pmd

PMD phenomenon in optical networks. Do you know what the PMD in your optical network is? If not, it will be necessary soon as speed of communication starts growing up. All our fiber optic cables are with guarantied PMD parameters according ITU recommendations.
What the PMD (Polarization Mode Dispesion) is and why is important?

Core assymetry

Build in stress

External stress

Bends

Twists

Internal sources of birefringence

Externall sources of birefringence

Many of the causes of fiber PMD result from the manufacturing process of optical fibers and next manufacturing cables itself. Developments of that reduces birefringence and improves PMD parameters.

Placement of PMD compensator generally prior to the receivers is of one methods of PMD correction of optical signal. Because PMD compensation is wavelength specific using compensators in DWDM systems impose making complicated engineering calculations which increases cost of overall optical network.

One of the key questions of newcomers in optical networks is:
I am not running high bit rates, like 10 or 40 Gbps, now, should I be concerned about PMD?

The timeframe for getting to 10 Gbps data rates or beyond and the length of time the fi ber is expected to last, determines the need for concern over high PMD. Once fi ber is purchased and installed, compensation if needed, can prove costly, complex or limiting. Many network builds are intended to be in service for well over twenty years. Over the last ten years, data rates have increased a hundred fold as personal computers have increased in processing speed. Looking forward, as Moore’s law driven improvements in microelectronics speed continue and optical transmission component costs decrease, transmission rates of 40 Gbps and beyond will be reasonable expectations and PMD will be important.

At the first beginning operators of HFC CATV networks noticed the impact of PMD due to the sensitive nature of the analog signal. But as networks migrate to higher speeds, the effect becomes more apparent, to the point where it is now affecting some short haul (metro) transmissions. And as bit rates continue to increase, the impact on the reliability, reach, and bandwidth of single-mode fiber optic systems will be more pronounced. Ofen it is measured improperly or not measured at all which decrease reliability of optical networks in use.

PMD occurs when different planes of light inside a fiber travel at slightly different speed, making it impossible to transmit data reliably at high speeds. PMD mainly derives from the irregularity of the fiber — i.e., the asymmetry of fiber due to imperfections in the manufacturing process. PMD is critical for optical networks with data transmit rates of 40Gbit/s. It is important at 10Gbit/s, even for transmitting at 2.5Gbit/s it must be taken into account in engineering calculations of optical networks.

Input

Output

Different polarizations of input signal travel at different speeds