Space Radiation Effect On The Erbium-doped Fiber Amplifiers For Inter-satellite Optical Communications

With the rapid growth of information, the limitations of inter-satellite microwave communication technique are gradually exposed in the improvement of the communication data rate in recent years. However, comparing to the technique, the inter-satellite optical communication technique has more advantages, such as smaller volume of equipment, higher anti-interference, better confidentiality, and so on. Especially, considering the potentiality of the communication date rate further, the inter-satellite optical communication technique has become one of the hottest research fields. Enormous human and material resources have been invested in this technique by the United States, Europe, Japan and other major countries since 1960s. For the same reason, our country has also given more concern to this technique.At present, the direct modulation technique, which is based on the semiconductor lasers, has been used in the most of the inter-satellite optical communication systems in overseas. However, there is no relay to amplify the signal in inter-satellite optical communication links. Therefore, with the growth of transmission data rate, it is more difficult to meet the requirements of high modulation rate under the condition of high output optical power. Usually, there are two good methods to solve the problem. One is the transitional modulation subsystem composed of semiconductor laser and eribium-doped fiber amplifier (EDFA). And the other is the next modulation subsystem composed of semiconductor lasers, LiNbO3 waveguide modulator and EDFA.It is clear that both methods indicate the EDFA has to be used as the key component in next inter-satellite optical communication systems. However, since the optical characteristics of EDFA will deteriorate after the radiation, the radiation effect on the EDFA will affect the communications quality of the inter-satellite optical communication systems. Therefore, in this dissertation, the space radiation effect on the EDFA has been investigated both in theory and experiment. The main contents of the dissertation include the following aspects:Since it is impossiable to measure the radiation characteristic of EDFA directly, an active measured method has been introduced to the passive measured model based on the rate equation and the transfer equation of radiation environment. The new active measured model can describe the gain characteristics of EDFA in the radiation environment, only by measuring the variation of optical signal output power with the dose. In this way, it can avoid measuring the deterioration of eribium-doped fiber (EDF) to get the gain characteristics of EDFA like the passive measured model. Therefore, it provides a more convinent method to the designers of the inter-satellite optical communication systems.In order to overcome the restriction of the measured time which caused by the recovery characterstics of EDF, a black box model (BBM) is introduced to describe the multi-wavelength gain characteristics of EDFA in the radiation environment successfully based on the analysis on the nature of the black box model. Then a method based on the BBM has been proposed to measure multi-wavelength gain characteristics of EDFA in radiation environment.In order to introduce the EDFA to the actual inter-satellite optical communication system better, the anti-radiation characteristics of EDFA has been further analyzed in three viewpoints. These are the relationship between the concentration of Er3+ in erbium-doped fiber and the radiation dose, the comparison of anti-radiation performance between the EDFA and the erbium-ytterbium co-doped fiber amplifier (EYDFA), and the the electron radiation effect on the EDFA.Finally, in order to understand the application of EDFA in satellite optical communication systems better, the radiation effect on the EDFA has been investigated in the communication viewpoints of signal to noise ratio and bit error rate. The calculation results indicate that the signal to noise ratio decreases with the increasement of radiation dose. And the bit error rate increases with the increasement of radiation doise. Especially, the anti-radiation performance of communication systems, in which the EDFA is used as the preamplifier, is better than the case in which the EDFA is used as the power amplifier.The research work mentioned above will be a good reference for the design of inter-satellite optical communication systems which contain the EDFAs. Especially, it is also really significant to solve the contradiction between the high output power and high modulation rate radically, and achieve the high transmission data rate for the inter-satellite optical communication eventually.