Few-mode fiber profile

A few mode optical waveguide according to 1 wherein said refractive index profile comprises a first core region of increased refractive index, an adjacent second core region of depressed refractive index being said refractive index ring, an adjacent third core region of increased refractive index, an adjacent fourth core region of depressed refractive index and an adjacent fifth core region of increased refractive index.

A few mode optical waveguide having a refractive index profile preselected to support no more than three modes at an operating wavelength, said refractive index comprising a refractive index step placed substantially at a location where one of said three modes has substantially zero energy.

A few mode optical waveguide according to 11 wherein said refractive index comprises a first core region of increased refractive index, an adjacent second core region of lower increased refractive index, an adjacent third core region of depressed refractive index and an adjacent fourth core region of increased refractive index.

A few mode optical waveguide designed to have specific characteristics in a desired high order mode comprising:

• a refractive index profile preselected to support at least three modes;
• said refractive index profile comprising a refractive index ring placed at a location where the desired mode has substantially zero energy,
• whereby only two modes other than said desired mode exhibit a loss less than 1 db/cm in a loop with a radius of no more than 4 cm.

A few mode optical waveguide according to claim 21 wherein said desired mode comprises the LP02 mode.

A method of designing a few mode fiber profile having no more than three modes, said modes being the desired modes, said fiber profile being further characterized by having a desired dispersion and dispersion slope for a signal in one of the desired modes, comprising the steps of:

• designing a base profile having similar dispersion and dispersion slope characteristics to the desired characteristics, said base profile supporting more than three modes;
• adding a refractive index ring or refractive index step to said base profile thereby creating an intermediate profile, said ring or step being located such that the energy of one of the desired modes is substantially zero in said refractive index ring or said refractive index step, such that only the desired modes are substantially supported in said intermediate profile, and
• modifying said intermediate profile to optimize the few mode fiber profile to achieve the desired dispersion and dispersion slope characteristics, while supporting only said desired modes.