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Unmanned aerial vehicle (UAV)-assisted free space optical (FSO) communication is emerging as a potential candidate for establishing high data rate ad-hoc wireless communication links. However, high data transmission rate and power-efficient intensity modulation schemes are required to be implemented in battery-constrained UAV-based FSO systems. As such, this paper presents the external modulators and signal processing-based novel schemes for generating discretized pulse amplitude modulated (PAM) optical pulses. A testbed link employing 4-PAM optical signalling with a 50% duty ratio is established under artificially induced foggy weather conditions to analyse the system performance in terms of received signal quality (Q) factor and bit error rate (BER). Experimental results indicate a reduced turn-on duration of the laser diode in the proposed system as compared to the conventional FSO systems incorporating non-return-to-zero optical signalling schemes. As such, the overall power required for data transmission by the proposed FSO system is significantly reduced; thereby, resulting in power saving of the battery-operated UAVs. Moreover, the link budget analysis of the proposed system indicates that the maximum allowable link length to maintain data transmission rate of 1 Gbps and BER = 10−6 in light fog (14 dB/km) and moderate fog (29 dB/km) conditions are 71 m and 51 m, respectively. [ABSTRACT FROM AUTHOR]

The key components of a polarization-independent electro-optic (EO) interferometer, including the beam splitter, mode converter, and directional coupler, are designed based on a lithium niobate (LN) platform on an integrated insulator to ensure high extinction ratios. By elaborately designing the geometric structure of the multimode interference (MMI) coupler, beam splitting of equal proportions and directional coupling of higher-order modes are realized. The most prominent characteristic of the proposed interferometer is polarization insensitivity, which is realized by converting TM polarization into TE polarization using a mode converter, providing conditions for the study of light with different polarizations. At 1550 nm, the visibility of the interferometer is 97.59% and 98.16% for TE and TM, respectively, demonstrating the high performance of the proposed LN polarization-independent interferometer. [ABSTRACT FROM AUTHOR]

The key components of a polarization-independent electro-optic (EO) interferometer, including the beam splitter, mode converter, and directional coupler, are designed based on a lithium niobate (LN) platform on an integrated insulator to ensure high extinction ratios. By elaborately designing the geometric structure of the multimode interference (MMI) coupler, beam splitting of equal proportions and directional coupling of higher-order modes are realized. The most prominent characteristic of the proposed interferometer is polarization insensitivity, which is realized by converting TM polarization into TE polarization using a mode converter, providing conditions for the study of light with different polarizations. At 1550 nm, the visibility of the interferometer is 97.59% and 98.16% for TE and TM, respectively, demonstrating the high performance of the proposed LN polarization-independent interferometer.

In this article, we propose and numerically demonstrate a novel dual-phase modulated time-delay signature (TDS) concealed communication system. The proposed system addresses the fatal disadvantage of conventional electro-optic chaotic systems in that TDS is vulnerable to detection. Combined with the dispersive devices ahead, which significantly expands the complexity of the signal, the scheme perturbs the transmitted data with the mutual injection of the feedforward and feedback branches in the phase, strengthening the nonlinear effect of the system considerably. In addition, the key space of the system against illegal users’ exhaustive attack within reasonable parameters reaches 1019, which is 14 orders of magnitude larger than that of the classical electro-optic system. A confidential 32 G/s OOK signal was transmitted over 100 km and successfully recovered. Numerical results demonstrate that the chaotic system can tolerate minor parameter mismatches which are controllable in practice, proving that the system can be used for secure communication.

Optical frequency combs (OFCs) are a unique kind of light source, which are represented as a series of equally spaced coherent spectral lines in the frequency domain. OFCs can mainly be divided into mode‐locked lasers, Kerr frequency combs, and electro‐optic frequency combs (E‐O combs), which have broad applications in optical communications, frequency metrology, atomic clocks, distance ranging, spectroscopy, and arbitrary waveform generation. Among them, E‐O combs feature some unique advantages, such as fast tunable repetition rate, high sidebands power, and reconfigurability of the comb spectrum. Especially in recent years, with the development of micro–nano processing technology, on‐chip E‐O combs have become a dynamic research topic with many fundamental scientific problems as well as engineering applications for further exploration. To summarize the past development and envision the prosperous future of E‐O combs, the area of E‐O combs is reviewed from the following aspects: development of E‐O combs; theory including the generation process of E‐O combs and the electro‐optic modulation models; important techniques including flattening, broadening, noise, and stability controlling; applications including communications, ranging, spectroscopy, wavelength calibration of astronomical spectrographs, and microwave generation; and pros and cons when compared with other OFCs. [ABSTRACT FROM AUTHOR]

Electro-optic (EO) modulation is a well-known and essential topic in the field of communications and sensing, while ultrahigh modulation efficiency is unprecedentedly desired in the current green and data era. However, dramatically increasing the modulation efficiency is difficult in conventional mechanisms, being intrinsically limited by the monotonic mapping relationship between the electrical driving signal and modulated optical signal. To break this bottleneck, a new mechanism termed phase-transition EO modulation is revealed from the reciprocal transition between two distinct phase planes arising from the Hopf bifurcation, being driven by a transient electrical signal to cross the critical point. A monolithically integrated mode-locked laser is implemented as a prototype, strikingly achieving an ultrahigh modulation energy efficiency of 3.06 fJ bit-1 improved by about four orders of magnitude and a contrast ratio exceeding 50 dB. The prototype is experimentally implemented for radio-over-fiber communication and acoustic sensing. This work indicates a significant advance on the state-of-the-art EO modulation technology and opens a new avenue for green communication and ubiquitous sensing applications. [ABSTRACT FROM AUTHOR]

Visible light communication system poses challenges in the modulation schemes, in particularly relating to the flickering and dimming support which limits its data rate and real-time practical implementation. This article has proposed MZM devices which work on visible wavelengths, 520 and 530 nm, with improved performance characteristics as ER 36.9337 dB & 36.9183 dB, respectively, and IL 0.056 dB and 0.0714 dB, respectively. The proposed devices have also been analyzed in an indoor environment working on 1 Gbps at 10 - 5 to 10 - 4 BER range. [ABSTRACT FROM AUTHOR]

Graphene silicon devices have attracted significant attention due to their outstanding electronic and optical properties. By electrically tuning the Fermi level of the monolayer graphene sheet, electro-optic (EO) modulators have been widely analyzed. Despite significant progress has been achieved on high-speed modulation with integrated graphene silicon waveguides, it remains challenging to realize a high modulation efficiency since the light absorption in graphene is limited. Here, we propose and experimentally demonstrate a high efficiency EO modulator using a graphene-assisted tapered silicon ring resonator, where the tapered zone is covered by a graphene/graphene capacitor. This graphene-assisted tapered zone strongly enhances the graphene-light interaction that the achieved static and dynamic modulation (1KHz) depths are up to 26 dB and 12 dB, respectively. Physical mechanism of the modulation based on this nanostructure is also discussed in detail. The proposed nanostructure provides a promising alternative method for high-performance EO modulator, which is essential for the on-chip optical communication, optical computing and optical signal processing.

A graphene-coated two-layer dielectric loaded surface plasmon polariton (GTDLSPP) rib waveguide is designed. The mode characteristics and electro-optic (EO) modulation performances of the four hybrid plasmonic modes (HPMs) in the designed waveguide are simulated by using the finite element method. The simulation results show that a 103 mm-scale propagation length and an effective mode field area of ~λ2/1333 are obtained by adjusting the bias voltage. The EO wavelength tunings are -68.6, -42.0, -49.7, and -11.1 nm/V for the HPM 1, HPM 2, HPM 3, and the peak 2 of HPM 4, which are two orders of magnitude larger than those of other EO modulation structures. For the peak 1 of the HPM 4, the EO wavelength tuning is the piecewise linear. For a 150-μm long waveguide, the modulation depths of ~98.7, ~87.9, and 99.5%, and FWHMs of ~450, ~100, and ~42 nm can be achieved for the HPM 1, HPM 2, and HPM 3. For the HPM 4, there are two peaks in the transmission spectrum. The modulation depths are ~97.3 and 75.2%, and FWHMs are ~92 and ~34 nm for the peaks 1 and 2. There is a tradeoff between the modulation depth and FWHM for different waveguide lengths. The GTDLSPP rib waveguide designed has small size, high modulation depth, broad bandwidth, and compatibility with the CMOS technology, soit has potential applications in the EO tunable devices, optical interconnects, and optical switches.

In modern microwave and optical communication systems, it is urgent to develop optical components with the same performance as electronic components. In this paper, a PT-symmetric structure including electro-optical medium is designed to construct optical triode. It is found that the structure has a pole effect of amplification under certain parameters. The frequency of the incident wave at the pole is taken as the carrier frequency, and the electrical signal is modulated into an optical signal. By setting the bias electric field, the modulated optical signal can be amplified in phase and out phase, and even by doubling frequency, and a new optical triode model is obtained. The designed model will play an important role in the design of optical integrated devices. [ABSTRACT FROM AUTHOR]

Solution‐processed organic electro‐optic (EO) chromophores are well suited for integration in optical modulators on silicon photonics chips. They contain highly conjugated molecules with polar functional groups offering large dipoles and a large nonlinear optical response. However, these molecules form centrosymmetric aggregates that hinder poling efficiency and the resultant macroscopic EO response. Furthermore, at elevated temperatures, the alignment of poled molecules can be lost, leading to a reduction in the EO response. Inorganic EO materials exhibit excellent thermal stability but lower performance. Here 2D metal halide perovskite scaffolds that align EO molecules are reported. The approach heralds a material design strategy that combines the features of organic and inorganic EO materials. The EO material exhibits promising thermal stability with a performance approaching that of organic EO materials. Anchor diammonium non‐centrosymmetric molecules are anchored inside a 2D metal halide perovskite scaffold, thereby avoiding aggregation. The authors lever the thermal stability of this compound and pole the organic molecules under an electric field at 533 K. The 2D perovskites exhibit a macroscopic EO coefficient of 68 pm V−1—a twofold increase over LiNbO3. Density functional theory calculations show that the in‐plane alignment of the molecular dipole moments can account for the EO response. [ABSTRACT FROM AUTHOR]

SEO100c, an EO-polymer, has been reported of having an r33 in excess of 100 pm/V. Experimental poling research was performed on rib waveguide modulator for device design and development. Reported is the determination of the impact that temperature and voltage have on the poling of a SEO100c waveguide device in order to maximize the r33 while avoiding damage to the device structure ensuring high yield in manufacture. The poling process is shown to have a nonlinear relationship between r33 and poling field aiding in the selection of achievable poling voltages for required r33 values. Device thermal stability is quantified and reported for the complete poling process and the impacts upon r33. Investigation into the possible relaxation of device r33 is measured over an extended period demonstrating desirable use within deployable devices. [ABSTRACT FROM AUTHOR]

Electro‐optic (E‐O) materials are essential to modern information society, especially for optical switches, modulators, and filters in optical communication. In this paper, ultrahigh transparent (1−x)Pb(Mg1/3Nb2/3)O3‐xPbTiO3 (PMN‐PT) relaxor ferroelectric ceramics are fabricated. The effect of Sm‐doping content (0, 0.5, 1.0, 1.5, and 2.0 mol%) on PMN‐PT transparent ceramics is systematically investigated on the optical transparency, electro‐optic coefficient, extinction ratio, and half‐wave voltage. Results indicate that 0.5 mol% Sm‐doped PMN‐PT ceramic shows the optimal comprehensive performance, including high transparency of 69.6%, large quadratic E‐O coefficient of 35 × 10–16 m2 V−2, decent extinction ratio of 32 dB, and low half‐wave voltage (113 V at d = L = 1 mm). An electro‐optic modulator is designed based on the PMN‐PT transparent ceramics and its application in optical communication is realized, such as rapid information modulation, analog signal (audio frequency), and digital signal (graphic patterns) transmission. These results indicate that Sm‐doped PMN–xPT transparent ceramics are promising candidates for E‐O modulation applications. [ABSTRACT FROM AUTHOR]

An optical phase shifter based on narrow-core hollow waveguide is proposed. The light is guided in an air core between the top and bottom reflectors made up of silicon and indium tin oxide (ITO) gratings. The proposed narrow-core hollow structure is able to guide slow light mode with a low loss of 0.2 dB/cm and a high group index of 64 in 0.8 μm thick air core. The presence of ITO enables electrically controlled phase shifting. In order to realize phase shifting, a p-i-n junction in ITO is used around the air core and in the top and bottom gratings. The geometry is optimized for enhanced interaction between the free charge carriers injected in the intrinsic region of ITO and the propagating optical mode. The proposed device shows a phase shifting of 180° for a 71-μm long device resulting from the slow-light effect.

Many applications of metasurfaces require an ability to dynamically change their properties in the time domain. Electrical tuning techniques are of particular interest, since they pave a way to on-chip integration of metasurfaces with optoelectronic devices. In this work, we propose and experimentally demonstrate an electro-optic lithium niobate (EO-LN) metasurface that shows dynamic modulations to phase retardation of transmitted light. Quasi-bound states in the continuum (QBIC) are observed from this metasurface. By applying external electric voltages, the refractive index of lithium niobate (LN) is changed by Pockels EO nonlinearity, leading to efficient phase modulations to the transmitted light around the QBIC wavelength. The EO-LN metasurface developed in this study opens up new routes for potential applications in the field of displaying, pulse shaping, and spatial light modulating. [ABSTRACT FROM AUTHOR]

Metal‐oxides are promising candidates to substitute silicon in intra‐chip optical interconnects, as they exhibit great electric field tuning capabilities. The development of crystal ion slicing of thin films from bulk crystals and the advances over epitaxial growth have allowed the integration of metal‐oxides on a single chip. In terms of performance, they possess strong electro‐optic response over broad bandwidths across near‐infrared. However, lattice and thermal expansion coefficient mismatch limits the compatibility with available substrates and other materials, while physical hardness makes high quality nanostructures difficult to implement. Here, a novel concept of electro‐optic (EO) switching is introduced: an adjacent BaTiO3 nanoparticle film to a plasmonic metasurface provides reflection changes up to 0.15% under 4 V of control signal for modulation frequencies up to 20 MHz, in the near‐infrared. The nanoparticle films show EO coefficients (37.04 ± 25.6 pm V−1) comparable to lithium niobate crystals, are deposited uniformly over large scale and on any type of substrate, while retain optical nonlinear properties (e.g. second‐harmonic generation). Photonic nanostructures such as metasurfaces incorporated with nanoparticle films can harness the multifunctional properties of metal‐oxides such as BaTiO3 to form a new family of switchable nano‐devices across the entire visible to near‐infrared part of the spectrum. [ABSTRACT FROM AUTHOR]

Resonator-enhanced electro-optic (RE-EO) frequency comb generators produce broad combs by coupling an optical field to a resonator containing a phase modulator driven at a harmonic of the resonator free spectral range (FSR). Recent advances in integration technologies have opened up the possibility of fabricating low-loss, efficient, and tunable ring-based RE-EO comb generators. In this work, we analyze the properties of a canonical ring-based RE-EO comb generator and propose a new dual-ring comb generator to increase comb conversion efficiency, an especially important characteristic for comb-based optical communications systems. After a brief review of RE-EO comb generator properties in the case of resonant operation, i.e., when the optical frequency and the modulation frequency are harmonics of the resonator FSR, we analyze the effect of input optical phase noise and modulation phase noise on the resulting comb. Additionally, we show analytically that in non-resonant operation the optical frequency offset and the modulation frequency offset can be much larger than the linewidth of the resonator, increasing the tolerance to fabrication errors. Then, we develop and validate numerical models to predict the output spectrum in the presence of dispersive waveguides, which cannot be modeled analytically. Using these accurate models, we analyze a dual-ring RE-EO comb generator that uses a small coupling ring to increase the conversion efficiency to 32%, compared to the 1.3% efficiency of a single-ring RE-EO comb generator. We then analyze a point-to-point inter-data center optical link and determine that a dual-ring RE-EO comb generator can support high-capacity coherent links at 20 Tb/s per fiber. [ABSTRACT FROM AUTHOR]

Free-space optical applications benefit greatly from actively reconfigurable metasurfaces. While static metasurfaces have demonstrated remarkable capabilities in manipulating optical wave characteristics, their fixed electromagnetic response faces a challenge for active device demands. This work presents an all-dielectric metasurface of lithium niobate with high Q-factor Fano resonances for enhanced electro-optic modulation. The resonance mechanism is investigated through multipole decomposition and near-field analysis, revealing that toroidal dipole contributions are dominant in all found three resonances. The strongest resonance arises from symmetry-protected bound states in the continuum (SP-BIC), and it is excited in an asymmetric metasurface by introducing a perturbation in the symmetric nanohole clusters, to enable polarization-independent operation. We numerically achieve a tuning efficiency of 0.65 nm/V and π-phase retardation driven by a bias of 0.53 V, due to the strong field confinement of quasi-BIC mode. Our work provides a scheme for compact, high-performance, and electrically tunable metasurfaces that can help in the development of spatial optical switches as well as tunable micro-lenses and displays. • Multiple toroidal resonance system of lithium niobate metasurface. • High-Q factor Fano resonance of symmetry-protected bound states in the continuum (SP-BIC). • Polarization-insensitive SP-BIC for the symmetry structure and dual-BIC modes from the anisotropic material. • An effective method to tuning the resonances and the underlying physical mechanism. [ABSTRACT FROM AUTHOR]

The active tunable metasurface can flexibly and effectively control the polarization, amplitude, phase and propagation mode of electromagnetic wave. Among them, LiNbO 3 metasurface has a unique advantage in integrating electro-optic (EO) tunable components, especially in enabling high-speed spatial light modulation. Here, based on guided mode resonance (GMR), a polarization independent LiNbO 3 nanopillar metasurface transmission spatial light modulator is demonstrated from the perspective of free space propagation light modulation. Utilizing GMR, most of the incident light is confined to a 380 nm LiNbO 3 layer with the high EO coefficient, enabling fast and efficient light modulation. A clear modulation of 100 MHz is observed by applying an electric bias voltage (±2.8 V) to the LiNbO 3 film. The lithium niobate metasurface developed in this study paves the attractive way for compact spatial light modulator. It also embarks on new potential applications in the fields of tunable display, light detection and near infrared imaging. • The metasurface device is polarization independent in telecom wavelength range. • A LiNbO 3 metasurface spatial light modulator utilizing guided mode resonance from nanopillar arrays is proposed. • The dynamic modulation speed can reach 100 MHz. [ABSTRACT FROM AUTHOR]

SEO100c, an EO-polymer, has been reported of having an r33 in excess of 100 pm/V. Experimental poling research was performed on rib waveguide modulator for device design and development. Reported is the determination of the impact that temperature and voltage have on the poling of a SEO100c waveguide device in order to maximize the r33 while avoiding damage to the device structure ensuring high yield in manufacture. The poling process is shown to have a nonlinear relationship between r33 and poling field aiding in the selection of achievable poling voltages for required r33 values. Device thermal stability is quantified and reported for the complete poling process and the impacts upon r33. Investigation into the possible relaxation of device r33 is measured over an extended period demonstrating desirable use within deployable devices.

We theoretically and numerically investigate the modulation efficiencies of integrated electro-optic (EO) modulators based on ferroelectric crystals with the point symmetry of orthorhombic mm2. An analytical expression describing the index-ellipsoid under the EO effect is derived, where all 5 non-zero linear EO coefficients of mm2-crystals are considered. As practical candidates for integrated EO platform, three mm2-crystals (KNbO 3 , KTiOPO 4 , and Ba 2 NaNb 5 O 15) that are well-established and commercially available are chosen for numerical simulations. The refractive-index (RI) changes caused by an external electric field applied to each crystal with an arbitrary direction are analyzed in detail for the given optical polarization states of input light wave. For each crystal, the modulation efficiency is evaluated in terms of the half-wave voltage required for a π-phase shift of input wave, which is compared with the established counterpart based on LiNbO 3. The results indicate that higher modulation efficiencies are achievable in the two schemes using KNbO 3 and Ba 2 NaNb 5 O 15 than those for other cases, meaning that either lower power-consuming or larger beam-window integrated EO devices are feasible. • Integrated electro-optic modulators are essential components in optical systems. • Lithium niobite crystal is the most common material-platform for electro-optics. • Other crystal platform for integrated electro-optics for the flexibility. • Higher electro-optic modulation efficiency and lower power-consuming devices. • Three promising candidates for integrated electro-optic platform. [ABSTRACT FROM AUTHOR]

The demand for wireless bandwidth is increasing rapidly; however, the throughput of short-range radio frequency (RF) solutions, such as WiFi, are quickly reaching limits due to limited bandwidth in the RF spectrum. This problem can be overcome by utilizing unregulated infrared wavelengths in the optical spectrum. On the other hand, free-space optical (FSO) communication presents a challenge for mobility due to the line-ofsight nature of optics. We present a dual-channel optical link for short-range FSO communication, which consists of a 100 Mb/s, large diameter (60 cm at 3 m distance) optical femtocell with a 1.5 Gb/s, small diameter (1 cm at 3 m distance) optical attocell embedded within the femtocell. This hybrid femtocell-attocell optical link addresses the needs of various users by providing a high mobility femtocell link combined with an enhanced bandwidth attocell hotspot. A prototype hybrid system was assembled and evaluated in terms of bandwidth, range, and bit error rate (BER). In addition, the relationship between the incident angle of the transmitted beam relative to the receiver and the BER of the received data was evaluated. At a communication distance of 3 m, the BER is <10-4 when the incident angle is smaller than 30 deg for the optical femtocell, while the incident angle must be smaller than 10 deg for the optical attocell to achieve the same level of BER. In addition, we experimentally demonstrated simultaneous, error-free recovery of the data from both the femtocell and the attocell when these two cells are overlapped, which proves the feasibility of the dual-channel optical link for FSO communication. [ABSTRACT FROM AUTHOR]

A stability improved optical frequency comb (OFC) generation system based on a single integrated polarization multiplexing dual-drive Mach-Zehnder modulator is proposed. Due to the influence of the modulator bias drift on the spectra of the OFC, the amplitude of the OFC spectra would fluctuate with time, which seriously deteriorates the stability of the OFC. The effect of the modulator bias drift on the stability of the OFC is analyzed by theoretical analyses and numerical simulations. A feedback system is proposed to improve the OFC stability. The ratio between the total power of the OFC and the optical carrier power is used as the feedback parameter. In the proof-of-concept experiment, by using the feedback structure, the seven-line OFC stability is experimentally improved from being large than 3 dB within 1.5 h to being below 2 dB more than 4 h. [ABSTRACT FROM AUTHOR]

An optical phase shifter based on narrow-core hollow waveguide is proposed. The light is guided in an air core between the top and bottom reflectors made up of silicon and indium tin oxide (ITO) gratings. The proposed narrow-core hollow structure is able to guide slow light mode with a low loss of 0.2 dB/cm and a high group index of 64 in 0.8 μm thick air core. The presence of ITO enables electrically controlled phase shifting. In order to realize phase shifting, a p-i-n junction in ITO is used around the air core and in the top and bottom gratings. The geometry is optimized for enhanced interaction between the free charge carriers injected in the intrinsic region of ITO and the propagating optical mode. The proposed device shows a phase shifting of 180° for a 71-μm long device resulting from the slow-light effect. [ABSTRACT FROM AUTHOR]

KTa0.65Nb0.35O3 and Fe-doped KTa0.65Nb0.35O3 crystals were grown by the top-seeded solution growth method (TSSG). Fe ion doping significantly improves the electro-optic properties of cubic KTN crystals. We describe their electro-optic modulation theory and experimental research. The electro-optic modulation waveform deduced by theoretical calculation is basically consistent with the waveform measured in the experiment. We observed the attenuation of light modulation under multiple voltage cycles. The modulation curve of the crystal is inconsistent when the crystal voltage is boosting and bucking. Under the same voltage condition, the higher the incident light power, the faster the modulation depth attenuation. In this experiment, the size of the KTN crystal chip is 6 mm × 5 mm × 2 mm. We obtain the effective electro-optic coefficient as s11 − s12 = 1.34 × 10−15 m2/V2; the half-wave voltage near the Curie temperature is 39 V.

To enhance the functionality of the standard silicon photonics platform and to overcome its limitations, in particular for light emission, ultrafast modulation, and nonlinear applications, integration with novel materials is being investigated by several groups. In this paper, we will discuss, among others, the integration of silicon waveguides with ferroelectric materials such as lead zirconate titanate (PZT) and barium titanate (BTO), with electro–optically active polymers, with 2-D materials such as graphene and with III–V semiconductors through epitaxy. We discuss both the technology and design aspects. [ABSTRACT FROM AUTHOR]

In modern radar systems, the target to achieve high-range resolution poses a high requirement on bandwidth and stability of probe radio frequency (RF) waveforms. We experimentally demonstrate the generation of RF waveforms with a low bandwidth electrical instrument and optical bandwidth multiplication method. Based on the high-order modulation-sideband of electro-optic modulators, wideband optical swept waveforms are generated from narrow band RF swept waveforms with a bandwidth multiplication factor of eight. By heterodyne beating the swept waveforms with a single tone frequency driven on the same dual-drive Mach–Zehnder modulator, we generate coherent wideband RF waveforms with linearly, V-shaped, and quadric frequency modulation, respectively. These waveforms exhibit high time-bandwidth products up to 2560 and high phase-noise performance. The utility of these generated RF waveforms for ranging radar system has been proven a pulse compression process. [ABSTRACT FROM AUTHOR]

Abstract: Electronic–photonic hybrid integrated circuits represent the essential basis of next‐generation ultrahigh‐speed information processing chips, which will require ultrafast and ultralow‐energy‐consumption electronic and photonic information interconversion and modulation, i.e., on‐chip dual electro‐optic and optoelectric modulation. However, this type of modulation has not been realized to date because of an absence of materials that demonstrate sufficient intrinsic electro‐optic and optoelectric responses simultaneously. On‐chip dual electro‐optic and optoelectric modulation is experimentally realized here based on refractive index variation of a ZnO nanowire driven by the gate voltage and electrical conductivity changes in this nanowire caused by the strong localized light field of a silicon nitride photonic crystal nanocavity mode. A low gate voltage of 1.5 V induces a large shift of 7 nm in the Fano‐like resonance wavelength and modulates the propagation state of an 800 nm light signal with a large modulation depth of 75%. Additionally, weak signal light with power as low as 0.4 µW induces a modulation depth of 60% in the electric signal. On‐chip conversion between electronic and photonic signals thus is achieved. This work paves the way toward realization of novel nanoscale multifunctional optoelectronic integrated devices and provides an on‐chip platform for the study of new optoelectronic functional materials. [ABSTRACT FROM AUTHOR]

We demonstrate 100 GBd operation of an optical transmitter module including a distributed feedback laser monolithically integrated with aMach-Zehnder modulator (DFBMZM), to the best of our knowledge for the first time. Combining high-speed optics and electronics with digital signal processing (DSP), different schemes for intensitymodulation and direct detection at 100, 200, and 300 Gbit/s are analyzed, using electrical signals from a 100 GSa/s BiCMOS DAC. Due to close-to-zero transmitter chirp, 100 Gbit/s NRZ transmission over 1.8 km and 200 Gbit/s PAM4 transmission over 1.2 km at 1550 nm with a bit error rate (BER) below the 7% overhead forward error correction (FEC) threshold (3.8 × 10-3) is achieved. At 200 Gbit/s PAM4, the DFBMZM module consumes only 0.85 pJ/bit, making it a promising device for attractive dual-lane 400 Gbit/s systems.We also achieve 300 Gbit/s PAM8 transmission over 1.2 km with a BER below the 20% overhead FEC threshold (1.9 × 10-2) by implementing advanced DSP based on a pattern-dependent lookup table tomitigate the electrical and optical device bandwidth limitations. [ABSTRACT FROM AUTHOR]

Dynamic control of the electromagnetic properties of metamaterials requires wide modulation bandwidth. Tunable metamaterials with large tunability and fast speed are thus highly desirable. Due to the small dimensions, subwavelength meta-atoms or resonant elements that constitute a metamaterial in the mid-to-near-infrared (IR) wavelength range are often not easy to be tuned at a high rate of several tens of megahertz (MHz). Here, we report on a nanoelectromechanical systems (NEMS)-based tunable IR metamaterial realized by unique embedding of nanocantilevers into complementary split ring resonators (c-SRRs) suspended over individual wells. The optical field confined in the air gap of the c-SRR is strongly influenced by electrostatically induced mechanical deflection of the nanocantilever, thus modulating the reflection spectrum of the metamaterial. With the easy-to-implement tunable meta-atom design, the IR metamaterial with 800-nm-long cantilevers provides an ultrahigh mechanical modulation frequency of 32.26 MHz for optical signal modulation at a wavelength of 2.1 \mu \textm , and is rather easy to manufacture and operate. We envision a compact, efficient, and high-speed electrooptic modulation platform in the IR region using this NEMS tunable metamaterial technology. [2017–0012] [ABSTRACT FROM PUBLISHER]

Black phosphorus stands out from the family of two-dimensional materials as a semiconductor with a direct, layer-dependent bandgap spanning the visible to mid-infrared (mid-IR) spectral range. It is, therefore, a very promising material for various optoelectronic applications, particularly in the important mid-IR range. While mid-IR technology has been advancing rapidly, both photodetection and electro-optic modulation in the mid-IR rely on narrow-band compound semiconductors, which are difficult and expensive to integrate with the ubiquitous silicon photonics. For mid-IR photodetection, black phosphorus has already been proven to be a viable alternative. Here, we demonstrate electro-optic modulation of mid-IR absorption in few-layer black phosphorus. Our experimental and theoretical results find that, within the doping range obtainable in our samples, the quantum confined Franz-Keldysh effect is the dominant mechanism of electro-optic modulation. A spectroscopic study on samples with varying thicknesses reveals strong layer dependence in the interband transition between specific pairs of sub-bands. Our results show that black phosphorus is a very promising material to realizing efficient mid-IR modulators. [ABSTRACT FROM AUTHOR]

A high output transmission and high quality factor, compact LiNbO3-based Fabry-Perot-type photonic crystal cavity is reported that can be used in electro-optical modulators at optical communication wavelengths. The electro-optic effect is 123 times enhanced as compared to the bulk material as a result of the slow light effect. The transmission wavelength is found to depend linearly on the applied voltage with 1.2 nm/V modulation sensitivity. Moreover, an externally switchable dual mode regime with high quality factors and transmissions is realized. High transmissions and high quality factors are also obtained for both transverse-electric and transverse-magnetic polarizations simultaneously. [ABSTRACT FROM AUTHOR]

The present study described a photonic-crystal-based ring resonator pin modulator on an InP-substrate. The device geometry was based on a single ring resonator coupled to one straight waveguide by creating line defect holes through slab layer stack InP/InGaAsP/InP having a hexagonal lattice. The radius of the hole was calculated to be 187 nm with a lattice constant of 500 nm. The distribution of carriers and the electrical field in the guiding and cladding layers determined the effective refractive index of the ring resonator. Transient analysis of the pin modulator was carried out by applying a pulse to the electrodes that switched between 0 and −7 V. The frequency response of the ring resonator modulator shows over 300 GHz of bandwidth. [ABSTRACT FROM AUTHOR]

Compact lithium niobate polarization-independent electrooptic modulators using integration of polarization splitters and mode converters are presented. Experimental results show polarization-dependent loss as low as 0.04 dB can be achieved for devices fabricated on Z-cut substrates with an applied voltage of 26 V. The electrode lengths required for electrooptic modulation are 10 and 6 mm for TE and TM modes, respectively, and the total device length is only 1.6 cm. Moreover, only one diffusion step is required that greatly simplifies the fabrication process. [ABSTRACT FROM PUBLISHER]

We proposed an integrated device for electro-optic (EO) modulation and dense wavelength division multiplexing (DWDM) based on photonic crystals (PhCs). The transmittance performance of the designed structure was modelled and analyzed according to the time-domain coupled mode theory (CMT), using three-dimensional finite-difference time-domain (3D-FDTD) method to calculate the parameters of the proposed device for verification. The numerical results show that the proposed integrated device can realize the functions of "on", "off" modulation and DWDM with a channel spacing of 0.8 nm at the operating wavelengths of 1555 nm and 1554.2 nm. The minimum insertion loss, channel crosstalk and modulation voltage are 0.7 dB, − 29.04 dB and 0.88 V, respectively. The maximum extinction ratio and modulation speed are 21.51 dB and 29.4 GHz. The designed integrated device has the advantages of low loss, compact size (41.28 μ m × 11.18 μ m), narrow channel spacing, large extinction ratio, which can be easily expanded the number of channels and used in highly integrated large-capacity optical communication systems and data center. [ABSTRACT FROM AUTHOR]

This paper studies integrated silicon light emitter implemented in standard CMOS technologies. A new MOS-like structure utilizing deep p-well is presented, and compared with conventional planar p-n junction diode at visible wavelength and avalanching bias conditions. Prototype light emitter is fabricated in a 3- \mu \textm standard CMOS technology, and its dc, phase shift, and direct modulation frequency response with nanowatt power level are characterized, with experimental results for a reverse-bias region showing light modulation with the simulated maximum modulation frequency around $\sim 45$ GHz being reported. [ABSTRACT FROM PUBLISHER]

A digital coherent radio-over-fiber (RoF) system comprising a microwave photonic integrated circuit (MPIC) as the main building block is proposed. The multifunction MPIC circuit is analyzed to operate as a single-sideband (SSB) modulator and as an in-phase and quadrature modulator (IQM) of a baseband signal in the RoF downlink. The circuit is also analyzed in the uplink as an SSB of a 60-GHz frequency-shifted input. The performance of the MPIC is assessed through numerical simulations, computing the harmonic distortions in the SSB, as well as the error vector magnitude in the IQM and coherent RoF system. Obtained results illustrate the advantage of the proposed MPIC for heterodyne mixing by providing the upper and lower sidebands spatially located in distinct ports. Moreover, simulation results yield insights into the feasibility of the circuit as an IQM of both baseband and low-power intermediate frequency signals. A comparison of an orthogonal frequency division multiplexing system and a single carrier system employing the proposed circuit in the end-to-end transport of high data rate is presented through error vector magnitude calculations. [ABSTRACT FROM PUBLISHER]