Few-mode optical fiber

A few-mode optical fiber, comprising:

• a core;
• and
• a cladding surrounding the core,
• wherein the cladding comprises:
• a first inner cladding surrounding the core;
• a first high-refractive-index mode filter layer surrounding the first inner cladding;
• a second inner cladding surrounding the first high-refractive-index mode filter layer;
• a second high-refractive-index mode filter layer surrounding the second inner cladding;
• and
• an outer cladding surrounding the second high-refractive-index mode filter layer,
• wherein the core has a refractive index of n1, the first inner cladding has a refractive index of n2, the first high-refractive-index mode filter layer has a refractive index of n3, the second inner cladding has a refractive index of n4, the second high-refractive-index mode filter layer has a refractive index of n5, the outer cladding has a refractive index of n6, satisfying:
• n1>n3>n5>n6 and n2=n4=n6;
• the core and the first inner cladding satisfy:
• 2.405<V<4.4, wherein
• V
• =
• 2
• 
• 
• π
• 
• 
• a
• 1
• λ
• 0
• 
• (
• n
• 1
• 2
• -
• n
• 2
• 2
• )
• 1
• /
• 2
• ,
• V denotes a normalized frequency, λ0=1625 nm, and al denotes a radius of the core;
• the refractive index n3 and a radial thickness a3 of the first high-refractive-index mode filter layer satisfy:
• 1.7<F<3.3 and V>F, wherein
• F
• =
• 2
• 
• π
• 
• 
• a
• 3
• λ
• 0
• 
• (
• n
• 3
• 2
• -
• n
• 6
• 2
• )
• 1
• /
• 2
• ;
• and the first inner cladding has a radial thickness of a2, the first high-refractive-index mode filter layer has the radial thickness of a3, the second inner cladding has a radial thickness of a4, the second high-refractive-index mode filter layer has a radial thickness of a5.