Optical communication systems have been widely preferred for network communications, especially for
Datacoms Local Area Network links. The optical technology is an excellent candidate for on-board systems
due to the potential weight saving and EMC immunity. According to the short length of the link and a cost
saving, Vertical Cavity Surface Emitting Laser (VCSEL) and multimode fiber are the best solution for gigabit
systems. In this context, we propose a modeling of 850nm VCSEL based on the rate equations analysis to
predict the optical interconnect performances (jitter, bit error rate). Our aim is to define the operation
conditions of VCSEL under large signal modulation in order to maximize the Extinction Ratio (current I<sub>OFF</sub>
below threshold) without affecting link performances. The VCSEL model is developed to provide large signal
modulation response. Biasing below threshold causes stochastic turn-on delay. Fluctuations of this delay
occur, due to the spontaneous emission. This leads to additional turn-on jitter. These stochastic effects are
included in the model by adding the Langevin photon and electron noise sources.
The VCSEL behavior under high-speed modulation is studied to observe the transient response and extract the
resonance frequency, overshoot and turn-on delay. The associated jitter is evaluated with the standard
deviation of the turn-on delay probability density function.
Simulations of stochastic and deterministic jitters are realized under different conditions of modulation (OFF
current levels). Comparing simulations with measurement results carried out on VCSEL and a short haul
gigabit link validates the approach.
Low cost and intrinsic performances of 850 nm Vertical Cavity Surface Emitting Lasers (VCSELs) compared
to Light Emitting Diodes make them very attractive for high speed and short distances data communication
links through optical fibers. Weight saving and Electromagnetic Interference withstanding requirements have
led to the need of a reliable solution to improve existing avionics high speed buses (e.g. AFDX) up to 1Gbps
To predict and optimize the performance of the link, the physical behavior of the VCSEL must be well
understood. First, a theoretical study is performed through the rate equations adapted to VCSEL in large
signal modulation. Averaged turn-on delays and oscillation effects are analytically computed and analyzed
for different values of the on- and off state currents. This will affect the eye pattern, timing jitter and Bit Error
Rate (BER) of the signal that must remain within IEEE 802.3 standard limits. In particular, the off-state
current is minimized below the threshold to allow the highest possible Extinction Ratio. At this level, the
spontaneous emission is dominating and leads to significant turn-on delay, turn-on jitter and bit pattern
effects. Also, the transverse multimode behavior of VCSELs, caused by Spatial Hole Burning leads to some
dispersion in the fiber and degradation of BER. VCSEL to Multimode Fiber coupling model is provided for
prediction and optimization of modal dispersion. Lastly, turn-on delay measurements are performed on a real
mock-up and results are compared with calculations.