We firstly derive the mathematical expression of degree of polarization (DOP) for Gauss pulse sequence, then analysis theoretically the relationship between DOP and differential group delay (DGD). The relevant experiments well demonstrate the relationship of DOP-DGD. We get the conclusions that the DOP-DGD curve is independent of fibre dispersion, line chip, and bit rate, and are affected by the width of optical spectrum and splitting ratio. Based on the theory, we successfully complete an automatic PMD compensation system for first-order PMD, which can compensate PMD in the optical link in real-time. The response time of compensation system can reach several milliseconds.
A novel bidirectional center wavelength tuning method of Fiber Bragg Grating (FBG) was put forward in this paper. It is based on bidirectional temperature control unit, including semiconductor cooler/heater, negative temperature coefficient (NTC) resistor and peripheral circuits. The cooler/heater, NTC and a FBG were integrated in a DIL metal package like common laserdiodes. Wavelength tuning experiments were carried out at three different environment temperature (0°C, 20°C and 40°C), and the temperature tuning range is from -20°C to 60°C with a step of 10°C. The experimental results show that center wavelength of FBG changes linearly along with temperature variation, and the linearity is better than 0.9986, moreover, environment temperature has little influence on FBG's center wavelength.