Finite element analysis employing the vector H-field formulation, with the aid of the perturbation technique, is used to calculate modal loss or gain for several different types of optical waveguides. Further, the complex propagation constant of an optical waveguide is obtained from the solution of the complex transcendental equation and the use of the effective index approach. Results obtained by both methods for different optical waveguides are found to be in good agreement for a wide range of gain/loss values. The accuracy limit for modal loss or gain calculation using the perturbation technique is also examined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>