Optical Networks

1. Optical Networks Arvind Gopu Raj Adhikari

2. Overview • High-capacity telecommunications network based on optical technologies and components • Based on the emergence of the optical layer in transport networks. • Provide higher capacity and reduced costs for applications such as the Internet, video and multimedia communication and advanced digital services.

3. Emergence of Optical Networks • Started with the advent of fiber optics • Researchers found that further technological improvements could: • Greatly increase capacity • Reduce cost in existing networks. • Led to optical networks as it is today.

4. Optical Amplifiers • Optical Networks use Erbium-doped optical amplifiers • By doping small strand of fiber with rare earth metal “erbium”, optical signals could be amplified without converting the signal back to an electrical state. • Provides enormous cost savings over electrical regenerators

5. Optical Amplifiers (Cont’d…) • Current amplifiers provide significantly lower noise and flatter gain • Essential to performance of optical amplifiers • Has helped DWDM systems improve significantly • Total power of amplifiers also has steadily increased, with amplifiers approaching +20–dBm outputs, • many orders of magnitude more powerful than the first amplifiers.

6. Narrowband Lasers • A narrow, stable, and coherent light source essential for the optical components • Advanced lasers with narrow bandwidths provide the narrow wavelength source that is the individual channel in optical networks. • These laser sources emit a highly coherent signal that has an extremely narrow bandwidth.

7. Fiber Bragg Grating • A small section of fiber that is modified to create periodic changes in the index of refraction • Important component for enabling WDM and optical networks • Depending on the space between the changes, a certain frequency of light—the Bragg resonance wavelength—is reflected back, while all other wavelengths pass through

8. Fiber Bragg Grating (cont’d…) • Wavelength-specific properties of the grating make fiber Bragg gratings useful in implementing optical add/drop multiplexers. • Multiplexer combines multiple wavelengths onto a single fiber which allows all the signals to be routed along the same fiber thus increasing the capacity on existing fiber routes without adding more fiber. • Is also being developed to aid in dispersion compensation and signal filtering as well

9. Thin Film Substrates • Coating a thin glass or polymer substrate with a thin interference film of dielectric material lets through only a specific wavelength and reflect all others. • Many optical network devices including multiplexers, demultiplexers and so forth are created by integrating several of these components

10. Improving Efficiency/Performance • In General, enterprise networks have long been built using TDM and Ethernet LAN technologies • Inadequate for broader services needs both from a cost/complexity and a services support perspective • Is the single wave optical network a solution? • NO

11. Broadband WDM • Using fused biconic tapered couplers twice the bandwidth could be attained using 1 fiber • Two signals could be combined on the same fiber.

12. Broadband WDM (cont’d…) • Flat-gain optical amplifiers also allow combination of many wavelengths across a single fiber • Limitations in the technology meant the signal frequencies had to be widely separated (Initially) • Today that limitation has been largely overcome

13. Dense WDM • Improvement on Broadband WDM • Combines more than two signal wavelengths on a fiber • Can range from 40 to 80 channels

14. UniDirectional/BiDirectional DWDM • All the wavelengths travel in the same direction on the fiber

15. UniDirectional/BiDirectional DWDM • Signals are split into separate bands, with both bands traveling in different directions.

16. Broad band channel Spectrum……

18. More on DWDM (Details) • Operates in the C and L band (1530-1560 nm and 1570-1600 nm, respectively) • DWDM channel frequencies typically spaced at either 200 GHz (1.6 nm) or 100 GHz (0.8 nm) yielding massive and unparalleled bandwidth scalability • These factors though increase cost of DWDM laser transmitters and related technologies

19. CWDM – Coarse WDM (An Alternative new technology) • Base of CWDM technology - offer acceptable optical bandwidth scalability at reduced price points but by defining much broader channel spacing, typically 2500 GHz (20 nm), over the available spectral bands • Helps curtail component costs • Most current CWDM components cover the C and L band region (similar to DWDM) and also operate in part of the S band (1460-1530 nm range)

20. The future of Optical Networks • Consumers will have access to new high-bandwidth services made possible by the increased capacity afforded by the optical layer • Services that today are considered prohibitively expensive such as videoconferencing to the desktop (or home), electronic commerce, and high-speed video imaging, will become commonplace because they will be technologically and economically feasible

21. Future – Optical Layer • Impact of the new optical layer in the telecommunications network is astounding • Can be measured in two ways: • Economic impact • Ability of carriers to offer new services • Optical-layer technology will increase network capacity, allowing network providers to transport more than 40 times the traffic on the same fiber infrastructure • Bandwidth becomes more affordable

22. Conclusion • In essence, optical-layer technology will improve the way we live!!!