30 Gbps 4-PAM transmission over 200 m of MMF using an 850 nm VCSEL

Abstract

We present high speed real time, error free 4-PAM transmission for short range optical links based on a VCSEL operating at 850 nm, a multimode fibre and a simple intensity detector. Transmission speeds of 25 Gbps and 30 Gbps are demonstrated, and the maximum fibre reaches were 300 m and 200 m, respectively. The 4-PAM is also compared with OOK transmission at 25 Gbps, and we find that at this bit rate 4-PAM increases the error free transmission distance in the multimode fibre by 100 m, compared to OOK.

Intersymbol Interference Penalties for OOK and 4-PAM in Short-range Optical Communications

“…The 4-PAM signal was generated and the BER measured in real time using methods demonstrated in [3]. Extra care was taken to ensure the same amplitude of the electrical signal driving the VCSEL for both OOK and 4-PAM.…”

“…Such communications systems predominantly use directly modulated, high speed and low cost vertical cavity surface emitting lasers (VCSELs), multimode fiber (MMF) and direct detection. Many modulation formats have been investigated, for example various forms of single and multiple subcarrier modulation [1,2], pulse amplitude modulation (PAM) [3] as well as many other formats. Short-range optical communications in a datacenter is subject to very stringent constraints on power consumption and cost, which limit the practical complexity of the modulation used.…”

Experimental and theoretical analyses of RSOA-based colorless-ONUs with 4PAM signal in the up-link

“…Multilevel modulation with higher spectral efficiency is one way of extending the reach of multimode fiber at a high bit rate, although complexity is critical in data communication links. Meanwhile, the 4-level pulse-amplitude-modulated (4PAM) signal offers the lowest implementation complexity in the multilevel modulation format with spectral efficiency of 2 bit/s/Hz [14] . The multilevel signal has been used in the re-modulated signal, which has higher dispersion tolerance than the non-return-to-zero (NRZ) signal; however, the light of the injected signal in RSOA is continuous wave (CW) light [15] .…”

“…The encoding method of the 4PAM signal used in our scheme has already been reported [14] . The original data sequence {b k } is pre-coded into the binary sequence {d k }, in accordance with…”

“…The method of calculated error was programmed with binary patterns that correspond to each level. This pattern was then used to calculate the aggregate symbol error rate (SER) and bit error rate (BER) to measure the SER on each level [14] . The optical spectra of the 4PAM signal was half of the NRZ signal spectra and required a smaller re-modulated bandwidth in the RSOA-based colorless ONU.…”