Search Results (49)

Graphene–plasmonic electro–optic (EO) modulators have attracted significant interest for compact and energy-efficient integrated photonic systems due to their electrically tunable optical response and strong light–matter interaction. In this work, an ultra-thin silicon-on-insulator (SOI) graphene–plasmonic slot modulator (G-PSM) is investigated using a combined semi-analytical and numerical framework. The analysis integrates finite-temperature Kubo conductivity modeling, perturbation-based effective-index analysis, overlap-factor evaluation, eigenmode analysis, and full-wave simulations to study the influence of silicon thickness on the EO performance of the proposed structure. The obtained results demonstrate that geometry engineering strongly affects modal confinement, overlap enhancement, effective-index perturbation, transmission characteristics, extinction ratio (ER), insertion loss (IL), energy-per-bit consumption, and EO bandwidth. Under optimized operating conditions, the proposed G-PSM achieves an effective refractive-index variation of approximately $3.1\times {10}^{-3}$, an ER of approximately 3.5 dB, an IL of 1.5–2 dB, an energy-per-bit consumption of approximately 7.5 fJ/bit, and a 3 dB EO bandwidth approaching 200 GHz. Strong electromagnetic confinement is achieved inside the plasmonic slot region near the graphene-active layer, enabling efficient electro–absorptive and electro–refractive modulation. Excellent agreement between the semi-analytical calculations and numerical simulations validates the developed framework and confirms the suitability of the proposed ultra-thin SOI G-PSM for compact broadband EO modulation in future integrated photonic systems. Full article

Directly modulated VCSEL transmitters are widely deployed in short-reach optical interconnects. However, further scaling of per-lane symbol rates in AI/HPC data center fabrics requires modulation schemes beyond the practical limits of direct current modulation. We demonstrate a laterally integrated VCSEL–electro-absorption modulator (EAM) transmitter enabled by resonance-detuned coupling on an oxide-confined half-VCSEL platform. A localized 20 nm surface etch produces > 5 nm resonance detuning, confirmed by measured spectra and supported by transfer-matrix and mode-matching simulations, which indicate strong slow-light-assisted lateral coupling into the modulator. Experimentally, the measured spectra confirm a 5 nm resonance separation. Static characterization shows a coupling ratio of 63% extracted from near-field profiles and an extinction ratio of 4 dB (based on modulator-side power) under a −2 V modulator bias, with an apparent 1 mW absorption at a 6 mA VCSEL drive current. Dynamic measurements demonstrate a small-signal 3 dB bandwidth of approximately 23 GHz and clear NRZ eye openings at 25 Gbps and 30 Gbps. These results validate resonance-detuned lateral integration as a compact and manufacturable approach to VCSEL-based externally modulated transmitters for next-generation short-reach interconnects. Full article

With the rapid deployment of artificial intelligence (AI) data centers, demand for optical modules surges—alongside faster upgrades and stricter low-power requirements. However, traditional optical driver integrated circuits (ICs) rely on device-specific customization, which lengthens driver design cycles, delays module deployment, and raises costs, becoming a bottleneck for optical module evolution. To address these issues, this work proposes a unified optical transmitter electronic integrated circuit (EIC) design approach featuring synergistic driver-laser/modulator co-design and a versatile output driver (VOD). The VOD can be configured into three output impedance states (open-drain, differential 50-$\Omega$, or differential 100-$\Omega$), enabling it to drive various optical devices like distributed feedback lasers (DFBs), vertical-cavity surface-emitting lasers (VCSELs), electro-absorption modulated lasers (EMLs), and Mach-Zehnder modulators (MZMs) with a single design, minimizing device-specific customization. Meanwhile, its power consumption is also adjustable to maximize the power efficiency. The proposed design approach demonstrates the potential to address the critical interoperability, cost, and power challenges faced by AI data centers, providing a scalable template for next-generation coherent and 4-level pulse amplitude modulation systems and facilitating rapid deployment. Full article

Waveguide-integrated electro-optical modulators play a crucial role in the design of new-generation photonic integrated circuits. The target of this paper is to demonstrate the potential offered by the association of graphene (Gr) and hydrogenated amorphous silicon (a-Si:H) in enhancing silicon photonics technology, enabling, in particular, the fabrication of efficient, wide-bandwidth, highly compact active devices. The design of the proposed electro-optic modulator is based on accurate numerical simulations where Gr is explored as the active material, absorbing (or not) the light propagating along the waveguide core, with its absorption coefficient being tunable through the application of an external electric bias. By strategically embedding two Gr monolayers where the propagating optical field is at its maximum, the performance of the modulator is maximized, resulting in a 39.5 GHz 3 dB bandwidth, corresponding to a 0.34 dB/µm modulation depth. The straightforward feasibility of the proposed structure is bolstered by the use of the Plasma-Enhanced Chemical Vapor Deposition technique, which allows for the deposition of a-Si:H on a silicon-on-insulator platform as a post-processing phase, ensuring potential scalability and practical implementation for advanced photonics. Full article

This study investigates the influence of vacancy engineering and nitrogen doping on the structural, electronic, and optical properties of T-graphene fragments (TFs) using density functional theory (DFT) and time-dependent DFT (TD-DFT). A central vacancy and five pyridinic nitrogen doping configurations are explored to modulate the optoelectronic behavior. All systems are thermodynamically stable, exhibiting tunable HOMO–LUMO gaps, orbital distributions, and charge transfer characteristics. Optical absorption spectra show redshifts and enhanced oscillator strengths in doped variants, notably v-NTF2 and v-NTF4. Nonlinear optical (NLO) analysis reveals significant enhancement in both static and frequency-dependent responses. v-NTF2 displays an exceptionally high first-order hyperpolarizability (⟨β⟩ = 1228.05 au), along with a strong electro-optic Pockels effect (β (−ω; ω, 0)) and second harmonic generation (β (−2ω; ω, ω)). Its third-order response, γ (−2ω; ω, ω, 0), also exceeds 1.2 × 10⁵ au under visible excitation. Conceptual DFT descriptors and energy decomposition analysis further supports the observed trends in reactivity, charge delocalization, and stability. These findings demonstrate that strategic nitrogen doping in vacancy-engineered TFs is a powerful route to tailor electronic excitation, optical absorption, and nonlinear susceptibility. The results offer valuable insight into the rational design of next-generation carbon-based materials for optoelectronic, photonic, and NLO device applications. Full article

The solvatochromic properties of 48 solvents of three benzo-[f]-quinolinium methylids (BfQs) were analyzed within the theories of the variational model and Abe’s model of the liquid. The electro-optical properties of BfQs in the first excited state were determined based on the charge transfer process that occurs from the ylid carbon to the nitrogen atom. The dipole moments and the polarizabilities in the first excited state were calculated according to the two models. The quantum chemical calculations helped in understanding the relationship between the molecular structure and absorption properties of the ground state. It is concluded that several key parameters modulate the strength of the charge transfer and they work in synergy, and the most important are as follows: (i) isomerism around the single polar bond, and (ii) the properties of the solvent. The link between geometrical conformation and the zwitterionic character make the studied BfQs very sensitive chromophores for sensors and optical switching devices. Full article

Graphene-based micro-ring modulators are promising candidates for next-generation optical interconnects, offering compact footprints, broadband operation, and CMOS compatibility. However, most demonstrations to date have relied on conventional straight bus coupling geometries, which limit design flexibility and require extremely small coupling gaps to reach critical coupling. This work presents a comprehensive comparative analysis of straight, bent, and racetrack bus geometries in graphene-on-silicon nitride (Si₃N₄) micro-ring modulators operating near 1.31 µm. Based on finite-difference time-domain simulation results, a proposed racetrack-based modulator structure demonstrates that extending the coupling region enables critical coupling at larger gaps—up to 300 nm—while preserving high modulation efficiency. With only 6–12% graphene coverage, this geometry achieves extinction ratios of up to 28 dB and supports electrical bandwidths approaching 90 GHz. Findings from this work highlight a new co-design framework for coupling geometry and graphene coverage, offering a pathway to high-speed and high-modulation-depth graphene photonic modulators suitable for scalable integration in next-generation photonic interconnects devices. Full article

With the rapid growth of data center demand driven by AI, high-speed optical modules (such as 800G and 1.6T) have become critical components. Traditional 800G modules face issues such as complex processes and large sizes due to the separate packaging of EML chips, AlN substrates, and capacitors. This study proposes a high-speed EML module based on silicon integration, where resistors, capacitors, and AuSn soldering areas are integrated onto the silicon substrate, enabling the bonding of the EML chip, reducing packaging costs, and enhancing scalability. Key achievements include: the development of a 100G EML chip; the fabrication of a high-speed silicon integrated carrier; successful Chip-on-Carrier (COC) packaging and testing, with a laser output power of 10 mW, extinction ratio of 10 dB, and bandwidth greater than 40 GHz; and reliability verified through 500 h of aging tests. This study provides an expandable solution for next-generation high-speed optical interconnects. Full article

This paper presents a highly stable and integrated silicon-based carrier with broad application prospects. Traditional 800 G optical modules employ architectures based on aluminum nitride (AlN) carriers with externally mounted capacitors. However, such AlN-based architectures suffer from issues including high process complexity, elevated costs, poor environmental temperature adaptability, and difficulties in systematic crosstalk optimization. To address these challenges, this study conducted research on coplanar waveguide (CPW) transmission line structure design and optimization, high-density capacitor design and process implementation, and multi-channel crosstalk suppression. Based on these investigations, a silicon-based integrated carrier was designed and fabricated, incorporating resistors, capacitors, high-speed signal lines, and preformed AuSn structures. Test results demonstrate that the CPW transmission line structures fabricated on the silicon carrier exhibit excellent radio frequency performance with transmission losses below 1 dB within 67 GHz. The developed high-density capacitor structure achieves a remarkable capacitance density of 26.83 nF/mm² and withstands voltages exceeding 24 V at 1 μA current, reaching state-of-the-art levels. This paper also proposes crosstalk reduction solutions including increased channel spacing, the addition of wave-absorbing materials, and the implementation of metal barriers. Experimental results confirm that the developed integrated carrier demonstrates outstanding performance and reliability in high-frequency communications and optoelectronic devices. Full article

Microwave photonics (MWP) applications often require a high optical input power (>100 mW) to achieve an optimal signal-to-noise ratio (SNR). However, conventional silicon spot-size converters (SSCs) are susceptible to high optical power due to the two-photon absorption (TPA) effect. To overcome this, we introduce a silicon nitride (SiN) SSC fabricated on a silicon-on-insulator (SOI) substrate. When coupled to a tapered fiber with a 4.5 μm mode field diameter (MFD), the device exhibits low coupling losses of <0.9 dB for TE modes and <1.4 dB for TM modes at relatively low optical input power. Even at a 1W input power, the additional loss is minimal, at approximately 0.1 dB. The versatility of the SSC is further demonstrated by its ability to efficiently couple to fibers with MFDs of 2.5 μm and 6.5 μm, maintaining coupling losses below 1.5 dB for both polarizations over the entire C-band. This adaptability to different mode diameters makes the SiN SSC a promising candidate for future electro-optic chiplets that integrate heterogeneous materials such as III-V for gain and lithium niobate for modulation with the SiN-on-SOI for all other functions using advanced packaging techniques. Full article

A new approach to the dynamic polarimetric method is proposed, which allows for the decoupling of electro-optical Kerr effect measurements from the electro-absorption effect in partially transparent liquids. The method is illustrated by using the results of engine oil measurements as a function of temperature and modulating field frequency. It was shown that the birefringence induced in the sample, the modulation of the ordinary wave transmission, and the modulation of the extraordinary wave transmission in the sample can be shifted in phase with respect to the square of the applied alternating modulating field. Each of these three phase shifts can depend differently on the temperature and frequency. Neglecting the influence of electro-absorption on electro-optical measurements in liquids or considering electro-absorption as an effect correlated in phase with induced birefringence may lead to significant measurement errors. This indicates that the Kerr constant and the electro-absorption coefficients for an alternating electric field should be considered as complex quantities instead of real values, as they have been traditionally. The proposed approach fills an important gap in measurement techniques described in the literature, which may provide erroneous results for measurements of the Kerr constant in partially transparent liquids including many industrially important liquids. Full article

Numerous preclinical results have been verified, and clinical results have validated the advantages of modulated electro-hyperthermia (mEHT). This method uses the nonthermal effects of the electric field in addition to thermal energy absorption. Modulation helps with precisely targeting and immunogenically destroying malignant cells, which could have a vaccination-like abscopal effect. A new additional modulation (high-power pulsing) further develops the abilities of the mEHT. My objective is to present the advantages of pulsed treatment and how it fits into the mEHT therapy. Pulsed treatment increases the efficacy of destroying the selected tumor cells; it is active deeper in the body, at least tripling the penetration of the energy delivery. Due to the constant pulse amplitude, the dosing of the absorbed energy is more controllable. The induced blood flow for reoxygenation and drug delivery is high enough but not as high as increasing the risk of the dissemination of malignant cells. The short pulses have reduced surface absorption, making the treatment safer, and the increased power in the pulses allows the reduction of the treatment time needed to provide the necessary dose. Full article

High-index contrast lithium niobate waveguides, fabricated by the High Vacuum Vapor-phase Proton Exchange (HiVac-VPE) technique, are very promising for increasing both the optical nonlinear and electro-optical efficiencies of photonic integrated devices. So as to play this role effectively, it is mandatory to know the crystallographic phase composition of waveguides and the position of protonated layers for appropriate tailoring and optimization based on the intended applications. In addition, the estimation of structural disorder and electro-optical properties of the waveguides are also of high interest. Benefiting from Raman spectroscopy, IR reflection, IR absorption, and UV-VIS absorption, the H_xLi_1−xNbO₃ phase compositions, as well as the structural disorder in waveguides, were determined. Based on experimental data on the shift of the fundamental absorption edge, we have quantitatively estimated the electro-optic coefficient r₁₃ in as-exchanged waveguides. The electro-optical properties of the waveguides have been found to be depending on the phase composition. The obtained results allow for reconsidering the proton exchange fabricating process of photonic nonlinear devices and electro-optic modulators based on high-index contrast channel waveguides on the LiNbO₃ platform. Full article

Recently, thin-film lithium niobate electro-optical modulators have developed rapidly and have become the core solution for the next generation of electro-optical problems. Compared with bulk lithium niobate modulators, these modulators not only retain the advantages of lithium niobate materials, such as low loss, high extinction ratio, high linear response and high optical power handling capabilities, but can also effectively improve some performance parameters, such as the voltage bandwidth performance of the modulator. Unfortunately, the extremely small electrode gap of thin-film lithium niobate EO (electro-optic) modulators causes metal absorption, resulting in higher microwave losses. The electro-optical performance of the modulator, thus, deteriorates at high frequencies. We designed traveling-wave electrodes with microstructures to overcome this limitation and achieve a 3 dB electro-optical bandwidth of 51.2 GHz. At the same time, we maintain low on-chip losses of <2 dB and a high extinction ratio of 15 dB. It is important to note that the devices we manufactured were metal-encapsulated and passed a series of reliability tests. The success of this modulator module marks a key step in the commercialization and application of thin-film lithium niobate modulation devices. Full article

This paper presents an investigation into the parasitic capacitance of an RF contact scheme for lumped-element EAMs. Test structures are fabricated to analyse this parasitic capacitance via $S_{11}$ characterisation using a vector network analyser (VNA). Optimisations of the contact scheme lead to the parasitic capacitance being reduced to <10 fF. EAMs using this contact scheme are fabricated and characterised using $S_{11}$ measurements. These $S_{11}$ measurements are used to simulate $S_{21}$ measurements, which predict a f_3dB bandwidth of near 80 GHz using an equivalent circuit model. Full article