1. B. Katselenbaum, Theory of Irregular Waveguides with Slowly Varying Parameters (Izd-vo AN SSSR, Moscow, 1961) [in Russian].
2. V. V. Shevchenko, Smoth Transitions in Open Waveguides (Nauka, Moscow, 1969) [in Russian].
3. D. Marcuse Light Transmission Optics (Van Nostrand, New York, 1972).
4. Integrated Optics, Ed. by T. Tamir (Springer, New York,1975; Mir, Moscow, 1978).
5. M. S. Sodha and A. K. Ghatak, Inhomogeneous Optical Waveguides (Plenum, New York, 1977; Svyaz’, Moscow, 1980).