Based on the coupled mode theory, analytical expression of crosstalk per unit length between two dielectric waveguides is derived. The minimum separation and center-to-center separation of two dielectric waveguides under certain crosstalk are defined. The minimum center-to-center separation serves as a measure of waveguide integration. The influences of waveguide size and refractive index difference on the minimum center-to-center separation are investigated. The analysis and simulation results indicate that strongly confined waveguides have small minimum separation and center-to-center separation. Under the condition of large refractive index difference, the minimum separation can be reduced to less than 1 μm. The minimum center-to-center separation has a minimum value for given wavelength and refractive index distribution.