Standards organizations and fiber-optical component vendors are working hard, creating the next generation of fiber-optic networks. The target is 40-Gbit/s and then 100-Gbit/s data rates over existing single-mode fiber. The big hangup so far has been the fiber impairments like chromatic dispersion that are slowing things down. Everything is okay up to 10 Gbits/s plus a little, but beyond that, distortion and attenuation take their toll.
One approach has been to trade off the one bit per symbol NRZ transmission method for a modulation method that transmits two or more bits per symbol The method showing the most promise is differential quadrature phase-shift keying (DQPSK), which transmits two bits per symbol. DQPSK has proved to be less sensitive to fiber impairments than other transmission methods at 40 Gbits/s at well over 1000 km. The roadblock has been a driver that can operate the modulators. Mach-Zehnder modulators can handle the higher data rates but require a driver that is differential with a wide output voltage swing.
Inphi Corp. now has just such a driver. The 2514DZ’s differential output voltage can swing from 4 to 8 V p-p at rates greater than 25 Gbits/s (see fig.). It works with leading differential Mach-Zehnder modulators from Fujitsu and the Sumitomo Osaka Cement Company. The driver supports NRZ data rates to 25 Gbits/s and clock frequencies up to 25 GHz. The output amplitude and the eye crossing are adjustable. With this component, vendors can begin making some of the transceivers that will reach the 40- and 100-Gbit/s targets.
The 2514DZ is sampling now. For more details on pricing and availability, contact the company.