Chromatic dispersion is a transmission impairment caused by the varying, frequency-dependent velocity of the components of an optical signal as it traverses an optical fiber. Traditionally, the effects of chromatic dispersion are mitigated by inserting lengths of dispersion-compensating fiber (DCF), within dispersion compensation units (DCU), into the signal path. While robust, cost effective, and widely deployed, DCF-based DCUs introduce significant network latency due to the additional propagation delay caused by the several kilometers of fiber they contain. New latency-sensitive network applications, such as high-frequency trading, real-time, interactive video, and cloud-based services demand the lowest possible latency and, therefore, a new approach to dispersion compensation. Fiber Bragg grating (FBG) dispersion compensation provides the same benefits as DCF-based compensation, but with lower and consistent loss, enhanced immunity to nonlinear effects, and almost no added latency.
Figure 1. Cisco ONS 15216 Fiber Bragg Grating Dispersion Compensation Unit.
Cisco ONS 15216 Fiber Bragg Grating Dispersion Compensation Units (FBG DCUs) complement the existing suite of Cisco ONS 15216 DCF DCUs, allowing network operators to choose the DCU technology that is most appropriate for their network requirements. Offered in ten increments between 165 picoseconds per nanometer (ps/nm) and 1983 ps/nm, Cisco ONS 15216 FBG DCUs (Figure 1) allow complete and accurate dispersion compensation for fiber of any length, because they can be cascaded, as well as used at the transmit or receive end (or both) of a network link. The addition of passive inventory capability through an integrated USB port allows Cisco ONS 15216 FBG DCUs to be managed and inventoried with Cisco Transport Controller and Cisco Prime™ Optical when used with the Cisco ONS 15454 Multiservice Transport Platform (MSTP) M6 or M2 chassis.
• Replacement of existing DCF-based DCUs to lower network latency
• Remote passive inventory of DCU modules
• Dispersion compensation for new, latency-sensitive, metro, or long-haul networks
Features and Benefits
• Uniform latency below 25 nanoseconds
• Uniform insertion loss below 3 dB
• 100-GHz channel grid support
• Slope-matched to G.652 fiber
• Support for all wavelength rates, including 10-Gbps, 40-Gbps, and 100-Gbps
• Point-to-point, ring, and mesh network architectures supported
• Passive inventory support with Cisco ONS 15454 MSTP M2 and M6 chassis
• Ideal for single-stage amplification
• ROHS 6-compliant
The Cisco ONS 15216 Dispersion Compensator Shelf (Figure 2) occupies one rack unit, and can hold up to two DCUs.
Figure 2. Cisco ONS 15216 Dispersion Compensator Shelf
The Cisco ONS 15216 FBG DCU can be installed in the dispersion compensation shelf in the following configurations:
• The first slot in the shelf is used for east-to-west traffic, and the second slot is used for west-to-east traffic (Figure 3).
• The first slot in the shelf is used for west-to-east traffic, and the second slot is used for east-to-west traffic (Figure 3).
• Both slots can be cascaded together east-to-west. In this case, the output of the first unit in the first slot is connected to the input of the second unit in the second slot. This configuration provides higher chromatic dispersion compensation than an individual module can provide (Figure 4).
• Both slots can be cascaded together west-to-east. In this case, the output of the first unit in the first slot is connected to the input of the second unit in the second slot. This configuration provides higher chromatic dispersion compensation than an individual module can provide (Figure 4).
Figure 3. Single-Shelf DCU Application East-to-West and West-to-East
Note: In Figures 3 and 4, the triangular symbol represents an amplifier.
Figure 4. Cascaded DCU Shelf per Direction
Tables 1 through 3 provide product specifications for the Cisco 15216 Fiber Bragg Grating Dispersion Compensation Units.