The Latest Trends in 100G

A hot topic that after several years of intense research and development is rapidly coming to fruition is the deployment of 100G transport in carrier networks.  After several 100G field trials were reported in conferences and technical literature, the first 100G system was taken into commercial service late last year in Europe, between Frankfurt and Paris.  The modulation format is based on polarization division multiplexed QPSK (i.e., 4 bits/symbol) and a coherent receiver with digital signal processing is used to provide signal recovery and mitigation of transport impairments such as chromatic dispersion and polarization mode dispersion.  Since several major component vendors and system integrators are close to introducing 100G products, I expect that several more 100G systems will be taken into service this year.

Given the continued rapid growth of traffic due to applications such as high-speed computing, high-definition video transport and peer-to-peer networking, research has started on optical communications systems that operate at line rates of 400Gb/s or even 1 Tb/s and achieve spectral efficiencies well above the 4 bits/symbol used by current 100G transport systems.  Note that this implies that higher SNR is needed.  The need for modulation techniques with very high spectral efficiency will require the development of photonic integrated circuits (PIC) that achieve excellent performance and allow cost-efficient system integration. 

Another key development area will be the development of very high speed analog-to-digital converters that provide the needed resolution to capture every bit in the signal constellation while allowing operation at higher symbol rates.  An interesting issue is that an increase in the symbol rate to achieve transport rates above 100G would require increasing the 50 GHz ITU spacing now common in long-haul transport systems, resulting in less wavelengths per fiber and therefore a smaller increase in aggregate system capacity than might have been expected based on the increase in line rate. 

Bert Basch
NFOEC General Chair

Note from OFC/NFOEC:  100G topics will be discussed in numerous programs at the conference.  More information on 100G programming can be found in the following areas of the Web site:

• Market Watch
• Workshops and Panels
• Conference Program
• Morning Technical Briefings