Nufern CMS-HP fiber is a photosensitive single-mode fiber designed for the production of complex Bragg grating structures, such as those with high channel count, wherein cladding mode suppression is a fundamental requirement. This fiber sets a new standard for photosensitive telecom fibers, with its excellent cladding mode suppression, high intrinsic photosensitivity, low birefringence, and low polarization mode dispersion (PMD). It allows easy, uniform grating writing; tighter channel spacing; and low splice loss to standard transmission fibers.