Detection and Evaluation of Fiber Noise Induced in Ultra-Stable Environments

We investigated phase noise induced in a piece of optical fiber installed in an ultra-stable environment. The ultra-stable environments were implemented by hermetically sealing, vacuuming, temperature stabilization, vibration isolation, and acoustic shielding. Moreover, in order to detect and evaluate such small fiber noise with high sensitivity, we employed the well-known self-heterodyne technique. The most stable environment drastically reduced the phase noise induced in a 10-m fiber; the noise corresponds to Allan deviation of $7\ \times {10^{-20}}$ at 1-s averaging time, and to $2 \times {10^{-21}}$ at 10000-s averaging time (measurement bandwidth: 500 Hz).