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本文从系统设计的角度讨论光纤模拟基带传输的几个基本性能极限,着重分析了随机杂波信噪比和非线性失真两项极限。当信噪比大于50dB时,它的提高受到散弹噪声的限制。在满足一定的信噪比时,所需的接收光功率反比于光调制系数的平方。因此,设计时的主要目标是减小接收机的热噪声,以采用PIN+FET比较有利,此外还应尽量减小装置电容,适当限制带宽。光发送机应有尽可能大的输出光功率和最大允许的光调制系数。由于加大光调制系数会带来较大的非线性失真,故应加装非线性校正电路,并选择发光管的最佳工作点。本文最后简要介绍了由我院与江苏电视台合作研制建立的、从江苏电视台的中心机房至发射台之间的一条彩色电视广播光纤传输系统。
This article discusses several basic performance limits of optical fiber analog baseband transmission from the system design point of view, focusing on the two limits of SNR and nonlinear distortion of random clutter. When the signal to noise ratio is greater than 50dB, its improvement is limited by shot noise. In meeting a certain signal-to-noise ratio, the required received optical power is inversely proportional to the square of the optical modulation factor. Therefore, the main goal of the design time is to reduce the thermal noise of the receiver, it is more advantageous to adopt PIN + FET, in addition should try to reduce the device capacitance, limit the bandwidth appropriately. The optical transmitter should have as large an output optical power as possible and a maximum allowable optical modulation factor. As a result of increasing the optical modulation coefficient will bring greater nonlinear distortion, it should be installed non-linear correction circuit, and choose the best LED operating point. At the end of this article, a color TV broadcast optical fiber transmission system is developed, which was developed by our institute in collaboration with Jiangsu TV Station. It is a transmission system of color TV broadcasts from the center room of Jiangsu TV Station to the launch pad.