this working range makes the manufacture of low bend loss singlemode fibers possible by using the profile design of the present invention because this working range includes a property regime with mfd values below 8 8 u03bcm the effect of the peak inner core delta on the optical properties of a fiber made according to the present invention is shown in fig8 the x axis of fig8 shows delta difference the difference between the peak inner core delta and the outer core delta between r i and r o curve 80 shows u03bb c curve 81 shows u03bb 0 and curve 82 shows mfd as functions of delta difference given that outer core delta is usually between 0 3 and 0 4 fig8 indicates that delta difference should be at most about 0 324 to maintain u03bb 0 below 1320 nm this translates into a maximum for peak inner core delta of about 0 7 with 0 5 to 0 65 being preferred the diameter of the inner core region also affects the optical properties fig5 shows how the optical properties change versus the relative width of the inner core region the horizontal axis in fig5 is the normalized width of the inner core region i e the ratio of the radius of the inner core region r i to the radius of.