Enhanced Modulation Efficiency Research Articles

Exergy assessment of a semi-transparent building integrated photovoltaic facade for mild weather conditions of Srinagar

Abstract Effective utilization of solar energy reduces the dependence on fossil fuel usage along with achieving the objective of carbon neutrality. The current work aims to numerically assess the performance of a facade based semi-transparent BIPVT system while considering four different weather conditions in a month for the climate of Srinagar, India. In the proposed configuration, the BiSPVT facade serves the dual purpose of generating electrical power gain and providing pre-heated air for space heating. PV module surface was cooled by flowing air through the air channel. Movement of air through the cavity takes away the heat from the PV module back surface reducing the temperature of the solar cells resulting in enhanced module efficiency. System performance has been evaluated in terms of obtained energy and exergy using a 1-D numerical model developed in MATLAB. The Exergy analysis presented shows an informative means of estimating system functioning based on qualitative aspect of useful energy gained. For a mild cold weather condition of Srinagar, with minimum ambient temperature dropping to 1.2 °C, useful daily exergy gain of 0.0545 kWh/m2 has been achieved signifying the increase of space heating during winters of cold climatic regions. Maximum temperature difference between room and ambient was obtained as 9.76 °C using the BiSPVT façade. Results shows that the proposed BiSPVT system was able to produce monthly electrical and thermal exergy gain of 12.56 kWh/m2 and 16.81 kWh/m2 respectively. Exergy efficiency of the system was determined in the range of 18.2%-19%. Further, environmental assessment of the PV façade system based on CO2 emission gave an estimated amount of 0.387-ton CO2 emission reduction for the month of November leading to environmental cost reduction of 5.615$/month.

Enhancing modulation performance by design of hybrid plasmonic optical modulator integrating multi-layer graphene and TiO2 on silicon waveguides

A novel way to enhance modulation performance is through the design of a hybrid plasmonic optical modulator that integrates multi-layer graphene and TiO2 on silicon waveguides. In this article, a design is presented of a proposed modulator based on the use of the two-dimensional finite difference eigenmode solver, the three-dimensional eigenmode expansion solver, and the CHARGE solver. Leveraging inherent graphene properties and utilizing the subwavelength confinement capabilities of hybrid plasmonic waveguides (HPWs), we achieved a modulator design that is both compact and highly efficient. The electrical bandwidth f 3dB is at 460.42 GHz and it reduces energy consumption to 12.17 fJ/bit with a modulator that functions at a wavelength of 1.55 μm. According to our simulation results, our innovation was the optimization of the third dielectric layer’s thickness, setting the stage to achieve greater modulation depths. This synergy between graphene and HPWs not only augments subwavelength confinement, but also optimizes light–graphene interaction, culminating in a markedly enhanced modulation efficiency. As a result, our modulator presents a high extinction ratio and minimized insertion loss. Furthermore, it exhibits polarization insensitivity and a greater bandwidth. Our work sets a new benchmark in optical communication systems, emphasizing the potential for the next generation of chip-scale with high-efficiency optical modulators that significantly outpace conventional graphene-based designs.

Non-resonant recirculating light phase modulator

High efficiency and a compact footprint are desired properties for electro-optic modulators. In this paper, we propose, theoretically investigate, and experimentally demonstrate a recirculating phase modulator, which increases the modulation efficiency by modulating the optical field several times in a non-resonant waveguide structure. The “recycling” of light is achieved by looping the optical path that exits the phase modulator back and coupling it to a higher order waveguide mode, which then repeats its passage through the phase modulator. By looping the light back twice, we were able to demonstrate a recirculating phase modulator that requires nine times lower power to generate the same modulation index of a single pass phase modulator. This approach to modulation efficiency enhancement is promising for the design of advanced tunable electro-optical frequency comb generators and other electro-optical devices with defined operational frequency bandwidths.

Membrane multiple quantum well electro-optical modulator employing low loss high-k radio-frequency slot waveguides.

A membrane multiple quantum well (MQW) electro-optical (EO) modulator exploiting low loss high-k radio-frequency (RF) slot waveguides is proposed for sub-terahertz bandwidth. By employing high-k barium titanate (BTO) claddings in place of doped InP cladding layers in traditional InP-based MQW modulators, the proposed modulator exhibits enhanced modulation efficiency and bandwidth as well as reduced insertion loss. A low half-wave voltage-length product of 0.24 V·cm is estimated, together with over 240 GHz bandwidth for a 2-mm-long modulation region, thus allowing sub-terahertz operation.

A modulation efficiency enhancement method of KTN electro-optic modulator in laser 3D imaging

A modulation efficiency enhancement method of KTN electro-optic modulator in laser 3D imaging

All-optical spatial terahertz modulator with surface-textured and passivated silicon.

For a Si-based all-optical spatial terahertz modulator (STM), an enhanced modulation efficiency under low illumination density would be of great significance to exploit the competence of THz technology in real-world applications. We presented here an implementation of such a device by microtexturing and passivating the Si surface, forming a truncated pyramidal array (TPA). This TPA structure with SiO2 passivating coatings not only decreases light reflectance and expands the active area for THz modulation but also remarkably increases the photogenerated carrier lifetime. These 3-fold benefits render Si-TPA superior to bare-Si with respect to the achievable modulation efficiency, especially at low irradiation power. Furthermore such a Si-TPA device is also more applicable than its counterpart that is only passivated by SiO2 nanocoatings, even though the Si-SiO2 has a slightly increased modulation efficiency. These periodically aligned pyramids resembled as a mesa array significantly suppress the lateral diffusion induced by longer diffusion, resulting in an equivalent resolution of bare-Si. This novel Si-TPA based STM is highly desired for realizing a high-performance THz imager and provides a feasible approach to breaking the trade-off between resolution and modulation efficiency.

Broadband graphene-on-silicon modulator with orthogonal hybrid plasmonic waveguides

Abstract Graphene, a two-dimensional nanomaterial, possess unique photoelectric properties that have potential application in designing optoelectronic devices. The tunable optical absorption is one of the most exciting properties that can be used to improve the performance of silicon modulators. However, the weak light–matter interaction caused by the size mismatch between the optical mode fields and graphene makes the graphene-on-silicon modulator (GOSM) has large footprint and high energy consumption, limiting the enhancement of modulation efficiency. Here, we propose a broadband GOSM with orthogonal hybrid plasmonic waveguides (HPWs) at near-infrared wavelengths. The orthogonal HPWs are designed to compress the interaction region of optical fields and enhance the light-graphene interaction. The results show that the GOSM has a modulation depth of 26.20 dB/μm, a footprint of 0.33 μm2, a 3 dB modulation bandwidth of 462.77 GHz, and energy consumption of 2.82 fJ/bit at 1.55 μm. Even working at a broad wavelength band ranging from 1.3 to 2 μm, the GOSM also has a modulation depth of over 8.58 dB/μm and energy consumption of below 4.97 fJ/bit. It is anticipated that with the excellent modulation performance, this GOSM may have great potential in broadband integrated modulators, on-chip optical communications and interconnects, etc.

Improving the Modulation Designs for Visible Light Communications with Signal-Dependent Noise

This article reviews the recent investigations on improving modulation designs for visible light communication (VLC) systems subject to signal-dependent noise (SDN). The existence of signal-dependent noise degrades the system performance and leads to modulation deficiency issues due to the constellation distortion caused by the SDN. For single-carrier systems, a joint constellation and threshold design was recently proposed to compensate the SDN, and it is re-analyzed in this article together with an improved design criterion based on the rotated minimum Euclidean distance (MIN-ED) that was employed to enhance modulation efficiency in multi-carrier systems. These design criteria are further ameliorated by optimizing the distance-range. Performance comparisons between improved and MIN-ED-based designs for VLC-SDN systems under communications and lighting constraints are also presented to illustrate the major limitations of current modulations. This article concludes with critical implementation challenges and future research opportunities.

A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part II CFD Simulation

A ducted photovoltaic façade (DPV) unit was simulated using computational fluid dynamics (CFD). This is Part II of the study, which is a repetition of Part I—a previous experimental study of the ducted photovoltaic unit with buoyancy cooling. The aim of this study is to optimize the duct width behind the solar cells to allow for the cells to achieve maximum buoyancy-driven cooling during operation. Duct widths from 5 to 50 cm were simulated. A duct width of 40 cm allowed for the maximum calculated heat to be removed from the duct; however, the lowest cell-operating temperature was reported for a duct width of 50 cm. The results showed that the change in temperature (ΔT) between the ducts’ inlets and outlets ranged from 8.10 to 19.32 °C. The ducted system enhanced module efficiency by 12.69% by reducing the photovoltaic façade (PV) temperature by 27 °C from 100 to 73 °C, as opposed to the increased temperatures that have been reported when fixing the PV directly onto the building fabric. The maximum simulated heat recovered from the ducted PV system was 529 W. This was 47.98% of the incident radiation in the test. The total summation of heat recovered and the power enhanced by the ducted system was 61.67%. The nature of airflow inside the duct was explored and visualized by reference to the Grashof number (Gr) and CFD simulations, respectively.

A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part I Experiment

A ducted photovoltaic façade (DPV) unit was studied using experimental prototype and simulated in a full scale computational fluid dynamics (CFD) model. The study comes in two parts; this is Part I, as detailed in the title above, and Part II is titled “A Ducted Photovoltaic Façade Unit with Buoyancy Cooling: Part II CFD Simulation”. The process adopted in the experimental study is replicated in the simulation part. The aim was to optimize the duct width behind the solar cells to allow for a maximum buoyancy-driven cooling for the cells during operation. Duct widths from 5 to 50 cm were tested in a prototype. A duct width of 45 cm had the maximum calculated heat removed from the duct; however, the lowest cell-operating temperature was reported for duct width of 50 cm. It was found that ΔT between ducts’ inlets and outlets range from 5.47 °C to 12.32 °C for duct widths of 5–50 cm, respectively. The ducted system enhanced module efficiency by 12.69% by reducing photovoltaic (PV) temperature by 27 °C from 100 °C to 73 °C. The maximum measured heat recovered from the ducted PV system was 422 W. This is 48.98% from the incident radiation in the test. The total sum of heat recovered and power enhanced by the ducted system was 61.67%.

High-efficiency optical terahertz modulation of aligned Ag nanowires on a Si substrate

High-efficiency optical modulation of a terahertz pulse transmitted through aligned silver nanowires on a silicon substrate is demonstrated. Without optical excitation, the terahertz pulses mostly pass through the silver nanowires. However, an optically excited sample significantly modulates the transmittance compared with an excited silicon substrate. The enhanced modulation efficiency is explained by the redistribution effect of photo-carriers due to the nanowires. The simple structure of metal nanowires on a semiconductor substrate could be useful in implementing optically tunable terahertz wave modulators.

Strip-loaded waveguide-based optical phase shifter for high-efficiency silicon optical modulators

We propose a novel silicon optical phase shifter structure based on heterogeneous strip-loaded waveguides on a photonic silicon on insulator (SOI) platform. The features of an etchless SOI layer and loaded strip would enhance the performance and uniformity of silicon optical modulators on a large-scale wafer. We implemented the phase shifter by loading an amorphous silicon strip onto an SOI layer with a vertical PN diode structure. Compared to the conventional lateral PN phase shifter based on half-etched rib waveguides, this phase shifter shows a >1.5 times enhancement of modulation efficiency and provides >20 GHz high-speed operation.

Polarization modulation of two-photon excited fluorescence in a V-shaped dipicolinate-triphenylamine compound.

Polarization modulation of two-photon excited fluorescence in a V-shaped dipicolinate-triphenylamine compound was investigated with 100 fs 800 nm laser pulses. The peak fluorescence intensity versus the input irradiance was measured to meet a square dependence, which offered evidence for two-photon excited fluorescence. The variations of the two-photon excited fluorescence intensity showed strong response to the different polarized incident lights and were tightly dependent on the linearly polarized component of the incident light. Furthermore, the polarization modulation efficiency of the two-photon excited fluorescence had an obvious concentration dependence when the concentration of solution was under 2.5×10(-4) mol/L. The enhancement of modulation efficiency was attributed to the concentration dependence of the two-photon absorption cross section.

Dependence of integrated acousto-optical devices with one and two modulated arms on the static phase difference.

In this paper, we develop an analytical model of an integrated acousto-optical (AO) device with arms modulated by a single surface acoustic wave beam. A comparison between one-arm and two-arm modulation is presented, which shows that two-arm modulation can significantly enhance modulation efficiency by an optimized design. A detailed analysis of the influence of static phase difference on the behavior of the AO devices has been provided, and some interesting results have been obtained. These will be helpful for an optimized design of AO devices for different functionalities.

A Graphene-Enhanced Fiber-Optic Phase Modulator With Large Linear Dynamic Range

We propose a graphene-based modulator integrated into currently used communication fibers. The graphene is directly built into the core of the fiber to ensure the coupling efficiency. The fiber is deliberately side-polished to enhance the light-graphene interaction. The two-dimensional model analysis method and three-dimensional finite difference time domain method are used to rigorously disclose the light modulation mechanism under the anisotropic graphene modeling, which is merely conducted in previous studies. Based on such a structure, a phase modulator with an arm length of 127 μm is numerically demonstrated with enhanced modulation efficiency. A quasi-linear relation between the phase change and chemical potential of graphene is found theoretically for the first time, providing a large linear dynamic range to control the phase of optical modulation.

The Multi-busbar Design: An Overview

The demand for highly efficient photovoltaic modules at low costs leads to new solar cell designs. For enhanced module efficiency the cell efficiency has to be optimized regarding later operation under module conditions. This implies that the interconnected solar cell structure has to be assessed. Commonly the solar cell itself is optimized separately.In this work an easy to implement cell design was investigated where the number of busbars was varied to decrease the total series resistance of the interconnected solar cell. For this study a simulation program based on the two-diode model was applied to determine the optimal efficiency of the device. Furthermore, the simulations revealed that a device with multiple busbars has a high potential in cost savings due to a reduction in metal consumption for the front side metallization. For an optimized cell structure the amount of Ag paste needed for a sufficient front side metallization could be reduced to 7mg Ag paste for a 6 inch solar cell. In the same time the efficiency can be increased. A detailed simulation of a screen printed and stringed rear side of a multi-busbar solar cell revealed the amount of rear side pads necessary for a sufficient interconnection leading to low series resistances.

Cascaded-ring-resonator-loaded Mach–Zehnder modulator for enhanced modulation efficiency in wide optical bandwidth

A cascaded-ring-resonator-loaded Mach–Zehnder modulator (CRR-MZM) is presented in which a number of cascaded ring resonators (RRs) are loaded in the interferometer as phase modulators. The ability of the design to provide enhanced modulation efficiency at a wide optical bandwidth is demonstrated in comparison with a conventional single-RR-type modulator without an interferometer. The optimization of RRs for the CRR-MZM is investigated experimentally by measuring the transmission spectra in both intensity and group delay of RRs having various structural parameters. Using the optimized parameters, we fabricated a CRR-MZM with 10 cascaded RRs loaded on each arm of the interferometer on a silicon-on-insulate substrate. The RRs had pin-diodes along the waveguides, which were operated with forward bias voltage. Its modulation efficiency was enhanced by a factor of 4.4 at the expense of additional loss of less than 3.5 dB compared with a standard non-resonant MZM. 10 Gb/s-operations of CRR-MZM were successfully demonstrated using pre-emphasized RF signals with amplitude of 1.5 Vpp in a wavelength range of 2 nm.

High‐Speed Laser Processing in Thin‐Film Module Manufacturing

AbstractThe key in thin‐film module production is reduced costs per Wattpeak (Wp). This can be achieved by cost‐effective production steps, shorter cycle times and enhanced module efficiency. Module efficiency depends on the weakest cell and active module area. That is the reason why high precision scribing is gaining in importance. Reducing cycle time is feasible by process parallelization and increasing process speed. This paper presents a summary of current laser processes in thin‐film module production.

Guided-Wave EO Intensity Modulator Using Coupled Microstrip Line Electrode of Higher-Order Harmonic Resonance Combined with Polarization-Reversed Structure

A novel structure of a resonator type guided-wave electrooptic intensity modulator is introduced that uses a higher-order harmonic resonant electrode of coupled microstrip lines combined with polarization-reversed structure. The light modulation cancellation caused by the light transit-time effect in the resonant electrode, which is longer than the wavelength of the standing wave, is compensated for to enhance modulation efficiency. The modulator for 26 GHz operation was designed and fabricated with a LiTaO 3 substrate. The modulation electrode is 9.03 mm long for seventh order harmonic resonance by RF signal. The workability of the modulator was confirmed by experiments with 1.3 μm wavelength light.

Optical Properties and Modulation Characteristics of Ultra-Strong Injection-Locked Distributed Feedback Lasers

The optical properties and the frequency responses of ultrastrong (injection ratio > 10 dB) injection-locked distributed feedback lasers are investigated experimentally and theoretically. We have observed three distinctive modulation regimes under different frequency detuning between the master and the slave lasers. At large negative frequency detuning, the laser exhibits enhanced modulation efficiency at low frequencies. At intermediate frequency detuning, a flat frequency response with large 3 dB bandwidth is observed. At large positive frequency detuning, the modulation response shows a pronounced resonance peak at high frequencies. These phenomena can be explained by the resonance enhancement of the slave laser cavity mode, with the resonance frequency equal to the difference between the injection-locked frequency and the cavity mode. The experimental results agree well with theoretical calculations based on three coupled rate equations. Depending on the applications, the injection locking conditions can be optimized to achieve high RF link gain, broadband, or high resonance frequency operations.