High-bandwidth coherent optical communication over 10.3 km of turbulent air.

We demonstrate 111.8 Gb/s coherent optical communication throughput over a 10.3 km folded free-space laser range.

Stabilized free space optical frequency transfer using digitally enhanced heterodyne interferometry.

Free-space continuous-wave laser interferometry using folded links has applications in precision measurement for velocimetry, vibrometry, optical communications, and verification of frequency transfer for metrology. However, prompt reflections from the transceiver optics degrade the performance of these systems, especially when the power of the returning signal is equal to or less than the power of the prompt reflections. We demonstrate phase stabilized free-space continuous-wave optical frequency transfer that exploits the auto-correlation properties of pseudo-random binary sequences to filter out prompt reflections.

Towards optical frequency geopotential difference measurements via a flying drone.

Geopotential and orthometric height differences between distant points can be measured via timescale comparisons between atomic clocks. Modern optical atomic clocks achieve statistical uncertainties on the order of 10, allowing height differences of around 1 cm to be measured. Frequency transfer via free-space optical links will be needed for measurements where linking the clocks via optical fiber is not possible, but requires line of sight between the clock locations, which is not always practical due to local terrain or over long distances.

Demonstration of 100 Gbps coherent free-space optical communications at LEO tracking rates.

Free-space optical communications are poised to alleviate the data-flow bottleneck experienced by spacecraft as traditional radio frequencies reach their practical limit. While enabling orders-of-magnitude gains in data rates, optical signals impose much stricter pointing requirements and are strongly affected by atmospheric turbulence. Coherent detection methods, which capitalize fully on the available degrees of freedom to maximize data capacity, have the added complication of needing to couple the received signal into single-mode fiber.

Optical couplers and step-index fibers fabricated using FDM 3D printers.

Step-index optical fiber preforms are manufactured and drawn into fibers using low-cost consumer-grade fused deposition modeling (FDM) 3D printers with no other specialist tooling. The fibers are fabricated from polyethylene terephthalate glycol (PETG) cladding with an acrylonitrile buatadiene styrene (ABS) core, resulting in V < 2.4 after drawing.

Angle-of-arrival variability of retroreflected lasers despite atmospheric reciprocity.

Corner cube retroreflectors are commonly used as cooperative targets in free-space laser applications. The previous literature suggests that due to path reciprocity, a retroreflected beam is self-corrected across a turbulent atmosphere and should show no angle-of-arrival variability in the near field. This is at odds with recent experiments that rely on angle-of-arrival measurements in retroreflected beams for effective tip/tilt correction.

Vulnerability of Satellite Quantum Key Distribution to Disruption from Ground-Based Lasers.

Satellite-mediated quantum key distribution (QKD) is set to become a critical technology for quantum-secure communication over long distances. While satellite QKD cannot be effectively eavesdropped, we show it can be disrupted (or 'jammed') with relatively simple and readily available equipment. We developed an atmospheric attenuation and satellite optical scattering model to estimate the rate of excess noise photons that can be injected into a satellite QKD channel by an off-axis laser, and calculated the effect this added noise has on the quantum bit error rate.

Point-to-point stabilized optical frequency transfer with active optics.

Timescale comparison between optical atomic clocks over ground-to-space and terrestrial free-space laser links will have enormous benefits for fundamental and applied sciences. However, atmospheric turbulence creates phase noise and beam wander that degrade the measurement precision. Here we report on phase-stabilized optical frequency transfer over a 265 m horizontal point-to-point free-space link between optical terminals with active tip-tilt mirrors to suppress beam wander, in a compact, human-portable set-up.

Fast beam steering with an optical phased array.

Optical phased arrays (OPAs) are devices that use the coherence of light to control the interference pattern in the far field, which enables them to steer a laser beam with no moving parts. As such, OPAs have potential applications in laser communications, target acquisition and tracking, metrology, and directed energy. In this Letter, we present a control architecture for an actively phase-locked OPA, capable of steering a laser beam at speeds limited by the actuation bandwidth of electro-optic modulators.

Characterization of optical frequency transfer over 154 km of aerial fiber.

We present measurements of the frequency transfer stability and analysis of the noise characteristics of an optical signal propagating over aerial suspended fiber links up to 153.6 km in length. The measured frequency transfer stability over these links is on the order of 10 at an integration time of 1 s dropping to 10 for integration times longer than 100 s.

Stabilized microwave-frequency transfer using optical phase sensing and actuation.

We present a stabilized microwave-frequency transfer technique that is based on optical phase sensing and optical phase actuation. This technique shares several attributes with optical-frequency transfer and, therefore, exhibits several advantages over other microwave-frequency transfer techniques. We demonstrated the stabilized transfer of an 8000 MHz microwave-frequency signal over a 166 km metropolitan optical fiber network, achieving a fractional frequency stability of 6.

High-precision optical-frequency dissemination on branching optical-fiber networks.

We present a technique for the simultaneous dissemination of high-precision optical-frequency signals to multiple independent remote sites on a branching optical-fiber network. The technique corrects optical-fiber length fluctuations at the output of the link, rather than at the input as is conventional. As the transmitted optical signal remains unaltered until it reaches the remote site, it can be transmitted simultaneously to multiple remote sites on an arbitrarily complex branching network.

When is high-dose intravenous iron repletion needed? Assessing new treatment options.

High doses of intravenous iron have a role in the treatment of a number of clinical situations associated with iron deficiency, iron deficiency anemia, and blood loss. In the presence of functioning erythropoiesis, iron supplementation alone may be adequate to replenish iron stores and restore blood loss. Where hormone replacement with an erythropoiesis-stimulating agent is required, iron adequacy will optimize treatment.