Development of millimeter/sub-millimeter radio-astronomy heterodyne detection system using photonics technology.

我们研制了一种使用单向传播载流子光电二极管（UTC-PD）的毫米和亚毫米波长光混频器。NTT开发的UTC-PD在保持快速响应的同时具有更高的饱和输出。在100 GHz附近，光混频输出功率为2 mW。我们已经证明，光混频可以用作射电天文接收机的本地振荡源。与古恩二极管相比，光子本振器的多余噪声小于几K。利用光子本振器和古恩振荡器在98 GHz处观测到一条指向高质量恒星形成区W51的CS J=2-1谱线。用光子本振器和传统的古恩本振器得到的光谱在数量上是一致的。

We have developed a millimeter and submillimeter wavelength photomixer using a uni-traveling-carrier photodiode (UTC-PD). The UTC-PD, which is developed by NTT, has higher saturation output while maintaining fast response. Output power of the photomixer is as same as 2mW around 100GHz. We have demonstrated that the photomixer can be used as a local oscillator source for a radio astronomy receiver. The excess noise of the photonic local oscillator compared with that of a Gunn diode was measured to be less than a few K. A CS J=2-1 line at 98GHz was observed toward a high-mass star-forming region W51 using the photonic local oscillator and a Gunn oscillator. The spectra obtained with the photonic local oscillator and the conventional Gunn local oscillator are quantitatively consistent with each other.