The dependence of the photo-elastic (or opto-elastic) constant upon the relative refractive index difference, the normalized frequency, and the wavelength for single-mode optical fibers has been investigated. From experimental results, it is found that the opto-elastic constant strongly depends upon wavelength, but not upon the relative refractive index difference or normalized frequency. The measured values of the opto-elastic constant at 1.30 and 1.50 μm are

(mm
2/kg) and

(mm
2/kg), respectively.