The syncang method for simultaneous measurement of film refractive index and thickness

The synchronous angle method (SYNCANG) for the simultaneous determination of the refractive index and film thickness of thin dielectric films is especially useful for researchers involved in integrated optics.The method involves the measurement of the synchronous angles θ_5E and θ_5M (see Fig. 1) required to couple transverse electric (TE) and transverse magnetic (TM) modes into light guides, and the solution of the resulting pair of simultaneous transcendental eigenvalue equations yields n₁ and W.The sensitivity of the method has been studied, and it is shown that n₁ may easily be resolved within 0.002 per minute of arc, considering θ_5E and θ_5M as having equal errors. W may be resolved within 0.02 μ (200 Å) per minute of arc, depending primarily on the proximity of the synchronous guide angle θ₁ to 90°. The method does not require a step in the film, and may be easily reduced to measuring n₁ knowing either the TE or the TM synchronous angle and W.