Frequency Stabilization of an Optoelectronic Oscillator Based on Phase-Locked-Loop
In this paper, frequency stabilization of an X-band optoelectronic oscillator (OEO) is obtained by phase locking to an oven-controlled crystal oscillator (OCXO) through a fractional phase-locked loop (PLL). The relationship between the loop transfer chara
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Frequency Stabilization of an Optoelectronic Oscillator Based on Phase-Locked-Loop Rongrong Fu, Yanhong Zhu and Xiaofeng Jin
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Introduction
High performance microwave oscillators are the foundation of modern microwave applications, which is critical for the sensitivity of communication, radar, sensing and measurement systems. Modern communication features large bandwidth and high frequency, which impose high spectral purity and stability of microwave oscillators. The optoelectronic oscillator (OEO) is proposed by Yao and Maleki at 1994 [1], which is capable of high spectral purity microwave signal generation even at frequencies up to 100 GHz. The OEO utilizes optical fibers or other microwave photonic filters with high quality (Q) as a low loss energy storage component to achieve ultra-low phase noise output at such high frequencies. However, most free-running OEOs suffer from inferior frequency stability since optical fibers or high Q components are highly sensitive to the temperature and vibration. A few exploration has been carried out to obtain frequency stabilization of the OEO in recent years. Injection locking (IL) proves to be viable for phase noise reduction of the oscillators [2, 3], while it requires an external microwave reference with high stability and low phase noise. Self-injection-locking (SIL) is a simpler scheme to suppress the phase noise of the OEO [4, 5], within which part of the oscillation is exported into a long delay line before injected back into the oscillating loop, where the overall phase noise reduction is proportional to the delay time. In spite of this, the long-term frequency stability of the OEO cannot be ensured since the drift of the environmental sensitive elements still exists [6]. Phase-locked loop (PLL) is recently applied to OEO to enhance the long-term stability of the OEO and reduce its close-in phase noise [7–9]. However, the equivalent phase noise of the reference after frequency multiplication in the PLL is of no superiority from R. Fu (&) Y. Zhu X. Jin Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China e-mail: [email protected] © Tsinghua University Press, Beijing and Springer Nature Singapore Pte Ltd. 2018 R. Shen and G. Dong (eds.), Proceedings of the 28th Conference of Spacecraft TT&C Technology in China, Lecture Notes in Electrical Engineering 445, DOI 10.1007/978-981-10-4837-1_42
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frequency offsets of several kilohertz or tens of kilohertz. Therefore, the frequency range of phase noise suppression is limited since the loop bandwidth of the PLL is generally chosen at this crossing offset. In this paper, frequency stabilization of an X-band OEO using the technique of PLL and self-injection-locking (SIL) is proposed. The employment of SIL suppresses the phase noise of OEO within frequency offsets from 10 Hz to 10 kHz. The long term frequency stabilization is implemented by phase-locking the SIL OEO to a 100 MHz oven-controlled crystal oscillator (OCXO) via a fractional PLL. The e
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