KEYWORDS: Dispersion, Microwave radiation, Telecommunications, Signal processing, Digital signal processing, Signal detection, Sensors, Transmitters, Fiber optic communications, Optical amplifiers
A feasible and cost-effective online chromatic dispersion (CD) monitoring scheme for high speed optical communication system is demonstrated in this paper. Based on the formerly verified theoretical model, the output electrical power of a specific frequency band is tested to reflect the residual chromatic dispersion online. Thus the microwave devices are selected to form the electrical power detecting circuit, which consists of a PIN photodiode, a microwave power filter and a power detector in tandem. In the experiments, frequency band center were chosen at 5 GHz for the 10 Gbit/s system and 12 GHz for the 40 Gbit/s system. Then the output voltage of the detector was processed and converted to digital signal and the signal was processed to obtain the amount of the chromatic dispersion of the tested systems. For the 40 Gbit/s system, the maximum detectable chromatic dispersion was around 130-ps/nm and a resolution of 5-ps/nm/db was achieved at the chosen frequency band centered at 12 GHz. Performance of the microwave devices and comparison of the experimental results at different frequency bands are also discussed, which verified that the chosen center frequency was suitable for detection of CD in optical communication system beyong 10 Gbit/s speed.
In this paper, a novel scheme of stabilizing all-optical clock recovery is proposed, which uses a mode-locked fiber ring to extract the same frequency clock pulses from the uneven multiplexing 4×10Gbps optical signals. The super-mode suppression ratio reaches 60dB (for signals of 10Gbit/s) and an improvement of 20dB is achieved by adding stabilization devices. Wavelength shift is less than 0.01nm within 2 hours, and this value is about one sixties of that without adding stabilization devices. The results show much better cavity length stability and noise suppression performance.
Based on the assumption of a quasi-monochromatic wave for light in fibres and 2□2 coherency matrix, a relationship of DO P with several parameters as well as DGD is derived from the common definition of DOP. A normalized coherent coefficient, showing the degree of correlation of optical signals in both principal states of polarization (PSPs), is derived theoretically. The value of this parameter indicates directly the degree of polarization of optical signals within the communications fibers. The correlation is also the straightforward express of differential group delay between two PSPs. With a pulse shape of Gaussian, we give a useful expression of DOP with power splitting ratio and differential group delay. Two curves of calculations are also given. When DGD becomes bigger, the coherent coefficient is smaller, meaning that the DOP is lower. DOP is one of feedback control signals for dynamic PMD compensation.
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