Adaptively Encoding Multimode VCSEL With Spectral Efficient Data Formats for Seamless Wired-Wireless Network Coverage

Abstract

The multiple data formats such as the quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM), generalized frequency division multiplexing (GFDM), and discrete multi-tone (DMT) are discussed for the 850-nm multi-mode vertical-cavity surface-emitting laser (MM-VCSEL) based transmission in back-to-back (BtB) and OM5-multimode fiber (OM5-MMF) cases. The 850-nm MM-VCSEL with 7-μm oxide aperture and 25-μm microstrip length was directly modulated using these advanced modulation schemes with high-spectral-usage bit-rate-coding efficiency. The MM-VCSEL biased at a DC of 20I _th exhibits about 6∼7 transverse modes. As bias current increases, the frequency response of the MM-VCSEL can be effectively broadened. Simultaneously, the relative intensity noise (RIN) around 10∼20 GHz also reduces to −146.6 dBc/Hz at 12 mA to further improve the transmitted signal-to-noise ratio (SNR) performance. However, the enhanced mode partition noise (MPN) occurs to degrade the SNR in frequency division multiplexing transmission in the low-frequency region. After using the pre-emphasis of data format, the QAM-OFDM transmission capacity can be improved to 136 Gbit/s in the BtB case and 100 Gbit/s in the 100-m OM5 MMF case. The promising GFDM for 5G/6G wireless with time/frequency synchronization insensitivity, low peak-to-average power ratio (PAPR), and low out-of-band radiation is also optimized for encoding the VCSEL under the trade-off between BER and PAPR. The PAPR of GFDM drops to 11 dB when setting the (K, M) = (128, 4) for achieving the complementary cumulative distribution function of PAPR as 0.1; however, which only enables BtB at 88 Gbit/s and 100-m-MMF at 68 Gbit/s as the SNR degrades in some blocked GFDM subchannels because of the over exhausted energy. To obtain the maximal bandwidth utilization efficiency, the DMT technique formed by adaptive QAM mapping and bit distribution is adopted to upgrade the data rate to 145 Gbit/s for the BtB link. Nevertheless, all coding formats enable the flexibility for seamless bridging of wired and wireless formats for future heterogeneous network transmission.