Photonic circuits, in which beams of light redirect the flow of other beams of light, are a long-standing goal for developing highly integrated optical communication components1,2,3. Furthermore, it is highly desirable to use silicon—the dominant material in the microelectronic industry—as the platform for such circuits. Photonic structures that bend, split, couple and filter light have recently been demonstrated in silicon4,5, but the flow of light in these structures is predetermined and cannot be readily modulated during operation. All-optical switches and modulators have been demonstrated with III–V compound semiconductors6,7, but achieving the same in silicon is challenging owing to its relatively weak nonlinear optical properties. Indeed, all-optical switching in silicon has only been achieved by using extremely high powers8,9,10,11,12,13,14,15 in large or non-planar structures, where the modulated light is propagating out-of-plane. Such high powers, large dimensions and non-planar geometries are inappropriate for effective on-chip integration. Here we present the experimental demonstration of fast all-optical switching on silicon using highly light-confining structures to enhance the sensitivity of light to small changes in refractive index. The transmission of the structure can be modulated by up to 94% in less than 500 ps using light pulses with energies as low as 25 pJ. These results confirm the recent theoretical prediction16 of efficient optical switching in silicon using resonant structures.

All-optical control of light on a silicon chip

The silicon chip has been the mainstay of the electronics industry for the last 40 years and has revolutionized the way the world operates. Today, a silicon chip the size of a fingernail contains nearly 1 billion transistors and has the computing power that only a decade ago would take up an entire room of servers. As the relentless pursuit of Moore's law continues, and Internet-based communication continues to grow, the bandwidth demands needed to feed these devices will continue to increase and push the limits of copper-based signaling technologies. These signaling limitations will necessitate optical-based solutions. However, any optical solution must be based on low-cost technologies if it is to be applied to the mass market. Silicon photonics, mainly based on SOI technology, has recently attracted a great deal of attention. Recent advances and breakthroughs in silicon photonic device performance have shown that silicon can be considered a material onto which one can build optical devices. While significant efforts are needed to improve device performance and commercialize these technologies, progress is moving at a rapid rate. More research in the area of integration, both photonic and electronic, is needed. The future is looking bright. Silicon photonics could provide low-cost opto-electronic solutions for applications ranging from telecommunications down to chip-to-chip interconnects, as well as emerging areas such as optical sensing technology and biomedical applications. The ability to utilize existing CMOS infrastructure and manufacture these silicon photonic devices in the same facilities that today produce electronics could enable low-cost optical devices, and in the future, revolutionize optical communications

http://ieeexplore.ieee.org/iel5/6668/34347/01638290.pdf

Silicon photonics

The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices...

Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

Silicon photonics could enable a chip-scale platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. This paper discusses mechanisms in silicon photonics for waveguiding, modulating, light amplification, and emission. These mechanisms, together with recent advances of fabrication techniques, have enabled the demonstration of ultracompact passive and active silicon photonic components with very low loss.

Guiding, modulating, and emitting light on Silicon-challenges and opportunities

After dominating the electronics industry for decades, silicon is on the verge of becoming the material of choice for the photonics industry: the traditional stronghold of III-V semiconductors. Stimulated by a series of recent breakthroughs and propelled by increasing investments by governments and the private sector, silicon photonics is now the most active discipline within the field of integrated optics. This paper provides an overview of the state of the art in silicon photonics and outlines challenges that must be overcome before large-scale commercialization can occur. In particular, for realization of integration with CMOS very large scale integration (VLSI), silicon photonics must be compatible with the economics of silicon manufacturing and must operate within thermal constraints of VLSI chips. The impact of silicon photonics will reach beyond optical communication-its traditionally anticipated application. Silicon has excellent linear and nonlinear optical properties in the midwave infrared (IR) spectrum. These properties, along with silicon's excellent thermal conductivity and optical damage threshold, open up the possibility for a new class of mid-IR photonic devices

Silicon Photonics

Mach–Zehnder (MZ) waveguide interferometers integrated on SOI (silicon on insulator) for 1.3 μm operation are studied on the basis of the large cross‐section single‐mode rib waveguide condition and the free‐carrier plasma dispersion effect in Si wafer direct bonding SOI by back‐polishing. And the MZ interferometers are fabricated by using KOH anisotropic etching. Their insertion losses and modulation depths are measured to be 4.81 dB and 98%, respectively, at the wavelength of 1.3 μm when a forward bias voltage applied to a p+n junction is 0.95 V and the active zone length of the MZ interferometers is 816.0 μm.

Silicon on insulator Mach–Zehnder waveguide interferometers operating at 1.3 μm

The first silicon 1×2 digital optical waveguide switch which relies on free-carrier plasma dispersion and waveguide-vanishing effect is demonstrated. Operation is demonstrated at a wavelength of 1.3µm.

Silicon 1*2 digital optical switch using plasma dispersion

Based on total internal reflection and plasma dispersion effect, a SiGe/Si asymmetric optical waveguide switch with transverse injection structure has been proposed and fabricated. The switch performance is measured at the wavelength of 1.55 μm. A modulation depth of 90% at an injection current of 110 mA is obtained, and the switching time is about 0.2 μs. The device reaches a maximum optical switching at the injection current of 120 mA. The extinction ratio is larger than 34 dB and the crosstalk and insertion loss are less than −18.5 and 2.86 dB, respectively.

1.55 μm reflection-type optical waveguide switch based on SiGe/Si plasma dispersion effect

A silicon-on insulator (SOI) zero-gap directional coupler switch is studied based on the large-cross-section singlemode rib waveguide condition, the dual-mode interference principle, and the free-carrier plasma dispersion effect, in which the SOI technique uses silicon and silicon dioxide thermal bonding and backpolishing. The SOI is fabricated by potassium hydroxide anisotropic etching. Its insertion loss and cross talk are measured to be less than 4.81 dB and 218.6 dB, respectively, at a wavelength of 1.3 microm and a switching voltage of 0.91 V. Response time is ~210 ns.

Zero-gap directional coupler switch integrated into a silicon-on insulator for 1.3-microm operation.

A low-loss multimode interference wavelength demultiplexer for 1.3- and 1.55-/spl mu/m operations based on the silicon-germanium alloy material has been proposed and demonstrated. The device was fabricated by molecular beam epitaxy followed by lithography and plasma etching. The input/output facets were polished mechanically. The measured insertion losses are 4.29 and 4.28 dB and the extinction ratios are 25 and 22 dB at 1.3 and 1.55 /spl mu/m, respectively.

Enke Liu

Papers

Silicon on insulator Mach–Zehnder waveguide interferometers operating at 1.3 μm

Silicon 1*2 digital optical switch using plasma dispersion

1.55 μm reflection-type optical waveguide switch based on SiGe/Si plasma dispersion effect

Zero-gap directional coupler switch integrated into a silicon-on insulator for 1.3-microm operation.

Low-loss 1/spl times/2 multimode interference wavelength demultiplexer in silicon-germanium alloy