We present results of experimental and theoretical investigations of intersymbol interference in 4-PAM transmission in short-range optical communications links based on the power penalty. A test link comprised of a directly modulated 850 nm VCSEL with up to 200 m of multimode fiber and direct detection was used. The link bandwidth was below 10 GHz and the maximum achieved data rate with 4-PAM was 44 Gbps over 100 m of fiber. In the same case and at similar sensitivity, only 32 Gbps could be achieved with OOK. If typical forward error correction could be applied, the sensitivity of the 4-PAM system was improved by up to 4 dB, reaching –10 dBm at 25 Gbps.
© 2013 IEEE
Krzysztof Szczerba, Petter Westbergh, Erik Agrell, Magnus Karlsson, Peter A. Andrekson, and Anders Larsson, "Comparison of Intersymbol Interference Power Penalties for OOK and 4-PAM in Short-Range Optical Links," J. Lightwave Technol. 31, 3525-3534 (2013)