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摘要: 针对现有微波光传输系统存在电光转换效率不足的问题，本文设计了一种基于调制器低偏与光放大器相结合的光发射结构，通过充分利用链路增益与光功率水平之间的平方关系以及低偏链路传输效率与光功率呈近似线性变化的特点，实现了光载微波信号传输效率的有效提升。经过测试可知，本方案较常规正交点传输方式在射频增益方面提高了13.5 dB，同时不会使噪声系数产生明显恶化，并且本方案可以采用现成产品以实现低成本制作，在电子信息装备中具有广泛的应用潜力。Abstract: Photonics have long been viewed as an enabling technology that extends the sensing and signal processing performances of Radio Frequency (RF) remoting systems such as radar and electronic-warfare because of its inherent advantages in multi-octave operating frequencies, broad instantaneous bandwidth, low transmission loss, and good phase linearity. In order to improve the efficiency of the analog optical transmitter during electronic-to-optical conversion, an Erbium-Doped Fiber Amplifier (EDFA) combing with a low-bias modulator in an external intensity modulation direct detection link is applied. According to our analysis, the RF gain reduces linearly with modulator’s optical power output when the bias becomes close to its minimum. Thus, the gain provided by the EDFA to the optical signal was transferred to increase RF transmission efficiency. Experimental results indicated that the RF gain improved by 13.5 dB compared to that of conventional quadrature bias point transmissions. Meanwhile, a small penalty is introduced to system noise. Most importantly, this can be achieved by using off-the-shelf devices, which can drastically reduce the system’s cost. Finally, the proposed scheme can be widely used in electronic information equipment.
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Key words:
- microwave photonics /
- analog optical transmitter /
- modulator low-bias /
- optical amplifier
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图 2 调制器出光功率及链路增益随偏置点位置的变化关系
Figure 2. The output optical power of modulator and link RF gain varying with modulator’s bias point
图 3 光放大器有效增益与链路附加增益随偏置点位置的变化关系
Figure 3. The gain provided by EDFA and the additional link gain varying with modulator's bias point
图 5 不同偏置点条件下链路增益随频率的变化情况。（a）不加光放大器；（b）加光放大器；（c）在1 GHz频点处增益随偏置点位置的变化情况
Figure 5. The RF gain versus RF frequency under the condition of different bias points. (a) Without EDFA; (b) with EDFA; (c) gain versus position of bias point at the frequency of 1 GHz.
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