optical telecommunication networks

 Introduction  Multiplexing  Optical Multiplexing  Components of Optical Mux  Application  Advantages  Shortcomings/Future Work  Conclusion  References

 Optical transmission uses pulses of light to transmit information from one place to another through an optical fiber.  The light is converted to electromagnetic carrier wave, which is modulated to carry information as the light propagates from one end to another.  The development of optical fiber has revolutionized the telecommunications industry.  Optical fiber was first developed in the 1970s as a transmission medium.  It has replaced other transmission media such as copper wire since inception, and it’s mainly used to wire core networks.  Today, optical fiber has been used to develop new high speed communication systems that transmit information as light pulses, examples are multiplexers.

 Multiplexing  What are Multiplexers? Multiplexers are hardware components that combine multiple analog or digital input signals into a single line of transmission. And at the receiver’s end, the multiplexers are known as de-multiplexers – performing reverse function of multiplexers.  Multiplexing is therefore the process of combining two or more input signals into a single transmission.  At receiver’s end, the combined signals are separated into distinct separate signal.  Multiplexing enhances efficiency use of bandwidth.

 MATLAB simulation example:  Sampled in time: Quantization Digitization

 Multiplexed Signals  Separation of signals  Using time slots.

 Optical multiplexer and de-multiplexer are required to multiplex and de-multiplex various wavelengths onto a single fiber link.  Each specific I/O will be used for a single wavelength.  One optical filter system can act as both multiplexer and de-multiplexer Laser 1 Laser 2 Laser 3 Laser 4 MultiplexerOptical FiberDe-multiplexer Regenerator + Receiver

 Optical multiplexer and de-multiplexer are basically passive optical filter systems, which are arranged to process specific wavelengths in and out of the transport system (usually optical fiber).  Process of filtering the wavelengths can be performed using:  Prisms  Thin film filter  Dichroic filters or interference filters  The filtering materials are used to selectively reflect a single wavelength of light but pass all others transparently.  Each filter is tuned for a specific wavelength

 Combiner  Tap Coupler  ADD/DROP  Filters  Prisms  Thin film  Dichroic  Splitter  Optical fiber

 There are different techniques in multiplexing light signals onto a single optical fiber link.  Optical Multiplexing Techniques  Optical Time Division Multiplexing (OTDM) Separating wavelengths in time  Wavelength division multiplexing (WDM) Each channel is assigned a unique carrier frequency Channel spacing of about 50GHz  Coarse Wavelength Division Multiplexing (CWDM)  Dense Wavelength Division Multiplexing Uses a much narrower channel spacing, therefore, many more wavelengths are supported.  Code Division Multiplexing Also used in microwave transmission. Spectrum of each wavelength is assigned a unique spreading code. Channels overlap both in time and frequency domains but the code guide each wavelength.

 The major scarce resource in telecommunication is bandwidth – users want transmit at more high rate and service providers want to offer more services, hence, the need for a faster and more reliable high speed system.  Reducing cost of hardware, one multiplexing system can be used to combine and transmit multiple signals from Location A to Location B.  Each wavelength, λ, can carry multiple signals.  Mux/De-Mux serve optical switching of signals in telecommunication and other field of signal processing and transmission.  Future next generation internet.

 High data rate and throughput  Data rates possible in optical transmission are usually in Gbps on each wavelength.  Combination of different wavelengths means more throughput in one single communication systems.  Low attenuation  Optical communication has low attenuation compare to other transport system.  Less propagation delay  More services offered  Increase return on investment (ROI)  Low Bit Error Rate (BER)

 Fiber output  loss + dispersion  Signal is attenuated by fiber loss and distorted by fiber dispersion  Then regenerator are needed to recover the clean purposes  Inability of current Customer Premises Equipment (CPEs) to receive at the same transmission rate of optical transmitting systems.  Achieving all-optical networks  Optical-to-Electrical conversion overhead  Optical signals are converted into electrical signal using photo-detectors, switched and converted back to optical. Optical/electrical/optical conversions introduce unnecessary time delays and power loss. End-to-end optical transmission will be better.

 Research in optical end user equipment  Mobile phones, PC, and other handheld devices receiving and transmitting at optical rate.  Fast regeneration of attenuated signal  Less distortion resulting from fiber dispersion.  End-to-end optical components  Eliminating the need for Optical-to-Electrical converter and vise versa.

 Optical multiplexing is useful in signal processing and transmission.  Transporting multiple signals using one single fiber link  The growth of the internet requires fiber optic transmission to achieve greater throughput.  Optical multiplexing is also useful in image processing and scanning application.  Optical transmission is better compare to other transmission media because of its low attenuation and long distance transmission profile.

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