High-power UTC-photodiodes for an optically pumped subharmonic terahertz receiver.
High-power UTC-photodiodes for an optically pumped subharmonic terahertz receiver.
复制标题
用于光泵分谐波太赫兹接收器的高功率 UTC 光电二极管。
DOI：
10.1364/oe.470375
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发表时间：
2022
期刊：
影响因子：
3.8
通讯作者：
A. Stöhr
中科院分区：
文献类型：
--
作者：
S. Makhlouf;Javier Martinez;M. Grzeslo;D. Moro;O. Cojocari;A. Stöhr
在这项工作中，我们提出了一种光学亚谐波泵浦wr3混频器，用于实现光子相干频率域太赫兹（THz）成像和光谱系统。所研究的混频器工作在wr3频段270 GHz至320 GHz的上范围内。研制了大功率单行载波光电二极管（utc - pd），用于在相应的wr6频段135 GHz ~ 160 GHz范围内提供亚谐波本振（LO）信号。提出的太赫兹混频器模块由基于砷化镓（GaAs）的低势垒肖特基二极管（lbsd）芯片和基于磷化铟（InP）的UTC-PD芯片组成。为了在混频器的LO输入端将UTC-PD与WR6集成，我们开发了一个e平面过渡和一个阶跃阻抗微带线低通滤波器（MSL-LPF），并将其与UTC-PD芯片单片集成在100 μ m厚的InP衬底上。E-plane转换将接地共面波导（GCPW）的准tem模式转换为WR6的优势TE10模式，并使GCPW的阻抗与WR6的阻抗相匹配。全波仿真结果表明，该过渡的1db带宽（BW）大于30 GHz (138.8-172.1 GHz)，回波损耗（RL）小于10 dB，而在150 GHz频率下的最小插入损耗（IL）为0.65 dB。实验结果表明，所制备跃迁的1 dB BW在140 ~ 170 GHz之间，与数值结果一致。最小测量IL为2.94 dB，即比模拟值大约2 dB。为了实现直接抽运混频器所需的LO功率（即，无需额外的LO放大器），对UTC-PD外延系统的设计进行了优化，以在wr6频段（110-170 GHz）内提供高输出功率。实验结果表明，在150 GHz频率下，当光电流为21 mA时，所制UTC-PD芯片的输出功率为+3.38 dBm。据我们所知，这是UTC-PD在150 GHz下实现的最高输出功率。最后，将研制的大功率utc - pd作为LO源泵浦亚谐波wr3混频器。在实验中，对于1 GHz的固定中频，在271 GHz和321 GHz之间的射频频率范围内，转换损耗（CL）取决于本端功率电平。所获得的结果揭示了CL和LO功率水平之间的反比关系，其中在最高应用LO功率水平下，对应于10 mA的光电流，平均最小CL为16.8 dB。这个CL值很有希望，并且在将LO源与混频器包装后，预计将达到电子泵浦和商用太赫兹混频器的CL （~ 12 dB）。此外，在150 GHz的固定LO频率和301 GHz至310 GHz的调谐RF频率（即1 GHz至10 GHz的中频）下测量的平均CL为17.2 dB。
In this work, we present an optically subharmonic pumped WR3-mixer for enabling photonic coherent frequency-domain terahertz (THz) imaging and spectroscopy systems in the future. The studied mixer operates within the upper range of the WR3-band from 270 GHz to 320 GHz. High-power uni-travelling carrier photodiodes (UTC-PDs) are developed for providing the subharmonic local oscillator (LO) signal within the corresponding WR6-band in the range between 135 GHz and 160 GHz. The proposed THz mixer module consists of a gallium arsenide (GaAs)-based low barrier Schottky diodes (LBSDs) chip and an indium phosphide (InP)-based UTC-PD chip. For integrating the UTC-PD with the WR6 at the mixer's LO input, an E-plane transition and a stepped-impedance microstrip line low pass filter (MSL-LPF) are developed and monolithically integrated with the UTC-PD chip on a 100 µm thick InP substrate. The E-plane transition converts the quasi-TEM mode of the grounded coplanar waveguide (GCPW) to the dominant TE10 mode of the WR6 and matches the GCPW's impedance with the WR6's impedance. According to full-wave EM simulations, the transition exhibits a 1 dB bandwidth (BW) of more than 30 GHz (138.8-172.1 GHz) with a corresponding return loss (RL) better than 10 dB, whereas the minimum insertion loss (IL) is 0.65 dB at a frequency of 150 GHz. Experimentally, the 1 dB BW of the fabricated transition is found to be between 140 GHz and 170 GHz, which confirms the numerical results. The minimum measured IL is 2.94 dB, i.e., about 2 dB larger than the simulated value. In order to achieve the required LO power for successfully pumping the mixer in a direct approach (i.e., without an additional LO amplifier), the design of the epitaxial system of the UTC-PD is optimized to provide a high output power within the WR6-band (110-170 GHz). Experimentally, at 150 GHz, the output power of the fabricated UTC-PD chip is measured to be +3.38 dBm at a photocurrent of 21 mA. To our knowledge, this is the highest output power ever achieved from a UTC-PD at 150 GHz. Finally, the developed high-power UTC-PDs are used as LO source to pump the subharmonic WR3-mixer. Experimentally, the conversion loss (CL) is determined in dependency of the LO power levels within the RF frequency range between 271 GHz and 321 GHz for a fixed IF at 1 GHz. The achieved results have revealed an inverse relation between the CL and LO power level, where the average minimum CL of 16.8 dB is achieved at the highest applied LO power level, corresponding to a photocurrent of 10 mA. This CL figure is promising and is expected to reach the CL of electronically pumped and commercially available THz mixers (∼12 dB) after packaging the LO source with the mixer. Furthermore, an average CL of 17.2 dB is measured at a fixed LO frequency of 150 GHz and a tuned RF frequency between 301 GHz and 310 GHz, i.e., IF between 1 GHz and 10 GHz.