Radio-over-fiber signal generation and transmission techniques utilizing photonic systems

Abstract

Recently, demands of high speed, low latency and broad bandwidth communication systems have been increased to serve high technology mobile applications including intenet of things and machine-to-machine communication. For this reason, radio-over-fiber (RoF) technology can be one of promise candidate future integrated wired and wireless communication system since it have ultra-wide bandwidth, ultra-low loss, and wide optical wavelength capacity. Therefore, RoF technology is most suitable for systems requiring a large number of antenna stations because most signal generation processes are performed at the central office. For this reason, optical frequency up- and down-conversion techniques are very important issue in RoF technology. In this thesis, various optical frequency up- and down-conversion techniques to generate high performance up- and down-converted signals are proposed and experimentally demonstrated. For optical frequency up-conversion, two type of all-optical single sideband (SSB) frequency up-converters utilizing nonlinear effect in SOA-MZI were proposed and analyzed. In chapter 3, all-optical SSB frequency up-conversion technique utilizing cross gain modulation (XGM) effect in SOA-MZI was proposed and experimentally demonstrated for 60 GHz band wired and wireless communication system. Proposed all-optical SSB frequency up-converter has high immunity for chromtic dispersion (CD) effect which induce electrical power fluctuation, at the receiving site, according to length of optical transmisstion line. Moreover, it has enhanced phase noise characteristic without compensation with an additional optical delay line. The proposed all-optical SSB frequency up-converter showed a conversion efficiency of 15 dB with 3-dB IF freuqency bandwidth of approximately 9.1 GHz. The linearility of proposed all-optical SSB frequency up-converter was measured approximately 74.66 dB/Hz2/3 with an up-converted 48 GHz RF signal. Measured SFDR performance meets the requirement for analog fiber-optics link in personal communication systems. In addition, transmission performance of 5 Gb/s OFDM-QPSK data modulated 60 GHz band RF signal was also experimentally demonstrated and lower BER than the forward error correction (FEC) was measured. In chapter 4, all-optical SSB frequency up-converter utilizing cross phase modulation (XPM) effect in an SOA-MZI for WDM application is proposed and experimentally demonstrated. Main purpose of the experiment in chapter 4 is generating WDM-RoF signals with a format of optical single sideband (OSSB). The proposed WDM all-optical SSB frequency up-converter simultaneously generates 8 channel of WDM-OSSB signal with a carrier frequency of 60 GHz. Th 3-dB IF bandwidth was measured approximately 10.5 GHz which is enough for future broadband wired and wireless communication system. Morevoer, proposed system has flat electrical up-converted RF signal power as a function of RF frequency upto 75 GHz. The performance of SFDR for each WDM channels were satisfying the requrment for analog fiber-optics link and the minimum SFDR was measured approximately 86.15 dB/Hz2/3 with an up-converted 48 GHz RF signal. The phase noise of up-converted electrical RF signals were measured without serious deteriorate comparing that of optical LO signal and it also not required additional optical delayline to compensate phase noise deteriorate phenomenon due to path length difference. Transmission performance of 10 Gb/s OFDM-16QAM data modulated 60 GHz band RF signal was also investigated and lower BER than the forward error correction (FEC) limit was measured at the overall WDM channels. In addition, the power penalty of simultaneous WDM signal generation (8 channel) was investigated and compred to the case of single channel all-optical SSB RF signal generation. In order to study and develop the high performance optical frequency down-converter, researches have been carried out to improve the efficiency and performance of optoelectronic oscillator (OEO), which can generates ultra-low phase noise electrical and optical micro- and millimeter-wave signals. In chapter 5, frequency-doubling optoelectronic oscillator (FD-OEO) utilizing two cascaded EAM was proposed and experimentally demonstrated. FD-OEOs provide more wide operation bandwidth compare to standard OEO. Moreover, proposed FD-OEO has simple strucuture and does not required additional optical devices such as polarization controller, polarizer, and dispersive optical materials. The phase noise of the OEO feedback loop signal of 10 GHz signal is measured to be -94.25 and that of the FD-OEO signal of 20 GHz signal is measured to be -87.71 dBc/Hz at a 10 kHz frequency offset. In chapter 6, optical freuqnecy down-converter based on FD-OEO utilizing two cascaded EAM was proposed and experimentally demonstrated. Proposed OEO based optical frequency down-converter has high RF-to-LO isolation characteristic so that data of RF signal is not affected on the performanc of OEO feedback-loop for direct down-conversion mode. The phase noise of down-converted IF signal (3 GHz) and that of frequency doubled LO signal (20 GHz) were measured -95.32 and -97.80 dBc/Hz, respectively. The 3-dB bandwidth of proposed photonic frequency down-converter was measured approximately 10 GHz, and was limited by the 3-dB bandwidth of EAM2. In addition, the BER performance of proposed photonic frequency down-converter was experimentally demonstrated with 1.25 Gb/s pseudorandom binary sequence (PRBS) data and bit error rate (BER) performance below error free condition was achieved.