LIGO Document T1400501-v1

Transportation of Ultra-Stable Light via Optical Fiber

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T - Technical notes
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It has been demonstrated that polarization-maintaining single mode optical fiber can be used to transport frequency-stable light. It is desired to transport stable light to other labs in West Bridge to serve as a frequency reference for various experiments investigating different sources of noise in gravitational-wave detectors. Stable light has been obtained from ultra-stable Fabry-P ́erot cavities. We have mode matched stable light into the fiber and are using a double-pass acousto-optic modulator (AOM) configuration to cancel fiber phase noise. We use a beamsplitter to interfere the stable light and double passed light onto a photodiode, which is connected to a phase-locked loop (PLL) to measure the beat frequency. From there, we analyze the noise in the system by measuring the power spectral density of the PLL control signal with a spectrum analyzer. We measured the expected dominant sources of noise in the set up by using a similar PLL set-up and found a large source of noise coming from the AOM driver. This was replaced with a low noise driver and we will proceed to transport the fiber to another lab once we identify and suppress any other possible noise sources.
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