Study On Large-Capacity Digital Coherent Fiber-Wireless Integration System And Network

Fiber-wireless integration communication can satisfy the double requirements for communication bandwidth and mobility in the future communication networks, and it has become a significant subject in the field of optical communication to investigate large-capacity high-spectral-efficiency high-receiver-sensitivity digital coherent fiber-wireless integration system and network. This dissertation has deeply studied the three kinds of key techniques for the realization of digital coherent fiber-wireless integration system and network:photonic milimeter-wave (mm-wave) generation technique based on romote heterodyning, heterodyne coherent detection technique based on advanced digital signal processing (DSP) as well as antenna multiple-input multiple-output (MIMO) technique. Moreover, based on these key techniques, this dissertation has proposed and experimentally demonstrated several novel large-capacity high-spectral-efficiency high-receiver-sensitivity fiber-wireless integration network architecture:100G fiber-wireless integration system based on optical polarization division multiplexing and antenna MIMO, 400G ultra-high-speed multi-dimensional multiplexing fiber-wireless integration system as well as large-capacity fiber-wireless-fiber integration system based on photonic mm-wave generation and demodulation. The main novelty of this dissertation can be conclued as follows:1. We have proposed a multi-channel frequency-locked optical multi-carrier source based on multi-wavelength recirculating frequency-shifting (RFS) loop. We also experimentally demonstrated, when the optical seed source adopts two individual lasers with-1 THz frequency spacing and the in-phase/quadrature (I/Q) modulator in the RFS loop are driven by a 25 GHz sinusoidal radio-frequency (RF) clock, the proposed multi-channel optical multi-carrier source can realize dual-channel optical multi-carrier generation:one channel includes 28 optical subcarriers with subcarrier spacing of 25 GHz and tone-to-noise ratio (TNR) larger than 20.0 dB, while the other includes 29 optical subcarriers with subcarrier spacing of 25 GHz and TNR larger than 23.0 dB. Because optical carrier frequency is much higher than mm-wave carrier frequency, two optical subcarriers with a frequency spacing equal to a certain mm-wave frequency can be selected from the generated multiple optical subcarriers via a tunable optical filter or wavelength selective switch, and then used to generate the desired mm-wave carrier frequency by heterodyne beating.2. We have proposed the simplified heterodyne coherent detection technique based on spectral shaping and advanced DSP algorithms, which can realize the high-sensitivity reception for the ultra-high-speed ultra-long-haul high-spectral-efficiency optical signal. We have experimentally demonstrated the heterodyne coherent reception for the 8×112 Gb/s wavelength-division-multiplexing (WDM) polarization-division-multiplexing quadrature-phase-shift-keying (PDM-QPSK) signal after 1120 km single-mode fiber-28 (SMF-28) transmission with 4 bit/s/Hz net spectral efficiency and 25 GHz channel spacing, the heterodyne coherent reception for the 4 X 196.8 Gb/s WDM PDM-QPSK signal after 1040 km SMF-28 transmission with 3.678 bit/s/Hz net spectral efficiency and 50 GHz channel spacing as well as the heterodyne coherent reception for the 8X240 Gb/s WDM PDM-QPSK signal after 2100 km SMF-28 transmission with 4 bit/s/Hz net spectral efficiency and 50 GHz channel spacing.3. We have experimentally demonstrated the seamlessly-integrated delivery of the 108 Gb/s@100 GHz PDM-QPSK signal first over 80 km SMF-28 and then over 1 m 2X2 MIMO wireless link based on optical polarization division multiplexing and antenna MIMO. At the wireless recevier, two-stage down conversion is performed for the received 100 GHz wireless mm-wave signal, that is, the first-stage analog down conversion based on sinusoidal RF signal and balanced mixer as well as the second-stage digital intermediate-frequency (IF) down conversion based on DSP. Then, signal polarization de-multiplexing is realized by classic constant modulus algorithm (CMA) equalization. The bit-error ratio (BER) for the 108 Gb/s@100 GHz PDM-QPSK signal is less than the hard-decision forward-error-correction (HD-FEC) threshold of 3.8×10-3 after both 1-m 2×2 MIMO wireless delivery and 80-km SMF-28 transmission.4. We have experimentally demonstrated the seamlessly-integrated delivery of the 2×56 Gb/s@ 37.5 GHz PDM-QPSK signal first over 80 km SMF-28 and then over 2 m 4×4 MIMO wireless link based on antenna horizontal-polarization (H-polarization) and vertical-polarization (V-polarization) multiplexing. We have experimentally investigated the antenna polarization crosstalk caused by the antenna polarization angle during the adoption of antenna polarization multiplexing and obtained the maximum antenna polarization angle the system can tolorate. At the wireless receiver, classic CMA equalization can simultaneously realize signal polarization de-multiplexing and the suppression of wireless interference at the same antenna polarization. The BER of each channel after 2-m MIMO wireless delivery can be under 1×10-5.5. We have experimentally investigated the wireless MIMO interference effect as well as the equivalent differential group delay (DGD) effect caused by different wireless transmission distance existing in the large-capacity fiber-wireless integration sytem. We have experimentally demonstrated the DSP-based long-tap CMA equalization at the receiver can effectively overcome both the wireless MIMO interference and equivalent DGD effects.6. We have experimentally demonstrated the low-wireless-interference easy-installation large-capacity fiber-wireless integration sytem based on antenna polarization diversity, which can realize the seamlessly-integrated delivery of up to 156 Gb/s@100 GHz PDM-QPSK signal first over 80 km SMF-28 and then over 2 m 2×2 MIMO wireless link. After removing 20% soft-decision forward-error-correction (SD-FEC) overhead, the 156 Gb/s total bit rate is corresponding to a net bit rate of 130 Gb/s, which, to our best knowledge, is the highest bit rate per polarization-division-multiplexing channel demonstrated for wireless signal delivery up to now.7. We have experimentally demonstrated a 400G ultra-high-speed multi-dimensional multiplexing fiber-wireless integration system simultaneously delivering 2x112 Gb/s two-channel polarization-division-multiplexing 16-ary quadrature amplitude modulation (PDM-16QAM) signal at 37.5 GHz wireless carrier and 2x108 Gb/s two-channel PDM-QPSK signal at 100 GHz wireless carrier, adopting photonic mm-wave generation, antenna polarization multiplexing, multiple mm-wave band multiplexing, MIMO and advanced DSP. To our knowledge, the 400 Gb/s bit rate after removing FEC overhead is the highest capacity record of wireless delivery.8. We have proposed the RF-transparent photonic demodulation technique, which can realize the conversion of the polarization-division-multiplexing wireless mm-wave signal to the optical signal as well as long-haul fiber transmission of the converted optical signal. Based on the RF-transparent photonic demodulation technique adopting push-pull Mach-zehnder modulator (MZM), we have experimentally demonstrated up to 40 Gb/s@40 GHz PDM-QPSK signal can be first transmitted over 20-km SMF-28, then delivered over 2-m 2x2 MIMO wireless link and finally transmitted over another 20-km SMF-28. We then experimentally demonstrated up to 109.6 Gb/s@95 GHz PDM-QPSK signal can be first transmitted over 80-km SMF-28, then delivered over 2-m 2x2 MIMO wireless link and finally transmitted over another 80-km SMF-28.