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组件主要由集成化光收发前端模块(A模块)和集成化光收发后端模块(B模块)组成,其工作原理如图1所示。
A模块位于天线阵面端,B模块位于雷达后端,通过光纤进行信息传输,实现射频信号的拉远。当组件处于上行状态时,微波信号通过B模块完成射频预处理和电光转换后通过光纤传输至A模块,A模块将信号还原为微波信号,并将信号放大后送至天线端。当组件处于下行状态时,A模块将天线接收的微波信号进行放大和电光转换,然后通过光纤将接收号传输至B模块,B模块完成信号的光电转换后将其输出至后端信号处理单元。
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模块原理架构如图2所示,A模块靠近天线阵面端,主要完成天线端与后端信号的电光和光电转换。B模块位于后端,主要完成天线端与后端信号的光电和电光转换。模块主要由射频部分、光电转换部分以及集成化光波分环形器组成。其中射频部分主要包括低噪声放大器(LNA)、射频开关、均衡器等,光电转换部分主要由MZM调制器、宽带探测器以及调制器控制电路等组成。
由于后端空间相较阵面端更充裕,所以外调制需要的大功率激光源也位于射频后端,B模块和大功率激光器直接相连,A模块所需连续光通过波分环形器解复用后传入A模块MZM调制器芯片输入端。
当组件上行时,B模块处于接收状态,A模块处于发射状态,其链路构成如图3(a)所示。
Name Parameter Producer RF switch HG127KB MAT Pre-amplifier IPA-0220-22 IC Valley MZM 15MZPE-50 CETC 44 Circulator with WDM TA2236 CETC 44 PD PD-20 CETC 44 Post amplifier 1 ILA-0118C IC Valley Equalizer IEQ-02183 IC Valley Post amplifier 2 IPA-0220-22 IC Valley 45° fiber module GTZ1-124 CETC 44 MZM control plate MZM_C1 CETC 44 Table 1. List of main components of uplink
Name Parameter Typical characteristics HG127KB Frequency/GHz DC-20 Insertion loss/dB 1 Isolation/dB 40 IPA-0220-22 Frequency/GHz 2-20 Gain/dB 19.5 P-1/dBm 21 NF/dB 5 15MZPE-50 Vπ/V 5@1 kHz Insertion loss/dB 4 Frequency/GHz DC-20 PD-20 Wavelength/nm 1100-1600 Frequency/GHz DC-20 Responsivity 0.85@1 550 nm ILA-0118C Frequency/GHz 1-18 Gain/dB 15 P-1/dBm 17 NF/dB 1.7 Table 2. Main parameters of components
根据上诉参数,设探测器芯片耦合后响应度为80%,上行时波分探测器的损耗为1 dB,可以对上行链路的增益进行估算:
式中: Gf为前级射频链路的增益即前级放大器增益减去开关插损Gf=18.5 dB;Gb为后级射频链路的增益即后放大器增益减去开关插损Gb=33.5 dB;Gopt为光链路的射频增益,其可由下式进行计算:
式中:Zin、Zout为输入、输出阻抗;Vπ为调制器芯片半波电压;Idc为探测器芯片输出光电流。
式中:Rpd为探测器芯片耦合后的响应度;Plaser为激光器输出功率,为50 mW;LM为调制器芯片光插损;LOPT为光链路的插损,是波分环形器的插损、2 km光纤的插损以及光纤弯曲造成的插损之和,约为4 dB。
将公式(3)代入公式(2)可得:
代入器件参数可得Gopt=−30 dB,则上行链路总增益Gup=22 dB。
当组件下行时,A模块处于发射状态,B模块处于接收状态,其链路构成与上行链路相似,主要区别在于下行时位于天线端的A模块调制器芯片所需连续光需通过波分环形器传递,调制后的光信号也需通过波分环形器传递至后端B模块的光电探测芯片处。该过程由于需要通过四次波分环形器,会造成7 dB的光插损。构成下行链路的主要元器件与上行相同,主要区别为后级放大芯片仅有IPA-0200-22一级,各器件主要指标如前所述,此处不做赘述。运用公式(1),对下行链路进行估算,可得Gdown=1 dB。
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通过上述关键技术,应用光电混合集成技术最终实现的组件如图8所示,其中A模块的尺寸为85 mm×45 mm×10 mm,B模块的尺寸为85 mm×35 mm×10 mm,实现了高度集成化。
为了对组件进行测试,搭建了如图8所示的由两个50 mW连续光激光器、集成化光收发组件、2 km光纤构成的测试平台。通过该测试平台,可以拟真B模块位于后端,A模块位于约2 km处天线阵面,通过单根光纤实现微波信号上/下行的场景。基于此测试系统,测量了链路的增益、平坦度、噪声系数以及相位线性度。其中,测试仪器采用的是德科技的N5247A微波网络分析仪,该仪器集成了噪声系数,P-1等测量功能,通过该仪器可以直接测量器件的S参数、噪声系数以及相位线性度等指标。测试结果如图9和表3所示。测试结果表明,对于上行链路,在6~18 GHz频带内,该组件实现了超过18 dB的增益,±1.5 dB以内的平坦度以及小于33 dB的噪声系数。对于下行链路,在6~18 GHz频带内,增益大于−1 dB,平坦度在±1.5 dB以内,而且全频带内噪声系数小于30 dB。在雷达重点工作频段8~12 GHz范围内,上行链路与下行链路均实现了小于±5°的相位线性度。对于测试增益和理论计算之间的差异,主要是由于理论计算时未考虑芯片微组装之后的实际增益、各芯片之间的互联的损耗以及对光纤盘绕损耗估算的准确性,总的来说,测试结果和理论计算结果吻合,该组件在高集成度的情况下实现了媲美分立元器件搭建系统的性能。
Figure 8. Photographs of the component and the test platform. (a) Module A; (b) Module B; (c) Test platform
Figure 9. Test curve of the link. (a) Uplink S-parameters; ( b) Downlink S-parameters; (c) Phase linearity
Up-link Frequency/GHz 6-18 Flatness/dB ±1.5 Gain/dB ≥18.5 NF/dB ≤33 Phase linearity/(°) ≤±5(@8-12 GHz) Down-link Frequency/GHz 6-18 Flatness/dB ±1.5 Gain/dB ≥−1 NF/dB ≤30 Phase linearity/(°) ≤±5(@8-12 GHz) Table 3. Test results
Miniaturized and highly integrated broadband optical transceiver assembly
doi: 10.3788/IRLA20210513
- Received Date: 2020-12-26
- Rev Recd Date: 2021-03-12
- Publish Date: 2021-06-30
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Key words:
- photoelectric hybrid integration /
- miniaturization /
- broadband /
- microwave photons
Abstract: At present, the volume and cost of discrete photonic devices severely restrict the application of microwave photonic technology in radar systems. Limited by the current integration capabilities and material systems, microwave photonic monolithic integrated chip is difficult to realize in a short time. Aiming at the urgent need for highly integrated microwave photonic devices in application scenarios such as radar, a new type of miniaturized and highly integrated broadband optical transceiver module was developed. The module adoped optoelectronic heterogeneous integrated packaging technology, which highly integrated MZM modulator chip, microwave chip, detector chip, optical circulator and wavelength division multiplexer. The size of a single module was only 85 mm×35 mm×10 mm, which was equivalent to the volume of a single MZM modulator. At the same time, its performance was comparable to the traditional discrete components. In the 6-18 GHz range, the component could achieve flatness of ±1.5 dB, gains of more than 18 dB in the uplink, and could achieve gains of more than −1 dB in the downlink and the link noise figure was less than 30 dB. The planarization and miniaturization design makes it can be used in phased array radar, electronic warfare and other application scenarios, and it has broad application prospects.