New type of optical fiber

during the investigation of a new type of optical fiber having an index of refraction n =1.33, a laser beam is aimed at the flat end of a straight fiber, as shown in the figure. what is the maximum angle of incidence A??o1 if the beam is not to escape from the sides of the fiber if it is surrounded by air?during the investigation of a new type of optical fiber having an index of refraction n =1.33, a laser beam is aimed at the flat end of a straight fiber, as shown in the figure. what is the maximum angle of incidence A??o1 if the beam is not to escape from the sides of the fiber if it is surrounded by air?