A single PIC can integrate upwards of fifty optical components that would otherwise each require a separate package.
Infinera’s latest photonic integrated circuits (PIC) is at the heart of a new 10-channel receiver, each channel operating at 100 Gbit/s data rates. This is the first in the industry to achieve a capacity of 1 Terabit/s on a single photonic integrated chip. It contains more than 150 optical components—such as frequency tunable local oscillator (LO) lasers, devices for mixing the LO and incoming signals, variable optical attenuators for LO power control, a spectral demultiplexer to separate the individual wavelength channels, and 40 balanced photodetector (receiver/transmitter) pairs—all integrated onto a chip smaller than a fingernail.
The key technical advance operating behind 100-Gbit/s-per-channel technology is the ability to detect incoming data encoded using the optical industry’s most spectrally efficient modulation technique, called polarization multiplexed Quadrature Phase-Shift Keying, or PM-QPSK. To explain the acronym, first PM: it is similar to the wireless communications technique of alternating the polarization of adjacent channels. How does QSPK work? In virtually all types of data transmission, the information is encoded in ways that allow it to travel the farthest while occupying the least amount of signal spectrum. Just as radio’s AM (amplitude modulation) and FM (frequency modulation) imprints information on, respectively, the amplitude and frequency of its broadcast waves, QPSK modifies the light’s phase to represent the data. All in all, PM-QPSK permits four times more information to be conveyed each second than was possible with the previous method, which simply switched the laser light on and off.
The news here is not about the PM-QPSK modulation scheme per se, but rather that Infinera has, for the first time, integrated it all onto a single 10×100 Gbit/s photonic integrated circuit.
“But just as important as a transmitter’s clever and efficient encoding method is a fast and reliable way for the receiver to convert the information back to its original form,” said Dr. Nagarajan. “For PM-QPSK, we designed and integrated narrow-linewidth lasers that detect the phase encoded data very efficiently.”
Infinera expects PICs with a capability of a terabit or more to be commercially available within a few years. The company has announced that a 500 Gbit/s PIC will be available in 2012. Infinera’s 100 Gbit/s PICs are widely deployed in long-haul and metro networks worldwide.
Transmitter and receiver PICs are typically installed at critical nodes and at each end of “long haul” optical networks. Like non-stop flights between airline hubs, these intercity and intercontinental optical fiber links carry the bulk of Internet traffic. Worldwide, more than 20 exabytes—20 trillion trillion bytes (or 160 exabits)—have been estimated to pass through the Internet every month.
The Future of Photonic Integration
Large-scale photonic integrated circuits (PICs) represent a significant technology innovation that simplifies optical system design, reduces space and power consumption, and improves reliability. In addition, by lowering the cost of optical-to-electrical-to-optical (OEO) conversion in optical networks, they provide a transformational opportunity to embrace the use of electronic ICs and system software in a “digital” optical network to simplify network operations and enable flexible and fast delivery of differentiated transport services.
Photonic integration is in its infancy relative to the electronics industry, and many of the techniques used in scaling silicon ICs can be leveraged to drive continuous improvement in the manufacture of PICs. This promises ongoing scaling of device capacity, functionality, and reductions in the “cost per bit” for optical transmission capacity.
But even in its infancy photonic integration has proven the ability to be a break-through technology; given the benefits it provides, once available why would optical transmission system designers revert back to the use of discrete single-function devices over photonic integrated circuits ? The impact of photonic integration on the telecommunications industry can therefore be as significant as that of electronicintegration, especially as network capacity grows and fiber deployments penetrate further into the network.
In the future, use of PICs, like today’s electronic ASICs, will be limited only by the imagination of designers. Future PIC developments could pave the way for even more advanced packages, integration of electronics and optics, and the development offunctional “macros” similar to those available for electronic ICs to enable standardized design and fab out-sourcing of PICs. Infinera is proud to have initiated these developments, and looks forward to leading the field of photonic integration.