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Organic single crystals with near‐infrared (NIR) emission demonstrate their excellent optical communications from well photonic confinement and low optical waveguide loss, which are considered as competitive candidates toward advanced optoelectronics. However, the increasingly diverse and sophisticated application demands result in the complicated design of NIR devices, which is hardly realized solely by the intrinsic properties of individual crystals. Herein, a programmable assembly strategy is presented to fabricate organic heterostructures. Triphenylene (TP), pyrene (Py) and 7,7,8,8‐tetracyanoquinodimethane (TCNQ) are primary selected to prepared organic cocrystals with narrow band gap and near‐infrared emission. Importantly, the charge‐transfer alloy with tunable emission from 700 nm to 850 nm and branched heterostructures with multichannel characteristics are prepared from these organic cocrystals by following the growth kinetics process at molecular level and lattice matching principle at structural level, respectively. Theses prepared heterostructures exhibit optical logic operation capabilities, which can serve as optical modulators. This work provides new insights into the manufacturing of organic NIR heterostructures applied in advanced optoelectronics. [ABSTRACT FROM AUTHOR]

With the growing trend in the information industry, silicon photonics technology has been explored in both academia and industry and utilized for high-bandwidth data transmission. Thanks to the benefits of silicon, such as high refractive index contrast with its oxides, low loss, substantial thermal–optical effect, and compatibility with CMOS, a range of passive and active photonic devices have been demonstrated, including waveguides, modulators, photodetectors, and lasers. The most challenging aspect remains to be the on-chip laser source, whose performance is constrained by the indirect bandgap of silicon. This review paper highlights the advancements made in the field of integrated laser sources on the silicon photonics platform. These on-chip lasers are classified according to their gain media, including V semiconductors, III–V semiconductors, two-dimensional materials, and colloidal quantum dots. The methods of integrating these lasers onto silicon are also detailed in this review. [ABSTRACT FROM AUTHOR]

On-chip optical modulators, which are capable of converting electrical signals into optical signals, constitute the foundational components of photonic devices. Photonics modulators exhibiting high modulation efficiency and low insertion loss are highly sought after in numerous critical applications, such as optical phase steering, optical coherent imaging, and optical computing. This paper introduces a novel accumulation-type vertical modulator structure based on a silicon photonics platform. By incorporating a high-K dielectric layer of ZrO2, we have observed an increase in modulation efficiency while maintaining relatively low levels of modulation loss. Through meticulous study and optimization, the simulation results of the final device structure demonstrate a modulation efficiency of 0.16 V·cm, with a mere efficiency–loss product of 8.24 dB·V. [ABSTRACT FROM AUTHOR]

Thin‐film lithium niobate (TFLN) modulators have garnered significant attention in the field of integrated photonics due to their ability to manipulate light. Numerous TFLN modulators have been demonstrated over the past few years, with speed records consistently being broken. However, due to the low refractive index contrast and anisotropic properties of TFLN, modulators based on this material feature larger device sizes and lower efficiency. A more compact and efficient modulator is important, as it is required for future dense integration and low power consumption applications. There have been some reports on how to reduce device size, and research is ongoing. A comprehensive summary can help individuals understand the current state of research and existing problems. In this review, we provide an overview of recent advancements in TFLN modulator technology, focusing on compactness and efficiency. Herein, various types of modulators, such as the Mach–Zehnder interferometer, Michelson interferometer, resonator cavity, and Z‐cut type modulators, are discussed. Moreover, potential improvement strategies and applications for compact and efficient TFLN modulators in advanced photonic systems are explored. In conclusion, in this review, the recent achievements in compact and efficient TFLN modulators are summarized and their significance in various optoelectronic applications is emphasized. [ABSTRACT FROM AUTHOR]

Silicon (Si) photonics has emerged as a prominent technology for meeting the escalating requirements of high-speed data transmission in optical communication systems. These systems need to be compact, energy-efficient, and capable of handling large amounts of data, driven by the advent of next-generation communication devices. Recently, there have been significant activities in exploring graphene within silicon-based components to enhance the overall performance metrics of optoelectronic subsystems. Graphene's high mobility of charge carriers makes it appealing for the next generation of high-performance devices, especially in high-speed optoelectronics. However, due to its zero bandgap, graphene is unlikely to replace silicon entirely, but it exhibits potential as a catalyst for silicon-based devices, namely in high-speed electronics and optical modulators, where its distinctive characteristics can facilitate progress in silicon photonics and other fields. This paper aims to provide an objective review of the advances made within the realm of graphene-integrated Si photonics for high-speed light modulation and detection. [ABSTRACT FROM AUTHOR]

Electro-optic modulators are an indispensable part of photonic communication systems, largely dictating the achievable transmission rate. Recent advances in materials and fabrication/processing techniques have brought new elements and a renewed dynamic to research on optical modulation. Motivated by the new opportunities, this Perspective reviews the state of the art in integrated electro-optic modulators, covering a broad range of contemporary materials and integrated platforms. To provide a better overview of the status of current modulators, an assessment of the different material platforms is conducted on the basis of common performance metrics: extinction ratio, insertion loss, electro-optic bandwidth, driving voltage, and footprint. The main physical phenomena exploited for electro-optic modulation are first introduced, aiming to provide a self-contained reference to researchers in physics and engineering. Additionally, we take care to highlight topics that can be overlooked and require attention, such as the accurate calculation of carrier density distribution and energy consumption, the correct modeling of thin and two-dimensional materials, and the nature of contact electrodes. Finally, a future outlook for the different electro-optic materials is provided, anticipating the research and performance trends in the years to come. [ABSTRACT FROM AUTHOR]

Integrated mid-infrared (MIR) photonics have various applications in optical fiber communication, spectral detection and identification, free-space communication, and light detection and ranging, etc. The MIR electro-optic (EO) modulator, which is one of the key components of MIR integrated photonic systems, has attracted a lot of research interests. In this paper, we review the reported integrated MIR EO modulators based on different modulation mechanisms and material platforms. The recent research progresses and challenges of MIR EO modulators are presented and discussed. The unique advantages and the corresponding applications of each type of MIR modulators are summarized as well. In the end, we provide our perspectives of a few areas in integrated MIR modulators that are worthy for research attention in future. [ABSTRACT FROM AUTHOR]

Optical modulators are vital for many applications, including telecommunication, data communication, optical computing, and microwave photonic links. A compact modulator with low voltage drive requirement, low power, high speed, and compatibility with CMOS foundry process is highly desirable. Current modulator technologies in Si suffer from trade-offs that constrain their power, performance (speed, drive voltage), and area. The introduction of additional materials to the silicon platform for efficient phase shift promises alternatives to relax those trade-offs. Si-organic-hybrid (SOH) devices demonstrate large modulation bandwidth leveraging the electro-optic (EO) effect and smaller drive voltage or footprint owing to a strong EO coefficient. In this study, we review various SOH modulators and describe their path towards integration to silicon, including their challenges associated with aging and temperature. We also briefly discuss other high-performance modulators such as plasmonic-organic-hybrid (POH), photonic-crystal-assisted SOH, and LiNbO3. [ABSTRACT FROM AUTHOR]

With the increasing need for large volumes of data processing, transport, and storage, optimizing the trade-off between high-speed and energy consumption in today's optoelectronic devices is getting increasingly difficult. Heterogeneous material integration into silicon- and nitride-based photonics has showed high-speed promise, albeit at the expense of millimeter-to centimeter-scale footprints. The hunt for an electro-optic modulator that combines high speed, energy efficiency, and compactness to support high component density on-chip continues. Using a double-layer graphene optical modulator integrated on a Silicon photonics platform, we are able to achieve 60 GHz speed (3 dB roll-off), micrometer compactness, and efficiency of 2.25 fJ/bit in this paper.The electro-optic response is boosted further by a vertical distributed-Bragg-reflector cavity, which reduces the driving voltage by about 40 times while maintaining a sufficient modulation depth (5.2 dB/V). Modulators that are small, efficient, and quick allow high photonic chip density and performance, which is critical for signal processing, sensor platforms, and analog- and neuromorphic photonic processors. [ABSTRACT FROM AUTHOR]

Coupled resonators and coupled waveguides with contrast of their gain and loss are non-Hermitian optical systems, which are based on energy-non-conserving processes. They have been reported to exhibit a number of unconventional phenomena that are expected to contribute to practical applications. We developed a coupled system of two current-injected photonic crystal lasers that enable precise control of gain and loss, thus establishing a promising non-Hermitian nanophotonic platform. We introduce our demonstration of a peculiar non-Hermitian mode degeneracy called an exceptional point (EP) and the EP-based enhancement of spontaneous emission with this system. [ABSTRACT FROM AUTHOR]

To develop a high-speed, large-capacity optical network with low power consumption, which is important for IOWN (the Innovative Optical and Wireless Network), we are conducting research and development on membrane optical devices that integrate III-V compound semiconductors on silicon-photonics circuits. Membrane optical devices are expected to be used for high-modulation efficient lasers and optical modulators because they can achieve high optical confinement in the core layer. This article introduces the current state of research and development focusing on optical modulators and the integration of such modulators and lasers on the basis of membrane-device technologies. [ABSTRACT FROM AUTHOR]

Silicon photonics (SiPh) shows considerable potential as a radiation-hard technology for building the optical data transmission links for future high-energy physics (HEP) experiments at CERN. Optical modulators are a key component of optical links, which will need to withstand radiation doses in excess of 10 MGy. The geometrical parameters and doping concentrations of two popular types of SiPh modulators, Mach–Zehnder and ring modulators (RMs), have been varied in order to study their impact on the device radiation tolerance. They were exposed to an X-ray beam to test their resistance to ionizing radiation. The RM with the highest doping concentration is shown to be the most tolerant, showing no degradation in performance up to the highest dose of 11 MGy. Moreover, we report first evidence of the dependence of the radiation tolerance on the RM operating temperature. [ABSTRACT FROM AUTHOR]

The metal‐to‐insulator transition behavior and the fast and reversible phase transition behavior in vanadium dioxide (VO2) have attracted widespread attention to study various potential applications. However, few studies have been focused on its nonlinear properties and applications in the pulsed laser field. Here, the authors report the design and synthesis of monoclinic nano‐VO2(M) saturable absorber with broadband absorption which spans the entire near‐infrared region, and high optical nonlinearity which is much higher than those of carbon nanomaterials, gold nanocrystals, and Cu1.8S nanocrystals, as measured in the same condition. The nano‐VO2(M) optical modulators are integrated into the fiber laser cavities, and demonstrate wideband Q‐switching operations at 1, 1.56, and 2 µm and mode‐locking operation at 2 µm, with a pulse duration of 765 fs. This work first reveals the outstanding nonlinear optical properties of nano‐VO2(M) and lays a foundation for its development in advanced nonlinear optical and photonic devices. [ABSTRACT FROM AUTHOR]

Silicon photonics is advancing rapidly in performance and capability with multiple fabrication facilities and foundries having advanced passive and active devices, including modulators, photodetectors, and lasers. Integration of photonics with electronics has been key to increasing the speed and aggregate bandwidth of silicon photonics based assemblies, with multiple approaches to achieving transceivers with capacities of 1.6 Tbps and higher. Progress in electronics has been rapid as well, with state-of-the-art chips including switches having many tens of billions of transistors. However, the electronic system performance is often limited by the input/output (I/O) and the power required to drive connections at a speed of tens of Gbps. Fortunately, the convergence of progress in silicon photonics and electronics means that co-packaged silicon photonics and electronics enable the continued progress of both fields and propel further innovation in both. [ABSTRACT FROM AUTHOR]

Implementing optical-frequency combs with integrated photonics will enable wider use of precision timing signals. Here, we explore the generation of an octave-span, Kerr-microresonator frequency comb using hybrid integration of an InP distributed-feedback laser and a SiN photonic-integrated circuit. We demonstrate electrically pumped and fiber-packaged prototype systems, enabled by self-injection locking. This direct integration of a laser and a microresonator circuit without previously used intervening elements, such as optical modulators and isolators, necessitates understanding self-injection-locking dynamics with octave-span Kerr solitons. In particular, system architectures must adjust to the strong coupling of microresonator backscattering and laser-microresonator frequency detuning that we uncover here. Our work illustrates critical considerations toward realizing a self-referenced frequency comb with integrated photonics. [ABSTRACT FROM AUTHOR]

Silicon (Si) photonics have established as leading technologies in addressing the rapidly increasing demands of huge data transfer in optical communication systems with compact footprints, small power consumption, and ultradense bandwidth, which are driven by the next generation supercomputers and big data era. Particularly, Si photonics will penetrate into optical communication links at an ever‐small scale, namely chip‐to‐chip and on‐chip. However, the nanostructures made of Si with an indirect bandgap are not ideal candidates for on‐chip light sources, modulators, and photodetectors, which most‐frequently require optical materials with direct bandgap. Thanks to the advent of graphene, transition metal dichalcogenides and other two‐dimensional (2D) materials, which can facilitate extraordinary progresses in improving device performance at the ultrathin scale, their integration with Si photonics furnishes a heterogeneous platform to construct fully functional and highly integrated photonic communication systems. In this work, the current advancements in the on‐chip applications of Si photonics‐2D materials heterostructures, inclusive of all essential chip‐scale modules and integrated circuits, as well as the future prospective and challenges are reviewed and discussed. The present study sets out to objectively measure the feasibility of the hybrid integration between Si photonics and 2D materials in on‐chip optical communications and the advanced applications beyond. [ABSTRACT FROM AUTHOR]

Toroidal moments in artificial media have received growing attention and considered as a promising framework for initiating novel approaches to manage intrinsic radiative losses in nanophotonic and plasmonic systems. In the past decade, there has been substantial attention on the characteristics and excitation methods of toroidal multipoles—in particular, toroidal dipole—in 3D bulk and planar metaplatforms. The remarkable advantages of toroidal resonances have thrust the toroidal metasurface technology from relative anonymity into the limelight, in which researchers have recently centered on developing applied optical and optoelectronic subwavelength devices based on toroidal metaphotonics and metaplasmonics. In this focused contribution, the key principles of 3D and flatland toroidal metastructures are described, and the revolutionary tools that have been implemented based on this topology are briefly highlighted. Infrared photodetectors, immunobiosensors, ultraviolet beam sources, waveguides, and functional modulators are some of the fundamental and latest examples of toroidal metadevices that have been introduced and studied experimentally so far. The possibility of the realization of strong plexciton dynamics and pronounced vacuum Rabi oscillations in toroidal plasmonic metasurfaces are also presented in this review. Ultimate efficient extreme‐subwavelength scale devices, such as low‐threshold lasers and ultrafast switches, are thus in prospect. [ABSTRACT FROM AUTHOR]

IV–VI semiconductors have attracted widespread attention in basic research and practical applications, because of their electrical and optoelectronic properties comparable to graphene. Herein, an optical modulator based on SnSSe with strong nonlinearity is prepared by chemical vapor transfer method. The modulation depth of proposed SnSSe saturable absorber (SA) is up to 57.5%. By incorporating SnSSe SA into the laser, the Q-switched pulses as short as 547.8 ns are achieved at 1530.07 nm. As far as we know, this is the first successful application of SnSSe in Q-switched lasers. Our investigation not only prove the optical nonlinearity of SnSSe, but also reveal the potential of SnSSe SA in ultrafast photonics. [ABSTRACT FROM AUTHOR]

Silicon photonic networks are revolutionizing computing systems by improving the energy efficiency, bandwidth, and latency of data movements. Optical modulators, such as microresonators (MRs) and Mach–Zehnder interferometers (MZIs), are the basic building blocks of silicon photonic networks. This paper proposes a SPICE-compatible electro-optical co-simulation model, basic optical switch integration model (BOSIM), to systematically study optical modulators using PN, PIN, and metal–insulator–silicon (MIS) capacitor device technologies. BOSIM holistically models both transient and steady state properties, such as switching speed, power, transmission spectrum, area, and carrier distribution. BOSIM is validated by the measured data from eight research groups and companies. Compared to MRs, BOSIM shows MZIs are fast, with a high extinction ratio and large bandwidth but in the sacrifice of loss, energy, and area. Using a PIN diode over a PN diode can save area, but retain the loss and energy, while an MIS capacitor has the shock response of carrier distribution in a narrow range and is marginalized gradually. For instance, an MZI can achieve a $2.5 {\times }$ bit rate, $6.06{\times }$ extinction ratio, $71.04 {\times }\,\,3$ -dB bandwidth, but costs at least $1.93 {\times }$ passing loss, $1.46 {\times }$ energy consumption, and $16.67 {\times }$ area, compared with MR. [ABSTRACT FROM AUTHOR]

InP membranes have appeared in the last decade as a viable integrated photonics platform, suitable for adding photonic functions to silicon electronics. It combines the strengths of silicon photonics (high index contrasts and therefore small footprint devices) with those of generic InP-platforms (monolithic integration of active and passive devices). A range of functionalities has been developed on this platform, which goes by the name of Indium phosphide membrane on silicon (IMOS). Competitive performances have been demonstrated for lasers, fast detectors, waveguides, filters, couplers, modulators, and more. Here, we provide an overview of IMOS and describe recent developments regarding technology and devices. This includes record low propagation losses, plasmonic waveguides, a variety of laser structures, and improved wavelength demuliplexers. These developments demonstrate that IMOS has potential to deliver photonic integrated circuits to a wide variety of application fields, e.g. telecom, datacom, sensing, terahertz, and many others. [ABSTRACT FROM AUTHOR]

We report on the performance of the quantum confined Stark effect (QCSE) in ultra-thin (~350 nm) Ge/SiGe quantum well stacks grown on Si. We demonstrate an absorption contrast $\Delta \alpha /\alpha $ of 2.1 at 1 Vpp swing in QCSE stacks grown on ultra-thin (100 nm) strain relaxed GeSi buffer layers on 300 mm Si wafers. Such ultra-thin QCSE stacks will enable future integration of highly efficient QCSE electro-absorption modulators with low optical coupling loss to passive Si waveguides in a sub-micron silicon photonics platform. [ABSTRACT FROM AUTHOR]

In the past years, significant progress has been made on the realization of high performance building blocks in photonic circuits, such as ultra-low loss waveguides, monolithic lasers, high-speed modulators, and high efficiency photodetectors. However, toward large scale integration with complete functions and breakthrough performance, there are still many challenging problems to solve. While silicon has proved to be an asset material for integrated optics, the combination of other materials with complementary properties has turned out to be critical for the realization of specific advanced photonic devices. Yet, the major challenge has been the materials' differences that cause difficulties in hybrid integration. APL Photonics' keen interest in the field leads us to offer this editorial, which will present a broad overview of the recent progress, current challenges, and future opportunities of hybrid photonics integration. [ABSTRACT FROM AUTHOR]

We explore the monolithic integration of conventional electronics with SOI photonics using the commercial silicon photonics foundry technology offered by A*STAR's Institute of Microelectronics (IME). This process offers optical waveguide modulators and photodetectors, but was not intended to support transistors. We present the implementation of junction field effect transistors (JFETs) integrated with optical waveguides and photodetectors. A simple SPICE model is developed for the JFETs based on the available ion implant parameters, and the geometry feature size allowed by the technology's layout rules. We have demonstrated the monolithic integration of photonics and electronics circuits. This work could be useful for application in waveguide sensors and optical telecommunications. [ABSTRACT FROM AUTHOR]

Abstract Using an important feature of the hybrid graphene nanophotonic waveguide that TM and TE modes residing in two separated areas, we design a TE mode modulator and optimize its performance by tuning the ridge width and the low index layer height. Furthermore, the essential parameters including the insertion loss, the modulation depth, the bandwidth and figure of merit have been investigated. Our designed modulator demonstrates a 3-dB modulation depth with extra-small dimension (2 μm × 1.1 μm × 12.17 μm) and then a small footprint (0.5 μm × 12.17 μm) can be achieved. In addition, the modulator offers a broad working wavelength range and 80 GHz high modulation bandwidth upon the energy 108.8 fJ/bit. [ABSTRACT FROM AUTHOR]

In this paper, we review and provide additional details about our progress on multilayer silicon nitride (SiN)-on-silicon (Si) integrated photonic platforms. In these platforms, one or more SiN waveguide layers are monolithically integrated onto a Si photonic layer. This paper focuses on the development of three-layer platforms for the O- and SCL-bands for very large-scale photonic integrated circuits requiring hundreds or thousands of waveguide crossings. Low-loss interlayer transitions and ultralow-loss waveguide crossings have been demonstrated, along with bilevel and trilevel grating couplers for fiber-to-chip coupling. The SiN and Si passive devices have been monolithically integrated with high-efficiency optical modulators, photodetectors, and thermal tuners in a single photonic platform. [ABSTRACT FROM AUTHOR]

Highlights • The repetition rate of the generated pulse is four times of the driving frequency. • The quadrupling RF modulation needs no special or fixed modulation index. • The repetition rate tenability in our scheme is more effective. Abstract We propose an improved approach to generate frequency-quadrupled triangular-shaped waveform signals based on two cascaded modulators. A dual-parallel Mach-Zehnder modulator (DP-MZM) is employed to provide the quadrupling RF modulation, after which two primary optical sidebands (±2nd) are generated in spectrum. Then a dual-drive Mach-Zehnder modulator (DD-MZM) is followed to perform the optical double sideband (ODSB) modulation and signal with four sidebands (±2nd and ±6th) is obtained. By adjusting modulation index carefully, the power ratio of ±2nd and ±6th sidebands can be tuned to 9.5 dB. A piece of single mode fiber (SMF) is applied to remove the undesired harmonic. The expression of optical intensity is approximately equal to the Fourier expansion of ideal triangular-shaped waveform. The principle is illustrated by theory, simulation, and experiment. Finally, triangular-shaped waveform signals with repetition rate of 8 GHz, 12 GHz, 16 GHz and 20 GHz are generated. [ABSTRACT FROM AUTHOR]

High-speed Silicon Photonics calls for solutions providing a small footprint, high density, and minimum crosstalk, as exemplified by the recent development of integrated optical modulators. Yet, the performances of such modulators are hindered by intrinsic material losses, which results in low energy efficiency. Using the concept of Adiabatic Elimination, here, we introduce a scheme allowing for the low-loss modulation in densely packed waveguides. Our system is composed of two waveguides, whose coupling is mediated by an intermediate third waveguide. The signal is carried by the two outer modes, while the active control of their coupling is achieved via the intermediate dark mode. The modulation is performed by the manipulation of the central-waveguide mode index, leaving the signal-carrying waveguides unaffected by the loss. We discuss how Adiabatic Elimination provides a solution for mitigating signal losses and designing relatively compact, broadband, and energy-efficient integrated optical modulators. [ABSTRACT FROM AUTHOR]

Silicon photonics has begun to use index tunable plasmonic materials, such as graphene and indium tin oxide (ITO), because these materials can have their properties tailored by an external voltage. In this article, a compact plasmonic device, which can work as an optical mode controller and electro-absorption (EA) modulator at 1550 nm, is proposed. The performance of the device is theoretically investigated for ITO. Numerical simulations show that, with a suitable applied voltage to thin ITO layers, the proposed structure can select either only one mode (TE/TM) or both modes initially and then modulate the selected mode: a modulation depth of about 30–50 dB/μm is achieved with a proper choice of the dielectric spacer material. In addition, the proposed structure performance is analysed by replacing the waveguide materials with germanium. The proposed nanoscale device, with high modulation bandwidth (f3 dB = 700–250 GHz) and low-energy consumption (~4.0 fJ/bit), may find applications in the future integrated nanophotonics. [ABSTRACT FROM AUTHOR]

A tantalum pentoxide-based (Ta2O5-based) micro-ring all-optical modulator was fabricated. The refractive index inside the micro-ring cavity was modified using the Kerr effect by injecting a pumped pulse. The transmittance of the ring resonator was controlled to achieve all-optical modulation at the wavelength of the injected probe. When 12 GHz pulses with a peak power of 1.2 W were coupled in the ring cavity, the transmission spectrum of the Ta2O5 resonator was red-shifted by 0.04 nm because of the Kerr effect. The relationship between the modulation depth and gap of the Ta2O5 directional coupler is discussed. An optimized gap of 1100 nm was obtained, and a maximum buildup factor of 11.7 with 84% modulation depth was achieved. The nonlinear refractive index of Ta2O5 at 1.55 μm was estimated as 3.4 × 10−14 cm2/W based on the Kerr effect, which is almost an order of magnitude higher than that of Si3N4. All results indicate that Ta2O5 has potential for use in nonlinear waveguide applications with modulation speeds as high as tens of GHz. [ABSTRACT FROM AUTHOR]

A graphene based top-gate optical modulator on a standard silicon photonic platform is proposed for the future optical telecommunication networks. On the basis of the device simulation, we proposed that an electro-absorption light modulation can be realized by an ultra-narrow metal top-gate electrode (width less than 400 nm) directly located on the top of a silicon wire waveguide. The designed structure also provides excellent features such as carrier doping and waveguide-planarization free fabrication processes. In terms of the fabrication, we established transferring of a CVD-grown mono-layer graphene sheet onto a CMOS compatible silicon photonic sample followed by a 25-nm thick ALD-grown Al2O3 deposition and Source-Gate-Drain electrodes formation. In addition, a pair of low-loss spot-size converter for the input and output area is integrated for the efficient light source coupling. The maximum modulation depth of over 30% (1.2 dB) is observed at a device length of 50 μm, and a metal width of 300 nm. The influence of the initial Fermi energy obtained by experiment on the modulation performance is discussed with simulation results. [ABSTRACT FROM AUTHOR]

Silicon photonics has been established as a mature and promising technology for optoelectronic integrated circuits, mostly based on the silicon-on-insulator (SOI) waveguide platform. However, not all optical functionalities can be satisfactorily achieved merely based on silicon, in general, and on the SOI platform, in particular. Long-known shortcomings of silicon-based integrated photonics are optical absorption (in the telecommunication wavelengths) and feasibility of electrically-injected lasers (at least at room temperature). More recently, high two-photon and free-carrier absorptions required at high optical intensities for third-order optical nonlinear effects, inherent lack of second-order optical nonlinearity, low extinction ratio of modulators based on the free-carrier plasma effect, and the loss of the buried oxide layer of the SOI waveguides at mid-infrared wavelengths have been recognized as other shortcomings. Accordingly, several novel waveguide platforms have been developing to address these shortcomings of the SOI platform. Most of these emerging platforms are based on heterogeneous integration of other material systems on silicon substrates, and in some cases silicon is integrated on other substrates. Germanium and its binary alloys with silicon, III-V compound semiconductors, silicon nitride, tantalum pentoxide and other high-index dielectric or glass materials, as well as lithium niobate are some of the materials heterogeneously integrated on silicon substrates. The materials are typically integrated by a variety of epitaxial growth, bonding, ion implantation and slicing, etch back, spin-on-glass or other techniques. These wide range of efforts are reviewed here holistically to stress that there is no pure silicon or even group IV photonics per se. Rather, the future of the field of integrated photonics appears to be one of heterogenization, where a variety of different materials and waveguide platforms will be used for different purposes with the common feature of integrating them on a single substrate, most notably silicon. [ABSTRACT FROM AUTHOR]

An integrated silicon photonic interconnect with surface-normal optical interface is demonstrated by connecting a bidirectional grating based E-O modulator and a germanium waveguide photodetector. To investigate this photonic interconnect, both static and dynamic performance of the discrete devices are characterized respectively. Based on the characterization work, data transmission experiment is carried out for the photonic interconnect. Eye diagram results indicate the photonic interconnect can operate up to 7 Gb/s. [ABSTRACT FROM AUTHOR]

We recently demonstrated orders of magnitude enhancement of two-photon absorption (2PA) in direct gap semiconductors due to intermediate state resonance enhancement for photons of very different energies. It can be expected that further enhancement of nondegenerate 2PA will be observed in quantum wells (QWs), since the intraband matrix elements do not vanish near the band center, as they do in the bulk, and the density of states in QWs is larger near the band edge. Here, we present a perturbation-theory-based theoretical description of nondegenerate 2PA in semiconductor QWs, where both the frequency and the polarization of two incident waves can vary independently. Analytical expressions for all possible permutations of frequencies and polarizations have been obtained, and the results are compared with the degenerate 2PA in QWs along with the degenerate 2PA and the nondegenerate 2PA in bulk semiconductors. We show that using QWs in place of bulk semiconductors with both the beams in the transverse magnetic-polarized mode leads to an additional order of magnitude increase in the nondegenerate 2PA. Explicit calculations for GaAs QWs are presented. [ABSTRACT FROM AUTHOR]

We present a tunable and wideband microwave photonic phase shifter based on polarization-dependence of the LiNbO 3 Mach–Zehender modulator (MZM). In the proposed device, an orthogonal single sideband modulation is implemented by using a MZM and an optical band-pass filter. With the polarizer to synthesize the polarization orthogonal optical carrier and sideband, the phase of the optical microwave signal output from the polarizer can be tuned from 0 to 360° by simply adjusting the polarization direction of the lights whereas the amplitude keeps constant. A full range tunable phase shifting in the frequency range of 10–35 GHz is achieved. [ABSTRACT FROM AUTHOR]

The real part of refractive index is important for the phase shift of light propagating in a dielectric medium. Modulation of the refractive index can be used for electro-optic modulators based on Mach–Zehnder interferometer. In this study we simulate Si-based 2D photonic crystal slabs and by comparing the performance of different lattice types and structure of holes, in respect to the value of effective refractive index change when modulating the refractive index of Si, we find the most promising structures for Si photonics electro-optic modulators based on transition between photonic bands. • The required effective RI change from an energy band shift of a PhC is generated. • Optimal structure is concluded among the comparison of 3 lattices with 8 hole shapes. • The 2D PhC slab optimized by GA can switch bands rapidly in a small frequency range. [ABSTRACT FROM AUTHOR]

A promising approach to the broadband optical modulation is discussed. Based on the experimental data and using numerical calculations, the static and dynamic modulation characteristics of submicron SOI-based photonic phase modulators are studied. The parameter optimization of submicron photonic devices for highly efficient broadband modulation in a band of over 100 GHz is investigated. [ABSTRACT FROM AUTHOR]

Abstract: We propose and demonstrate a novel photonic microwave mixer based on an integrated dual-parallel Mach–Zehnder modulator (DPMZM). The local oscillator (LO) signal is frequency doubled and modulated onto the optical carrier through one sub-modulator which is biased at the maximum transmission point, while the radio-frequency (RF) signal is modulated onto the optical carrier through the other sub-modulator. The mixer is simple in structure, stable in performance, and the frequency requirement of the LO is only one-half of that of conventional schemes. Experimental results demonstrate a significant improvement of 17.1dB in conversion efficiency, 10.5dB in noise figure (NF) and 7.7dB in spurious free dynamic range (SFDR) as compared with the scheme based on two cascaded intensity modulators (IMs). [Copyright &y& Elsevier]

Abstract: We have characterized photonic-wire waveguides with Si/SiGe/Si heterostructure ribs for Si-based optical modulators. The Si (80nm)/Si0.72Ge0.28 (40nm) layers grown on Si-on-insulator by molecular beam epitaxy for optical modulators were evaluated by in-situ reflection high-energy electron diffraction, atomic force microscope, X-ray diffraction and Raman spectroscopy, exhibiting that the fully-strained highly-crystalline SiGe layer was obtained. We have evaluated the propagation loss of the Si/strained SiGe/Si photonic-wire waveguides. The wavelength dependence of the propagation loss exhibits the bandgap narrowing of the strained Si0.72Ge0.28, while the optical absorption of the strained Si0.72Ge0.28 is not significant for the optical modulator application at 1.55-μm wavelength. [Copyright &y& Elsevier]

An integrated erbium-based light emitting diode has been realized in a waveguide configuration allowing 1:54 μm light signal routing in silicon photonic circuits. This injection device is based on an asymmetric horizontal slot waveguide where the active slot material is Er3+ in SiO2 or Er3+ in Si-rich oxide. The active horizontal slot waveguide allows optical confinement, guiding and lateral extraction of the light for on-chip distribution. Light is then coupled through a taper section to a passive Si waveguide terminated by a grating which extracts (or inserts) the light signal for measuring purposes. We measured an optical power density in the range of tens of μW=cm2 which follows a super-linear dependence on injected current density. When the device is biased at high current density, upon a voltage pulse (pump signal), free-carrier and space charge absorption losses become large, attenuating a probe signal by more than 60 dB/cm and thus behaving conceptually as an electro-optical modulator. The integrated device reported here is the first example, still to be optimized, of a fundamental block to realize an integrated silicon photonic circuit with monolithic integration of the light emitter. [ABSTRACT FROM AUTHOR]

We present the vision of back-end deposited silicon photonics (BDSP) and review works that have been done in this field. Individual aspects of BDSP platform including excimer-laser-annealed polycrystalline silicon, low-loss plasma-enhanced chemical vapor deposition silicon nitride waveguide, modulator, detector, electrical interface, back-end CMOS compatibility, and benefits of the platform are discussed in detail. [ABSTRACT FROM PUBLISHER]

The article below presents a review of current research on silicon photonics. Herein, an overview of current silicon modulator types and modern integration approaches is presented including direct bonding methods and micro-transfer printing. An analysis of current state of the art silicon modulators is also given. Finally, new prospects for III–V-silicon integration are explored and the prospects of an integrated modulator compatible with current CMOS processing is investigated. [ABSTRACT FROM AUTHOR]

• The exponential demand for bandwidth in data centers is on high alert. • The design of optical modulators is crucial for communication systems. • Designing optical modulators is still challenging. The exponential demand for bandwidth in data centers is on high alert with the increase in data traffic. In this scenario, the design of optical modulators is crucial for the continuous evolution of communication systems. For data center interconnect (DCI) applications, this mean that modulators should offer high bandwidth and low optical loss. In addition, devices must operate with low power consumption and be compatible with complementary metal–oxide–semiconductor (CMOS) processes for low-cost and large-scale manufacturing. These facts show the importance of advancement in Silicon (Si) modulators solutions, since they have the potential to fulfill all these requirements. However, designing a device that meets all these requirements at the same time is still challenging, because there are several trade-offs problems involved for which different Silicon modulators types are not yet able to solve. In this context, this paper reviews the challenges in Silicon photonics (SiPh) modulators for data center interconnect applications. [ABSTRACT FROM AUTHOR]