Electroabsorption Waveguide Modulator Research Articles

56 Gbps high-speed Ge electro-absorption modulator

A high-speed evanescent-coupled Ge waveguide electro-absorption modulator (EAM) with simple fabrication processes was realized on a silicon-on-insulator platform with a 220 nm top Si layer. Selectively grown Ge with a triangle shape was directly used for Ge waveguides of the EAM. An asymmetric p-i-n junction was designed in the Ge waveguide to provide a strong electric field for Franz–Keldysh effect. The insertion loss of the Ge EAM was 6.2 dB at 1610 nm. The EAM showed the high electro-optic bandwidth of 36 GHz at − 1 V . Clear open 56 Gbps eye diagrams were observed at 1610 nm with a dynamic extinction ratio of 2.7 dB and dynamic power consumption of 45 fJ/bit for voltage swing of 3Vpp.

Double-layer graphene on photonic crystal waveguide electro-absorption modulator with 12 GHz bandwidth

Abstract Graphene has been widely used in silicon-based optical modulators for its ultra-broadband light absorption and ultrafast optoelectronic response. By incorporating graphene and slow-light silicon photonic crystal waveguide (PhCW), here we propose and experimentally demonstrate a unique double-layer graphene electro-absorption modulator in telecommunication applications. The modulator exhibits a modulation depth of 0.5 dB/μm with a bandwidth of 13.6 GHz, while graphene coverage length is only 1.2 μm in simulations. We also fabricated the graphene modulator on silicon platform, and the device achieved a modulation bandwidth at 12 GHz. The proposed graphene-PhCW modulator may have potentials in the applications of on-chip interconnections.

Numerical investigation of the linearity of graphene-based silicon waveguide modulator.

We investigated the linearity of graphene-based silicon waveguide modulators used in microwave photonics links. A theoretical model was developed to systematically analyze the linearity performance for the second-order harmonic distortions (SHD2) and the third-order intermodulation distortions (IMD3). For the graphene-based silicon waveguide electro-absorption (EA) modulator, the distortions were suppressed through bias optimization. As a result, the maximal spurious free dynamic range (SFDR) obtained for SHD2 and IMD3 were 105.9 dB ·Hz1/2 and 117.8 dB·Hz2/3, respectively. For the graphene-based silicon waveguide electro-refraction (ER) phase modulator, SHD2 was fully eliminated through the push-pull modulation and quadrature biasing, while the remaining IMD3 term was linearized by the proper adjustment of the bias voltage and phase shifter length to obtain an ultrahigh SFDR of 130 dB ·Hz2/3. Moreover, the graphene-based silicon waveguide ER modulator is more compact and tolerant to bias errors than a pure silicon modulator. These results reveal that the graphene-based silicon waveguide EA and ER modulators can be potentially utilized in integrated microwave photonics.

Modeling and Experiment Verification of Lateral Current Spreading Effect in Ridge Waveguide Electroabsorption Modulators

We investigate the lateral current spreading effect and its influences on the transmission characteristics of ridge waveguide electroabsorption modulators. An RF equivalent circuit based on a transmission line model explicitly accounting for this effect is proposed. The equivalent circuit parameters in our model extracted from $S_{11}$ curve fitting are used to simulate the $S_{21}$ response (electro-optical response (E/O) response), which matches well with the measured direct $S_{21}$ small-signal modulation response. The physical significance of our model parameters can be well explained based on the secondary ion mass spectroscopy doping profiling and the simulation of the current spreading effect in our device structure.

56 Gb/s Germanium Waveguide Electro-Absorption Modulator

We report a Germanium waveguide electro-absorption modulator with electro-optic bandwidth substantially beyond 50 GHz. The device is implemented in a fully integrated Si photonics platform on 200 mm silicon-on-insulator wafers with 220 nm top Si thickness. Wide open eye diagrams are demonstrated at 1610 nm operation wavelength for nonreturn-to-zero on-off keying (NRZ-OOK) modulation at data rates as high as 56 Gb/s. Dynamic extinction ratios up to 3.3 dB are obtained by applying drive voltages of 2 V peak-to-peak, along with an optical insertion loss below 5.5 dB. The device has a low junction capacitance of just 12.8 fF, resulting in 12.8 fJ/bit of dynamic and ∼1.2 mW of static power consumption in typical operating conditions. Wafer-scale performance data are presented and confirm the manufacturability of the device. The demonstrated modulator shows great potential for realizing high-density and low-power silicon photonic transceivers targeting short-reach optical interconnects at serial data rates of 56 Gb/s and beyond.

Enhanced performance of graphene-based electro-absorption waveguide modulators by engineered optical modes

Electro-absorption modulators based on electrically contacted double-layer graphene optimally incorporated in plasmonic and photonic waveguide configurations were simulated and analyzed in terms of the device performance at telecom wavelengths. It is shown that increasing the mode electric field strength on the graphene layers enhances absorption of graphene and, in consequence, improves the electro-optic performances. The ratio of the change in extinction ratio and the waveguide loss (Δα/α) is used as a figure of merit. A plasmonic waveguide configuration with a silicon ridge has a simulated 3 dB modulation depth for a device length of ~140 nm and Δα/α ~ 20. The calculated energy consumption per bit is as low as ~240 aJ bit−1 and ~1.8 aJ bit−1 for plasmonic modulators with polymer and silicon ridge waveguides respectively. Much higher figures of merit were obtained for modulators based on photonic waveguides with Δα/α exceeding 220 for a waveguide with a TM-supported mode. This comes at the cost of the modulator length, which increases to over 500 nm, and the calculated energy per bit of 1.93 fJ bit−1 for polymer and ~10.3 aJ bit−1 for silicon waveguides. The photonic waveguides were designed to support both TM and TE modes. The TE mode requires a much longer modulation length of ~10 µm to achieve a 3 dB modulation depth and shows a lower figure of merit of ~12 compared to the TM mode, but has a low energy per bit of ~44.0 aJ bit−1. The TE mode is in the OFF state at low applied voltage.

An all-solid-state, WDM silicon photonic digital link for chip-to-chip communications.

We describe a multiwavelength hybrid-integrated solid-state link on a 3 µm silicon-on-insulator (SOI) nanophotonic platform. The link spans three chips and employs germanium-silicon electroabsorption waveguide modulators, silicon transport waveguides, echelle gratings for multiplexing and demultiplexing, and pure germanium waveguide photo-detectors. The 8λ WDM Tx and Rx components are interconnected via a routing "bridge" chip using edge-coupled optical proximity communication. The packaged, retimed digital WDM link is demonstrated at 10 Gb/s and 10(-12) BER, with three wavelength channels consuming an on-chip power below 1.5 pJ/bit, excluding the external laser power.

Theoretical investigation of tensile strained GeSn waveguide with Si₃N₄ liner stressor for mid-infrared detector and modulator applications.

We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect.

Ultracompact vanadium dioxide dual-mode plasmonic waveguide electroabsorption modulator

AbstractSubwavelength modulators play an indispensable role in integrated photonic-electronic circuits. Due to weak light-matter interactions, it is always a challenge to develop a modulator with a nanometer scale footprint, low switching energy, low insertion loss and large modulation depth. In this paper, we propose the design of a vanadium dioxide dual-mode plasmonic waveguide electroabsorption modulator using a metal-insulator-VO2-insulator-metal (MIVIM) waveguide platform. By varying the index of vanadium dioxide, the modulator can route plasmonic waves through the low-loss dielectric insulator layer during the “on” state and high-loss VO2 layer during the “off” state, thereby significantly reducing the insertion loss while maintaining a large modulation depth. This ultracompact waveguide modulator, for example, can achieve a large modulation depth of ~10 dB with an active size of only 200×50×220 nm3 (or ~λ3/1700), requiring a drive-voltage of ~4.6 V. This high performance plasmonic modulator could potentially be one of the keys towards fully-integrated plasmonic nanocircuits in the next-generation chip technology.

Tensile-Strained Ge/SiGeSn Quantum Wells for Polarization-Insensitive Electro-Absorption Waveguide Modulators

We present design and modeling of a polarization-insensitive electro-absorption waveguide modulator operating at 1550 nm. Our design uses tensile-strained Ge-Si <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> Ge <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x-y</sub> quantum wells as the active material grown on a relaxed SiGeSn buffer on a silicon substrate, compatible with complementary metal-oxide semiconductor (CMOS) processes. Introducing tensile strain in the Ge wells can effectively reduce the direct bandgap for optimal modulation at the critical 1550 nm wavelength, and provide polarization-insensitive electro-absorption properties. We present a theoretical model for the electronic band structure, excitonic absorption coefficient, and polarization-dependent optical confinement factor. We also bring forth a waveguide design based on index guidance, where we calculate the optical confinement factors of various regions to determine the extinction ratio and insertion loss. The proposed modulator operating at 1550 nm can offer unique advantages for use in high-performance, CMOS-compatible electronic-photonic integrated circuits.

Ge/SiGe Quantum Well Waveguide Modulator Monolithically Integrated With SOI Waveguides

We report a Ge/SiGe quantum well waveguide electroabsorption modulator that is monolithically integrated with silicon-on-insulator waveguides. The active quantum well section is selectively grown on a silicon-on-insulator substrate and has a footprint of 8 . The integrated device demonstrates more than 3.2-dB contrast ratio with 1-V direct voltage swing at 3.5 GHz. We also show the potential of this device to operate in the telecommunication C-band at room temperature.

Investigation of Semiconductor Quantum Dots for Waveguide Electroabsorption Modulator

In this work, we investigated the use of 10-layer InAs quantum dot (QD) as active region of an electroabsorption modulator (EAM). The QD-EAM is a p-i-n ridge waveguide structure with intrinsic layer thickness of 0.4 μm, width of 10 μm, and length of 1.0 mm. Photocurrent measurement reveals a Stark shift of ~5 meV (~7 nm) at reverse bias of 3 V (75 kV/cm) and broadening of the resonance peak due to field ionization of electrons and holes was observed for E-field larger than 25 kV/cm. Investigation at wavelength range of 1,300–1320 nm reveals that the largest absorption change occurs at 1317 nm. Optical transmission measurement at this wavelength shows insertion loss of ~8 dB, and extinction ratio of ~5 dB at reverse bias of 5 V. Consequently, methods to improve the performance of the QD-EAM are proposed. We believe that QDs are promising for EAM and the performance of QD-EAM will improve with increasing research efforts.

Optically controlled electroabsorption modulators for unconstrained wavelength conversion

We introduce a proof-of-concept, optically controlled, optical switch based on the monolithic integration of a surface-illuminated photodetector and a waveguide electroabsorption modulator. We demonstrate unconstrained wavelength conversion over the entire center telecommunication wavelength band (C band) and optical switching up to 2.5 Gbit/s with extinction ratios exceeding 10 dB. Our approach offers both high-speed, low-power, switching operation and two-dimensional array scalability for the fabrication of chip-scale reconfigurable multichannel wavelength converters.

Fabrication of wide-band electro-absorption waveguide modulator arrays using quantum well-intermixing process

The present paper reports on the demonstration of wide optical bandwidth electro-absorption waveguide modulator arrays fabricated on a single InGaAs/InGaAsP wafer chip using a gray-mask-based quantum well intermixing. Both micro-Raman and photoluminescence measurements have shown that the quality of the material concerning is maintained after the ion implantation-induced process. Multiple energy bandgap sections for absorbing at different wavelengths with a large modulation depth have been achieved in modulator arrays, with around 60 nm as the modulating bandwidth. An intensity modulation depth of about −16 dB has been obtained at −5 V bias for these modulator arrays.

Dynamical simulation of quantum-well structures

For the design and development of optical semiconductor devices based on quantum-well structures, the investigation of saturation phenomena is necessary for high optical power operation. By applying stationary physical models, nonlinear effects cannot be described adequately; hence, transient models are important for an accurate analysis. By utilizing transient models, saturation phenomena, signal delays, and distortions can be investigated. For the analysis of integrated optoelectronic devices, such as lasers and modulators, transient transport or density matrix equations for carriers and photons and the Poisson equation have to be solved self-consistently. A transient model which is useful for the investigation of a wide range of optoelectronic applications is presented. Quantum optical phenomena are included by applying the interband density matrix formalism in real-space representation, where the Coulomb singularity is treated exactly in the limits of the discretization. As we focus on electroabsorption modulators, a drift-diffusion model adequately approximates the transport properties. Here, quantum effects are considered by a quantum correction, the Bohm potential. The model is applied to investigate transport effects in InP-based waveguide electroabsorption modulators including strained lattices.

A Wannier-Stark waveguide electroabsorption modulator as a low-power switch and its application as NAND, NOR or EXOR all-optical logic gates

A resistor-biased self-electro-optic-effect device in waveguide geometry has been realized with an electroabsorption modulator containing an InGaAs/InP superlattice as the waveguide core. Room-temperature all-optical switching has been experimentally observed over a wide wavelength range between 1.51 and 1.58 µm. Simulation of the device response to time-varying digital optical input signals shows that it is possible to obtain optical logic operation using these devices. Boolean functions such as NAND and NOR can be realized at 1.55 µm and EXOR operation at 1.51 µm at fairly low optical power levels. The functionality is however rather sensitive to optical bias power variations.

High-efficiency fiber-to-chip coupling using low-loss tapered single-mode fiber

We report on the wet chemical fabrication of tapered step-index single-mode fibers and the low-loss coupling between these fibers and III-V semiconductor waveguide structures. Nearly adiabatic tapered fibers with an average transformation loss of 0.13 dB and mode field diameters ranging between 10.6 μm and 0.8 μm have been fabricated. Experimentally, tapered fibers have been coupled to 1.55-μm InGaAsP-InP waveguide electroabsorption modulators with a minimum coupling loss of only 1.1 dB.

Combined Franz-Keldysh and quantum-confined Stark effect waveguide modulator for analog signal transmission

A novel approach to the design of electroabsorption waveguide modulators for use in broadband, analog radio frequency (RF) links is presented. The approach utilizes a linear combination of two electroabsorption effects (the Franz-Keldysh effect and the quantum-confined Stark effect) to improve the spurious-free dynamic range of the waveguide modulator. Measured transfer curves verify simultaneous improvement in linearity and modulation efficiency for an exemplary combination structure. Residual absorption is modeled to determine the impact on modulation efficiency.

RIGOROUS ANALYSIS OF 3D OPTICAL AND OPTOELECTRONIC DEVICES BY THE COMPACT-2D-FDTD METHOD

Continous advances in material technology, in the field of integrated optics and optoelectronics, allow the realization of devices with geometries more and more compact and complex. Because of this trend, there is a parallel need for accurate fully numerical CAD tools. Among new ones, the FDTD method, already widely and successfully used for the characterization of microwave and millimeter-wave devices, is emerging in optics community because of its accuracy and versatility. However, in spite of the tremendous increase in computing power, the applicability of the method is still limited by the typical dimensions of optical structures. To overcome these limitations a specialized version of the FDTD algorithm for the rigorous analysis of 3D optical and optoelectronic devices is proposed and validated. This new technique is then used to characterize the optical behaviour of a MQW waveguide electroabsorption modulator.

Low-loss 1.3-/spl mu/m MQW electroabsorption modulators for high-linearity analog optical links

Low-loss InAsP-GaInP multiquantum-well electroabsorption waveguide modulators have been developed for transmitting microwaves as subcarriers over optical fibers. The fiber-to-fiber insertion loss is only 5 dB at 1.32-/spl mu/m wavelength. The electrooptic slope efficiency of an 185-/spl mu/m-long 11-GHz bandwidth device is equivalent to a Mach-Zehnder modulator with a V/sub /spl pi// of 2.2 V. The linearity performance was characterized for a test link without any form of amplification. A RF-to-RF link efficiency of -25.5 dB, noise figure of 27 dB and suboctave spurious-free dynamic range of 114 dB.Hz/sup 4/5/ have been achieved with 16 mW input optical carrier power. The measured 3-dB electrical bandwidth exceeds 20 GHz for a 90-/spl mu/m-long device.