Patent ID: 8320726

Claim:
A method of fabricating an optical fiber wherein said fiber comprises a core region having a longitudinal axis, and a cladding region surrounding said core region, said core and cladding regions configured to support and guide the propagation of signal light in a fundamental transverse mode in said core region in the direction of said axis, said cladding region including an outer cladding region having a refractive index (n out ) less than that of said core region, a pedestal region having a refractive index (n ped ) approximately equal to that of said outer cladding region, an annular inner trench region disposed between said core region and pedestal region, an annular outer trench region disposed between said pedestal region and said outer cladding region, said pedestal region having a refractive index greater than the refractive index (n tri ) of said inner trench region and the refractive index (n tro ) of said outer trench region, and said pedestal region being configured to resonantly couple at least one transverse mode of said core region, other than said fundamental mode, to at least one transverse mode of said pedestal region, and wherein said method includes the steps of: 1) providing a first starting tube comprising silica and having an index n tro ; 2) depositing a multiplicity of first glass layers on the inside of the first tube; the first layers forming the pedestal region; 3) depositing a multiplicity of down-doped second glass layers on the first layers; the second glass layers forming the deeper-index inner trench region; 4) depositing a multiplicity of up-doped third glass layers on the second layers; the third layers forming the core region; 5) collapsing the first tube to form a first rod; 6) providing a second tube comprising silica and having an index n out ; 7) placing the first rod inside the second tube; 8) collapsing the second tube to form a fiber preform.