Reconfigurable liquid metal fiber optic mirror
A true time delay system for optical signals includes a hollow core optical waveguide, a droplet of reflective liquid metal disposed in the hollow core, and an actuator coupled to a first end of the waveguide to move the droplet longitudinally within the hollow core. In one example, the waveguide is a hollow core photonic bandgap fiber. In one example, the actuator is a pressure actuator that introduces or removes gas into the core. Light enters the optical fiber, is transmitted through the fiber toward the reflective surface of the droplet, and is reflected back through the fiber and exits at the same end of the photonic bandgap optical fiber that it entered. The fiber optic device can provide a continuously-variable optical path length of over 3.6 meters (corresponding to a continuously-variable true-time delay of over 12 ns, or 120 periods at a 10 GHz modulation frequency), with negligible wavelength dependence across the C and L bands.
1. A true time delay system for optical signals, comprising:
a hollow core optical fiber;
a droplet of reflective liquid metal disposed in the hollow core; and
a pressure actuator coupled to a first end of the hollow core optical fiber configured to change a position of the droplet within the hollow core;
a single mode fiber optically coupled to a second end of the hollow core optical fiber; the second end of the hollow core optical fiber configured to receive optical energy, to transmit the optical energy through the hollow core toward the reflective droplet, and to return the reflected optical energy toward the second end of the hollow core optical fiber.
2. The true time delay system according to claim 1 , wherein the hollow core optical fiber is a hollow core photonic bandgap fiber.
3. The true time delay system according to claim 2 , wherein holes in the hollow core photonic bandgap fiber cladding surrounding the hollow core are substantially free of the reflective liquid.
4. The true time delay system according to claim 1 , wherein the droplet is mercury.
5. The true time delay according to claim 1 , further comprising an optical circulator optically coupled to an end of the hollow core optical fiber for separating input optical signals and output time-delayed optical signals.
6. The true time delay system according to claim 1 , wherein the droplet has a length along the core of the hollow core optical fiber of between about two core diameters and three core diameters.
7. The true time delay system according to claim 1 , wherein the droplet has a length along the core of the hollow core optical fiber of between one core diameter and about ten core diameters.
8. A true time delay system for optical signals, comprising:
a hollow core photonic bandgap optical fiber;
a droplet of reflective liquid metal disposed in a hollow core of the hollow core optical fiber;
an actuator coupled to at least a first end of the hollow core optical fiber to introduce gas into or remove gas from the hollow core at a near side of the droplet, thereby increasing or decreasing a gas pressure at the near side of the droplet and changing a position of the droplet within the hollow core;
a single mode fiber optically coupled to a second end of the hollow core photonic bandgap optical fiber, the second end of the hollow core photonic bandgap optical fiber configured to receive optical energy from outside the hollow core photonic bandgap optical fiber, to transmit the received optical energy through the hollow core toward the reflective droplet, and to return the reflected optical energy toward the second end of the hollow core optical fiber.
9. The true time delay according to claim 8 , further comprising an optical circulator optically coupled to an end of the hollow core photonic bandgap optical fiber for separating input optical signals and output time-delayed optical signals.
10. The true time delay system according to claim 8 , wherein holes in the hollow core photonic bandgap fiber cladding surrounding the hollow core are substantially free of the reflective liquid.
11. The true time delay system according to claim 8 , wherein the droplet has a length along the core of the hollow core optical fiber of between about two core diameters and three core diameters.
12. The true time delay system according to claim 8 , wherein the droplet has a length along the core of the hollow core optical fiber of between one core diameter and about ten core diameters.
13. The true time delay system according to claim 8 , wherein the pressure actuator is in contact only with the first end of the hollow core photonic bandgap optical fiber.