Research for optical mixing with advanced functions

近年来，利用高速晶体管将光纤与微波技术相结合，实现宽带移动通信系统的光混频，由于光纤与微波技术具有宽带宽和固有的隔离性，引起了人们的广泛关注。到目前为止，人们对高电子迁移率晶体管（hemt）或mesfet等高速晶体管的光混合和光探测机制进行了研究。然而，光照射条件对光学响应极性变化的影响尚未见报道。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，并发现其正、负光学响应随照射位置的变化而变化。我们还研究了这些光响应在光控微波振荡器中的应用。用于L至k波段低噪声放大的市售InGaAs HEMT安装在微带状线上…更多信息请参见50Ω。来自激光二极管的光束被聚焦并注入到HEMT表面。聚焦后的光束光斑尺寸约为3μm。使用显微镜和CCD相机监测HEMT上光束光斑的位置，并使用x -平台进行调整。当在栅极附近设置来自635nm激光二极管的50μW的连续激光束光斑，并向HEVIT提供适当的直流偏置电压时，漏极电流增加至8mA，信号增益小至20dB。当我们将光束光斑与栅极电极分开时，可以清楚地观察到漏极电流和增益的减小。我们认为这种负光学响应是由于在深阱中捕获载流子，称为“侧门效应”。我们通过光照将这些有趣的特性应用于光控微波振荡器。利用HEMT设计并制作了一个振荡频率为11.7GHz的串联反馈微波振荡器。采用选择性的光脉冲照射，测量了微波振荡的变化。在适当的直流偏置条件下，改变光脉冲对HEMT在正响应区和负响应区之间的照射位置，光学控制HEMT的增益，光脉冲对正响应区照射触发11.7GHz微波振荡，对负响应区照射停止。通过调整直流偏置条件，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