crystals with compositions R 5 Ba 3 (B 3 O 6 ) 3 and R 6 Ba 3 (B 3 O 6 ) 3 ( R = Nd, Tb, Sm, Dy, Gd, Yb, Er). Using configurational entropy as a tuning knob, these systems have been grown as large, highly crystalline boules that exhibit a bandgap of ≈5 eV and significantly enhanced optical transparency (20–50%) over singlecomponent systems. The presence of multiple rare‐earth elements results in broadband photoluminescence in both the visible and the near‐infrared wavelength ranges, with co‐existing emission bands at 605, 705, 813, 910, and 1030 nm. Further, broken inversion symmetry enables optical second‐harmonic generation (SHG) with potential for both type‐I and type‐II phase matching. Our highest observed effective phase‐matched SHG coefficient of ≈ 2.1 pm V −1 at 800–400 nm wavelength conversion is 20% better than the commercial β‐BaB 2 O 4 (BBO), while its laser‐induced surface damage threshold is 5‐6 × larger for 100 fs 800 nm pulse, enabling potentially an order of magnitude improvement in the frequency conversion efficiency. This work illuminates the promise of high‐entropy synthesis strategy for designing next‐generation optoelectronic materials that combine increased transparency, strong broadband luminescence, and enhanced nonlinear response in a single platform.

We demonstrate thermo-optic tuning of parametric wavelength conversion in integrated Bragg gratings- an approach that enables dynamic control of nonlinear optical processes on-chip. Bragg gratings offer enhanced phase matching through sharp dispersion near the photonic stopband, enabling significantly improved four-wave mixing efficiency compared to uniform photonic waveguides. Leveraging this grating-induced dispersion, we achieve continuous-wave four-wave mixing with a 20 dB enhancement in on/off conversion efficiency relative to a reference waveguide of the same length. Crucially, we show that thermal tuning from 25 °C to 75 °C yields up to a 5 dB modulation in conversion efficiency and induces a 5 nm spectral shift in the stopband-representing a level of control not attainable in conventional waveguides. Experimental results show good agreement with theoretical predictions. These results establish integrated Bragg gratings as a powerful and reconfigurable platform for actively tunable nonlinear photonic devices.

Demonstration of 2-Channel Mid-Infrared Mode-Division Multiplexing Using a Single Wavelength Converter for IM/DD and Coherent Free-Space Optical Communication

We demonstrate a compact mid-infrared (MIR) free-space optical transceiver based on packaged, fiber-coupled intracavity difference-frequency generation (DFG) and sum-frequency generation (SFG) modules operating at room temperature. The system achieves stable MIR generation, recovery of modulated signals up to 1.3 Gb/s, and outdoor validation over a 160 m rooftop link. Link stability measurements confirm robust performance and compatibility with silicon/GaAs detectors, overcoming the limitations of conventional infrared photodiodes. Future work includes rooftop high-speed bit error rate testing, drone-based ∼1km demonstrations, and balloon-assisted ∼25km trials, establishing wavelength conversion as a scalable foundation for next-generation, weather-resistant MIR satellite high-throughput communication systems and quantum communications with short-wavelength detectors.

Cavity-enhanced four-wave mixing lays the foundation for a variety of nonlinear applications such as wavelength conversion, parametric oscillation, Kerr frequency comb generation, etc. While the dramatic enhancement in nonlinear conversion efficiency is commonly attributed to the resonance quality factor, the influence of the resonance extinction ratio has often been overlooked. In this work, we uncover the pivotal role of the extinction ratio in FWM processes through integrated innovations in ring-bus coupler design. Pulley couplers are engineered to selectively excite TE and TM modes within microresonators, enabling precise control over polarization-dependent resonance excitation. We demonstrate that the extinction ratio of the cavity resonance directly dictates FWM efficiency. By optimizing the coupling conditions to achieve high extinction ratios (6.6 dB), we realize an 11.95 dB enhancement in FWM efficiency compared to low-extinction-ratio cavities (3.3 dB), in excellent agreement with theoretical predictions. These findings highlight the importance of designing microring resonators at critical coupling conditions to maximize nonlinear conversion efficiency. To the best of our knowledge, this is the first systematic investigation of FWM conversion efficiency using pulley couplers in the gallium phosphide-on-insulator (GaP-OI) platform. In addition, thermal bistability measurements quantify the material absorption-induced propagation loss, clarifying the dominant loss origin. The results presented here provide valuable insights into the development of highly efficient integrated Kerr nonlinear photonic devices, with significant implications for integrated quantum sources and other nonlinear photonic applications.

We present a mid-infrareddual comb spectrometer for the precisedetermination of the isotopic ratio of the stable CO2 isotoplogues 12C16O2 and 13C16O2 under atmospheric pressure. The spectrometer is basedon electro-optic intensity modulation at 1550 nm wavelength and subsequentwavelength flexible conversion to the mid-infrared. Here, the fundamentalabsorptions of CO2 in the ν3 band around4.3 μm wavelength (2300 cm–1) were accessedto achieve the needed sensitivity to investigate the isotopic compositionat atmospheric concentrations. The high spectral resolution of 0.004cm–1 and spectral coverage of 8 cm–1 enable the measurements of the three most abundant CO2 isotopologues 12C16O2, 13C16O2 and 16O12C18O at ambient pressure. The high average signal-to-noise ratioper comb mode of 51 dB and a noise equivalent absorption coefficientof 5.4(9)·10–6 cm–1 Hz–1/2 ensures high precision. After an integration timeof 172 s a precision on the stable isotopic ratio (δ13C) of <0.1‰ is achieved according to Allan deviation analysis.A linearity analysis on the measured concentrations of the singleisotopologues results in coefficients of determination (R2) of 0.999 for CO2 concentrations rangingfrom 300 to 450 ppm, whereas for the measurement of δ13C-values ranging from −36.5‰ and −5.4‰a coefficient of determination of 0.998 was achieved. This linearbehavior and the high precision on the measurements demonstrate thegreat potential of the presented dual comb spectrometer for atmosphericresearch. Especially, where measurements under low pressure must beavoided, the here presented system is a promising alternative to establishedquantum cascade laser-based systems.

Here, a technique for implementing an all-optical wavelength converter based on the quantum-confined Stark effect (QCSE) influenced by piezoelectric fields in a semiconductor optical amplifier with compressively strained zinc-blende multi-quantum well grown along the [111]A direction and embedded in the intrinsic layer of a p-i-n diode is presented. The originality and crucial aspect of the technique used is that the piezoelectric fields, induced by the compressive strain within the quantum wells (QWs) of the amplifier with an orientation parallel to that of the built-in field of the structure, make it possible to accelerate the absorption recovery and to perform a fast wavelength conversion over a wide range of the continuum. Specifically, the built-in p-i-n electric field and the piezoelectric fields induce a QCSE and unevenly tilt the potential energy profile of the QWs. This dramatically reduces the energy between the effective height of barriers and the quantized energy of carriers, remarkably due to the piezoelectric fields, thereby decreasing the escape time of carriers from wells and accelerating absorption recovery. Consequently, a strong negative chirp is induced into the converted signal pulses, allowing their compression after passing through a blue-shifted optical filter. Up- and down-conversions at 150 and 1300 Gb/s, respectively, were theoretically predicted in an ideal case, and experimentally, both were error-free demonstrated at 40 Gb/s in a total range of 29 nm, employing a straightforward scheme, with the possibility of operating at 100 Gb/s.

High-efficiency integrated difference frequency generation (DFG) has long been pursued for optical communications and signal processing. Recent developments of the thin-film lithium niobate platform enable strong optical confinement in nanoscale waveguides, greatly enhancing the nonlinear efficiencies. However, the absolute DFG conversion efficiencies (CEs) in recent studies are limited because of fail to satisfy the phase-matching condition strictly. Here, we demonstrate an integrated DFG device based on an adapted thin-film periodically poled lithium niobate waveguide. The generated idler wave achieves a maximum output power of 13.2 dBm and a CE of 48.6%. Furthermore, our device exhibits flat optical responses and high-quality eye diagrams when converting a signal at 1638 nm to an idler at 1556 nm, enabling bringing unique-band light into the amplifier’s gain band. By overcoming the efficiency limitations of previous DFG implementations, our work opens wider possibilities for practical applications in optical communications, wavelength conversion, and signal amplification.

Abstract Nonlinear optical crystals with second-order optical susceptibility χ (2) are crucial for quantum light generation and high-speed electro-optic modulation. However, SiN x , a common material for photonic integrated circuits, lacks χ (2) . We fabricated a horizontally aligned AlN/SiN x hybrid waveguide using standard semiconductor processes and demonstrated second harmonic generation by pumping in the telecommunication band. This study demonstrates a practical method for achieving χ (2) -based wavelength conversion by integrating AlN and SiN x .

High-efficiency all-optical wavelength conversion via polarization-insensitive four-wave mixing for 10 Gbps digital signals

A sandwich-structured material with wavelength conversion functionality for all-day radiative cooling

Abstract Polarity inversion is a well-known phenomenon in AlN, GaN, and InN with wurtzite structure. Control of the crystalline polarity is essential because it affects growth and impurity incorporation, and is needed for developing a wavelength conversion device using quasi-phase-matched structures. Improving polarity control requires understanding the mechanism of polarity inversion. In this study, polarity inversion boundaries in GaN involving an oxidation interlayer are investigated using first-principles calculations. Interfacial stability is examined for polarity inversion from N-polar to Ga-polar and from Ga-polar to N-polar by comparing interface energies, and the reason for stability is discussed according to the electron counting rule.