1. Transmisi Optik Pertemuan 10 Matakuliah: H0122 / Dasar Telekomunikasi Tahun: 2008

2. Bina Nusantara 2 Mahasiswa dapat menyebutkan prinsip transmisi optik, jenis komponen serta kelebihan dan kerugiannya dibandingkan media lainnya. Learning Outcomes

3. Bina Nusantara 3 Karakreristik Serat optik Jenis & kinerja serat optik Sumber & detektor Sistem Transmisi Outline Materi

4. Bina Nusantara 4 Basic Components Signal conditioner (encoder for digital) Signal conditioner (decoder for digital) Photo detector Fiber/detector coupling Light/fiber coupling mechanism Light source, LED or laser Optical fiber Input information signal Amplifier Output information

5. Bina Nusantara 5 Characteristics – Use around 360 terahertz (3.6 x 10 14 Hz) – Use wavelength between 600 and 1500 nanometer – Visible light spans 430 to 690 nm Advantages: – Tremendous bandwidth and high rate which can support 100 Mbit/s – No interference – Immune to nearby signals and EMI/RFI – Complete electrical isolation between end of the link Characteristiscs

6. Bina Nusantara 6 Advantages: – Tremendous bandwidth and high rate which can support 100 Mbit/s – No interference, immune to nearby signals and EMI/RFI – Complete electrical isolation between end of the link – Secure from unauthorized listeners – Can be used in danger area, Lightweight Disadvantages: – Cost relatively expensive – Difficult to splice optical fibers to make them longer or to repair breaks – Complex to attach to the cable and require precise physical equipment – Switching and routing of fiber optics signals is difficult Adv/Disadvantages

7. Bina Nusantara 7 Optical fiber is a thin strand glass or plastic and consist of three parts: – Core - is transmission area of the fiber – Cladding - has a different index of refraction – Coating - surrounds the core and cladding Core and cladding act as an optical waveguide or light pipe Fiber Optic

8. Bina Nusantara 8 Fibers are identified by the type of paths, or modes – Multiple pathway  multimode Dispersion limit the maximum data rate and bandwidth – Dispersion is much less critical at lower data rates Two types of multimode fibers : – Step index and graded index Fiber Types

9. Bina Nusantara 9 Fiber Types

10. Bina Nusantara 10 Show a sharp-like difference in the refractive index of the core vs the surrounding cladding Relatively inexpensive to produce and useful at lower rates or shorter distance Step Index Bina Nusantara

11. 11 More complex Contain many thin layers, each with a lower index of refraction than the adjacent inner core The dispersion of graded index fibers is less than step index fibers Useful at longer distances and higher rates but more costly Diameter of core is 50 through 100 μm Graded Index

12. Bina Nusantara 12 Only a single light wave ray path or mode to be transmitted down to core Virtually eliminating any possibility of dispersion and overlap The core diameter is about 5 μm Gives the highest rate and longest distances Highest overall cost Mono/Single Mode

13. Bina Nusantara 13 The two most important parameter are bandwidth and transmission loss or attenuation Factors that limit the bandwidth are dispersion and transmission loss The attenuation due to transmission loss reduces the optical signal power, measured in dB/km There are five causes of this attenuation and loss of optical power within the fiber: optical fiber loss, micro bending loss, connector loss, splice loss, and coupling loss. Fiber Performance

14. Bina Nusantara 14 There are two fiber optic sources: light emitting diode (LED) or laser diode LED are low cost and produce output that is nearly linear with the applied drive current, current greater than a very low threshold level must be applied to them before they begin to operate LED has efficiencies between 30 and 70% LED used for shorter distance fiber optics system, up to several tens of kilometers LED can only achieve pulse rates up to about 100 Mhz The spectrum of output LED is not very sharp is about an 850 nm center Light Source

15. Bina Nusantara 15 The relatively large numerical aperture of LEDs requires larger fiber for effective coupling of emitted light into the fiber Uses a much smaller junction area than that in LED and the concentration of injected carriers (holes and electrons) is much higher Can produce large amount of optical output power (20 to 100 mW) with a very narrow output spectrum Produces a very tightly directed beam with small NA which can be directed into the fiber with little loss Suitable for use with the thin single mode fibers Can operate at rates exceeding 1 Ghz but need more complex circuitry to drive Laser Diodes

16. Bina Nusantara 16 Detectors converts the small amount of light energy received (photon) into an electrical signal efficiently. Detector must be a low noise device Three type of devices are used as detectors: 1. Photoconductors Inexpensive, have dark current that reduces overall performance of the system, and its resistance is determined by the device gain 2. PIN diodes 3. Avalanche photodiodes Light Detectors

17. Bina Nusantara 17 2. PIN diodes – Relatively inexpensive, have low noise, and interface easily with conventional electronic circuitry. – Fabricated from Si for maximum sensitivity at 850 nm, and Ge or InGaAsP for operation with wavelengths of about 1000 nm – Are reverse biased in operation – Gives bandwidth greater than 10 GHz 3. Avalanche photodiodes (APD) Are similar to Pin diodes but more sensitive and have higher SNR. Light Detectors

18. Bina Nusantara 18 Telah dipelajari gambaran umum sistem optik. Telah dipelajari klasifikasi serat optik. Telah dipelajari komponen sistem optik. Summary