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

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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.