Xiaogeng Xu

LDPC convolutional codes using layered decoding algorithm for high speed coherent optical transmission

We successfully realized layered decoding for LDPC convolutional codes designed for application in high speed optical transmission systems. A relatively short code with 20% redundancy was FPGA-emulated with a Q-factor of 5.7dB at BER of 10-15.

Beyond 100-Gb/s Transmission Over 80-km SMF Using Direct-Detection SSB-DMT at C-Band

For short-reach links, direct detection offers the advantages of low cost and low complexity. Discrete multitone (DMT) is a promising format due to its high spectral efficiency, flexibility and tolerance to chromatic dispersion (CD). In this study, we experimentally demonstrate a beyond 100-Gb/s DMT transmission over 80-km single mode fiber (SMF) without CD compensation. Using dual-drive Mach-Zehnder modulator-assisted single-sideband modulation, CD-induced power fading is eliminated after direct detection. Trellis coder modulation (TCM) is used to increase the Euclidean distance of the constellation points and nonlinearity equalization (NLE) is employed to mitigate system nonlinearities. Both TCM and NLE algorithms have contributions to improve the system performance. The experimental results show that high capacities up to 122, 110 and 105 Gb/s are achieved with bit error rate at 4.5 × 10-3 for back to back, 40- and 80-km SMF transmissions, respectively. The required OSNR after 80-km SMF transmission is 34.2 dB. To the best of our knowledge, this study reports the lowest required OSNR and highest capacity for C-band direct-detection transmission over 80-km SMF.

Advanced modulation formats for 400-Gbps short-reach optical inter-connection

Besides the long-haul optical networks covering over thousands of kilometers for backbone transmission, short reach optical networks (SR-ONs) are widely deployed in metro-area for aggregation and accessing. The SR-ONs include the metro optical transport networks (Metro-OTN), optical access networks or other optical inter-connection systems with even shorter distance. As predicted, the growing bandwidth demanding from SR-ONs will be much more than that from the long-haul optical networks in the near future. Besides, there are tremendous amounts of optical terminals and end-users in SR-ONs compared with the long-haul transmission systems and thus will induce large cost and huge energy consumption. So, the power and cost efficiency should be the key consideration for SR-ONs besides the transmission performance. To improve the power and cost efficiency in SR-ONs, advanced modulations and detection techniques based on low power, low cost and integrated optical modulators should be utilized. In this paper, different advanced modulation formats have been discussed. 56Gbps PAM4, 112Gbps poly-binary and 100Gbps DMT that can be used to realize 400-Gbps SR-ONs for different applications have also been demonstrated respectively. In addition, low-cost and low-power opto-electronic components suitable for SR-ONs, the impairments induced by all kinds of defects and bandwidth limitation of opto-electronic components and the corresponding compensation techniques based on DSP algorithms have also been discussed in the experiments.

O-band 400 Gbit/s Client Side Optical Transmission Link

We present an O-band 400 Gbit/s optical client side Ethernet link with 40 km SSMF reach employing four LAN-WDM lanes, MultiCAP modulation and direct detection.

Generation of square or hexagonal 16-QAM signals using a single dual drive IQ modulator driven by binary signals

A simple square or hexagonal 16-QAM generation technique using a commercially available dual drive IQ modulator driven by 4 binary signals is proposed. Square or hexagonal polarization multiplexed (PM) 16-QAM signals at 25Gbaud/s are experimentally demonstrated.

C-band 56Gbps transmission over 80-km single mode fiber without chromatic dispersion compensation by using intensity-modulation direct-detection

C-band 56Gbps transmission over 80-km single mode fiber without chromatic dispersion compensation is realized by using discrete multi-tone modulation based on low cost electro-absorption modulated laser and receiver. The required OSNR of 26.3 dB at BER of 4E-3 is achieved.

Generation of square or hexagonal 16-QAM signals using a dual-drive IQ modulator driven by binary signals

We propose a simple square or hexagonal 16-QAM signal generation technique using a commercially available dual-drive IQ modulator driven by four binary electrical signals with properly designed amplitudes. We analytically derive the required driving signal amplitudes for square and hexagonal 16-QAM and characterize its implementation penalty. Polarization-multiplexed (PM)-16-QAM signals at 28 Gbuad are experimentally demonstrated and stable performance is achieved with simple bias control.

Ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser

An ultra-narrow linewidth full C-band tunable single-frequency linear-polarization fiber laser based on self-injection locking has been demonstrated. By the use of a tunable narrow-band fiber Fabry-Perot interferometer, the laser wavelength could be flexibly tuned from 1527 to 1563 nm with linewidths of < 700 Hz. The laser frequency noise is less than 40 dB re Hz/Hz1/2 at low frequencies (< 100 Hz) and reaches -5 dB re Hz/Hz1/2 at around 25 kHz. The measured relative intensity noise (RIN) is less than -130 dB/Hz with regard to frequencies of over 3 MHz, while the obtained linear polarization extinction ratio (LPER) is higher than 28 dB. This ultra-narrow linewidth low-noise tunable single-frequency linear-polarization fiber laser provides a promising candidate for high-order quadrature amplitude modulation (QAM) optical communication system.

112-Gb/s duobinary 4-PAM transmission over 200-m multi-mode fibre

We experimentally demonstrated an 850-nm VCSEL based 112-Gb/s short reach interconnection system with 200-m MMF transmission employing a duobinary 4-PAM format. The sensitivity of -4.8 dBm at the 6.7% overhead FEC limit (BER=4.2×10-4) was achieved.

Towards 100 Gbps over 100m MMF using a 850nm VCSEL

Employing MultiCAP signaling, successful 70.4 Gbps transmission over 100 m of OM3 MMF using off-the-shelf 850 nm VCSEL with 10.1 GHz 3-dB bandwidth is experimentally demonstrated indicating the feasibility of achieving 100 Gbps with a single 25 GHz VCSEL.