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Photo Detectors for Fiber Optic Communication

Eric Gallo. Fiber Optics ECE-E641 Winter 2003. Photo Detectors for Fiber Optic Communication. Photo-detectors. Convert light energy (photons) back into electrical signals in communication Broad range of devices with varying range of light absorption

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Photo Detectors for Fiber Optic Communication

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  1. Eric Gallo Fiber Optics ECE-E641 Winter 2003 Photo Detectors for Fiber Optic Communication

  2. Photo-detectors • Convert light energy (photons) back into electrical signals in communication • Broad range of devices with varying range of light absorption • Speed, efficiency and cost vary widely from device to device

  3. Operation of Detectors

  4. Types of Detectors • Photo Conductors • PIN photodiodes • Avalanche photodiodes • Phototransistors • MSM Photodetectors • Heterostructure MSM Photodetectors

  5. Quality Factors • Responsivity • Ratio of photons incident to current produced • Quantum Efficiency • Ratio of photons incident to EHP produced • Capacitance • Gain-Bandwidth Product • FWHM, rise time, fall time • Noise • Signal-to-noise ratio

  6. PIN Photodiodes • Large absorption area • Simple fabrication • Unity gain • Speed dependent on width • Thermally generated carriers create noise within region

  7. PIN Photo diodes

  8. Avalanche Effect

  9. Avalanche Photodiodes • High gain due to avalanche multiplication effect • Increased noise • Silicon has high gain but low noise • Si-InGaAs APD often used(diagram on right)

  10. Metal-Semiconductor-Metal Photodiodes • Similar operation to PIN diodes • Low noise due to Schottky barriers • Speeds dependent on carrier transit time (350GHz measured)

  11. Faster Response Time Lower Dark Current due to enhanced Schottky barriers Compatible with HEMT technology Heterostructure MSM Photodiodes

  12. FWHM 11ps Internal quantum efficiency approximately 1 Dark Current 15pA High wavelength selectivity HMSM with Distributed Bragg Reflector

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