Fiber Optic DWDM Up to 100 Gbps Per Wavelength

The incredible growth of bandwidth demand continues unabated. Odd, perhaps, in these soft economic times. It’s the proliferation of video and especially high definition video that has dramatically increased network bandwidth requirements, including metro and long haul WAN networks. Now a new benchmark has been achieved at 100 Gbps per wavelength in DWDM or Dense Wavelength Division Multiplexing fiber optic systems.

It wasn’t all that long ago that we were hearing of the move from 10 Gbps to 40 Gbps channels. Alcatel-Lucent is offering a new upgrade module that operates at both 40 Gbps and 100 Gbps using a single optical carrier. It’s available in their 1830 Photonic Service Switch (PSS).

What does it take to achieve such speeds on existing fiber that was intended for 10 Gbps transmissions? After all, you can’t exactly rip up all that installed fiber and lay new cables just to up the bandwidth. Also complicating the design is that in wavelength division multiplexing not all wavelengths will be scheduled for simultaneous upgrade. What’s needed in an upgrade that won’t interfere with existing 10 Gbps and 40 Gbps signals nor demand larger amounts of rack space and power.

Alcatel-Lucent has met these design goals with a new electro-optics engine that depends heavily on digital signal processing and better modulation and detection techniques for the optical signal. It starts with a change from amplitude shift keying (ASK) to phase shift keying (PSK). With a constant amplitude, the signal has better resilience against non-linear effects in the fiber. Both two-phase-state and four-phase-state coding schemes can be used to load more information on the signal. They then double the bit rate again without increasing the symbol rate by adding PDM or polarization division multiplexing on the same signal.

As you probably guessed, transmitting more information on the same wavelength has a price. That price is sophistication of the electronics. Coherent detection uses a local oscillator mixed with the optical signal to produce interferences that give an output of phase, amplitude and polarization to the digital signal processor. Some heavy duty number crunching allows the DSP to compensate for linear distortions in the fiber while it recovers the bit information.

Alcatel-Lucent proved all this out last fall during a field trial in Spain, by transmitting 112 Gbps per channel along with 40 Gbps and 10 Gbps channels on a 1088 km link between Madrid and Merida via Seville, as described in their technology white paper, “Next-generation Electro-Optics Technology with Coherent Detection”.

Ciena has a competing system, the OME or Optical Multiservice Edge 6500 that also runs at 100 Gbps. These two companies should set the standard at 100 Gbps... at least for awhile. You know that whenever there is competition, there will be the competitive spirit to take things to the next level. What is that? 200 Gbps? 500 Gbps? 1 Tbps?

Service providers worldwide are in a scramble to provide higher speed services at lower costs. Prices have dropped so much in the last few years that you can probably afford more bandwidth than you think. Why wonder when you can get high bandwidth fiber optic service quotes quickly and easily. It only takes a minute to inquire, so why not take that minute right now?