Graham T. Reed

Silicon photonics : an introduction

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.

50-Gb/s Silicon Optical Modulator

Optical modulators formed in silicon are the keystone to many low cost optical applications. Increasing the data rate of the modulator benefits the efficiency of channel usage and decreases power consumption per bit of data. Silicon-based modulators which operate via carrier depletion have to the present been demonstrated at data rates up to 40 Gb/s; however, here we present for the first time optical modulation at 50 Gb/s with a 3.1-dB extinction ratio obtained from carrier depletion based phase shifter incorporated in a Mach-Zehnder interferometer. A corresponding optical insertion loss of approximately 7.4 dB is measured.

High contrast 40Gbit/s optical modulation in silicon

Data interconnects are on the verge of a revolution. Electrical links are increasingly being pushed to their limits with the ever increasing demand for bandwidth. Data transmission in the optical domain is a leading candidate to satisfy this need. The optical modulator is key to most applications and increasing the data rate at which it operates is important for reducing power consumption, increasing channel bandwidth limitations and improving the efficiency of infrastructure usage. In this work silicon based devices of lengths 3.5mm and 1mm operating at 40Gbit/s are demonstrated with extinction ratios of up to 10dB and 3.5dB respectively. The efficiency and optical loss of the phase shifter is 2.7V.cm and 4dB/mm (or 4.5dB/mm including waveguide loss) respectively.

Device physics: The optical age of silicon

The silicon chip has been the mainstay of the electronics industry and it may similarly come to dominate photonics. A key component — a high-frequency optical modulator — has now been fabricated.

Silicon-on-insulator optical rib waveguide loss and mode characteristics

Optical rib waveguides with rib heights of 3.17 and 7.67 microns with various widths have been formed in separation by implantation of oxygen (SIMOX) based silicon-on-insulator (SOI) structures. The effect of waveguide rib etch depth, width, and interface roughness on loss and mode characteristics have been studied at wavelengths of 1.15 and 1.523 microns. The experimental results support the hypothesis that certain rib dimensions can lead to single mode SOI waveguides even though planar SOI waveguides of similar multimicron dimension are not single mode. Mode loss was found to be strongly dependent on interface roughness and mode confinement. >

A sub-micron depletion-type photonic modulator in Silicon On Insulator

We provide detailed analysis of a four terminal p+pnn+ optical modulator integrated into a silicon-on-insulator (SOI) rib waveguide. The proposed depletion device has been designed to approach birefringence free operation. The modulation mechanism is the carrier depletion effect in a pn junction; carrier losses induced are minimised in our design and because we use a depletion device, the device is insensitive to carrier lifetime. The rise time and fall time of the proposed device have both been calculated to be 7 ps for a reverse bias of only 5 volts. A maximum excess loss of 2 dB is predicted for TE and TM due to the presence of p type and n type carriers in the waveguide.

High-speed modulation of a compact silicon ring resonator based on a reverse-biased pn diode

We demonstrate high speed modulation based on a compact silicon ring resonator operating in depletion mode. Our device features an electrical small signal bandwidth of approximately 19 GHz, which is the fastest silicon ring resonator modulator reported to date.

40 Gb/s silicon photonics modulator for TE and TM polarisations

A key device in future high speed short reach interconnect technology will be the optical modulator. These devices, in silicon, have experienced dramatic improvements over the last 6 years and the modulation bandwidth has increased from a few tens of MHz to over 30 GHz. However, the demands of optical interconnects are significant. Here we describe an approach based on a self-aligned wrap around p-n junction structure embedded in a silicon waveguide that can produce high-speed optical phase modulation, whilst at the same time, capable of a high extinction ratio. An all-silicon optical modulator using a CMOS compatible fabrication process with a data rate of 40 Gb/s and extinction ratio up to approximately 6.5 dB for TE and TM polarisations is demonstrated. This technology is not only compatible with conventional complementary MOS (CMOS) processing, but is also intended to simplify and improve the reliability of, the fabrication process.

Roadmap on silicon photonics

Silicon photonics research can be dated back to the 1980s. However, the previous decade has witnessed an explosive growth in the field. Silicon photonics is a disruptive technology that is poised to revolutionize a number of application areas, for example, data centers, high-performance computing and sensing. The key driving force behind silicon photonics is the ability to use CMOS-like fabrication resulting in high-volume production at low cost. This is a key enabling factor for bringing photonics to a range of technology areas where the costs of implementation using traditional photonic elements such as those used for the telecommunications industry would be prohibitive. Silicon does however have a number of shortcomings as a photonic material. In its basic form it is not an ideal material in which to produce light sources, optical modulators or photodetectors for example. A wealth of research effort from both academia and industry in recent years has fueled the demonstration of multiple solutions to these and other problems, and as time progresses new approaches are increasingly being conceived. It is clear that silicon photonics has a bright future. However, with a growing number of approaches available, what will the silicon photonic integrated circuit of the future look like? This roadmap on silicon photonics delves into the different technology and application areas of the field giving an insight into the state-of-the-art as well as current and future challenges faced by researchers worldwide. Contributions authored by experts from both industry and academia provide an overview and outlook for the silicon waveguide platform, optical sources, optical modulators, photodetectors, integration approaches, packaging, applications of silicon photonics and approaches required to satisfy applications at mid-infrared wavelengths. Advances in science and technology required to meet challenges faced by the field in each of these areas are also addressed together with predictions of where the field is destined to reach.

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

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.