Silicon Photonics Increase Capacity and Save Energy

2019-05-22  |  6 min read 

Silicon photonics technology offers a solution to enable significantly higher and more efficient bandwidth transmission within and between data centers. Silicon photonics technology involves creating photonic devices with new optical components on a silicon substrate. Optical-based systems use light to transmit data much faster and more efficiently over fiber optics lines compared to systems that transmit data with electrical signals over copper lines. Multi-level pulse amplitude modulation (PAM4), advanced optical modulation formats like quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM), and coherent detection techniques improve spectral efficiency.

Silicon photonics is highly beneficial in a range of distances, from short range chip-to-chip to local area networks (LANs) and wide area networks (WANs) with ranges beyond 100 km. For telecommunications, silicon photonics technology increases the amount of data transmitted over the same fiber lines without the need to expand fiber cabling. For data center interconnects at distances typically less than 80 km, silicon photonics promises higher capacity and more efficient data transfer. As new developments continue, silicon photonics technology will enable the creation of new designs for semiconductors, chips, optical components, and entire data systems. These new optical components will offer higher bandwidth, greater power efficiency, and more speed than traditional electrical systems.

Moore’s Law and Photonic Integrated Circuits

Moore’s Law states that the number of transistors placed onto silicon chips within integrated circuits doubles about every two years. For many years, Moore’s Law held true. However, transistor size is now approaching the size of an atom, and quantum mechanics are hindering development. The latest circuit technology, which produces nanometer-sized transistors, is highly complex and expensive. Traditional silicon chip technology struggles to keep pace with increasing processing speeds needed by data centers and high-performance computing technology.

PICs integrate multiple photonic functions in a single device in a very compact way, like an electronic integrated circuit, using light instead of electricity to transmit signals. PICs provide numerous advantages over conventional circuits including higher bandwidth, expanded wavelength division multiplexing, increased multiple switching, smaller size, lower power consumption, and improved reliability. PICs are optical engines that move the optical interfaces closer to the digital processors avoiding long energy consuming PCB board traces.

PIC fabrication involves wafer-scale technology and lithography to create three-dimensional images of the circuit on substrate materials such as silicon, silica, or lithium niobate. For example, in silicon photonics, photonic functions are implemented directly on silicon chips, enabling inexpensive, mass-produced optical components through photonics integration.

PICs offer significant advantages when used in computing and communications. The transistors, memory, modulators, and detectors in PICs work seamlessly, and more efficiently than those in conventional electrical circuits. PICs enable increased bandwidth and circuit speeds while drastically reducing energy consumption. PICs are highly efficient, and multiplexing enables significantly increased signal transmission through optical fiber compared to electrical signals sent through copper.

Hybrid photonics technology

Since photonic technology is still in development, full photonic systems with PICs have not yet completely replaced the large, complex infrastructures found in electronic systems. Instead, a hybrid approach that includes a high-level integration of electronics and optics provides new functionalities and benefits. There are now silicon chips that include optical transmitters and receivers that work in conjunction with electrical circuits.

Hybrid photonics are now in widespread use in data centers and long-haul communication networks. These systems use specialized PICs to convert photonic data into electrical signals for processing, as data networks are primarily electrical systems. New developments in photonic switching components allow switching to occur at the speed of light, which is thousands of times faster than conventional switching technology.

Within the next five to ten years, photonic technology will progress to the point when photonic systems and components can replace entire electronic systems. However, current limitations require supplementing and replacing specific components in electrical systems, including the integration of both PICs and integrated circuits (ICs), switches, and more into electrical systems.

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