Silicon lasers have long been a goal for semiconductor scientists, and a number of important breakthroughs in the past decade have focused attention on silicon as a photonic platform. Here we review the most recent progress in this field, including low-threshold silicon Raman lasers with racetrack ring resonator cavities, the first germanium-on-silicon lasers operating at room temperature, and hybrid silicon microring and microdisk lasers. The fundamentals of carrier transition physics in crystalline silicon are discussed briefly. The basics of several important approaches for creating lasers on silicon are explained, and the challenges and opportunities associated with these approaches are discussed. Silicon lasers have long been a goal for semiconductor scientists. This Progress Article reviews the most recent developments in this field, including silicon Raman lasers, the first germanium-on-silicon lasers operating at room temperature, and hybrid silicon microring and microdisk lasers. Challenges and opportunities for the present approaches are also discussed.

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Recent progress in lasers on silicon

Integrated multiple-wavelength laser sources, critical for important applications such as high-precision broadband sensing and spectroscopy1, molecular fingerprinting2, optical clocks3 and attosecond physics4, have recently been demonstrated in silica and single-crystal microtoroid resonators using parametric gain2,5,6. However, for applications in telecommunications7 and optical interconnects8, analogous devices compatible with a fully integrated platform9 do not yet exist. Here, we report a fully integrated, CMOS-compatible, multiple-wavelength source. We achieve optical ‘hyper-parametric’ oscillation in a high-index silica-glass microring resonator10 with a differential slope efficiency above threshold of 7.4% for a single oscillating mode, a continuous-wave threshold power as low as 54 mW, and a controllable range of frequency spacing from 200 GHz to more than 6 THz. The low loss, design flexibility and CMOS compatibility of this device will enable the creation of multiple-wavelength sources for telecommunications, computing, sensing, metrology and other areas. Through optical ‘hyper-parametric’ oscillation in a high-index silica glass microring resonator, scientists demonstrate a fully integrated CMOS-compatible low-loss multiple-wavelength source that has high differential slope efficiency at only a few tens of milliwatts of continuous-wave power. The achievement has significant implications for telecommunications and on-chip optical interconnects in computers.

CMOS-compatible integrated optical hyper-parametric oscillator

Photonic integrated circuits are a key component1 of future telecommunication networks, where demands for greater bandwidth, network flexibility, and low energy consumption and cost must all be met. The quest for all-optical components has naturally targeted materials with extremely large nonlinearity, including chalcogenide glasses2 and semiconductors, such as silicon3 and AlGaAs (ref. 4). However, issues such as immature fabrication technology for chalcogenide glass and high linear and nonlinear losses for semiconductors motivate the search for other materials. Here we present the first demonstration of nonlinear optics in integrated silica-based glass waveguides using continuous-wave light. We demonstrate four-wave mixing, with low (5 mW) continuous-wave pump power at λ = 1,550 nm, in high-index, doped silica glass ring resonators5. The low loss, design flexibility and manufacturability of our device are important attributes for low-cost, high-performance, nonlinear all-optical photonic integrated circuits. The ability to perform low-power, continuous-wave nonlinear optics, in particular four-wave mixing, is demonstrated in doped-silica-glass waveguide ring resonators. The device's low loss and ease of manufacture may make the approach suitable for nonlinear all-optical photonic integrated circuits.

Low-power continuous-wave nonlinear optics in doped silica glass integrated waveguide structures

In this paper, we review the current status of the hybrid silicon photonic integration platform with emphasis on its prospects for increased integration complexity. The hybrid silicon platform is maturing fast as increasingly complex circuits are reported with tens of integrated components including on-chip lasers. It is shown that this platform is well positioned and holds great potential to address future needs for medium-scale photonic integrated circuits.

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Hybrid Silicon Photonic Integrated Circuit Technology

Silicon photonics have progressed to a point where the next step for commercialization depends on the accessibility of manufacturing foundries. The implementation of a fabless foundry model using standardized process technology platforms is crucial for that to occur. Research and development (R&D) foundries are beginning to play bigger roles in transforming silicon photonics into a mature technology for mass production. R&D foundry services such as multi-project wafer (MPW) shuttles, customized process developmental runs and small volume manufacturing are discussed. The development of commercial foundries for low cost, high volume production is also shown to be underway, and key results from an on-going effort to set-up a manufacturing silicon photonics foundry line are presented.

Review of Silicon Photonics Foundry Efforts

This paper surveys technical challenges involved in designing and manufacturing integrated optoelectronic devices in a high-volume complementary metal-oxide-semiconductor (CMOS) microelectronic fabrication facility. The paper begins by introducing the motivations for building these devices in silicon. We discuss the advantages and challenges of both hybrid and monolithic strategies for optoelectronic integration. We then discuss the issues involved in building the devices in a standard CMOS facility, including specific technical examples. These include low-loss waveguides (WGs) for Raman lasers, fast silicon modulators, SiGe heterostructures for infrared photodetection, silicon-oxynitride (SiON) devices on silicon-on-insulator (SOI), silicon optical bench (SiOB) technology, and waveguide tapers. We conclude with a discussion and recommendations for future work in silicon photonics

Development of CMOS-Compatible Integrated Silicon Photonics Devices

A monolithically integrated eight-channel optical multiplexer (Mux) with a 400 GHz channel spacing ~1550 nm is presented based on a silicon-on-insulator rib waveguide and an asymmetric Mach-Zehnder interferometer. All channels were optimized independently with integrated heaters. The fully tuned Mux shows an adjacent channel isolation of ~13 dB, an excess loss of ~2.6 dB, and a channel uniformity of ~1.5 dB over a 25 nm wavelength span. In addition, the phase tuning efficiency for different interlevel dielectric layer thicknesses and thermal crosstalk were investigated.

Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers

We demonstrate a triplexer with an integrated wavelength splitter, two photodetectors and a transmit laser. The measured 3dB bandwidth of the integrated laser and photodetectors are 2GHz and 16GHz, respectively.

Integrated hybrid silicon triplexer.

Feature Issue on Nanoscale Integrated Photonics for Optical Networks Fiber optic communication is well established today in long-haul, metro, and some data communication segments. Optical technologies continue to penetrate more into the network owing to the increase in bandwidth demands; however, they still suffer from too expensive solutions. Silicon photonics is a new technology developing integrated photonic devices and circuits based on the unique silicon material that has already revolutionized the face of our planet through the microelectronics industry. This paper reviews silicon photonics technology at Intel, showing how using the same mature, low-cost silicon CMOS technology we develop many of the building blocks required in current and future optical networks. After introducing the silicon photonics motivation for networks, we discuss the various devices--waveguides, modulators, Raman amplifiers and lasers, photodetectors, optical interconnects, and photonic crystals--from the points of view of applications, principle of operation, process development, and performance results.

Integrated silicon photonics for optical networks [Invited]

A low-loss polarization independent mode converter for coupling standard single mode fiber to a silicon chip is presented. For a micrometer size silicon waveguide, we demonstrate a coupling loss of 1-1.5 dB/facet.

Assia Barkai

Papers

Development of CMOS-Compatible Integrated Silicon Photonics Devices

Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers

Integrated hybrid silicon triplexer.

Integrated silicon photonics for optical networks [Invited]

Efficient Mode Converter for Coupling between Fiber and Micrometer Size Silicon Waveguides