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Principles of CDMA

Principles of CDMA. Optical CDMA advantages:. Perform signal encoding/decoding in optical domain directly – potentially high speed (>100Gbit/s). Avoid electrical/optical and optical/electrical conversion bottleneck. Efficient bandwidth utilization.

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Principles of CDMA

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  1. Principles of CDMA

  2. Optical CDMA advantages: • Perform signal encoding/decoding in optical domain directly – potentially high speed (>100Gbit/s). • Avoid electrical/optical and optical/electrical conversion bottleneck. • Efficient bandwidth utilization. • Data format and protocol transparent – simplified architecture and network maintenance. • Simplified network architecture, less equipment inventory, flexible, scalable network.

  3. Fiber to the home (FTTH)

  4. Challenges: • Accurate and tunable phase control • All-optical switch and amplitude modulation • Integrated circuits with these functionalities Polymeric waveguide based photonic circuits: • Large electro-optic (EO) and Thermo-Optic coefficients: • - polymer TO ~ -1.4 x 10-4/°C; silica, T.O. ~ 1 x 10-5/°C • - Polymer EO ~ 80pm/V, LiNbO3 ~ 33pm/V • Low dielectric constant -- Potentially high–speed operation: • - polymer: r ~ 2.3, Si: r ~ 10 • - Capacitance ~ 5 times smaller than Si based circuits.

  5. 4 Electro-optic SSB modulator Si Electronics l1, l2, l3 l filter EO phase shifter Amplifier Polymeric waveguide based photonic circuits: • Multifunction capability --- Photonic integrated circuits • Flexible substrate, low cost and relative simple fabrications

  6. Fiber to the home (FTTH)

  7. Polymeric waveguide based OCDMA decoder

  8. Received signal SNR • High bit error rate (BER) due to correction noise. • Need long sequence to reduce the correction error.

  9. Orthogonal Amplitude-phase Coding

  10. Optical CDMA Modulation CDMA modulated signal CDMA modulated signal Channel 1 Channel 1 Channel 2 Channel 2

  11. Received signal Time scale 25ps/100units CDMA demodulated channel 1 signal CDMA demodulated channel 2 signal

  12. Polymer Waveguide optical Time Gate

  13. 100Gb/s Tranceivers Difficulties of traditional transceivers • High-speed (>40Gb/s) external modulators not available. • Extremely difficult to achieve CDR using high-bandwidth (>40GHz) electronic circuitry even with low k and scale VLSI technologies. • SNR degradation for ultra-high frequency circuitry. • Very expensive.

  14. 100Gb/s All-optical Transceiver Interface Module Why All-optical Module • Interface the relative slow electronics circuit. • Perform pulse reshape and retiming without OE-EO conversion. • Future all-optical packet routing. Challenges: • 100GHz optical clock generation. • Optical threshold gate. • Re-shaping and re-timing.

  15. Architecture of 100Gb/s Transceiver Interface Module • Photonics integrated circuit approach • Precisely controlled time delays

  16. Architecture of 100Gb/s Transceiver Module Pulse compressor:

  17. Kerr Nonlinearity in Semiconductors Kerr Nonlinearity: in InP semiconductor • Index change and tuning range: • For high index contrast (3.5:1), 10mW laser power induces index changes of 0.03. • Pulse compression ratio >10.

  18. Architecture of 100Gb/s Transceiver Module DeMux:

  19. Architecture of 100Gb/s Transceiver Module Re-timing and re-shaping:

  20. Other possible application – Optical Threshold Gates

  21. Optical phase corruption

  22. 2-D EO phase array

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