Residual Vibration-induced Pm Noise of a Rigid Optical Fiber Spool

Oscillators operating in field applications are subject to much more strenuous environmental effects than those in the laboratory. These environmental effects, such as vibration and temperature fluctuation, have a great impact on the performance of the oscillators; however, many applications require this laboratory-level performance in situ. Opto-electronic oscillators (OEOs) have emerged in recent years as excellent low-noise sources that rival the best radio-frequency (RF) oscillators over broad offset frequencies. An OEO is a delay-line oscillator based on a long optical fiber wound on a spool. The OEO uses an RF-modulated optical signal transmitted down a long fiber-optic cable as a high-Q RF frequency discriminator. OEOs hold promise for many field applications requiring very low noise levels to maintain a high level of precise timing. The phase modulated (PM) noise of these OEOs at offset frequencies below 1 kHz is dominated by environmental effects such as temperature and vibration. This paper studies the impact of external environmental vibration on the optical fiber wound on a spool. Mechanical distortions in the fiber induce time-delay (phase) fluctuations. The spool onto which the fiber is wound is primarily responsible for imparting these vibration-induced delay fluctuations to the fiber and, thus, diminishing the performance of the OEO. In this paper, we compare the vibration-induced phase fluctuations of a 3km optical fiber wound on spools made of four materials—plastic, foam-covered plastic, ceramic, and foam-covered ceramic. We investigate fiber-on-spool winding and mounting techniques that reduce vibration susceptibility. We present residual PM measurements that compare the vibration sensitivity of an optical fiber wound on these different materials. From this, we give an estimate of the vibration sensitivity of the bare-fiber and associated optical-fiber connectors that may constitute an RF photonic link, serving primarily as a long-distance, low-loss carrier of RF signals, replacing high-loss coaxial cables, for example.