Patent ID: 6995900

Claim:
A method of producing a short-pass fiber comprising the following steps: a) producing a preform comprising: 1) a core having a core cross-section and a refractive index n 0 ; 2) a depressed cladding surrounding said core and having depressed cladding cross-section larger than said core cross-section and a refractive index n 1 ; 3) a secondary cladding surrounding said depressed cladding and having a refractive index n 2 ; b) measuring said core cross-section; c) measuring said depressed cladding cross-section; d) setting a minimum fundamental mode cutoff wavelength λ m ; e) measuring a variation of said refractive index n 0 and said refractive index n 1 along said axis; f) deriving from measurements of said core cross-section, said depressed cladding cross-section, and said variation a drawing ratio at which said core cross-section has a final value defining a fundamental mode cutoff wavelength λ c such that λ c ≧λ m along said axis; g) pulling said preform by said drawing ratio to produce said short-pass fiber.