Transcript Optical Link Budget

Optical Link Budget
ECE 4006
Gb Ethernet Optoelectronic Links
Logical Flow for
Optical Link Power Budget
Output
current from
laser driver
(mA)
Vertical Cavity Surface
Emitting Laser
Slope Efficiency
(mW/mA)
Input optical signal to
photodetector
Responsivity (A/W)
Input current
to receiver
(mA)
Optical signal
on
optical fiber
Sample VCSEL Specs
Honeywell- HFE4380-521 VCSEL specifications.
Honeywell- HFE4384-522 VCSEL specifications.
Sample Photodetector Specs
Lasermate
RSC M85A306 photodetector specifications.
Hammamatsu S5973 photodetector specifications.
Sample Optical Power Link Budget
HFE4380-521 HFE4384-522
Ith (mA)
6
6
7.2
7.2
0.04
30
0.15
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
0.4
0.4
0.47
0.47
57.6 - 240
67.7 - 282
216 - 900
253.8 - 1057.5
DC bias of laser (mA)
Slope Efficiency (mW/mA)
Modulation Current of TX (mA)
Responsivity of Lasermate PD (A/W)
Responsivity of Hamamatsu PD (A/W)
Range of Current from Lasermate PD (uA)
Range of Current from Hamamatsu PD (uA)
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).
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
Alignment Tolerant
Fiber/OE Component Connection
Fiber core
Fiber core
VCSEL/PD
VCSEL/PD
Transverse
Misalignment
Longitudinal
Misalignment