Research Of Optical Performance Monitoring Techniques

Nowadays, the optical network has evolved to be high speed, reconfigurable and transparent, which has posed challenge to performance ensurrance and also introduced greater complexity of management. The conventional monitoring technique operated in the electrical layer havenot been able to offer solutions for the future reconfigurable optical network. To cope with this, optical performance monitoring technique is investigated to monitor the physical impairments and supply the imformation for futher compensation and rerouting. Optical performance monitoring will be one of the most important techniques to ensure the signal quality and management of the reconfigurable optical network.The following original contributions to the field of optical performance monitoring are made in the course of this reseach:1. We propose a novel OSNR monitoring technique using nonlinear effects with wider OSNR monitoring range and higher sensitivity. The ratio between the transmission and reflection output power of NOLM is used. The theoretical model is built up and the selection of the optimum operation point is shown. The impacts of nonlinear coefficient, length, attenuator factor to the operation point, dispersion and peak power deviation to the monitoring performances are also investigated. We demonstrate the nice performances for NRZ/RZ66/RZ50/RZ33-OOKand-DPSK signals at40Gb/s by simulation and present experimentally that for80Gb/s RZ-DQPSK signal,12.16dB maximum output power variation and13-39.8dB OSNR monitoring range can be achieved. It is shown that this novel technique significantly improves the dynamic range of the output power by7.05dB and monitoring range by13.8dB through comparison experiments between with and without the reflection port. Dispersion less than1.7ps/nm can be tolerated to ensure nice performance. Higher dispersion will deteriorate the performance. The experimental results are consistent with the theoretical forecast. This technique is cost-effective. Furthermore, given the femto-second response time of the highly nonlinear fiber (HNLF), the scheme is promising in ultra-speed systems.2. RF spectrum analyzing techniques which use the characteristics induced by impairments on spectrum have many advantages such as steady performances, without transmitter modification and feasibility for phase modulated signals, and so on. We propose two schemes and investigate the performances of monitoring OSNR, CD and PMD independently and simultaneously.First, we investigate the OSNR monitoring using beat noise at the low RF frequency band. It only uses a narrow band filter located at the carrier wavelength and low frequency detector. The theoretical model is given and the performance for80Gb/s NRZ-DQPSK signal is investigated. The impacts of filter bandwidth, power at the receiver, monitoring frequency, CD and PMD are also investigated. The8-33.5dB OSNR monitoring range with25.4dB dynamic output power variation can be achieved at100MHz RF frequency.Second, based on the technique of CD-insensitive PMD monitoring, we propose a novel scheme of PMD-insensitive CD monitoring based on the RF power ratio. The monitoring performance for80Gb/s NRZ-DQPSK signal is demonstrated. With the offset position of the band-stop filter set at10GHz, DGD monitoring with50ps range and42.7dB output dynamic range, and CD monitoring with246.7ps/nm range and22.3dB dynamic range can be achived. The impacts of DGD, position and bandwidth of the band-stop filter, RF frequency and bandwidth of electrical band-pass filter for the CD monitoring are also investigated. The simple scheme has the ability of monitor PMD and CD simultaneously. It can use low frequency detector and doesn’t have to modificate the transmitter.3. All-optical logic gates are crucial elements in future to perform ultra-fast optical signal processing functions. Reconfigurable and multi-functional logic gates are highly preferred as they can provide a more flexible set of network functions.It is the first time that a reconfigurable logic gate for NRZ-PolSK signals based on FWM in a HNLF are proposed and experimentally demonstrated. By adjusting the PCs at the input and output, half-subtracter, XOR, AB, AB or XNOR, AND and NOR gates can be realized simultaneously. The measured Q factors for eye-diagrams are all above8dB. Among them, Q factors of AB, AB, AND and NOR gates are higher than those of XOR and XNOR gates. The input power for the HNLF is optimized to be as low as about15.2dBm, which can help to alleviate the impact of ASE noise brought by EDFAs. Error-free operation is achieved for10Gb/s27-1pseudorandom bit sequence (PRBS) data. Power penalties for the reconfigurable logic gate are less than3dB. Simulation analysis of wavelength characteristic for all logic gates predicts that the reconfigurable logic gate can realize error-free operation when the wavelength separation is less than5nm. The setup is simple and flexible.Based on the above experimental demonstration, we exploit a new bidirectional structure to realize the simultaneous implementation for RZ-PolSK signals at40Gb/s using bidirectional FWM in HNLF. The structure not only decreases the cost because only one spool of HNLF is used, but also implement all the logic functions simultaneously, including simple functions such as XOR, XNOR, AB, AB, AND, NOR and the complex functions such as half adder, half subtracter, decoder and comparator. To ensure error-free operation, wavelength separation should be kept less than7nm. Given the femtosecond response time of Kerr-effect in HNLF, the module is promising in ultra-speed systems.