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16 March 2011
Infinera has given first details of its terabit coherent detection photonic integrated circuits (PICs). The transmitter and receiver PIC pair implement ten 100Gbps channels over a fibre.  Infinera has also demonstrated its 5x100Gbps PICs carrying traffic on Interoute Communications’ pan-European network.
The transmitter PIC demonstrated in the lab operates at 10x112Gbps, an aggregate capacity of 1.12Tbps. The PIC pair implements polarization-multiplexing, quadrature phase-shift keying (PM-QPSK) modulation and, because it is a multi-channel design, arrayed-waveguide grating technology is also required. According to the company, the terabit receiver PIC integrates 150 optical components, while the 5x100Gbps PIC pair already incorporates the equivalent of 600 optical components.
There are several challenges associated with developing such a complex optically integrated device.  The path lengths of the optical waveguides must be accurately manufactured to tens of nanometers precision because the modulation scheme is based on optical phase. Another is achieving a high manufacturing yield of devices comprising hundreds of optical functions. The design must also minimise unwanted interactions between the channels’ optics and electronics.  Turning on a laser can create distortion in an adjacent channel, for example.
Infinera will come to market with its 5x100Gbps PICs first, partly because of the overall power consumption limit of a line card. The big, power-hungry culprit is not the PICs, but the associated coherent-detection digital signal processing (DSP) chips.  DSP is needed to correct the distortions during transmission.  At present five channels on a line card is the limit.  For the terabit PIC, Infinera will need to manufacture its ASICs using a more advanced CMOS process node.
The company has said that its 500 Gigabit PIC will be in volume manufacturing in 2012.  Infinera is also validating the system platform that will use the PICs, which has a five-terabit switching capacity.  Infinera has not said when it will bring its 10x100Gbps device to market, but 2014 is a realistic estimate based on the duration between previous company PIC announcements and market availability.