Showing papers by "Mario J. Paniccia 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.

Net optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering

Abstract: We observe for the first time net optical gain in a low loss silicon waveguide in silicon-on-insulator (SOI) based on stimulated Raman scattering with a pulsed pump laser at 1.545 μm. We show that pulsed pumping with a pulse width narrower than the carrier recombination lifetime in SOI significantly reduces the free carrier generation rate due to two-photon absorption (TPA) in silicon. For a 4.8 cm long waveguide with an effective core area of ~1.57 μm2, we obtained a net gain of 2 dB with a pump pulse width of ~17 ns and a peak pump power of ~470 mW inside the waveguide.

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.

Polarization-independent optical racetrack resonators using rib waveguides on silicon-on-insulator

Abstract: In an effort to find low-cost alternatives for components currently used in dense wavelength division multiplexing, optical ring resonators fabricated on silicon on insulator are currently being investigated. Their performance can be further enhanced if they are polarization independent. Herein we use rib waveguides to control the polarization properties of the devices and hence produce polarization-independent racetrack ring resonators. Transverse electric and transverse magnetic resonant peaks are measured to within 2 pm of one another over four cycles of the free spectral range. The racetrack resonators also exhibit measured Q factors of approximately 90 000 and finesse values of 12.

Fast silicon optical modulator

Abstract: We present design, fabrication, and testing of a high-speed all-silicon optical phase modulator in silicon-on-insulator (SOI). The optical modulator is based on a novel silicon waveguide phase shifter containing a metal-oxide-semiconductor (MOS) capacitor. We show that, under the accumulation condition, the drive voltage induced charge density change in the silicon waveguide having a MOS capacitor can be used to modulate the phase of the optical mode due to the free-carrier plasma dispersion effect. We experimentally determined the phase modulation efficiency of the individual phase shifter and compared measurements with simulations. A good agreement between theory and experiment was obtained for various phase shifter lengths. We also characterized both the low- and high-frequency performance of the integrated Mach-Zehnder interferometer (MZI) modulator. For a MZI device containing two identical phase shifters of 10 mm, we obtained a DC extinction ratio above 16 dB. For a MZI modulator containing a single-phase shifter of 2.5 mm in one of the two arms, the frequency dependence of the optical response was obtained by a small signal measurement. A 3-dB bandwidth exceeding 1 GHz was demonstrated. This modulation frequency is two orders of magnitude higher than has been demonstrated in any silicon modulators based on current injection in SOI.

Method and apparatus for preparing a plurality of dice in wafers

Abstract: An apparatus and method for preparing a plurality of dice on a semiconductor wafer. In one embodiment, a method according to embodiments of the present invention includes arranging a plurality of dice in a semiconductor wafer such that there is a separation region between each neighboring die of the semiconductor wafer. One or more trenches are etched in the separation region of the semiconductor wafer to form one or more lateral surfaces of one or more of the plurality of dice. The semiconductor wafer is then fractured into separate pieces at the one or more trenches to separate the plurality of dice from each other.

A gigahertz silicon-on-insulator Mach-Zehnder modulator

Abstract: We report a modulator in which a polysilicon-oxide-silicon capacitor forms a ridge waveguide to achieve unprecedented performance in silicon: 2.5 GHz small-signal bandwidth and a driver-limited extinction ratio of 5 dB at 1 gigabit per second.

Polarization-independent optical ring resonators on silicon-on-insulator

Abstract: Because of their compact size, ring resonators can be a cost effective solution for many Dense Wavelength Division Multiplexing (DWDM) components, as well as many low cost applications such as part of optical sensor circuits, or low cost optical signal processing. Modulators, filters, add-drop multiplexers, and switches are all components that can be realised with a ring resonator. Their potentially large Free Spectral Range (FSR), finesse, and quality factor, together with the potential for low cost fabrication, make them a viable alternative to many current DWDM devices. However, for such devices to be commercially viable, they need to be insensitive to the polarisation state of the input signal. The results obtained herein show that a single input/output optical racetrack resonator has been fabricated so that the minima in the resonance spectra align to better than 1pm. The rings also exhibit relatively low loss with measured Q-factors of approximately 90,000 and finesse values of 12.

Opportunities and integration challenges for CMOS-compatible silicon photonic and optoelectronic devices

Abstract: Silicon photonics, especially that based upon silicon on insulator (SOI), has recently attracted a great deal of attention since it offers an opportunity for low cost optoelectronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects. The presentation will give an overview of these opportunities as well as discuss some practical issues and challenges with processing silicon photonic devices in a high volume CMOS manufacturing environment.

Tunable Bragg grating filters in SOI waveguides

Abstract: We present a thermally tunable Bragg grating filter based on silicon-on-insulator (SOI) technology. The grating’s periodic refractive index modulation is achieved with alternating regions of single-crystalline silicon and polycrystalline silicon (polySi).

Design and experimental results of small silicon-based optical modulators

Abstract: In silicon based photonic circuits, optical modulation is usually performed via the plasma dispersion effect or via the thermo-optic effect, both of which are relatively slow processes. Until relatively recently, the majority of the work in Silicon-on-Insulator (SOI) was based upon waveguides with cross sectional dimensions of several microns. This limits the speed of devices based on the plasma dispersion effect due to the finite transit time of charge carriers, and on the thermo-optic effect due to the volume of the silicon device. Consequently moving to smaller dimensions will increase device speed, as well as providing other advantages of closer packing density, smaller bend radius, and cost effective fabrication. As a result, the trend in recent years has been a move to smaller waveguides, of the order of 1 micron in cross sectional dimensions. In this paper we discuss both the design of small waveguide modulators (of the order of ~1 micron) together with a presentation of preliminary experimental results. In particular two approaches to modulation are discussed, based on injection of free carriers via a p-i-n device, and via thermal modulation of a ring resonator.

Small devices in SOI: Fabrication and design issues

Abstract: There is a trend in photonic circuits to move to smaller device dimensions for improved cost efficiency and device performance. However, the trend also comes at some cost to performance, notably in the polarisation dependence of the circuits, the difficulty in coupling to the circuits, and in some cases, in increased device complexity. This paper discusses a range of Silicon-on-Insulator (SOI) based optical devices, and the advantages and disadvantages in moving to smaller waveguide dimensions. In particular optical phase modulators based upon the plasma dispersion effect and ring resonators are considered, together with a device for coupling to small waveguides, the so-called Dual Grating Assisted Directional Coupler (DGADC). The advantages of moving to small dimensions are considered, and some preliminary experimental results are given. In particular, progress of the DGADC is evaluated in the light of promising experimental results.

Polarisation independent devices in small SOI waveguides

Abstract: In silicon photonics, there is a trend to smaller device dimensions. This means that polarisation independent devices become more difficult to design and fabricate whilst maintaining monomode behaviour. By way of example we discuss a polarisation independent ring resonator.

Fabrication of optical ring resonators in silicon on insulator

Abstract: In an effort to determine low-cost alternatives for components currently used in DWDM, optical ring resonators are currently being investigated. The well-known microfabrication techniques of silicon, coupled with the low propagation loss of single crystal silicon, make SOI an attractive material. Laterally coupled racetrack resonators utilising rib waveguides have been fabricated and preliminary results are discussed. An extinction ratio of 15.9 dB and a finesse of 11 have been measured.

Modular reconfigurable multi-server system and method for high-speed photonic burst-switched networks

Abstract: A modular reconfigurable multi-server system with hybrid optical and electrical switching fabrics for high-speed networking within a wavelength-division-multiplexed based photonic burst-switched (PBS) network with variable time slot provisioning. An optical high-speed I/O module within the multi-server system includes an optical switch with the control interface unit. A server module of the multi-server system statistically multiplexes IP packets and/or Ethernet frames to be transmitted over the PBS network, generate control and data bursts and schedule their transmission. Then, the server E-O converts the bursts, and then transmits the optical bursts to the optical I/O module. The optical I/O module then optically transmits the bursts to the next hop in the optical path after processing the optical control burst to configure the optical switch, which then optically switches the optical data burst without performing an O-E-O conversion.

Optical characterization of 1-GHz silicon-based optical modulator

Abstract: In this paper the optical characterization of a novel, metal-oxide-silicon (MOS) capacitor-based, high speed, silicon optical modulator is presented By using a capacitor based rather than the conventional p-i-n junction based architecture to modulate the free carrier density inside the waveguide, we show the realization of a fast, 25-GHz, optical modulator

Three dimensional semiconductor based optical switching device

Abstract: A device with optical switching between multiple layers of a semiconductor die is disclosed. In one aspect of the present invention, the disclosed apparatus includes a first semiconductor material layer of a semiconductor die. The first semiconductor material layer has a first optical waveguide. A second semiconductor material layer is also included in the semiconductor die. The second semiconductor material layer has a second optical waveguide. An insulating layer is disposed between the first and second semiconductor material layers such that there is an evanescent coupling between the first and second semiconductor material layers. There are modulated charge layers proximate to the insulating layer such that a coupling length of the evanescent coupling is controlled in response to the modulated charge layers.