支撑RoF技术的新型光电子器件及技术

号通过调制器被调制到光载波上并通过光纤传送回中心站，由于基站中只有光电探测器、调制器和天线，整个体积可以得到很大缩减，成本也大大降低，为RoF密集型"蜂窝"的发展起到了较大的促进作用。

2.1 UTC-PD光探测器

由RoF系统的配置可见，光纤链路接收端的高速的光探测器是另一个关键器件。它必须具有与常规光通信系统要求不同的性能：一是高速率；二是高功率输出，即高的饱和工作点；三是能够在器件上直接转换为毫米波功率，并从微波天线发射出去；最后，当然也要求价格低廉。一个能够满足这几个要求的器件，单行波波导探测器(UTC-PD)，已经问世。其基本原理是，将电子利用为激活载流子，而将空穴限制在一定的区域，利用电子的高迁移率大大提高器件的响应速率。UTC-PD还采用波导结构，增加光吸收的作用长度，设计最佳传输线阻抗，获得高响应速率和高饱和功率。它的能带结构如图11(a)所示，图11(b)则是一个将发射天线与UTC-PD集成为一体的器件[19]。据文献[20]报道，UTC-PD器件探测速度可达310 GHz、50 ?赘负载上输出电压达1.5 V(相当于输出功率7.5 dBm)，并已在RoF研发中被证明了其可行性[21]。

2.2 光子微波接收机

图12是基于微腔的光子微波接收机[22]。由于采用了高Q值的光学微腔，利用光在微腔中的谐振，可以大大提高整个系统的调制效率。同时采用的金属电极也是一种微波谐振结构，这样在射频信号耦合到电极的同时会因为微波的谐振而被放大，从而克服了Moodie等人提出的结构由于射频能量损耗很大，只能用于短距离的无线通信的缺陷。利用这一种光子微波接收结构，Levi等人实现了100 M/s的数据传输，与此同时，Ilchenko等人也利用这一结构实现了亚微瓦级的光子微波接收机。

2.3 电光调制器

在文献[22]中，也有人设计了一种天线耦合的电光调制器，这种设计最初是为了实现接收的射频信号和光载波相位匹配。调制器上的电极同时用作接收天线。电磁波以特定角度入射的时候，相临的天线接收的信号间的相位差正好等于光波经过它们之间距离的相位变化，从而实现相位匹配。

3 结束语

如今，RoF 技术已是国际学术界微波毫米波领域的一个研究热点，用于无线通信、雷达等系统中，是微波光子学的一个重要应用。长期以来，人们对微波光子学中涉及的光源、调制器、传输介质和探测器等器件技术作了大量的研究工作，正是微波光子学领域新型功能器件研究的快速发展，极大地推进RoF 系统的应用进展。根据文献资料的调研和相关市场发展的趋势，现阶段RoF在移动通信和个人通信中毫米波副载波光通信技术的真正使用，除了决定于新技术在经济上的竞争力，也在很大程度上有赖于相关关键功能器件技术的突破，这些研究与进展都将决定RoF技术向市场化推进的步伐。

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