Silicon-organic Hybrid Research Articles

Silicon-organic hybrid slot waveguide based three-input multicasted optical hexadecimal addition/subtraction.

By exploiting multiple non-degenerate four-wave mixing in a silicon-organic hybrid slot waveguide and 16-ary phase-shift keying signals, we propose and simulate three-input (A, B, C) multicasted 40-Gbaud (160-Gbit/s) optical hexadecimal addition/subtraction (A + B − C, A + C − B, B + C − A, A + B + C, A − B − C, B − A − C). The error vector magnitude (EVM) and dynamic range of signal power are analyzed to evaluate the performance of optical hexadecimal addition/subtraction.

Low-power silicon-organic hybrid (SOH) modulators for advanced modulation formats.

We demonstrate silicon-organic hybrid (SOH) electro-optic modulators that enable quadrature phase-shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM) with high signal quality and record-low energy consumption. SOH integration combines highly efficient electro-optic organic materials with conventional silicon-on-insulator (SOI) slot waveguides, and allows to overcome the intrinsic limitations of silicon as an optical integration platform. We demonstrate QPSK and 16QAM signaling at symbol rates of 28 GBd with peak-to-peak drive voltages of 0.6 V(pp). For the 16QAM experiment at 112 Gbit/s, we measure a bit-error ratio of 5.1 × 10⁻⁵ and a record-low energy consumption of only 19 fJ/bit.

Optical data exchange of m-QAM signals using a silicon-organic hybrid slot waveguide: proposal and simulation.

We present modulation-format-transparent data exchange for m-ary quadrature amplitude modulation (m-QAM) signals using a single silicon-organic hybrid slot waveguide which offers tight light confinement and enhanced nonlinearity. By exploiting the parametric depletion effect of non-degenerate four-wave mixing (ND-FWM) process in the slot waveguide, we simulate low-power (<10 mW) ultrahigh-speed optical data exchange of 640 Gbaud (2.56 Tbit/s) optical time-division multiplexed (OTDM) 16-QAM and 640 Gbaud (3.84 Tbit/s) OTDM 64-QAM signals and characterize the operation performance in terms of error vector magnitude (EVM) and bit-error rate (BER). The calculated signal-to-noise ratio (SNR) penalties of data exchange are negligible for 2.56 Tbit/s 16-QAM signals and less than 2 dB for 3.84 Tbit/s 64-QAM signals at a BER of 2e-3. For a given pump power of 9 mW, the operation performance dependence on the waveguide length is studied, showing an optimized waveguide length of ~17 mm. For a given waveguide length of 17 mm, the SNR penalty of data exchange, at a BER of 2e-3, is kept below 4 dB when varying input pump power from 8.4 to 9.8 mW for 2.56 Tbit/s 16-QAM and from 8.9 to 9.2 mW for 3.84 Tbit/s 64-QAM. In addition, data exchange running at low speed (e.g. 20 Gbaud) and data exchange taking into account waveguide propagation loss are also analyzed with favorable operation performance.

Optimum Exchange for Calculation of Excitation Energies and Hyperpolarizabilities of Organic Electro-optic Chromophores.

Organic electro-optic (OEO) materials integrated into silicon-organic hybrid devices afford significant improvements in size, weight, power, and bandwidth performance of integrated electronic/photonic systems critical for current and next generation telecommunication, computer, sensor, transportation, and defense technologies. Improvement in molecular first hyperpolarizability (β), and in turn electro-optic activity, is crucial to optimizing device performance. Common hybrid density functional theory (DFT) methods, while attractive due to their computational scaling, often perform poorly for optical properties in systems with substantial intramolecular charge-transfer character, such as OEO chromophores. This study evaluates the utility of the long-range corrected (LC) DFT methods for computation of the molecular second-order nonlinear optical response. We compare calculated results for a 14-molecule benchmark set of OEO chromophores with the corresponding experimentally measured β and one-photon absorption energy, λmax. We analyze the distance dependence of the fraction of exact exchange in LC-DFT methods for accurately computing these properties for OEO chromophores. We also examine systematic tuning of the range-separation parameter to enforce Koopmans'/ionization potential theorem. This tuning method improves prediction of excitation energies but is not reliable for predicting the hyperpolarizabilities of larger chromophores since the tuning parameter value can be too small, leading to instabilities in the computation of βHRS. Additionally, we find that the size dependence of the optimal tuning parameter for the ionization potential has the opposite size dependence of optimal tuning parameter for best agreement with the experimental λmax, suggesting the tuning for the ionization potential is unreliable for extended conjugated systems.

Wavelength conversion in highly nonlinear silicon-organic hybrid slot waveguides.

Wavelength conversion based on four-wave mixing (FWM) in a silicon-organic hybrid slot waveguide is theoretically investigated in the telecommunication bands. Compared with vertical slot waveguides, the horizontal slot waveguide structure exhibits much flatter dispersion. The maximum nonlinearity coefficient γ of 1.5×10⁷ W⁻¹ km⁻¹ and the minimum effective mode area A(eff) of 0.065 μm² are obtained in a horizontal slot waveguide with a 20-nm-thick optically nonlinear layer by controlling the geometric parameters. The wavelength conversion efficiency of 7.45 dB with a pump power of 100 mW in a 4-mm-long horizontal slot waveguide is obtained. This low power on-chip wavelength convertor will have potential applications in highly integrated optical circuits.

High-Speed, Low Drive-Voltage Silicon-Organic Hybrid Modulator Based on a Binary-Chromophore Electro-Optic Material

We report on the hybrid integration of silicon-on-insulator slot waveguides with organic electro-optic materials. We investigate and compare a polymer composite, a dendron-based material, and a binary-chromophore organic glass (BCOG). A record-high in-device electro-optic coefficient of 230 pm/V is found for the BCOG approach resulting in silicon-organic hybrid Mach-Zehnder modulators that feature low $U_{\pi }L$ -products of down to 0.52 Vmm and support data rates of up to 40 Gbit/s.

100 GHz silicon–organic hybrid modulator

AbstractElectro-optic modulation at frequencies of 100 GHz and beyond is important for photonic-electronic signal processing at the highest speeds. To date, however, only a small number of devices exist that can operate up to this frequency. In this study, we demonstrate that this frequency range can be addressed by nanophotonic, silicon-based modulators. We exploit the ultrafast Pockels effect by using the silicon–organic hybrid (SOH) platform, which combines highly nonlinear organic molecules with silicon waveguides. Until now, the bandwidth of these devices was limited by the losses of the radiofrequency (RF) signal and the RC (resistor-capacitor) time constant of the silicon structure. The RF losses are overcome by using a device as short as 500 µm, and the RC time constant is decreased by using a highly conductive electron accumulation layer and an improved gate insulator. Using this method, we demonstrate for the first time an integrated silicon modulator with a 3dB bandwidth at an operating frequency beyond 100 GHz. Our results clearly indicate that the RC time constant is not a fundamental speed limitation of SOH devices at these frequencies. Our device has a voltage–length product of only VπL=11 V mm, which compares favorably with the best silicon-photonic modulators available today. Using cladding materials with stronger nonlinearities, the voltage–length product is expected to improve by more than an order of magnitude.

Integrated Photonic Electromagnetic Field Sensor Based on Broadband Bowtie Antenna Coupled Silicon Organic Hybrid Modulator

We present the design, fabrication and characterization of a compact and highly sensitive integrated photonic electromagnetic field sensor based on a silicon-organic hybrid modulator driven by a bowtie antenna. Slow-light effects in the electro-optic (EO) polymer refilled silicon slot photonic crystal waveguide (PCW), together with broadband electric field enhancement provided by the bowtie antenna, are utilized to enhance the interaction of microwaves and optical waves, enabling an ultra large effective in-device EO coefficient over 1000 pm/V and thus a high sensitivity. The EO polymer refilled slot PCW is designed for low-dispersion slow-light propagation, high poling efficiency, and high optical mode confinement inside the slot. The bowtie antenna acts not only as a receiving antenna, but also as poling electrodes during the fabrication process. A bowtie antenna integrated on doped silicon slot PCW is demonstrated to have a broad operational bandwidth, with a maximum resonance at the frequency of 10 GHz. The strongly enhanced broadband electric field is used to directly modulate the phase of the optical waves propagating through the slot PCW embedded inside the feed gap of the bowtie antenna. The phase modulation is then converted to intensity modulation using an external reference arm to form a Mach-Zehnder interferometer in our experimental setup. The sensing of electromagnetic field at 8.4 GHz is experimentally demonstrated, with a minimum detectable electromagnetic power density of 8.4 mW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , corresponding to a minimum detectable electric field of 2.5 V/m.

Electro-Optic Organic Crystal Silicon High-Speed Modulator

Silicon waveguides can be functionalized with an organic χ(2)-nonlinear cladding. This complements silicon photonics with the electro-optic (EO) effect originating from the cladding and enables functionalities such as pure phase modulation, parametric amplification, or THz-wave generation. Claddings based on a polymer matrix containing chromophores have been introduced, and their strong χ(2) nonlinearity has already been used to demonstrate ultralow power consuming modulators. However, these silicon-organic hybrid (SOH) devices inherit not only the advantageous properties; these polymer claddings require an alignment procedure called poling and must be operated well below their glass transition temperature. This excludes some applications. In contrast, claddings made from organic crystals come with a different set of properties. In particular, there is no need for poling. This new class of claddings also promises stronger resilience to high temperatures, better long-term stability, and photo-chemical stability. We report on the deposition of an organic crystal cladding of N-benzyl-2-methyl-4-nitroaniline (BNA) on silicon-on-insulator (SOI) waveguides, which have a CMOS-like metal stack on top. Adhering to such an architecture, which preserves the principal advantage of using CMOS-based silicon photonic fabrication processes, permits the first demonstration of high-speed modulation at 12.5 Gbit/s in this material class, which proves the availability of the EO effect from BNA on SOI also for other applications.

Silicon-organic hybrid (SOH) frequency comb sources for terabit/s data transmission

We demonstrate frequency comb sources based on silicon-organic hybrid (SOH) electro-optic modulators. Frequency combs with line spacings of 25 GHz and 40 GHz are generated, featuring flat-top spectra with less than 2 dB power variations over up to 7 lines. The combs are used for WDM data transmission at terabit/s data rates and distances of up to 300 km.

Silicon-Organic Hybrid Electro-Optical Devices

Organic materials combined with strongly guiding silicon waveguides open the route to highly efficient electro-optical devices. Modulators based on the so-called silicon-organic hybrid (SOH) platform have only recently shown frequency responses up to 100 GHz, high-speed operation beyond 112 Gbit/s with fJ/bit power consumption. In this paper, we review the SOH platform and discuss important devices such as Mach-Zehnder and IQ-modulators based on the linear electro-optic effect. We further show liquid-crystal phase-shifters with a voltage-length product as low as VπL = 0.06 V·mm and sub-μW power consumption as required for slow optical switching or tuning optical filters and devices.

Low Power Mach–Zehnder Modulator in Silicon-Organic Hybrid Technology

We report on a silicon-organic hybrid modulator based on a Mach-Zehnder interferometer (MZI) operating at 10 Gbit/s with an energy consumption of 320 fJ/bit. The device consists of a striploaded slot waveguide covered with an electro-optic polymer cladding. The MZI modulator is poled to be driven in push-pull operation by a single coplanar RF line. Our nonlinear coefficient r33 = 15 pm/V in combination with an 80 nm narrow slot enables RF peak-to-peak drive voltages as low as 800 mVpp to suffice for an extinction ration of 4.4 dB for a 1.5 mm long modulator.

Efficient second harmonic generation from mid-infrared to near-infrared regions in silicon-organic hybrid plasmonic waveguides with small fabrication-error sensitivity and a large bandwidth

We theoretically investigate the quadratic nonlinear property of a silicon-organic hybrid plasmonic waveguide with a thin polymer layer deposited on top of a silicon slab and covered by a metal cap. Due to the hybridization property of the waveguide modes, efficient phase-matched second harmonic generation (SHG) from mid-infrared (IR) (~3.1 μm) to near-IR (~1.55 μm) wavelengths are achieved with a small fabrication-error sensitivity (225 nm ≤ tolerated waveguide width ≤ 378 nm) and a large bandwidth (Δλ=100 nm). The SHG yield is as large as 8.8% for a pumping power of 100 mW.

Silicon-organic hybrid (SOH) IQ modulator using the linear electro-optic effect for transmitting 16QAM at 112 Gbit/s

Advanced modulation formats call for suitable IQ modulators. Using the silicon-on-insulator (SOI) platform we exploit the linear electro-optic effect by functionalizing a photonic integrated circuit with an organic χ(2)-nonlinear cladding. We demonstrate that this silicon-organic hybrid (SOH) technology allows the fabrication of IQ modulators for generating 16QAM signals with data rates up to 112 Gbit/s. To the best of our knowledge, this is the highest single-polarization data rate achieved so far with a silicon-integrated modulator. We found an energy consumption of 640 fJ/bit.

Silicon-Organic Hybrid MZI Modulator Generating OOK, BPSK and 8-ASK Signals for Up to 84 Gbit/s

We report on high-speed multilevel signal generation and arbitrary pulse shaping with silicon-organic hybrid (SOH) Mach-Zehnder interferometer (MZI) modulators. Pure phase modulation exploiting the linear electrooptic effect allows the generation of multiple modulations formats at highest speed such as 40-Gbit/s on-off-keying (OOK) and binary-phase-shift keying (BPSK) and 28-Gbd 4-ASK and 8-ASK with data rates up to 84 Gbit/s. Additionally, beside NRZ pulse shaping, for the first time, Nyquist pulse shaping with silicon modulators is demonstrated to enable multiplexing at highest spectral efficiency.

A New Route to Nondestructive Top-Contacts for Molecular Electronics on Si: Pb Evaporated on Organic Monolayers.

Thermally evaporated Pb preserves the electronic properties of an organic monolayer (ML) on Si and surface passivation of the Si surface itself. The obtained current-voltage characteristics of Pb/ML/Si junctions agree with results obtained with the well-established Hg contact and preserve both the molecule-induced dipole effect on, and length-attenuation of, the current. We rationalize our findings by the lack of interaction between the Pb and the Si substrate. This method is fast, scalable, and compatible with standard semiconductor processing, results in close to 100% yield, and can help the development of large-scale utilization of silicon-organic hybrid electronics. Our experimental data show a dependence of the transport across the molecules on the substrate orientation, expressed in the smaller distance decay parameter with Si(100) than that with Si(111).

Second-order nonlinear silicon-organic hybrid waveguides

We describe a concept for second-order nonlinear optical processes in silicon photonics. A silicon-organic hybrid (SOH) double slot waveguide is dispersion-engineered for mode phase-matching (MPM). The proposed waveguide enables highly efficient nonlinear processes in the mid-IR range. With a cladding nonlinearity of χ(2) = 230 pm/V and 20 dBm pump power at a CW wavelength of 1550 nm, we predict a gain of 14.7 dB/cm for a 3100 nm signal. The suggested structure enables for the first time efficient second-order nonlinear optical mixing in silicon photonics with standard technology.

Silicon-organic hybrid phase shifter based on a slot waveguide with a liquid-crystal cladding

A highly efficient phase shifter based on the silicon-organic hybrid (SOH) platform is theoretically investigated and experimentally tested. The device consists of a silicon slot waveguide covered with an organic liquid-crystal (LC) cladding. A record-low voltage-length product of U(π)L = 0.085 Vmm can be achieved for high-purity materials where an optimum operation point can be set by a DC bias. With standard materials and without a DC bias, we measure a phase shift of 35π with a drive voltage of only 5 V for a 1.7 mm long device corresponding to a voltage-length product of U(π)L = 0.24 Vmm. The power dissipation is about six orders of magnitude smaller than that of state-of-the-art thermo-optic devices, thereby enabling dense integration of LC phase shifters in advanced photonic integrated circuits.

A high speed electro-optic phase shifter based on a polymer-infiltrated P-S-N diode capacitor

A polymer-infiltrated P-S-N diode capacitor configuration is proposed and a high speed electro-optic phase shifter based on a silicon organic hybrid platform is designed and modeled. The structure enables fast carrier depletion in addition to the second order nonlinearity so that a large electro-optic overlapped volume is achievable. Moreover, the device speed can be significantly improved with the introduction of free carriers due to a reduced experienced transient capacitance. The advantages of the diode capacitor structure are highly suitable for application to a class of low aspect ratio slot waveguides where the RC limitation of the radio frequency response is minimized. According to our numerical results, by optimizing both the waveguide geometry and polarization mode, at least 269 GHz 3-dB bandwidth with high efficiency of 5.5 V-cm is achievable. More importantly, the device does not rely on strong optical confinement within the nano-slot, a feature that gives considerable tolerance in the use of nano-fabrication techniques. Finally, the high overlap and energy efficiency of the device can be applied to slow light or optical resonance media for realizing photonic integrated circuits-based green photonics.

427 Gbit/s electro-optic modulator in silicon technology

CMOS-compatible optical modulators are key components for future silicon-based photonic transceivers. However, achieving low modulation voltage and high speed operation still remains a challenge. As a possible solution, the silicon-organic hybrid (SOH) platform has been proposed. In the SOH approach the optical signal is guided by a silicon waveguide while the electro-optic effect is provided by an organic cladding with a high χ(2)-nonlinearity. In these modulators the optical nonlinear region needs to be connected to the modulating electrical source. This requires electrodes, which are both optically transparent and electrically highly conductive. To this end we introduce a highly conductive electron accumulation layer which is induced by an external DC "gate" voltage. As opposed to doping, the electron mobility is not impaired by impurity scattering. This way we demonstrate for the first time data encoding with an SOH electro-optic modulator. Using a first-generation device at a data-rate of 42.7 Gbit/s, widely open eye diagrams were recorded. The measured frequency response suggests that significantly larger data rates are feasible.