Fiber Optics for Advanced Aircraft – Key Notes

Fiber-Optic Benefits for Advanced Aircraft

• Immunity to electromagnetic effects (EME) ➔ eliminates shielding, surge protection, and corrosion issues.

• Weight & volume reduction by replacing metal wiring with glass fibers.

• Passive optical sensors need no electrical power ➔ higher reliability & lower maintenance.

FOCSI Program Essentials

• Joint NASA/DOD effort (began $1985$) to integrate a totally fiber-optic propulsion/flight control system for an advanced supersonic fighter.

• Objectives: system concept, environment definition, sensor specs, tech readiness schedule.

• Cooperative partners: NASA-Lewis, Naval Air Centers, Army (Ft. Eustis), Air Force (WPAFB).

Phase I Key Findings

• Operating temperature envelope for most components: $-55$ to $200$ °C; turbine-case zones up to $450$ °C.

• Typical sensor counts (no redundancy): propulsion $\rightarrow$ $3$ pressures, $8$ temperatures, $4$ linear positions, $1$ rotary position, etc.; airframe $\rightarrow$ $22$ linear, $14$ rotary positions, $6$ rates, $4$ accelerometers.

• Trade study vs. baseline FADEC shows:
  • Full EME immunity.
  • Significant harness weight savings (further increased when controls move off-engine in future high-speed aircraft).
  • Comparable projected reliability.

• Industry gap: lack of rugged passive optical sensors for pressure, temperature, position, speed, vibration & flow.

Optical Sensor Technology Status

• Passive sensors: intrinsic (e.g., microbend) or extrinsic (e.g., code plate).

• Most mature: optical temperature sensors.

• Position (TDM/WDM) & speed sensors proven at low temps.

• Pressure, flow, torque sensors need further R&D, especially for temperature compensation.

Electro-Optic Architecture (EOA) Concepts

1. One source + detector per sensor (simple, but high piece-count).

2. Clustered sensors via passive couplers (FOCSI contractor proposal).

3. Central high-power source, computer-controlled optical switches, passive TDM/WDM multiplexers (minimal fibers; complex switching).

• Selection depends on chosen sensor mix, redundancy, maintainability.

Integrated Optic Sensors & High-Temp Needs

• Supersonic/hypersonic vehicles demand new high-temperature fibers, connectors & uncooled sensors placed near measurement points.

• Micromachined silicon transducers with integrated optics envisioned for dual-parameter sensing (e.g., combined pressure/temperature, Fig. 7 concept):
  • Reference, pressure, and temperature optical paths with time delays $T<em>1$ & $T</em>2$ or wavelength filters.

• Critical component R&D: high-temp gratings, filters, splitters, delay lines.

Critical Time & Data Requirements

• $7$-year lag from technology freeze to production ➔ accelerated work required now.

• Need exhaustive reliability baseline for fibers, connectors, light sources, detectors, and sensors under aircraft conditions.

• Development of standards/specifications for all optical components is urgent.

Bottom Line

Fiber-optic links with passive sensors are feasible and advantageous for advanced aircraft, offering EME immunity and weight savings. Technology gaps—especially high-temperature sensors, materials, and robust electro-optic architectures—must be closed quickly to meet future production timelines.