Showing papers on "Silicon photonics published in 2004"

A high-speed silicon optical modulator based on a metal–oxide–semiconductor capacitor

Abstract: Silicon has long been the optimal material for electronics, but it is only relatively recently that it has been considered as a material option for photonics1. One of the key limitations for using silicon as a photonic material has been the relatively low speed of silicon optical modulators compared to those fabricated from III–V semiconductor compounds2,3,4,5,6 and/or electro-optic materials such as lithium niobate7,8,9. To date, the fastest silicon-waveguide-based optical modulator that has been demonstrated experimentally has a modulation frequency of only ∼20 MHz (refs 10, 11), although it has been predicted theoretically that a ∼1-GHz modulation frequency might be achievable in some device structures12,13. Here we describe an approach based on a metal–oxide–semiconductor (MOS) capacitor structure embedded in a silicon waveguide that can produce high-speed optical phase modulation: we demonstrate an all-silicon optical modulator with a modulation bandwidth exceeding 1 GHz. As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible.

Silicon Photonics: An Introduction

Abstract: About the Authors.Foreword.Acknowledgements.1. Fundamentals.2. The Basics of Guided Waves.3. Characteristics of Optical Fibres for Communications.4. Silicon-on-Insulator (SOI) Photonics.5. Fabrication of Silicon Waveguide Devices.6. A Selection of Photonic Devices.7. Polarisation-dependent Losses: Issues for Consideration.8. Prospects for Silicon Light-emitting Devices.Index.

Optical bistability on a silicon chip.

Abstract: We demonstrate, for the first time to our knowledge, optical bistability on a highly integrated silicon device, using a 5-microm-radius ring resonator. The strong light-confinement nature of the resonator induces nonlinear optical response with low pump power. We show that the optical bistability allows all-optical functionalities, such as switching and memory with microsecond time response and a modulation depth of 10 dB, driven by pump power as low as 45 microW. Silicon optical bistability relies on a fast thermal nonlinear optical effect presenting a 500-kHz modulation bandwidth.

Influence of nonlinear absorption on Raman amplification in Silicon waveguides.

Abstract: We model the TPA-induced free carrier absorption effect in silicon Raman amplifiers and quantify the conditions under which net gain may be obtained. The achievable Raman gain strongly depends on the free carrier lifetime, propagation loss, and on the effective Raman gain coefficient, through pump-induced broadening.

All optical switching and continuum generation in silicon waveguides

Abstract: First demonstration of cross phase modulation based interferometric switch is presented in silicon on insulator waveguides. By using Mach-Zehnder interferometric configuration we experimentally demonstrate switching of CW signal ~25 nm away from the pump laser. We present the effect of free carrier accumulation on switching. Additionally, we theoretically analyze the transient effects and degradations due to free carrier absorption, free carrier refraction and two photon absorption effects. Results suggest that at low peak power levels the system is governed by Kerr nonlinearities. As the input power levels increase the free carrier effects becomes dominant. Effect of free carrier generation on continuum generation and power transfer also theoretically analyzed and spectral broadening factor for high input power levels is estimated.

Theory of optical signal amplification and processing by quantum-dot semiconductor optical amplifiers

Abstract: This work presents a theory of optical signal amplification and processing by quantum-dot semiconductor optical amplifiers (SOA's) based on the density matrix equations to treat electron-light interaction and the optical pulse propagation equations. The theory includes the linear optical response as well as the incoherent and coherent nonlinear response of the new devices with arbitrary spectral and spatial distribution of quantum dots in the active region under the multimode light. The incoherent nonlinear response was due to the incoherent spectral hole burning and the reduction in the carrier density by the stimulated emission. The coherent nonlinearity was due to the dynamic spectral hole burning caused by the population beating at the electronic states resonant to the multimode light and the carrier density pulsation caused by the carrier relaxation dynamics. Based on the theory, we numerically simulated the operation of quantum-dot SOA's, and succeeded in presenting their diverse promising features in a very systematical manner. We expect amplifiers with low power consumption, high saturation power, broad gain bandwidth, and pattern-effect-free operation under gain saturation, and also signal processing devices to realize high-speed (40 to 160 Gb/s) pattern-effect-free wavelength conversion by the cross-gain modulation with low frequency chirping and symmetric highly-efficient 1 to 2 THz wavelength conversion by the nondegenerate four-wave mixing. We point out that the nonlinear optical response due to the spectral hole burning plays a decisive role in the high-speed optical signal processing. Many of the theoretical predictions in this paper agree well with recent experimental demonstrations of device performance. This work will help not only design practical quantum-dot devices working in the photonic networks but also understand how carrier dynamics relates to the optical response of quantum dots with optical gain under current injection.

All-optical switching on a silicon chip.

Abstract: We present an experimental demonstration of fast all-optical switching on a silicon photonic integrated device by employing a strong light-confinement structure to enhance sensitivity to small changes in the refractive index. By use of a control light pulse with energy as low as 40 pJ, the optical transmission of the structure is modulated by more than 97% with a time response of 450 ps.

Very Compact Arrayed-Waveguide-Grating Demultiplexer Using Si Photonic Wire Waveguides

Abstract: We demonstrated an arrayed-waveguide-grating (AWG) demultiplexer using Si photonic wire waveguides, for the first time. We designed and fabricated an AWG of 110 ×93 µm2 size on a silicon-on-insulator substrate. The demultiplexing function was observed in the wavelength range of 1.50–1.57 µm with a channel spacing of ~6 nm and a free spectral range of > 90 nm. A narrower channel spacing of 1 nm is possible in an area of ~(500 µm)2, using an optimization of arrayed waveguides and slab waveguides.

Size influence on the propagation loss induced by sidewall roughness in ultrasmall SOI waveguides

Abstract: Silicon-on-insulator (SOI) optical waveguides with high electromagnetic field confinement suffer from sidewall roughness which is responsible for strong scattering effects. This letter reports a numerical investigation on the size influence of ultrasmall SOI waveguides on the propagation loss due to sidewall roughness. It is shown that for a size smaller than 260 /spl times/ 260 nm the roughness-induced propagation loss decreases. As the optical mode confinement is reduced, a very low loss light coupling from and to a single-mode fiber can be achieved with propagation loss as low as 0.5 dB/cm for a 150 /spl times/ 150 nm cross-sectional waveguide.

Magneto-optical nonreciprocal phase shift in garnet/silicon-on-insulator waveguides

Abstract: We demonstrate the integration of a single-crystal magneto-optical film onto thin silicon-on-insulator (SOI) waveguides by use of direct wafer bonding. Simulations show that the high confinement and asymmetric structure of SOI allows an enhancement of ∼3× over the nonreciprocal phase shift achieved in previous designs; this value is confirmed by our measurements. Our structure will allow compact magneto-optical nonreciprocal devices, such as isolators, integrated on a silicon waveguiding platform.

Raman gain and nonlinear optical absorption measurements in a low-loss silicon waveguide

Abstract: We fabricated a low-loss (∼0.22dB∕cm) rib waveguide (WG) in silicon-on-insulator with a small effective core area of ∼1.57μm2 and measured the stimulated Raman scattering gain in the WG. We obtained 2.3dB Raman gain in a 4.8-cm-long S-shaped WG using a 1455nm pump laser with a cw power of 0.9W measured before the WG. In addition, we observed nonlinear dependence of Raman gain and optical propagation loss as a function of the pump power. Our study shows that this mainly is due to two-photon absorption (TPA) induced free carrier absorption in the silicon WG. We experimentally determined the TPA induced free carrier lifetime of 25ns, which agrees well with our modeling.

Efficient Raman amplification in silicon-on-insulator waveguides

Abstract: We describe a silicon-on-insulator waveguide Raman amplifier which achieves a large fiber-to-fiber optical gain of 6.8dB using stimulated Raman scattering in a 1.7-cm-long silicon waveguide. By using picosecond pulse pumping at 1557.4nm wavelength, high net optical gain at the first-order Stokes wavelength of 1694.6nm was measured. The optical loss from two-photon absorption generated free carriers was reduced by using a low pulse duty cycle and picosecond pulse pumping.

Time-resolved study of Raman gain in highly confined silicon-on-insulator waveguides

Abstract: We show time-resolved measurement of Raman gain in Silicon submicron-size planar waveguide using picosecond pump and probe pulses. A net nonlinear gain of 6 dB is obtained in a 7-mm long waveguide with 20.7-W peak pump power. We demonstrate an ultrafast all-optical switch based on the free-carrier dispersion effect in the silicon waveguide, whose transmission is enhanced by more than 13 dB due to the Raman effect.

Integrated optical waveguides with liquid cores

Abstract: We report the design, fabrication, and demonstration of single-mode integrated optical waveguides with liquid cores. The principle of the device is based on antiresonant reflecting optical (ARROW) waveguides with hollow cores. We describe design principles for waveguide loss optimization down to 0.1∕cm. Using a fabrication process based on conventional silicon microfabrication and sacrificial core layers, waveguides of varying widths and lengths with volumes covering the pico- to nanoliter range were fabricated. We observe confined mode propagation, measure waveguide losses of 2.4∕cm, and demonstrate that the waveguides possess tailorable wavelength selectivity. The potential for highly integrated, sensitive devices based on these properties of the ARROW waveguides is discussed.

Nonlinear propagation of ultrafast 1.5 μm pulses in high-index-contrast silicon-on-insulator waveguides

Abstract: Propagation through silicon-on-insulator (SOI) waveguide structures of 153 μm, 100 fs laser pulses with peak powers up to 400 W is studied experimentally and theoretically The dominant nonlinear effects are two-photon absorption and self-phase modulation The two-photon absorption coefficient and the nonlinear refractive index of Si obtained in this work are β2=09 cm/GW and n2=07×10−13 cm2/W, respectively At high intensities, free carriers generated by two-photon absorption are demonstrated to have a significant influence on pulse spectra and transmitted power The figure of merit for all-optical switching obtained in this work (T=18) indicates that a switch based on a SOI waveguide structure might be possible at 155 μm

Optical phase modulators for MHz and GHz modulation in silicon-on-insulator (SOI)

Abstract: This paper reports the simulation of the direct current (dc), transient, and optical characteristics of low-loss single-mode optical phase modulators based on silicon-on-insulator (SOI) material. The devices operate by injecting free carriers to change the refractive index in the guiding region and have been modeled using the two-dimensional (2-D) device simulation package SILVACO and the optical simulator BeamPROP to determine their electrical and optical performance, respectively. These simulators have been employed to optimize the overlap between the injected free carriers in the intrinsic region and the propagating optical mode. Attention has been paid to both the steady state and transient properties of the device. In order to produce quantitative results, a particular p-i-n device geometry has been employed in the study, but the trends in the results are sufficiently general to be of help in the design of many modulator geometries. The specific example devices used are designed to support a single optical guided mode and are of approximately 1 mm in cross-sectional dimensions. The modeling results predict that the transient performance of the device is affected significantly by the contact width and the rib doping depth. Results presented encompass Gaussian and constant doping profiles in the n/sup +/ regions. The doping profile of the contacts has a tremendous effect on both the dc and transient performances. Phase modulators with drive currents as low as 0.5 mA and transient rise times of 0.3 ns and fall times of 0.12 ns are predicted. Following from these results, a realistic doping profile is proposed that surpasses the electrical results of the Gaussian and most of the constant doping profiles. The improvements in electrical device characteristics are at the expense of a slightly increased optical absorption loss. An alternative switching technique is also presented that could further improve the device speed.

Nonlinearity enhancement in finite coupled-resonator slow-light waveguides

Abstract: In this paper, we derive the exact dispersion relation of one dimensional periodic coupled-resonator optical waveguides of finite length, from which the reduced group velocity of light is obtained. We show that the group index strongly depends on the number of cavities in the system, especially for operation at the center frequency. The nonlinear phase sensitivity shows an enhancement proportional to the square of the group index (or light slowing ratio). Aperiodic coupled ring-resonator optical waveguides with optimized linear properties are then synthesized to give an almost ideal nonlinear phase shift response. For a given application and bandwidth requirement, the nonlinear sensitivity can be increased by either decreasing resonator length or by using higher-order structures. The impact of optical loss, including linear and two-photon absorption is discussed in post-analysis.

Waveguiding in air by total external reflection from ultralow index metamaterials

Abstract: Metamaterials composed of metal-dielectric nanostructures can be engineered to have the real part of the effective refractive index less than unity at optical wavelengths. These materials show intriguing optical properties including total external reflection. We utilize this effect to design and analyze slab waveguide structures that guide visible light in an air core.

Strain-tunable silicon photonic band gap microcavities in optical waveguides

Abstract: We report the design, device fabrication, and measurements of tunable silicon photonic band gap microcavities in optical waveguides, using direct application of piezoelectric-induced strain to the photonic crystal. We show, through first-order perturbation computations and experimental measurements, a 1.54 nm shift in cavity resonances at 1.56 μm wavelengths for an applied strain of 0.04%. The strain is applied through integrated piezoelectric microactuators. For operation at infrared wavelengths, we combine x-ray and electron-beam lithography with thin-film piezoelectric processing. This level of integration permits realizable silicon-based photonic chip devices, such as high-density optical filters, with active reconfiguration.

Nonlinear absorption and Raman scattering in silicon-on-insulator optical waveguides

Abstract: We study the nonlinearities in silicon-on-insulator (SOI) optical waveguides, which include two-photon absorption (TPA), free-carrier absorption, and spontaneous and stimulated Raman scattering (SRS). We show experimentally that free carriers generated by TPA in the SOI waveguides produce large optical loss at room temperature. The experimental results confirmed the presence of relative optical signal amplification from SRS, but it was found that net gain was hardly achieved because the stimulated Raman gain was less than the induced loss from TPA-generated free carriers at room temperature with continuous-wave pumping source in a SOI rib waveguide. We also experimentally investigated the temperature dependence of Raman scattering in the SOI waveguide and observed the Raman gain to be greater than TPA-generated free-carrier absorption loss at 77 K.

Optical gain in monodispersed silicon nanocrystals

Abstract: Stimulated emission from silicon-nanocrystal planar waveguides grown via phase separation and thermal crystallization of SiO∕SiO2 superlattices is presented. Under high power pulsed excitation, positive optical gain can be observed once a good optical confinement in the waveguide is achieved and the silicon nanocrystals have proper size. A critical tradeoff between Auger nonradiative recombination processes and stimulated emission is observed. The measured large gain values are explained by the small size dispersion in these silicon nanocrystals.

Demonstration of 11dB fiber-to-fiber gain in a silicon Raman amplifier

Abstract: We report the demonstration of 11dB fiber-to-fiber optical gain in a silicon Raman amplifier. Pulsed pumping is employed to reduce the TPA induced free carrier losses resulting in net signal amplification. The influence of free carriers is elucidated by observing the dependence of gain on pulse energy.

High-performance all-optical silicon microswitch

Abstract: An integrated micron-size all-optical Si switch capable of 94.7 GHz operation frequency is presented. The device consists of a microring resonator formed by Si/SiO/sub 2/ slot-waveguides with a low-index nonlinear optical material in the slot region. Strong optical confinement in the slot permits an achievement of low switching power of 6.2 mW.

All-optical quantization scheme based on fiber nonlinearity

Abstract: We have proposed a novel all-optical quantization scheme that may be useful for analog-to-digital conversion. The preprocess of optical sampling is performed by four-wave mixing, and optical quantizing is realized by soliton phenomena. We have conducted a simple proof-of-principle experiment, and demonstrated the optical multilevel thresholding to show the feasibility of the proposed method.

Microresonators as building blocks for VLSI Photonics

Abstract: In the last years much effort has been taken to arrive at optical integrated circuits with high complexity and advanced functionality For this aim high index contrast structures are employed resulting in photonic wires in conventional index guiding waveguides or in photonic bandgap structures In both cases the number of functional elements within a given chip area can be enhanced by several orders of magnitude: VLSI photonics In this talk optical microresonators are presented as promising basic building blocks for filtering, amplification, modulation, switching and sensing Active functions can be obtained by monolithic integration or a hybrid approach using materials with thermo‐, electro‐ and opto‐optic properties and materials with optical gain Examples are mainly taken from work at MESA+

Nonlinear optical tuning of a two-dimensional silicon photonic crystal

Abstract: We use the real (Kerr) and imaginary (two photon absorption) parts of a third order optical nonlinearity to tune the long s1.6 mmd and short wavelength s1.3 mmd band edges of a stop gap in a two-dimensional silicon photonic crystal. From pump-probe reflectivity experiments using 130 fs pulses, we observe that a 2 mm pulse induces optical tuning of the 1.3 mm edge via the Kerr effect whereas a 1.76 mm pulse induces tuning of the 1.6 mm band edge via both Kerr and Drude effects with the latter related to two-photon induced generation of free carriers with a lifetime of ,900 ps.

Monolithic suspended optical waveguides for InP MEMS

Abstract: We present a novel waveguide design for InP microelecromechanical systems. The substrate is removed from underneath the waveguide by sacrificial etching, and the suspended waveguide is supported by lateral tethers. This allows segments of the waveguide to be moved and prevents substrate leakage loss in the fixed segments of the waveguides. A single-mask fabrication process is developed that can be extended to more complex devices employing electrostatic actuation. Fabricated suspended waveguides exhibit a loss of 2.2 dB/cm and tether pairs exhibit 0.25-dB additional loss.

Wavelength conversion in silicon using Raman induced four-wave mixing

Abstract: Conversion of digital- and analog-modulated optical signals from the 1550nm band to the 1300nm band is demonstrated in silicon waveguides. The conversion is based on parametric Stokes to anti-Stokes coupling using the Raman susceptibility of silicon.

Parametric amplification of soliton steering in optical lattices.

Abstract: We report on the effect of parametric amplification of spatial soliton swinging in Kerr-type nonlinear media with longitudinal and transverse periodic modulation of the linear refractive index. The parameter areas are found where the soliton center motion is analogous to the motion of a parametrically driven pendulum. This effect has potential applications for controllable soliton steering.

Development of a low-cost low-loss polymer waveguide technology for parallel optical interconnect applications

Abstract: We report on the material evaluation, design, fabrication, and characterization of low-loss multimode polymer waveguides that are compatible with standard PCB manufacturing processes for use in large-area high-density high speed optical backplane interconnects.