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Fiber Optics, Low Loss Ion Assisted Deposition (IAD) Thin Film Coatings

Client: Free-Space Optical (FSO) Laser Communications

Application Requirements:

  • <0.01 percent reflectivity for specific telecom bands, including infrared wavelength 1.535um.
  • Coating vacuum deposition residual heat must be <75 C. 
  • Wavelength targeting and uniformity from fiber to fiber must be within 0.5%.

Critical Issues:

  •  The low-loss dielectric coating required calibrations between atmospheric spectral measurements and the vacuum-use environment for space. 
  • Low-temperature deposition involved multiple chamber parameter developments, thermal property considerations, and adhesion testing. 
  • Several test runs were necessary to ensure that the ratio between the witness samples and the fiber optics were targeted correctly for this tight tolerance.

Design Basis:

  •  Blue Ridge Optics used a thin layer of high index deposition material and a thick layer low index deposition material for lower loss and increased durability on the fiber optics. 
  • Special ion preclean and ion assisted deposition (IAD) parameters were developed with optimal blends of argon and oxygen to ensure adhesion and low loss. 
  • Chamber software with real-time optical monitoring along with secondary crystal monitoring were used throughout the deposition process. The optical monitoring system measures transmission across the specified wavelength once per planetary revolution while the parts are in chamber vacuum.

Results:

Specifications were met as Blue Ridge Optics utilized IAD and real-time optical monitoring to control wavelength targeting shifts from vacuum to atmosphere on the fiber optics.

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