Showing papers on "Optical modulator published in 2022"

High performance thin-film lithium niobate modulator on a silicon substrate using periodic capacitively loaded traveling-wave electrode

Abstract: Thin-film lithium niobate (TFLN) based traveling-wave modulators maintain simultaneously excellent performances, including large modulation bandwidth, high extinction ratio, low optical loss, and high modulation efficiency. Nevertheless, there still exists a balance between the driving voltage and modulation bandwidth. Here, we demonstrate an ultra-large bandwidth electro-optic modulator without compromising the driving voltage based on the TFLN platform on a silicon substrate, using a periodic capacitively loaded traveling-wave electrode. In order to compensate the slow-wave effect, an undercut etching technique for the silicon substrate is introduced to decrease the microwave refractive index. Our demonstrated devices represent both low optical and low microwave losses, which leads to a negligible optical insertion loss of 0.2 dB and a large electro-optic bandwidth with a roll-off of 1.4 dB at 67 GHz for a 10 mm-long device. A low half-wave voltage of 2.2 V is also achieved. Data rates up to 112 Gb s−1 with PAM-4 modulation are demonstrated. The compatibility of the proposed modulator to silicon photonics facilitates its integration with matured silicon photonic components using, e.g., hybrid integration technologies.

Integrated silicon carbide electro-optic modulator

Abstract: Owing to its attractive optical and electronic properties, silicon carbide is an emerging platform for integrated photonics. However an integral component of the platform is missing-an electro-optic modulator, a device which encodes electrical signals onto light. As a non-centrosymmetric crystal, silicon carbide exhibits the Pockels effect, yet a modulator has not been realized since the discovery of this effect more than three decades ago. Here we design, fabricate, and demonstrate a Pockels modulator in silicon carbide. Specifically, we realize a waveguide-integrated, small form-factor, gigahertz-bandwidth modulator that operates using complementary metal-oxide-semiconductor (CMOS)-level voltages on a thin film of silicon carbide on insulator. Our device is fabricated using a CMOS foundry compatible fabrication process and features no signal degradation, no presence of photorefractive effects, and stable operation at high optical intensities (913 kW/mm2), allowing for high optical signal-to-noise ratios for modern communications. Our work unites Pockels electro-optics with a CMOS foundry compatible platform in silicon carbide.

2D materials-enabled optical modulators: From visible to terahertz spectral range

Abstract: Two-dimensional (2D) materials with layered structures have a variety of exceptional electronic and optical attributes for potentially developing basic functions of light wave technology from light-emitting to -modulating and -sensing. Here, we present state-of-the-art 2D materials-enabled optical intensity modulators according to their operation spectral ranges, which are mainly determined by the optical bandgaps of the 2D materials. Leveraging rich electronic structures from different 2D materials and the governed unique light–matter interactions, the working mechanisms and device architectures for the enabled modulators at specific wavelength ranges are discussed. For instance, the tunable excitonic effect in monolayer transition metal dichalcogenides allows the modulation of visible light. Electro-absorptive and electro-refractive graphene modulators could be operated in the telecom-band relying on their linear dispersion of the massless Dirac fermions. The bendable electronic band edge of the narrow bandgap in few-layer black phosphorus promises the modulation of mid-infrared light via the quantum-confined Franz–Keldysh or Burstein–Moss shift effect. Electrically and magnetically tunable optical conductivity in graphene also supports the realizations of terahertz modulators. While these modulators were demonstrated as proof of concept devices, part of them have great potential for future realistic applications, as discussed with their wavelength coverage, modulation depth, insertion loss, dynamic response speed, etc. Specifically, benefiting from the well-developed technologies of photonic chips and optical fibers in telecom and datacom, the 2D materials-based modulators integrated on these photonic structures are expected to find applications in fiber and chip optical communications. The free-space mid-infrared and terahertz modulators based on 2D materials can expect application in chemical bond spectroscopy, free-space communications, and environment/health sensing.

Harmonic dual-wavelength and multi-soliton pattern fiber laser based on GO-Sb2Se3 saturable absorbers

Abstract: As new two-dimensional materials, antimony selenide (Sb2Se3) and graphene oxide (GO) are ideal photoelectric materials due to their appropriate band gap structure and strong light-matter interaction, which can be used in optical modulators, broadband ultrafast optical switches, and other photoelectric fields. The GO and Sb2Se3/GO measurements show excellent nonlinear characteristics with the modulation depth of 3.18% and 4.78%, respectively. This work proposes a harmonic dual-wavelength (HDW) fiber laser based on GO. This provides new possibilities for the research of ultrashort pulse sources with both high repetition frequency and multiple wavelengths. Furthermore, the conventional soliton mode-locking with 984 fs pulse width and soliton bundles mode-locking is obtained. The Sb2Se3/GO SA is coupled into the laser cavity for the first time to achieve higher performance mode-locked pulse. The results show that Sb2Se3/GO SA can shorten the pulse width and increase the output power more effectively than GO, such as the pulse width is shortened from 984 fs to 511 fs and the slope efficiency increased from 11.9% to 16.18%, which confirms its potential application in nonlinear optical material and ultrafast pulse generation. The results provide a new opportunity to apply traditional broadband nonlinear optical materials in ultrafast photonics and make a fundamental contribution to the development of advanced nanophotonic devices.

A full degree-of-freedom spatiotemporal light modulator

Abstract: Harnessing the full complexity of optical fields requires the complete control of all degrees of freedom within a region of space and time—an open goal for present-day spatial light modulators, active metasurfaces and optical phased arrays. Here, we resolve this challenge with a programmable photonic crystal cavity array enabled by four key advances: (1) near-unity vertical coupling to high-finesse microcavities through inverse design; (2) scalable fabrication by optimized 300 mm full-wafer processing; (3) picometre-precision resonance alignment using automated, closed-loop ‘holographic trimming’; and (4) out-of-plane cavity control via a high-speed μLED array. Combining each, we demonstrate the near-complete spatiotemporal control of a 64 resonator, two-dimensional spatial light modulator with nanosecond- and femtojoule-order switching. Simultaneously operating wavelength-scale modes near the space–bandwidth and time–bandwidth limits, this work opens a new regime of programmability at the fundamental limits of multimode optical control. Panuski et al. demonstrate a programmable photonic crystal cavity array, enabling the spatiotemporal control of a 64 resonator, two-dimensional spatial light modulator with nanosecond- and femtojoule-order switching.

Compact thin film lithium niobate folded intensity modulator using a waveguide crossing.

Abstract: A small footprint, low voltage and wide bandwidth electro-optic modulator is critical for applications ranging from optical communications to analog photonic links, and the integration of thin-film lithium niobate with photonic integrated circuit (PIC) compatible materials remains paramount. Here, a hybrid silicon nitride and lithium niobate folded electro-optic Mach Zehnder modulator (MZM) which incorporates a waveguide crossing and 3 dB multimode interference (MMI) couplers for splitting and combining light is reported. This modulator has an effective interaction region length of 10 mm and shows a DC half wave voltage of roughly 4.0 V, or a modulation efficiency (Vπ ·L) of roughly 4 V·cm. Furthermore, the device demonstrates a power extinction ratio of roughly 23 dB and shows .08 dB/GHz optical sideband power roll-off with index matching fluid up to 110 GHz, with a 3-dB bandwidth of 37.5 GHz.

Mid-infrared Integrated Electro-optic Modulator Operating up to 225 MHz between 6.4 and 10.7 μm Wavelength

Abstract: Mid-infrared spectroscopy is essential for identifying molecular species, while related electro-optic modulators are crucial for signal-to-noise enhancement via synchronous detection. Therefore, the development of integrated modulators is expected to have a major impact in compact and widespread sensing applications. In this work, we experimentally demonstrate a broadband integrated electro-optic modulator, based on a graded-index SiGe photonics platform and free-carrier plasma dispersion effect. Optical modulation is reported from 6.4 to 10.7 μm wavelength, showing an operational frequency up to 225 MHz. These results pave the way for the development of multimolecule on-chip spectroscopic systems, operating at the longest mid-infrared wavelengths.

Silicon–Lithium Niobate Hybrid Intensity and Coherent Modulators Using a Periodic Capacitively Loaded Traveling-Wave Electrode

Abstract: High-performance silicon and thin-film lithium niobate hybrid electro-optic modulators are demonstrated. In order to break the voltage–bandwidth limit in a normal traveling-wave modulator, a periodic capacitively loaded traveling-wave electrode is employed in this hybrid platform. The silicon substrate is undercut-etched to achieve index matching of the optical wave and microwave. A hybrid waveguide with a lithium niobate thin film bonded on a silicon wire is employed. Lithium niobate etching is not required for making the hybrid optical waveguides. We realize an intensity modulator of 12.5 mm long modulation section, which exhibits a low half-wave voltage of 1.7 V and a large 3 dB modulation bandwidth of >70 GHz. Data transmissions with various modulation formats beyond 100 Gbit/s are successfully achieved with dynamic extinction ratios of >8 dB. Combining the advantages of the silicon and thin-film lithium niobate platforms, a compact dual polarization coherent modulator is also experimentally demonstrated, on which 96 Gbaud 16-level quadrature amplitude modulation signals in both polarizations are successfully transmitted.

Ultrahigh-Performance ENZ Modulator Based on a Stack of Three-Layer Graphene and ITO

Abstract: A high-performance electro-absorption optical modulator based on the epsilon-near-zero (ENZ) effect is proposed. The structure consists of a waveguide with a silicon (Si) core over which a stack of graphene/HfO $_2$ /graphene/ITO/HfO $_2$ /graphene is grown, covered by a Si cladding. An external voltage is applied across the graphene layers to change the carrier concentration in the indium tin oxide (ITO) layers. Using a self-consistent theory, the required voltage to achieve the ENZ points in the ITO layers is calculated up to 3.42 V for an ITO thickness of 5 nm. The operation of the modulator is investigated using a three-dimensional finite-difference time-domain (FDTD) method, resulting in a modulation depth as high as 5.23 dB/ $\boldsymbol{\mu}$ m (5.36 dB/ $\boldsymbol{\mu }$ m) at a wavelength of 1.55 $\boldsymbol{\mu }$ m for the TE (TM) polarization, which ensures the polarization-insensitivity of our proposed modulator. It is also calculated that the insertion loss of the modulator is in the order of $\boldsymbol{ 2.5 \times 10^{-3}}$ dB/ $\boldsymbol{\mu }$ m that yields the figure of merit (FOM) of more than 1800. The outstanding features of our proposed modulator are mainly attributed to using the Si cladding layer instead of metal cladding. Furthermore, in contrast to the previously studied structures with metal electrodes, graphene layers significantly reduce the insertion loss.

Integrated ultra-high-performance graphene optical modulator

Abstract: Abstract 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.

Compact 100GBaud driverless thin-film lithium niobate modulator on a silicon substrate.

Abstract: Electro-optic (EO) modulators with a high modulation bandwidth are indispensable parts of an optical interconnect system. A key requirement for an energy-efficient EO modulator is the low drive voltage, which can be provided using a standard complementary metal oxide semiconductor circuity without an amplifying driver. Thin-film lithium niobate has emerged as a new promising platform, and shown its capable of achieving driverless and high-speed EO modulators. In this paper, we report a compact high-performance modulator based on the thin-film lithium niobate platform on a silicon substrate. The periodic capacitively loaded travelling-wave electrode is employed to achieve a large modulation bandwidth and a low drive voltage, which can support a driverless single-lane 100Gbaud operation. The folded modulation section design also helps to reduce the device length by almost two thirds. The fabricated device represents a large EO bandwidth of 45GHz with a half-wave voltage of 0.7V. The driverless transmission of a 100Gbaud 4-level pulse amplitude modulation signal is demonstrated with a power consumption of 4.49fj/bit and a bit-error rate below the KP4 forward-error correction threshold of 2.4×10-4.

Linearity-Enhanced Dual-Parallel Mach–Zehnder Modulators Based on a Thin-Film Lithium Niobate Platform

Abstract: In this work, we report a linearity-enhanced dual-parallel Mach–Zehnder modulator (MZM) on a thin-film lithium niobate platform. By setting the optical and electrical splitting ratios at a specific condition, the third-order intermodulation distortions (IMD3) of the child MZMs cancel with each other, whereas the first-order harmonics (FH) reach the maximum. Passive devices instead of thermo-optical switches are used to control the optical power and phase of the child MZMs, which greatly improve the device stability and simplify the operation complexity. To the best of our knowledge, the experimental results show a record-high spurious-free dynamic range on a thin-film lithium niobate platform (110.7 dB·Hz2/3 at 1 GHz). The E-O response decayed about 1.9 dB from 10 MHz to 40 GHz, and the extrapolated E-O 3 dB bandwidth is expected to be 70 GHz. A half-wave voltage of 2.8 V was also achieved. The proposed modulator provides a promising solution for high-bandwidth and low-voltage analog optical links.

Ultrahigh Modulation Enhancement in All-Optical Si-Based THz Modulators Integrated with Gold Nanobipyramids.

Abstract: Optical regulation strategy with the aid of hybrid materials can significantly optimize the performance of terahertz devices. Gold nanobipyramids (AuNBPs) with synthetical tunability to the near-infrared band show strong local field enhancement, which improves optical coupling at the interface and benefits the modulation performance. We design AuNBPs-integrated terahertz modulators with multiple structured surfaces and demonstrate that introducing AuNBPs can effectively enhance their modulation depths. In particular, an ultrahigh modulation enhancement of 1 order of magnitude can be achieved in the AuNBPs hybrid metamaterials accompanied by the multifunctional modulation characteristics. By application of the coupled Lorentz oscillator model, the theoretical calculation suggests that the optical regulation with AuNBPs originates from increased damping rate and higher coupling coefficient under pump excitation. Additionally, a terahertz spatial light modulator is constructed to demonstrate multiple imaging display and consume extremely low power, which is promising for the potential application in spatial and frequency selective imaging.

Compact substrate-removed thin-film lithium niobate electro-optic modulator featuring polarization-insensitive operation

Abstract: A compact polarization-insensitive electro-optic (EO) modulator, which allows the laser and modulator to be located at different locations while using a standard single-mode fiber to interconnect them, is highly desirable for 5G or future 6G wireless networks. Herein, we propose a modulator based on substrate-removed thin-film lithium niobate. The proposed device exhibits a polarization-dependent loss of 0.35 dB and on-chip loss of approximately 2 dB. The polarization insensitivity of the proposed device was experimentally demonstrated using a four-level pulse-amplitude modulation format at 50 Gbaud (100 Gb/ s).

Electro-optic metasurface-based free-space modulators.

Abstract: Research in optical metasurfaces has explosively grown in recent years, primarily due to their ability of exercising complete control over the transmitted and reflected fields. Application prospects in many emerging technologies require this control to become dynamic, so that the metasurface response could be tuned with external stimuli. In this work, electrically tunable optical metasurfaces operating in reflection as optical free-space modulators are demonstrated. The intensity modulation is achieved by exploiting the electro-optic Pockels effect and tuning the Fabry-Perot resonance in a 320 nm-thick lithium niobate (LN) film sandwiched between a continuous thick gold film and an array of gold nanostripes, serving also as control electrodes. The proposed compact (<1000 μm2) modulators operate in the wavelength range of 900-1000 nm, featuring a maximum intensity modulation depth of ∼20% at the driving voltage of ± 10 V within the bandwidth of 8.0 MHz (with the potential bandwidth of ∼25 GHz). By arranging a 2 × 2 array of individually addressable modulators, space-variant control of light reflection is demonstrated, therefore opening a way towards the realization of inertia-free, ultrafast, and robust spatial light modulators based on tunable LN flat optics components.

Graphene optical modulators using bound states in the continuum

Abstract: Graphene-based optical modulators have been widely investigated due to the high mobility and tunable permittivity of graphene. However, achieving a high modulation depth with a low insertion loss is challenging owing to low graphene-light interaction. To date, only waveguide-type modulators have been extensively studied to improve light-graphene interaction, and few free-space type modulators have been demonstrated in the optical communication wavelength range. In this study, we propose two graphene-based optical free-space type modulators in a simple silicon photonic crystal structure that supports bound states in the continuum. The designed modulator with an ultra-high quality factor from the bound states in the continuum achieves a high modulation depth (MD = 0.9972) and low insertion loss (IL = 0.0034) with a small Fermi level change at the optical communication wavelength. In addition, the proposed modulators support outstanding modulation performance in the normal chemical vapor deposition (CVD) graphene (mobility = 0.5 m2/Vs). We believe the scheme may pave the way for graphene-based optical active devices.

Longitudinal piezoelectric resonant photoelastic modulator for efficient intensity modulation at megahertz frequencies

Abstract: Intensity modulators are an essential component in optics for controlling free-space beams. Many applications require the intensity of a free-space beam to be modulated at a single frequency, including wide-field lock-in detection for sensitive measurements, mode-locking in lasers, and phase-shift time-of-flight imaging (LiDAR). Here, we report a new type of single frequency intensity modulator that we refer to as a longitudinal piezoelectric resonant photoelastic modulator. The modulator consists of a thin lithium niobate wafer coated with transparent surface electrodes. One of the fundamental acoustic modes of the modulator is excited through the surface electrodes, confining an acoustic standing wave to the electrode region. The modulator is placed between optical polarizers; light propagating through the modulator and polarizers is intensity modulated with a wide acceptance angle and record breaking modulation efficiency in the megahertz frequency regime. As an illustration of the potential of our approach, we show that the proposed modulator can be integrated with a standard image sensor to effectively convert it into a time-of-flight imaging system.

Polarization-independent electro-absorption optical modulator based on trapezoid polymer-graphene waveguide

Abstract: A polarization-independent electro-absorption modulator based on the trapezoid polymer-graphene waveguide (PGW) was proposed. The modulator was constructed on a trapezoid polymer waveguide, and the insulting dielectric spacer sandwiched in the two graphene layers was placed on the surface of the trapezoid polymer waveguide core. The simulation results show that by applying different gate voltages on the graphene layers, effective mode index of the TE and TM modes in the PGW can realize the similar changes in the C-band, which provides the possibility for realizing the polarization-independent modulation. Here, through simulation and optimization, the presented modulator has a compact size and the extinction ratio (ER) of 37 dB can be achieved by reasonably setting working points of “OFF” and “ON” states with 800 μm long active graphene length. The ER variation between the two operating modes is about 0.46 dB. The corresponding power consumption of the modulator is about 23.6 pJ/bit.

Polymer modulators in silicon photonics: review and projections

Abstract: Abstract 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.

Transflective spatial terahertz wave modulator.

Abstract: Spatial light modulators can digitally manipulate the amplitude, phase, and polarization of light. Their counterparts in the terahertz band are highly pursued to meet the requirements of numerous applications such as wireless communications and biomedical detection. Here, we propose a spatial terahertz wave modulator based on a liquid-crystal-integrated metadevice. The modulator consists of 8 × 8 pixels. The liquid crystal layer is sandwiched between an asymmetric split ring resonator array and pixelated interdigital electrodes. Fano resonance occurs for the transmitted wave, while the reflected wave is perfectly absorbed. By separately driving the liquid crystal with pixelated interdigital electrodes, both the Fano resonance and absorption peak can be continuously tuned due to the variation in the environmental refractive index. This work provides a transflective spatial terahertz wave modulator that can dynamically reconfigure a terahertz wavefront.

Thin-film lithium-niobate modulator with a combined passive bias and thermo-optic bias.

Abstract: It is essential to bias a thin-film lithium-niobate Mach-Zehnder electro-optic (EO) modulator at the desired operation condition to ensure optimal performance of the modulator. While thermo-optic (TO) control can solve the problem of bias drift, it consumes significant electric power. In this paper, we propose a technique to largely reduce bias power consumption by combining passive bias and TO bias. In our design, waveguide sections with different widths are introduced in the two arms of the MZ modulator to produce a desired phase difference of π/2 rad (the desired operation condition), and local heating with electrode heaters placed on the waveguides is employed to provide compensation for any phase drift caused by fabrication errors and other effects. As the TO control only serves to compensate for small errors, the electric power required is low and the response is fast. To demonstrate our technique experimentally, we fabricate several modulators of the same design on the same chip. Our experimental modulators can operate up to ∼40 GHz with a half-wave voltage of ∼2.0 V over a wide optical bandwidth, and the performances are insensitive to ambient temperature variations. The TO bias powers required range from 1 mW to 15 mW, and the thermal rise and fall times are 47 µs and 14 µs, respectively. Our technique can facilitate the development of practical high-speed EO modulators on the lithium-niobate-on-insulator platform.

Low insertion loss and high modulation depth Tunable modulator at Telecommunications Band enable by graphene/hBN multilayer gratings

Abstract: In this paper, a novel Graphene Plasmonic Grating modulator is composed of four-layer graphene, encapsulated in hBN layers, and merged with a Fabry-Perot (FP) cavity presented. The main aim of graphene in the proposed modulator is to tune the FP cavity's resonant frequencies. The Standing electric field waves induced by the FP interferometer are strongly formed at the top of grating, where the hBN/graphene layers are established. Therefore, propagation surface plasmon polaritons (SPPs) on graphene sheets strongly confines the electric field between the graphene and hBN layer at the top of the gratings, causing the high absorption of the proposed structure and allowing for modification of the optical signals in the telecommunications range wavelengths. An Au electrode keeps transmission light from the proposed structure at zero. Therefore, the incident light is either absorbed or reflected, which gives the proposed modulator another feature since it can operate in both the absorption and reflection modes and can be adjusted to any desired wavelengths. Moreover, the proposed structure can be used as a perfect absorber since its absorption spectra reach a high value of 100 %. A reflection (absorption) type modulator with a central wavelength of $1.55\mu \mathbf{m}$, a modulation depth of 97% (98%), insertion loss of 0.20 dB (0.22 dB), with a gate voltage difference of 0.18 V is designed. In addition, the modulation depth of 97 % for both regimes are evaluated in the wavelength of 1.3 and 1.8 μm, Moreover, numerous modulators with different modulation parameters are designed in any desired wavelength of 1–2 μm simply by adjusting the FP interferometer resonance by electrostatically tuning the graphene chemical potential via gate voltage.

Non-resonant Recirculating Light Phase Modulator

Abstract: 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 of 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.

Superiorly low half-wave voltage electro-optic polymer modulator for visible photonics.

Abstract: Chip-scale optical devices operated at wavelengths shorter than communication wavelengths, such as LiDAR for autonomous driving, bio-sensing, and quantum computation, have been developed in the field of photonics. In data processing involving optical devices, modulators are indispensable for the conversion of electronic signals into optical signals. However, existing modulators have a high half-wave voltage-length product (VπL) which is not sufficient at wavelengths below 1000 nm. Herein, we developed a significantly efficient optical modulator which has low VπL of 0.52 V·cm at λ = 640 nm using an electro-optic (EO) polymer, with a high glass transition temperature (Tg = 164 °C) and low optical absorption loss (2.6 dB/cm) at λ = 640 nm. This modulator is not only more efficient than any EO-polymer modulator reported thus far, but can also enable ultra-high-speed data communication and light manipulation for optical platforms operating in the ranges of visible and below 1000 nm infrared.

High-Performance All-Optical Modulator Based on Graphene-HBN Heterostructures

Abstract: Graphene has emerged as an ultrafast photonic material for on-chip all-optical modulation. However, its atomic thickness limits its interaction with guided optical modes, which results in a high switching energy per bit or low modulation efficiencies. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we present a practical design of an all-optical modulator that is based on graphene and hexagonal boron nitride (hBN) heterostructures that are hybrid integrated into silicon slot waveguides. Using this device, a high extinction ratio (ER) of 7.3 dB, an ultralow insertion loss (IL) of <0.6 dB, and energy-efficient switching (<0.33 pJ/bit) are attainable for a 20{\mu}m long modulator with double layer graphene. In addition, the device performs ultrafast switching with a recovery time of <600 fs, and could potentially be employed as a high-performance all-optical modulator with an ultra-high bandwidth in the hundreds of GHz. Moreover, the modulation efficiency of the device is further enhanced by stacking additional layers of graphene-hBN heterostructures, while theoretically maintaining an ultrafast response. The proposed device exhibits highly promising performance metrics, which are expected to serve the needs of next-generation photonic computing systems.

Recent Progress in Silicon-Based Slow-Light Electro-Optic Modulators

Abstract: As an important optoelectronic integration platform, silicon photonics has achieved significant progress in recent years, demonstrating the advantages on low power consumption, low cost, and complementary metal–oxide–semiconductor (CMOS) compatibility. Among the different silicon photonics devices, the silicon electro-optic modulator is a key active component to implement the conversion of electric signal to optical signal. However, conventional silicon Mach–Zehnder modulators and silicon micro-ring modulators both have their own limitations, which will limit their use in future systems. For example, the conventional silicon Mach–Zehnder modulators are hindered by large footprint, while the silicon micro-ring modulators have narrow optical bandwidth and high temperature sensitivity. Therefore, developing a new structure for silicon modulators to improve the performance is a crucial research direction in silicon photonics. Meanwhile, slow-light effect is an important physical phenomenon that can reduce the group velocity of light. Applying slow-light effect on silicon modulators through photonics crystal and waveguide grating structures is an attractive research point, especially in the aspect of reducing the device footprint. In this paper, we review the recent progress of silicon-based slow-light electro-optic modulators towards future communication requirements. Beginning from the principle of slow-light effect, we summarize the research of silicon photonic crystal modulators and silicon waveguide grating modulators in detail. Simultaneously, the experimental results of representative silicon slow-light modulators are compared and analyzed. Finally, we discuss the existing challenges and development directions of silicon-based slow-light electro-optic modulators for the practical applications.

Design of Ultracompact High‐Speed‐Integrated Lithium–Niobate Periodic Dielectric Waveguide Modulator

Abstract: Modern communications and microwave photonics require compact electro‐optic modulators with ultrahigh bandwidth and low power consumption. These requirements can be satisfied by integrated lithium–niobate electro‐optic modulators with high bandwidth and low power consumption. However, most integrated lithium–niobate modulators cannot achieve a good balance between an ultracompact size and a high modulation bandwidth. These challenges are overcome by designing an integrated lithium–niobate periodic dielectric waveguide modulator, featuring a compact modulation length of 87.4 μm, a theoretical modulation bandwidth over 600 GHz, a voltage‐length product of 0.0874 V cm, and a high sideband suppression ratio up to 36.1 dB. These performances are achieved by taking advantage of a capacitor configuration consisting of a nonresonant periodic dielectric waveguides sandwiched between two indium tin oxide (ITO) electrodes. This design provides an ultrabroadband and compact solution to next‐generation communications and microwave photonics.

Phase modulators in hybrid silicon and lithium niobate thin films

Abstract: The hybridization of mono-crystalline silicon and lithium niobate thin films (Si-LNOI) can combine the physical properties of Si and the optical properties of LN, and it has emerged as a new material platform for integrated photonics. In this paper, phase modulators in Si-LNOI were demonstrated. First, the phase modulator was designed. According to the simulation, the Si loading strip waveguide had a small mode area due to the large refractive index of Si. This allowed a small electrode gap that resulted in enhancement of the overlap of the optical field and the electrostatic field, and the V π L of the phase modulator could be as small as 3.3 V·cm. Second, phase modulators with a Si loading strip waveguide with a top width of 0.5 μm were fabricated by plasma etching, and the V π L of the phase modulator was measured to be 4.74 V·cm. This study provides useful information for the devices in the Si-LNOI.

Linearity of a silicon-based graphene electro-absorption modulator.

Abstract: A silicon-based graphene modulator, holding the advantages of high modulation efficiency, high speed, and being ultra-compact, is regarded as a promising candidate for next-generation communication networks. Although the properties involved for optical communications have been widely studied, very few works evaluate the performance required for the microwave scenarios. Here, for the first time, to the best of our knowledge, the linearity of silicon-based graphene electro-absorption modulator (EAM) is analyzed and experimentally characterized through spurious free dynamic range (SFDR) with 82.5 dB·Hz1/2 and 100.3 dB·Hz2/3. Further calculations reveal that a higher SFDR value could be achieved through optimizing the bias voltage. Variations of capacitor structural parameters have little influence on the linearity. Such performance leads to the first, to the best of our knowledge, demonstration of a Gbps-level pulse-amplitude 4-level modulation scheme (PAM-4) eye diagram in a silicon-based graphene modulator.

Compact MZI modulators on thin film Z-cut lithium niobate.

Abstract: In this paper, we designed, implemented, and characterized compact Mach-Zehnder interferometer-based electro-optic modulators. The modulator utilizes spiral-shaped optical waveguides on Z-cut lithium niobate and the preeminent electro-optic effect which is applied using top and bottom electrodes. Optical waveguides are made of rib etched lithium niobate waveguides with bottom silicon oxide cladding, while SU8 polymer covers the top and sides of the rib waveguides. The proposed implementation resulted in low optical losses < 1.3 dB/cm. Moreover, we achieved compact modulators that fit 0.286 cm and 2 cm long optical waveguides in 110 µm × 110 µm and 300 µm × 300 µm areas, respectively. For single arm modulation, the modulators achieved a VπL of 7.4 V.cm and 6.4 V.cm and 3-dB bandwidths of 9.3 GHz and 2.05 GHz, respectively. Push-pull modulation is expected to cut these VπL in half. The proposed configuration avoids traveling wave modulation complexities and represents a key development towards miniature and highly integrated photonic circuits.