Silicon-organic Hybrid Slot Waveguide Research Articles

Enhanced optical nonlinearity in a silicon–organic hybrid slot waveguide for all-optical signal processing

Silicon photonic integrated devices used for nonlinear optical signal processing play a key role in ultrafast switching, computing, and modern optical communications. However, current devices suffer from limited operation speeds and low conversion efficiencies due to the intrinsically low nonlinear index of silicon. In this paper, we experimentally demonstrate enhanced optical nonlinearity in a silicon–organic hybrid slot waveguide consisting of an ultranarrow slot waveguide coated with a highly nonlinear organic material. The fabricated slot area is as narrow as 45 nm, which is, to the best of our knowledge, the narrowest slot width that has been experimentally reported in silicon slot waveguides. The nonlinear coefficient of the proposed device with a length of 3 mm is measured to be up to 1.43 × 10 6 W − 1 km − 1 . Based on the nanostructure design, the conversion efficiencies of degenerate four-wave mixing showed enhancements of more than 12 dB and 5 dB compared to those measured for an identical device without the organic material and a silicon strip waveguide, respectively. As a proof of concept, all-optical canonical logic units based on the prepared device with two inputs at 40 Gb/s are analyzed. The obtained logic results showed clear temporal waveforms and wide-open eye diagrams with error-free performance, illustrating that our device has great potential for use in high-speed all-optical signal processing and high-performance computing in the nodes and terminals of optical networks.

Phase-frequency jointly quantizing method for cost-effective all-optical analog-to-digital conversion

We propose for the first time a two-dimensional phase-frequency jointly quantizing method for cost-effective all-optical analog-to-digital conversion (ADC), both on power consumption and structure complexity. By fully harnessing the power-dependent phase and frequency shift of the probe and pump light, respectively, that simultaneously occurs during the cross-phase modulation process, the method is studied with an on-chip interferometer structure based on nonlinear silicon-organic hybrid slot waveguide. Simulation results show the 4-bit quantization resolution is achieved by using only one interferometer, where N interferometers should be used in the conventional methods with resolution of N-bit. The proposed method provides an efficient optical quantization technique for all-optical ADC, also opens a new mind for exploring advanced all-optical ADC techniques using multi-dimensional degrees of freedom of light.

Comparative Study of Nano-Slot Silicon Waveguides Covered by Dye Doped and Undoped Polymer Cladding

Nonlinear optical dyes doped in optical polymer matrices are widely used for electro-optical devices. Linear optical properties change with dye concentration, which leads to a change in modal properties, especially in nano-structured integrated waveguides such as silicon slot-waveguides. Here, we investigate the influence of a nonlinear optical dye on the performance of a silicon-organic hybrid slot-waveguide. A simulation study of the modal and optical confinement properties is carried out and dependence of the structural parameters of the slot-waveguide and the organic cladding material is taken into account. As cladding material, a guest-host polymer system is employed comprising the nonlinear optical dye Disperse Red 1 (DR1) doped in a poly[methyl methacrylate] (PMMA) matrix. The refractive indices of doped and undoped PMMA were deduced from ellipsometric data. We present a guideline for an optimized slot-waveguide design for the fabrication in silicon-on-insulator technology giving rise to scalable, high-performance integrated electro-optical modulators.

Impact of two-photon absorption and free-carrier effects on time lens based on four-wave mixing in silicon waveguides

We investigate the influences of two-photon absorption (TPA) and free-carrier effects on a time lens via four-wave mixing in silicon waveguides. It is found that the output waveform is severely modulated and the conversion efficiency is sharply reduced in temporal imaging owing to the impacts of the nonlinear absorption. A silicon–organic hybrid slot waveguide with negligible TPA is proposed for the time lens, which could realize 600× magnification of femtosecond pulses. These results can increase the signal bandwidth from gigahertz to terahertz and give rise to important potential applications for ultrafast optical signal processing in integrated optics, ultrafast optics, and optical communications.

Advanced Nanophotonics: Silicon-Organic Hybrid Technology

Integrated photonic devices have gained increasing research interests. Especially silicon photonics have become very attractive for various optical applications. Using silicon-on-insulator as a material platform provides the ability to fabricate photonic devices with electronic devices on a single chip. Driven by substantial research investments, the integration of photonic devices on silicon-on-insulator substrates has reached a degree of maturity that already permits industrial adoption. However, silicon has the disadvantage of linear electro-optical effects, and, therefore, advanced modulation formats are difficult to realize when using silicon-based high-speed modulators. Hence, a new approach was proposed: the silicon-organic hybrid technology. This technology is a viable extension of the silicon-on-insulator material system for efficient high-speed modulation. We herewith present our theoretical and experimental investigations of the silicon-organic hybrid slot-waveguide ring resonator. The advanced device design is described in detail, which allows using both, the efficient silicon-on-insulator strip-waveguides and the silicon-organic hybrid slot-waveguides in single ring resonator. For the first time, we report the transmission spectra of such a resonator covered with an electro-optical polymer.

On-chip integratable all-optical quantizer using strong cross-phase modulation in a silicon-organic hybrid slot waveguide.

High performance all-optical quantizer based on silicon waveguide is believed to have significant applications in photonic integratable optical communication links, optical interconnection networks, and real-time signal processing systems. In this paper, we propose an integratable all-optical quantizer for on-chip and low power consumption all-optical analog-to-digital converters. The quantization is realized by the strong cross-phase modulation and interference in a silicon-organic hybrid (SOH) slot waveguide based Mach-Zehnder interferometer. By carefully designing the dimension of the SOH waveguide, large nonlinear coefficients up to 16,000 and 18,069 W−1/m for the pump and probe signals can be obtained respectively, along with a low pulse walk-off parameter of 66.7 fs/mm, and all-normal dispersion in the wavelength regime considered. Simulation results show that the phase shift of the probe signal can reach 8π at a low pump pulse peak power of 206 mW and propagation length of 5 mm such that a 4-bit all-optical quantizer can be realized. The corresponding signal-to-noise ratio is 23.42 dB and effective number of bit is 3.89-bit.

Strong Modulation Instability in a Silicon–Organic Hybrid Slot Waveguide

In this paper, we investigate the strong modulation instability (MI) at telecommunication band in a silicon–organic hybrid slot waveguide. The organic material of polymer poly (bis para-toluene sulfonate) of 2, 4-hexadiyne 1, 6 diol (PTS), which has high third-order nonlinear refractive index and very low two-photon absorption, is used to fill the slot of the waveguide. The optical gain can be up to $\sim$ 3600 ${\rm m}^{-1} $ with a low pump peak power of 300 mW. By using Gaussian pulses with width of 10 ps and peak power of 250 mW, deep modulation of the pump is achieved, and the ultrashort pulse trains with the periods of 27 and 24 fs are obtained in the anomalous and normal group-velocity dispersion regions, respectively.

Chip-scale optical interconnects and optical data processing using silicon photonic devices

Recent advances in the density and complexity of photonic integrated circuits have facilitated possible implementation of chip-scale optical communication systems. Chip-scale optical interconnects and optical data processing are two important functions to transmit and process signal in the optical domain. Silicon photonics offers a promising platform to enable chip-scale optical interconnects and optical data processing using silicon photonic devices. In this paper, we review our recent progress in the design, modeling, and fabrication of silicon photonic devices and their applications in chip-scale optical interconnects and optical data processing with advanced modulation formats. For chip-scale optical interconnects, we experimentally demonstrate digital signal transmissions in silicon microring and silicon vertical slot waveguide. Terabit chip-scale optical interconnect is demonstrated in the experiment. Also, we experimentally demonstrate analog signal transmissions in silicon microring and silicon photonic crystal nanocavity. For chip-scale optical data processing, we experimentally demonstrate all-optical wavelength conversion using a silicon waveguide, simultaneous polarization and wavelength demultiplexing using 2D grating coupler connected with microrings, two-mode (de)multiplexing using a tapered asymmetrical grating-assisted contra-directional coupler, and two-/three-mode (de)multiplexing using asymmetrical directional converter. In addition, we propose and simulate chip-scale optical data exchange, chip-scale high-base optical computing, and chip-scale optical coding/decoding by using nonlinear interactions in a silicon-organic hybrid slot waveguide. The obtained theoretical and experimental results of chip-scale optical interconnects and optical data processing indicate possible integration of optical communication functions on a monolithic chip.

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.

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.

All-optical high-speed signal processing with silicon–organic hybrid slot waveguides

Integrated optical circuits based on silicon-on-insulator technology are likely to become the mainstay of the photonics industry. Over recent years an impressive range of silicon-on-insulator devices has been realized, including waveguides1,2, filters3,4 and photonic-crystal devices5. However, silicon-based all-optical switching is still challenging owing to the slow dynamics of two-photon generated free carriers. Here we show that silicon–organic hybrid integration overcomes such intrinsic limitations by combining the best of two worlds, using mature CMOS processing to fabricate the waveguide, and molecular beam deposition to cover it with organic molecules that efficiently mediate all-optical interaction without introducing significant absorption. We fabricate a 4-mm-long silicon–organic hybrid waveguide with a record nonlinearity coefficient of γ ≈ 1 × 105 W−1 km−1 and perform all-optical demultiplexing of 170.8 Gb s−1 to 42.7 Gb s−1. This is—to the best of our knowledge—the fastest silicon photonic optical signal processing demonstrated. A silicon–organic hybrid slot waveguide with a strong optical nonlinearity is demonstrated to perform ultrafast all-optical demultiplexing of high-bit-rate data streams. The approach could form the basis of compact high-speed optical processing units for future communication networks.