Research for optical mixing with advanced functions

近年来，由于光纤和微波技术的宽带和RF信号之间固有的隔离，通过高速晶体管的光混频在宽带移动的通信系统中引起了广泛的兴趣。到目前为止，已经研究了诸如高电子迁移率晶体管（HEMT）或MESFFET的高速晶体管的光混合和光电检测机制。然而，还没有关于光照射条件引起的光学响应极性变化的报道。在本研究中，我们尝试使用显微镜和激光束对HEMT进行选择性光束照射，发现其正和负光学响应取决于照射位置。我们还研究了这些光响应在光控微波放大器中的应用，将一种用于L-到K-波段低噪声放大的商用InGaAs HEMT安装在微带线上 ...更多信息 50Ω。来自激光二极管的光束被聚焦并注入到HEMT的表面上。聚焦光束的光斑尺寸约为3μm。用显微镜和CCD摄像机监测HEMT上光斑的位置，用XY工作台调整光斑的位置，当用635 nm激光二极管在HEMT栅电极附近输出50μW的连续激光光斑，并给HEMT施加适当的直流偏置电压时，漏电流最高可达8 mA，小信号增益最高可达20 dB。当我们将束斑设置为远离栅电极时，可以清楚地观察到漏电流和增益的减小。我们认为，这种负的光学响应是由于载流子在深陷阱中的捕获，称为“侧门效应”。我们将光照射下的这些有趣特性应用到光控微波振荡器中，设计并制作了一个振荡频率为11.7GHz的HEMT串联反馈微波振荡器。用脉冲光选择性地辐照振荡器中的HEMT，测量了微波振荡的变化。在适当的直流偏置条件下，通过改变光脉冲对HEMT的照射位置，使其处于正、负响应区之间，实现了对HEMT增益的光学控制，并在正响应区实现了11.7GHz微波振荡的触发，在负响应区实现了11.7GHz微波振荡的停止。通过调节直流偏置条件，得到了光束对微波振荡的调制。少

Recently, optical mixing by high-speed transistors has been attracted much interest for broadband mobile communication systems by combining the optical fiber and the microwave technologies because of their wide bandwidth and inherent isolations between RF signals. Until now, the optical mixing and the photodetection mechanisms of high-speed transistors such as high-electron mobility transistors (HEMTs) or MESFETs have been studied. However, there have not been reported about the change of the polarities of optical responses by light irradiation conditions. In this research, we tried to do the selective optical beam irradiation to the HEMT by use of a microscope and a laser beam and we found its positive and negative optical responses depending on irradiation position. We also studied the application of these optical responses to optically controlled microwave oscillators.A commercially available InGaAs HEMT for low noise amplification in the L- to K-band was mounted on a microstripline … More of 50Ω. An optical beam from a laser diode was focused and injected onto the surface of the HEMT. The spot size of the focused optical beam was about 3μm. The position of the beam spot on the HEMT was monitored by using a microscope and a CCD camera, and adjusted by using an XY-stage.When we set the CW laser beam spot with 50μW from a laser diode of 635nm near the gate electrodes and supplied appropriate DC-bias voltages to the HEVIT, increases of the drain current up to 8mA and the small signal gain up to 20dB were obtained. While we set the beam spot apart from the gate electrodes, decreases of the drain current and the gain were observed clearly. We believe that this negative optical response was due to the capture of carriers in the deep traps, called as the "side-gating effect". We applied these interesting characteristics by light illumination to the optically controlled microwave are oscillators.We designed and fabricated a series feedback microwave oscillator with an oscillating frequency of 11.7GHz by using the HEMT. The HEMT in the oscillator was irradiated by optical pulse beams selectively and the changes of the microwave oscillation were measured. By changing the irradiated position of an optical pulse to the HEMT between the positive and the negative response regions on an appropriate DC-bias condition, the gain of the HEMT was controlled optically and the 11.7GHz microwave oscillation was triggered by the irradiation of a light pulse to the positive response region and stopped by the irradiatinn to the negative response region. By tuning the DC-bias condition, the modulation of the microwave oscillation by the optical beam was also obtained. Less