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Optical fibre directional coupler

  • US 4,474,431 A
  • Filed: 12/05/1983
  • Issued: 10/02/1984
  • Est. Priority Date: 12/20/1978
  • Status: Expired due to Fees
First Claim
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1. An optical fibre directional coupler comprising:

  • a first optical fibre having oppositely located first and second ports, an optical core of a predetermined refractive index and an optical cladding surrounding said core and having a lower refractive index than said core;

    a second optical fibre having oppositely located third and fourth ports, a core of a predetermined refractive index, a primary optical cladding surrounding said core and having an index of refraction lower than said core and a cross-sectional area larger than the cross-sectional area of the core, and a secondary optical cladding surrounding said primary cladding and having a refractive index lower than said primary cladding, said secondary cladding having a refractive index less than said core of said first optical fibre, said first and second optical fibres being positioned adjacent each other to form a coupling region wherein the optical cladding of the first fibre and the secondary cladding of the second fibre have been removed, said first and third ports being positioned on the same side of the coupling region positioned in use that said third port receives light and transmits the core modes thereof through said core of said second fibre to said fourth port and into an additional fibre positioned adjacent thereto, said fourth port receives a greater proportion of cladding modes than core modes from the additional fibre, and the cladding modes from the fourth port are conveyed through the coupling region predominantly to said first port for detection thereat; and

    means for holding said first and second optical fibres in intimate contact in said coupling region.

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