Optical fiber–based sensing technology can drastically improve Earth observations by enabling the use of existing submarine communication cables as seafloor sensors. Previous interferometric and polarization-based techniques demonstrated environmental sensing over cable lengths up to 10,500 kilometers. However, measurements were limited to the integrated changes over the entire length of the cable. We demonstrate the detection of earthquakes and ocean signals on individual spans between repeaters of a 5860-kilometer-long transatlantic cable rather than the whole cable. By applying this technique to the existing undersea communication cables, which have a repeater-to-repeater span length of 45 to 90 kilometers, the largely unmonitored ocean floor could be instrumented with thousands of permanent real-time environmental sensors without changes to the underwater infrastructure.
The development of a transportable microwave frequency standard based on the ground-state transition of 171 Yb + at ~12.6 GHz requires a compact laser system for cooling the ions, clearing out of long-lived states and also for photoionisation. In this paper, we describe the development of a suitable compact laser system based on a 6U height rack-mounted arrangement with overall dimensions 260 194 335 mm. Laser outputs at 369 nm (for cooling), 399 nm (photoionisation), 935 nm (repumping) and 760 nm (state clearout) are combined in a fiber arrangement for delivery to our linear ion trap and we demonstrate this system by cooling of 171 Yb + ions. Additionally, we demonstrate that the lasers at 935 nm and 760 nm are close in frequency to water vapor and oxygen absorption lines respectively; specifically, at 760 nm, we show that one 171 Yb + transition is within the pressure broadened profile of an oxygen line. These molecular transitions form convenient wavelength references for the stabilization of lasers for a 171 Yb + frequency standard.
We report on the development of a trappedion, microwave frequency standard based on the 12.6 GHz hyperfine transition in lasercooled ytterbium-171 ions. The entire system fits into a 6U 19-inch rack unit (51×49×28 cm) and comprises laser, electronics and physics package subsystems. As a first step towards a full evaluation of the system capability, we have measured the frequency instability of our system which is 3.6 × 10 −12 / √ τ for averaging times between 30 s and 1500 s.
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