| With the rapidly growing demands for the communication bandwidth, optical fiber communication system is developing towards larger capacity and higher speed. The 10 G passive optical network(PON) access technology, such as optical fiber to the home(FTTH), is currently entering the stage of commercialization. As a result, the lasing source with a high performance-to-cost ratio becomes paramount in such PON networks, which has been the research focus in this field. According the current standard of 10G-EPON and XG-PON, downstream wavelength of the lasing source in optical line terminal(OLT) is set as 1574-1580nm(L-band). Unfortunately, the widely deployed G.652 optical fiber has a relatively large dispersion effect within this wavelength band. Currently, the electric absorption modulation laser(EML) and the chirp management laser(CML) are being employed as the downstream light source due to their reduced chirp solutions. However,the EML and the CML are not ideal candidates for their large power consumptions and high cost. Directly modulated laser(DML) based on the distributed feedback(DFB)grating has the advantage of simple and compact structure, low power consumption and low cost. However, the parasitic frequency(wavelength) chirp caused by direct current modulation further broadens the line width of the laser output spectrum, and aggravates the signal waveform distortion during its transmission in the dispersive fiber, and ultimately leads to a serious deterioration of the received bit error ratio(BER). By theoretical and experimental study based on the developed transmission platform, this paper aims to examine the possibility of such 10 G L-band DML to be applied in the 10 G PON infrastructure. The major research work and outcomes of this paper include:(1) Research and simulation of 10 G L-band DML transmission system. The transmission system under investigation includes three parts, the DML light source, the standard single mode optical fiber and the receiver. The theoretical model and simulation method of each part are established, and its validity is proved by comparing with the literature. After that, the laser performance is simulated based on the optimized material and structural parameters in the active region adopting the gain detuning technique. And the transmission performance of the device is then simulated and evaluated by thedeveloped system simulation platform. Finally, the initial design of the laser chip which satisfies the requirements of 10 G PON protocol is presented.(2) The tests on both the optimized design as well as the conventional design of the DML chip have been conducted. The laser parameter extraction has also been implemented according to the actual device's performances and the extracted parameters are then input to the developed simulation platform to estimate the system performance of the actual fabricated devices.(3) Package the chip in TOSA and test the transmission performance on the module at modulation speed of 6.25Gb/s and 10Gb/s, including the eye diagram, the BER and the system power penalty. Moreover, we compare the test results with the theoretical prediction, and analyze the reason of the disagreement. Finally, based on the simulation and test results, the chirp characteristics of 10 G L-band DML and its influence on the transmission performance of the system are studied and analyzed, in order to further improve the transmission performance. |
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