Metro|NS - A Perspective on Coherent Optics

Metro|NS is a leading optical network planning, design, construction and maintenance firm with a successful history of serving the financial, service provider, wireless, enterprise and carrier communities.

Delivering the lowest latency and most reliable networks and connections in and around the New York metro area, Metro|NS can assist with any stage of network development.

To learn more, please visit www.MetroNS.com or to follow the discussion on Twitter, click HERE

Read the latest blog by their CTO, Doug Haluza, below:

COHERENT OPTICS

As the need for speed took fiber optic transmission beyond 10 Gbps per channel, long-range optical transponders have moved beyond the Morse code-like on-off keying (OOK) used in fiber optic communications for decades. More sophisticated modulation and demodulation schemes are commonly used in modern wireless equipment where radio frequency bandwidth is scarce, but had not been widely applied to optical transmission where bandwidth is more plentiful. For example, a 50 MHz channel bandwidth is relatively wide-band for licensed microwave radio, while 50 GHz channel spacing in DWDM optical transmission is relatively common.

OOK is cheap and works well on standard single-mode fiber up to speeds around 10 Gbps, providing little commercial demand for more efficient optical modulation to this point. At 10 Gbps, fiber impairments like dispersion come into play, and fiber characterization testing and dispersion compensation are needed to ensure reliable operation. At higher data rates dispersion sensitivity increases, and more dispersion compensation is required. Quadrupling the data rate using the same modulation would require sixteen times the dispersion compensation. 40 Gbps optics would not be as widely deployed if network operators had to re-engineer their DWDM networks again, as was the case when moving from 2.5 to 10 Gbps.

Coherent optical receivers had been a hot topic of research in the 1970s and 1980s when system reach was limited by signal attenuation in the fiber. A coherent receiver is less noisy and can reliably detect a weaker signal, thereby extending the distance between network elements. Once optical amplifiers were developed, they became the preferred solution to the attenuation problem, and work on coherent optics was largely abandoned.

To read the rest of the blog, please click HERE or visit http://www.metrons.com/blog