Wide-Frequency-Range Phase-Locked Photonic-Microwave Oscillator Operated in a Fiber-Coupled Remote Station

In the latest radio interferometer, a system equipped with a large number of receivers from low frequency to high frequency (~THz) was realized. In addition, an ultra-wide bandwidth receiver and a super-terahertz receiver are being developed as next-generation receivers. In this situation, a new local oscillator capable of handling next-generation receivers is necessary. Due to the very wide bandwidth requirement, an optical local oscillator, which can correspond to a system that conventionally requires a high-frequency phase-locked oscillator with a different amplifier for each receiver, is expected. An optical phase-locked oscillator can be realized at a remote station that is synchronized with a transmitted dual-wavelength reference signal from a reference station. The high-frequency reference signal transmission is required because it is necessary to suppress the multiplication order to reduce individual multiplied noise at the remote station. In this work, we focus on an external modulator-scheme optical phase-locked oscillator that performs a high-frequency phase comparison between photonic microwave signals at a remote station. The system makes fiber-coupled stations a coherent system. It is possible for the optical phase-locked oscillator to handle a very wide bandwidth receiver, a set of receivers with many bands, and a multifeed receiver with one device.