Terabit-per-second interfaces

The IEEE 802.3ab Task Force has largely defined the standards for 40 and 100 Gigabit Ethernet, but how will optics deliver one terabit per second interfaces?

That is the question that a US $6m NIST Advanced Technology Programme is seeking to address.  The three-year project, involving CyOptics and silicon photonics specialist Kotura, is half way through and involves the development of increasingly complex prototypes using indium phosphide laser arrays and hybrid integration.

The first stage 100Gbps interface – 10 channels, each 10Gbps based on directly modulated lasers (DMLs) – has been completed. The design uses two arrays of five lasers each, operating using widely spaced wavelengths or coarse wavelength division multiplexing (CWDM). A five-laser array was a compromise between the best level integration while ensuring a good manufacturing yield.

The wavelengths are multiplexed into an Echelle grating optical multiplexer while the receiver circuitry uses the grating to perform demultiplexing, each wavelength being fed to the discrete photo-detectors.

The project’s second stage, already begun, is a 12x43Gbps prototype. The design is the most complex development step since it uses higher performance electro-absorption modulated lasers (EMLs) - three arrays of four lasers.

The one terabit transceiver, to be completed in 2010, will extend the design using 25-channels, each at 40Gbps.

Table 1: Status and specification of the NIST Advanced Technology Programme involving CyOptics and Kotura.