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Optical Link Budget

Optical Link Budget

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Optical Link Budget

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  1. Optical Link Budget ECE 4006 Gb Ethernet Optoelectronic Links

  2. Logical Flow for Optical Link Power Budget Output current from laser driver (mA) Vertical Cavity Surface Emitting Laser Slope Efficiency (mW/mA) Optical signal on optical fiber Input optical signal to photodetector Responsivity (A/W) Input current to receiver (mA)

  3. Sample VCSEL Specs Honeywell HFE4380-521 VCSEL specifications. - Honeywell HFE4384-522 VCSEL specifications. -

  4. Sample Photodetector Specs Lasermate RSC M85A306 photodetector specifications. - Hammamatsu S5973 photodetector specifications.

  5. HFE4380-521 HFE4384-522 Ith (mA) 6 6 DC bias of laser (mA) 7.2 7.2 Slope Efficiency (mW/mA) 0.04 0.15 Modulation Current of TX (mA) 30 30 Range of Power Output (mW) 0.288 - 1.2 1.08 - 4.5 Range of Power Output (w/ Loss) (mW) 0.144 - 0.6 0.54 - 2.25 Responsivity of Lasermate PD (A/W) 0.4 0.4 Responsivity of Hamamatsu PD (A/W) 0.47 0.47 Range of Current from Lasermate PD (uA) 57.6 - 240 216 - 900 Range of Current from Hamamatsu PD (uA) 67.7 - 282 253.8 - 1057.5 Sample Optical Power Link Budget

  6. Optical Link Budget Issues • Choose only components that will achieve Gb Ethernet compliant data rates. • What is the range of output currents from the laser driver? • What is the slope efficiency and min/max output from the VCSEL? • What are the fiber and connector losses? • What is the total input power to the PD? • What is the responsivity of the PD? • What is the dark current of the PD? • What is the max PD input power? • What is the min/max PD output current such that the receiver operates? • What is the capacitance of the PD? (this needs to be matched to the receiver to achieve Gb Ethernet compliant data rates).

  7. Optical Packaging Issues • Alignment tolerance and power dissipation directly affect the cost of the module. Consider these issues when specifying the VCSEL, PD, and fiber. • Alignment tolerance: maximize the alignment tolerance (how much the fiber/VCSEL and fiber/PD can be misaligned, yet still get a Gb Ethernet compliant eye) • Evaluate the effect of the VCSEL aperture and divergence angle • Evaluate the effect of the MMF (multimode fiber) core diameter and numerical aperture (NA) • Evaluate the effect of the PD responsivity and aperture • Power dissipation: minimize the power dissipation (run the optical link at the lowest power possible, and with the least power dissipation, yet still get a Gb Ethernet compliant eye) • Evaluate the effect of the VCSEL slope efficiency • Evaluate the effect of the PD responsivity • Note: the bandwidth/distance product for 50 mm diameter core MMF is larger than for 62.5 mm diameter core fiber. We will use 62.5 mm MMF in this class

  8. Alignment Tolerant Fiber/OE Component Connection Fiber core Fiber core VCSEL/PD VCSEL/PD Longitudinal Misalignment Transverse Misalignment